Krakatau volcano in the Sunda Strait between Indonesia’s Java and Sumatra Islands experienced a major caldera collapse around 535 CE; it formed a 7-km-wide caldera ringed by three islands. Remnants of this volcano joined to create the pre-1883 Krakatau Island which collapsed during the major 1883 eruption. Anak Krakatau (Child of Krakatau), constructed beginning in late 1927 within the 1883 caldera (BGVN 44:03, figure 56), was the site of over 40 eruptive episodes until 22 December 2018 when a large explosion and flank collapse destroyed most of the 338-m-high edifice and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions from February (BGVN 44:08) through November 2019. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake. Activity from August 2019 through January 2020 is covered in this report with information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG). Aviation reports are provided by the Darwin Volcanic Ash Advisory Center (VAAC), and photographs are from the PVMBG webcam and visitors to the island.

Explosions were reported on more than ten days each month from August to October 2019. They were recorded based on seismicity, but webcam images also showed black tephra and steam being ejected from the crater lake to heights up to 450 m. Activity decreased significantly after the middle of November, although smaller explosions were witnessed by visitors to the island. After a period of relative quiet, a larger series of explosions at the end of December produced ash plumes that rose up to 3 km above the crater; the crater lake was largely filled with tephra after these explosions. Thermal activity persisted throughout the period of August 2019-January 2020. The wattage of Radiative Power increased from August through mid-October, and then decreased through January 2020 (figure 96).

Figure 96. Thermal activity persisted at Anak Krakatau from 20 March 2019-January 2020. The wattage of Radiative Power increased from August through mid-October, and then decreased through January 2020. Courtesy of MIROVA.

Activity during August-November 2019. The new profile of Anak Krakatau rose to about 155 m elevation as of August 2019, almost 100 m less than prior to the December 2018 explosions and flank collapse (figure 97). Smaller explosions continued during August 2019 and were reported by PVMBG in 12 different VONAs (Volcano Observatory Notice to Aviation) on days 1, 3, 6, 17, 19, 22, 23, 25, and 28. Most of the explosions lasted for less than two minutes, according to the seismic data. PVMBG reported steam plumes of 25-50 m height above the sea-level crater on 20 and 21 August. They reported a visible ash cloud on 22 August; it rose to an altitude of 457 m and drifted NNE according to the VONA. In their daily update, they noted that the eruption plume of 250-400 m on 22 August was white, gray, and black. The Darwin VAAC reported that the ash plume was discernable on HIMAWARI-8 satellite imagery for a short period of time. PVMBG noted ten eruptions on 24 August with white, gray, and black ejecta rising 100-300 m. A webcam installed at month’s end provided evidence of diffuse steam plumes rising 25-150 m above the crater during 28-31 August.

Figure 97. Only one tree survived on the once tree-covered spit off the NE end of Sertung Island after the December 2018 tsunami from Anak Krakatau covered it with ash and debris. The elevation of Anak Krakatau (center) was about 155 m on 8 August 2019, almost 100 m less than before the explosions and flank collapse. Panjang Island is on the left, and 746-m-high Rakata, the remnant of the 1883 volcanic island, is behind Anak Krakatau on the right. Courtesy of Amber Madden-Nadeau.

VONAs were issued for explosions on 1-3, 11, 13, 17, 18, 21, 24-27 and 29 September 2019. The explosion on 2 September produced a steam plume that rose 350 m, and dense black ash and ejecta which rose 200 m from the crater and drifted N. Gray and white tephra and steam rose 450 m on 13 and 17 September; ejecta was black and gray and rose 200 m on 21 September (figure 98). During 24-27 and 29 September tephra rose at least 200 m each day; some days it was mostly white with gray, other days it was primarily gray and black. All of the ejecta plumes drifted N. On days without explosions, the webcam recorded steam plumes rising 50-150 m above the crater.

Figure 98. Explosions of steam and dark ejecta were captured by the webcam on Anak Krakatau on 21 (left) and 26 (right) September 2019. Courtesy of MAGMA Indonesia and PVMBG.

Explosions were reported daily during 12-14, 16-20, 25-27, and 29 October (figure 99). PVMBG reported eight explosions on 19 October and seven explosions the next day. Most explosions produced gray and black tephra that rose 200 m from the crater and drifted N. On many of the days an ash plume also rose 350 m from the crater and drifted N. The seismic events that accompanied the explosions varied in duration from 45 to 1,232 seconds (about 20 minutes). The Darwin VAAC reported the 12 October eruption as visible briefly in satellite imagery before dissipating near the volcano. The first of four explosions on 26 October also appeared in visible satellite imagery moving NNW for a short time. The webcam recorded diffuse steam plumes rising 25-150 m above the crater on most days during the month.

Figure 99. A number of explosions at Anak Krakatau were captured by the webcam and visitors near the island during October 2019, shown here on the 12th, 14th, 17th, and 29th. Black and gray ejecta and steam plumes jetted several hundred meters high from the crater lake during the explosions. Webcam images courtesy of PVMBG and MAGMA Indonesia, with 12 October 2019 (top left) via VolcanoYT. Bottom left photo on 17 October courtesy of Christoph Sator.

Five VONAs were issued for explosions during 5-7 November, and one on 13 November 2019. The three explosions on 5 November produced 200-m-high plumes of steam and gray and black ejecta and ash plumes that rose 200, 450, and 550 m respectively; they all drifted N (figure 100). The Darwin VAAC reported ash drifting N in visible imagery for a brief period also. A 350-m-high ash plume accompanied 200-m-high ejecta on 6 November. Tephra rose 150-300 m from the crater during a 43 second explosion on 7 November. The explosion reported by PVMBG on 13 November produced black tephra and white steam 200 m high that drifted N. For the remainder of the month, when not obscured by fog, steam plumes rose daily 25-150 m from the crater.

Figure 100. PVMBG’s KAWAH webcam captured an explosion with steam and dark ejecta from the crater lake at Anak Krakatau on 5 November 2019. Courtesy of PVMBG and MAGMA Indonesia.

A joint expedition with PVMBG and the Earth Observatory of Singapore (EOS) installed geophysical equipment on Anak Krakatau and Rakata during 12 and 13 November 2019 (figure 101). Visitors to the island during 19-23 and 22-24 November recorded the short-lived landscape and continuing small explosions of steam and black tephra from the crater lake (figures 102 and 103).

Figure 101. A joint expedition to Anak Krakatau with PVMBG and the Earth Observatory of Singapore (EOS) installed geophysical equipment on Anak Krakatau and Rakata (background, left) during 12 and 13 November 2019. Images of the crater lake from the same spot (left) in December and January show the changes at the island (figure 108). Monitoring equipment installed near the shore sits over the many layers of ash and tephra that make up the island (right). Courtesy of Anna Perttu.

Figure 102.The crater lake at Anak Krakatau during a 19-23 November 2019 visit was the site of continued explosions with jets of steam and tephra that rose as high as 30 m. Courtesy of Andrey Nikiforov and Volcano Discovery, used with permission.

Figure 103. The landscape of Anak Krakatau recorded the rapidly evolving sequence of volcanic events during November 2019. Fresh ash covered recent lava near the shoreline on 22 November 2019 (top left). Large blocks of gray tephra (composed of other tephra fragments) were surrounded by reddish brown smaller fragments in the area between the crater and the ocean on 23 November 2019 (top right). Explosions of steam and black tephra rose tens of meters from the crater lake on 23 November 2019 (bottom). Courtesy of and copyright by Pascal Blondé.

Activity during December 2019-January 2020. Very little activity was recorded for most of December 2019. The webcam captured daily images of diffuse steam plumes rising 25-50 m above the crater which occasionally rose to 150 m. A new explosion on 28 December produced black and gray ejecta 200 m high that drifted N; the explosion was similar to those reported during August-November. A new series of explosions from 30 December 2019 to 1 January 2020 produced ash plumes which rose significantly higher than the previous explosions, reaching 2.4-3.0 km altitude and drifting S, E, and SE according to PVMBG (figure 104). They were initially visible in satellite imagery and reported drifting SW by the Darwin VAAC. By 31 December meteorological clouds prevented observation of the ash plume but a hotspot remained visible for part of that day.

Figure 104.The KAWAH webcam at Anak Krakatau captured this image of incandescent ejecta exploding from the crater lake on 30 December 2019 near the start of a new sequence of large explosions. Courtesy of PVMBG and Alex Bogár.

The explosions on 30 and 31 December 2019 were captured in satellite imagery (figure 105) and appeared to indicate that the crater lake was largely destroyed and filled with tephra from a new growing cone, according to Simon Carn. This was confirmed in both satellite imagery and ground-based photography in early January (figures 106 and 107).

Figure 105. Satellite imagery of the explosions at Anak Krakatau on 30 and 31 December 2019 showed dense steam rising from the crater (left) and a thermal anomaly visible through moderate cloud cover (right). Left image courtesy of Simon Carn, and copyright by Planet Labs, Inc. Right image uses Atmospheric Penetration rendering (bands 12, 11, and 8a) to show the thermal anomaly at the base of the steam plume, courtesy of Sentinel Hub Playground.

Figure 106. Sentinel-2 images of Anak Krakatau before (left, 21 December 2019) and after (right, 13 January 2020) explosions on 30 and 31 December 2019 show the filling in of the crater lake with new volcanic material. Natural color rendering based on bands 4,3, and 2. Courtesy of Sentinel Hub Playground.

Figure 107. The crater lake at Anak Krakatau changed significantly between the first week of December 2019 (left) and 8 January 2020 (right) after explosions on 30 and 31 December 2019. Compare with figure 101, taken from the same location in mid-November 2019. Left image courtesy of Piotr Smieszek. Right image courtesy of Peter Rendezvous.

Steam plumes rose 50-200 m above the crater during the first week of January 2020. An explosion on 7 January produced dense gray ash that rose 200 m from the crater and drifted E. Steam plume heights varied during the second week, with some plumes reaching 300 m above the crater. Multiple explosions on 15 January produced dense, gray and black ejecta that rose 150 m. Fog obscured the crater for most of the second half of the month; for a brief period, diffuse steam plumes were observed 25-1,000 m above the crater.

General Reference: Perttu A, Caudron C, Assink J D, Metz D, Tailpied D, Perttu B, Hibert C, Nurfiani D, Pilger C, Muzli M, Fee D, Andersen O L, Taisne B, 2020, Reconstruction of the 2018 tsunamigenic flank collapse and eruptive activity at Anak Krakatau based on eyewitness reports, seismo-acoustic and satellite observations, Earth and Planetary Science Letters, 541:116268. https://doi.org/10.1016/j.epsl.2020.116268.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Amber Madden-Nadeau, Oxford University (URL: https://www.earth.ox.ac.uk/people/amber-madden-nadeau/, https://twitter.com/AMaddenNadeau/status/1159458288406151169); Anna Perttu, Earth Observatory of Singapore (URL: https://earthobservatory.sg/people/anna-perttu); Simon Carn, Michigan Tech University (URL: https://www.mtu.edu/geo/department/faculty/carn/; https://twitter.com/simoncarn/status/1211793124089044994); VolcanoYT, Indonesia (URL: https://volcanoyt.com/, https://twitter.com/VolcanoYTz/status/1182882409445904386/photo/1; Christoph Sator (URL: https://twitter.com/ChristophSator/status/1184713192670281728/photo/1); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Pascal Blondé, France (URL: https://pascal-blonde.info/portefolio-krakatau/, https://twitter.com/rajo_ameh/status/1199219837265960960); Alex Bogár, Budapest (URL: https://twitter.com/AlexEtna/status/1211396913699991557); Piotr (Piter) Smieszek, Yogyakarta, Java, Indonesia (URL: http://www.lombok.pl/, https://twitter.com/piotr_smieszek/status/1204545970962231296); Peter Rendezvous (URL: https://www.facebook.com/peter.rendezvous ); Wulkany swiata, Poland (URL: http://wulkanyswiata.blogspot.com/, https://twitter.com/Wulkany1/status/1214841708862693376).

Mayotte is a volcanic island in the Comoros archipelago between the eastern coast of Africa and the northern tip of Madagascar. A chain of basaltic volcanism began 10-20 million years ago and migrating W, making up four principal volcanic islands, according to the Institut de Physique du Globe de Paris (IPGP) and Cesca et al. (2020). Before May 2010, only two seismic events had been felt by the nearby community within recent decades. New activity since May 2018 consists of dominantly seismic events and lava effusion. The primary source of information for this report through February 2020 comes from semi-monthly reports from the Réseau de Surveillance Volcanologique et Sismologique de Mayotte (REVOSIMA), a cooperative program between the Institut de Physique du Globe de Paris (IPGP), the Bureau de Recherches Géologiques et Minières (BRGM), and the Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP); Lemoine et al. (2019), the Centre National de la Recherche Scientifique (CNRS), and the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER).

Seismicity was the dominant type of activity recorded in association with a new submarine eruption. On 10 May 2018, the first seismic event occurred at 0814, detected by the YTMZ accelerometer from the French RAP Network, according to BRGM and Lemoine et al. (2019). Seismicity continued to increase during 13-15 May 2018, with the strongest recorded event for the Comoros area occurring on 15 May at 1848 and two more events on 20-21 May (figure 1). At the time, no surface effusion were directly observed; however, Global Navigation Satellite System (GNSS) instruments were deployed to monitor any ground motion (Lemoine et al. 2019).

Figure 1. A graph showing the number of daily seismic events greater than M 3.5 occurring offshore of Mayotte from 10 May 2018 through 15 February 2020. Seismicity significantly decreased in July 2018, but continued intermittently through February 2020, with relatively higher seismicity recorded in late August and mid-September 2018. Courtesy of IPGP and REVOSIMA.

Seismicity decreased dramatically after June 2018, with two spikes in August and September (see figure 1). Much of this seismicity occurred offshore 50 km E of Mayotte Island (figure 2). The École Normale Supérieure, the Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP), and the REVOSIMA August 2019 bulletin reported that measurements from the GNSS stations and Teria GPS network data indicated eastward surface deformation and subsidence beginning in July 2018. Based on this ground deformation data Lemoine et al. (2019) determined that the eruptive phase began fifty days after the initial seismic events occurred, on 3 July 2018.

Figure 2. Maps of seismic activity offshore near Mayotte during May 2019. Seismic swarms occurred E of Mayotte Island (top) and continued in multiple phases through October 2019. New lava effusions were observed 50 km E of Petite Terre (bottom). Bottom image has been modified with annotations; courtesy of IPGP, BRGM, IFREMER, CNRS, and University of Paris.

Between 2 and 18 May 2019, an oceanographic campaign (MAYOBS 1) discovered a new submarine eruption site 50 km E from the island of Mayotte (figure 2). The director of IPGP, Marc Chaussidon, stated in an interview with Science Magazine that multibeam sonar waves were used to determine the elevation (800 m) and diameter (5 km) of the new submarine cone (figure 3). In addition, this multibeam sonar image showed fluid plumes within the water column rising from the center and flanks of the structure. According to REVOSIMA, these plumes rose to 1 km above the summit of the cone but did not breach the ocean surface. The seafloor image (figure 3) also indicated that as much as 5 km3 of magma erupted onto the seafloor from this new edifice during May 2019, according to Science Magazine.

Figure 3. Seafloor image of the submarine vent offshore of Mayotte created with multibeam sonar from 2 to 18 May 2019. The red line is the outline of the volcanic cone located at approximately 3.5 km depth. The blue-green color rising from the peak of the red outline represents fluid plumes within the water column. Courtesy of IPGP.

On 17 May 2019, a second oceanographic campaign (MAYOBS 2) discovered new lava flows located 5 km S of the new eruptive site. BRGM reported that in June a new lava flow had been identified on the W flank of the cone measuring 150 m thick with an estimated volume of 0.3 km3 (figure 4). According to REVOSIMA, the presence of multiple new lava flows would suggest multiple effusion points. Over a period of 11 months (July 2018-June 2019) the rate of lava effusion was at least 150-200 m3/s; between 18 May to 17 June 2019, 0.2 km3 of lava was produced, and from 17 June to 30 July 2019, 0.3 km3 of lava was produced. The MAYOBS 4 (19 July 2019-4 August 2019) and SHOM (20-21 August 2019) missions revealed a new lava flow formed between 31 July and 20 August to the NW of the eruptive site with a volume of 0.08 km3 and covering 3.25 km2.

Figure 4. Bathymetric map showing the location of the new lava flow on the W flank of the submarine cone offshore to the E of Mayotte Island. The MAYOBS 2 campaign was launched in June 2019 (left) and MAYOBS 4 was launched in late July 2019 (right). Courtesy of BRGM.

During the MAYOBS 4 campaign in late July 2019, scientists dredged the NE flank of the cone for samples and took photographs of the newly erupted lava (figure 5). Two dives found the presence of pillow lavas. When samples were brought up to the surface, they exploded due to the large amount of gas and rapid decompression.

Figure 5. Photographs taken using the submersible interactive camera system (SCAMPI) of newly formed pillow lavas (top) and a vesicular sample (bottom) dredged near the new submarine eruptive site at Mayotte in late July 2019. Courtesy of BRGM.

During April-May 2019 the rate of ground deformation slowed. Deflation was also observed up to 90 km E of Mayotte in late October 2019 and consistently between August 2019 and February 2020. Seismicity continued intermittently through February 2020 offshore E of Mayotte Island, though the number of detected events started to decrease in July 2018 (see figure 1). Though seismicity and deformation continued, the most recent observation of new lava flows occurred during the MAYOBS 4 and SHOM campaigns on 20 August 2019, as reported in REVOSIMA bulletins.

References: Cesca S, Heimann S, Letort J, Razafindrakoto H N T, Dahm T, Cotton F, 2020. Seismic catalogues of the 2018-2019 volcano-seismic crisis offshore Mayotte, Comoro Islands. Nat. Geosci. 13, 87-93. https://doi.org/10.1038/s41561-019-0505-5.

Lemoine A, Bertil D, Roulle A, Briole P, 2019. The volcano-tectonic crisis of 2018 east of Mayotte, Comoros islands. Preprint submitted to EarthArXiv, 28 February 2019. https://doi.org/10.31223/osf.io/d46xj.

Geologic Background. Mayotte, located in the Mozambique Channel between the northern tip of Madagascar and the eastern coast of Africa, consists two main volcanic islands, Grande Terre and Petite Terre, and roughly twenty islets within a barrier-reef lagoon complex (Zinke et al., 2005; Pelleter et al., 2014). Volcanism began roughly 15-10 million years ago (Pelleter et al., 2014; Nougier et al., 1986), and has included basaltic lava flows, nephelinite, tephrite, phonolitic domes, and pyroclastic deposits (Nehlig et al., 2013). Lavas on the NE were active from about 4.7 to 1.4 million years and on the south from about 7.7 to 2.7 million years. Mafic activity resumed on the north from about 2.9 to 1.2 million years and on the south from about 2 to 1.5 million years. Several pumice layers found in cores on the barrier reef-lagoon complex indicate that volcanism likely occurred less than 7,000 years ago (Zinke et al., 2003). More recent activity that began in May 2018 consisted of seismicity and ground deformation occurring offshore E of Mayotte Island (Lemoine et al., 2019). One year later, in May 2019, a new subaqueous edifice and associated lava flows were observed 50 km E of Petite Terre during an oceanographic campaign.

Information Contacts: Réseau de Surveillance Volcanologique et Sismologique de Mayotte (REVOSIMA), a cooperative program of a) Institut de Physique du Globe de Paris (IPGP), b) Bureau de Recherches Géologiques et Minières (BRGM), c) Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP); (URL: http://www.ipgp.fr/fr/reseau-de-surveillance-volcanologique-sismologique-de-mayotte); Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); Bureau de Recherches Géologiques et Minières (BRGM), 3 avenue Claude-Guillemin, BP 36009, 45060 Orléans Cedex 2, France (URL: https://www.brgm.fr/); Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), 1625 route de Sainte-Anne, CS 10070, 29280 Plouzané, France (URL: https://wwz.ifremer.fr/); Centre National de la Recherche Scientifique (CNRS), 3 rue Michel-Ange, 75016 Paris, France (URL: http://www.cnrs.fr/); École Normale Supérieure, 45 rue d'Ulm, F-75230 Paris Cedex 05, France (URL: https://www.ens.psl.eu/); Université de Paris, 85 boulevard Saint-Germain, 75006 Paris, France (URL: https://u-paris.fr/en/498-2/); Roland Pease, Science Magazine (URL: https://science.sciencemag.org/, article at https://www.sciencemag.org/news/2019/05/ship-spies-largest-underwater-eruption-ever) published 21 May 2019.

Fernandina is a volcanic island in the Galapagos islands, around 1,000 km W from the coast of mainland Ecuador. It has produced nearly 30 recorded eruptions since 1800, with the most recent events having occurred along radial or circumferential fissures around the summit crater. The most recent previous eruption, starting on 16 June 2018, lasted two days and produced lava flows from a radial fissure on the northern flank. Monitoring and scientific reports come from the Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN).

A report from IG-EPN on 12 January 2020 stated that there had been an increase in seismicity and deformation occurring during the previous weeks. On the day of the report, 11 seismic events had occurred, with the largest magnitude of 4.7 at a depth of 5 km. Shortly before 1810 that day a circumferential fissure formed below the eastern rim of the La Cumbre crater, at about 1.3-1.4 km elevation, and produced lava flows down the flank (figure 39). A rapid-onset seismic swarm reached maximum intensity at 1650 on 12 January (figure 40); a second increase in seismicity indicating the start of the eruption began around 70 minutes later (1800). A hotspot was observed in NOAA / CIMSS data between 1800 and 1810, and a gas plume rising up to 2 km above the fissure dispersed W to NW. The eruption lasted 9 hours, until about 0300 on 13 January.

Figure 39. Lava flows erupting from a circumferential fissure on the eastern flank of Fernandina on 12 January 2020. Photos courtesy of Parque Nacional Galápagos.

Figure 40. Graph showing the Root-Mean-Square (RMS) amplitude of the seismic signals from the FER-1 station at Fernandina on 12-13 January 2020. The graph shows the increase in seismicity leading to the eruption on the 12th (left star), a decrease in the seismicity, and then another increase during the event (right star). Courtesy of S. Hernandez, IG-EPN (Report on 13 January 2020).

A report issued at 1159 local time on 13 January 2020 described a rapid decrease in seismicity, gas emissions, and thermal anomalies, indicating a rapid decline in eruptive activity similar to previous events in 2017 and 2018. An overflight that day confirmed that the eruption had ended, after lava flows had extended around 500 m from the crater and covered an area of 3.8 km² (figures 41 and 42). Seismicity continued on the 14th, with small volcano-tectonic (VT) earthquakes occurring less than 500 m below the surface. Periodic seismicity was recorded through 13-15 January, though there was an increase in seismicity during 17-22 January with deformation also detected (figure 43). No volcanic activity followed, and no additional gas or thermal anomalies were detected.

Figure 41. The lava flow extents at Fernandina of the previous two eruptions (4-7 September 2017 and 16-21 June 2018) and the 12-13 January 2020 eruption as detected by FIRMS thermal anomalies. Thermal data courtesy of NASA; figure prepared by F. Vásconez, IG-EPN (Report on 13 January 2020).

Figure 42. This fissure vent that formed on the E flank of Fernandina on 12 January 2020 produced several lava flows. A weak gas plume was still rising when this photo was taken the next day, but the eruption had ceased. Courtesy of Parque Nacional Galápagos.

Figure 43. Soil displacement map for Fernandina during 10 and 16 January 2020, with the deformation generated by the 12 January eruption shown. Courtesy of IG-EPN (Report on 23 January 2020).

Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Dirección del Parque Nacional Galápagos (DPNG), Isla Santa Cruz, Galápagos, Ecuador (URL: http://www.galapagos.gob.ec/).

Masaya is a basaltic caldera located in Nicaragua and contains the Nindirí, San Pedro, San Juan, and Santiago craters. The currently active Santiago crater hosts a lava lake, which has remained active since December 2015 (BGVN 41:08). The primary source of information for this August 2019-January 2020 report comes from the Instituto Nicareguense de Estudios Territoriales (INETER) and satellite -based imagery and thermal data.

On 16 August, 13 September, and 11 November 2019, INETER took SO2 measurements by making a transect using a mobile DOAS spectrometer that sampled for gases downwind of the volcano. Average values during these months were 2,095 tons/day, 1,416 tons/day, and 1,037 tons/day, respectively. August had the highest SO2 measurements while those during September and November were more typical values.

Satellite imagery showed a constant thermal anomaly in the Santiago crater at the lava lake during August 2019 through January 2020 (figure 82). According to a news report, ash was expelled from Masaya on 15 October 2019, resulting in minor ashfall in Colonia 4 de Mayo (6 km NW). On 21 November thermal measurements were taken at the fumaroles and near the lava lake using a FLIR SC620 thermal camera (figure 83). The temperature measured 287°C, which was 53° cooler than the last time thermal temperatures were taken in May 2019.

