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Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.


Recently Published Bulletin Reports

Krakatau (Indonesia) Tephra and steam explosions in the crater lake; explosions in December 2019 build a tephra cone

Mayotte (France) Seismicity and deformation, with submarine E-flank volcanism starting in July 2018

Fernandina (Ecuador) Fissure eruption produced lava flows during 12-13 January 2020

Masaya (Nicaragua) Lava lake persists with lower temperatures during August 2019-January 2020

Reventador (Ecuador) Nearly daily ash emissions and frequent incandescent block avalanches August 2019-January 2020

Pacaya (Guatemala) Continuous explosions, small cone, and lava flows during August 2019-January 2020

Kikai (Japan) Single explosion with steam and minor ash, 2 November 2019

Nevado del Ruiz (Colombia) Intermittent ash, gas-and-steam, and SO2 plumes, and thermal anomalies during January 2018-December 2019

Erebus (Antarctica) Lava lakes persist through 2019

Sangay (Ecuador) Continuing ash emissions, lava flows, pyroclastic flows, and lahars through December 2019

Shishaldin (United States) Multiple lava flows, pyroclastic flows, lahars, and ashfall events during October 2019 through January 2020

Sangeang Api (Indonesia) Ash emissions and lava flow extrusion continue during May 2019 through January 2020



Krakatau (Indonesia) — February 2020 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 155 m

All times are local (unless otherwise noted)


Tephra and steam explosions in the crater lake; explosions in December 2019 build a tephra cone

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (France) — March 2020 Citation iconCite this Report

Mayotte

France

12.83°S, 45.17°E; summit elev. 660 m

All times are local (unless otherwise noted)


Seismicity and deformation, with submarine E-flank volcanism starting in July 2018

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Ecuador) — March 2020 Citation iconCite this Report

Fernandina

Ecuador

0.37°S, 91.55°W; summit elev. 1476 m

All times are local (unless otherwise noted)


Fissure eruption produced lava flows during 12-13 January 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Nicaragua) — February 2020 Citation iconCite this Report

Masaya

Nicaragua

11.985°N, 86.165°W; summit elev. 594 m

All times are local (unless otherwise noted)


Lava lake persists with lower temperatures during August 2019-January 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Ecuador) — February 2020 Citation iconCite this Report

Reventador

Ecuador

0.077°S, 77.656°W; summit elev. 3562 m

All times are local (unless otherwise noted)


Nearly daily ash emissions and frequent incandescent block avalanches August 2019-January 2020

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).

Month Average Number of Explosions Max plume height above the crater Max SO2
Aug 2019 26 1.6 km --
Sep 2019 32 1.7 km 428 tons/day
Oct 2019 29 1.3 km 502 tons/day
Nov 2019 25 1.2 km 432 tons/day
Dec 2019 25 2.5 km 331 tons/day
Jan 2020 12 1.7 km --

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Guatemala) — February 2020 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Continuous explosions, small cone, and lava flows during August 2019-January 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Kikai (Japan) — February 2020 Citation iconCite this Report

Kikai

Japan

30.793°N, 130.305°E; summit elev. 704 m

All times are local (unless otherwise noted)


Single explosion with steam and minor ash, 2 November 2019

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Colombia) — January 2020 Citation iconCite this Report

Nevado del Ruiz

Colombia

4.892°N, 75.324°W; summit elev. 5279 m

All times are local (unless otherwise noted)


Intermittent ash, gas-and-steam, and SO2 plumes, and thermal anomalies during January 2018-December 2019

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Antarctica) — January 2020 Citation iconCite this Report

Erebus

Antarctica

77.53°S, 167.17°E; summit elev. 3794 m

All times are local (unless otherwise noted)


Lava lakes persist through 2019

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 (see Caption) 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.

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec SUM
2017 0 21 9 0 0 1 11 61 76 52 0 3 234
2018 0 21 58 182 55 17 137 172 103 29 0 0 774
2019 2 21 162 151 55 56 75 53 29 19 1 0 624
Figure (see Caption) 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/).


Sangay (Ecuador) — January 2020 Citation iconCite this Report

Sangay

Ecuador

2.005°S, 78.341°W; summit elev. 5286 m

All times are local (unless otherwise noted)


Continuing ash emissions, lava flows, pyroclastic flows, and lahars through December 2019

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (United States) — February 2020 Citation iconCite this Report

Shishaldin

United States

54.756°N, 163.97°W; summit elev. 2857 m

All times are local (unless otherwise noted)


Multiple lava flows, pyroclastic flows, lahars, and ashfall events during October 2019 through January 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Indonesia) — February 2020 Citation iconCite this Report

Sangeang Api

Indonesia

8.2°S, 119.07°E; summit elev. 1912 m

All times are local (unless otherwise noted)


Ash emissions and lava flow extrusion continue during May 2019 through January 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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/).

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Bulletin of the Global Volcanism Network - Volume 38, Number 03 (March 2013)

Managing Editor: Richard Wunderman

Azufral (Colombia)

Expanded monitoring efforts and explosive hydrothermal event in July 2009

Diables, Morne aux (Dominica)

Earthquake swarm began in mid-2009

Fujisan (Japan)

2000-2001 epicenter migration; deep magma; 2011 M 6 aftershock at volcano

Galeras (Colombia)

Ash emissions and elevated seismicity during May 2012-March 2013

Kanaga (United States)

18 February 2012 eruption; new fissure

Lokon-Empung (Indonesia)

Eruptions continue into early 2013

Nikko-Shiranesan (Japan)

Felt earthquakes nearby during April-September 2011

Niuatahi (Tonga)

New research data collected from submarine volcano

Tungurahua (Ecuador)

Return of explosions and earthquakes through at least October 2010



Azufral (Colombia) — March 2013 Citation iconCite this Report

Azufral

Colombia

1.08°N, 77.68°W; summit elev. 4070 m

All times are local (unless otherwise noted)


Expanded monitoring efforts and explosive hydrothermal event in July 2009

Previously reported activity from Azufral included seismic swarms in 1971 (CSLP 43-71) and fluctuating conditions within the crater lake, Laguna Verde during July-August 1990 (BGVN 15:08) (figure 1). In this report, we highlight explosive hydrothermal activity that occurred during July-August 2009. We also provide observations of Azufral's hydrothermal and fumarolic activity and review monitoring efforts that expanded since 2005.

Figure (see Caption) Figure 1. Looking E from Azufral's crater rim, the moat-like Lake Verde encloses nearly half of the central dome complex. The pale dome rock at the far left side of the lake was also the location of small fumarolic vents. While the lake level has fluctuated by ~1 m (gradual change over months), the bright green color persisted. This photo was taken on 4 September 2008 at 1210 by Servicio Geológico Colombiano (SGC) technicians.

Fumarolic activity within Azufral's largest crater had long been observed by Colombia's earliest inhabitants and investigators including Alexander von Humboldt in the 1800s (Yudilevich Levy, 2004). In one of his many journals, Diario VII "Viaje de Pasto a Quito," this naturalist noted the rugged morphology of the edifice, describing it as a volcano that had broken apart; similar in appearance to Sotará, a volcano he had already visited. At the time of his visit in December 1801, there were significant deposits of sulfur and strong gas emissions within the crater, particularly around the largest crater lake (he noted that there were several craters in the complex, the largest now known as Laguna Verde).

"Una de estas bocas es una charca hirviente de azufre, parecida al de Puracé, de furioso estrépito. Los vapores de azufre se escapan, además, de la tierra húmeda arcillosa y arrojan el lodo a lo alto, como si fuesen cañones." (Yudilevich Levy, 2004, p. 74).

With the assistance of Rüdiger Escobar-Wolf (Michigan Technological University), we translated the above passage as follows. Note that the works of von Humboldt were originally written in German.

"One of the depressions [of Azufral] contains a pond boiling and churning with sulfur, similar in appearance and furiously loud noises to the one at Puracé volcano. Sulfur vapors were also escaping from the clayey, humid earth, throwing the mud high in the air as if fired from cannons."

Local inhabitants shared their observations with von Humboldt, mentioning ash plumes (termed "polvo" in the diary), mud explosions, boiling water, and flames (sometimes starting brush fires) (Yudilevich Levy, 2004).

Explosive volcanic activity at Azufral had not been observed recently (a hydrothermal event was observed in July 2009, see the subsection below), but the geologic record has preserved evidence of large-scale eruptions dating from 2,095-950 BC (Siebert and others, 2010). In the January 2009 Technical Bulletin, the Servicio Geológico Colombiano (SGC) described Azufral as one of the most explosive volcanoes in Colombia due to its extensive pyroclastic and surge deposits.

Research by Hall and Mothes (2008) assessed Holocene volcanism and its impact on pre-Columbian indigenous cultures within the Interandean Valley. They synthesized the region's pyroclastic deposits (including source locations and event magnitudes) and highlighted the wide distribution of Azufral's deposits (figure 2). They argued that despite the extensive lahar and debris avalanche deposits within the valley, "the greatest impact upon mankind was probably not these short-lived violent events, but rather the burying of settlements and agricultural fields by ash fallout, the effect of which may have lasted hundreds of years. Ash fall layers are observed in pre-Columbian cultural horizons in the soil profile, occurring in the Interandean Valley, the lower flanks of the Andes, and along Ecuador's Pacific coast..."

Figure (see Caption) Figure 2. This regional map of Colombia's southern-most volcanoes includes the volcano El Soche, located in Ecuador and the distribution of Holocene volcanic products. Eruptions from Galeras, Azufral, Cumbal, Cerro Negro, Chiles, and El Soche have affected the NE-trending Interandean Valley (heavy dashed lines with hachure indicating downslope sides). Black arrows indicate directions of pyroclastic flows. Note that a ~930 BC (~2,900 ybp) date for Azufral's deposits is also cited by Siebert and others (2010); see the Geologic Summary. This map was modified from Hall and Mothes (2008).

Monitoring efforts 2005-2013. The base of operations for monitoring Azufral has been located in Pasto (~48 km ENE of Azufral) since ~2005. Over time, the Servicio Geológico Colombiano (SGC), formerly known as Instituto Colombiano de Geología y Minería (INGEOMINAS), expanded monitoring capabilities at Azufral through instrumentation and field investigations (table 1, figure 3).

Table 1. Azufral's monitoring network in March 2013 included EDM, seismometers, tiltmeters, a video camera, and a wind station. Figure 3, below, shows a map of various sites. Courtesy of SGC.

Station Description Instrument Location(s)
Electronic Distance Meter (EDM) survey stations 12 reflectors; 4 base stations (see figure 14)
Seismic stations (telemetered) Chaitán, ~4 km ENE (broadband); Laguna, 0.5 km SW (broadband); La Roca, 1.2 km E (short period)
Electronic tilt station (telemetered) Chaitán, ~4 km ENE; La Roca, 1.2 km E
Web camera (telemetered) Laguna, 0.5 km SW
Weather station (wind and precipitation) La Roca, 1.2 km E
Figure (see Caption) Figure 3. Map of Azufral's EDM network from the March 2013 Technical Bulletin. Courtesy of SGC.

Aerial observations had been conducted since 2005 focusing primarily on the lake's characteristics such as color, water level, and shoreline morphology. Overflights with a thermal camera were conducted during 2007-2011; during that time period, the maximum surface temperatures ranged from 22.5-38°C.

Changes in the lake level were observed based on repeat aerial photos; in particular, between 5 December 2006 and 23 August 2009, Laguna Verde had a noticeably narrower shoreline, suggesting that the lake volume had increased.

Field investigations established baselines for lake chemistry, diffuse radon gas emissions, SO2 flux within the crater, thermal emissions from fumarolic sites, EDM measurements, and the geochemistry of four local hot springs (figure 4).

Figure (see Caption) Figure 4. A map of hot spring locations within the region of Azufral (green circles with red text). Data from regular monitoring efforts was available between May 2010 and April 2013. Major local towns are labeled with black text. Courtesy of SGC.

During 2007-2008, SGC expanded the monitoring network by installing telemetered seismic stations and tiltmeters (figure 5). In the second quarter of 2008, the first monitoring stations were installed at Azufral; this timing coincided with monitoring developments at the neighboring volcanoes Doña Juana and Cumbal (volcanoes also managed by the Pasto Volcanological and Seismological Observatory, OVSP).

Figure (see Caption) Figure 5. The monitoring network at Azufral as of April 2013 included three sites, Laguna, La Roca, and Chaitán where seismometers, tiltmeters, a meteorological station, and a web camera were installed. Courtesy of SGC.

Seismicity 2009-2011. When Azufral's seismic stations came online in 2009, SGC began characterizing seismicity as volcano-tectonic (VT), long period (LPS), hybrid (HYB), tremor (TRE), tornillo (TOR), and unclassified (VOL). The VOL category, sometimes noted as "VC" in their reports, includes earthquakes from the region of Azufral that do not correspond with the other classes. SGC stated that these events will be analyzed in more detail after more baseline data is collected. This category was also applied to seismic analyses of Cumbal and Doña Juana, volcanos that were instrumented around the same time.

Unclassified seismicity (VOL) dominated the records through 2011, however, as SGC established baseline data, events falling in this category generally decreased over time. Total seismicity was also decreasing. During 2010-2011, tremor (TRE) and hybrid (HYB) events became sporadic to nonexistent.

During 5-6 February 2010, a seismic swarm was detected (figure 6). During January 2010-March 2013, this was the only swarm noted in the SGC Technical Bulletins. In early February 2010, two seismic stations were operating; Chaitán and La Roca. Unlike the Chaitán station, La Roca had broadband capabilities. "Broadband, high-dynamic-range seismometers are particularly important because existing instruments always saturate for large eruptions, and because energy at long periods (>>1 s) is simply not seen on standard short-period seismometers" (McNutt, 2000).

Figure (see Caption) Figure 6. This seismogram from Azufral shows the onset of a seismic swarm at 0935 on 5 February 2010 from the Chaitán short period station. Three components (vertical, Z (top); N-S horizontal (middle); and E-W horizontal (bottom)) recorded the motion during this 45 second interval. Courtesy of SGC.

During April 2010, the highest number of earthquakes was detected (493 events); most of those events were VOL and LPS (table 2). Seismicity also increased in September (228 events); however, they were primarily VOL earthquakes.

Table 2. Azufral's seismicity from December 2009 to December 2011. No tornillo events were detected during this time period. For most of 2009, seismic station Chaitán was not fully functional. Abbreviations explained in text; "--" indicates intervals when the category was not included in the Technical Bulletins. Courtesy of SGC.

Month VT LPS HYB TRE VOL Total
Dec 2009 68 15 1 23 -- 107
Jan 2010 2 3 0 3 0 8
Feb 2010 47 125 2 48 95 317
Mar 2010 20 25 0 18 80 143
Apr 2010 28 125 1 34 305 493
May 2010 23 45 0 14 97 179
Jun 2010 18 21 0 2 140 181
Jul 2010 36 29 0 15 119 199
Aug 2010 11 9 0 0 83 103
Sep 2010 12 6 0 -- 210 228
Oct 2010 23 17 0 -- 179 219
Nov 2010 21 11 0 -- 72 104
Dec 2010 26 3 0 -- 93 122
Jan 2011 32 21 0 -- 93 146
Feb 2011 30 2 0 -- 109 141
Mar 2011 14 23 0 -- 68 105
Apr 2011 29 20 0 -- 86 135
May 2011 11 1 0 -- 40 52
Jun 2011 18 9 1 -- 30 58
Jul 2011 20 3 0 -- 21 44
Aug 2011 4 0 0 -- 10 14
Sep 2011 4 1 0 -- 14 19
Oct 2011 8 2 1 -- 12 23
Nov 2011 12 7 3 -- 33 55
Dec 2011 13 -- -- -- 22 35

Overall 2011 seismicity averaged ~69 events per day (table 2). Earthquakes occurred more frequently earlier in the year; during January-May they averaged 116 events per month compared with 35 per month during June-December.

