The Mount Bromo pyroclastic cone within the Tengger Caldera erupts frequently, typically producing gas-and-steam plumes, ash plumes, and explosions (BGVN 44:05). Information compiled for the reporting period of May-July 2019 is from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

The eruptive activity at Tengger Caldera that began in mid-February continued through late July 2019, including white-and-brown ash plumes, ash emissions, and tremors. During the months of May through June 2019, white plumes rose between 50 to 600 m above the summit. Satellite imagery captured a small gas-and-steam plume from Bromo on 5 June (figure 18). Low-frequency tremors were recorded by a seismograph from May through July 2019.

Figure 18. Sentinel-2 satellite image showing a small gas-and-steam plume rising from the Bromo cone (center) in the Tengger Caldera on 5 June 2019. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

According to PVMBG and a Volcano Observatory Notice for Aviation (VONA), an ash eruption occurred on 19 July 2019; however, no ash column was observed due to weather conditions. A seismograph recorded five earthquakes and three shallow volcanic tremors the same day. In addition, rainfall triggered a lahar on the SW flank of Bromo.

On 28 July the Darwin VAAC reported that ash plumes originating from Bromo rose to a maximum altitude of about 3.9 km and drifted NW from the summit, based on webcam images and pilot reports. PVMBG reported that lower altitude ash plumes (2.4 km) on the same day were also recorded by webcam images, satellite imagery (Himawari-8), and weather models.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).

Large areas of floating pumice, termed rafts, were encountered by sailors in the northern Tonga region approximately 80 km NW of Vava'u starting around 9 August 2019; the pumice reached the western islands of Fiji by 9 October (figure 7). Pumice rafts are floating masses of individual clasts ranging from millimeters to meters in diameter. The pumice clasts form when silicic magma is degassing, forming bubbles as it rises to the surface, which then rapidly cools to form solid rock. The isolated vesicles formed by the bubbles provide buoyancy to the rock and in turn, the entire pumice raft. These rafts are spread and carried by currents across the ocean; rafts originating in the Tonga area can eventually reach Australia. This report summarizes the pumice raft eruption from early August 2019 using witness accounts and satellite images (acquisition dates are given in UTC). Pending further research, the presumed source is the unnamed Tongan seamount (volcano number 243091) about 45 km NW of Vava'u, the origin of an earlier pumice raft produced during an eruption in 2001.

Figure 7. The path of the pumice from the unnamed Tongan seamount from 9 August to 9 October 2019 based on eye-witness accounts and satellite data discussed below, as well as additional Aqua/MODIS satellite images from NASA Worldview. Blue Marble MODIS/NASA Earth Observatory base map courtesy of NASA Worldview.

The first sighting of pumice was around 1430 on 9 August NW of Vava'u in Tonga (18° 22.068' S, 174° 50.800' W), when Shannon Lenz and Tom Whitehead on board SV Finely Finished initially encountered isolated rocks and smaller streaks of pumice clasts. The area covered by rock increasing to a raft with an estimated thickness of at least 15 cm that extended to the horizon in different directions, and which took 6-8 hours to cross (figure 8). There was no sulfur smell and the sound was described as a "cement mixer, especially below deck." There was also no plume or incandescence observed. Their video, posted to YouTube on 17 August, showed a thin surface layer of cohesive interconnected irregular streaks of pumice with the ocean surface still visible between them. Later footage showed a continuous, undulating mass of pumice entirely covering the ocean surface. Larger clasts are visible scattered throughout the raft. The pumice raft was visible in satellite imagery on this day NW of Late Island (figure 9). By 11 August the raft had evolved into a largely linear feature with smaller rafts to the SW (figure 10). Approximately four hours later, about 15 km to the WSW, Rachel Mackie encountered the pumice. Initially the pumice was "ribbons several hundred meters long and up to 20m wide. It was quite fine and like a slick across the surface of the water." By 2130 they were surrounded by the pumice, and around 25 km away the smell of sulfur was noted.

Figure 8. The pumice raft from the unnamed Tongan seamount on 9 August 2019 taken by Shannon Lenz and Tom Whitehead on board SV Finely Finished. The photos show the pumice raft extending to the horizon in different directions. Scattered larger clasts protrude from the relatively smooth surface that entirely obscures the ocean surface. Courtesy of Shannon Lenz and Tom Whitehead via noonsite.