Figure 82. Sentinel-2 thermal satellite imagery showed the consistent presence of an active lava lake within the Santiago crater at Masaya during August 2019 through January 2020. Images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 83. Thermal measurements taken at Masaya on 21 November 2019 with a FLIR SC620 thermal camera that recorded a temperature of 287°C. Courtesy of INETER (Boletin Sismos y Volcanes de Nicaragua, Noviembre, 2019).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent low-power thermal anomalies compared to the higher-power ones before May 2019 (figure 84). The thermal anomalies were detected during August 2019 through January 2020 after a brief hiatus from early may to mid-June.

Figure 84. Thermal anomalies occurred intermittently at Masaya during 21 February 2019 through January 2020. Courtesy of MIROVA.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); La Jornada (URL: https://www.lajornadanet.com/, article at https://www.lajornadanet.com/index.php/2019/10/16/volcan-masaya-expulsa-cenizas/#.Xl6f8ahKjct).

Reventador is an andesitic stratovolcano located in the Cordillera Real, Ecuador. Historical eruptions date back to the 16th century, consisting of lava flows and explosive events. The current eruptive activity has been ongoing since 2008 with previous activity including daily explosions with ash emissions, and incandescent block avalanches (BGVN 44:08). This report covers volcanism from August 2019 through January 2020 using information primarily from the Instituto Geofísico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and various infrared satellite data.

During August 2019 to January 2020, IG-EPN reported almost daily explosive eruptions and ash plumes. September had the highest average of explosive eruptions while January 2020 had the lowest (table 11). Ash plumes rose between a maximum of 1.2 to 2.5 km above the crater during this reporting period with the highest plume height recorded in December. The largest amount of SO2 gases produced was during the month of October with 502 tons/day. Frequently at night during this reporting period, crater incandescence was observed and was occasionally accompanied by incandescent block avalanches traveling as far as 900 m downslope from the summit of the volcano.

Table 11. Monthly summary of eruptive events recorded at Reventador from August 2019 through January 2020. Data courtesy of IG-EPN (August to January 2020 daily reports).

During the month of August 2019, between 11 and 45 explosions were recorded every day, frequently accompanied by gas-and-steam and ash emissions (figure 119); plumes rose more than 1 km above the crater on nine days. On 20 August the ash plume rose to a maximum 1.6 km above the crater. Summit incandescence was seen at night beginning on 10 August, continuing frequently throughout the rest of the reporting period. Incandescent block avalanches were reported intermittently beginning that same night through 26 January 2020, ejecting material between 300 to 900 m below the summit and moving on all sides of the volcano.

Figure 119. An ash plume rising from the summit of Reventador on 1 August 2019. Courtesy of Radio La Voz del Santuario.

Throughout most of September 2019 gas-and-steam and ash emissions were observed almost daily, with plumes rising more than 1 km above the crater on 15 days, according to IG-EPN. On 30 September, the ash plume rose to a high of 1.7 km above the crater. Each day, between 18 and 72 explosions were reported, with the latter occurring on 19 September. At night, crater incandescence was commonly observed, sometimes accompanied by incandescent material rolling down every flank.

Elevated seismicity was reported during 8-15 October 2019 and almost daily gas-and-steam and ash emissions were present, ranging up to 1.3 km above the summit. Every day during this month, between 13 and 54 explosions were documented and crater incandescence was commonly observed at night. During November 2019, gas-and-steam and ash emissions rose greater than 1 km above the crater except for 10 days; no emissions were reported on 29 November. Daily explosions ranged up to 42, occasionally accompanied by crater incandescence and incandescent ejecta.

Washington VAAC notices were issued almost daily during December 2019, reporting ash plumes between 4.6 and 6 km altitude throughout the month and drifting in multiple directions. Each day produced 5-52 explosions, many of which were accompanied by incandescent blocks rolling down all sides of the volcano up to 900 m below the summit. IG-EPN reported on 11 December that a gas-and-steam and ash emission column rose to a maximum height of 2.5 km above the crater, drifting SW as was observed by satellite images and reported by the Washington VAAC.

Volcanism in January 2020 was relatively low compared to the other months of this reporting period. Explosions continued on a nearly daily basis early in the month, ranging from 20 to 51. During 5-7 January incandescent material ejected from the summit vent moved as block avalanches downslope and multiple gas-and-steam and ash plumes were produced (figures 120, 121, and 122). After 9 January the number of explosions decreased to 0-16 per day. Ash plumes rose between 4.6 and 5.8 km altitude, according to the Washington VAAC.

Figure 120. Night footage of activity on 5 (top) and 6 (bottom) January 2020 at the summit of Reventador, producing a dense, dark gray ash plume and ejecting incandescent material down multiple sides of the volcano. This activity is not uncommon during this reporting period. Courtesy of Martin Rietze, used with permission.

Figure 121. An explosion at Reventador on 7 January 2020, which produced a dense gray ash plume. Courtesy of Martin Rietze, used with permission.

Figure 122. Night footage of the evolution of an eruption on 7 January 2020 at the summit of Reventador, which produced an ash plume and ejected incandescent material down multiple sides of the volcano. Courtesy of Martin Rietze, used with permission.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent and strong thermal anomalies within 5 km of the summit during 21 February 2019 through January 2020 (figure 123). In comparison, the MODVOLC algorithm reported 24 thermal alerts between August 2019 and January 2020 near the summit. Some thermal anomalies can be seen in Sentinel-2 thermal satellite imagery throughout this reporting period, even with the presence of meteorological clouds (figure 124). These thermal anomalies were accompanied by persistent gas-and-steam and ash plumes.

Figure 123. Thermal anomalies at Reventador persisted during 21 February 2019 through January 2020 as recorded by the MIROVA system (Log Radiative Power). Courtesy of MIROVA.

Figure 124. Sentinel-2 thermal satellite images of Reventador from August 2019 to January 2020 showing a thermal hotspot in the central summit crater summit. In the image on 7 January 2020, the thermal anomaly is accompanied by an ash plume. Courtesy of Sentinel Hub Playground.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Radio La Voz del Santuario (URL: https://www.facebook.com/Radio-La-Voz-del-Santuario-126394484061111/, posted at: https://www.facebook.com/permalink.php?story_fbid=2630739100293291&id=126394484061111); Martin Rietze, Taubenstr. 1, D-82223 Eichenau, Germany (URL: https://mrietze.com/, https://www.youtube.com/channel/UC5LzAA_nyNWEUfpcUFOCpJw/videos).

Pacaya is a highly active basaltic volcano located in Guatemala with volcanism consisting of frequent lava flows and Strombolian explosions originating in the Mackenney crater. The previous report summarizes volcanism that included multiple lava flows, Strombolian activity, avalanches, and gas-and-steam emissions (BGVN 44:08), all of which continue through this reporting period of August 2019 to January 2020. The primary source of information comes from reports by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) in Guatemala and various satellite data.

Strombolian explosions occurred consistently throughout this reporting period. During the month of August 2019, explosions ejected material up to 30 m above the Mackenney crater. These explosions deposited material that contributed to the formation of a small cone on the NW flank of the Mackenney crater. White and occasionally blue gas-and-steam plumes rose up to 600 m above the crater drifting S and W. Multiple incandescent lava flows were observed traveling down the N and NW flanks, measuring up to 400 m long. Small to moderate avalanches were generated at the front of the lava flows, including incandescent blocks that measured up to 1 m in diameter. Occasionally incandescence was observed at night from the Mackenney crater.

In September 2019 seismicity was elevated compared to the previous month, registering a maximum of 8,000 RSAM (Realtime Seismic Amplitude Measurement) units. White and occasionally blue gas-and-steam plumes that rose up to 1 km above the crater drifted generally S as far as 3 km from the crater. Strombolian explosions continued, ejecting material up to 100 m above the crater rim. At night and during the early morning, crater incandescence was observed. Incandescent lava flows traveled as much as 600 m down the N and NW flanks toward the Cerro Chino crater (figure 116). On 21 September two lava flows descended the SW flank. Constant avalanches with incandescent blocks measuring 1 m in diameter occurred from the front of many of these lava flows.

Figure 116. Webcam image of Pacaya on 25 September 2019 showing thermal signatures and the point of emission on the NNW flank at night using Landsat 8 (Nocturnal) imagery (left) and a daytime image showing the location of these lava effusions (right) along with gas-and-steam emissions from the active crater. Courtesy of INSIVUMEH.

Weak explosions continued through October 2019, ejecting material up to 75 m above the crater and building a small cone within the crater. White and occasionally blue gas-and-steam plumes rose 400-800 m above the crater, drifting W and NW and extending up to 4 km from the crater during the week of 26 October-1 November. Lava flows measuring up to 250 m long, originating from the Mackenney crater were descending the N and NW flanks (figure 117). Avalanches carrying large blocks 1 m in diameter commonly occurred at the front of these lava flows.

Figure 117. Photo of lava flows traveling down the flanks of Pacaya taken between 28 September 2019 and 4 October. Courtesy of INSIVUMEH (28 September 2019 to 4 October Weekly Report).

Continuing Strombolian explosions in November 2019 ejected material 15-75 m above the crater, which then contributed to the formation of the new cone. White and occasionally blue gas-and-steam plumes rose 100-600 m above the crater drifting in different directions and extending up to 2 km. Multiple lava flows from the Mackenney crater moving down all sides of the volcano continued, measuring 50-700 m long. Avalanches were generated at the front of the lava flows, often moving blocks as large as 1 m in diameter. The number of lava flows decreased during 2-8 November and the following week of 9-15 November no lava flows were observed, according to INSIVUMEH. During the week of 16-22 November, a small collapse occurred in the Mackenney crater and explosive activity increased during 16, 18, and 20 November, reaching RSAM units of 4,500. At night and early morning in late November crater incandescence was visible. On 24 November two lava flows descended the NW flank toward the Cerro Chino crater, measuring 100 m long.

During December 2019, much of the activity remained the same, with Strombolian explosions originating from two emission points in the Mackenney crater ejecting material 75-100 m above the crater; white and occasionally blue gas-and-steam plumes to 100-300 m above the crater drifted up to 1.5 km downwind to the S and SW. Lava flows descended the S and SW flanks reaching 250-600 m long (figure 118). On 29 December seismicity increased, reaching 5,000 RSAM units.

Figure 118. Lava flows moving to the S and SW at Pacaya on 31 December 2019. Courtesy of INSIVUMEH (28 December 2019 to 3 January 2020 Weekly Report).

Consistent Strombolian activity continued into January 2020 ejecting material 25-100 m above the crater. These explosions deposited material inside the Mackenney crater, contributing to the formation of a small cone. White and occasionally blue fumaroles consisting of mostly water vapor were observed drifting in different directions. At night, summit incandescence and lava flows were visible descending the N, NW, and S flanks with the flow on the NW flank traveling toward the Cerro Chino crater.

During August 2019 through January 2020, multiple lava flows and bright thermal anomalies (yellow-orange) within the crater were seen in Sentinel-2 thermal satellite imagery (figures 119 and 120). In addition, constant strong thermal anomalies were detected by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during 21 February 2019 through January 2020 within 5 km of the summit (figure 121). A slight decrease in energy was seen from May to June and August to September. Energy increased again between November and December. According to the MODVOLC algorithm, 37 thermal alerts were recorded during August 2019 through January 2020.

Figure 119. Sentinel-2 thermal satellite images of Pacaya showing thermal activity (bright yellow-orange) during August 2019 to November. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 120. Sentinel-2 thermal satellite images of Pacaya showing thermal activity (bright yellow-orange) during December 2019 through January 2020. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 121. The MIROVA thermal activity graph (log radiative power) at Pacaya during 21 February 2019 to January 2020 shows strong, frequent thermal anomalies through January with a slight decrease in energy between May 2019 to June 2019 and August 2019 to September 2019. Courtesy of MIROVA.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The 19-km-wide submerged Kikai caldera at the N end of Japan’s Ryukyu Islands was the source of one of the world's largest Holocene eruptions about 6,300 years ago, producing large pyroclastic flows and abundant ashfall. During the last century, however, only intermittent minor ash emissions have characterized activity at Satsuma Iwo Jima island, the larger subaerial fragment of the Kikai caldera; several events have included limited ashfall in communities on nearby islands. The most recent event was a single day of explosions on 4 June 2013 that produced ash plumes and minor ashfall on the flank. A minor episode of increased seismicity and fumarolic activity was reported in late March 2018, but no ash emissions were reported. A new single-day event on 2 November 2019 is described here with information provided by the Japan Meteorological Agency (JMA).

JMA reduced the Alert Level to 1 on 27 April 2018 after a brief increase in seismicity during March 2018 (BGVN 45:05); no significant changes in volcanic activity were observed for the rest of the year. Steam plumes rose from the summit crater to heights around 1,000 m; the highest plume rose 1,800 m. Occasional nighttime incandescence was recorded by high-sensitivity surveillance cameras. SO₂ measurements made during site visits in March, April, and May indicated amounts ranging from 300-1,500 tons per day, similar to values from 2017 (400-1,000 tons per day). Infrared imaging devices indicated thermal anomalies from fumarolic activity persisted on the N and W flanks during the three site visits. A field survey of the SW flank on 25 May 2018 confirmed that the crater edge had dropped several meters into the crater since a similar survey in April 2007. Scientists on a 19 December 2018 overflight had observed fumarolic activity.

There were no changes in activity through October 2019. Weak incandescence at night continued to be periodically recorded with the surveillance cameras (figure 9). A brief eruption on 2 November 2019 at 1735 local time produced a gray-white plume that rose slightly over 1,000 m above the Iodake crater rim (figure 10). As a result, JMA raised the Alert Level from 1 to 2. During an overflight the following day, a steam plume rose a few hundred meters above the summit, but no further activity was observed. No clear traces of volcanic ash or other ejecta were found around the summit (figure 11). Infrared imaging also showed no particular changes from previous measurements. Discolored seawater continued to be observed around the base of the island in several locations.

Figure 9. Incandescence at night on 25 October 2019 was observed at Satsuma Iwo Jima (Kikai) with the Iwanogami webcam. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 1st year of Reiwa [2019]).

Figure 10. The Iwanogami webcam captured a brief gray-white ash and steam emission rising above the Iodake crater rim on Satsuma Iwo Jima (Kikai) on 2 November 2019 at 1738 local time. The plume rose slightly over 1,000 m before dissipating. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 1st year of Reiwa [2019]).

Figure 11. During an overflight of Satsuma Iwo Jima (Kikai) on 3 November 2019 no traces of ash were seen from the previous day’s explosion; only steam plumes rose a few hundred meters above the summit, and discolored water was present in a few places around the shoreline. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 1st year of Reiwa [2019]).

For the remainder of November 2019, steam plumes rose up to 1,300 m above the summit, and nighttime incandescence was occasionally observed in the webcam. Seismic activity remained low and there were no additional changes noted through January 2020.

Geologic Background. Kikai is a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake lava dome and Inamuradake scoria cone, as well as submarine lava domes. Historical eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Tokara-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Tokara-Iojima.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html).

Nevado del Ruiz is a glaciated stratovolcano located in Colombia. It is most known for the eruption on 13 November 1985 that produced an ash plume and pyroclastic flows onto the glacier, triggering a lahar and killing approximately 25,000 people in the towns of Armero (46 km W) and Chinchiná (34 km E). Since the September 1985-July 1991 eruption, volcanism has occurred dominantly at the Arenas crater, with eruptive periods during February 2012-July 2013 and November 2014-May 2017 (BGVN 42:06 and 44:12). The previous eruption included ash and gas-and-steam plumes, ashfall, and thermal anomalies through May 2017, after which no clear observations of ongoing activity were available until an ash plume was seen in satellite and webcam images on 18 December 2017. This report provides data and observations from January 2018 through December 2019 using information primarily from reports by the Servicio Geologico Colombiano and the Observatorio Vulcanológico y Sismológico de Manizales, the Washington Volcanic Ash Advisory Center (VAAC) notices, and various satellite data.

Summary of activity during December 2017-December 2019. Although data is incomplete, the current eruptive period is considered to have begun with the emission of an ash plume on 18 December 2017. The Washington VAAC issued an advisory that day for an ash plume to 6 km that was moving west and dispersing, further describing it as a "thin veil of volcanic ash and gasses" that was seen in visible satellite imagery, NOAA/CIMSS, and supported by webcam imagery.

Reports of significant ash plumes visible in satellite imagery were infrequent in 2018 and 2019, with a few notable pulses in July 2018, February-March 2019, and August-September 2019 (figure 95). Sentinel-2 thermal satellite data in comparison with Suomi NPP/VIIRS sensor data, and the MODVOLC algorithm for MODIS data registered infrared thermal hotspots intermittently throughout 2018 to 2019 with more frequent anomalies during January-March 2018, August 2018, October 2018-February 2019, and November-December 2019; observations during March-June of each year were low. Identification of SO₂ emissions were frequent and consistent during all of 2018-2019 (figure 96).

Figure 95. Timeline summary of observed activity at Nevado del Ruiz from January 2018 through December 2019. VAAC reports typically indicate a significant ash plume. Satellite-based SO2 data is variable with respect to volume of emitted gas, but reflects a point source at the volcano. For Sentinel-2, MODVOLC, and VIIRS data, the dates indicated represents detected thermal anomalies. White areas indicate no activity was observed, which may also be due to meteoric clouds. Data courtesy of Washington VAAC, NASA Goddard Space Flight Center, Sentinel Hub Playground, HIGP, and NASA Worldview using the "Fire and Thermal Anomalies" layer.

Figure 96. Examples of SO2 plumes from Nevado del Ruiz detected by the Aura/OMI instrument during 12 May (top left), 7 October (top middle), and 29 November 2018 (top right) and 9 January (bottom left), 30 March (bottom middle), and 6 October 2019 (bottom right). Courtesy of NASA Goddard Space Flight Center.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows weak thermal anomalies within 5 km of the summit occurring dominantly between October 2018 through March 2019 (figure 97). Between April and October 2019, the number of thermal anomalies was low, registering eight during this time. The number of thermal signatures increased at the beginning of November 2019 and continued through the rest of 2019.

Figure 97. Weak thermal anomalies at Nevado del Ruiz for 25 September 2018 through December 2019 as recorded by the MIROVA system (log radiative power) occurred mostly during December 2018 through March 2019. Activity was low during April to October 2019 with renewed signatures in November 2019. Courtesy of MIROVA.

Seismicity that occurred during 2018-2019 was located mainly in the Arenas crater and consisted of low-frequency (LF) and very low-frequency (VLF) earthquakes and volcanic tremors, many of which were associated with minor gas-and-steam and ash emissions confirmed through webcams. The number of earthquakes reported by SGC fluctuated each week, but the energy remained relatively consistent. The highest magnitude earthquake that occurred during 2018 was on 26 October reaching 3.1 ML (local magnitude) and during 2019 the largest was 2.8 ML on 21 April.

Activity during 2018. Throughout 2018, gas-and-steam plumes, mostly composed of water vapor and sulfur dioxide frequently occurred, rising to a maximum of 2.2 km above the Arenas crater on 24 March. Weak thermal anomalies were seen intermittently in thermal satellite imagery from Sentinel-2 and NASA Worldview during 4 January through March and September to December (figure 98). Activity during March to April 2018 was relatively low and consisted dominantly of gas-and-steam emissions, low-energy seismicity, and intermittent thermal anomalies. Between 9 May and 5 August, no thermal signatures were detected.

Figure 98. Sentinel-2 thermal satellite imagery detected thermal anomalies (bright yellow-orange) within the Arenas crater at Nevado del Ruiz that were mostly visible during the beginning and last months of 2018. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Ash plumes were seen in GOES-EAST satellite imagery, through webcams, and by SGC personnel. The first ash plume of 2018 occurred on 21 April at 0800, six days after NASA Worldview detected a thermal anomaly within the Arenas crater. The plume rose 6 km altitude and drifted NW as seen in GOES-EAST satellite imagery and reported by the Washington VAAC. Weak gas-and-steam and ash emissions were confirmed by webcams on 22 July, associated with a volcanic tremor. On 11 August 2018, another ash plume was reported in a VAAC notice rising 6.7 km altitude drifting W. During the week of 21 August, SGC reported that seismicity in the Arenas crater was associated with minor gas-and-steam and ash emissions, as confirmed by webcams.

The number of ash plumes increased during September (figure 99), one of which reached a maximum altitude of 7.3 km on 2 September. On 5 September, a continuous volcanic tremor occurred and was accompanied by an ash plume rising 7 km altitude drifting W, according to a Washington VAAC report. Ashfall was observed during the week of 11 September in Manizales (30 km NW) and Villamaría (27 km NW). A new volcanic tremor occurred on 15 September and was accompanied by various ash emissions reaching 1.4 km above the crater and drifting NW as confirmed by PNNN, inhabitants within the vicinity of the volcano, and the Washington VAAC. Seismicity continuing into the weeks of 25 September and 2 October was also accompanied by ash emissions, rising to an altitude of 1.4 km above the crater on 22 September. The number of reported gas-and-steam and ash emissions decreased after September; ash emissions were reported by SGC on 19, 22, 26, and 31 October, 6, 9, and 17 November, and 14 December.

Figure 99. Webcam images of gas-and-steam and ash plumes rising from Nevado del Ruiz during 2018. Courtesy of Servicio Geologico Colombiano.

Activity during 2019. Gas-and-steam and ash emissions continued intermittently through 2019, with an increased number of ash emissions compared to the previous year. Infrared hotspots were detected in Sentinel-2 satellite imagery primarily during January-February 2019 and December 2019, often accompanied by gas-and-steam emissions (figure 100). An ash plume was seen in GOES-EAST satellite imagery on 2 January 2019, rising to an altitude of 5.8 km and drifting NW, according to a Washington VAAC report. On 7 January, ashfall in Manizales and Villamaría was observed. A thermal hotspot was detected in multispectral imagery, according to a Washington VAAC report on 29 January. Slight ground deformation was observed by GNSS and electronic inclinometers during the weeks of 29 January and 10 September. Volcanism was relatively low during February to March and consisted of mostly gas-and-steam emissions and rare ash plumes; these ash emissions were reported on 2 and 9 February and 16 March by the Washington VAAC rising between 5.8-6.7 km altitude. Gas-and-steam emission were detected on 6 and 17 February and 17 and 21 March.

Figure 100. Sentinel-2 thermal satellite imagery detected thermal anomalies (bright yellow-orange) mostly visible within the Arenas crater at Nevado del Ruiz during the last three months of 2019 and were accompanied by gas-and-steam emissions. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

The number of ash emissions detected in satellite imagery increased after March, occurring on 4, 7, 16, 17-19, and 23-26 April and 2 and 4-5 May. Ash plumes were detected on 27 June, 4, 7, 8, and 29 July, 1 August, and on 19, 29, and 30 September. Los Nevados National Natural Park (PNNN) personnel reported that the ash plume on 8 July was accompanied by gas-and-steam emissions and a continuous tremor occurring at 0722 (figure 101). These emissions rose 450 m above the crater and drifted W. On 29 September, a tremor associated with an ash plume occurred at 2353. The ash plume rose to a maximum altitude of 8.5 km drifted NW, resulting in ashfall confirmed by PNNN, GOES-EAST satellite imagery, and SGC personnel in the field.

Seismicity increased during the week of 1 October compared to the previous week, which was accompanied by several gas-and-steam and ash emissions rising 1 km altitude drifting NW observed by webcams, PNNN personnel, and GOES-EAST satellite imagery. An ash plume rising 7 km altitude drifting NW on 4 October resulted in fine ashfall in Manizales. Ash plumes rose to an altitude of 7.3 km drifting N on 5, 9, and 16 October and was seen in the GOES-EAST satellite according to Washington VAAC notices. Ash emissions were observed frequently during November; 11 Washington VAAC notices, the most for any month during 2019, reported emissions ranging 5.8 to 7 km altitude drifting in different directions. Gas-and-steam plumes rose to a maximum of 2.4 km above the crater during 14 and 30 November. The number of reported emissions decreased during December with one ash emission observed on 4 December.

Figure 101. Webcam images of gas-and-steam and ash plumes rising from Nevado del Ruiz during 2019. Courtesy of Servicio Geologico Colombiano.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: Servicio Geologico Colombiano (SGC), Diagonal 53 No. 34-53 - Bogotá D.C., Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/).

Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Antarctica's Ross Island, 35 km SSW. Because of the remoteness of the volcano, activity is primarily monitored using satellites (figure 27), including MODIS infrared detectors aboard the Aqua and Terra satellites and analyzed using the MODVOLC algorithm.

Figure 27. Satellite image of Erebus (on left) acquired on 19 October 2019 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite. The false-color combines visible and near-infrared wavelengths of light (ASTER bands 3, 2, 1). The area was just days away from constant 24-hour sunlight when this image was acquired, with the Sun angle low enough to cast a long shadow towards the west. The blue patches are areas clear of surface snow, exposing glacial ice. Nearby areas that appear smooth are the snow- and ice-topped waters of McMurdo Sound. Courtesy of NASA Earth Observatory: image by Joshua Stevens, using data from NASA/METI/AIST/Japan Space Systems and U.S./Japan ASTER Science Team; description by Kathryn Hansen.

Available since 2000, MODIS-MODVOLC data have shown a strong and nearly continuous thermal signal through 2019. A compilation of thermal alert pixels during 2017-2019 (table 5, continuing the table in BGVN 44:01) shows a wide range of detected activity in 2019, with a high of 162 in April. Infrared satellite imagery from Sentinel-2 identified one or two lava lakes during January-March and September-December 2019; a few of the images showed gas emissions, possibly from melted snow (figure 28).