On 20 July 2011 at 0353, an earthquake was felt by local populations, particularly in the town of El Panamal (~5 km SW). The event was an ML 3 at 12.8 km depth (measured relative to the summit) and epicenter at 9.5 km SW. This was the only located earthquake that month; at that time, two seismic stations were operating (Chaitán and La Roca).

Seismicity in 2012-2013. In 2012, 5-45 VT earthquakes were recorded per month and 1-19 were located (table 3). At 19:41 on 4 May 2012, an earthquake was felt by local populations in Túquerres, San Roque, and Sapuyes (for town locations, see figure 3). It was an ML 3.3 with an epicenter ~12.2 km of Azufral at a depth of 8.64 km. The maximum intensity of shaking was III on the Modified Mercalli scale.

Table 3. Seismicity at Azufral from January 2012 through April 2013. Note that depths of events are measured relative to the established summit elevation (4,070 m elevation). Courtesy of SGC.

Month VT VT Located VT ML VT Depths VT Epicenter VOL Total
Jan 2012 19 -- -- -- -- 15 34
Feb 2012 45 -- -- -- -- 20 65
Mar 2012 10 -- -- -- -- 5 15
Apr 2012 20 -- -- -- -- 3 23
May 2012 14 2 3.3; 1.7 8.6 km; 7.4 km 12.2 km E; 6 km NW 1 15
Jun 2012 6 -- -- -- -- 1 7
Jul 2012 5 1 1.4 15 km 3.4 km NE 2 7
Aug 2012 7 -- -- -- -- 0 7
Sep 2012 9 2 2.1; 2.9 ~6 km; ~14 km 10 km SE; 14 km E 0 9
Oct 2012 42 19 0.5-2.1 < 16 km 1.5-15 km E 8 50
Nov 2012 22 2 0.6-0.7 < 2 km 4 km NE; 11 km NE 5 27
Dec 2012 24 1 0.8 16 km 10.4 km NE 50 74
Jan 2013 15 1 1.1 4.7 km 2.5 km N 9 24
Feb 2013 15 6 0.3-1.9 2.5-15 km < 1-< 11 km 6 21
Mar 2013 16 2 < 1.3 5.4 km; 7.3 km 7 km S; 3.5 km N 0 16
Apr 2013 39 26 < 2.1 < 11 km 4-10 km dispersed 15 54

During 2012, the largest number of located earthquakes occurred in October 2012. Located earthquakes peaked later in April 2013. Of the 39 VT detected, 26 of these earthquakes were located, primarily in a scattered cluster ~8 km NW of the summit (figure 7).

Figure (see Caption) Figure 7. Map of the 26 located VT earthquakes at Azufral during April 2013 (see key at upper left). Three seismic stations (gray squares) were online near the volcano: LAGZ (Laguna), ROCZ (La Roca) and CHAZ (Chaitán). The vertical cross-sections (N-S and E-W) have depths measured in 3 km intervals. Note that the original topographic contours are aligned with a hillshade image of the region. Courtesy of SGC.

Field observations in 2008 and mid-2009. During geophysical campaigns carried out in 2008 by SGC (then INGEOMINAS), fumarolic activity was observed from one of its domes, Domo Pequeño, in an area lacking vegetation. That location was also known for sulfur deposits, causing the surface to appear greenish-yellow; sulfur odors could were also detected. Bubbles in Laguna Verde were also apparent, rising from deep in Laguna Verde.

Aerial photos taken on 13 April 2009 showed clear views of the pale dome rock and bright green lake. A visit on 23 June 2009, revealed a zone of cloudy water in the green lake; low-level fumarolic activity was also observed (figure 8).

Figure (see Caption) Figure 8. Azufral's Laguna Verde as seen on 23 June 2009 during a visit made possible by the Colombian Air Force (FAC). Look direction is approximately SW. The typically green lake contained anomalous cloudy features. Dome rock and sulfur deposits are located within the white areas along the shoreline, particularly within an area known as La Playa (the narrow white peninsula on the lake's NE side, the right-hand side of the photo). The smallest pond (lower left-hand side) is referred to as Laguna Barrosa/Laguna Cristalina; out of view to the left is a smaller pond known as Laguna Negra. Courtesy of SGC.

Hydrothermal explosion in July 2009. SGC technicians had visited Azufral on 12 July 2009 to take water samples for analysis, but a group of scientists visiting on 18 July were surprised by a sudden change within the crater. They discovered a new deposit, 8-10 m long extending from the fumarolic region known as La Playa; the deposits were described as hot and they had extended into the lake. The SGC surmised that the activity must have occurred between the 13 and 18 July 2009. The group determined that this was an eruptive process likely of hydrothermal origin. The visiting scientists (from Fundación Ambiental Andes) reported observations including fresh-looking cracks and several slope failures which had allowed hot fluids to escape; those areas continued to steam during their visit (figure 9).

Figure (see Caption) Figure 9. The NE end of Azufral's Laguna Verde was visited twice in July 2009 by field investigators and led to the discovery of newly erupted deposits. Red arrows indicate the extent of the area known as La Playa in both images. (Top) On 12 July SGC scientists visited the lake shore and sampled the water at six locations (numbered locations in white circles). The rounded dome in the center has been referred to as "Domo Pequeño" and was the location of persistent fumarolic activity. Courtesy of SGC. (Bottom) On 18 July, visitors from the Fundación Ambiental Andes encountered persistent steam rising from a fresh deposit of dark, dense material that extended into Laguna Verde (yellow arrow) from La Playa. They noted fresh cracks and deposits within this area already known for altered rock and sulfur deposits. Photo by Oliver Oviedo.

In looking for monitoring signals during 13-18 July, SGC found that seismic and tilt data lacked clear elevated activity in July 2009; there were few earthquakes and mainly minor changes detected by the tilt instruments at Chaitán). Looking in more detail, the tilt station recorded some variations during 12-23 July, particularly from the X component (radial to the crater lake) (figure 10). A total decrease of 45 µrad was recorded while the Y component (tangential to the crater lake) was relatively stable with a slight increase of ~10 µrad and temperatures were between 6.5 and 9°C.

Figure (see Caption) Figure 10. Variations at the Chaitán tilt station during July 2009 correlated with the time period when Azufral's hydrothermal event occurred during 13-18 July (within the red rectangle). The strongest signal was recorded by the x-component (radial to the crater lake) although the decreasing trend continued until ~24 July; the y-component (tangential to the crater lake) responded less robustly but the main offset was confined to the 13-18 July window. The lower two plots show the instrument area's temperature and battery voltage. Courtesy of SGC.

August 2009 field investigations. On 3 August, a local observer noted unusual activity while walking along the higher peaks of Azufral; he stated that he saw "material being set on fire in the beach of Azufral and there were gases smelling like sulfur." A local landowner also explained that hot springs could be found ~6.5 km away at a site called Tutachag; these springs had persisted for several months. SGC alerted the local disaster prevention representative (Comité Regional de Prevención y Atención de Desastres de Nariño, CREPAD-N) after receiving the report of these observations; the CREPAD-N is responsible for communicating with local residents and visitors who frequent sites around Azufral.

During field investigations on 18 August, SGC staff learned from an additional local inhabitant (from the town of San Roque Alto) that, while walking the road to La Palma early in the morning of 3 August, he thought there was a fire on La Playa, possibly started by tourists. The fire was blue and red (although mostly blue) and gray smoke was rising, sometimes dense gray; he also noted sulfur odors.

After reviewing the seismicity during the first week of August 2009, SGC staff noted small events had been detected by the Chaitán station. At that time, seismic monitoring was not robust enough to provide earthquake locations, but the records determined that low pulses of spasmodic tremor had occurred in the range of 6-12 Hz and 12-18 Hz, lasting up to 4 minutes. LP events were also apparent in the record.

On 19 August, visiting scientists noted increased bubbling from more locations within Laguna Verde; primarily around the N shore of the lake. Few emissions were observed from the La Playa area; however, they noted intermittent sulfur odors while they conducted fieldwork.

SGC scientists traversed the NE shoreline with a FLIR (Forward Looking Infrared) thermal camera. The temperatures reached a maximum of 57.9°C along the N shore of La Playa (figure 11). Maximum temperatures corresponded with known locations of past hydrothermal activity.

Figure (see Caption) Figure 11. SGC scientists visited Azufral on 19 August 2009 to monitor changes in the hydrothermal system and to install additional equipment. (Top) Installation of a radon trap (Rn222) along the N shore of La Playa. The analysis conducted that day determined significant amounts of diffuse radon emissions from the central collapse zone on La Playa (641 pCi/L; see the middle photo of figure 12 for this location) and from the shoreline of the new peninsula (311 pCi/L). (Bottom) At the same location as the top photo, the FLIR camera detected the highest temperatures in the water closest to the shoreline (up to 57.9°C). Rectangles and circles highlight selected temperatures. Courtesy of SGC.

On 19 August, SGC scientists measured SO2 emissions along a traverse with Mobile DOAS. The team followed ~50 m of the shore and calculated an average flux of 0.5 tons per day, a value considered relatively low. They noted that the wind was from the N at 2.5 m/s.

Samples of the deposits attributed to the 13-18 July event on La Playa were distinctively cemented and possibly rich in silica and alteration minerals (figure 12). The SGC scientists collected samples for lab analysis including x-ray diffraction (XRD). Two samples were analyzed at SGC laboratory in Cali where XRD determined abundant (>40%) sulfur was present; amorphous silica (opal) was sparse (3-10%) and trace quantities (

Figure (see Caption) Figure 12. This series of photos from 19 August 2009 shows where the 13-18 July deposit had formed a dark gray peninsula jutting from the La Playa shore into Laguna Verde. (Top) A scientist inspects a slab broken from the peninsula. The thin gray deposit had a rugged surface but also a planar contact with the underlying (yellow) material. (Middle) A view of the flowpath that emerged at a series of depressions located upslope from the lake's edge. SGC described these new features as circular collapses 17-20 m wide and cut by many groundcracks. Temperatures measured with the FLIR were in range of 19-40°C for this region. The red arrows mark the extent of the new deposit, starting at the point where scientists were observing groundcracks. The look direction is approximately SSE. (Bottom) A view of the La Playa region centered on the disturbed area where dark gray material was deposited in the middle ground (during 13-18 July 2009) and extended into the lake forming a small peninsula. The red arrows are consistent with the previous photo where they mark the long extent of the new deposit. The look direction is approximately NW. Courtesy of SG.

On 30 August an experiment was conducted with small fragments of this material. In a lab setting, SGC scientists demonstrated that the material was flammable and produced heat and sulfur odors that stung the eyes and nose; red and blue flames were also observed immediately when the fragments encountered an open flame (tested with a lighted match). After a few seconds of exposure to an open flame, the samples melted and immediately crumbled into an inert, brittle solid. This demonstration may explain the explosive phenomena that local inhabitants observed on 3 August 2009.

Aerial observations during August-December 2009. During 11 and 19 September, the FAC facilitated observations of Azufral. Photographs and thermal imagery revealed few changes. The highest temperatures detected were in range of 25 to 30°C. The largest region of thermal anomalies was located on the opposite shore from La Playa (figure 13), a region where dacitic domes have been known to emit steam and have sulfur deposits.

Figure (see Caption) Figure 13. This FLIR image of Azufral's crater lake from 19 September 2009 shows elevated temperatures along the shoreline of Laguna Verde, Laguna Barrosa, and the dacitic domes on the E side of the lake. The distance scale is an approximation; the color scale on the right was adjusted for visual effects and records between 1 and 28°C. The highest temperatures in view were between 25 and 28°C. Courtesy of FAC and SGC in collaboration with Germany's Federal Institute for Geosciences and Natural Resources (BGR).

A return trip to Azufral during 7-11 December 2009 determined that some emissions were visibly rising from the dome located on the E side of Laguna Verde (figure 14). A maximum temperature measured from the dome was 85°C. SGC scientists also measured concentrations of CO2 higher than 10,000 ppm from fumarolic sites.

Figure (see Caption) Figure 14. An annotated photo taken on 9 December 2009 by visiting scientists in the NE sector of Azufral. Notable emissions were rising from the dome labeled "Domo Pequeño." Courtesy of SGC.

Emission sites were also revisited along La Playa on 9 December. Temperatures measured with a thermocouple were in the range of 65-84°C. Those temperatures were measured at locations that had elevated temperatures when last measured with a FLIR. CO2 emissions from these zones reached 3,200 ppm.

2010-2012 monitoring highlights. Routine monitoring from January 2010 to 2012 included sampling Laguna Verde at several locations as well as sampling the local hotsprings (figure 4). By October 2010, a baseline of geochemical data was developed by SGC and the four distal hot springs were evaluated and characterized as primarily mature-to-peripheral water (figure 15).

Figure (see Caption) Figure 15. Regular sampling of four local hot springs located within 5 km of Azufral was conducted in May (triangles), August (squares), and October 2010 (circles). Based on geochemical results, SGC scientists classified four of Azufral's hot springs. Within this ternary diagram, the datapoints were generally well within the "Periferal Water" (Aguas Periféricas, significant HCO3) class. Some datapoints from Quebrada Blanca and San Ramon were within the "Mature Water" class (Aguas Maduras, significant Cl); no datapoints were within the "Volcanic Water" class (Aguas Calentadas por Vapor, significant SO4) class. Courtesy of SGC.

Monitoring temperatures from Laguna Verde and selected sites also continued during 2010-2012. SGC scientists frequently conducted traverses along the shore with a thermocouple and established baseline temperature data (figure 16).

Figure (see Caption) Figure 16. On 18 March 2011, SGC measured temperatures from Azufral's shoreline and fumarolic sites. Temperatures were highest (86.8°C, 86.4°C, 86°C, and 85.2°C) near the crest of Domo Pequeño (circled in green). Temperatures 76°C and 75.2°C (circled in red) were measured from a fumarolic site and water near the shore of La Playa (respectively). Look direction is approximately SW. Courtesy of SGC.

During field campaigns, SCG staff noted variable emissions from fumarolic sites, clustering of bubbles within Laguna Verde, and also changes in the lake level. To aid visual monitoring, a web camera was installed within the crater of Azufral on 24 November 2012 (figure 17). The camera was positioned to include a wide view of Domo Pequeño (a regular source of steam emissions) and La Playa (the location of the hydrothermal event in July 2009).

Figure (see Caption) Figure 17. The new webcamera captured a small, diffuse steam plume rising from Azufral's Domo Pequeño on 29 November 2012. The look direction is approximately NE. Courtesy of SGC.