Figure 9. The pumice raft from the unnamed Tongan seamount on 9 August 2019 (UTC) can be seen NW of Late Island of Tonga in this Aqua/MODIS satellite image. The dashed white line encompasses the visible pumice. The location of the pumice in this image is shown in figure 7. Courtesy of NASA WorldView.

Figure 10. The Sentinel-2 satellite first imaged the pumice from the unnamed Tongan seamount on 11 August 2019 (UTC). This image indicates the pumice distribution with the main raft towards the W and the easternmost area of pumice approximately 45 km away. The eastern tip of the pumice area is located approximately 30 km WNW of Lake islands in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Michael and Larissa Hoult aboard the catamaran ROAM encountered the raft on 15 August (figure 11). They initially saw isolated clasts ranging from marble to tennis ball size (15-70 mm) at 18° 46′S, 174° 55'W. At around 0700 UTC (1900 local time) they noted the smell of sulfur at 18° 55′S, 175° 21′W, and by 0800 UTC they were immersed in the raft with visible clasts ranging from marble to basketball (25 cm) sizes. At this point the raft was entirely obscuring the ocean surface. On 16 and 21 August the pumice continued to disperse and drift NW (figures 12 and 13). On 20 August Scott Bryan calculated an average drift rate of around 13 km/day, with the pumice on this date about 164 km W of the unnamed seamount.

Figure 11. Images of pumice from the unnamed Tongan seamount encountered by Michael and Larissa Hoult aboard the catamaran Roam on 15 August. Left: Larissa takes photographs with scale of pumice clasts; top right: a closeup of a pumice clast showing the vesicle network preserving the degassing structures of the magma; bottom left: Michael holding several larger pumice clasts. The location of their encounter with the pumice is shown in figure 7. Courtesy of SailSurfROAM.

Figure 12. The pumice from the unnamed Tongan seamount (volcano number 243091) on 16 August 2019 UTC. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Figure 13. On 21 August 2019 (UTC) the pumice from the unnamed Tongan seamount (volcano number 243091) had drifted at least 120 km WNW of Late Island in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

An online article published by Brad Scott at GeoNet on 9 September reported the preliminary size of the raft to be 60 km2, significantly smaller than the 2012 Havre seamount pumice raft that was 400 km2. Satellite identification of pumice-covered areas by GNS scientists showed the material moving SSW through 14 August (figure 14).

Figure 14. A compilation of mapped pumice raft extents from 9 August (red line) through to 14 August (dark blue) from Suomi NPP, Terra, Aqua, and Sentinel-2 satellite images. The progression of the pumice raft is towards the SW. Courtesy of Salman Ashraf, GNS Science.

On 5 September the Maritime Safety Authority of Fiji (MSAF) issued a notice to mariners stating that the pumice was sighted in the vicinity of Lakeba, Oneata, and Aiwa Islands and was moving to the W. On 6 September a Planet Labs satellite image shows pumice encompassing the Fijian island of Lakeba over 450 km W of the Tongan islands (figure 15). The pumice entered the lagoon within the barrier reef and drifted around the island to continue towards the W. The pumice was imaged by the Landsat 8 satellite on 26 September as it moved through the Fijian islands, approximately 760 km away from its source (figure 16). The pumice is segmented into numerous smaller rafts of varying sizes that stretch over at least 140 km. On 12 September the Fiji Sun reported that the pumice had reached some of the Lau islands and was thick enough near the shore for people to stand on it.

Figure 15. Planet Labs satellite images show Lakeba Island to the E of the larger Viti Levu Island in the Fiji archipelago. The top image shows the island on 7 July 2019 prior to the pumice raft from the unnamed Tongan seamount. The bottom image shows pumice on the sea surface almost entirely encompassing the island on 6 September. The location of the pumice in this image is shown in figure 7. Courtesy of Planet Labs.

Figure 16. Landsat 8 satellite images show the visible extent of the unnamed seamount pumice on 26 September 2019 (UTC), up to approximately 760 km from the Tongan islands. The pumice seen here extends over a distance of 140 km. The top image shows the locations of the other three images in the white boxes, with a, b, and c indicating the locations. White arrows point to examples of the light brown pumice rafts in these images, seen through light cloud cover. The island in the lower right is Koro Island, the island to the lower left is Viti Levu, and the island to the top right is Vanua Levu. The location of the pumice in this image is shown in figure 7. Landsat 8 true color-pansharpened satellite images courtesy of Sentinel Hub.