Table 5. Number of monthly MODVOLC thermal alert pixels recorded at Erebus from 1 January 2017 to 31 December. Table compiled using data provided by the Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System.

Figures 28. Sentinel-2 satellite image of Erebus in color infrared (bands 8, 4, 3) on 20 October 2019 showing two lava lakes in the summit crater. Courtesy of Sentinel Hub Playground.

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. It is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3,200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater; other lava lakes are sometimes present. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger Strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars since 1628. Its remoteness on the east side of the Andean crest has made ground observations difficult until recent times. The current eruption began in March 2019; this report covers ongoing activity from July through December 2019. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and a number of sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery.

The eruption that began in March 2019 continued during July-December 2019 with activity focused on two eruptive centers at the summit, the Cráter Central and the Ñuñurco (southeast) vent. The Cráter Central produced explosive activity which generated small ash emissions that rose up to 3.2 km above the crater and were frequently directed towards the W and SW. Associated with these emissions in early November, ashfall was reported in Chimborazo province and elsewhere, and ejecta from explosions was deposited on all the upper flanks. At the Ñuñurcu vent, effusive activity resulted in an almost continuous emission of material down the SE flank. Small rockfalls and pyroclastic flows along the fronts and sides of the flows reached the basin and upper channel of the Volcán river which flows into the Upano river. These deposits were remobilized by rainfall and formed mud and debris flows (lahars) in the Volcán river, which caused damming at the confluence with the Upano river downstream. Increased thermal activity was recorded by the MIROVA system from mid-May 2019 through the end of the year, corresponding to the ongoing lava flow and explosive activity (figure 36).

Figure 36. Increased heat flow at Sangay was recorded beginning in mid-May 2019 and continued steadily through the end of the year as seen in this graph of Log Radiative Power produced by the MIROVA project. Courtesy of MIROVA.

Activity during July-September 2019. Several ash emissions were reported by the Washington VAAC during the first part of July 2019. On 1 July a plume rose to 6.7 km altitude and extended 45 km WSW from the summit. During 3-4 July a plume rose 6.4 km and drifted WNW; it included occasional discrete emissions that extended approximately 35 km from summit. The VAAC recorded a bright hotspot in SWIR imagery on 4 July. On 11 July a 7.3-km-altitude ash plume detached from the summit and extended from immediately W of the summit S past Segu. Webcam and satellite imagery on 11 July demonstrated the continuing thermal activity of the lava flow on the SE flank and ash emissions drifting W (figure 37). On 29 July a plume rose to 7.6 km altitude and drifted 65 km WSW. Later in the day continuous emissions were drifting SW from the summit at 5.8 km altitude before dissipating. The first satellite images of 30 July showed a plume extending 110 km WSW from the summit at 7 km altitude. Activity decreased later in the day and the plume extended W about 45 km from the summit at 6.4 km altitude. Composite satellite imagery on 31 July showed almost constant ash emissions extending over 150 km W of the summit (figure 38).

Figure 37. The local webcam at Sangay (left) and Sentinel satellite imagery (right, bands 12, 11, and 8A) both confirmed the high heat output from the active lava flow on the SE flank on 11 July 2019. The flow is about 2 km long. A plume of steam and ash also drifted W from the summit (right). Courtesy of IG-EPN (left) and Sentinel Hub Playground (right).

Figure 38. An ash emission from Sangay on 29 July 2019 drifted tens of km WSW as seen in the webcam (left). Two days later on 31 July a small dark ash plume was visible above the dense cloud cover in Sentinel satellite imagery; the VAAC reported ash drifting W throughout the day. Courtesy of IG-EPN (left) and Sentinel Hub Playground (right).

During an overflight on 6 August 2019 scientists from IG-EPN observed ash emissions from the Cráter Central, and the lava flow continuing from the Vento Ñuñurco in a similar location to where it was in May 2019 (figure 39). Light-colored sediments filled much of the upper basin of the Volcán river. Thermal images of the area also showed that some of the deposits were elevated in temperature, even in the riverbed (figure 40).

Figure 39. The E and SE flanks of Sangay showed continuing activity during August 2019 (right) that was similar to activity going on during May (left). In May, steam issued from the Cráter Central and a lava flow descended the SE flank from Vento Ñuñurco (photo by M. Almeida, IG-EPN). In August, diffuse ash and steam issued from the Crater Central, and a new flow descended from the same area of the Vento Ñuñurco seen in May (photo by P. Ramón , IG-EPN). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 5, Quito, 13 de noviembre del 2019).

Figure 40. The upper Volcán River basin was filled with deposits of pyroclastic material associated with the most recent activity at Sangay when observed during an overflight on 6 August 2019 (left). Thermal analysis of the drainage indicated that several of the deposits were still hot, as was the active flow (right). Left photo by P. Ramón, thermal image by Silvia Vallejo; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 5, Quito, 13 de noviembre del 2019).

Frequent ash emissions continued during August 2019. Diffuse ash was seen moving W from the summit at 5.8 km altitude on 1 August. Another short-lived plume was observed extending 15 km WSW the next day at 5.8-6.1 km altitude. Continuous ash emissions were visible in satellite imagery extending 35 km SW from the summit at 6.1 km altitude on 5 August. During the next two days, the emissions extended 45 km WSW and a prominent hot spot was visible through the meteoric clouds. The ash plume altitude rose to 6.7 km on 8 August and a larger ash emission extended more than 100 km WSW. A new emission the next day drifted 25-35 km W at 6.1 km altitude. A well-defined hotspot seen in shortwave imagery on 10 August accompanied an ash emission that extended 35 km WSW from the summit at 6.7 km altitude. On 12 August a plume drifted 65 km due W at 6.4 km altitude; emissions continued the next day in the same direction at 6.1 km altitude. An ash plume extended 100 km WNW of the summit at 5.8 km altitude on 18 August. A very bright hotspot was observed in infrared imagery the next day. The ash emissions continued to be visible in satellite imagery through 20 August.

An ash plume extending 10 km N from the summit on 25 August coincided with the appearance of a vivid hot spot, according to the Washington VAAC. The plume was initially reported at 7.6 km altitude and later in the day was at 6.7 km altitude. The leading edge of an ash emission reported on 31 August was 350 km W of the summit late that day moving at 5.8 km altitude, and over 950 km WSW before it dissipated on 1 September. Fewer ash emissions were reported during September 2019. The leading edge of a plume extended about 160 km W from the summit on 2 September at 7.6 km altitude; a second emission that day moved NE at 6.4 km altitude. On 4 September a small emission rose to 6.4 km altitude and drifted SW; on 9 September a plume was observed moving W at 5.5 km. A new emission on 19 September was seen in satellite imagery moving in many different directions (N, NE, E, and SE) at 6.7 km altitude. The lava flow on the SE flank produced a strong thermal signature that appeared unchanged from late August through late September (figure 41).

Figure 41. The thermal signature from the lava flow on the SE flank of Sangay appeared unchanged from late August (top left) to late September 2019 (bottom right) in Sentinel-2 imagery (bands 12, 11, and 8A); an ash emission drifted in multiple directions on 19 September 2019. Courtesy of Sentinel Hub Playground and IG-EPN.

Activity during October-December 2019. Pulses of ash were reported during 1, 9-11, 14, 26, and 31 October 2019 by the Washington VAAC. On 1 October the plume rose to 5.8 km altitude and drifted NE. A narrow plume on 9 October extending 55 km NW corresponded with a bright hotspot at its source. Concentrated emissions the next day rose to 7.3 km altitude and extended over 200 km WNW. Later in the day on 10 October emissions were reported at 5.8 km drifting W. A substantial thermal anomaly and a constant plume of diffuse ash appeared in satellite imagery on 14 October at 6.1 km altitude drifting 15 km W. Diffuse emissions on 26 October appeared 35 km NW of the summit at 5.8 km altitude. The intensity of the thermal anomaly from the lava flow on the SE flank remained strong during the month, and emissions of steam and ash were also visible in satellite images (figure 42). In a site visit on 19 October 2019, IG-EPN scientists measured a recent lahar deposited near the confluence of the Volcán and Upano rivers. It was full of sand-sized particles and approximately 30 cm thick at the river’s edge (figure 43).

Figure 42. The thermal anomaly from the lava flow on the SE flank of Sangay remained strong during October 2019, and both ash and steam emissions were seen in Sentinel-2 satellite images (bands 12, 11, and 8A). The lava flow is about 2 km long. Courtesy of Sentinel Hub Playground.

Figure 43. A lahar deposit at the confluence of Río Volcán and Río Upano at Sangay was about 30 cm thick on 19 October 2019. Photograph by Francisco Vasconez, courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 5, Quito, 13 de noviembre del 2019).

Ash emissions during 10-26 November 2019 were reported daily by the Washington VAAC, each lasting for less than 24 hours before dissipating. The first report of ash detected in satellite imagery on 10 November indicated that the plume extended 25 km WSW at 6.7 km altitude. On the subsequent days, the plumes drifted in many different directions at altitudes of 5.8-7.3 km, usually around 6.4 km. The plumes generally drifted 25-45 km from the summit, although some were still visible over 100 km away, depending on weather conditions. The highest plume reached 7.3 km altitude on 18 November and drifted W. The plume on 26 November rose to 6.4 km altitude and was last seen 140 km SW of the summit before it dissipated. Pyroclastic flows were witnessed on 20 November 2019 (figure 44). The last plume of the month, on 29 November, rose to 6.4 km altitude and drifted 65 km W, dissipating quickly, and was accompanied by a very bright thermal anomaly.

Figure 44. Ash plumes from Sangay rose to 5.8 km altitude on 20 November 2019 and drifted 25 km NE before dissipating, according to the Washington VAAC. Pyroclastic flows appeared on the flank that day. Courtesy of Walter Calle C.

Ashfall was reported during November in the provinces of Chimborazo (Alao, 20 km NW, Cebadas, 35 km NW, and Guaguallá), Morona Santiago (Macas, 40 km SE), and Azuay (120 km SW). Samples of ash collected from two locations indicated that the amount of material was very small (less than10 g/m2) with a high content of extremely fine ash (between 40 and 60% ash less 63 μm in diameter). The larger fraction over 63 μm was mainly composed of juvenile magma (80%) and a small fraction of free crystals (10% plagioclase and pyroxenes), oxidized fragments (5%), and gray lithics (5%) (figure 45).

Figure 45. Photos from a binocular microscope of the greater than 63 μm fraction of ash from Sangay collected in Macas and at the SAGA station during November 2019. See text for details. Courtesy if IG (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

In a report issued in early December 2019 the IG-EPN noted that eruptive activity which increased in May 2019 was continuing (figure 46); a small amount of inflation was observed during November. Explosive activity continued at the Cráter Central with ash plumes reaching 2 km above the summit, and plumes drifting frequently towards the NE causing small amounts of ash to fall in the Chimborazo, Morona Santiago, and Azuay provinces. Effusive activity from the Ñuñurco vent produced almost continuous lava that flowed down the SE flank. Small pyroclastic flows around the margins of the lava flows reached the basin and the upper channel of the Volcán river, causing temporary dams that turned to mudflows during rain events.

Figure 46. IG-EPN published this multi-parameter chart of activity of the Sangay volcano from May to 1 December 2019. a: seismic activity (number of events per day) detected at the PUYO station (source: IG-EPN); b: SO2 emissions (tons per day) detected by the Sentinel-5P satellite sensor (source: MOUNTS); c: height of ash clouds (m above crater level) detected by the GOES-16 satellite sensor (source: Washington VAAC); d: thermal emission power (megawatt) detected by the MODIS satellite sensor (source: MODVOLC) and estimated accumulated lava volume (million m3, dotted lines represent the error range). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

During an overflight on 3 December 2019 a strong smell of sulfur was noted 1 km above the summit. The Ñuñurco vent continued to emit lava with a maximum apparent temperature of 100 to 210°C (figure 47). IG-EPN scientists concluded that approximately 58 ± 29 million m³ of lava had been emitted through 3 December.

Figure 47. Views of the SE flank of Sangay on 3 December 2019 with visible (left) and thermal (right) imagery. Photograph by C. Viracucha, thermal analysis by F. Naranjo; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Recurring lahars in the Río Volcán during the period occasionally reached the Rio Upano (figure 48). By late November, they had partially dammed the Upano river (figure 49). On 26 November 2019 when IG-EPN and Sangay National Park officials inspected the area, they recorded deposits more than 2 m thick at the confluence of the two rivers (figure 50). During an overflight the next day, additional deposits were identified along 16 km upstream. The total volume of the lahar deposits was estimated at 5 million m³ to date.

Figure 48. Inferred lahar deposits at Sangay along the Río Volcán from the foot of the volcano up to its confluence with Río Upano shown in red. Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Figure 49. Lahar deposits at Sangay filled Río Volcán and dammed part of the confluence where it joins río Upano when photographed during an overflight on 26 November 2019. Photographs by Pedro Espín; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Figure 50. Lahar deposits from Sangay exceeded 2 m in thickness at the confluence of the Upano and Volcán rivers on 26 November 2019. Photography by Pedro Espín; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Another extended period of ash emissions began on 4 December 2019 and continued daily through 19 December. The Washington VAAC reported that an ash plume was initially at 6.7 km altitude drifting S on 4 December. Continuous emissions were observed at 4.6 km altitude later in the day and were visible in satellite images located 25 km S at 5.8 km altitude that evening. The drift directions were initially mostly SW in early December, but migrated to mostly SE during 10-16 December, then back to SW. Plume altitudes ranged from 5.8 to 7.3 km and satellite images revealed ash as far as 160 km away; most plumes were visible to about 25 km before dissipating or disappearing into meteoric clouds. IG-EPN reported steam and gas emissions with small amounts of ash on 13 December that drifted SE (figure 51). Small block avalanches from the active flow were also observed on the SE flank. The next day, ash and gas emissions rose to 1,170 m above the summit and drifted NE while the lava flow appeared incandescent on the SE flank.

During the night of 14-15 December ashfall was reported in San Isidro in the Province of Morona Santiago (30 km SE). Ash plumes rose 870 m above the summit on 15 December and 1,470 m high the next day. Ashfall was reported in the Guasuntos (60 km SW) and Llagos (80 km SW) areas of the Chimborazo province on the morning of 16 December. The next day plumes drifted SE and SW, and minor ashfall was reported that night (16-17 December) in Macas (40 km SE), Morona Santiago province. Satellite images captured gas and ash emissions on 25 December, and ashfall was reported in Alausí (60 km SW) in the province of Chimborazo. An explosion on 29 December produced an ash plume that rose to 6.1 km and first drifted WNW then in an arc to the SW almost 185 km to the coast. Multiple plumes at 5.8-6.7 km drifted westerly for tens of kilometers that day and the next. Prominent thermal anomalies were noted in satellite imagery on 8, 15, 17, and 30 December.

Figure 51. Numerous explosions produced ash emissions from Sangay during 4-30 December 2019, shown here on days 13, 14, 16, and 25. Courtesy of IG-EPN (Informe Diario del Estado del Volcán Sangay No. 2019-1, 13 Diciembre; No. 2019-2, 14 Diciembre; No. 2019-5, 17 Diciembre; No. 2019-13, 25 Diciembre 2019).

By late December 2019, the lahar deposits in Rio Volcán had backed up noticeably further into the Upano river from a month earlier (figure 52). Sulfur dioxide emissions were not recorded during July through August 2019, but small, pulsing plumes were captured in satellite images during September, October and November, gradually increasing in density. Several plumes were detected hundreds of kilometers from the volcano before dissipating; by December, larger, more frequent pulses of SO₂ were measured during many days when ash emissions were reported (figure 53).

Figure 52. Lahar deposits from Sangay in the Rio Volcán (right) continued to dam up the Rio Upano into late December 2019. Compare with figure 49 taken one month earlier. Photo by WJ Hernandes, courtesy of Edgar Chulde, posted online 21 December 2019.

Figure 53. Sulfur dioxide emissions from Sangay were weak but persistent during September-November 2019 (top row), often drifting in narrow plumes with distinct pulses. During December, the density of the SO2 emissions increased noticeably (bottom row). Columbia’s Nevado del Ruiz was also producing plumes of SO2 at the same time. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Walter Calle C., Macas, Ecuador (Twitter: @walterc333; URL: https://twitter.com/walterc333/status/1197273200822046720); Edgar Chulde, Quito, Ecuador (Twitter: @EdgarChulde2; URL: https://twitter.com/EdgarChulde2/status/1208547471024173056).

Shishaldin is located near the center of Unimak Island in Alaska and has been frequently active in recent times. Activity includes steam plumes, ash plumes, lava flows, lava fountaining, pyroclastic flows, and lahars. The current eruption phase began on 23 July 2019 and through September included lava fountaining, explosions, and a lava lake in the summit crater. Continuing activity during October 2019 through January 2020 is described in this report based largely on Alaska Volcano Observatory (AVO) reports, photographs, and satellite data.

Minor steam emissions were observed on 30 September 2019, but no activity was observed through the following week. Activity at that time was slightly above background levels with the Volcano Alert Level at Advisory and the Aviation Color Code at Yellow (figure 17). In the first few days of October weak tremor continued but no eruptive activity was observed. Weakly elevated temperatures were noted in clear satellite images during 4-9 October and weak tremor continued. Elevated temperatures were recorded again on the 14th with low-level tremor.

Figure 17. Alaska Volcano Observatory hazard status definitions for Aviation Color Codes and Volcanic Activity Alert Levels used for Shishaldin and other volcanoes in Alaska. Courtesy of AVO.

New lava extrusion was observed on 13 October, prompting AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch. Elevated surface temperatures were detected by satellite during the 13th and 17-20th, and a steam plume was observed on the 19th. A change from small explosions to continuous tremor that morning suggested a change in eruptive behavior. Low-level Strombolian activity was observed during 21-22 October, accompanied by a persistent steam plume. Lava had filled the crater by the 23rd and began to overflow at two places. One lava flow to the north reached a distance of 200 m on the 24th and melted snow to form a 2.9-km-long lahar down the N flank. The second smaller lava flow resulted in a 1-km-long lahar down the NE flank. Additional snowmelt was produced by spatter accumulating around the crater rim. By 25 October the northern flow reached 800 m, there was minor explosive activity with periodic lava fountaining, and lahar deposits reached 3 km to the NW with shorter lahars to the N and E (figure 18). Trace amounts of ashfall extended at least 8.5 km SE. There was a pause in activity on the 29th, but beginning at 1839 on the 31st seismic and infrasound monitoring detected multiple small explosions.

Figure 18. PlanetScope satellite images of Shishaldin on 3 and 29 October 2019 show the summit crater and N flank before and after emplacement of lava flows, lahars, and ashfall. Copyright PlanetLabs 2019.

Elevated activity continued through November with multiple lava flows on the northern flanks (figure 19). By 1 November the two lava flows had stalled after extending 1.8 km down the NW flank. Lahars had reached at least 4 km NW and trace amounts of ash were deposited on the north flank. Elevated seismicity on 2 November indicated that lava was likely flowing beyond the summit crater, supported by a local pilot observation. The next day an active lava flow moved 400 m down the NW flank while a smaller flow was active SE of the summit. Minor explosive activity and/or lava fountaining at the summit was indicated by incandescence during the night. Small explosions were recorded in seismic and infrasound data. On 5 November the longer lava flow had developed two lobes, reaching 1 km in length. The lahars had also increased in length, reaching 2 km on the N and S flanks. Incandescence continued and hot spatter was accumulating around the summit vent. Activity continued, other than a 10-hour pause on 4-5 November, and another pause on the 7th. The lava flow length had reached 1.3 km on the 8th and lahar deposits reached 5 km.

Figure 19. Sentinel-2 thermal satellite images show multiple lava flows (orange) on the upper northern flanks of Shishaldin between 1 November and 1 December 2019. Blue is snow and ice in these images, and partial cloud cover is visible in all of them. Sentinel-2 Urban rendering (bands 21, 11, 4) courtesy of Sentinel Hub Playground.

After variable levels of activity for a few days, there was a significant increase on 10-11 November with lava fountaining through the evening and night. This was accompanied by minor to moderate ash emissions up to around 3.7 km altitude and drifting northwards, and a significant increase in seismicity. Activity decreased again during the 11-12th while minor steam and ash emissions continued. On 14 November minor ash plumes were visible on the flanks, likely caused by the collapse of accumulated spatter. By 15 November a large network of debris flows consisting of snowmelt and fresh deposits extended 5.5 km NE and the collapse of spatter mounds continued. Ashfall from ash plumes reaching as high as 3.7 km altitude produced thin deposits to the NE, S, and SE. Activity paused during the 17-18th and resumed again on the 19th; intermittent clear views showed either a lava flow or lahar descending the SE flank. Activity sharply declined at 0340 on the 20th.

Seismicity began increasing again on 24 November and small explosions were detected on the 23rd. A small collapse of spatter that had accumulated at the summit occurred at 2330 on the 24th, producing a pyroclastic flow that reached 3 km in length down the NW flank. A new lava flow had also reached several hundred meters down the same flank. Variable but elevated activity continued over 27 November into early December, with a 1.5-km-long lava flow observed in satellite imagery acquired on the 1st. On 5 December minor steam or ash emissions were observed at the summit and on the north flank, and Strombolian explosions were detected. Activity from that day produced fresh ash deposits on the northern side of the volcano and a new lava flow extended 1.4 km down the NW flank. Three small explosions were detected on the 11th.

At 0710 on 12 December a 3-minute-long explosion produced an ash plume up to 6-7.6 km altitude that dispersed predominantly towards the W to NW and three lightning strokes were detected. Ash samples were collected on the SE flank by AVO field crews on 20 December and analysis showed variable crystal contents in a glassy matrix (figure 20). A new ash deposit was emplaced out to 10 km SE, and a 3.5-km-long pyroclastic flow had been emplaced to the north, containing blocks as large as 3 m in diameter. The pyroclastic flow was likely a result from collapse of the summit spatter cone and lava flows. A new narrow lava flow had reached 3 km to the NW and lahars continued out to the northern coast of Unimak island (figure 21). The incandescent lava flow was visible from Cold Bay on the evening of the 12th and a thick steam plume continued through the next day.

Figure 20. An example of a volcanic ash grain that was erupted at Shishaldin on 12 December 2019 and collected on the SE flank by the Alaska Volcano Observatory staff. This Scanning Electron Microscope images shows the different crystals represented by different colors: dark gray crystals are plagioclase, the light gray crystals are olivine, and the white ones are Fe-Ti oxides. The groundmass in this grain is nearly completely crystallized. Courtesy of AVO.

Figure 21. A WorldView-2 satellite image of Shishaldin with the summit vent and eruption deposits on 12 December 2019. The tephra deposit extends around 10 km SE, a new lava flow reaching 3 km NW with lahars continuing to the N coast of Unimak island. Pyroclastic flow deposits reach 3.5 km to the N and contain blocks as large as 3 m. Courtesy of Hannah Dietterich, AVO.

A new lava flow was reported by a pilot on the night of 16 December. Thermal satellite data showed that this flow reached 2 km to the NW. High-resolution radar satellite images over the 15-17th showed that the lava flow had advanced out to 2.5 km and had developed levees along the margins (figure 22). The lava channel was 5-15 m wide and was originating from a crater at the base of the summit scoria cone, which had been rebuilt since the collapse the previous week. Minor ash emissions drifted to the south on the 19tt and 20th (figure 23).

Figure 22. TerraSAR-X radar satellite images of Shishaldin on 15 and 17 December 2019 show the new lava flow on the NW flank and growth of a scoria cone at the summit. The lava flow had reached around 2.5 km at this point and was 5-15 m wide with levees visible along the flow margins. Pyroclastic flow deposits from a scoria cone collapse event on 12 December are on the N flank. Figure courtesy of Simon Plank (German Aerospace Center, DLR) and Hannah Dietterich (AVO).

Figure 23. Geologist Janet Schaefer (AVO/DGGS) collects ash samples within ice and snow on the southern flanks of Shishaldin on 20 December 2019. A weak ash plume is rising from the summit crater. Photo courtesy of Wyatt Mayo, AVO.

On 21 December a new lava flow commenced, traveling down the northern slope and accompanied by minor ash emissions. Continued lava extrusion was indicated by thermal data on the 25th and two lava flows reaching 1.5 km and 100 m were observed in satellite data on the 26th, as well as ash deposits on the upper flanks (figure 24). Weak explosions were detected by the regional infrasound network the following day. A satellite image acquired on the 30th showed a thick steam plume obscuring the summit and snow cover on the flanks indicating a pause in ash emissions.

Figure 24. This 26 December 2019 WorldView-2 satellite image with a close-up of the Shishaldin summit area to the right shows a lava flow extending nearly 1.5 km down the NW flank and a smaller 100-m-long lava flow to the NE. Volcanic ash was deposited around the summit, coating snow and ice. Courtesy of Matt Loewen, AVO.

In early January satellite data indicated slow lava extrusion or cooling lava flows (or both) near the summit. On the morning of the 3rd an ash plume rose to 6-7 km altitude and drifted 120 km E to SE, producing minor amounts of volcanic lightning. Elevated surface temperatures the previous week indicated continued lava extrusion. A satellite image acquired on 3 January showed lava flows extending to 1.6 km NW, pyroclastic flows moving 2.6 km down the western and southern flanks, and ashfall on the flanks (figure 25).