References. Hall, M.L and Mothes, P.A., 2008. Volcanic impediments in the progressive development of pre-Columbian civilizations in the Ecuadorian Andes, Journal of Volcanology and Geothermal Research, 176, 344-355.

McNutt, S.R., 2000, Volcanic seismicity. In: Sigurdsson, H., ed., Encyclopedia of volcanoes. New York, Academic Press, p. 1,015-1,033.

Siebert, L., Simkin, T., Kimberly, P., 2010, Volcanoes of the World, 3rd edn. University of California Press, Berkeley.

Yudilevich Levy, D., 2004, Mi viaje por el camino del Inca (1801-1802): Antología, 1a. ed., Editorial Universitaria, S.A., Santiago, Chile [in Spanish].

Geologic Background. Azufral stratovolcano in southern Colombia, also known as Azufral de Túquerres, is truncated by a 2.5 x 3 km caldera containing a Holocene rhyodacitic lava-dome complex. A crescent-shaped lake, Laguna Verde, occupies the NW side of the caldera. Nearly a dozen lava domes are present, the latest of which were formed about 3600 years ago and have active fumaroles. Azufral rocks are more silicic than those of nearby Colombian volcanoes; an apron of rhyodacitic pyroclastic-flow deposits rings the volcano. The last known eruption took place about 1000 years ago.

Information Contacts: Servicio Geológico Colombiano (SGC), Observatorio Vulcanológico y Sismológico de Pasto, Pasto, Colombia (URL: http://www.SGC.gov.co/Pasto.aspx); Patricia Ponce Villarreal, Servicio Geológico Colombiano (SGC), Observatorio Vulcanológico y Sismológico de Pasto, Pasto, Colombia (URL: http://www.SGC.gov.co/Pasto.aspx); Rüdiger Escobar-Wolf, Michigan Technological University, Department of Geological and Mining Engineering and Science, Houghton, MI, USA (URL: http://www.mtu.edu/geo/).


Morne aux Diables (Dominica) — March 2013 Citation iconCite this Report

Morne aux Diables

Dominica

15.612°N, 61.43°W; summit elev. 861 m

All times are local (unless otherwise noted)


Earthquake swarm began in mid-2009

Morne aux Diables is the northermost of the nine volcanic centers on the island of Dominica (Lindsay and others, 2005) (figure 1). The complex (figures 2 and 3) is comprised of five intact andesitic crystal rich lava domes that form a central depression. Within the depression, a 'Cold Soufrière' is evident with hydrothermally altered rocks and many small bubbling pools. No historical eruptions are known, although the volcano has a youthful appearance, and activity at flank domes likely continued into the late Pleistocene and Holocene (Lindsay and others, 2005). Robert Watts, at the University of the West Indies (UWI) Seismic Research Centre, reported that the volcano remains quiet, though with noteworthy seismicity in 2009 and 2010.

Figure (see Caption) Figure 1. Geologic map of Dominica, West Indies, showing the Morne aux Diables complex at the N end of island. From N to S, generally, these nine centers are Morne aux Diables, Morne Diablotins, Morne Trois Pitons, Wotten Waven caldera, Valley of Desolation, Grande Soufrière Hills, Morne Watt, Morne Anglais, and Morne Plat Pays. Original map by Roobol and Smith (2004a) (see Roobol and Smith, 2004b); copied from Lindsey and others (2005).
Figure (see Caption) Figure 2. Panoramic view from E. Cabrits dome looking E to the Morne aux Diables complex. Morne Aux Diables is on the left and Morne Destinee to the right. Courtesy of Richard Arculus and Robert Watts.
Figure (see Caption) Figure 3. Photograph of the Morne aux Diables complex, taken from near Portsmith Town. The topographic high Morne Aux Diables is on the left; Morne Heritiers, center; and Morne Destinee, right. Courtesy of Robert Watts.

Watts, and Lindsay and others (2005), reported that in 2002 SeaBeam bathymetry highlighted a double peaked lava dome (known informally as Twin Peaks) on the sea floor a few kilometers off the northern coastline of Dominica. The summit of the higher dome (at 15.671?N, 61.476?W) was 153 m below sea level. This northern coastline terminating the N end of the Morne aux Diables complex forms a linear cliff that may represent a fault.

Seismic swarm during 2009-2010. The most common area of seismicity, as noted by Watts and others (2012a and 2012b), has been in the SE sector of Dominica. In the north there were spurts in activity in 1841, 1893, 2000, and a particularly intense week-long burst of more than 500 earthquakes in 2003. Following six years of low-level activity, a nearly continuous series of earthquakes was recorded beneath the central area of Morne aux Diables beginning in June 2009. The seismic swarm continued through at least 2010 with variations in activity that are consistent with volcano-tectonic (VT) activity.

The VT series reached a peak in December 2009, with many events felt by villagers on the flanks of the volcano, but earthquake activity afterwards gradually been diminishing. Beginning in December 2010, VT earthquakes exhibited a gradual shallowing with time (a few approaching 1 km depth), indicating that they are related to a vertical re adjustment of the stresses below the volcano, most likely caused by magma movement (Watts and others, 2012b).

References. Lindsay, J.M., Smith, A.L., Roobol, M.J., and Stasiuk, M.V., 2005, Dominica in Lindsay, J.M., Robertson, R.E.A., Shepherd, J.B. and Ali, S. (eds), Volcanic Hazard Atlas of the Lesser Antilles, Seismic Research Centre, The University of the West Indies, Trinidad & Tobago, West Indies, p. 1-48.

Roobol, M.J., and Smith, A.L., 2004a. Volcanology of Saba and St. Eustatius, northern Lesser Antilles, Amsterdam: Royal Netherlands Academy of Arts and Letters, 320 p.

Roobol, M.J., and Smith, A.L., 2004b, Geologic map of Dominica, West Indies (URL: http://www.caribbeanvolcanoes.com/dominica/content/dominicamap.pdf).

Watts, R.B., Robertson, R.E., Abraham, W., Cole, P., de Roche, T., Edwards, S., Higgins, M., Johnson, M., Joseph, E.P., Latchman, J., Lynch, L., Nisha, N., Ramsingh, C., and Stewart, R.C., 2012a , Elevated seismic activity beneath the slumbering Morne aux Diables volcano, Northern Dominica and the monitoring role of the Seismic Research Center, poster presentation at the 2012 American Geophyhsical Union Fall Meeting, San Francisco, CA.

Watts, R., Robertson, R., Abraham, W., Cole, P., Corriette, D., de Roche, T., Edwards, S., Higgins, M., Issacs, N., Johnson, M., Joseph, E., Latchman, J., Lynch, L., Nisha, N., Phillip, B., Ramsingh, C., and Stewart, R., 2012b, Elevated seismic activity beneath the slumbering Morne aux Diables volcano, northern Dominica, poster on UWISRC web (URL: http://www.uwiseismic.com/Downloads/Dominica_activity_Poster_Watts.pdf).

Geologic Background. The lava dome complex of Morne aux Diables (Devils' Peak) forms the northern tip of the island of Dominica. Several nested craters and a 90-m-high, 335-m-wide lava dome are located within a larger 1.2-km-wide crater. The complex overall includes seven andesitic lava domes with a central depression where a cold soufriere is located. A chain of lava domes, two of which form a peninsula on the SW flank, form an E-W belt across the S flank. Bathymetry shows a double-peaked lava dome (known informally as Twin Peaks) off the northern coast, truncated by a 4-km-long fault-bounded cliff. No eruptions are known in historical time, although the volcano has a youthful appearance and activity at flank domes likely continued into the late-Pleistocene and Holocene. The youngest (NW) summit crater contains an active thermal area with bubbling springs. Severe earthquake swarms in 1841 and 1893 were associated with either Morne aux Diables or Morne Diablotins to the south. Shallow volcano-tectonic seismicity was detected as recently as February 2010.

Information Contacts: Robert B. Watts, The University of the West Indies (UWI) Seismic Research Centre, St. Augustine, Trinidad & Tobago, West Indies (URL: http://www.uwiseismic.com/).


Fujisan (Japan) — March 2013 Citation iconCite this Report

Fujisan

Japan

35.361°N, 138.728°E; summit elev. 3776 m

All times are local (unless otherwise noted)


2000-2001 epicenter migration; deep magma; 2011 M 6 aftershock at volcano

Fuji remains non-eruptive. Fujita and others (2013) investigate the likelihood that Fuji may erupt due to the 2011 E Shizuoka earthquake (M 6) centered on the volcano. Our previous reports of February 2001 (BGVN 26:02) and September 2001 (BGVN 26:09) described the 2000-2001 deep low-frequency (DLF) earthquake swarm under Fuji. In the first section below, we summarize work by Ukawa (2005) and Nakashimi and others (2004) who provide further details and analysis of DLF swarm activity, and discuss midcrustal, low-frequency earthquakes (MLFs) recorded during 1998-2003. Discussion in those papers noted likely molten material at depth below the volcano.

The next section reports the stress-field and pressure changes to Fuji's magmatic system due to the 11 March 2011 Tohoko megathrust, an MW 9 earthquake, which created the tsunami that devastated parts of costal NE Honshu including the Fukushima nuclear power plant. In addition, an MW 5.9 aftershock was centered below Fuji. Fujita and others (2013) assessed the possibility that the stress-field and pressure changes could enable magma to escape to the surface. Although they concluded that preexisting faults could rupture the chamber walls, the changes were seemingly insufficient to do so, suggesting no eruption was imminent.

Background. During the early 1980s, the National Research Institute for Earth Science and Disaster Prevention (NIED) installed the Kanto-Tokai seismic network in central Japan (figure 2). Later refinements included adding stations SSN and SHJ (not shown), and in the 1990s, stations, FJN, FJY, FJS and FJH, each with three component seismometers and two component tiltmeters at the bottom of 200-m-deep boreholes. In April 1995, Mt Fuji seismic data recording began using the constellation of stations.

Figure (see Caption) Figure 2. (Main map) Mt. Fuji seismic stations shown on a contour map with elevation contours at 500 m intervals. Symbols as follows: crosses, permanent stations maintained by ERI; diamond, Mt. Fuji summit Weather Station maintained since 1987 by JMA; and open circles, stations maintained by NIED. Stations FJH, FJN, FJS and FJY have borehole tiltmeters and 3-component short-period seismometers installed at 200 m depth. (inset map) Tectonic map, with solid lines indicating Eurasian (EUR), N American (NAM) and Philippine Sea (PHS) plate boundaries. Taken from Nakamichi and others, 2004.

The Fuji DLF earthquake epicenters were located using 1987 to 2001 data from the early 1980 Kanto-Tokai seismic network and later data taken at the four Fuji stations installed in 1990 (figure 3). Nakamichi and others (2005) reexamined epicenter locations of Ukawa (2004). JMA updated safety and evacuation plans.

Figure (see Caption) Figure 3. Cumulative number of DLF events (dotted curve) at Fuji during 1980-2004 and their cumulative wave energy (solid line). Note new instruments and processing accounted for some of the increase seen in 2000-2001 (right of the vertical line), however there was a clear marked increase in events there. After Ukawa (2005).

DLFs during 2000-2001. Ukawa (2005) examined the 2000-2001 DLF swarm beneath Fuji. The typical activity here since the early 1980s was 10-20 earthquakes a year at midcrustal depth described as burst-like activity lasting from several minutes to 30 minutes.

The cumulative occurrence of DLF earthquakes their associated cumulative wave energy are plotted in figure FUJ2. The cumulative number rate, or the slope of the curve, is almost constant between 1980-1995, followed by several small slope changes before the later months of 2000 due to the improvements in the seismic network and the new data processing system. The sharp increase in 2000-2001 is far larger than the increase due to the enlarged seismic network. In total, 286 events were identified during the eight months from October 2000 to May 2001. The wave energy increased to approximately twice the average recorded during the prior years.

Regarding Fuji, Ukawa (2005) notes, "On the basis of the DLF earthquake observations by the NIED seismic network, we investigated the temporal change of their occurrence rate from 1980 to 2003 and the hypocenter locations from 1987 to May 2001. The occurrence rate and the seismic wave energy release rate show an abrupt increase from October 2000 to May 2001, suggesting a change in the environment. ...Relocation of hypocenters of the DLF earthquakes indicates that hypocenters of the DLF earthquakes cluster mainly in an elongated region measuring 5 km along the long axis in a NW-SE direction, the center of which is located about 3 km NE from the summit. In addition to the main cluster, hypocenters extend to the southwest from the summit. During the swarm activity in 2000 to 2001, activity in the primary hypocenter region on the northeastern side of Mount Fuji increased greatly. The focal depths of well located DLF events range from 10 to 20 km. The sharp increase of DLF earthquake activity at Mount Fuji began soon after magma discharge and intrusion events in the Miyake-jima and Kozu-shima region in July and August 2000. These events may have modified the state of the deep magmatic system beneath Mount Fuji, thus triggering the DLF earthquake swarm."

Figure 4 shows the three volcanoes mentioned above: Fuji, Miyake-jima, and Kozu-shima. Several more volcanoes also of Holocene age did not erupt.

Figure (see Caption) Figure 4. Ukawa (2005) noted the 2000-2001 DLF swarm beneath Fuji occurred soon after the July-August 2000 magma discharge and intrusion events located at Kozu-shima and Miyake-jima. Those two volcanoes are located in the Pacific ~135 km from Fuji. Fuji did not erupt. The yellow triangles show locations of other Holocene volcanoes listed in the GVP database. Like Fuji, these also did not erupt. Base map courtesy of the Microsoft Corporation with labels by BGVN editors.

MLF earthquakes during 1998-2003. Nakamichi and others (2004) revisited Fuji MLF data, that like the DLFs of 2000-2001, they also clustered near the summit. "We have determined the hypocenter locations of MLFs using the hypoDD program [a double-difference algorithm; Waldhauser and Ellsworth, 2000] and repicked arrival times from the seismic networks of ERI, JMA and NIED in and around Mt. Fuji between 1998 and 2003 including the active periods from September 2000 to May 2001, [figure 5]".

Figure (see Caption) Figure 5. Comparison between the Fuji hypocenters of the MLFs by Nakamichi and others (2004) (red circles) and the routine processing at NIED (black circles). (a) Map view of hypocenters, (b) E-W cross-section, and (c) N-S cross-section. Taken from Nakamichi and others (2004).

The authors summarized their results as follows: "(1) Hypocenters of MLFs define an ellipsoidal volume, 5 km in diameter ranging from 11 to 16 km in focal depth. (2) This volume is centered at 3 km NE of the summit and its long axis is trending NW. This orientation coincides with the major axis of tectonic compression around Mt. Fuji. (3) The center of the MLF epicenters migrated upward and 2-3 km from SE to NW in 1998-2001."

Nakamichi and others, (2004) continue, "We interpret that the hypocentral migration of MLFs reflects magma movement associated with a NW-SE oriented dike beneath Mt. Fuji, figure 6. The relative error ranges of the hypocenters relocated here are from 100 to 500 m horizontally and from 200 to 700 m vertically. No elongated structure in the direction of the observed NW- SE strike is observed in the simulations, indicating that the observed strike is not an artifact of the relocation procedure [seen in Figure 6b along the plane A-A']. The extent of this depth range is also supported by the spread in S-P readings for individual earthquakes. S-P arrival time differences for well-recorded MLFs at station KMR range from 1.9 to 2.4 s, verifying that MLFs beneath Mt. Fuji span a depth range of at least 4 km, and are not confined to a very small volume."