Pumice had reached the Yasawa islands in western Fiji by 29 September and was beginning to fill the eastern bays (figure 17). By 9 October bays had been filled out to 500-600 m from the shore, and pumice had also passed through the islands to continue towards the W (figure 18). At this point the pumice beyond the islands had broken up into linear segments that continued towards the NW.

Figure 17. These Sentinel-2 satellite images show the pumice from the unnamed Tongan seamount drifting towards the Yasawa islands of Fiji. The 24 September 2019 (UTC) image shows the beaches without the pumice, the 29 September image shows pumice drifting westward towards the islands, and the 9 October image shows the bays partly filled with pumice out to a maximum of 500-600 m from the shore. These islands are approximately 850 km from the Tongan islands. The Yasawa islands coastline impacted by the pumice shown in these images stretches approximately 48 km. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Figure 18. This Sentinel-2 satellite image acquired on 9 October 2019 (UTC) shows expanses of pumice from the unnamed Tongan seamount that passed through the Yasawa islands of Fiji and was continuing NWW, seen in the center of the image. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Salman Ashraf, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Scott Bryan, School of Earth, Environmental & Biological Sciences, Science and Engineering Faculty, Queensland University of Technology, R Block Level 2, 204, Gardens Point (URL: https://staff.qut.edu.au/staff/scott.bryan); Shannon Lenz and Tom Whitehead, SV Finely Finished (URL: https://www.noonsite.com/news/south-pacific-tonga-to-fiji-navigation-alert-dangerous-slick-of-volcanic-rubble/, YouTube: https://www.youtube.com/watch?v=PEsHLSFFQhQ); Michael and Larissa Hoult, Sail Surf ROAM (URL: https://www.facebook.com/sailsurfroam/); Rachel Mackie, OLIVE (URL: http://www.oliveocean.com/, https://www.facebook.com/rachel.mackie.718); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Fiji Sun (URL: https://fijisun.com.fj/2019/09/12/pumice-menace-hits-parts-of-lau-group/).

The current eruptive period of Popocatépetl began on 9 January 2005 and it has since been producing frequent explosions accompanied by ash plumes, gas emissions, and ballistic ejecta that can impact several kilometers away from the crater, as well as dome growth and destruction. This activity continued through March-August 2019 with an increase in volcano alert level during 28 March-6 May. This report summarizes activity during this period and is based on information from Centro Nacional de Prevención de Desastres (CENAPRED), Universidad Nacional Autónoma de México (UNAM), and various webcam and remote sensing data.

An overflight on 28 February confirmed that dome 82, which was first observed on 14 February, was still present and was 200 m in diameter. During March there were 3,291 observed low-intensity emissions, and 33 larger explosions that produced ash plumes to a maximum height of 5 km, accompanied by near-continuous emission of water vapor and volcanic gases. Explosions ejected blocks that fell on the flanks out to 1.2-2 km on 1, 10, 13, 17, 26, 27, and 29 March. The events on the 17th and 27th resulted in vegetation fires. Frequent sulfur dioxide (SO₂) plumes were detected by TropOMI (figure 130). An overflight on 7 March showed intense degassing and an ash plume at 1142, preventing visibility into the crater (figure 131). On 13 March Strombolian activity was observed for approximately 15 minutes at 0500, accompanied by incandescent ejecta that deposited mainly on the ESE flank.

An overflight on 15 March was taken by CENAPRED and UNAM personnel to observe changes to the crater after explosions on the 13th and 14th. They reported that dome 82 had been destroyed and the crater maintained its previous dimensions of 300 m in diameter and 130 m deep. An explosion on the 27th ejected incandescent rocks out to 2 km from the crater and produced a 3-km-high ash plume that dispersed to the NE. Ashfall was reported in Santa Cruz, Atlixco, San Pedro, San Andrés, Santa Isabel Cholula, San Pedro Benito Juárez, and in the municipalities of Puebla, Hueyapan, Tetela del Volcán, and Morelos.

On 28 March an explosion at 0650 generated a 2.5-km-high ash plume and ejecta out to 1 km from the crater, and a 130-minute-long event produced gas and ah plumes (figure 132). On this day the volcano alert level was increased from Yellow Phase 2 to Yellow Phase 3. On the 29th an ash plume rose to 3 km and was accompanied by ejecta that reached 2 km away from the crater. Later that day a 20-minute-long event produced ash and gas. During a surveillance flight on 30 March a view into the crater showed no dome present, and the crater size had increased to 350 m in width and 250-300 m in depth after recent explosions (figure 131). On this day Strombolian activity was also observed lasting for 14 minutes, producing an ash plume to 800 m and ejecta out to 300 m from the crater. Incandescence at the crater was often seen during nighttime throughout the month.