Figure 25. This WorldView-2 multispectral satellite image of Shishaldin, acquired on 3 January 2019, shows the lava flows reaching 1.6 km down the NW flank and an ash plume erupting from the summit dispersing to the SE. Ash deposits cover snow on the flanks. Courtesy of Hannah Dietterich, AVO.

On 7 January the most sustained explosive episode for this eruption period occurred. An ash plume rose to 7 km altitude at 0500 and drifted east to northeast then intensified reaching 7.6 km altitude with increased ash content, prompting an increase of the Aviation Color Code to Red and Volcano Alert Level to Warning. The plume traveled over 200 km to the E to NE (figure 26). Lava flows were produced on the northern flanks and trace amounts of ashfall was reported in communities to the NE, resulting in several flight cancellations. Thermal satellite images showed active lava flows extruding from the summit vent (figure 27). Seismicity significantly decreased around 1200 and the alert levels were lowered to Orange and Watch that evening. Through the following week no notable eruptive activity occurred. An intermittent steam plume was observed in webcam views.

Figure 26. This Landsat 8 satellite image shows a detached ash plume drifts to the NE from an explosive eruption at Shishaldin on 7 January 2020. Courtesy of Chris Waythomas, AVO.

Figure 27. This 7 January 2019 Sentinel-2 thermal satellite image shows several lava flows on the NE and NW flanks of Shishaldin, as well as a steam plume from the summit dispersing to the NE. Blue is snow and ice in this false color image (bands 12, 11, 4). Courtesy of Sentinel-Hub playground.

Eruptive activity resumed on 18 January with lava flows traveling 2 km down the NE flank accompanied by a weak plume with possible ash content dispersing to the SW (figure 28). A steam plume was produced at the front of the lava flow and lahar deposits continued to the north (figures 29 to 32). Activity intensified from 0030 on the 19th, generating a more ash-rich plume that extended over 150 km E and SE and reached up to 6 km altitude; activity increased again at around 1500 with ash emissions reaching 9 km altitude. AVO increased the alert levels to Red/Warning. Lava flows traveled down the NE and N flanks producing meltwater lahars, accompanied by elevated seismicity (figures 33). Activity continued through the day and trace amounts of ashfall were reported in False Pass (figure 34). Activity declined to small explosions over the next few days and the alert levels were lowered to Orange/watch shortly after midnight. The next morning weak steam emissions were observed at the summit and there was a thin ash deposit across the entire area. Satellite data acquired on 23 January showed pyroclastic flow deposits and cooling lava flows on the northern flank, and meltwater reaching the northern coast (figure 35).

Figure 28. This Worldview-3 multispectral near-infrared satellite image acquired on 18 January 2020 shows a lava flow down the NE flank of Shishaldin. A steam plume rises from the end of the flow and lahar deposits from snowmelt travel further north. Courtesy of Matt Loewen, AVO.

Figure 29. Steam plumes from the summit of Shishaldin and from the lava flow down the NE flank on 18 January 2020. Lahar deposits extend from the lava flow front and towards the north. Photo courtesy of Matt Brekke, via AVO.

Figure 30. A lava flow traveling down the NE flank of Shishaldin on 18 January 2020, seen from Cold Bay. Photo courtesy of Aaron Merculief, via AVO.

Figure 31. Two plumes rise from Shishaldin on 18 January 2020, one from the summit crater and the other from the lava flow descending the NE Flank. Photos courtesy of Woodsen Saunders, via AVO.

Figure 32. A low-altitude plume from Shishaldin on the evening of 18 January 2020, seen from King Cove. Photo courtesy of Savannah Yatchmeneff, via AVO.

Figure 33. This WorldView-2 near-infrared satellite image shows a lava flow reaching 1.8 km down the N flank and lahar deposits filling drainages out to the Bering Sea coast (not shown here) on 19 January 2020. Ash deposits coat snow to the NE and E. Courtesy of Matt Loewen, AVO.

Figure 34. An ash plume (top) and gas-and-steam plumes (bottom) at Shishaldin on 19 January 2020. Courtesy of Matt Brekke, via AVO.

Figure 35. A Landsat 8 thermal satellite image (band 11) acquired on 23 January 2019 showing hot lava flows and pyroclastic flow deposits on the flanks of Shishaldin and the meltwater flow path to the Bering Sea. Figure courtesy of Christ Waythomas, AVO.

Activity remained low in late January with some ash resuspension (due to winds) near the summit and continued elevated temperatures. Seismicity remained above background levels. Infrasound data indicated minor explosive activity during 22-23 January and small steam plumes were visible on 22, 23, and 26 January. MIROVA thermal data showed the rapid reduction in activity following activity in late-January (figure 36).

Figure 36. MIROVA thermal data showing increased activity at Shishaldin during August-September, and an even higher thermal output during late-October 2019 to late January 2020. Courtesy of MIROVA.

Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/); Simon Plank, German Aerospace Center (DLR) German Remote Sensing Data Center, Geo-Risks and Civil Security, Oberpfaffenhofen, 82234 Weßling (URL: https://www.dlr.de/eoc/en/desktopdefault.aspx/tabid-5242/8788_read-28554/sortby-lastname/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Sangeang Api is located in the eastern Sunda-Banda Arc in Indonesia, forming a small island in the Flores Strait, north of the eastern side of West Nusa Tenggara. It has been frequently active in recent times with documented eruptions spanning back to 1512. The edifice has two peaks – the active Doro Api cone and the inactive Doro Mantori within an older caldera (figure 37). The current activity is focused at the summit of the cone within a horseshoe-shaped crater at the summit of Doro Api. This bulletin summarizes activity during May 2019 through January 2020 and is based on Darwin Volcanic Ash Advisory Center (VAAC) reports, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, or CVGHM) MAGMA Indonesia Volcano Observatory Notice for Aviation (VONA) reports, and various satellite data.

Figure 37. A PlanetScope satellite image of Sangeang Api with the active Doro Api and the inactive Doro Mantori cones indicated, and the channel SE of the active area that contains recent lava flows and other deposits. December 2019 monthly mosaic copyright of Planet Labs 2019.

Thermal anomalies were visible in Sentinel-2 satellite thermal images on 4 and 5 May with some ash and gas emission visible; bright pixels from the summit of the active cone extended to the SE towards the end of the month, indicating an active lava flow (figure 38). Multiple small emissions with increasing ash content reached 1.2-2.1 km altitude on 17 June. The emissions drifted W and WNW, and a thermal anomaly was also visible. On the 27th ash plumes rose to 2.1 km and drifted NW and the thermal anomaly persisted. One ash plume reached 2.4 km and drifted NW on the 29th, and steam emissions were ongoing. Satellite images showed two active lava flows in June, an upper and a lower flow, with several lobes descending the same channel and with lateral levees visible in satellite imagery (figure 39). The lava extrusion appeared to have ceased by late June with lower temperatures detected in Sentinel-2 thermal data.

Figure 38. Sentinel-2 satellite thermal images of Sangeang Api on 20 May and 9 June 2019 show an active lava flow from the summit, traveling to the SE. False color (urban) image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 39. PlanetScope satellite images of Sangeang Api show new lava flows during June and July, with white arrows indicating the flow fronts. Copyright Planet Labs 2019.

During 4-5 July the Darwin VAAC reported ash plumes reaching 2.1-2.3 km altitude and drifting SW and W. Activity continued during 6-9 July with plumes up to 4.6 km drifting N, NW, and SW. Thermal anomalies were noted on the 4th and 8th. Plumes rose to 2.1-3 km during 10-16th, and to a maximum altitude of 4.6 km during 17-18 and 20-22. Similar activity was reported during 24-30 July with plumes reaching 2.4-3 km and dispersing NW, W, and SW. The upper lava flow had increased in length since 15 June (see figure 39).

During 31 July through 3 September ash plumes continued to reach 2.4-3 km altitude and disperse in multiple directions. Similar activity was reported throughout September. Thermal anomalies also persisted through July-September, with evidence of hot avalanches in Sentinel-2 thermal satellite imagery on 23 August, and 9, 12, 22, and 27 September. Thermal anomalies suggested hot avalanches or lava flows during October (figure 40). During 26-28 October short-lived ash plumes were reported to 2.1-2.7 km above sea level and dissipated to the NW, WNW, and W. Short-lived explosions produced ash plumes up to 2.7-3.5 km altitude were noted during 30-31 October and 3-4 November 2019.

Figure 40. Sentinel-2 satellite thermal images of Sangeang Api on 7 and 22 October 2019 show an area of elevated temperatures trending from the summit of the active cone down the SE flank. False color (urban) image rendering (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Discrete explosions produced ash plumes up to 2.7-3.5 km altitude during 3-4 November, and during the 6-12th the Darwin VAAC reported short-lived ash emissions reaching 3 km altitude. Thermal anomalies were visible in satellite images during 6-8 November. A VONA was released on 14 November for an ash plume that reached about 2 km altitude and dispersed to the west. During 14-19 November the Darwin VAAC reported short-lived ash plumes reaching 2.4 km that drifted NW and W. Additional ash plumes were observed reaching a maximum altitude of 2.4 km during 20-26 November. Thermal anomalies were detected during the 18-19th, and on the 27th.

Ash plumes were recorded reaching 2.4 km during 4-5, 7-9, 11-13, and 17-19 December, and up to 3 km during 25-28 December. There were no reports of activity in early to mid-January 2020 until the Darwin VAAC reported ash reaching 3 km on 23 January. A webcam image on 15 January showed a gas plume originating from the summit. Several fires were visible on the flanks during May 2019 through January 2020, and this is seen in the MIROVA log thermal plot with the thermal anomalies greater than 5 km away from the crater (figure 41).

Figure 41. MIROVA log plot of radiative power indicates the persistent activity at Sangeang Api during April 2019 through March 2020. There was a slight decline in September-October 2019 and again in February 2020. Courtesy of MIROVA.

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, Doro Api and Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent historical eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/).

The current eruption at Dukono has been ongoing since 1933, with frequent explosions and ash plumes between August 2014 and March 2017 (BGVN 42:06). Similar activity has continued during April 2017-March 2018. Monitoring of the volcano is the responsibility of the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM).

Thermal measurements made by MODIS satellite instruments and processed by MIROVA show regular low-to-moderate thermal anomalies from April to October 2017 (figure 8), but none after December 2017 or in early 2018. MODVOLC analyses of thermal satellite data identified anomalies on 11 April, 29 April, 9 July, 1 August, and 21 August 2017.

Figure 8. Thermal anomalies recorded by the MIROVA system for the year ending 9 March 2018. Courtesy of MIROVA.

Explosions were frequently reported by both PVMBG and the Darwin Volcanic Ash Advisory Centre (VAAC), with ash plumes rising only a few hundred meters above the Malupang Warirang crater and drifting in various directions (table 17). Some plumes during this reporting period drifted for more than 100 km, with the longest reaching 230 km W on 27 May 2017.

Table 17. Monthly summary of reported ash plumes from Dukono for March 2017-March 2018. The direction of drift for the ash plume through each month is highly variable; only notable significant plumes are listed. Data courtesy of Darwin VAAC and PVMBG.

According to NASA Goddard Space Flight Center, SO₂ emissions are commonly detected from Dukono, but usually only at low levels, using the Ozone Monitoring Instrument (OMI) aboard NASA's Earth Observing System (EOS) Aura satellite and the Ozone Mapping and Profiler Suite (OMPS) aboard the NASA/NOAA Suomi National Polar-orbiting Partnership (SNPP) satellite. The strongest emissions captured in satellite data during this report period was on 6 March 2018 (figure 9).

Figure 9. Sulfur dioxide emissions from Dukono can be identified using the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite, as seen in this example from 6 March 2018. The highest amount of SO2 (red) is centered over the volcano. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Ethiopia's Erta Ale basaltic shield volcano has had at least one active lava lake since the mid-1960s, and possibly much earlier. Two active craters (North Pit and South Pit) within the larger oval-shaped Summit Caldera have exhibited periodic lava fountaining and lava lake overflows over the years. A new eruptive event located about 3 km SE of the Summit Crater appeared on 21 January 2017. Activity at the eruption site increased during subsequent months, sending lava flows several kilometers NE and SW from a newly formed lava lake. This report discusses activity from February 2017 through March 2018 as the flows traveled as far as 16 km from the main vent. Information comes from satellite thermal and visual imagery, and photographs and reports from ground-based expeditions that periodically visit the site.

Summary of activity, February 2017-March 2018. The 21 January 2017 activity at Erta Ale was the first time a vent outside of the Summit Caldera has been observed (figure 50). The initial vent or vents created multiple lava flows that traveled generally NE and SW from their sources, creating at least one lava lake that persisted for about a year (figure 51). The flows began inside an older caldera at a location about 3 km SE of the South Pit Crater, but eventually overflowed the caldera rim in multiple directions. As the flow fields enlarged, thermal imagery captured hot-spots along the flows that were likely produced by breakouts, skylights into lava tunnels, and hornitos, as well as multiple surges of flows across the growing fields (figure 52). The imagery also showed the locations of the advancing flow fronts which had reached over 5 km SW of the source by August 2017 and over 16 km NE of the source by March 2018, eventually reaching the alluvial plain NE of Erta Ale. Thermal anomaly data indicated that the maximum thermal energy output happened in April 2017, gradually decreasing through March 2018. The far NE front of the northeast flow field was still active at end of March 2018.

Figure 50. The summit of Erta Ale has two oblong NW-trending calderas. The northern Summit Caldera contains the North Pit Crater and the South Pit Crater. The North Pit Crater has had a solidified lava lake with a large hornito emitting magmatic gases and incandescence at night, and the South Pit Crater has had an active lava lake for many years that last overflowed its rim during mid-January 2017. The new eruption began at vents located about 3 km SE of the South Pit Crater near the northern rim of a second caldera referred to here as the Southeast Caldera, on 21 January 2017. The new eruption had not yet begun in this 16 January 2017 image. See figure 46 (BGVN 42:07) for additional images the following week that show the first flows from the new vents. Images copyright by Planet Labs Inc., 3 m per pixel resolution, and used with permission under a Creative Commons license (CC BY-SA 4.0), annotated by GVP.

Figure 51. A new lava lake formed during late January 2017 at the new eruption site about 3 km SE of the South Pit Crater at Erta Ale, inside the Southeast Caldera. This view is likely from the rim of the Southeast Caldera, looking SE or E, taken in February 2017. Visitors were not able to get closer to the vent due to the active flows for several months. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 52. An active new pahoehoe lava field flowed over older lava flows inside the Southeast Caldera at Erta Ale during February 2017. This photo was likely taken from the northern or western rim of the Southeast Caldera. Copyrighted photo by Stefan Tommasini, used with permission.

When the new eruptive episode began, the lava lake at the South Pit Crater drained rapidly to around 80-100 m below the rim, according to visitors to the site a few weeks later. The crater was emitting a strong thermal signal by early March 2017 as the lake level rose again. Visitors in April witnessed a fluctuating lake level rising and falling by up to 20 m every 30 minutes over several days. The thermal signal remained strong at the South Pit Crater through March 2018. Due to significant political instability in the area, ground visits are intermittent, but high-quality photographs were taken in February 2017, December 2017, and January 2018 that show the new lava lake and parts of the new flow fields.

Activity during late January-March 2017. The new eruptive event at Erta Ale began in late January 2017 at the northern end of the Southeast Caldera located; the first lava flows observed were locatedabout 3 km SE from the main Summit Caldera (figure 45 (BGVN 42:07) and figure 50). Two separate vent areas appeared active initially. The northern vent sent lava flows to the NE for several kilometers and to the SW a much shorter distance. The southern vent sent a stream of lava to the S. By the end of January 2017 the North and South Pit Craters at the Summit Caldera were still thermally active, but the signals were much stronger from the new vent areas in the Southeast Caldera (figure 53). A faint thermal signal from about 5 km E of the northern vent suggested the extent of the new flows in that direction.

Figure 53. A Sentinel-2 image from 29 January 2017 shows the initial activity at the new Southeast Caldera vents of Erta Ale (labelled Event 1 and Event 2). Weak thermal signals are apparent from the North and South Pit Craters (Pit Crater Nord, Pit Crater Sud) within the Summit Caldera, and much stronger thermal signals are evident from two areas inside the Southeast Caldera. A faint signal from about 5 km E of the new vents indicates possible flow activity breaking out of lava tubes in that region (Skylight). Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Etna, Erta Ale, Fuego, Piton de la Fournaise et Bogoslof, 3 février 2017).

A small group of travelers led by Ethiopian geologist Enku Mulugeta visited Erta Ale during the first half of February 2017. They reported that within the main Summit Caldera, the hornito in the North Pit Crater had collapsed and the lava lake in the South Pit Crater was about 80-100 m below the caldera floor level. The eruption in the Southeast Caldera was still very active, and they photographed the sizable new lava field which contained numerous pahoehoe flows, actively spattering hornitos, and a large lava lake (figures 51, 52, and 54). During the following months activity remained high both at the new eruption site and at the Summit Caldera where the lava lake in the South Pit Crater gradually rose back up to about 50 m below the caldera floor. Culture Volcan annotated a series of Sentinel-2 satellite thermal images which show the progression of the lava flows through the following year.

Figure 54. A large new lava field quickly formed inside the Southeast Caldera at Erta Ale after the beginning of the new eruptive event in late January 2017. When photographed here in February 2017, pahoehoe flows had spread outward from a central vent area (glow at top center) for over a kilometer in multiple directions. View is likely to the E from the W rim of the Southeast Caldera. Copyrighted photo by Stefan Tommasini, used with permission.

By 10 March 2017 only the southern vent area was active inside the Southeast Caldera. It continued to feed the lava field; lava was actively flowing S from the vent towards the W rim of the Southeast Crater, and NE, breaking out from lava tubes which blocked the thermal signal until about 2.6 km NE of the vent (figure 55). Thermal signals from both the North and South Pit Craters were distinct and stronger than in late January.

Figure 55. The thermal signals at both the North and South Pit Craters at Erta Ale were stronger in this 10 March 2017 image than in late January. Only one main source of lava is apparent at the Southeast Caldera. Lava flows directly from the primary vent SW towards the W rim of the caldera, and also surfaces from tunnels about two kilometers NE in an actively moving lava front. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité des volcans Etna et Erta Ale, 13 mars 2017).

A site visit to the South Pit Crater on 20 March 2017 demonstrated that the lake level had risen significantly since its drop in early February, and was once again actively convecting (figure 56). By the end of March 2017, satellite thermal imagery made clear the increasing thermal signal at the South Pit Crater, and in the Southeast Caldera, the major increase in effusion to the NE from the main vent. The width of the flow field had increased to about 1,400 m, and the farthest front was about 3,400 m NE from the vent (figure 57). The lava at the source measured about 180 x 75 m in size, suggesting a lava lake; a smaller overflow to the SW appeared to have reached the W rim of the Southeast Caldera by 30 March 2017 near the area where a new flow had first appeared in a 23 January 2017 satellite image (see figure 46, BGVN 42:07).

Figure 56. The South Pit Crater of Erta Ale on 20 March 2017 had risen significantly from its drop in February and was actively convecting. Photo by Jean-Michel Escarpit, courtesy of Cultur Volcan (Un point sur l'activité des volcans Fuego, Manam et Erta Ale, 22 mars 2017).

Figure 57. The thermal signal at the South Pit Crater continued to increase in this 30 March 2017 satellite image of Erta Ale. The main vent in the Southeast Caldera had dimensions of about 180 x 75 m, suggesting a lake had formed. A large increase in the thermally active area to the NE indicated that the flow field was expanding significantly in that direction, with a few small thermal anomalies between the lake and lava field suggesting a number of small flows or lava tube breakouts. Flow activity also continued to the SW reaching the W rim of the Southeast Crater where lava had flowed past the crater rim in late January (see figure 46, BGNV 42:07). Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité des volcans Klyuchevskoy et Erta Ale, 31 mars 2017).

Activity during April-May 2017. In the next Sentinel-2 satellite image from 9 April (figure 58), the distance to the farthest front of the lava flow had increased to about 4,600 m from the lava lake, and a new flow had appeared a few hundred meters east of the lake that extended about 1,100 m ENE from its source. Lava also flowed SW from the source to the SW rim of the Southeast Crater, appearing to pond against and flow slightly beyond the rim.

Figure 58. The lava flows continued to extend NE from their source inside the Southeast Crater at Erta Ale in this Sentinel-2 satellite image from 9 April 2017. The farthest edge of the northeast flow front was about 4,600 m from the lake. A new arm of lava flowed more than a kilometer ENE from its source close to the lake. Another thermal signature SW of the lake indicated an accumulation of lava near or slightly spilling over the SW rim of the Southeast Crater. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Erta Ale et Bogoslof, 16 avril 2017).

A group visited Erta Ale during 11-15 April 2017 in collaboration with Addis Ababa University geologist Enku Mulugeta. They noted that fluctuating lava lake levels at the South Pit Crater were cycling every 30 minutes or so between 40 and 50 m below the caldera floor (figures 59 and 60). Lava tubes from the walls of the crater would feed the lake with fresh lava after it drained. Two coalesced hornitos, about 7 m high, were present in the NE part of the crater, emitting SO2 gas and occasional lava. At the North Crater Pit, noisy degassing of SO2 from several hornitos at the center of the solidified crust was apparent. Observers at the Southeast Caldera could see the lava lake with the top about 10 m below its crater rim, and minor fountaining during the night, but they were not able to get closer than about 700 m due to the active flows.

Figure 59. The lava lake level at the South Pit Crater at Erta Ale during April 2017 was fluctuating by 10-20 m every 30 minutes or so. The high-stand of the lava is shown here. Courtesy of Toucan Photo.

Figure 60. The lava lake level at the South Pit Crater at Erta Ale during April 2017 was fluctuating by 10-20 m every 30 minutes or so. The low stand of the lava is shown here as the lava drains away. Courtesy of Toucan Photo.

By the end of April 2017 satellite thermal imagery indicated that the northeast flow field at the Southeast Caldera extended more than 7 km NE from the lake and was curving towards the E (figure 61). The lava lake was still thermally active, as was the South Pit Crater to the NW.

Figure 61. Sentinel-2 satellite imagery of Erta Ale on 29 April 2017 shows the growth of the northeast lava field from earlier in the month to more than 7 kilometers from its source. The South Pit Crater was still active, as was the source of the northeast lava field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (L'activité effusive reste soutenue à l'Erta Ale, 3 mai 2017).

Eleven days later, activity was quite different in the Southeast Caldera. Satellite imagery from 9 May 2017 (figure 62) showed a new, relatively narrow but bright lava flow moving NE for 2-3 km originating in a location slightly NE of the original lava lake; activity farther NE had diminished from the previous image. A subsequent image on 18 May looked similar, but by 19 May the narrow flow had been replaced by a much broader area of thermal anomaly in the region immediately E of the source. By 29 May 2017, the source of the lava appeared to have shifted several hundred meters SE of the earlier location, and a strong thermal signal once again extended NE across the northeast flow field from the new source for about two kilometers (figure 63).

Figure 62. A Sentinel-2 satellite image of Erta Ale on 9 May 2017 showed a shift to the NE in the location of the source of the active flows. A new narrow flow had traveled 2-3 km NE from a source located NE of the lava lake. The more distant northeast flow field had a much smaller thermal signature than on 29 April. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Breakout sur le volcan Erta Ale, 11 mai 2017).

Figure 63. A significant shift to the SE in the location of the lava source from a few weeks earlier is apparent in this Sentinel-2 satellite image of Erta Ale captured on 29 May 2017. A strong thermal anomaly trended NE across the northeast flow field for about two kilometers. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: une éruption vraiment exceptionnelle, 11 juin 2017).

Activity during June-August 2017. The rapidly changing flow field was significantly different again less than two weeks later in satellite imagery captured on 8 June 2017. Lava was flowing N, SE, and S across the northeast lava field, extending beyond the rim of the Southeast Caldera to the N and E. Another very strong thermal signal emerged from the SW corner of the Southeast Caldera where lava was flowing W and S outside the caldera rim forming a new southwest lava field (figure 64).

Figure 64. A Sentinel-2 satellite image of Erta Ale on 8 June 2017 shows significant changes in the location of the active flow fields from less than two weeks earlier. The South Pit Crater in the Summit Caldera still had a strong thermal signal suggesting an active lake in the crater. Flows in the Southeast Caldera appeared to be moving N, E, and S across the northeast lava field, and a new area with flows moving S and W from the SW rim of the Southeast Caldera formed the new Southwest lava field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: une éruption vraiment exceptionnelle, 11 juin 2017).

During June 2017, the most aggressive flow activity contributed to significant growth of the southwest lava field. By 28 June, infrared imaging detected flow fronts 4,500 m SW of the vent; they had extended to about 5,100 m, nearing the base of the SW flank of Erta Ale, by 5 July (figure 65). Flow activity also persisted in the northeast flow field with activity concentrated about 1.5 km NE of the vent on 28 June. Movement increased at the northeast flow field beginning in late June and it had extended to about 3.5 km NE of the lava lake by 5 July 2017.