Figure (see Caption) Figure 6. Hypocentral distributions of the Fuji MLFs, as determined by the hypoDD program. (a) Map view of relocated hypocenters. Hypocenters at the intersection of A-A' with B-B' shown enlarged as a circle above and to the right. (b) Cross-section A-A'. (c) Cross-section B-B'. Cross-sections A-A' and B-B' include earthquake hypocenters projected from up to 10 km on either side of the cross section line. Taken from Nakamichi and others, 2004.

The MLFs also shifted with time. The spatial and temporal variations of MLF hypocenters plotted on figure 7. Nakamichi and others (2004) observed focal depths of MLFs in 1998- 1999 that were 12-16 km deep and "seemed to move deeper gradually."

Figure (see Caption) Figure 7. Spatial and temporal variations of the Fuji hypocenters of 1998-2003 MLFs. Top plot records distances from hypocenters on the NW-SE horizontal plane projected to zero on the line A-A' of Figure 6. Bottom plot records focal depths vs. time projected to the vertical plane through A-A'. Some or all these variations were interpreted as a manifestation of magma recharge and migration. Nakamichi and others, 2004.

Two key points from Nakamichi and others (2004) were (1) the MLF processing indicated that the hypocenters migrated 2-3 km upward during 1998-2001, and (2) they interpreted the MLF hypocenter migration as reflecting magma movement associated with a NW-trending dike beneath Fuji.

2011 Fuji stress change after the MW 9 Tohoko earthquake. Fujita and others (2013) studied the Tohoko earthquake and aftershocks in order to see whether the changes in the stress field and pressure changes would cause the known active magma system to erupt. The Tohoku earthquake, MW~9, struck on 11 Mar 2011. Extension occurred over a wide region of the Japanese mainland (Fujita and others, 2013). Aftershocks included those at N Nagano (MW 6.3) on 12 March, at E Shizoka (MW 5.9) on 15 March, and at N Ibaraki (MW 5.8) on 19 March, figure 8. The E Shizuoka aftershock struck beneath Fuji's S flank above its magma system. Fujita and others (2013) selected parameters of the two highest magnitude Tohoko earthquakes from Ozawa et al. (2011) plus the E. Shizuoka earthquake to investigate the change below Fuji. Using seismic data and later modeling they found the change in static pressure below Fuji insufficient to cause an eruption.

Figure (see Caption) Figure 8. A map showing Fuji on Honshu Island with a 500 x 200 km box enclosing the epicenters in the main sequence of the Tohoko megathrust earthquake. Epicenters of key aftershocks are shown as blue stars and one green star. The later struck 15 March, 4 days after the main event at 7-12 km depth below Fuji. After Fujita and others, 2013.

The fault parameters of the Tohoko earthquakes (Table 3) were estimated by Ozawa and others (2011). With regard to the E Shizouka earthquake, Fujita and others (2013) determined the East Shizuoka source fault using the method of Ueda and others (2005) and "determined the best-fit fault model to be almost strike-slip with some reverse components, located a few kilometers south of the summit trending from depths of 7-12 km." Note that on table 3 the "Depth (top)" value of 7 km locates the top of the fault.

Table 3. Fault parameters computed for two of the strongest Tohoku earthquakes and the E Shizuoka aftershock. Tohoku parameters are from Ozawa and others (2011); those for the E Shizuoka were obtained by applying the method of Ueda and others (2005). Taken from Fujita and others (2013).

Parameters Tohoku 1 Tohoku 2 East Shizuoka
Latitude 38.80°N 37.33°N 35.3161°N
Longitude 144.00°E 142.80°E 138.7130°E
Depth (top), km 5.1 17 7
Length, km 186 194 6
Width, km 129 88 8
Strike, degrees 203 203 24
Dip, degrees 16 15 80
Rake, degrees 101 83 20
Dislocation, m 24.7 6.1 0.86
Magnitude 8.8 8.3 6.0

Figure 9 shows the distribution of hypocenters of both tectonic (blue) and DLP (red) earthquakes during 1996-2011. Tectonic earthquakes occurring during 1996-2011 (blue circles) cluster to the S at ~5-15 km depth and NE from ~17 km deep to below the 25 km scale limit with little temporal change in number until a detectable rate rise in early 2011. Hypocenters of DLFs occurring during 1996-2011 (red circles) cluster nearest the crater N at ~10-15 km depth with little temporal change in number until a detectable rate rise in early 2011. The largest event shown, the E Shizuoka tectonic earthquake (15 March 2011) occurred on the S flank of Mount Fuji at a depth of 12 km (table 3 lists the top of the fault at 7 km). Remote aftershocks were centered a few kilometers N of the summit. Taken from Fujita and others (2013).

Figure (see Caption) Figure 9. Mt Fuji summit, yellow triangle, shown with tectonic and DLF earthquakes during 1996 to 2011. Red circles correspond to hypocenters of Deep Long Period (DLP) events, and blue circles correspond to tectonic earthquakes. Note the DLP increase in 2000 and 2001, shortly after the Miyake-jima volcano eruption and huge ground deformation on Izu peninsula ~100 km SE of Mount Fuji. Courtesy of Fujita and others (2013).

The relocated hypocenters computed by Fujita and others (2013) compared to the hypocenters of the same events routinely obtained by NIED (Ukawa, 2001), showed improvement in location accuracy (figure 10). The hypocenters by NIED are distributed in a larger volume and not along a particular plane while in this study they are much more concentrated and trending NNE. As seen on figure FUJ 9, Fujita and others (2013) noted "The dislocation was 86 cm toward the NNE with a strike of 240, dip of 800, and rake of 200." Aftershocks of the E Shizouka earthquake also occurred along this fault."

Figure (see Caption) Figure 10. Topographic station location map of Fuji showing an estimated dislocation of 86 cm along a 6x6 km fault plane based on GPS data from NIED and Graphical Survey Institute (GEONET) data. Observed (red) and calculated (blue) displacement vectors are shown. Courtesy of Fujita and others (2013).

The static stress change caused by the E Shizouka earthquake was on the order of 0.1-1 MPa, or 0.2%, at the boundary of the magma reservoir, which was theoretically sufficient to trigger an eruption (Walter and others 1997; Walter and others 2009).

The deformation of Fuji's magma system was based on finite-element modeling of the Japanese mainland and Fuji seismic tomography. At Fuji, the stress changes to the magma reservoir were on the order of 0.001-0.01 MPa for the Tohoku earthquake and 0.1-1 MPa for the East Shizuoka earthquake (Fujita and others, 2013). Were these static stress changes sufficient to promote new fractures at the magma reservoir wall and magma injection? Fujita and others, 2013 maintain, "This is less than the magnitude required to break new faults but could trigger some perturbation in unstable faults or in the hydrothermal and magmatic systems. However, the magma beneath Mount Fuji does not seem to have enough potential to erupt at this moment".

References. Fujita, E., Kozono, T., Ueda, H., Kohno, Y., Yoshioka, S., Toda, N., Kikuchi, A., and Ida, Y. 2013, Stress field change around the Mount Fuji volcano magma system caused by the Tohoku megathrust earthquake, Japan. Bulletin of Volcanology, 75(1), 1-14.

Koyama M., 2002, Mechanical coupling between volcanic unrests and large earthquakes: a review of examples and mechanics. J Geogr 111:222-232, in Japanese with English abstract.

Koyama M., 2007, Database of eruptions and other activities of Fuji Volcano, Japan, based on historical records since AD 781. Yamanashi Institute of Environmental Sciences, Fuji Volcano, pp 119- 136, in Japanese with English abstract.

Nakamichi H., Ukawa, M., Sakai S., 2004, Precise hypocenter locations of midcrustal low-frequency earthquakes beneath Mt. Fuji, Japan, Earth, Planets and Space, 56, e37-e4.

Nakamichi, H., Hamaguchi , H. Tanaka S., Ueki S., Nishimura T., Hasegawa A., 2003, Source mechanisms of deep and intermediate-depth low frequency earthquakes beneath Iwate volcano, northeastern Japan, Geophysical Journal International, 154, 811-828.

Nishimura T., Ozawa S., Murakami M., Sagiya T., Tada T., Kaidzu M., Ukawa M., 2001, Crustal deformation caused by magma migration in the northern Izu Islands, Japan. Geophysical Research Letters 28:3745-3748.

Ozawa S., Nishimura T., Suito H., Kobayashi T., Tobita M., Imakiire T., 2011, Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake. Nature 475:373-377.

Ueda H., Fujita E., Ukawa M., Yamamoto E., Irawan M., Kimata F., 2005, Magma intrusion and discharge process at the initial stage of the 2000 activity of Miyakejima, Central Japan, inferred from tilt and GPS data. Geophysical Journal International 161:891-906.

Ukawa, M., 2005, Deep low-frequency earthquake swarm in the mid crust beneath Mount Fuji (Japan) in 2000 and 2001, Bulletin of Volcanology, 68 (2005), pp. 47-56.

Waldhauser, F. and W. L. Ellsworth, 2000, A double-difference earthquake location algorithm: Method and application to the northern Hayward fault, California, Bull. Seismol. Soc. Am., 90, 1353-1368.

Walter T., 2007, How a tectonic earthquake may wake up volcanoes: stress transfer during the 1996 earthquake-eruption sequence at the Karymsky Volcanic Group, Kamchatka. Earth and Planetary Science Letters 264:347-359.

Walter T., Amelung F., 2007, Volcanic eruptions following M≥9 megathrust earthquakes: implications for the Sumatra-Andaman volcanoes. Geology 35:539-542.

Walter, T., Wang, R., Zimmer, M., Grosser, H., Luhr, B., and Ratdomopurubo, A., 2007, Volcanic activity influenced by tectonic earthquake: static and dynamic stress triggering at Mt. Merapi. Geophysical Research Letters 34:L05304.

Walter, T., Wang, R., Acocella, V., Neri, M., Grosser, H., and Zschau, J., 2009, Simultaneous magma and gas eruptions at three volcanoes in southern Italy: an earthquake trigger? Geology 37:251-254.

Geologic Background. The conical form of Fujisan, Japan's highest and most noted volcano, belies its complex origin. The modern postglacial stratovolcano is constructed above a group of overlapping volcanoes, remnants of which form irregularities on Fuji's profile. Growth of the Younger Fuji volcano began with a period of voluminous lava flows from 11,000 to 8000 years before present (BP), accounting for four-fifths of the volume of the Younger Fuji volcano. Minor explosive eruptions dominated activity from 8000 to 4500 BP, with another period of major lava flows occurring from 4500 to 3000 BP. Subsequently, intermittent major explosive eruptions occurred, with subordinate lava flows and small pyroclastic flows. Summit eruptions dominated from 3000 to 2000 BP, after which flank vents were active. The extensive basaltic lava flows from the summit and some of the more than 100 flank cones and vents blocked drainages against the Tertiary Misaka Mountains on the north side of the volcano, forming the Fuji Five Lakes, popular resort destinations. The last confirmed eruption of this dominantly basaltic volcano in 1707 was Fuji's largest during historical time. It deposited ash on Edo (Tokyo) and formed a large new crater on the east flank.

Information Contacts: National Research Institute for Earth Science and Disaster Prevention (NIED), 3-1 Tennodai, Tsukuba-shi, Ibaraki-ken, 305, Japan (URL: http://www.bosai.go.jp); Japan Meteorological Agency (JMA), Volcanological Division, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html).


Galeras (Colombia) — March 2013 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Ash emissions and elevated seismicity during May 2012-March 2013

The elevated activity previously covered in May 2012 (BGVN 37:04) continued through March 2013. This report describes the ash events and monitoring efforts during that time as well as trends in seismic, gas, and geodetic data. The Servicio Geológico Colombiano (SGC) maintained Alert Level III (Yellow; "changes in the behavior of volcanic activity") during this 11-month reporting period.

From the observatory based in Pasto (~10 km E of Galeras's summit), the SGC (formerly known as Instituto Colombiano de Geología y Minería "INGEOMINAS") maintained an extensive monitoring network (table 11). During May 2012-March 2013, they highlighted the following events in their monthly activity reports (available online): ash plumes, ashfall, elevated seismicity (including swarms), SO2 emissions, and sulfur odors detected by observers near the volcano.

Table 11. The SGC network for monitoring Galeras included more than 50 instruments during May 2012-March 2013; the newest station, added in March 2013, is an additional magnetic and self-potential monitoring station. Courtesy of SGC.

Instrument Description Quantity Instrument Location(s)
Radon gas sensors (diffuse soil emissions) 20 Two transects covering the E (Galeras Line) and N (Barranco Line) sectors
Seismic stations (seven short period and five broadband; telemetered) 12 See Figure 116 in BGVN 37:04
Electronic tilt stations (telemetered) 8 See Figure 116 in BGVN 37:04 and figure 9
DOAS stations; three ScanDOAS (telemetered) and one portable MiniDOAS (NOVAC Program) 4 Santa Bá, Alto Jimenez, Alto Tinajillas (figure 116 in BGVN 37:04 and figure 6)
GPS stations (telemetered) 4 Cráter, Cóndor, Barranco, (Mapachio stopped in Aug. 2012), San Cavetano (figure 116 in BGVN 37:04 and figure 9)
Infrasound stations 3 Seismic stations Cráter-2, Cóndor, and Calabozo (figure 116 in BGVN 37:04)
Video cameras 3 Two in towns (Pasto and Consacá in figure 6) and one at seismic station Barranco Alto (figure 116 in BGVN 37:04)
Flood monitoring stations 2 Watershed of Mijitayo (figure 6) (including geophone and flood gauges; telemetered)
Magnetic and self-potential systems 2 Stations Frailejónes and Barranco (added in March 2013; figure 116 in BGVN 37:04)
Wind station (speed and direction; telemetered) 1 Seismic station Cráter-2 (figure 116 in BGVN 37:04)
Figure (see Caption) Figure 122. This geologic map of Galeras includes regional geology and a detailed stratigraphic column. Heavy blue lettering was added to emphasize those names in this report. The geology of Galeras was mapped by Armando Murcia L. and Hector Cepeda V. in 1984 and published by the Instituto Colombiano de Geología y Minería, now known as the Servicio Geológico Colombiano (SGC), in 1991.

May 2012 seismicity and ash emissions. Compared with previous activity (see table 13 in BGVN 37:04), seismicity at Galeras increased in May in terms of energy released as well as the number of events and tremor duration (table 12). During 9-10 May, a swarm of 49 volcano-tectonic (VT) earthquakes was detected.

Table 12. Seismicity at Galeras during May 2012-March 2013. Earthquake counts for four types of events: volcano-tectonic (VT), long-period (LP), tremor (TRE), and hybrid (HYB); events labeled "Unclassified" were described by SGC as earthquakes that did not correspond to the current categories. Tornillos did not occur during this reporting period. Courtesy of SGC.