Figure 130. Significant SO2 plumes at Popocatépetl detected by the TROPOMI instrument on the Sentinel-5P satellite during 3-11 March 2019. SO2 plumes are frequently observed and these images show examples of plume drift directions on 3 March 2019 (top left), 6 March 2019 (top right), 7 March 2019 (bottom left), and 11 March 2019 (bottom right). Date, time, and measurements are provided at the top of each image. Courtesy of NASA Goddard Flight Center.

Figure 131. Activity at Popocatépetl and views of the crater during surveillance flights in March 2019. The top images show an ash plume (left) and a gas-and-steam plume (right) on 7 March. On 30 March (bottom left and right) no lava dome was observed in the crater, which was measured to be 350 m in diameter and 250-300 m deep. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Figure 132. Explosive activity at Popocatépetl on 28 March 2019 producing ash plumes (top and bottom left) and ejecting incandescent ejecta out to 2 km from the crater at 1948. Courtesy of Carlos Sanchez/AFP (top), CENAPRED (bottom left and right), and Webcams de Mexico (bottom left).

There was a decrease in events during the next two months with 1,119 recorded low-intensity emissions and no larger ash explosions throughout April, followed by 1,210 low-intensity emissions and seven larger ash explosions through May (figure 133). Water vapor and volcanic gas emissions were frequently observed through this time and incandescence was observed some nights. A surveillance overflight on 26 April noted no new dome within the crater. On 6 May the alert level was lowered back to Yellow Phase 2. Another overflight on 9 May showed no change in the crater. An explosion at 1910 on 22 May produced an ash plume to 3.5 km above the crater with ashfall reported in Ozumba, Temamatla, Atlautla, Cocotitlán, Ayapango, Ecatzingo, Tenango del Aire and Tepetlixpa.

Figure 133. Graph showing the number of daily ash explosions and low-intensity emissions at Popocatépetl during March-August 2019. There was a decrease in the number of events during April and March, with an increase from March onwards. Data courtesy of CENAPRED.

Through the month of June there were 2,820 low-intensity emissions and 21 larger ash explosions recorded. Gas emissions were observed throughout the month. Two explosions on 3 June produced ash plumes up to 3.5 and 2.8 km, with ejecta out to 2 km S during the first explosion. On 11 June an explosion produced an ash plume to 1 km above the crater and ballistic ejecta out to 1 km E. Observers on a surveillance overflight on the 12th reported no changes within the crater

Explosions with estimated plume heights of 5 km occurred on the 14th and 15th, with the latter producing ashfall in the municipalities of San Pablo del Monte, Tenancingo, Papantla, San Cosme Mazatencocho, San Luis Teolocholco, Acuamanala, Nativitas, Tepetitla, Santa Apolonia Teacalco, Santa Isabel Tetlatlahuaca, and Huamantla, in the state of Tlaxcala, as well as in Nealtican, San Nicolás de los Ranchos, Calpan, San Pedro Cholula, Juan C. Bonilla, Coronango, Atoyatempan, and Coatzingo, in the state of Puebla.

On 17 June an explosion produced an ash plume that reached 8 km above the crater and dispersed towards the SW. An ash plume rising 2.5 km high was accompanied by incandescent ejecta impacting a short distance from the crater on the 21st, and another ash plume reached 2.5 km on the 22nd. Explosions on 26, 29, and 30 June resulted in ash plumes reaching 1.5 km above the crater and ballistic ejecta impacting on the flanks out to 1 km.

For the month of July there was an increased total of 5,637 recorded low-intensity emissions, and 173 larger ash explosions (figure 134). On 8 July an explosion produced ballistic ejecta out to 1.5 km and an ash plume up to 1 km above the crater. An ash plume up to 2.6 km was produced on the 12th. On 19 July a surveillance overflight observed a new dome (dome 83) with a diameter of 70 m and a thickness of 15 m (figure 135). Explosions on 20 July produced ashfall, and minor explosions that ejected incandescent ballistics onto the slopes. An event on the 24th produced an ash plume that reached 1.2 km, and ash plumes the following day reached 1 km. An overflight on 27 July confirmed that these explosions destroyed dome 83, and the crater dimensions remained the same (figure 136). The following day, ash plumes reached up to 1.6 km above the crater, and up to 2 km on the 29th. Minor ashfall was reported in the municipality of Ozumba on 30 June.