Figure 65. Lava flow activity at the Southeast Caldera of Erta Ale during June 2017 was concentrated in the growing southwest flow field which had extended about 5,100 m from its lava lake source by 5 July 2017 in this Landsat 8 satellite image. The northeast flow field began extending farther NE during the first week of July, reaching 3,500 m from the lake by 5 July. Courtesy of ESA/Copernicus and NASA/USGS with annotations provided by Culture Volcan (Un point sur l'activité des volcans Copahue et Erta Ale, 8 juillet 2017).

Significant movement to the NE in the northeast flow field was apparent in satellite images beginning on 21 July 2017; the head of the flow had reached about 9.5 km from the lava lake by 28 July 2017, mostly focused in a narrow channel (figure 66). Activity decreased in the southwest flow field during July; the lava front had advanced only a few hundred meters by the end of July from its position on 5 July.

Figure 66. The northeast flow field at Erta Ale lengthened significantly during July 2017; the leading edge was about 9.5 km NE of the lava lake by 28 July 2017, as captured in this Sentinel-2 satellite image. The southwest flow field had extended just a few hundred meters SW from its location on 5 July. The distance between the South Pit Crater and the Southeast Caldera lava lake is about 2.7 km. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Les actus du jour: Katla en alerte jaune et quelques changements à l'Erta Ale, 29 juillet 2017).

During August 2017, lava continued to flow from the Southeast Caldera lava lake in two directions. The northeast flow front extended to 12 km from the vent by 17 August and had reached over 14 km by 7 September. The southwest flow field, while it remained in roughly the same area, had a decreased but still significant thermal signature in early September, suggesting continued but diminished activity throughout the period (figures 67).

Figure 67. During August 2017, lava continued to flow in two directions from the Southeast Caldera lava lake at Erta Ale. The northeast flow field had reached over 14 km from the lake by 7 September 2017 when this Landsat 8 satellite image was taken. The Southwest flow field, while it remained in roughly the same area, still had a significant thermal signature suggesting continued activity. Courtesy of ESA/Copernicus and NASA/USGS with annotations provided by Culture Volcan (volcan Erta Ale: ça continue; Fernandina: c'est moins sûr, 12 septembre 2017).

Activity during September-December 2017. In a Sentinel-2 satellite image from 26 September 2017, it was clear that the South Crater Pit was still thermally active, and that the southwest flow field had largely cooled with only a small area on its NW edge still producing a thermal anomaly (figure 68). In contrast, the northeast flow field had advanced about 1 km in the previous three weeks and was less than a kilometer from the edge of the valley alluvium. It finally reached the edge of the older lava field and began to advance across the alluvium NE of the volcano, more than 16 km from the lava lake, on 16 October 2017 (figure 69). Based on satellite imagery, Cultur Volcan interpreted that activity slowed significantly during November 2017, and while the thermal signal remained strong near the head of the flow, it did not advance significantly across the alluvium.

Figure 68. The South Pit Crater at Erta Ale still had an active lava lake on 26 September 2017 in this Sentinel-2 satellite image. The southwest lava field had largely cooled, with only a small thermal anomaly along it NW edge. The northeast lava field continued to be active; it had advanced about 1 km NE in about three weeks and was about 650 m from the edge of the alluvium. A significant number of hotspots along the northeast lava flow suggest that several skylights existed into lava tubes or there were small breakouts. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Les actus du jour: Heard Island, Erta Ale, Pacaya, Fuego, Sangay, Ol Doynio Lengai, 5 octobre 2017).

Figure 69. Erta Ale's northeast flow field reached the alluvium about 16 km E of the Southeast Caldera lava lake by 16 October 2017, as recorded in this Sentinel-2 satellite image. The distance between the ends of the two easternmost tongues of lava is about 1 km. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: ça y est, le champ de lave entre dans la plaine!, 18 octobre 2017).

Visitors to the South Pit Crater in mid-December 2017 reported that its lava lake continued to be active and its level was about 60 m below the rim. They were also able to visit the Southeast Caldera lava lake, 2.7 km SE of the South Pit Crater, and take photographs from its rim; it was about 200 m long and 100 m wide and filled with slowly convecting lava (figures 70, 71). Satellite imagery from 25 December 2017 showed the active lake at the South Pit Crater, the active lake at the Southeast Caldera, and numerous skylights and overflows along the 16-km-long northeast flow field (figure 72).

Figure 70. The Southeast caldera lava lake at Erta Ale, its surface crusted over with slightly cooled lava, with dimensions of about 200 x 100 m in mid-December 2017. Photograph by FB88, courtesy of Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Figure 71. The Southeast Caldera lava lake at Erta Ale was slowly convecting during mid-December 2017. Photographed by FB88, courtesy of Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Figure 72. Sentinel-2 satellite imagery from 25 December 2017 of Erta Ale showed the active lake at the South Pit Crater (Summit lava lake), the active lake at the Southeast Caldera (Rift-Zone lava lake), and numerous skylights and overflows along the 16-km-long northeast flow field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Activity during January-March 2018. By mid-January 2018 thermal activity was concentrated a few kilometers back from the front of the northeast flow, about 12 km from the lava lake (figure 73). A Volcano Discovery tour group visited during 13-26 January 2018 and was able to access and photograph both the North and South Pit Craters and the new lake and flow fields around the Southeast Caldera with ground-based and aerial drone photography (figures 74-84).

Figure 73. By 19 January 2018, thermal activity at Erta Ale's northeast flow field was concentrated a few kilometers back from the front of the flow, about 12 km from the Southeast Caldera lava lake. The South Pit Crater and Southeast Caldera lava lakes are visible on the left. Small hot-spots near the Southeast Caldera lava lake could be hornitos or skylights into lava tubes. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Erta Ale, Kadovar (Mis à jour) et Nevados de Chillan, 21 janvier 2018).

Figure 74. In this aerial view taken during 13-26 January 2018 by a drone of the central part of Erta Ale's Summit Caldera, steam plumes rose from the North Pit Crater (left) and South Pit Crater (right). The fresh black lava around the South Pit Crater overflowed onto the caldera floor in January 2017 shortly before the beginning of the eruptive events in the Southeast Caldera a few kilometers to the south. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 75. The North Pit Crater inside the Summit Caldera at Erta Ale contained a large collapsed vent in January 2018 that formed after the magma drained away from the crater in January 2017. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 76. The lava lake in the South Pit Crater of Erta Ale's Summit Caldera was tens of meters below the rim in January 2018. Magma drained away and parts of the crater walls collapsed in January 2017, followed by repeated filling and draining of the lava lake during 2017. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 77. This aerial view by drone shows the large lava lake that formed at Erta Ale's Southeast Caldera during 2017; it was still slowly convecting in January 2018. The lake dimensions were about 100 x 200 m. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 78. Recently cooled black crust is overrun and consumed by molten lava that quickly cools and crusts over in Erta Ale's Southeast Caldera lava lake in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 79. Lava appears to flow into the Southeast Caldera lava lake at Erta Ale from a vent at the far edge and slowly spread across the lake during January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 80. Lava splashes as it flows into the Southeast Caldera lava lake at Erta Ale in January 2018. Photograph by Anastasia Ganuschenko taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 81. Downwelling consumes lava inside the Southeast Caldera lava lake at Erta Ale in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 82. Incandescence is visible inside a hornito that formed through lava spattering along the new flows in the Southeast Caldera at Erta Ale in January 2018. Photograph by Anastasia Ganuschenko taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 83. Many layers of fresh Pahoehoe lava flows were cool enough to walk on in some areas of the Southeast Caldera lava fields in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

Figure 84. Fresh lava flows were easily distinguished from older ones by their silver hue and dark black crust at Erta Ale's Southeast Caldera lava fields in January 2018. Photo taken during 13-26 January 2018. Copyrighted photo by Stefan Tommasini, used with permission.

By late March 2018 no thermal signal appeared in satellite imagery at the site of the Southeast Caldera lava lake, although the South Pit Crater was still visible. A large increase in the area of fresh flows and multiple thermal anomalies were present at the flow front of the northeast lava field 14-16 km from the former lava lake (figure 85). During the second half of March, the flow progressed several hundred meters out into the alluvial plain.

Figure 85. Sentinel-2 satellite imagery captured on 15 March 2018 showed a large increase in the area of fresh lava flows at the NE front of the northeast lava field at Erta Ale when compared with an image from 19 January 2018. Over the next ten days, images showed the narrow finger of lava that just touches the alluvium in this image creep about a kilometer out into the alluvial plain. Courtesy of Courtesy of ESA/Copernicus, published by Cultur Volcan (Les actus volcaniques du jour: Erta Ale, Maly-Semiachik, Suwanose-Jima et Ebeko, 28 mars 2018).

MIROVA thermal anomaly data. The MIROVA thermal anomaly data captures information about the distance of the anomalies from the summit as well as the radiative power released from Erta Ale. Both sets of information agree well with observations from the Sentinel-2 and Landsat satellite data. The plot of distance from the summit (figure 86) shows that during August 2016-mid-January 2017 the thermal anomalies were located very close to the summit point, representing heat flow from both the South and North Pit Craters within the Summit Caldera. Beginning on 21 January 2017, the jump in location of the anomalies corresponded with the beginning of the eruption in the Southeast Caldera. The MIROVA thermal anomalies progressed farther from the summit point during March and April 2017, when the northeast flow field was lengthening to the NE. The thermal signal jumps back closer to the summit point in early May corresponding to when new breakouts were spotted near the Southeast Caldera lava lake; the flows again traveled away from the lake during June and July 2017. Active lava flows from mid-August 2017 through March 2018 were visible in satellite imagery 12-16 km from the lava lake, which is reflected in the MIROVA data (figure 86).

Figure 86. MIROVA data showing the distance from the summit point of thermal anomalies at Erta Ale. Upper graph is the year ending 18 July 2017. Lower graph is the year ending 9 March 2018. They correspond well with locations of thermal anomalies that appear in numerous satellite images during that time. Note the distance scale change. See text and earlier figures for details. Courtesy of MIROVA.

The MIROVA data for the radiative power released from Erta Ale during August 2016-March 2018 also corresponds well with satellite and ground observations (figure 87). The levels of radiative power were moderate and constant during August 2016 to mid-January 2017 when only the lava lake and hornitos at the South and North Pit Craters were active (see also figure 47, BGVN 42:07). A moderate spike in the radiative power corresponds to the overflow of the South Pit Crater during 16-20 January 2017, followed by a large spike in radiative power on 21 January when the eruption started in the Southeast Caldera. This was followed by an extended period of increased radiative power as extensive flow fields formed in the Southeast Caldera. The graph is also able to distinguish the movement of the flows from near the Southeast Caldera lava lake to farther away and then near again during March-June 2017. The radiative power graph from 10 March 2017-9 March 2018 clearly shows a gradual decrease in the amount of radiative power over the period, suggesting a decline in flow activity, which corresponds well to satellite observations.

Figure 87. MIROVA plots of radiative power at Erta Ale for 18 July 2016-18 July 2017 (upper) and 9 March 2017-9 March 2018 (lower). Note the different y-axis scales for VRP due to the large spike on 21 January 2017 at the beginning of the Southeast Caldera eruptive episode. The plots record both the movement of the flow fields away from and closer to the summit point during March-June 2017, and then the gradual decrease in radiative energy from May 2017 through early March 2018. Courtesy of MIROVA.

Geologic Background. Erta Ale is an isolated basaltic shield that is the most active volcano in Ethiopia. The broad, 50-km-wide edifice rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: European Space Agency (ESA), Copernicus (URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus; Robert Simon, Sr., Data Visualization Engineer, Planet Labs Inc. (URL: http://www.planet.com/) [Images used under https://creativecommons.org/licenses/by-sa/4.0/]; Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com); Toucan Photo (URL: http://www.toucan.photo/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Stefan Tommasini (URL: http://vulkane-und-natur.de/).

Italy's Mount Etna on the island of Sicily has had historically recorded eruptions for the past 3,500 years and has been erupting continuously since September 2013 through at least March 2018. Lava flows, explosive eruptions with ash plumes, and lava fountains commonly occur from its major summit crater areas that include the North East Crater (NEC), the Voragine-Bocca Nuova (or Central) complex (VOR-BN), the South East Crater (SEC) (formed in 1978), and the New South East Crater (NSEC) (formed in 2011). A new crater, referred to as the "Cono della sella" or CdS, emerged during early 2017 in the saddle between SEC and NSEC (figure 206).

Figure 206. A modified digital elevation model (DEM) of the summit area at Etna showing the major craters. The hatched black lines highlight the rims of the summit craters: BN = Bocca Nuova, which contains the NW depression (BN-1) and the SE depression (BN-2); VOR = Voragine with an active vent on its E rim that opened in August 2016; NEC = Northeast Crater; SEC = South-East Crater; NSEC = New Southeast Crater; and "Cono della Sella" or CdS, which emerged in early 2017, shown in red. The yellow dots indicate the locations of significant degassing vents at VOR, BN, and NSEC. Courtesy of INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 11/12/2017-17/12/2017, issue date-19/12/2017).

The most recent eruptive episode began with ash emissions from a new vent in the saddle between NSEC and SEC on 20 January 2017, followed by Strombolian activity a few days later (BGVN 42:10). Activity intensified at the end of February when the first of several lava flows emerged from this and other adjacent vents. By mid-March 2017, Strombolian activity, ash emissions, and lava flows had created a cone higher than the adjacent NSEC and SEC cones, referred to as the "Cono della Sella" (CdS) or saddle cone. An effusive episode at the end of April 2017 sent flows down both the N and S flanks of the new cone from multiple vents. Intermittent Strombolian activity and persistent fumarolic activity continued from multiple crater areas, and minor ash emissions were observed a few times through August 2017. The Osservatorio Etneo (OE), which provides weekly reports and special updates on activity, is run by the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV). This report uses information from INGV to summarize events between September 2017 and March 2018.

Although still exhibiting intermittent volcanism, activity at Etna was at low levels during September 2017-March 2018. A comparison of the thermal activity of that period with the previous interval of November 2016-August 2017 (figure 186, BGVN 42:10) demonstrates the order of magnitude decrease from the earlier period (figure 207). Persistent degassing occurred throughout this interval, often with incandescent gas and periodic ash emissions resulting from continued subsidence around crater vents and from small explosive events. Ashfall was reported once in the cities S of Etna in mid-January 2018, and a minor episode of Strombolian activity and ash emissions took place at the eastern vent of NSEC in mid-February 2018.

Figure 207. Thermal activity at Etna was substantially decreased compared to earlier in 2017 (figure 186, BGVN 42:10) as seen in this MIROVA graph that plots data for the year ending on 12 July 2018. Courtesy of MIROVA.

Activity during September-December 2017. Active degassing at the beginning of September 2017 occurred from the vent at the E rim of the Voragine crater (VOR), and from the NW vent of Bocca Nuova (BN-1) (figure 208). At the Northeast Crater (NEC) and the SE Crater (SEC)-New South East Crater (NSEC) complex, which included the new "Cono del Sella" (CdS), there was widespread degassing from the fumarolic fields located in the bottoms and walls of the craters. Minor explosive activity was reported on 19 September 2017 from BN and NSEC, and nighttime incandescence was reported from the other craters. On 20 September small sporadic ash emissions were noted from NSEC and VOR. Incandescence at night was observed at the SEC-NSEC complex for the remainder of the month, and strong degassing continued at the VOR vent.

Figure 208. Active degassing was evident at the summit craters of Etna on 24 August 2017. a) degassing from Bocca Nuova (BN). b) the active vent on the E rim of Voragine (VOR) was mostly steam. Courtesy of INGV (Report 35/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 21/08/2017-27/08/2017, issue date 29/08/2017).

Occasional ash emissions were observed during the second week of October 2017 from the Cono della Sella (CdS) (figure 209). A minor ash emission was also reported on 16 October from the SEC-NSEC complex. Minor emissions of brown ash were reported from BN-1 during the last week of October. In the late afternoon of 26 October, a single explosion occurred at one of the three mouths of the Cono della Sella crater. The explosion generated a short jet of incandescent material and a small ash plume that quickly dispersed.

Figure 209. An ash emission occurred on 13 October 2017 from the Cono della Sella (CdS) at Etna. These images were taken from the M. Cagliato (left) and La Montagnola (right) webcams. Intense degassing from VOR was also visible in the La Montagnola image. Courtesy of INGV (Report 42/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 09/10/2017-15/10/2017, issue date 17/10/2017).

Cloudy weather during November resulted in limited visibility for much of the month. A small, isolated explosion containing minor ash occurred at SEC on 14 November 2017. During the third week of November, a new pit crater appeared at the bottom of NEC that measured 70 x 50 m (figure 210), and intense degassing was observed from BN-1. Frequent small ash emissions were reported from CdS during 24-26 November. In the last week of the month, pulsating degassing from the craters could be detected during periods of limited visibility, as well as a series of explosions with ash emissions from SEC.

Figure 210. A new pit crater opened at the bottom of NEC at Etna during the third week of November 2017. A) Map of the summit crater area (DEM 2014) showing the pit crater location at the bottom of the NEC and one of the main fumaroles at the bottom (orange arrow). B) View of the bottom of NEC from the S on 23 November 2017, the orange arrow is the fumarole and the white hatched line indicates the rim of the new pit crater. C) The S flank of the NEC, showing the locations of the thermal cameras that created the images of the new pit in images D and E. Courtesy if INGV, (Report 48/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 20/11/2017-26/11/2017, issue date 28/11/2017).

Degassing from the summit craters persisted throughout December 2017 with intermittent incandescence observed from fumaroles at NSEC. A few ash emissions were recorded from CdS, including overnight on 14-15 December (figure 211).

Figure 211. Minor degassing, fumaroles, and incandescence were recorded at the summit craters of Etna in early December 2017. a) Degassing from BN and VOR on the morning of 13 December 2017, seen from the S. b) Image taken from the high-resolution webcam at Monte Cagliato (EMCH, E side of Etna) showing incandescence at the E vent of NSEC in the early hours of 12 December 2017. c) Puff of ash emitted by CdS on the morning of 15 December 2017, recorded by the Montagnola (EMOV) webcam. Courtesy of INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 11/12/2017-17/12/2017, issue date 19/12/2017).

Activity during January-March 2018. Similar activity continued throughout January 2018; a small ash emission was observed from CdS on 5 January, and a puff of brown ash emerged from NSEC the next day. Incandescence degassing also continued from the NSEC vents. During the second week of the month, 20 small explosive events were observed from the eastern vent at NSEC, although cloud cover obscured the summit for much of the time. Minor ash emissions continued from NSEC for the rest of the month, along with nighttime incandescence, especially strong from BN-1. On 22 January a modest ashfall affected the communities S of Etna including the city of Catania (27 km S); the lack of visibility prevented identification of which crater produced the ash. By the end of the month, the pit crater at the base of NEC had expanded, causing erosion of the inner E wall (figure 212). In spite of the low level of activity during this period, SO₂ emissions were occasionally recorded with satellite instruments. The most significant SO₂ plumes were measured during the last few days of January (figure 213).

Figure 212. Activity during January 2018 at Etna included strong incandescence from BN-1, numerous small explosive events from NSEC, and expansion of the pit crater at the base of NEC. The hatched black lines highlight the edge of the summit craters: BN = Bocca Nuova, including the NW depression (BN-1) and the SE depression (BN-2); VOR = Voragine; NEC = Northeast Crater; SEC = South-East Crater; NSEC = New Southeast Crater. The yellow dots indicate the positions of the degassing vents of VOR, NEC and NSEC (E vent and "Cono della Sella"). The yellow dots with a red border indicate the vents characterized by strong incandescence (BN-1) and occasional ash emissions (NSEC, E vent). Courtesy of INGV, Report 06/2018, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 29/01/2018-04/02/2018, issue date, 06/02/2018).

Figure 213. Significant SO2 plumes were measured from Etna on 29 (left) and 31 (right) January 2018 by the OMI instrument on NASA's Aura satellite. Courtesy of NASA Goddard Space Flight Center.

Two weak ash emissions occurred at NSEC during the first week of February 2018. The frequency of explosions increased during 15-16 February to 1-2 events per hour, producing moderate amounts of brown-gray ash and incandescent pyroclastic material (figure 214); heightened activity lasted for several days. The explosions were heard 20 km E and S from the summit. Faint, non-explosive emissions of gray ash were observed on the morning of 17 February 2018 from NEC (figure 215).

Figure 214. Ash and incandescent material were ejected from the E vent of NSEC at Etna during 17 February 2018. a) Ash emission from the E vent at NSEC viewed by the Tremestieri Etneo webcam from the S flank on the morning of 17 February 2018. b) Incandescent material ejected during one of the explosions from the same vent, on the evening of 17 February 2018. Photo by Michele Mammino, used by INGV with permission of the author. Courtesy of INGV (Report 08/2018, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 12/02/2018-18/02/2018 (issue date 20/02/2018).

Figure 215. A weak ash emission rose from Etna's NEC at 1005 local time on 17 February 2018, as seen by the Zafferana Etnea webcam. Courtesy of INGV, Report 08/2018, Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 12/02/2018-18/02/2018, issue date 20/02/2018).

Degassing continued at the summit craters for the remainder of February and throughout March 2018. During an inspection by INGV on 10 March, the expansion of the pit crater at the bottom of NEC was noted, as was continuing collapses of the internal walls which produced minor ash emissions. Activity at the E vent of NSEC included a minor ash emission on 2 March 2018; occasional ejection of incandescent pyroclastic material and modest ash emissions continued throughout the month (figure 216). The ash emissions occurred at irregular intervals, varying from a few tens of minutes to a few hours, more frequently in the last days of the month.

Figure 216. Explosive activity from the vent on the E side of NSEC at Etna, taken from the Tremestieri Etneo webcam on the S flank on 8 March 2018. Ash emissions were accompanied by incandescent tephra that landed on the flanks. Photographic sequence by B. Behncke. Courtesy of INGV, Report 11/2018, Bollettino Settimanale, 05/03/2018-11/03/2018, issue date 13/03/2018).

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/ ); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The first confirmed historical eruption at Kadovar began around mid-day local time on 5 January 2018, according to witnesses. The steeply-sloped island is approximately 1.4 km in diameter and is located about 25 km NNE from the mouth of the Sepik River on the mainland of Papua New Guinea (figure 1). This report covers activity from the beginning of the eruption on 5 January through March 2018. Information about the eruption is provided by the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), satellite sources, news reports, and local observers. A possible eruption was witnessed by explorers in 1700; no other activity was reported until an outbreak of thermal activity in 1976 (NSEB 01:14-01:11, SEAN 03:09) and a short period of seismic unrest in 2015, according to RVO.

Figure 1. Kadovar Island is located about 25 km NNE from the mouth of the Sepik River on the mainland of Papua New Guinea. Nearby active volcanoes include Blup Blup (12 km N) and Bam (21 km W); residents of Kadovar were evacuated initially to Blup Blup before being moved to an area near Wewak, the nearest community on the mainland, about 105 km W. The red triangles are Holocene volcanoes, and the blue (cyan) triangles are Pleistocene volcanoes. Base map courtesy of Google Earth.

Ash and steam emissions from Kadovar were first reported on 5 January 2018. After about 24 hours, more than half of the island was covered by volcanic debris. Activity intensified over the next two weeks; RVO identified five distinct vents located at the summit and along the SE coast. Dense ash plumes and steam rose from the summit vents, and a slowly-extruding lava flow emerged from a vent near the shoreline on the SE flank. Persistent steam and intermittent ash plumes were produced from the summit vent through the end of March. The lava flow grew outward from the shore for tens of meters before collapsing in early February, but it reappeared a few days later. By the end of the first week of March 2018 the flow was about 17 m above sea level; its growth rate had slowed, adding only one meter by late March.

The NOAA/CIMSS Volcanic Cloud Monitoring system generated an alert for an ash cloud moving WNW, as imaged by S-NPP VIIRS, at 0330 UTC on 5 January 2018; Himawari-8 imagery subsequently showed that the eruption began around 0220 UTC. The Darwin VAAC reported two discrete ash plumes drifting W at 2.1 km altitude during the day. After local reports of the eruption Samaritan Airlines flew administrators from the Wewak district to investigate, enabling photographs of ash and steam emissions (figure 2).

Figure 2. Steam and ash emerged from a vent near the summit of Kadovar Island and drifted WNW on 5 January 2018. The view is looking NW with the SE flank of Kadovar in the foreground. In the upper photo, the island in the background is Viai Island about 30 km NW. Photo by Ricky Wobar, administrator of the Wewak district. Courtesy of Samaritan Aviation, posted on Facebook on 5 January 2018.

The following day, 6 January 2018, photos from a Samaritan Air flight showed that dark gray ash and steam plumes rising from a crater on the SE side of the summit had intensified (figures 3 and 4). It was estimated that 50 or 60% of the island was covered in volcanic debris, which appeared to be primarily ash along with some pyroclastic flows. According to the International Federation of Red Cross and Red Crescent Societies (IFRC), the entire population of Kadovar, about 600 people who lived on the N side of the island, was relocated to nearby Blup Blup Island which is home to about 800 residents. RVO reported minor ashfall on Kairiru and Mushu islands (115 km WNW), and on mainland Papua New Guinea at Mt. Uru in Yangoru (130 km W), Woginara (140 km W), and the Wewak District (100 km W).