Month VT LP TRE HYB Tremor Duration (min) Range ML (VT) Depths (km) Hypocenters Located Unclassified
May 2012 29 67 347 5 1944 -0.2-2 0-14.5 95 2343
Jun 2012 21 285 353 3 1746 -0.2-1.8 1.4-13 70 1621
Jul 2012 17 276 233 1 986 0-2.5 0-15 43 1808
Aug 2012 8 163 181 2 525 -0.4-2.5 0.1-18 36 1413
Sep 2012 10 225 188 8 575 -0.1-2.2 1.8-10.8 30 1574
Oct 2012 17 149 310 6 1113 -0.2-2.3 0.2-13.7 58 2323
Nov 2012 6 64 246 9 931 -0.5-1.6 0-13.2 33 2335
Dec 2012 22 54 202 3 2828 -0.2-1.7 0.2-16 48 1771
Jan 2013 18 101 292 12 4223 -0.5-1.7 0-16 53 1827
Feb 2013 13 91 282 4 6131 -0.1-1.5 0.8-15 35 1775
Mar 2013 16 84 231 15 705 -0.1-3.1 0-11 44 2300

Figure 123 plots 95 VT and hybrid earthquakes and reveals two primary clusters of epicenters, close to the crater and a deeper one ~14 km SW of the active cone. The most distant earthquakes were dispersed in the region and had depths between 4-14.5 km (measured relative to the summit).

Figure (see Caption) Figure 123. Map and cross sections plotting 95 epicenters and hypocenters of volcano-tectonic and hybrid earthquakes that occurred during 1-31 May 2012 at Galeras (scale bar, upper left). In the N-S section (right) and the E-W section (bottom), each line represents 1.2 km of depth with respect to the summit (elevation, ~4,200 m). Magnitudes of seismic events are indicated by circle size. Colors indicate depths, which ranged from

On 13 May 2012, SGC noted a change in volcanic activity when tremor occurred associated with gas and ash emissions. Ash rose in small pulses and was deposited at high elevations on the edifice and toward the NW in prevailing winds. During clear conditions on 17 May, an ash plume was observed rising from the crater to ~200 m above the summit.

Clouds obscured visibility on 28 May, but on other days during 22-29 May SGC observers saw ash plumes rising 800 m above the crater. According to the Cruz Roja Departamento Nariño, ashfall was reported in Santa Bárbara (~8 km NNW) during the week of 22 May.

June-July 2012 seismicity and plume activity. Elevated seismicity continued through June, primarily comprised of tremor and long-period (LP) events. In July, seismicity decreased (both in the number of events, table 12, and the energy released) although a swarm of LP events occurred on 15 July.

Gas emissions were frequently observed during the first week of June in images captured by the network of video cameras. Ash emissions rose from the central crater on 2 June, and on 5 June plumes rose 1 km and drifted W. The Washington Volcanic Ash Advisory Center (VAAC) released advisories during 5-6 June, but no volcanic ash or hotspots were detected by satellite instruments.

During 5, 6, and 12-19 June, cameras recorded gas-and-ash emissions; an ash plume rose 1.4 and 2.4 km above the crater on 14 and 17 June, respectively. Ashfall was reported in the towns of Sandoná, Samaniego, Mapachico (this location does not appear on all maps, see figure 116 in BGVN 37:04), and Genoy. During 19-22 and 24 June cameras recorded gas-and-ash emissions that drifted NW.

The SGC noted gas-and-ash emissions via the network of video cameras during 4-5 July. On 18 July, ashfall was also reported to the N in the Quebrada Maragato area (figure 122).

August-September 2012 seismicity and plume activity.Seismicity continued to decrease in August. In September, there were two seismic swarms but the seismic energy released for the month had decreased compared with August. The swarms (on 25 and 28 September) were shallow VT events, M

Ash plumes were frequently observed in August and SGC correlated many episodes of tremor with pulses of ash (figure 124). On 3 August a steam plume rose 1.1 km above the crater. On 4 August ash emissions were observed in the morning, and at 1519 a seven-minute-long episode of tremor was accompanied by a gas-and-ash plume that rose 1.4 km above the crater and drifted N. Ashfall was reported in Genoy. During 7-9 and 11 August gas-and-ash plumes rose 0.9-1.3 km above the crater and drifted W and S. White plumes were observed during 16 (and ash that day) and 18-21 August. Cameras around the volcano recorded emissions during 21-26 August; the emissions contained ash on 26 August.

Figure (see Caption) Figure 124. The SGC correlated tremor from Galeras with an explosion of ash on 7 August 2012. (Top) Tremor signals were detected between 1415 and 1420 at six stations (Anganoy, Cufiño, Urcunina, Cobanegra-3, Arlés, and Cóndor). (Bottom) The video camera located at Barranco station captured an impulsive ash plume emitted between 1417 and 1421 that day; see locations in figure 116 in BGVN 37:04. The look direction is SE. Courtesy of SGC.

SGC reported that, during 18-22 and 24-25 September, cameras around Galeras recorded emissions that were mostly water vapor. On 18 and 24 September the emissions contained some ash. Plumes rose to 2 km above the summit and ashfall primarily affected the summit region. A seismic swarm occurred on 28 September.

October-November 2012 seismicity and plume activity. SGC reported that seismicity increased in October and gas-and-ash emissions (up to 1.8 km above the summit) were visible during clear viewing conditions throughout the month. The duration of tremor had doubled compared to the two previous months (table 11).

Episodes of tremor associated with gas-and-ash emissions were frequently detected in October. In particular, on 19 October tremor and a significant ash plume occurred (figure 125); ash covered the NE sector of the edifice where observatory staff conducted fieldwork.

Figure (see Caption) Figure 125. Images of Galeras captured from a camera located at the Antonio Nariño airport (~20 km NE of the summit) on 19 October 2012 beginning at 1036. These images show an ash plume rising from the summit and quickly dissipating. Tremor was concurrently detected by the local network. Courtesy of SGC.

In October, epicenters of VT and HYB earthquakes were widely distributed throughout the area, up to 15 km from the edifice. Low energy and very shallow seismic swarms were detected on 25 and 26 October; there were 130 events in total. In November, seismic energy decreased but seismic swarms were detected during 8, 13-15, 19, and 28 November. These events were low-energy VT earthquakes (M less than 0.9), very shallow, and clustered beneath the central crater. Gas-and-ash emissions were recorded by the network of video cameras during 1, 7, 14, 22-23, and 29-30 November. Plumes rose to less than 1 km above the summit and ash was deposited at the highest elevations, primarily within the N and W sectors.

December 2012-March 2013 seismicity and plume activity. Tremor duration per month increased significantly during December 2012-February 2013 (2,828 to 6,131 minutes) (table 12). Seismic swarms frequently occurred in the months of December (more than 100 earthquakes), January, and March.

Six gas-and-ash emissions were observed between 17-29 December with plume heights less than 1.3 km. Ashfall occurred on the N and W sectors of the edifice.

In January 2013, nine gas-and-ash plumes were detected with the video monitoring system. Those plumes rose less than 1 km above the summit and deposited ash at the highest elevations within the N and W sectors of the edifice. On 22 January, Civil Defense reported ashfall in the area of Sandoná; the timing of that ashfall event suggested a correlation with an episode of tremor detected at 1309.

Gas-and-ash plumes occurred throughout February 2013. During more than 10 of these events, plumes rose to less than 1.5 km above the summit. A significant ash event occurred on the morning of 24 February; Civil Defense reported ashfall in the region of San Isidro (~14 km NW, figure 122).

The SGC reported gas-and-ash plumes throughout March; on five separate days (6, 7, 11, 22 and 25), the tallest plumes reached 1 km above the summit.

An M 3.1 earthquake was felt by residents on 14 March 2013 with a maximum intensity of II on the Modified Mercalli scale. The hypocenter was 5.6 km WNW from the crater at a depth of 7.78 km. Shaking was felt in the towns of Sandoná, Florida, and Consacá (figure 122).

SO2 flux during February 2012-March 2013. The SGC monitored sulfur dioxide gas emissions with a MobileDOAS and three ScanDOAS instruments. The MobileDOAS was acquired through the Network for Observation of Volcanic and Atmospheric Change (NOVAC), an international effort developed by the European Union to monitor SO2 emissions. SGC conducted 2-5 traverses each month with this instrument primarily along roads that circumnavigate the volcano.

The three ScanDOAS installations were telemetered systems located within 12 km WNW of the edifice (figure 116 in BGVN 37:04). These instruments each took measurements on a near-daily basis allowing for regular coverage when all three stations were operating.

The SGC monthly Technical Bulletins reduced these four sources of gas data in units of tons per day (figure 126) after incorporating wind speed and direction based on a local anemometer located at the Cráter station ~1 km E of the summit.

Figure (see Caption) Figure 126. Galeras SO2 flux measured during February 2012-March 2013 from four instruments (three ScanDOAS and one MobileDOAS). For the time interval August 2012-March 2013, three plots were merged (boundaries are marked in red, orange, blue); the vertical scale is consistent for all three time intervals but the horizontal scale has been skewed. On both plots, the gray regions signify the reporting period in which the plots appeared in SGC Technical Bulletins. Courtesy of SGC.

Very high SO2 was detected in March, May, and July of 2012 (up to 3,467 tons per day); relatively high levels were detected during August-October. The SGC established the following criteria for describing SO2 flux at Galeras: Low (under 500 t/d); Moderate (500-1,000 t/d); High (1,000-3,000 t/d); Very High (over 3,000 t/d). In these terms, SO2 detected during November 2012-March 2013 stood at moderate to low levels. The highest values during that time period were recorded in mid to late January (up to 1,194 t/d).

People noticed strong sulfur odors on 18 July; 1 and 6 August; 12 and 19 October; 30 November; 5 December; 25 and 28 February; and 1, 5, and 11 March. Reports were primarily from SGC staff working near the crater, but on 12 October, the staff at Galeras National Park Wildlife Sanctuary noted sulfur odors on the E side of the volcano. On 19 October the odor was present in the towns of Consacá (~13 km W) and Sandoná (~15 km NW).

May 2012-March 2013 deformation monitoring. In May, deformation recorded by most of the tilt stations was dominated by inflation in the W sector of the volcano; a zone that coincided with a cluster of earthquake epicenters during 9-10 May. Inflation continued to register in that region through March 2013. The four permanent GPS stations (Cráter, Cóndor, Barranco, and Mapachico) were operating during this time period (figure 116, BGVN 37:04). Unfortunately, the Mapachico site was vandalized on 27 August 2012 and thereafter its signal was lost.

On 31 October 2012, a new GPS station was brought online, San Cayetano, located ~4 km E (figure 127). The testing period for the new instrument continued through November. SGC did not highlight any deformation trends during December 2012-March 2013.

Figure (see Caption) Figure 127. Map of the Galeras geodetic monitoring network from the March 2013 online Technical Bulletin. GPS and tiltmeter station locations are marked with symbols including the newest station, San Cayetano (within 4 km E of the active cone). Courtesy of SGC.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: Servicio Geológico Colombiano (SGC), Observatorio Vulcanológico y Sismológico de Pasto, Pasto, Colombia (URL: http://www.SGC.gov.co/Pasto.aspx); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).


Kanaga (United States) — March 2013 Citation iconCite this Report

Kanaga

United States

51.923°N, 177.168°W; summit elev. 1307 m

All times are local (unless otherwise noted)


18 February 2012 eruption; new fissure

In our last report on Kanaga, issued in 1995 (BGVN 20:08), we discussed an eruption during January through mid-October 1994. In addition to a brief explosion in February 2012, more information from the Alaska Volcano Observatory (AVO) has come to our attention, some discussing events more than a decade ago. This information suggested either renewed low level eruptions or vigorous steaming from lava cooling in the summit crater.

What follows is condensed from reports, primarily by researchers at AVO, describing the time span from 1996 to 2012. Data for 2012 is in a separate subsection. The last section looks at Kanaga seismicity in terms of located earthquakes and MC, Magnitude of Completeness, a means of looking at seismic data quality, homogeneity, and consistency, and the smallest events reliably recorded in the cataloged data (Wiemer and Wyss, 2000).

Figures 1 and 2 comprise three maps showing, respectively, the location of Kanaga Island in the Aleutian Islands, a physical map of Kanaga Island showing the location of Kanaga volcano, and a geological map of the volcano.

Figure (see Caption) Figure 1. (a) Map of the western Aleutian Islands, Alaska, showing the location of Kanaga Island. Courtesy of AVO. (b) Topographic map of Kanaga Island showing Kanaga volcano on the northernmost portion of the island. Courtesy of U.S. Geological Survey (USGS) and Amar Andalkar.
Figure (see Caption) Figure 2. Preliminary geologic map showing Kanaga volcano. Notice that concentric to Kanaga to the SE is the arcuate Kanaton Ridge, inferred to be the remnant of Mount Kanaton, an ancestral volcano destroyed by structural collapse; see generalized geologic cross section in the lower right-hand side of the figure. Courtesy Miller and others (2003, Sheet 1).

According to McGimsey and Neal (1997), a commercial airline crew noted a small, bluish brown cloud possibly containing some ash on 11 June 1996, "rising a few hundred feet above the summit of the volcano." Strong winds carried the cloud down the SE flank of the volcano, depositing ash that discolored the snow. The flight crew noted a sulfur odor upon descent into nearby Adak Island. A ground observer on Adak noted dark splotches on the E flank of Kanaga, but a ballistic origin for the pattern (i.e., volcanic bombs) was never confirmed. It should be noted that these observations occurred several days after an M 6 earthquake in the area, and extensive rockfalls and increased steaming had been observed at Gareloi and Kasatochi volcanoes E and W of Kanaga.

Kevin Bell, the captain of the RV Tiglax, watched Kanaga from a point off its N flank on 3 September 1996. He observed that the extent of lava flows was similar to that inferred from 1995 photographs. Small wisps of steam persisted along the upper reaches of the lava flow on the NW flank. Bell also saw material rolling down the steep flank of the volcano during the Summer and Fall of 1996.

Waythomas and others (2002) noted that ash clouds from Kanaga could interfere with the commercial airliners flying between East Asia and Alaska. Figure 3 shows a satellite image of Kanaga volcano taken 13 August 2002.

Figure (see Caption) Figure 3. An astronaut's photograph acquired late in the day of 13 August 2002 of Kanaga volcano; N is approximately to the left. The volcano is known for its active fumaroles and hot springs (located, in this image, by fine steam plumes on the NE flank of the volcano). A small lake to the SE of the cone is situated on the floor of a larger, more ancient volcanic caldera. Astronaut photograph ISS005 E 10097, from NASA Earth Observatory; courtesy of the Earth Sciences and Image Analysis Laboratory at Johnson Space Center.

Coombs and others (2007) described subaerial evidence for large-scale prehistoric collapse at Kanaga volcanic center and conducted submarine side-scan sonar profiling N of the volcano. These data reveal a hummocky seafloor topography suggestive of landslide debris.

2012 Activity. AVO detected volcanic tremor at Kanaga from 1523 to 1527 UTC on 18 February 2012. This was followed by numerous small earthquakes at Kanaga continuing for about an hour.

A possible weak ash cloud ~8 km in length, ~39 km NE of the volcano, was detected by the Advanced Very High Resolution Radiometer (AVHRR) aboard a polar-orbiting satellite, at 1535 UTC. The plume was observed as far as ~39 km NE of the volcano.

Because of the new unrest and possible explosive activity with the likely ash cloud, AVO raised the Alert Level to Advisory and the Aviation Color Code to Yellow. Somewhat elevated seismicity continued at Kanaga on 19 February 2012, but was not detectable on 20 February. Low amplitude tremor was detected on 25 February. On 2 March, citing continued background level seismicity, AVO returned Kanaga to Normal and the Aviation Color Code to Green.