Figure 134. Examples of ash plumes at Popocatépetl on 1 July (top left), 18 July (top right and bottom left), and 30 July (bottom right) 2019. In the night time image taken on 18 July hot rocks are visible on the flank. Webcam images courtesy of CENAPRED and Webcams de Mexico.

Figure 135. A surveillance overflight at Popocatépetl on 19 July 2019 confirmed a new dome, dome number 83, with a width of 70 m and a thickness of 15 m. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Figure 136. Photos of the summit crater of Popocatépetl taken during a surveillance flight on 27 July 2019 confirmed that the 83rd lava dome was destroyed by recent explosions and the crater maintained the same dimensions as previously measured. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Throughout August the number of recorded events was higher than previous months, with 5,091 low-intensity emissions and 204 larger ash explosions (figure 137). Two explosions generated ash plumes and incandescent ejecta on 2 August, the first with a plume up to 1.5 km with ejecta impacting the slopes, and the second with an 800 m plume and ejecta landing back in the crater. Ashfall from the events was reported in in the municipalities of Tenango del Aire, Ayapango and Amecameca. On the 14th ashfall was reported in Juchitepec, Ayapango, and Ozumba. Explosions on 16 August produced ash plumes up to 2 km that dispersed to the WSW. Over the following two days ash plumes reached 1.2 km and resulted in ashfall in Cuernavaca, Tepoztlán, Tlalnepantla, Morelos, Ozumba, and Ecatzingo. Over 30-31 August ash plumes reached between 1-2 km above the crater and ashfall was reported in Amecameca, Atlautla, Ozumba, and Tlalmanalco. Incandescence was sometimes observed at the crater through the month.

Figure 137. Ash plumes at Popocatépetl on 7 August (top) and 26 August 2019 (bottom). Courtesy of CENAPRED and Webcams de Mexico.

The MODVOLC algorithm for MODIS thermal anomalies registered thermal alerts through this period, with 22 in March, three in May, five in July, and one in August. The MIROVA system showed that the frequency of thermal anomalies at Popocatépetl was higher in March, sporadic in April and May, low in June, and had increased again in July and August (figure 138). Elevated temperatures were frequently visible in Sentinel-2 thermal satellite data when clouds and plumes were not covering the crater (figure 139).

Figure 138. Thermal activity at Popocatépetl detected by the MIROVA system showed frequent anomalies in March, intermittent anomalies through April-May, low activity in June, and an increase in July-August 2019. Courtesy of MIROVA.

Figure 139. Sentinel-2 thermal satellite images frequently showed elevated temperatures in the crater of Popocatépetl during March-August 2019, as seen in this representative image from 7 May 2019. Sentinel2- atmospheric penetration (bands 12, 11, 8A) scene courtesy of Sentinel Hub Playground.

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

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/); Universidad Nacional Autónoma de México (UNAM), University City, 04510 Mexico City, Mexico (URL: https://www.unam.mx/); 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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Webcams de Mexico (URL: http://www.webcamsdemexico.com/); Agence France-Presse (URL: http://www.afp.com/).

The ongoing eruption at Semeru weakened in intensity during 2018, with occasional ash plumes and thermal anomalies (BGVN 44:04); this reduced but ongoing level of activity continued through August 2019. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC). The current report summarizes activity from 1 March to 31 August 2019. The Alert Level remained at 2 (on a scale from 1-4); the public was warned to stay 1 km away from the active crater and 4 km away on the SSE flank.

Based on analysis of satellite images, the Darwin VAAC reported that ash plumes rose to an altitude of 4-4.3 km on 19 April, 20 June, 10 July, and 13 July, drifting in various directions. In addition, PVMBG reported that at 0830 on 26 June an explosion produced an ash plume that rose around 600 m above the summit and drifted SW. A news article (Tempo.com) dated 12 August cited PVMBG as stating that the volcano had erupted 17 times since 8 August.