Figure 3. Ash and steam plumes rose from distinct vents on the SE side of the summit at Kadovar. View is to the NE, with Blup Blup volcano located about 12 km in the distance. Photo by Ricky Wobar likely taken on 6 January 2018, published by ABC News on 8 January 2018. Courtesy of ABC News.

Figure 4. Ash and steam emissions intensified from vents at the summit of Kadovar Island on 6 January 2018. Posted on Facebook, 6 January 2018 by Samaritan Aviation.

Also on 6 January 2018, missionary Brandon Buser set out from Wewak to visit Bam by boat. He observed the steam and ash plumes of Kadovar from about 75 km away. About 25 km W of the island, he felt falling ash. From a few hundred meters offshore he witnessed the ash and steam plumes rising from near the summit as he circled the S and E sides of the island (figures 5-8).

Figure 5. Locations of the following photographs of the eruption at Kadovar on 6 January 2018 correspond closely to the purple spots where the boat slowed down on its trip around the island. North is to the top. Numbers indicate approximate locations of the following figures 6-12. Courtesy of Brandon Buser. Base map courtesy of Google Earth.

Figure 6. An ash plume drifted NW from the summit of Kadovar as viewed from a boat a few hundred meters off the SW flank on 6 January 2018. Courtesy of Brandon Buser.

Figure 7. Ash drifted WNW from Kadovar and also covered the vegetation on the SSW flank on 6 January 2018 in this view from a boat a few hundred meters off the SSW flank. Courtesy of Brandon Buser.

Figure 8. Dark ash and white steam both rose from vents at the summit of Kadovar on 6 January 2018. Debris and ashfall killed and denuded the trees on the SE flank, and covered the ground. View is from a boat a few hundred meters off the SE flank. Courtesy of Brandon Buser.

While preparing to head E to Bam, Buser witnessed an explosion that sent large plumes of ash and steam skyward from the SE flank, and a significant cloud of volcanic debris was ejected outward and down the SE flank; large boulders fell into the ocean. Heading rapidly E away from the eruption, he took additional photographs (figures 9-12).

Figure 9. Dark gray ash and white steam billowed up from a vent near the summit of Kadovar on 6 January 2018 at the start of an explosion. The denuded vegetation and bare slopes on the SE flank indicated the extent of the recent activity. The view is from a boat a few hundred meters offshore of the NE flank. Courtesy of Brandon Buser.

Figure 10. An explosion witnessed at Kadovar on 6 January 2018. Steam rose from a vent near the summit (right), dark gray ash billowed up from the SE flank, and brown dust and debris descended the SE flank into the ocean (left) in this view from a few hundred meters off the NE flank. Courtesy of Brandon Buser.

Figure 11. A large explosion at Kadovar witnessed on 6 January 2018. Light gray steam and ash rose from near the summit and drifted NW covering the N half of the island in ash; a large eruption of dark gray ash shot upward from a different vent on the SE flank surrounded by dust and debris that traveled outward at its base. Larger debris caused splashing in the water off the SE flank (left). View is from a few kilometers off the NE flank. Courtesy of Brandon Buser.

Figure 12. The plumes of steam, ash, and debris from the explosion moments earlier at Kadovar on 6 January 2018 rose and began to drift NW covering the island. Blocks landing in the ocean on the SE flank created spray along the shoreline (left). View is from a boat a few kilometers NE of the island. Courtesy of Brandon Buser.

The Darwin VAAC reported on 6 January 2018 that a continuous ash plume was identifiable in satellite imagery moving W and WNW at 2.1 km altitude. By 7 January, the plume could be identified about 220 km WNW in satellite images (figure 13). During their return trip from Bam on 8 January 2018, the missionaries again circled the island and noted that the eruption seemed to be occurring from different vents. The island was covered in ash, and they became covered with wet ash as they traveled under the drifting ash plume. The Darwin VAAC reported the plume drifting WNW extending about 185 km on 8 January. They also noted that the influence of the sea breeze was also spreading minor ash to the SW. Continuous ash emissions were observed by the Darwin VAAC through 11 January, drifting W and NW at 2.1 km altitude.

Figure 13. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured the eruption of Kadovar that began two days earlier on 7 January 2018 as a plume of ash and steam that streamed NW from its crater. A second smaller plume, also drifting NW, is visible SE of Kadovar from unrelated activity at nearby Manam, one of Papua New Guinea's most active volcanos. Brown-green plumes visible in the water S of Kadovar near the coast of the mainland, are caused by sediment from the Sepik and Ramu rivers on the mainland. Courtesy of NASA Earth Observatory.

RVO reported a significant escalation in activity during 12-13 January 2018. An explosion during the previous night ejected large incandescent boulders from the fracture on the SE flank. Residents on Blup Blup (15 km N) could see incandescence high on the volcano's flank. During a flyover on 13 January, RVO noted variable steam and gas emissions rising to 1 km above the Main Crater and identified five distinct vents (figure 14). The SE Coastal Vent was very active with dense white steam emissions rising 600 m from the vent (figure 15). A dome of lava was visible at the base of the steam plume, but no incandescence was observed. The Southern Coastal Vent had been vigorously steaming a few days earlier, and RVO interpreted it to be the source of the incandescent blocks in the explosion a few days before.

Figure 14. A sketch map of the five newly identified vents at Kadovar, 14 January 2018, from an RVO overflight the previous day. Courtesy of RVO (VOLCANO INFORMATION BULLETIN- No. 08 14/01/2018).

Figure 15. A vigorous steam plume rose from the SE Coastal Vent at Kadovar on 13 January 2018 while an ash plume rose from Main Crater at the summit. Photo by the office of Allan Bird, Governor of East Sepik Province. Courtesy of RVO (VOLCANO INFORMATION BULLETIN- No. 08 14/01/2018).

Reports of continuous ash emissions at 2.1 km altitude drifting WNW from the Darwin VAAC resumed on 16 January. A brief emission to 3.7 km was also noted that day. Pilot reports on 17 and 18 January indicated that ash was still in the area as high as 3-3.7 km altitude drifting W. The reports of emissions from the Darwin VAAC continued through 24 January. Ash emissions were generally continuous at altitudes from 2.4 to 3 km, although low level emissions of primarily steam and gas were observed on 20 January that included intermittent phases of increased ash content. The plume drift direction was variable, with periods when ash drifted S and SE in addition to the generally prevailing NW and W directions.

During 18-22 January 2018, the Main Crater continued to produce moderate to dark gray ash plumes that rose 500-800 m above the summit, drifting locally S and SE, and a continuous steam plume from the SE Coastal Vent rose as high as 800 m above the island. An incandescent lava flow slowly extruded from the SE Coastal Vent. By the last week of January, the ash plumes were only rising about 100 m above the Main Crater and drifting W; weak incandescence was still observed at night. The white steam plume from the SE Coastal Vent rose closer to 400 m above the island. RVO estimated that the lava flow had risen to about 50 m above sea level and extended 150-200 m out from the coast.

In their report on 2 February 2018, RVO noted that the lava flow continued to grow. A distinct lobe had pushed out from the seaward nose of the flow, by about 20-30 m; it appeared to be channeled by levees which had developed at the flow's sides. At 1830 local time on 1 February, a collapse of the side of the flow facing Blup Blup was observed; it resulted in a plume of gray ash and then vigorous steaming at the collapse site, which also was incandescent at night. The main body of the flow significantly bulged upwards, with a distinct 'valley' visible between the bulge and the island's flank.

RVO reported that on 9 February the lava flow at the SE Coastal Vent had collapsed, causing 5-6 minor tsunamis less than 1 m high that were observed by residents on Blup Blup's E and W coasts. The waves were reported at 1050, before the main collapse of the dome. In a 12 February report, RVO noted that activity from Main Crater consisted of white plumes rising 20 m and drifting a few kilometers SE accompanied by weak nighttime crater incandescence. Activity renewed at the SE Coastal Vent shortly after the collapse of the flow on 9 February 2018; lava re-emerged a few days later, connecting a lava island to the coastline again. Continuous steam emissions from both the Main Crater and the SE Coastal Vent were interrupted by dark ash plumes on 16 and 20-22 February, and occasional explosions were heard by residents on nearby islands. Minor ashfall was reported on Blup Blup on 21 and 22 February.

Eruptive activity continued during March 2018, although at a slower rate. The Main Crater generally produced continuous emissions of white steam and intermittent explosions with dark ash plumes; incandescence was usually visible at night from Blup Blup. According to the Darwin VAAC, a pilot reported an ash plume at 3.9 km altitude drifting SE on 2 March; it was not visible in satellite imagery due to meteoric clouds. The lava flow extruding from the SE Coastal Vent continued to grow, creating a dome that grew from 7-8 m above sea level to 10-17 m above sea level by 8 March. Dark ash emissions from the vent and nighttime incandescence were common. The growth rate slowed later in the month, and only one meter of change was observed between 10 and 20 March.

Satellite data. The MIROVA project recorded thermal anomalies from Kadovar in early January and early March 2018 (figure 16). MODVOLC thermal alerts were issued on three days; 15 and 22 January, and 7 February 2018. During January, small SO₂ plumes were recorded by NASA satellites on four occasions (figure 17).

Figure 16. The MIROVA project thermal anomaly graph for Kadovar from 11 May 2017 through March 2018. The first anomaly in early January 2018 correlates with observations of the first reported explosion. Courtesy of MIROVA.

Figure 17. SO2 plumes from Kadovar were detected several times during January 2018 by the OMI instrument on NASA's Aura satellite. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea, Contact: steve_saunders@mineral.gov.pg, ima_itikarai@mineral.gov.pg; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NOAA, Cooperative Institute for Meteorological Satellite Studies (CIMSS), Space Science and Engineering Center (SSEC), University of Wisconsin-Madison, 1225 W. Dayton St., Madison, Wisconsin 53706, USA (URL: http://cimss.ssec.wisc.edu/); International Federation of Red Cross and Red Crescent Societies (IFRC) (URL: http://www.ifrc.org/); Samaritan Aviation (URL: http://samaviation.com/, https://www.facebook.com/samaritanaviation/); Brandon Buser (URL: https://ethnos360.org/missionaries/brandon-and-rachel-buser, https://www.facebook.com/brandon.buser.35); ABC News (URL: http://www.abc.net.au/news/2018-01-08/tsunami-warning-for-communities-near-erupting-png-volcano/9311544); Google Earth (URL: https://www.google.com/earth/).

Recent activity at Karymsky has consisted of ash explosions on 4 June and 20 September 2017, separated by a period of relative quiet (BGVN 42:11). The volcano was quiet after 20 September until another ash explosion on 4 December 2017. This report covers activity from 1 December 2017 through March 2018, using information compiled from the Kamchatka Volcanic Eruptions Response Team (KVERT) and the Tokyo Volcanic Ash Advisory Center (VAAC). According to KVERT, an explosion on 27 January 2018 was last through at least 31 March.

Based on satellite data, KVERT reported that an explosion began at about 0630 on 4 December 2017 and generated an ash cloud that rose to an altitude of 2.7 km and drifted 200 km E. An ash cloud 16 x 12 km in dimension was identified in satellite images about three hours after the explosion, 92 km E of the volcano. The Aviation Color Code was raised from Green to Orange (the second highest level on a four-color scale). A thermal anomaly was identified in satellite data during 3 and 5-6 December.

According to KVERT, another ash plume was identified in satellite data drifting 114 km ENE on 14 December. No further ash emissions were noted afterward; the Aviation Color Code was thus lowered on 24 December to Yellow.

A small ash cloud was identified in satellite imagery drifting near Karymsky on 18 January 2018, and a thermal anomaly was identified on 19 and 23 January. Gas-and-steam plumes drifted 30 km NE and NW on 21 and 25 January, and an ash plume drifted about 100 km NE on 23 January. An explosion at 1430 on 27 January generated ash plumes that rose to an altitude of 5.2 km and drifted 80 km NE-NNE, prompting KVERT to raise the Aviation Color Code to Orange.

Moderate gas-and-steam emissions continued during February and March. Thermal anomalies were detected in satellite images on 3, 9, and 18 February, and 23-26 March; during other days, the volcano was either quiet or obscured by clouds. The Aviation Color Code remained at Orange through the end of the reporting period.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

The large Kusatsu-Shiranesan volcanic complex comprises three overlapping pyroclastic cones and numerous summit craters; it is located about 150 km NW of Tokyo in the Gunma Prefecture of central Japan. Intermittent short-lived historic activity has been reported from the northernmost Shiranesan cone since the beginning of the 19th century. An explosion at the southernmost Motoshiranesan cone in January 2018 resulted in one fatality and several injuries. Information about the event was gathered from the Japan Meteorological Agency (JMA) and various news sources.

Summary of activity during 1976-2014. Small phreatic explosions in the Mizugama and Yugama craters at the northernmost part of the Kusatsu-Shiranesan volcanic complex occurred in 1976, 1982, and 1983 (figure 14). Larger ash-bearing explosions in November and December 1983 sent tephra 30-40 km to communities downwind to the SE from the Yugama and adjacent Karagama craters on the Shiranesan cone. Intermittent increases in seismic activity near the Yugama crater coincided with water discoloration in the crater lake, and possible ejections of debris from hydrothermal activity in 1989 and 1996. Increased hydrothermal activity was noted on the N flank of Yugama during 2013-2014. Seismic swarms, deformation, thermal, and fumarolic activity increased briefly during early June 2014 in the area around the Yugama crater lake, but no eruption was observed. In late June 2014, JMA reported dying vegetation in a forested area 3 km SW of the Motoshiranesan summit area.

Figure 14. Subfeatures of the Kusatsu-Shiranesan volcanic complex as seen in Google Earth imagery, looking N. The northernmost bleached area includes the historically active Yugama, Mizugama, and Karagama craters, part of the Shiranesan cone. In the center of the complex is the Ainomine cone which has a ski area on the S flank. The southernmost edifice is the Motoshiranesan cone which has multiple craters at its summit, including Kagamiike or "Mirror pond". The explosions of 23 January 2018 occurred at Kagamiike and the adjacent crater to the N, in area referred to by JMA as Honkonoyama. Courtesy of Google Earth.

Activity during 2014-2017. Seismicity remained elevated from March to mid-August 2014 around the Yugama crater area. Ground deformation data suggested inflation between March 2014 and April 2015 in that area. Field surveys conducted on 4-5 and 10-11 November 2014 indicated fumarolic areas on the N and NE flanks of the Mizugama crater, but no other significant activity. Short-lived increases in seismicity were observed during January-February 2015. A field survey in May 2015 confirmed ongoing thermal activity on the N and NE wall of the Yugama crater, and the N and NE flank of the Mizugama crater. A small-amplitude, 2-minute-long tremor during late June 2015 was the first since January 2013; it was not accompanied by eruptive activity. The fumarolic activity on the N wall of the Yugama Crater was higher during a field survey in October 2015 than in had been the previous May.

Thermal activity was ongoing at Yugama and Mizugama craters during 2015-2017 along with intermittent fumarolic activity in the same general area, but no significant seismicity was reported. By June 2017 the decrease in the concentration of components derived from high-temperature volcanic gas in the lake, and the stable low-level seismicity in the area, led JMA to lower the warning level from 2 to 1 (on a 5 level scale) on 7 June 2017; they noted that the thermal activity continued around the Yugama crater throughout the rest of the year (figures 15-17).

Figure 15. A minor thermal anomaly persisted inside the NE crater wall at Yagama Crater at Kusatsu-Shiranesan throughout 2015-2017. Both visual (upper) and thermal (lower) images were taken during an overflight on 1 November 2017. View is to the north. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, November 2017).

Figure 16. Thermal anomalies persisted on the N and NE flank of the Mizugama crater at Kusatsu-Shiranesan during 2015-2017. These visual (upper) and thermal (lower) images were captured on 1 November 2017. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, November 2017).

Figure 17. Daily earthquake frequency at Kusatsu-Shiranesan during 1 January 2011-30 November 2017. Although earthquake counts temporarily increased during March-August 2014 and in January and February 2015, no eruptive activity was reported. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, November 2017).

Activity during January-March 2018. JMA reported that at 0959 on 23 January 2018 an eruption began at Kusatsu-Shiranesan coincident with the onset of volcanic tremor which prompted JMA to raise the Alert Level to 3 (on a scale of 1-5); there had been no prior indications of an impending eruption. Skiers at the popular Kusatsu Kokusai ski resort, located on the Ainomine cone, took video showing a plume of tephra and ejected bombs rising from vents around the Kagamiiki and adjacent crater at the summit of the Motoshiranesan cone (see Information Contacts for Mainichi for video link). Motoshiranesan is immediately adjacent S of the Ainomine cone and about 2 km SSE of the Yagama Crater on the Shiranesan cone where all previous historical activity had been reported (figures 14 and 18).

Figure 18. Locations and images of the active vents at Kusatsu-Shiranesan during the eruptive event of 23 January 2018. Upper left: View is looking W at the Motoshiranesan summit craters. The crater with the pond in Box 1 is Kagamiike (yellow Japanese characters). Boxes 1 and 2 in the upper left photo are enlarged in the lower photos. Upper right topographic map shows the locations in red of the three vents. The upper red line and dot correspond to the vents shown in the lower right box 2. The lower red bar on the topographic map (near the small pond) corresponds to the vent shown in the lower left image as box 1. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, January 2018).

Photos and video posted in news articles showed tephra shooting tens of meters into the air, drifting E, and blanketing the nearby hillside (figure 19); JMA noted ashfall in Nakanojo-machi, in the Gunma Prefecture, about 8 km E. Tephra hit a gondola, shattering glass and injuring four skiers (figure 20). Material fell through the roof of a lodge, where about 100 people had already been evacuated. Ground Self-Defense Force troops were engaging in ski training at the time of the event; one member died from the impact of large tephra blocks, and seven others were injured.

Figure 19. Tephra from Mount Kusatsu-Shiranesan covers the N flank of the Motoshiranesan cone and much of the Ainomine cone in this view to the W taken on 23 January 2018. Photo by Suo Takeuma, AP, courtesy of CNN (Japanese man killed by falling rocks after volcano erupts at ski resort, 23 January 2018).

Figure 20. Fist-sized tephra blocks and ash ejected from the eruption of Mount Kusatsu-Shiranesan cover the floor of a damaged gondola at the Kusatsu Kokusai Ski Resort on 24 January 2018, courtesy of The Mainichi Japan (Damaged ski resort gondolas show the power of Gunma Pref. volcanic eruption, 25 January 2018).

The following day, on 24 January 2018, JMA noted that volcanic earthquakes were numerous but decreasing in number, and two 2-3-minute-long periods of volcanic tremor were detected at 1015 and 1049. Minor but elevated seismicity continued through 30 January, punctuated by periods of tremor. The largest fissure where the eruption occurred was oriented E-W, located just inside the N rim of the northernmost crater at the Motoshiranesan summit (figure 21). Kenji Nogami, a professor at the Tokyo Institute of Technology, confirmed that the event appeared to have been "a typical phreatic eruption" (Japan Times).

Figure 21. The largest fissure vent active in the 23 January 2018 explosion at Kusatsu-Shiranesan was still surrounded by ash and tephra when photographed during an overflight on 28 January 2018. The summit ropeway station of the ski area is at the image top just NW of the explosion vent. Courtesy of The Mainichi (Visitor traffic plunges in Kusatsu hot spring resort after deadly eruptions, 30 January 2018).

The Tokyo Volcanic Ash Advisory Center issued a single volcanic ash advisory on 23 January indicating a possible eruption, but it was not identifiable from satellite data. Observations made on 14 February 2018 confirmed the presence of the vents in the Kagamiike and adjacent crater, but there was no evidence of thermal activity and little fumarolic activity in the area (figure 22). Seismicity decreased steadily after the explosion on 23 January 2018 through the end of March 2018 and no further activity was reported (figure 23).

Figure 22. Vents from the 23 January 2018 eruption at Kusatsu-Shiranesan were still visible at the craters on 14 February 2014 during a helicopter overflight by JMA. The upper image, looking W, shows the large vent at the N side of the crater immediately N of the Kagamiike crater, as well as a smaller vent located to the W on the E flank of the adjacent slope. The lower image shows two smaller vents on the inner wall of the adjacent Kagamiike crater. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, February 2018).

Figure 23. Seismicity decreased steadily at Kusatsu-Shiranesan after the explosion on 23 January 2018. Graph shows the number of daily seismic events during 1 January-31 March 2018. Courtesy of JMA (Volcanic activity monthly report, Kusatsu-Shirane, March 2018).

Geologic Background. The Kusatsu-Shiranesan complex, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid-Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S, and SW flanks. The latest eruptive stage began about 14,000 years ago. Historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); The Mainichi (URL: http://mainichi.jp/english/, eruption video URL-https://mainichi.jp/movie/video/?id=121708141#cxrecs_s); The Japan Times (URL: https://www.japantimes.co.jp/); Cable News Network (CNN), Turner Broadcasting System, Inc. (URL: http://www.cnn.com/).

Steep-sloped and symmetrical Mayon has recorded historical eruptions back to 1616 that range from Strombolian fountaining to basaltic and andesitic flows, as well as large ash plumes, and devastating pyroclastic flows and lahars. A lava dome that grew during August-October 2014 resulted in rockfalls, pyroclastic flows, and lava flows from the summit crater that led to evacuations in nearby communities (BGVN 41:03). Activity declined during November and December 2014 and remained low throughout 2015. By February 2016 the Alert Level was reduced to 0 (on a 0-5 scale) by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) which monitors the volcano. A seismic swarm in August 2016, and the beginning of a new eruption in January 2018 are covered in this report with information provided primarily by PHIVOLCS.

After a brief seismic swarm in August 2016, Mayon remained quiet until a phreatic explosion on 13 January 2018 sent an ash plume 2,500 m above the summit and scattered ash over numerous nearby communities. The growth of a new lava dome sent lava flows down the flanks and ash plumes multiple kilometers above the summit during subsequent weeks. Lava fountaining produced incandescence at the summit for many weeks. Lava collapse events from the flow fronts sent pyroclastic density currents (PDC's) down multiple ravines during January and February 2018. Lava fountaining activity became nearly continuous at the beginning of February but began to taper off by mid-month. Flows had reached as far as 4.5 km down ravines, and lava-collapse generated pyroclastic density currents reached 5 km from the summit crater. The pyroclastic activity continued through February from the gravity-driven collapsing flow fronts even though fountaining and lava effusion had decreased. Brief periods of fountaining and gravity-driven lava flow were noted throughout March 2018, but activity had essentially ceased by month's end.

Activity during 2016-2017. Very low seismicity of 0-2 volcanic earthquakes per day was typical for January and early February 2016; the largest number recorded was 12 on 9 January. On 12 February 2016, PHIVOLCS noted that seismicity had remained at baseline levels of 0-2 earthquakes per day for the previous six months, indicating that rock fracturing associated with magmatic activity had diminished. Ground deformation information suggested a return to pre-2014 eruption positions, and low levels of SO₂ flux had been consistent since November 2015. They reduced the Alert Level to 0.

Increasing SO₂ flux above 1,000 tons/day beginning in July 2016 was accompanied by ground deformation measurements suggesting renewed inflation. A brief swarm of 146 earthquakes was recorded by the Mayon Volcano Observatory's seismic network from 3-6 August; they were located 10 km away on the SE flank. This change led PHIVOLCS to raise the Alert Level back to 1 on 8 September 2016. Seismicity and SO₂ levels remained very low through the end of 2016, but GPS data suggested continued inflation. Slight inflation was recorded throughout 2017. Rare days of small seismic swarms of more than 10 earthquakes occurred during 2017, but otherwise seismicity and SO₂ flux values remained within background levels.

Activity during January 2018. A sudden phreatic eruption at 1621 local time on 13 January 2018 sent a gray steam-and-ash plume 2,500 m above the summit that drifted SW. The activity lasted for a little under two hours. Traces of ash fell on the Barangays of Anoling (4 km SW), Sua (6 km SW), Quirangay (9 km SW), Tumpa (9 km SW), Ilawod (10 km SW), and Salugan (8 km SW) in the city of Camalig and in the Barangays of Tandarora (26 km WSW), Maninila (8 km SW), and Travesia (10 km SW) in the municipality of Guinobatan. Incandescence at the summit crater was first observed a few hours later. As a result, PHIVOLCS raised the Alert Level from 1 to 2 early the next day.

Two more phreatic explosions occurred the following morning (14 January) at 0849 and 1143 that each produced ash plumes, but they were largely obscured by summit clouds. Minor amounts of ash were reported in Camalig. By the evening, PHIVOLCS had raised the Alert Level again to 3 after three explosions, 158 rockfall events, and the observation of bright incandescence at the summit crater. By 2000 on 14 January they noted the growth of a new lava dome and the beginnings of a lava flow towards the southern flank.