Photographs taken by a local observer on 19 February showed a small steam plume rising from Kanaga's crater (figure 4), who thought that the two dark stripes extending down the flank possibly represent fresh ash and/or flowage deposits.

Figure (see Caption) Figure 4. Kanaga volcano emitting a steam plume at 1226 on 19 February 2012. Photo taken from the White Alice site, ~3 km W of Adak, Alaska; courtesy of Marjorie Tillion, from AVO web site.

Figures 5-7 show images and photographs of Kanaga taken in the weeks and months following the brief 18 February eruption. The fissure, which vented steam, developed sometime after October 2011.

Figure (see Caption) Figure 5. Radar image of Kanaga collected on 5 March 2012. N is to the right. AVO workers described an E-trending fissure crossing the S crater rim and continuing part way down the W flank. Total length of the fissure was estimated at ~600 m. It developed sometime after October 2011. As mentioned in text, a short duration explosive eruption occurred on 18 February 2012. It was unclear whether that 18 February activity and the development of the fissure were related. TerraSar-X image copyright ©2012 Infoterra GmbH courtesy of Zhong Lu and David Schneider AVO/USGS.
Figure (see Caption) Figure 6. Aerial photograph taken at 1200 on 30 June 2012 of Kanaga's summit with a fissure emitting steam. Photograph by Cyrus Read; image courtesy of AVO/USGS.
Figure (see Caption) Figure 7. Aerial photograph of Kanaga looking E, taken November 2012. The steam discharged from the E-trending fissure on the S side of the dome Photograph courtesy of Roger Clifford.

Located earthquakes enable computation of MC. Table 1 shows the annual number of located earthquakes recorded by the U.S. Geological Survey (USGS) within 20 km of the Kanaga volcanic center for the years of 2004-2011. References for this table came from USGS catalogs of earthquake hypocenters at Alaskan volcanoes are cited in a separate list below. The catalog for 2012 is not yet available. The first seismic monitoring station at Kanaga was installed in September 1999.

Table 1. Number of earthquakes for various years located for the Kanaga volcano seismograph subnetwork within 20 km of the volcanic center. The column of "Other" earthquakes refers to those outside the defined categories of VT and LP (including hybrid, regional-tectonic, teleseismic, shore-ice, calibrations, other non-seismic, and cause unknown). Compiled from the U.S. Geological Survey's annual Catalog of Earthquake Hypocenters at Alaskan Volcanoes.

Year Earthquakes Located Volcano-tectonic (VT) Low-frequency (LF) Other
2004 32 30 2 0
2005 42 42 0 0
2006 56 56 0 0
2007 48 48 0 0
2008 478 403 0 75
2009 28 26 0 2
2010 43 43 0 0
2011 21 21 0 0

According to Dixon and others (2009), the large number of earthquakes located at Kanaga in 2008 was the result of an M ~6.6 tectonic earthquake of 2 May 2008 and its aftershocks. That publication also includes a map with stations and epicenters, cross sections with hypocenters, and a plot of depth in a time series during 2011.

The USGS annual Catalog of earthquake hypocenters at Alaskan Volcanoes include a category for each volcano entitled Magnitude of Completeness (MC), defined as the magnitude at which 90% of the data can be modeled by a power law fit (Wiemer and Wyss, 2000). Below MC, some fraction of small earthquakes are missed by the network, for reasons such as: those earthquakes were too small to be reliably recorded; geophysicists decided to exclude events below some threshold; and for aftershocks and in the midst of various kinds of overriding signal or noise, smaller earthquakes may have been too small to be detected (eg. swamped by the coda of larger events).

According to Dixon and others (2012), Mc for AVO seismograph subnetworks using data from Kanaga (6 stations) for the period March 2002-December 2011 was 1.2. In practice, this means that 1.2 was the lowest magnitude at which all earthquakes in a space time frame are reliably detected. Approximately 25 located earthquakes are needed to calculate MC.

References. Coombs, M.L., White, S.W., and Scholl, D.W., 2007, Massive edifice failure at Aleutian arc volcanoes, Earth and Planetary Science Letters, v. 256, p. 403-418.

McGimsey, R.G., and Neal, C.A., 1997, 1996 Volcanic activity in Alaska and Kamchatka: Summary of events and response or the Alaska Volcano Observatory, U.S. Geological Survey Open File Report 97 433, 34p.

Miller, T.P., Waythomas, C.F., and Nye, C.J., 2003, Preliminary geologic map of Kanaga Volcano, Alaska, U.S. Geological Survey Open File Report 03-113, 1p.

Neal, C.A., McGimsey, R.G., Dixon, J.P., Cameron, C.E., Nuzhdaev, A.A., and Chibisova, M., 2011, 2008 Volcanic activity in Alaska, Kamchatka, and the Kurile Islands: Summary of events and response of the Alaska Volcano Observatory, U.S. Geological Survey Scientific Investigations Report 2010 5243, 94 p.

Waythomas, C.F., Miller, T.P., and Nye, C. J., 2001, Geology and Late Quaternary Eruptive History of Kanaga Volcano, a Calc Alkaline Stratovolcano in the Western Aleutian Islands, in Galloway, J.P. (ed), Alaska Studies by the U.S. Geological Survey in Alaska 2001, U.S. Geological Survey Professional Paper 1678, Chapter 15, pp.181-197.

Waythomas, C.F., Miller, T.P., and Nye, C. J., 2002, Preliminary volcano hazard assessment for Kanaga Volcano, Alaska, U.S. Geological Survey Open File Report 02 397, 27 p.

Wiemer, S and Wyss, M, 2000, Minimum Magnitude of Completeness in Earthquake Catalogs: Examples from Alaska, the Western United States, and Japan, Bulletin of the Seismological Society of America, vol. 90 no. 4, pp. 859 869 (DOI: 10.1785/0119990114).

References - Catalogs of earthquake hypocenters at Alaskan Volcanoes.

Dixon, J.P., Stihler, S.D., Power, J.A., Tytgat, G., Estes, S., Prejean, S., Sánchez, J.J., Sanches, R., McNutt, S.R., and Paskievitch, J., 2005, Catalog of Earthquake Hypocenters at Alaskan Volcanoes: January 1 through December 31, 2004, U.S. Geological Survey Open File Report 2005 1312, 74p.

Dixon, J.P., Stihler, S.D., Power, J.A., Tytgat, G., Estes, S., and McNutt, S.R., 2006, Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2005, U.S. Geological Survey Open File Report 2006 1264, 78 p.

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, Cheryl, 2008, Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2006, U.S. Geological Survey Data Series 326, 79 p.

Dixon, J.P., Stihler, S.D., and Power, J.A., 2008, Catalog of Earthquake Hypocenters at Alaskan Volcanoes: January 1 through December 31, 2007, U.S. Geological Survey Data Series 367, 82p.

Dixon, J.P., and Stihler, S.D., 2009, Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2008, U.S. Geological Survey Data Series 467, 86 p.

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, Cheryl, 2010, Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2009, U.S. Geological Survey Data Series 531, 84 p.

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, C.K., 2011, Catalog of earthquake hypocenters at Alaskan Volcanoes: January 1 through December 31, 2010, U.S. Geological Survey Data Series 645, 82 p.

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, C.K., 2012, Catalog of earthquake hypocenters at Alaskan Volcanoes: January 1 through December 31, 2011, U.S. Geological Survey Data Series 730, 82 p.

Geologic Background. Symmetrical Kanaga stratovolcano is situated within the Kanaton caldera at the northern tip of Kanaga Island. The caldera rim forms a 760-m-high arcuate ridge south and east of Kanaga; a lake occupies part of the SE caldera floor. The volume of subaerial dacitic tuff is smaller than would typically be associated with caldera collapse, and deposits of a massive submarine debris avalanche associated with edifice collapse extend nearly 30 km to the NNW. Several fresh lava flows from historical or late prehistorical time descend the flanks of Kanaga, in some cases to the sea. Historical eruptions, most of which are poorly documented, have been recorded since 1763. Kanaga is also noted petrologically for ultramafic inclusions within an outcrop of alkaline basalt SW of the volcano. Fumarolic activity occurs in a circular, 200-m-wide, 60-m-deep summit crater and produces vapor plumes sometimes seen on clear days from Adak, 50 km to the east.

Information Contacts: Alaska Volcano Observatory (AVO), a joint program of theUnited States Geological Survey (USGS), theGeophysical Institute of the University of Alaska Fairbanks (UAFGI), and theState of Alaska Division of Geological and Geophysical Surveys (ADGGS), Anchorage, AK (URL: http://www.avo.alaska.edu); Christina A. Neal, USGS/AVO Anchorage, AK (URL: http://www.avo.alaska.edu); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).


Lokon-Empung (Indonesia) — March 2013 Citation iconCite this Report

Lokon-Empung

Indonesia

1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)


Eruptions continue into early 2013

This report discusses ash-bearing eruptions seen during the reporting interval, 15 September 2012 to April 2013. As described in our 2012 report (BGVN 37:05) the twin volcanoes of Lokon-Empung have remained restless since 2008, typically with small eruptions amid seismic unrest. Recent activity is based on summaries that have been posted by the Center of Volcanology and Geological Hazard Mitigation (CVGHM, also known as Pusat Vulkanologi dan Mitigosi Bencana Geologi-PVMBG). The active crater is referred to as Tompaluan, a vent that resides in the saddle between the peaks of Lokon and Empung (figure 12). An estimated 120,000 people live within 10 km of the volcano. Lokon-Empung lies 20 km S of Manado, the second largest city in Sulawesi (2010 pop. 2.27 million), a metropolis served by the Sam Ratulangi International Airport that closed for four days during Lokon's 1991 eruption (see figures 9 and 10 in BGVN 37:05). In April 2012, CVGHM raised the hazard Alert Level to 4 (on a scale of 1-4).

Figure (see Caption) Figure 12. Lokon-Empung volcano showing the Tompaluan vent between the two principal volcano peaks. Photo by Agus Solihin, 1998 (Volcanological Survey of Indonesia).

According to the Darwin Volcanic Ash Advisory Center (VAAC), ground based observers reported that on 15 September (2012) an ash plume from Lokon-Empung rose to an altitude of ~3 km. Satellite imagery showed the ash plume drifting 185 km SE. Another ash plume was reported on 21 September, rising to an altitude of ~3 km; however, in this case an ash plume was not identified in satellite imagery.

According to the Darwin VAAC, CVGHM reported that on 6 October an ash plume from Lokon Empung rose to an altitude of ~3.7 km; the plume altitude was determined by wind data. A thermal anomaly was also detected in satellite imagery on 6 October.

Several news sources (Examiner.com, Jakarta Globe, XINMSN News (Singapore), Jakarta Post) were amalgamated to describe the October activity. According to a news article, an eruption on 7 October 2012 ejected incandescent tephra as high as 350 m above the crater and generated an ash plume that rose ~1.5 km. The article also noted that Lokon Empung had erupted 41 times in September and 3 times on 5 October.

Government volcanologist Farid Bina reported from the volcano's monitoring post in North Sulawesi province, "The eruption on 7 October was the seventh biggest eruption since mid-September". Thunderous sounds were heard nearly 6 km away. The National Agency for Disaster Management (BNPB) said the eruption ejected debris 350 m high and produced an ash plume at least 1.5 km high that drifted NE. It wasn't clear how high the ascending ash actually reached because the mountain was engulfed in ash and heavy rain fell around its cloud covered crater. Bina said that there were no casualties or damages. The head of North Sulawesi Disaster Mitigation Agency (BPBD), Hoyke Makarawung, said that the amount of ashfall blanketing the affected areas was insignificant. BPBD reminded residents about the danger of respiratory ailments, urging those in ash-prone areas to wear masks. A 2.5-km exclusion zone around the volcano continued to be enforced during this heightened activity.

Figure 13 shows Lokon-Empung erupting on 8 October 2012. The plume rises from Tompaluan, the active vent at Lokon which lies in the saddle between the two peaks. The ash column mixed with atmospheric clouds, rising to an uncertain altitude.

Figure (see Caption) Figure 13. Lokon-Empung eruption seen 8 October 2012. Courtesy of the Reuters.com and Guardian.cu.uk.

Based on a Significant Meteorological Notice (SIGMET), the Darwin VAAC reported that on 11 November an ash plume from Lokon Empung rose to an altitude of ~1.5 km. The VAAC again reported that on 28 November, an eruption from Lokon Empung produced an ash plume that rose to an altitude of ~4.9 km; the plume was not however detected in satellite imagery.

On 6 December, Lokon emitted a billowing ash plume (figure 14) that produced ash that fell mostly on the SE flank. Milder activity resumed on 8 and 9 December as shown in figures 15 and 16. December's second small eruption took place on 10 December.

Figure (see Caption) Figure 14. Two views of the ash plume emitted at Lokon on 6 December 2012. Courtesy of Photovolcanica.com.
Figure (see Caption) Figure 15. The Tompaluam vent at Lokon-Empung viewed at night on 8 December 2012. Courtesy of welt.da.
Figure (see Caption) Figure 16. Lokon degassing on 9 December with red and orange glow reflecting of a blowing plume; and a small emission on 10 December. Courtesy of Photovolcanica.com.

The eruptions seen on 6 and 10 December were typical of Lokon's recent behavior. They involved a succession of overlapping explosions resulting in sustained ash emission and the production of an ash plume. According to Darwin VAAC, these two eruptions produced ash clouds reaching ~3.4 and~ 4.3 km in altitude, respectively.

According to CVGHM there were no reports of casualties or damages during the December 2012 eruptions. Enlarging the current exclusion zone by specifying a new radius of larger size would cut the main road connecting the towns of Manado and Tomohon and thus burden a much larger population. Consequently, the Alert Level was held at "3" (out of 4) that has been in effect since July 2011. Immediate precursors to eruptions at Lokon are typically small and of short duration (minutes to hours), and eruptions may occur with very little additional warning.

In January (2013), based on ground reports, the Darwin VAAC reported ash plumes from Lokon-Empung rose to an altitude of ~2.4 km during the period 2-8 January, that report was not however confirmed by satellite imagery. The VAAC again issued a special Notice to Airmen (NOTAM) for volcanic ash during 15-16 January, again based on reports from CVGHM and the Aviation Volcanic Information site (ASHTAM - www.ashtam.co.uk). The ash plumes reportedly rose to altitudes of ~3.7 4.5 km, but satellite imagery did not confirm the ash reports.

According to news articles, Lokon Empung erupted twice on 31 January, producing an ash plume that rose 800 m above the crater after the first eruption. Seismicity had increased the day before. In another article the head of the Lokon observation post reported that eruptions from Lokon occurred daily, and specifically that nine eruptions had occurred on 2 February. The CVGHM reported that a significant explosion occurred at Lokon on 3 February which produced an ash plume which rose ~3-4 km and which drifted S and SW, but the ash plume was not detected in satellite imagery.

CVGHM observers at the Kakaskasen Volcano Observatory (KKVO) in North Sulawesi, Indonesia reported increased seismic unrest on 9 February. The character of the seismicity suggested to CVGHM that a magmatic intrusion was occurring. Lokon did erupt on 12 February. Seismicity remained elevated at Lokon and small explosions have been occurred frequently.