During March-August 2019 thermal anomalies were detected with the MODIS satellite instruments analyzed using the MODVOLC algorithm only on 5 July and 22 August. No explosions were recorded on those two days. Scattered thermal anomalies within 5 km of the volcano were detected by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system, also based on analysis of MODIS data: one at the end of March and 3-6 hotspots over the following months, almost all of low radiative power. Satellite imagery intermittently showed thermal activity in the Jonggring-Seloko crater (figure 37), sometimes with material moving down the SE-flank ravine.

Figure 37. Sentinel-2 satellite images showing the persistent elevated thermal anomaly in the Jonggring-Seloko crater of Semeru were common through August 2019, as seen in this view on 20 July. Hot material could sometimes be identified in the SE-flank ravine. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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); Tempo.com (URL: https://www.tempo.com/).

Historical observations of eruptive activity from the glacier-covered Mount Michael stratovolcano on Saunders Island in the South Sandwich Islands were not recorded until the early 19th century at this remote site in the southernmost Atlantic Ocean, and remain extremely rare. With the advent of satellite observation technology, indications of more frequent eruptive activity have become apparent. Vapor emission is frequently reported from the summit crater, and AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater (Lachlan-Cope and others, 2001). Limited thermal anomaly data and satellite imagery indicated at least intermittent activity during May 2000-November 2013, and from November 2014 through April 2018 (Gray and others, 2019). Ongoing observations, including photographs from two site visits in February and May 2019 suggest continued activity at the summit during most months through May 2019, the period covered in this report. Information, in addition to on-site photographs, comes from MIROVA thermal anomaly data, NASA SO₂ instruments, and Sentinel-2 and Landsat satellite imagery.

Near-constant cloud coverage for much of the year makes satellite data intermittent and creates difficulty in interpreting the ongoing nature of the activity. Gray and others (2019) concluded recently after a detailed study of shortwave and infrared satellite images that there was continued evidence for the previously identified lava lake on Mount Michael since January 1989. MIROVA thermal anomaly data suggest intermittent pulses of thermal energy in September, November, and December 2018, and April 2019 (figure 17). Satellite imagery confirmed some type of activity, either a dense steam plume, evidence of ash, or a thermal anomaly, each month during December 2018-March 2019. Sulfur dioxide anomalies were recorded in January, February, and March 2019. Photographic evidence of fresh ash was captured in February 2019, and images from May 2019 showed dense steam rising from the summit crater.

Figure 17. MIROVA thermal anomaly data from 19 September 2018 through June 2019 showed sporadic, low-level pulses of thermal energy in late September, November, and December 2018, and April 2019. Courtesy of MIROVA.

After satellite imagery and thermal anomaly data in late September 2018 showed evidence for eruptive activity (BGVN 43:10, figure 16), a single thermal anomaly in MIROVA data was recorded in mid-November 2018 (figure 17). A rare, clear Sentinel-2 image on 2 December revealed a dense steam plume over the active summit crater; the steam obscured the presence of any possible thermal anomalies beneath (figure 18).

Figure 18. Sentinel-2 images of Mount Michael on Saunders Island on 2 December 2018 revealed a dense steam plume over the summit crater that was difficult to distinguish from the surrounding snow in Natural Color rendering (bands 4,3,2) (left), but was clearly visible in Atmospheric Penetration rendering (bands 12,11, 8a) (right). Courtesy of Sentinel Hub Playground.

Clear evidence of recent activity appeared on 1 January 2019 with both a thermal anomaly at the summit crater and a streak of ash on the snow (figure 19). Steam was also present within the summit crater. A distinct SO₂ anomaly appeared in data from the TROPOMI instrument on 14 January (figure 20).

Figure 19. A thermal anomaly and dense steam were recorded at the summit of Mount Michael on Saunders Island on 1 January 2019 in Sentinel-2 Satellite imagery with Atmospheric Penetration rendering (bands 12, 11, 8a) (left). The same image shown with Natural Color rendering (bands 4,3,2) (right) shows a recent streak of brown particulates drifting SE from the summit crater. Courtesy of Sentinel Hub Playground.

Figure 20. A distinct SO2 plume was recorded drifting NW from Saunders Island by the TROPOMI instrument on the Sentinel 5-P satellite on 14 January 2019. Courtesy of NASA Goddard Space Flight Center.