Two lava collapse events on the morning on 15 January each lasted 5-10 minutes. They originated from the lava flow front and produced rockfall and small-volume pyroclastic density currents. Ash plumes drifted SW and rained ash on Travesia, Muladbucad Grande, Maninila, Masarawag, Poblacion, Iraya, Ilawod, Calzada, Inamnan Grande, Inamnan Pequeno, Maguiron, Quitago and Mauraro in the municipality of Guinobatan and on the Baranguays of Cabangan, Anoling, Sua, Tumpa, Quirangay, Gapo, and Sumlang, and Baranguays 1 to 7 in the municipality of Camalig. A degassing event at 1107 produced a grayish to dirty white ash column that rose to a maximum of height of approximately 1,000 m above the summit before drifting WSW.

Lava effusion continued from the summit during 16-21 January 2018 with flows down the Mi-isi and Bonga gullies and occasional short-duration lava fountaining. Tens of daily lava collapse events accompanied the growth of the flow in the Mi-isi gully which had reached about 3 km from the summit by 18 January. Debris from the growing summit dome also descended the Matanag and Buyuan Gullies. Pyroclastic density currents descended the Mi-isi, Matanag, and Buyuan Gullies. Ash plumes rose up to 2 km and drifted SW from the summit crater and caused ashfall in Camalig, Guinobatan, and Polangui (figures 26-28).

Figure 26. Mayon emitted ash and steam along with pyroclastic density currents that flowed down the SW flank on 16 January 2018. View is looking N from S of the airport in Lagazpi City, Philippines, about 12 km S. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 27. Pyroclastic density currents (PDC's) descended the W flank of Mayon on 16 January 2018. Incandescence at the base of the PDC was also visible. Lava was fountaining at the summit and incandescent blocks were rolling down the Mi-isi drainage on the S flank. Image taken near Legazpi city, 12 km S. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 28. Lava flows at Mayon descended the Mi-isi drainage on the S flank and were visible from Legazpi city on 17 January 2018. Courtesy of The Express, photo from European Pressphoto Agency.

Activity increased on 22 January 2018 with lava fountains at the summit reaching 200-500 m high, the lava flow into the Mi-isi drainage extending beyond 3 km, and two new flows in the Bonga gully and upper Buyuan watershed. A dense 5-km-tall ash plume erupted at 1243 during a phreatomagmatic event that lasted for 8 minutes (figure 29). It generated pyroclastic density currents in several drainages within 4 km of the summit vent including Mi-isi, Bonga, Buyuan, Basud, San Andres, Buang, Anoling and other minor drainages. Ash was blown W and fell on the municipalities of Guinobatan, Camalig, Oas, Polangui and Iriga City. Five additional episodes of lava fountaining to 700 m occurred overnight that fed the Mi-isi and Bonga gully flows, and generated ash plumes to 2.5 and 3 km above the summit. This increase in activity led PHIVOLCS to raise the Alert Level to 4. By the following day, more than 50,000 people had evacuated to emergency shelters and civil aviation authorities temporarily closed airports in the cities of Legazpi and Naga.

Figure 29. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite acquired this image of the area around Mayon in the Philippines on 22 January 2018. The image combines natural-color data with thermal infrared bands (7-2-1). The substantial ash plume from the explosion that day rose to 10.9 km altitude and drifted NW and W, and the emerging lava dome appeared as a thermal hotspot at the summit. Courtesy of NASA Earth Observatory.

Numerous episodes of intense lava fountains during the nights of 23-26 January each lasted from a few minutes to more than an hour. They generated 150-600 m high fountains and continued to feed the flows in the Mi-isa and Bonga gullies. Ash plumes also rose from 0.5-5 km above the crater. The Mi-isa gully flow remained at 3 km from the summit, and the Buyuan flow had reached 1 km by 24 January. Pyroclastic density currents in the Mi-isi, Lidong/Basud, and Buyuan drainages were also observed. The PDCs in the Buyuan drainage traveled more than 5 km from the summit crater (figures 30-33).

Figure 30. Ash and steam plumes rose from the summit crater of Mayon while lava flows descended drainages on the S flank as seen from the town of Daraga, 10 km S, on 23 January 2018. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 31. An ash plume rises, likely from a pyroclastic density current, in a drainage on the SE flank of Mayon, a few kilometers N of the town of Daraga on 23 January 2018. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 32. Ash and pyroclastic density currents emerged from the summit of Mayon on 24 January 2018, sending ashfall to nearby communities and filling drainages with pyroclastic debris. Image taken from Daraga, 10 km S. Courtesy of The Express, photo from European Pressphoto Agency.

Figure 33. Lava flows were very active on the S flank of Mayon, visible from about 12 km SSE in Legazpi on 25 January 2018. Courtesy of The Express, AFP/Getty Images.

By the evening of 26 January 2018, the lava fountaining episodes had transitioned into aseismic lava effusion, feeding incandescent flows into the Bonga and Mi-isi gullies on the S flank, and advancing the flow in the Bonga significantly downslope to 1.8 km. Fewer fountaining episodes continued during 27-28 January. Heavy rainfall during 28-29 January remobilized deposits from pyroclastic density currents and generated sediment-laden stream flows in several channels (figure 34) and channel-confined lahars on the Binaan Channel.

Figure 34. Sediment-laden streams posed hazards to residents of Camalig (11 km SW) at Mayon on 28 January 2018 after heavy rains and numerous PDC's had filled the drainages with debris. Courtesy of The Express, photo from European Pressphoto Agency.

A significant increase in lava effusion and fountaining at the summit during the evening of 29 January 2018 fed PDCs into the Mi-isi and Bonga Gullies, and resulted in significant ashfall in Camalig and Guinobatan to the SW. Intermittent lava fountaining to 200 m, flow-front collapses that generated PDC events, low-level ash emissions, and slow lava effusion from the summit crater continued during 30 January-4 February (figures 35 and 36). The Mi-isi and Basud lava flows had advanced to 3.2 and 3.6 km, respectively, from the summit crater by 1 February, and the Bonga-Buyuan flow had advanced 4.3 km by 3 February.

Figure 35. Steam-and-ash plumes rose steadily above Mayon on 31 January 2018. Image taken at the port in Legazpi City, about 15 km S. Courtesy of The Express, Getty Images.

Figure 36. Lava effusion at the summit of Mayon had decreased from a week earlier (see figure 33) by 31 January 2018. Courtesy of The Express, Getty Images.

Activity during February-March 2018. Lava fountaining reached 550 m above the summit crater on 5 February and increased to near-continuous activity the next day. Lava flows and incandescent rockfalls were observed throughout the night in the Mi-isi and Bonga-Buyuan channels. High volumes of incandescent lava flows advanced to 3.2, 4.5, and approximately 3.0 km down the Mi-isi, Bonga-Buyuan and Basud channels. Pyroclastic density currents from the collapsing flow fronts reached 4.6, 4.4, and 4.2 km from the summit crater in the same drainages during 7 February. Near-continuous fountaining accompanied by steam plumes that rose up to 800 m continued through 10 February.

Lava fountaining became sporadic and weak beginning on 11 February. Heavy rainfall during 13 February generated channel-confined lahars in the Anoling channel. By 14 February, lava flows remained at 3.3 km, 4.5 km, and 900 m down the Mi-isi, Bonga and Basud gullies, and PDCs had deposited material to distances of 4.6, 4.5, and 4.2 km in the same drainages. Intermittent lava fountaining continued through 22 February. The fountains generally rose 100-600 m above the summit and were often audible more than 10 km from the summit.

Quieter lava effusion with fewer fountaining events was more typical behavior beginning on 23 February. Numerous episodes of lava-collapse pyroclastic density currents were visually observed on the Mi-isi, Basud, and Bonga-Buyuan Gullies within 2-4 kilometers of the summit crater during the second half of February. Deflation of the lower slopes that began on 20 February was recorded by electronic tiltmeter, consistent with the transition to seismically quieter lava effusion at the summit crater. However, the overall electronic tiltmeter and the continuous GPS data indicated that the volcano was still inflated relative to October and November 2017 levels.

Weak fountaining, lava effusion, and degassing were noted during 25-28 February. The sporadic fountains generated plumes that rose 800 m, and weak effusion continued to feed the flows in the drainages. Gravity-driven lava flow movement and degassing with ash plumes rising 600 m above the summit were the primary activity at Mayon on 1 March, although occasional lava fountaining events were still observed. Based on the decrease in activity at the summit, the decrease in seismicity, continued deflation, and significantly lower SO₂ emissions, PHIVOLCS lowered the Alert Level to 3 on 6 March 2018.

Brief periods of weak fountaining and lava flows were observed during 7-24 March. The fountaining generated dark gray ash plumes that rose 100-300 m above the summit crater before drifting SW, and were sometimes audible more than 10 km from the summit crater. At night, lava flows continued moving downslope within 3.3, 4.5, and 1.9 km of the crater in the Mi-isi, Bonga, and Basud gullies. Steam plumes rose as high as 2.5 km above the summit before drifting SW on 7 March. Intermittent bluish steam-laden plumes rose to 700 m before drifting SW on 14 March. A slight inflation of the lower flanks beginning on 11 March 2018 was recorded by electronic tiltmeters through at least 22 March. Overall deformation data indicated that the edifice was still inflated relative to pre-eruption baselines.

Beginning around 24 March 2018, the primary activity consisted of intermittent lava collapse events in the Mi-isi gully located between 4-5 km from the summit and steam-laden plumes that drifted SW from the summit. Lava flow effusion at the crater was last detected on 18 March. Ground deformation since 20 February 2018 recorded deflation despite short-term episodes of inflation of its lower and middle slopes, and incandescence at the summit had diminished from intense to faint. Lava flows had begun to stabilize, producing fewer rockfalls and infrequent pyroclastic density currents, the last of which was observed on 27 March 2018. This continued decrease in activity led PHIVOLCS to lower the Alert Level to 2 on 29 March 2018.

VAAC, SO₂, and MIROVA information. The Tokyo VAAC reported the first ash emission from Mayon on 13 January 2018 as a plume that rose to 5.2 km altitude and drifted SW. Many subsequent ash emissions were obscured by meteoric clouds and were only occasionally observed in satellite imagery. The ash plume from the large explosion on 22 January was observed in satellite imagery at 10.9 km altitude drifting NW. Numerous daily VAAC reports were issued through February; they were intermittent in March, ending on 23 March 2018. Plumes generally were reported at 5.2-7.6 km altitudes. Small sulfur dioxide plumes were captured by the OMI and OMPS satellite instruments on several days between 22 and 31 January 2018 (figure 37).

Figure 37. SO2 anomalies from Mayon were captured by the OMPS and OMI instruments on the SUOMI and AURA satellites during January 2018. Upper left: 22 January 2018; upper right: 23 January 2018; lower left: 26 January 2018; lower right: 31 January 2018. Courtesy of NASA Goddard Space Flight Center.

The MIROVA project thermal anomaly graph of log radiative power clearly captured the onset of activity at Mayon in mid-January 2018 (figure 38). Thermal activity increased through early February and then slowly decreased through mid-March 2018 when lava effusion ended.

Figure 38. The sudden onset of thermal activity at Mayon is apparent in this MIROVA project graph of log radiative power for the year ending on 11 May 2018. The data is based on the satellite-based MODIS infrared thermal imagery. Thermal activity peaked at the end of January and dropped off gradually through mid-March 2018; it then decreased abruptly after that. Courtesy of MIROVA.

Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); The Express (URL: https://www.express.co.uk); European Pressphoto Agency (EPA) (URL: http://www.epa.eu/); Getty Images (URL: https://www.gettyimages.com/); Agence France Presse (AFP) (URL: https://www.afp.com/).

Located 60 km SE of Mexico City, frequent historical eruptions have been reported from Popocatépetl going back to the 14th century. Activity increased in the mid-1990s after about 50 years of quiescence, and the current eruption, which has been ongoing since January 2005, has included frequent ash plumes and numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple emissions of steam and gas occur daily, rising generally 1-4 km above the 5.4-km-elevation summit; many contain small amounts of ash. Larger, more explosive events that generate ashfall in neighboring communities often occur every week.

Activity through July 2017 was typical of the ongoing eruption with near-constant emissions of water vapor, gas, and minor ash, as well as multiple explosions every week with ash-plumes and incandescent blocks sent down the flanks (BGVN 42:09). This report covers similar activity through February 2018. Information about Popocatépetl comes from daily reports provided by México's Centro Nacional de Prevención de Desastres (CENAPRED); ash emissions are also reported by the Washington Volcanic Ash Advisory Center (VAAC). Satellite visible and thermal imagery and SO₂ data also provide important observations.

Near-constant emissions of steam and gas, often with minor ash content, were typical activity for throughout August 2017-February 2018. Intermittent larger explosions with plumes of moderate ash content that generated ashfall in nearby communities were reported in most months, including several times during October and November 2017, reaching communities as far as 70 km away. Incandescence at the summit was often observed on clear nights, and Strombolian activity that sent incandescent blocks several hundred meters down the flanks occurred at least once each month during September 2017-January 2018. The tallest ash plumes during the period reached 9.1 km altitude in mid-October and 10.3 km altitude at the end of January 2018. Thermal anomalies were persistently detected in satellite data throughout the period, and SO₂ plumes were recorded every month with satellite instruments.

Activity during August-September 2017. The Washington VAAC reported satellite observations of an ash plume extending 55 km W of the summit at 6.4 km altitude on 31 July 2017; the plume was mostly gas and steam with a small amount of ash. CENAPRED reported ashfall in Ozumba (18 km W) on 1 August from a plume that rose 2 km above the summit. They also noted numerous low-intensity explosions with steam, gas, and ash during 5-7 August. A small explosion early on 14 August produced a 500-m-high plume with minor ash content that drifted SW. Two explosions later in the day generated ash plumes that rose 0.8 and 1.5 km from the summit and drifted W (figure 94). Another explosion on 15 August produced a plume over 1 km in height with moderate ash content. On 21 August CENAPRED reported an ash plume that rose 4 km and drifted NW (figure 95). The Washington VAAC reported this plume extending 33 km W from the summit at 7.6 km altitude. Later in the day the ash cloud was observed about 230 km W of the summit, and a new cloud at a slightly lower altitude had drifted 45 km NW.

Figure 94. An ash plume drifted W from Popocatépetl on 14 August 2017 as seen from the Tlamacas webcam located about 5 km N of the volcano. Courtesy of CENAPRED.

Figure 95. An ash plume at Popocatépetl rose 4 km above the summit on 21 August 2017 and drifted over 200 km W before dissipating. View is from the Altzomoni webcam, located about 10 km N of the summit. Courtesy of CENAPRED.

CENAPRED noted 22 explosions with ash during 25-26 August that drifted N and NW. They were observed in satellite imagery by the Washington VAAC at 7.6 km altitude. Eleven explosions with small amounts of ash were reported by CENAPRED on 27 August. There were daily explosions during 28-31 August, but weather clouds obscured views of the summit. Incandescence at the summit crater was observed on many clear nights during August.

During 1-11 September 2017 cloudy conditions generally prohibited observations of the summit, but low-intensity emissions of steam and gas were briefly observed, many containing minor ash. Five explosions with minor ash emissions were reported by CENAPRED on 12 September; the Washington VAAC noted the ash plume in satellite imagery at 6.7 km altitude drifting slowly N. CENAPRED reported 22 explosions with ash and incandescent rocks on the NE flank during 12-13 September.

The Washington VAAC reported ash plumes on 13 September at 8.2 km altitude, on 18 September at 6.4 km altitude drifting W, and on 23 September near 7 km altitude moving to the NNE. Numerous explosions were reported by CENAPRED during 27 and 28 September (figure 96). The Washington VAAC reported the dense ash plume from these explosions at 6.7 km altitude drifting WSW. It extended 130 km W of the volcano by early afternoon on 27 September. CENAPRED reported that an explosion late on 30 September sent incandescent fragments 0.8 km from the crater and produced a dense ash column that rose more than 2 km above the summit.

Figure 96. A dense ash emission from Popocatépetl on 27 September 2017 extended 130 km W before dissipating as viewed from the Altzomoni webcam, located about 10 km N of the summit. Courtesy of CENAPRED.

Activity during October-November 2017. The ash plume from the explosion late on 30 September 2017 was visible in satellite imagery the following morning located 15 km SW from the summit at 7.9 km altitude according to the Washington VAAC. CENAPRED reported three explosions on 2 October and five explosions the next day, causing ashfall in Atlautla (17 km W), Tepetlixpa (21 km W), and Ozumba. Three explosions on 5 October resulted in ashfall in Totolapan (32 km W), Tlalnepantla (40 km W), and Cuernavaca (64 km W), and closer to the volcano in Ecatzingo (15 km SW), Atlautla, and Tepetlixpa. Lahars were also observed on the W flank, but there were no reports of damage. Two more explosions on 6 October led to ashfall reported from Zacualpan de Amilpas (30 km SW) and Tetela del volcán (18 km SW) (figure 97). The Washington VAAC reported the 6 October emissions at 6.4 km altitude.

Figure 97. Webcam image showing one of the two explosions on 6 October 2017 at Popocatépetl that caused ashfall in Zacualpan de Amilpas (30 km SW) and Tetela del volcán (18 km SW). The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

The first of two explosions on 7 October 2017, shortly after midnight, produced a plume that rose over 2 km and drifted SW with ashfall reported in Tetela del volcán; incandescent blocks were also sent down the flanks (figure 98). The second explosion produced an ash plume that rose 3 km and drifted NNE. The Washington VAAC reported continuing ash emissions during 7-11 October. Numerous plumes rose to 5.8-9.1 km altitude and drifted in several different directions; the plume extended 130 km SW from the summit on 10 October. CENAPRED reported three explosions on 8 October (figure 99) and two on 9 October. Numerous low-intensity exhalative events during 10-12 October produced ash plumes less than 1 km above the crater that drifted SW. Ashfall was reported in several communities during this time including Ozumba, México City (60 km NW), Milpa Alta (45 km NW), Xochimilco (56 km NW), Tlalpan (68 km NW), Coyoacán (66 km NW), Iztapalapa (57 km NW), Magdalena Contreras (72 km NW), and Iztacalco (64 km NW).

Figure 98. Incandescent blocks visible in this image traveled down the flanks of Popocatépetl during the early morning of 7 October 2017. The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

Figure 99. Multiple explosions from Popocatépetl on 8 October 2017, including the one seen here, caused ashfall in several communities NW of the volcano. The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

CENAPRED noted incandescence at the crater during most nights from 14 to 31 October, as well as steam, gas, and minor ash from hundreds of low-intensity emission events each day. The Washington VAAC reported ash emissions visible in satellite imagery on 16, 20-22, and 26 October drifting in several different directions at altitudes of 5.8-7.6 km. The plume observed on 22 October reached 60 km from the summit before dissipating. CENAPRED reported two explosions with ash plumes each day during 25-27 October. The Washington VAAC reported an ash plume on 29 October at 6.1 km altitude drifting E about 35 km from the summit, and another at 6.7 km the following day along with an infrared hotspot visible at the summit.

The Washington VAAC issued multiple daily ash advisories throughout November 2017. CENAPRED reported hundreds of daily low intensity emissions of gas and steam that often contained minor ash; the plumes generally rose about 1 km above the summit and most often drifted SW. They also observed incandescence at the crater on all clear nights. They reported Strombolian activity on 3 November in the early morning that lasted for several hours. Explosions early on 4 November resulted in minor ashfall in Yecapixtla (29 km SW) and Zacualpan de Amilpas and other areas to the SW. A Strombolian episode later that day lasted for about an hour and resulted in minor ashfall in Tetela del Volcán. Another explosion that night sent incandescent fragments 200 m down the flanks.

An explosion on 6 November sent an ash plume 2.5 km above the summit crater that drifted SW and sent incandescent fragments 500 m down the flank. Another explosion during the early morning of 7 November produced a 2-km-high ash plume. Moderate amounts of ash rose 1 km above the summit on 8 November. There were three explosions on 10 November; the largest produced a 3-km-high ash plume that drifted SW. Continuous low-level emission of gas and ash on 14 November resulted in ashfall reported in Totolapan, Yecapixtla, Ocuituco (23 km SW), Tetela del Volcán, and Ecatzingo. An explosion on 17 November sent an ash plume 2.5 km above the summit that drifted SW. During 18-19 November five explosions caused ash plumes to rise 2 km above the summit and incandescent blocks to fall down the E flank.

Around 1030 on 20 November, seismic activity increased and was accompanied by a constant plume of steam, gas, and moderate ash that rose about 1.5 km and drifted E. During 20-21 November eight explosions were reported, with five more the following day. During the afternoon of 23 November a continuous ash emission that lasted 90 minutes drifted SSE at 2 km above the summit, and spread ash over communities to the SSE including Huaquechula (30 km SSE), Tepeojuma (38 km SE), Atlixco (23 km SE), and Izúcar de Matamoros (50 km SE) (figure 100). Another significant ash emission during the afternoon of 24 November sent a column of ash to 4 km above the summit, drifting SSE; it lasted for almost two hours (figure 101). The Washington VAAC reported the plume at 8.5 km altitude. Ashfall was reported in San Pedro Benito Juárez (12 km SE) and Atlixco. Late that evening, an explosion sent incandescent fragments 1 km down the flanks and generated an ash plume that rose to 2.5 km above the summit and also drifted SSE.

Figure 100. A continuous ash emission at Popocatépetl that lasted for 90 minutes drifted SSE at 2 km above the summit, and spread ash over several communities to the SSE on 23 November 2017. The Tlamacas webcam is located about 5 km N of the volcano. Courtesy of CENAPRED.

Figure 101. A substantial ash emission at Popocatépetl during the afternoon of 24 November 2017 sent a column of ash to 4 km above the summit that drifted SSE; it lasted for almost two hours. The Washington VAAC reported the plume at 8.5 km altitude. The Altzomoni webcam is located about 10 km N of the summit. Courtesy of CENAPRED.

A flyover by CENAPRED and the Federal Police on 25 November 2017 allowed evaluation of the changes in the summit crater from the recent explosions. They noted that the internal crater within the summit crater had increased its dimensions, reaching a diameter of 370 m and a depth of 110 m (figure 102). A 3-km-tall ash plume resulted from continuous emissions that began in the afternoon of 27 November and lasted for two hours. The Washington VAAC reported the plume at 7.9 km altitude. The plume drifted SSE, and dispersed ash over communities in that region including Tochimilco (16 km), Izucar de Matamoros, Atlixco, and Huaquechula.

Figure 102. During a flyover on 25 November 2017, CENAPRED observed that the increased size of the internal summit crater at Popocatépetl was 370 m in diameter and 110 m deep. Courtesy of CENAPRED.

Activity during December 2017-February 2018. The Washington VAAC issued multiple daily reports of ash emissions during 1-12 and 24-31 December 2017. CENAPRED noted hundreds of daily low-intensity emissions of gas and steam, most with small quantities of ash, throughout December, as well as multiple ash emissions on many days that rose generally 1-2.5 km above the summit. In the early morning of 2 December an explosion caused an ash plume to rise 2.5 km above the summit. A second plume rose 1 km later that day; they both drifted SSE. An explosion in the afternoon of 9 December sent an ash plume over 2.5 km above the summit that drifted NE. The Washington VAAC reported the plume at 7.6 km altitude. Later that evening Strombolian activity sent incandescent blocks down the flanks and generated an ash plume that drifted E. Incandescence was observed at the summit crater during the nights of 17-21 and 24-29 December. Continuous emissions of steam, gas, and moderate-density ash were reported drifting NW for about 90 minutes on 29 December. An explosion on 31 December at 1032 generated a 2-km-high ash plume that also drifted NW.

There were multiple daily reports of ash emissions issued by the Washington VAAC during most days of January 2018. CENAPRED noted hundreds of daily low-intensity emissions of gas and steam, many with small quantities of ash, throughout the month, as well as explosions with ash emissions on many days that generally rose 1-2.5 km above the summit. They also observed incandescence at the summit crater multiple days each week. Ongoing low-level emissions of steam, gas, and minor ash were reported during 4-5 January. During the evening of 5 January activity increased, and the ash plume rose to 800 m and drifted SE. In addition, incandescent blocks were ejected 200-300 m down the flanks for about two hours.

An explosion on 18 January 2018 generated an ash plume that rose 1.5 km above the summit and drifted E while incandescent blocks were ejected up to 700 m down the flanks. An episode of Strombolian activity in the early morning of 25 January produced an ash plume that rose 2 km above the summit and drifted N and NE, resulting in reports of ashfall in San Pedro Nexapa (14 km NE) and Amecameca (19 km NE). It lasted for about 2 hours. Four explosions were reported during the afternoon of 29 January and an explosion the following afternoon produced an ash plume that rose more than 3 km above the summit, and was dispersed to the NW. An explosion on 31 January also produced a substantial ash plume that the Washington VAAC reported at 10.3 km altitude moving NNE (figure 103).

Figure 103. An ash plume rose to 10.3 km altitude from Popocatépetl on 31 January 2018 and drifted NNE. The Altzomoni webcam is located about 10 km N of the summit. Courtesy of CENAPRED.

Activity was somewhat quieter at Popocatépetl during February 2018. The Washington VAAC reported ash emissions on 14 days during the month. CENAPRED reported tens, not hundreds, of daily low-intensity emissions of gas and steam that often contained minor amounts of ash. They also noted one or more explosions with ash emissions on many days that rose generally 1-1.5 km above the summit and drifted in various directions. During many clear days they observed nearly constant emissions of steam, gas, and minor ash that reached 500-800 m above the summit. An explosion on 20 February produced an ash plume that rose 1.5 km above the summit. Continuous steam and gas emissions during 22-23 February were accompanied by minor incandescence intermittently observed at the summit.