On 20 March, the Jakarta Post reported a new eruption at Lokon which spewed a ~2 km m high dark brown and black ash cloud from the Tompaluan crater, easily visible from Manado, the regional capital to the NE, and was heard up to 6 km distance. Farid Ruskanda Bina, head of Mount Lokon and Mount Mahawu observation post at the Bandung Geology Agency's volcanology and geological disaster mitigation center (PVMBG) reported "There was an increase in volcanic tremors which culminated in an eruption" (Antara News). Warno, an official at the observation post, added that the increases in Mount Lokon's volcanic tremors were not very significant. The frequency of the volcano's eruptions has continued to decline from previous eruptions of two to three times a week.

A series of 3 moderately large explosions occurred on 25 March that was followed by minor ash emissions. Mount Lokon erupted again from the Tompaluan crater on 26 March, again with ash plumes rising up to ~2 km above the vent. Residents heard a loud boom after the eruption. Indonesia's National and Local Board for Disaster Management and Volcanology agency warned people not to go within 2.5 km of the volcano; authorities held the situation at Alert Level 3 but, however have not advised residents to evacuate the area. There were no reports of casualties, but three villages in the area, Dalian, Wadena and Walloon were covered in ash from the eruption.

On 2 April, seismicity at Lokon increased. Based on both CVGHM and ground reports, the Darwin VAAC reported that on 3 April an eruption from Lokon Empung produced an ash plume that rose to altitudes of ~3 3.4 km and drifted SW. New explosions occurred on 4 April. Volcanic ash plumes reached 700 m above the crater and were blown to the S. Another explosion occurred on 8 April. A relatively large ash plume rose about 3 km above the crater to an altitude of ~4.5 km and drifted SW. The eruption was heard up to 6 km away. The volcano observatory recorded that the eruption was preceded by a strong increase in seismicity. After the main eruption, the volcano continued to erupt ash. Based on both web-camera views and ground reports, the Darwin VAAC reported that on 11 April an ash plume from Lokon rose to an altitude of ~4.6 km and drifted SW; but the ash plume was not confirmed by satellite imagery.

Another relatively large eruption occurred on 14 April. The explosion produced an ash plume ~4 km high, and strong vibrations were felt up to 5 km from the volcano.

KKVO is monitoring the activity closely using equipment for a volcano hazard mitigation project in Indonesia.

Geologic Background. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2 km apart), has a flat, craterless top. The morphologically younger Empung volcano to the NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred. A ridge extending WNW from Lokon includes Tatawiran and Tetempangan peak, 3 km away.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 5+7, 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/); The Jakarta Post (URL: http://www.thejakartapost.com/); Jakarta Globe (URL: http://jakartaglobe.id/); Kompas.com (URL: http://www.kompas.com/); Straits Times (URL: http://www.straitstimes.com); ITN News (URL: http://www.itn.co.uk/); Volcano Discovery (URL: https://www.volcanodiscovery.com/); Activolcans, VSI (webcam); Geoforum; Xinhua; NewKerala.


Nikko-Shiranesan (Japan) — March 2013 Citation iconCite this Report

Nikko-Shiranesan

Japan

36.799°N, 139.376°E; summit elev. 2578 m

All times are local (unless otherwise noted)


Felt earthquakes nearby during April-September 2011

This is our first report on Nikko-Shirane (also known as Nikko-Shiranesan). The volcano is located in the Nikko National Park in central Honshu, the main island of Japan (figures 1 and 2).

Figure (see Caption) Figure 1. A photo and a sketch map highlighting the Nikko-Shirane's morphology and location. The volcano sits ~124 km NNW of Tokyo. Courtesy of JMA.
Figure (see Caption) Figure 2. Photo of Nikko-Shirane taken on 8 October 2012 with Goshikinuma Pond in the foreground. Courtesy of futurelight(*busy*) on Flickr.

According to the Japan Meteorological Agency (JMA), after the massive 11 March 2011 MW 9.03 earthquake off the Pacific coast of Tohoku (38.297°N, 142.372°E), seismicity briefly increased 5-10 km E and SE of Nikko-Shirane at a depth of about 5 km W and NW. On 9 April 2011, an M 3.5 earthquake occurred about 5 km W of the summit, followed by several aftershocks. On JMA's earthquake intensity scale, the M 3.5 earthquake ranged from 1 (felt slightly by some people in quiet environments) to 3 (felt by most people in buildings and some people walking; many people awoken). (JMA's earthquake intensity scale is explained on their website.)

In May, two small earthquakes occurred NW of the volcano. Afterward, seismicity gradually declined through December 2011, although several additional small earthquakes through September 2011 were felt in nearby Nikko city, about 4-5 km E of the summit. No volcanic tremor or fumaroles were observed. No changes were also noted during a 2 November 2011 field survey.

The next JMA-translated report on Nikko-Shirane, in February 2013, noted that volcanic seismicity remained low. However, on 25 February an M 6.3 earthquake occurred, the hypocenter of which was 10 km NNE of the summit and 3 km below sea level. The earthquake's maximum seismic intensity on JMA's scale was 5+ in Nikko City (scale of 5 indicates that many people find it hard to move and walking is difficult). Aftershocks with maximum seismic intensities between 1 and 4 on the JMA scale continued until 28 February, when seismicity declined. This seismicity was not accompanied by volcanic tremor, fumarolic activity, crustal deformation, or any other volcanic activity.

Geologic Background. Nikko-Shiranesan is a relatively small, 2578-m-high andesitic volcano consisting of a group of four lava domes resting on a shield volcano that rises to the NW of scenic Lake Chuzenji in Nikko National Park. All historical eruptions, recorded during the 17th-20th centuries, have consisted of phreatic explosions from Shiranesan, the youngest lava dome. Viscous lava flows with prominent levees from the underlying shield volcano Keizukayama were responsible for the formation of several scenic lakes north of the volcano.

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


Niuatahi (Tonga) — March 2013 Citation iconCite this Report

Niuatahi

Tonga

15.379°S, 174.003°W; summit elev. -1270 m

All times are local (unless otherwise noted)


New research data collected from submarine volcano

Richard Arculus (2012), David Butterfield (2012), and Keener and Vailea (2012) discussed the Submarine Ring of Fire Expedition 2012 of the Research Vessel R/V Revelle during 14-15 September 2012. They conducted bathymetric profiles and submersible observations of a caldera originally called 'Volcano O' in the Tonga arc (figure 1). During this cruise, the name 'Niua Tahi' was given to this extraordinarily symmetrical, circular caldera, 15 km in diameter at 1.2 to 2 km depth, by a Senior Geological Assistant aboard from the Tonga Ministry of Lands, Environment, Climate Change and Natural Resources. According to Keener and Vailea (2012), "Volcano O, was named 'Niua Tahi' during our expedition by the Ministry, which in Tongan means 'sea', with the small cone within it being named 'Motu Tahi', or 'island in the sea'."

Figure (see Caption) Figure 1. Map of operations of Submarine Ring of Fire 2012 in the NE Lau Basin. Map features the NE Lau Basin area, where the majority of cruise took place. The inset in the upper left shows a key to the various tasks for the entire cruise, and the insert map in the lower right shows the general area with respect to the locations of Samoa and Fiji. Niua Tahi volcano is identified as 'Q324: MotutahiI' (the new name for the volcano's small cone) on the map. Image from Resing and Embley (2012); courtesy of Submarine Ring of Fire 2012: NE Lau Basin, NOAA-OER.

Niua Tahi is a giant, near-circular caldera ~15 km in diameter, with a floor at a depth of about 2 km (Arculus, 2012). A young cone (Motu Tahi) in the SE sector rises 730 m above the floor to a summit at a depth of 1,270 m depth. The volcano is in the rear arc of the Tonga system, located ~40 km W of the chain of subaerial-submarine volcanic edifices that define the volcanic front of the Tonga Arc, and 25 km E of the spreading ridge of the Northeast Lau Spreading Center. The composition of the cone and surrounding floor is predominantly dacite. Towing with sea-floor cameras over the cone and various parts of the caldera resulted in the discovery of at least three sources of hydrothermal particle venting on the cone's summit and adjacent to the inner caldera walls.

During the cruise, the remotely operated vehicle (ROV) Quest 4000 (operated by MARUM, the Center for Marine Environmental Sciences at the University of Breman, Germany) traversed from W to E over the volcano summit and around the margins of the central cone. The cone contained a shallow pit surrounding what appears to be a volcanic vent, probably the site of the most recent volcanism (figures 2a and 2b). The ROV showed that the summit of the cone was mantled with a ubiquitous sulfur-rich layer that coated rugged blocks of pillow lava, lava tubes, and ash-and-blocks deposits.

Figure (see Caption) Figure 2. (a) Multibeam bathymetry image of Niua Tahi, looking N, with two-fold vertical exaggeration. Color scale for depths is shown in upper right. (b) Multibeam bathymetry image of the cone in the caldera of Niua Tahi. The image is viewed looking E, without vertical exaggeration. The color scale for depths from Figure 2a is the same for this figure. Both images courtesy of Susan Merle, Oregon State University, Submarine Ring of Fire 2012 Exploration, NOAA Vents Program; on web site of Arculus (2012).

The ROV images revealed the presence of a NE-trending elongated pit crater at the cone's summit emitting a plume bearing a sulfurous particulate-rich plume. Several previous observations of the water column detected similar plumes. Hot, clear water (~105°C) welled up in numerous places through the loosely agglomerated pyroclastic materials forming both the rim of the crater and flanks of the cone. The attempt to descend the ROV into the pit for a closer look was thwarted by the dense clouds of sulfurous 'smoke.' The most recent volcanic activity was likely dominated by lava and volcaniclastic debris.

References. Arculus, R., 2012 (14 September), Crossing the cone at "Volcano O," Ocean Explorer (URL: http://oceanexplorer.noaa.gov/explorations/12fire/logs/sept14/sept14.html).

Butterfield, D., 2012 (15 September), Chemistry and ecology at volcano O, Ocean Explorer (URL: http://oceanexplorer.noaa.gov/explorations/12fire/logs/sept15/sept15.html).

Keener, P., and Vailea, A., 2012 (24 September), In keeping with tradition, Ocean Explorer (URL: http://oceanexplorer.noaa.gov/explorations/12fire/logs/sept24/sept24.html).

Resing, J., and Embley, B., 2012, Mission summary, NOAA Ocean Explorer web site (URL: http://oceanexplorer.noaa.gov/explorations/12fire/logs/summary/summary.html).

Geologic Background. Niuatahi is a giant, near circular caldera ~15 km in diameter, with a floor at a depth of about 2 km (Arculus, 2012); it had been preliminarily called "Volcano O." A young cone (Motu Tahi) in the SE sector rises 730 m above the floor to a summit depth of 1,270 m. The volcano is in the rear arc of the Tonga system, ~40 km W of the chain of edifices that define the volcanic front of the Tonga Arc, and 25 km E of the spreading ridge of the Northeast Lau Spreading Center. The composition of the cone and surrounding floor is predominantly dacite. Towing with sea floor cameras over the cone and various parts of the caldera in 2012 resulted in the discovery of at least three sources of hydrothermal particle venting on the cone's summit and adjacent to the inner caldera walls. The Tonga Ministry of Lands, Environment, Climate Change and Natural Resources named the volcano Niuatahi, which means 'sea' in Tongan, with the small cone of Motutahi meaning 'island in the sea.'

Information Contacts: Richard Arculus, Research School of Earth Sciences, The Australian National University, Canberra, Australia; Susan Merle, Oregon State University, Eugene, OR, Submarine Ring of Fire 2012 Exploration, NOAA Vents Program; Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany (URL: https://www.marum.de/); NOAA Vents Program (URL: https://www.pmel.noaa.gov/eoi/laubasin.html).


Tungurahua (Ecuador) — March 2013 Citation iconCite this Report

Tungurahua

Ecuador

1.467°S, 78.442°W; summit elev. 5023 m

All times are local (unless otherwise noted)


Return of explosions and earthquakes through at least October 2010

As noted in our last report (BGVN 34:08), activity at Tungurahua had started to decline in late June 2009, a trend that continued through mid-December 2009. This report summarizes heightened activity witnessed from 30 December 2009 to 4 February 2010, and again from 26 May to very early August 2010. Seismicity began to increase in mid-December 2009 in prelude to the above-mentioned escalation.

This report is based on reports received from and direct correspondence with staff members of the Instituto Geofísico Politécnica Nacional Casilla ("Instituto Geofísico," IG).

Seismic overview. A plot by IG presented a synthesis of seismicity (figure 45) during the interval of 1 January 2006 to 17 October 2010, and is one way to portray the long-term pace of Tungurahua's eruption. The x-axis shows time with small tick marks every 30 days, and years indicated. The y-axis shows level of seismic activity on a scale indexed to an unstated normalized peak value. During the time period plotted, the number of recorded events assessed had a maximum peak at index value of ~74%. That peak occurred around 14 July 2006 ("2006 07 14" at left on the plot).

Figure (see Caption) Figure 45. A plot of Tungurahua's seismicity versus time for the interval 1 January 2006 to 17 October 2010. The scale on the left (Index value) is in terms of percent of the IG's custom defined index of activity scale (IAS) for Tungurahua. The bar was auto-scaled with 4.6 units between horizontal lines. The X-Y intercept is slightly below zero (-0.3). The Y-axis on the right shows the IG's defined 'level of the IAS.' The horizontal red dots refer to thresholds during 1999-2005, corresponding to index values at 22.8 and 26.6% (95% and 99% confidence intervals, respectively). Modified from a plot by IG.

During 2010 seismicity rose sharply in January, peaked at index values near 27%, and then descended during February into June 2010. The intervals of low seismicity in late 2009 and early 2010 are some of the lowest index values during the ~5 years displayed on this plot. The second peak during 2010 was sudden and ascended from low index values; it reached maximum values in late May 2010, approaching index values 50%. The downward arrow at the right side of the plot calls attention to the last day on the plot, 17 October 2010, when the index value stood at 11%.

The seismicity shown in figure 45 shows strong correlation with Tungurahua's behavior summarized below.

Renewed activity (and SO2 compilations). After six months of calm that included occasional diffuse emissions of vapor that rose no higher than 100 m, more intense activity resumed on 30 December 2009. On 1 January ash plumes rose to ~6 km altitude, and on 3 and 4 January they rose as high as ~9 km. Similar plume altitudes were seen at times during the rest of January and February. On 11-12 January, Strombolian outbursts ejected material ~1 km above the crater and to distances of ~1.5 km away from the vent. Ash often blew in a broadly westerly direction (see below).

Significant SO2 fluxes were measured in January 2010. On 6 January, SO2 fluxes reached a value of 3,200 metric tons/day (t/d); on 8 January, they reached 7,500 tons/day. In contrast, some recent values during the 6 month lull were between 100 and 200 tons/day.