Satellite data. Sulfur dioxide emissions were large enough to be recorded by satellite instruments several times every month during August 2017-February 2018 (figure 104). Variable wind directions and persistent emissions produced relatively long-lived plumes that dispersed over large areas of Mexico.

Figure 104. The OMI instrument on NASA's AURA satellite recorded evidence of significant monthly SO2 emissions at Popocatépetl, including on 27 September 2017 (upper left), 13 October 2017 (upper right), 31 October 2017 (lower left) and 25 December 2017 (lower right). Variable wind directions and persistent emissions produced relatively long-lived plumes that dispersed over large areas of Mexico. Courtesy of NASA Goddard Space Flight Center.

Thermal anomaly data provided by the MIROVA project are consistent with the visual record of persistent incandescent and explosive activity at the summit (figure 105). Multiple MODVOLC thermal alerts were also recorded every month from October 2017-February 2018.

Figure 105. Thermal anomalies detected by satellite-based MODIS instruments and recorded through the MIROVA project show the pattern of continued moderate-level activity at Popocatépetl during the year ending 12 July 2018. Courtesy of MIROVA.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/), Daily Report Archive http://www.cenapred.unam.mx:8080/reportesVolcanGobMX/BuscarReportesVolcan); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Indonesia's Sinabung volcano has been highly active since its first confirmed Holocene eruption during August and September 2010; ash plumes initially rose up to 2 km above the summit, and falling ash and tephra caused fatalities and thousands of evacuations (BGVN 35:07). It remained quiet after the initial eruption until 15 September 2013, when a new eruptive phase began that has continued uninterrupted through February 2018. Ash plumes rising several kilometers, avalanche blocks falling several kilometers down the flanks, and deadly pyroclastic flows travelling more than 4 km have all been documented repeatedly during the last several years. Details of events during October 2017-March 2018, including the largest explosion to date on 19 February 2018, are covered in this report. Information is provided by, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB). Additional information comes from satellite instruments and local observers.

When activity began in 2010, and again when eruptions resumed in 2013, many news accounts included statements that Sinabung had last been active 400 years ago, or even saying specifically that the last eruption was in 1600 CE. Those claims appear to have been caused by a misunderstanding related to the boundary time that Indonesian volcanologists use to categorize volcanoes. Those volcanoes with historical activity, defined as being about 400 years ago (corresponding to the beginning of the Dutch East India Company era), are in the "Type A" group. Those in the "Type B" group, including Sinabung prior to 2010, have not had reported activity in more than 400 years. Using charcoal associated with the most recent pyroclastic flow, Hendrasto et al. (2012) determined that the last previous eruptive activity was 1200 years before present using carbon dating techniques, or 740-880 CE (at 1 sigma).

Although activity remained high from October 2017 through March 2018, a gradual decline in the overall eruptive activity from the beginning of 2017 was apparent. The number of explosions per month generally declined, with no explosions reported during March 2018, for the first time since August 2013 (figure 45). The thermal anomaly record was similar; periods of high heat flow persisted through mid-November 2017, followed by a gradual reduction in the amount of thermal activity, although the intensity remained consistent, according to the MIROVA project (figure 46). Much of the heat flow was attributed to the dome growth at the summit; the dome was destroyed in the large explosion of 19 February 2018.

Figure 45. The number of explosions per month at Sinabung as reported by PVMBG from January 2017-March 2018. Only partial data was reported for 18-31 January 2018, and no explosions were observed during March 2018.

Figure 46. Thermal anomaly data at Sinabung from satellite-based MODIS instruments, plotted on a Log Radiative Power scale, persisted through the end of 2017 and then decreased in frequency through the end of February 2018. Much of the heat flow was attributed to a dome near the summit which was destroyed in the 19 February 2018 explosion. Graph shows thermal anomalies between 11 May 2017 and 1 April 2018. Courtesy of MIROVA.

Throughout the period from October 2017 through 19 February 2018, steam plumes were constantly rising to heights of 1,000-2,400 m above the summit. Avalanche blocks were ejected daily down the E and S flanks from 500-3,500 m, and multiple pyroclastic flows each month traveled between 1,000 and 4,600 m down the SE flank. Tens of explosions occurred monthly, generating ash plumes that rose from 500 to 5,000 m above the summit. Explosive activity was more intermittent during February than the previous months, until 19 February when the largest explosion to date occurred; it included an ash plume that rose to at least 16.8 km altitude and at least ten pyroclastic flows. In spite of the size of the explosion, no injuries or fatalities were reported as most nearby communities had been evacuated from the ongoing activity. Activity decreased substantially during March 2018; there were no explosions, block avalanches, or pyroclastic flows reported, only steam plumes rising 1,000 m above the summit.

Activity during October 2017-January 2018. During October 2017, steam plume heights reached 1,500 m above the summit. Avalanche blocks traveled down the E and S flanks 500-2,500 m, and eight pyroclastic flows traveled 1,000-4,500 m down the SE and S flanks. Ash plume heights ranged from 500 to 3,600 m above the summit. The Darwin VAAC issued 38 aviation alerts during the month. On 1 October they reported an ash plume drifting both NW at 4.6 km altitude and NE at 3.7 km. The next day, the webcam observed an ash emission that rose to 5.5 km altitude. On 4 October an ash plume was spotted in the webcam rising to 5.8 km altitude and drifting ENE. Later that day it had detached from the volcano and was seen drifting NW in satellite imagery. An ash plume on 5 October rose to 3.9 km altitude and drifted ESE. Two ash emission were reported on 7 October; the first rose to 3 km altitude, the second rose to 4.3 km, they both dissipated quickly. On 8 October, three plumes were reported. The first rose to 4.6 km and drifted WSW, the second rose to 3 km and drifted S and the third rose to 3.4 km and also drifted S. The following day, an ash plume rose to 4.6 km and drifted E. BNPB stated that on 11 October, an event at Sinabung generated an ash plume that rose 1.5 km above the crater and drifted ESE, causing ashfall in several local villages. On 12 October an event produced an ash plume that rose 2 km above the crater and was followed by pyroclastic flows traveling 1.5 and 2 km down the S and ESE flanks, respectively.

PVMBG reported ash plumes rising to 3.7 km on 11, 12, and 13 October 2017. Later on 13 October the Jakarta MWO reported an ash plume at 4.3 km. The next day PVMBG reported an ash plume at 5.5 km altitude. A plume on 15 October rose to 3 km and drifted E. A steam plume on 16 October drifted down the SE flank before drifting SE no 16 October (figure 47). On 17 October, a discrete emission rose a few hundred meters above the summit drifted NE. Later that day, an ash plume was seen in the webcam moving SE at 3.4 km. On 18 October, two ash emissions were reported. The first rose to 3.7 km and drifted E, the second rose to 3.9 km and drifted W. An ash plume rose to 4.6 km altitude on 21 October, and to 3.9 km, drifting S, on 23 October. The next day, three ash plumes were reported; the first rose to 3 km, the second to 4.6 km, and the third to 3.7, all drifting E. After five days of quiet, the webcam observed ash plumes that rose to 4.3 km on 30 October, and to 3.9 km on 31 October. Only two MODVOLC thermal alerts were issued, on 20 and 27 October.

Figure 47. A steam plume drifted down the SW flank of Sinabung before moving SE on 16 October 2017. View is from the SE. Courtesy of PVMBG.

Steam plumes were higher during November 2017, rising 2,400 m above the summit. Block avalanches traveled 500-3,000 m down the E and S flanks most days, and ten pyroclastic flows traveled between 2,000-3,500 m down the ESE and S flanks. The ash plumes rose 700-3,200 m above the summit. The Darwin VAAC issued 41 aviation alerts in November. Near-daily ash plumes were observed mostly in the webcam and occasionally in satellite imagery. They generally rose to 3.4-4.9 km altitude; the most common drift directions were S and SW. A number of times, multiple ash plumes were reported in a single day. On 14 November, four ash plumes were observed. The first rose to 3.7 km, the second and third rose to 4.6 km and drifted S and SSW, the last rose to 3.9 km and also drifted SSW. On 20 November a discrete emission produced an ash plume that rose to 5.5 km altitude and drifted SSW. Three ash plumes were recorded the next day, rising 3.9-4.6 km and drifting in multiple directions under variable winds. An ash plume on 23 November was reported by PVMBG at 6.7 km altitude drifting W, the highest noted for the month. MODVOLC thermal alerts appeared twice on 5 November, once on 14 November, and three times on 17 November.

Activity during December 2017 was similar to the previous two months; steam plumes rose 2,000 m above the summit, block avalanches traveled 500-3,500 m down the E and S flanks numerous times, and nine pyroclastic flows descended the ESE and S flanks distances ranging from 2,000 to 4,600 m. Ash plume heights were from 700-4,000 m above the summit. The Darwin VAAC issued 43 aviation alerts in December 2017. They reported ash plume heights of 3.4-4.9 km altitude on most days. Every day during 10-19 December, ash plumes were reported at altitudes of 4.6-5.5 km drifting SW, E or SE. PVMBG reported ash plumes on 26, 27 and 28 December that rose to 3.9, 5.2, and 5.5 km, respectively. BNPB reported pyroclastic flows on 27 December that traveled 3.5-4.6 km SE, and ashfall was reported in many nearby villages including Sukanalu Village (20 km SE), Tonggal Town, Central Kuta, Gamber (4 km SE), Berastepu (4 km SE), and Jeraya (6 km SE). The highest ash plume of the month rose to 6.4 km altitude on 29 December and drifted E. This was followed by another discrete ash emission the same day that rose to 5.8 km and two plumes the next day that rose to 5.2 km and drifted W. There was only one MODVOLC thermal alert issued on 7 December.

The Darwin VAAC issued 56 aviation alerts for January 2018. Multiple discrete ash emissions were reported on most days. Plume altitudes generally ranged from 3.4 to 5.5 km. A 6.1 km altitude plume was visible in satellite imagery on 18 January (figure 48). The drift directions were highly variable throughout the month. Most plumes dissipated within six hours. Incandescent blocks were reported by PVMBG falling 500-1,500 m down the ESE flank on most days when the summit was visible. They also reported a pyroclastic flow on 27 January that traveled 2,500 m ESE from the summit (figure 49). Three MODVOLC thermal alerts were issued on 6 January, and one on 12 January.

Figure 48. An ash plume rose 3,000 m from the summit of Sinabung on 18 January 2018 in this view looking at the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 49. A pyroclastic flow descended 2,500 m down the SE flank of Sinabung on 27 January 2018 while an ash plume also drifts SE in this view of the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Activity during February 2018. During most of February, steam plumes rose only 1,000 m above the summit, and avalanche blocks traveled 500-2,500 m down the ESE and S flanks. Far fewer ash emissions were reported than previous months, but the largest explosive event recorded to date took place on 19 February (figure 50). The Darwin VAAC issued 29 aviation alerts during February 2018. Short-lived ash emissions were reported on 1, 3, 5, 11, and 15 February. The ash plume heights ranged from 3.4-4.6 km altitude, and they drifted S or SW.

Figure 50. A very large ash plume rose to 16.8 km altitude from Sinabung on 19 February 2018. Image is from several tens of kilometers from the volcano a few hours after the eruption. No fatalities were reported. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

The large explosion was first reported by the Darwin VAAC at 0255 UTC on 19 February 2018. It produced an ash plume, which was clearly observed in satellite imagery (figure 51), that quickly rose to at least 16.8 km altitude and began drifting NW (figure 52). It also produced a large SO2 plume that was recorded by satellite instruments (figure 53). Over the next 15 hours the plume dispersed in three different directions at different altitudes. The highest part of the plume drifted NW at 13.7 km and was visible over 300 km from the summit. The lower part of the plume drifted S initially at 6.7 km and gradually lowered to 4.3 km; it was visible 75 km from the summit before dissipating. A middle part of the plume drifted NW at 9.1 km during the middle of the day. Three subsequent minor ash emissions were observed on 20 and 25 February that rose to 3.4 km altitude. There were no VAAC reports issued during March 2018. A MODVOLC thermal alert issued on 11 February was the last for several months.

Figure 51. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this natural-color image of the ash plume at Sinabung at 0410 UTC on 19 February 2018, just a few hours after it began. The ash plume rose over 16 km high and drifted in multiple directions. Courtesy of NASA Earth Observatory.

Figure 52. The large ash plume of 19 February 2018 at Sinabung, viewed here from within a few kilometers of the summit in the first hour or so after the eruption, rose quickly to over 16 km altitude. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 53. Two different Ozone Monitoring Instruments measured the SO2 plume released by Sinabung in the explosion on 19 February 2018. The upper left image was recorded about three hours after the explosions (0616-0621 UTC, 19 February 2018) by the Ozone Mapper Profiler Suite (OMPS) instrument on the Suomi NPP satellite. The upper right image was recorded about 27 hours after the explosion (0619-0802 UTC, 19 February 2018) by the Ozone Monitoring Instrument (OMI) on the Aura satellite, and shows the multi-directional dispersal of the SO2 plume during that time. The lower image uses the data captured at the same time as the upper left image and displays it using different software and detailed background information. The maximum gas concentrations reached 140 Dobson Units. Upper images courtesy of NASA Goddard Space Flight Center, and lower image courtesy of NASA Earth Observatory.

As many as 10 pyroclastic flows were observed during the 19 February explosion, traveling as far as 4.9 km SSE and 3.5 km E (figures 54 and 55). Ash and tephra as large as a few millimeters in diameter fell in areas downwind, including Simpang Empat (7 km SE), the Namanteran district, Pqyung (5 km SSW), Tiganderket (7 km W), Munthe, Kutambaru (20 km NW), Perbaji (4 km SW), and Kutarayat (figure 56 and 57).

Figure 54. A pyroclastic flow traveled several kilometers SSE from Sinabung on 19 February 2018 as tephra fell from the rising ash cloud in this view from several kilometers away to the NE. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 55. The dark gray ash plume rose skyward while the large brown pyroclastic flows traveled SE from Sinabung on 19 February 2018 as viewed from the town of Kutarakyat located 5 km NE of the volcano. Photo by Endro Rusharyanto, courtesy of the Associated Press (AP).

Figure 56. Small tephra fragments fell on the village of Gurukinayan (13 km E) and other villages SE of Sinabung during the eruption of 19 February 2018. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 57. Ash from the eruption at Sinabung on 19 February 2018 covered vegetable plants the following day in the village of Payung (5 km SSW). Photograph by Antara Foto, Ahmad Putra via Reuters.

Villagers were temporarily evacuated from nearby villages, but were able to return a few days later (figure 58). Conditions in five districts were so dark that visibility was reduced to about 5 m. In addition, ashfall was recorded as far away as the town of Lhokseumawe, 260 km N. Magma Indonesia reported that the lava dome that had been growing at the summit for some time was destroyed in the 19 February explosion (figure 59). A PVMBG volcanologist reported the volume of the destroyed lava dome was at least 1.6 million cubic meters.

Figure 58. Villagers from Gurukinayan (13 km E) were evacuated as ash spread over the town from the eruption of Sinabung on 19 February 2018, but they returned to their homes a few days later. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 59. The summit of Sinabung, before (top) and after (bottom) the large explosion of 19 February 2018. The dome size in the upper photo is similar to that shown figure 43 (BGVN 42:12) from September 2017. The lower image was taken within a week after the explosion. Courtesy of MAGMA Indonesia, via Twitter.

Reference: Hendrasto M, Surono, Budianto A, Kristianto, Triastuty H, Haerani N, Basuki A, Suparman Y, Primulyana S, Prambada O, Loeqman A, Indrastuti N, Andreas A S, Rosadi U, Adi S, Iguchi M, Ohkura T, Nakada S, Yoshimoto M, 2012. Evaluation of Volcanic Activity at Sinabung Volcano, After More Than 400 Years of Quiet. Journal of Disaster Research, vol. 7, no. 1, p. 37-44.

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Sutopo Purwo Nugroho, Head of Information Data and Public Relations Center of BNPB via Twitter (URL: https://twitter.com/Sutopo_PN); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Associated Press (AP), Endro Rusharyanto, Photographer (URL: http://www.ap.org/); Reuters (http://www.reuters.com/).

Confirmed historical eruptions at Stromboli go back 2,000 years; this island volcano in the Tyrrhenian Sea has been a natural beacon with its near-constant fountains of lava for eons. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N Area) and a southern crater group (S or CS Area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the island. Thermal and visual cameras that monitor activity at the vents are located on the nearby Pizzo Sopra La Fossa, above the Terrazza Craterica, and at a location closer to the summit craters.

Eruptive activity during January-October 2017 peaked during June and then declined through August, returning to background levels in September; it included intermittent periods of frequent explosions from both crater areas that sent ash, lapilli, and bombs across the Terrazza Craterica and onto the head of the Sciara del Fuoco (BGVN 43:02). This report covers similar activity from November 2017-February 2018. Weekly reports of activity were provided by Italy's Instituto Nazionale de Geofisica e Vulcanologia (INGV), Sezione de Catania, which monitors the gas geochemistry, deformation, and seismicity, as well as surficial activity.

An explosive sequence on 1 November 2017 followed less than two weeks after a similar event on 23 October (BGVN 43:02) in the CS Area, creating Strombolian activity that sent ejecta 300 m high. Intermittent explosions and spattering continued until the next large explosion on 1 December, also in the CS Area. A general increase in seismicity was recorded during December 2017; intense spattering in the N Area on 15 December formed a lava flow that traveled 100 m N from the rim of the vent before stopping. The number of explosive events remained high (more than 20 per hour) through December, when both the intensity and rate of activity declined significantly, reaching levels below 10 events per hour in early February, and remaining there for the rest of the month. The general levels of intensity in the N and CS Areas, apart from the larger explosive events, were variable throughout November 2017-February 2018, generally increasing during December and decreasing during January (table 3). This pattern of activity is also reflected in the variation of the thermal activity that was recorded in the MIROVA thermal data during that time (figure 117), and the MODVOLC thermal alert data which recorded two alerts in November, and 14 in December, but none after that through February 2018.

Table 3. General intensity and activity levels at the summit vents in the N Area and CS Area at Stromboli, November 2017-February 2018. Intensity values correspond to the height of the ejecta above the vent: Low = less than 80 m high, Med-Low = less than 120 m High, Medium = less than 150 m high, Med-High = sometimes to 200 m, High = over 200 m. Coarse ejecta consisted of lapilli and bombs, and fine ejecta was primarily ash and smaller lava fragments.

Figure 117. MIROVA thermal data for Stromboli for the year ending on 2 May 2018 showed a gradual increase in thermal energy during mid-November 2017, peaking in mid-December, and then decreasing rapidly in early January to low levels by the end of the month that persisted through February 2018. Courtesy of MIROVA.

On 1 November 2017 at 0829 UTC a strong explosive sequence that lasted about 2 minutes was observed in the CS Area of the Terrazza Craterica (figure 118). The first explosion sent bombs and lapilli around the slopes of the terrace and the ejecta exceeded 300 m in height. Two more explosions followed soon after, sending material about 150 m into the air.

Figure 118. The explosive sequence of 1 November 2017 at Stromboli, taken from the INGV thermal and visual cameras at the 400 m level sent ash, bombs, and lapilli as high as 300 m. The time period covered by the explosions is about two minutes. Courtesy of INGV (Report 45/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 07/11/2017).

A survey by INGV scientists during 3-5 November 2017 evaluated the effects of this and the previous explosion on 23 October on the Terrazza Craterica. They noted that a large depression with a vent at the base, formed in the CS Area after the 23 October explosions, had been significantly enlarged during the 1 November explosions. Continuous spattering and strong incandescence were observed during the survey at the 4-m-wide C vent. They also observed that the explosive activity at S2 was produced by three emission points. They noted that the N1 site consisted of a single hornito and a secondary vent on the side flank (figure 119).

Figure 119. Several changes to the Terrazza Craterica at Stromboli were visible after the two strong explosive sequences of 23 October and 1 November 2017. a) The Terrazza Craterica on 5 November 2017; b) vent C on 30 September 2017 and c) on 5 November 2017 after the two major explosions; d) vent N1 on 30 September and e) on 5 November 2017. Photograph by D. Andronicus, courtesy if INGV (Report 45/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 07/11/2017).

The 23 October 2017 explosions ejected light brown scoriaceous material S and SE, almost reaching the Pizzo Sopra La Fossa 300 m to the E. A wide band of lithic blocks was also observed on the N flank of the W part of the Valle della Luna, an open area located S of the Terrazza, over a ridge at a higher elevation. During the 1 November explosions abundant black scoriaceous material formed spatter that covered the entire Terrazza Craterica and reached the W wall of the Pizzo facing the craters. Some of this material additionally landed on the NW ridge of the Valle della Luna and on its N flank. Blocks as large as 2 m were ejected during the 1 November event, along with reddish debris that dispersed in a wide area of the Terrazza Craterica and onto the SE flank at the S end of the Pizzo.

Vent C exhibited continuous degassing activity interrupted by short spattering episodes observed mainly on 15 and 21 November 2017. During 20-24 November, a new vent opened between vents S2 and C, which was sporadically active with incandescence and small explosions of fine-grained material. Three emission points were active from the C vent area at the end of November (figure 120).

Figure 120. The two crater areas on the Terrazza Craterica at Stromboli are visible from the thermal camera on the Pizzo Sopra La Fossa, seen here on 27 November 2017. The abbreviations and arrows indicate the names and locations of the active vents. Three emission points were active at vent C at the end of November 2017. Courtesy of INGV (Report 48/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 28/11/2017).

On 1 December 2017 at 1242 UTC a strong new explosive sequence in the CS crater area was recorded by the seismic network, although weather conditions permitted only observations of incandescence during the event. A large crater was noted a few days later in the area where the three emission points had been active at vent C. A general increase in seismic activity was observed beginning on 4 December that included increases in tremor amplitude, frequency and amplitude of VLP quakes, and the amplitude of explosion earthquakes. On 9 December, numerous explosions from vent S2 combined with strong winds and sent debris as far as the Pizzo Sopra La Fossa located 300 m E (figure 121).

Figure 121. The infrared camera on the Pizzo Sopra La Fossa captured an explosion produced by vent S2 in the CS Area at Stromboli on 9 December 2017; ejecta reached the Pizzo area. Courtesy of INGV (Report 50/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 12/12/2017).

The general increase in seismicity continued into the second week of December 2017. On 15 December 2017 intense spattering began at vent N1 at 1019 UTC. At 1330 the lava overflowed the crater rim and flowed N towards the Pianoro area, the N facing slope of the Terrazza Craterica, reaching about 100 m from the rim of N1 before stopping by 1530 that afternoon (figure 122).

Figure 122. Images taken by the infrared camera at the 400 m level of the lava overflow on 15 December 2017 from the N1 vent at Stromboli. Courtesy of INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 19/12/2017).

A survey by INGV scientists on 15 December 2017 revealed that the biggest change caused by the 1 December explosion was the formation of a new cone at vent S2 (figure 123a) with an inner crater that was almost 40 m wide. Emissions of dark ash 2-3 times per hour were observed along with spattering and ejected blocks of lava. Vent C, which had been a small pit crater prior to the explosion (figure 123b), had become a small cone that was degassing from the crater, with two smaller lateral vents exhibiting weak but continuous spattering activity (figure 123c). Vent N2 was characterized by infrequent Strombolian activity (1-2 explosions per hour). Most of the activity on 15 December was at vent N1 (figure 123a, e), where INGV scientists observed a new vent with continuous and increasing spattering that soon formed a lava flow. The flow traveled quickly across the crater area. Between 1300 and 1420, 3-4 violent and prolonged explosions at N1 ejected lava fragments tens of meters from at least four emission points. The area was covered with abundant scoriaceous material with average dimensions of 5-6 cm, and numerous fragments of black scoriaceous spatter ranging in size from 20 to 40 cm long; a few were as large as 100 cm.

Figure 123. INGV scientists recorded the changes at Stromboli's summit on 15 December 2017 that resulted from the explosions of 1 December, as well as events that day that generated a short lava flow. a) the Terrazza Craterica on 15 December 2017; b) vent C on 5 November and c) on 15 December after the explosions of 1 December created a cone; d) vent N1 on 5 November and e) on 15 December; the lava flows were produced by vents N1a and N1d. Photo by D. Andronicus, courtesy if INGV (Report 51/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 19/12/2017.

Activity diminished during January 2018; low- to medium-intensity explosions were typical in the N Area and degassing continued with intermittent explosive activity at the CS Area. During February 2018 activity decreased further with the overall explosion rate averaging generally less than 10 events per hour, a significant decline after the increases in activity that began in early November 2017 (figure 124).

Figure 124. The hourly frequency of the explosive events at Stromboli as recorded by the surveillance cameras from 1 July 2017-5 March 2018, averaged by day. The information is grouped by explosions at the N Area and the CS Area, and also shown as the total average. The Total value is the sum of the average hourly frequency by day of all the explosive events produced by the active vents. Courtesy of INGV (Repprt 10/2018, Stromboli, Bollettino Settimanale, 26/02/2018 - 04/03/2018, issue date 06/03/2018).

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).