On the broader subject of Tungurahua SO2 output, more comprehensive assessments and compilations have been captured than ever before, but the details are beyond the scope of this report. One group, NOVAC (Network for Observation of Volcanic and Atmospheric Change) established a global network of stations to measure emissions of SO2 (and BrO) by UV absorption spectroscopy by local instruments. Trained personnel working at various volcanoes and following protocols assured standard practices (DOAS, mini DOAS, Flyspec). The instruments are based at over 21 volcanoes, including Tungurahua. SO2 is also monitored from instruments on satellites (e.g. OMI, GOME 2, and SCIAMACHY). Understanding and possibly reconciling those two set of atmospheric measurements, local (ground- and aircraft-based measurements) and satellite based, has also been the subject of recent papers. Tungurahua and adjacent degassing volcanoes have played a major roles in this effort (McCormick and others, in press, Carn and others, 2008, and Arellano and others, 2008).

Figure 46 shows Tungurahua in a Strombolian eruption on or about 10 January 2010. Incandescent material fell onto the flanks.

Figure (see Caption) Figure 46. After 6 months of comparative quiet, Tungurahua renewed more vigorous eruptions during 30 December 2009 to 1 January 2010. This extended-exposure night photo was taken on or around 10 January 2010. The volcano's profile appears dark, almost black, whereas Strombolian discharges at the summit crater glow a bright red-orange. The extended exposure captured the paths of glowing projectiles arcing out of the crater, and impacting and in many cases bouncing down the upper flanks. An ash cloud in the background reflects a softer more continuous glow across a broad area including, in fainter light, portions of the plume trailing off to the upper right. Photo by Jorge Bustillos A., IG.

Strong explosions were heard on the evening of 14 January. Small amounts of ash fell nearby and as far away as the Chimborazo glaciers and Guaranda (64 km SW).

The return of ongoing ash plumes initiated a variety of civil responses. In towns close in and on Tungurahua's W to SW flanks (e.g., Choglontús), roofs were inspected and where necessary, ash was removed. This measure was undertaken to prevent ash loading and potential roof collapse. Many building roofs are nearly flat, requiring ash removal with brooms and shovels.

Figure 47 shows an elementary schematic created to address the upsurge in Tungurahua's ash falls, and to broaden understanding and raise public awareness of ash fall processes and hazards from Tungurahua. It shows the progressive shift in the range of grain sizes falling out of ash plumes as they drift, in this idealized case, W to SW with plume tops rising to altitudes approaching 10 km. More complex depositional patterns may develop owing to factors like discharges to variable height, discharges containing differing grain-size distributions, and shifts in wind velocity. Assessment of ashfall often results in maps displaying the thickness or mass of these deposits on the ground (respectively, isopach and isopleth maps). Several isopach maps appear below, describing the Tungurahua's January-February 2010 upsurge in ashfall in more quantitative and technical terms.

Figure (see Caption) Figure 47. An idealization of ash plume evolution emphasizing the expected changes in grain sizes falling from Tungurahua plumes and the range of distance to some settlements. The plume shown is assumed to blow W to SW (common wind directions in this region). Graphics like this help inform the public. Courtesy of IG.

Tungurahua's ash clouds are also closely monitored out of concern for keeping aircraft out of potentially damaging plumes, some of which extended ~150 km W of the summit during the reporting interval. Ecuador maintains a Meteorological Watch Office (MWO) in the city of Guayaquil, ~180 km SSW of the summit (figure 48; and see inset map showing Guayaquil's location on the coast in figure 25 in BGVN 30:06). The Guayaquil MWO feeds critical data, including observations made by IG at Tungurahua and satellite data they interpret about Tungurahua's plumes, to the Buenos Aires Volcanic Ash Advisory Center. Tungurahua was a frequent subject of aviation reports during the reporting interval. As seen on figure 48, Guayaquil sits just S of the ends of W-directed envelopes around the January 2010 ash clouds.

Figure (see Caption) Figure 48. Plan view of the overall atmospheric dispersion patterns of Tungurahua ash during January 2010. This is vital information to the aviation community. Although the key is in Spanish, the gist is this: The yellow and blue envelopes apply to ash above and below 7.6 km altitude, respectively (note scale at far left). Courtesy of IG (graphic and key composed by Jorge Bustillos A. after a graphic found at the Washington VAAC).

Figures 49 and 50 respectively show 1-10 and 11-31 January ash-fall deposits created by plumes that rose to the 5.4-9.1 km altitude range (up to 3 km above the crater). On these maps, the farthest measured isopach, 1 mm in thickness, was as far away as 19 km from the crater. For figure 49, the points where the thickness was measured (yellow) best constrained the deposits maximum extent on the N, NW, and W sides. For that map, ash volumes estimated using conventional approaches (Pyle, 1989; Fierstein and Nathenson, 1992; and Legros, 2000) yielded 313,000 m3 (stated in terms of vesicle-free rock; often abbreviated as DRE, dense-rock equivalent).

Figure (see Caption) Figure 49. The isopach map IG compiled for Tungurahua ash deposited during 1-10 January 2010. Key shows the following (from top): Isopach thicknesses (3 colors), points where the thickness data were collected (yellow dots); population centers (black shaded areas), and Tungurahua (reddish shading). Courtesy of IG (composed by Jorge Bustillos A.).
Figure (see Caption) Figure 50. The isopach map IG compiled for Tungurahua ash deposited during 11-31 January 2010. The thickest area was inferred to lie ~9 km WSW of the summit at Cahual (where 15 mm fell). Key at left shows isopach thicknesses (9 colors), points where the thickness data were collected (green dots); and population centers (black shaded areas). Courtesy of IG (composed by Jorge Bustillos A.).

In figure 50, the thickest ash (1.5 cm) was mapped at the town of Cahual (~9 km WSW of the summit), and the mapped pattern suggested lobes trending both WNW and WSW. Such thickening at a spot well away from the summit is unusual but not unprecedented. Future studies considering meteorological or other data may help explain this pattern, which could have public safety implications.

IG's report for 11-31 January noted near constant ash plumes during that interval. Ash had impacted banana plantations and livestock, falling over an area of ~15,000 km2.

The ash volume estimate in DRE for 11-31 January was 806,000 m3 (figure 50). Taken with the earlier (1-10 January) estimate based on figure 49, this made the January total ~1,120,000 m3 (DRE). This is best shown to two significant figures, thus 1.1 x 106 m3. In contrast, the volume for the full month of February was estimated at 1.6 x 106 m3.

Figure 51, an isopach map created for the entire month of February 2010, extends farther outward than either of the two maps representing January. February's 1 mm isopach extends up to 22 km from the summit in the WNW direction. February's map also shows some thicker deposits close to the active summit crater (25 mm thickness at Cahuaji), but it reflects a longer time interval than each of the two January maps. February's elevated deposition of ash conformed with IG's Special Bulletin (No. 6), which explained that after 6 February 2010 they had seen a notable increase in the frequency and magnitude of explosions, and plumes rising 4 km above the summit. People tens of kilometers away heard blasts. Observers noted glowing blocks thrown more than 1.5 km and rolling downslope. Infrasonic microphones recorded signals suggesting four explosions of high energy during 8-9 February.

Figure (see Caption) Figure 51. An isopach map showing Tungurahua's ash accumulation during February 2010 (thicknesses in millimeters). Courtesy of IG (composed by Jorge Bustillos A.).

5 February ash plume dynamics. Figure 52 shows intriguing ash plume behavior on 5 February 2010, disclosing complexities infrequently discussed in the literature. At discharge, the plume rises vertically in a thrust phase that appears to be well on its way to farther ascent in a convective phase. The continued rise of earlier emissions (perhaps less energetic or perhaps in gusts of stronger wind) were thwarted by wind having sheared and carried them off. That portion of the plume appears to the right of the crater. As these earlier components progressed downwind and above the lee side of the volcano, their path descended rather than ascended. Farther downwind and away from the volcano the plume appears much broader and its top has risen higher than the original thrust phase. The presence of weather clouds like those in the background could compromise ground-based estimates of the ultimate height for the plume's top.

Figure (see Caption) Figure 52. Tungurahua discharged this vapor-dominated emission (containing low-to-medium density of ash) at 2200 on 5 February 2010. That day's eruptions were described as rising 1 km above the summit and continuing W to SW. The scene is discussed further in text. Image taken from IG's 1-7 February 2010 report (photo credit to J. Bourquin IG).

Geometries like this may also complicate reliable estimates of gas-flux, although scanning imaging infrared spectrometers compensate for these problems (e.g. Grutter and others, 2008). Pilots and meteorologists are familiar with these topographic wind-related effects, which they call lee waves. An acclaimed book by Pretor-Pinney (2007) discusses and provides a diagram to explain similar wind-driven topographic effects and lenticular clouds common near tall peaks.

11 February secondary pyroclastic flows. As IG reported (in their Special Bulletin Number 6), on 11 February an M 3.3 volcano-tectonic earthquake struck in vicinity of Tungurahua. Strong explosions ensued, and about 20 minutes later an ash plume rose ~4 km above the summit. About three hours later IG observers at the Tungurahua Volcano Observatory (OVT) in Guadalupe, (11 km N of the summit), photographed the paths and thermal images revealed still hot deposits from small pyroclastic flows. These flows started at the crater rim and descended several kilometers down the upper one-third of the volcano on the N and NNW flanks.

The pyroclastic flows were interpreted as secondary, generated by the gravitational instability of still-hot ejecta that had accumulated at the crater rim and adjacent areas downslope.

February rain brings destructive lahars. Special Bulletin No. 5 of 4 February 2010 contains a detailed set of notes compiled as strong rains fell and caused lahars to descend along gullies and ravines. The Ulba river (on the volcano's E to NE flanks) was strongly impacted. The lahars also closed some recently repaired roads.

At 1100 on 4 February 2010, a large amount of rock debris flowed down the Chinchín river, which flows from the S to the N along the outer NE flank as close as ~10 km from the summit crater. According to the Baños Fire Department, the lahars destroyed or damaged ~18 homes in Chinchín (16 km NE of the summit). Four people were injured (two children, two adults) and four people were missing. The lahars carried debris up to 5 m in diameter. Debris flowed over the brink of Bride's Veil waterfall, disrupting a well-known scenic attraction.

March to June activity. Although poor visibility hampered views in March, seismicity remained high and indicative of explosions with several ash emissions reaching altitudes of 8-9 km. Comparative quiet prevailed during April and the earlier parts of May, although visibility was often compromised. Early May reports noted lahars on the N, W, and S flanks.

Eruptive vigor rose again on 26 May 2010, when an eruption resulted in small (~1 km runout distance) pyroclastic flows and an ash plume that rose to 12 km altitude.

An eruption on 28 May produced a plume that rose to 15 km altitude, resulting in pumice-fall in some inhabited areas. Pyroclastic flows extended as far as 3 km down the NW, N, and SW flanks, distances insufficient to impact inhabited areas. According to news articles, residents from two towns about 8 km NW were evacuated, and ashfall at the airport in Guayaquil temporarily shut it down.

On 2 and 7 June pyroclastic flows traveled 1.5 km down the NW flank; this took place amid the early June seismic low on figure 47.

Clouds often prevented observations during June and July, but when visible, plumes again rose to altitudes of 5-8 and occasionally 9 km. Some intervals of comparative quiet also occurred (e.g., 23 June to 4 July). As had occurred during many intervals of high eruptive vigor, loud booming noises associated with explosions often caused structures to vibrate. For example, on 6 June large windows vibrated at OVT.

During 28 July-2 August steam emissions, often containing ash, 1-2 km above the crater and drifted NW or W. Minor ashfall was reported to the SW in the Choglontus area during 28-29 July.

According to IG's October report, a lull in activity began in late July and continued through all of October. Figure 47 shows that comparatively low seismicity prevailed through at least 17 October 2010.

Online book in Spanish on Tungurahua. Readers searching for background on this restless, dangerous, news-making volcano, will find it summarized in accessible terms in a compact (118 page) well-illustrated book (Le Pennec and others (2005), in Spanish; available free online as a PDF file). Topics include events from Tungurahua's geologic past, the onset of the current eruption in 1999, and approaches to monitoring. The book covers behavior as late as mid-2005. A few important recent eruptions after the book's publication included those in July and August 2006 (respectively, VEI 2 and 3) and in February 2008 (VEI 1-2).

Figure 53 features a map from the book. In the book's digital version (a PDF file), the search function will identify place names on this map, a welcome feature.

Figure (see Caption) Figure 53. Location of Tungurahua and surroundings showing cities and districts, places confronting varying degrees of impacts from the ongoing eruption. Translation of terms in key: province capital, cantonal capital, paved road, dirt road, pipeline, province margin, and drainage network. Taken from Le Pennec and others (2005).

References. Arellano, S.R., Hall, M., Samaniego, P., Ruiz, A., Molina, I., Palacios, P., Yepes, H., OVTIGEPN staff, 2008. Degassing patterns of Tungurahua volcano (Ecuador) during the 1999-2006 eruptive period, inferred from remote spectroscopic measurements of SO2 emissions. J. of Volcanology and Geothermal Research 176, 151-162.

Carn, S.A., A.J. Krueger, N.A. Krotkov, S. Arellano, and K. Yang, 2008, Daily monitoring of Ecuadorian volcanic degassing from space, J. of Volcanology and Geothermal Research, 176(1), 141-150.

Grutter, M., Basaldud, R., Rivera, C., Harig, R., Junkerman, W., Caetano, E., and Delgado Granados, H., 2008, SO2 emissions from Popocatpetl volcano: emission rates and plume imaging using optical remote sensing techniques, Atmos. Chem. Phys., 8, 6655-6663.

Le Pennec. J-L, Samaniego, P, Eissen, J-P, Hall, MP, Molina, I, Robin, C, Mothes, P, Yepes, H, Ramón, P, Monzier, M, and Egred, J., 2005, Los peligros volcánicos asociados con el Tungurahua, 2nd edición, Serie: Los peligros volcánicos en el Ecuador. Corporación Editora Nacional, ISBN: 9978-84-402-3 (118 pp., in Spanish). [PDF online at http://horizon.documentation.ird.fr/exl doc/pleins_textes/divers11 12/010036187.pdf]

McCormick, B.T., M. Herzog, J. Yiang, M. Edmonds, T.A. Mather, S.A. Carn, S. Hidalgo, and B. Langmann (2013), An integrated study of SO2 emissions from Tungurahua volcano, Ecuador, Journal of Geophysical Research (under review).

Pretor Pinney, G., 2007, The Cloudspotter's Guide: The Science, History, and Culture of Clouds by Gavin, Penguin Group (USA).

Geologic Background. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano (Tungurahua III) was constructed. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 1701-2759, Quito, Ecuador; Jorge E. Bustillos A. (IG), Patricia A. Mothes (IG), and Buenos Aires and Washington Volcanic Ash Advisory Centers.

Atmospheric Effects

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

Atmospheric Effects (1980-1989)  Atmospheric Effects (1995-2001)

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements

Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


Additional Reports (database)

08/1997 (BGVN 22:08) False Report of Mount Pinokis Eruption

False report of volcanism intended to exclude would-be gold miners

12/1997 (BGVN 22:12) False Report of Somalia Eruption

Press reports of Somalia's first historical eruption were likely in error

11/1999 (BGVN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (BGVN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube



False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)


False report of volcanism intended to exclude would-be gold miners

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.


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


Press reports of Somalia's first historical eruption were likely in error

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.


False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

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.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

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 (see Caption) 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 (see Caption) 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 (see Caption) 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.


Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)


False report of activity; confusion caused by burning dung in a lava tube

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/).