Multiple sources of satellite data and sea-based visual observation confirmed activity during February 2019. SO₂ emissions were recorded with the TROPOMI instrument on 10, 11, 15, and 16 February (figure 21). A Landsat image from 10 February showed a dense steam plume drifting NW from the summit crater, with the dark rim of the summit crater well exposed (figure 22). Sentinel-2 images in natural color and atmospheric penetration renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February (figure 23). An expedition to the South Sandwich Islands between 15 February and 8 March 2019 sponsored by the UK government sailed by Saunders in late February and observed a stream of ash on the NNE flank beneath the cloud cover (figure 24).

Figure 21. Faint but distinct SO2 plumes were recorded drifting away from Saunders Island in various directions on 10, 11, 15, and 16 February 2019. Courtesy of NASA Goddard Space Flight Center.

Figure 22. The dark summit crater of Mount Michael on Saunders Island was visible in Landsat imagery on 10 February 2019. A dense steam plume drifted NW and cast a dark shadow on the underlying cloud cover. Courtesy of Sentinel Hub Playground.

Figure 23. At the summit of Mount Michael on Saunders Island, Sentinel-2 images in Natural Color (bands 4,3,2) (left) and Atmospheric Penetration (bands 12, 11, 8a) (right) renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February 2019. Courtesy of Sentinel Hub Playground.

Figure 24. Recent ash covered the NNE flank of Mount Michael on Saunders Island in late February 2019 when observed by an expedition to the South Sandwich Islands sponsored by the UK government. Courtesy of Chris Darby.

Faint SO₂ emissions were recorded twice during March 2019 (figure 25), and a dense steam plume near the summit crater was visible in Landsat imagery on 23 March (figure 26). Two thermal anomalies were captured in the MIROVA data during April 2019 (figure 17).

Figure 25. Faint SO2 plumes were recorded on 1 and 11 March 2019 emerging from Saunders Island. Courtesy of NASA Goddard Space Flight Center.

Figure 26. A dense steam plume drifted E from the summit crater of Mount Michael at Saunders Island on 25 March 2019. Landsat-8 image courtesy of Sentinel Hub Playground.

A volcano-related research project "SSIVOLC" explored the South Sandwich Islands volcanoes during 15 April-31 May 2019. A major aim of SSIVOLC was to collect photogrammetric data of the glacier-covered Mount Michael (Derrien and others, 2019). A number of still images were acquired on 17 and 22 May 2019 showing various features of the island (figures 27-30). The researchers visually observed brief, recurrent, and very weak glow at the summit of Mount Michael after dark on 17 May, which they interpreted as reflecting light from an active lava lake within the summit crater.

Figure 27. The steep slopes of an older eroded crater on the E end of Saunders island in the 'Ashen Hills' shows layers of volcanic deposits dipping away from the open half crater. In the background, steam and gas flow out of the summit crater of Mount Michael and drift down the far slope. Drone image PA-IS-03 taken during 17-22 May 2019, courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

Figure 28. A dense steam plume drifts away from the summit of Mount Michael on Saunders Island in this drone image taken during 17-22 May 2019. The older summit crater is to the left of the dark patch in the middle of the summit. North is to the right. Image SU-3 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

Figure 29. This close-up image of the summit of Mount Michael on Saunders Island shows steam plumes billowing from the summit crater, and large crevasses in the glacier covered flank, taken during 17-22 May 2019. The old crater is to the left. Image TL-SU-1 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

Figure 30. A dense plume of steam rises from the summit crater of Mount Michael on Saunders Island and drifts over mounds of frozen material during 17-22 May 2019. The older crater is to the left, and part of the Ashen Hills is in the foreground. Image TL-SU-2 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

References: Lachlan-Cope T, Smellie J L, Ladkin R, 2001. Discovery of a recurrent lava lake on Saunders Island (South Sandwich Islands) using AVHRR imagery. J. Volcanol. Geotherm. Res., 112: 105-116.

Gray D M, Burton-Johnson A, Fretwell P T, 2019. Evidence for a lava lake on Mt. Michael volcano, Saunders Island (South Sandwich Islands) from Landsat, Sentinel-2 and ASTER satellite imagery. J. Volcanol. Geotherm. Res., 379:60-71. https://doi.org/10.1016/j.volgeores.2019.05.002.

Derrien A, Richter N, Meschede M, Walter T, 2019. Optical DSLR camera- and UAV footage of the remote Mount Michael Volcano, Saunders Island (South Sandwich Islands), acquired in May 2019. GFZ Data Services. http://doi.org/10.5880/GFZ.2.1..2019.003

Geologic Background. Saunders Island is a volcanic structure consisting of a large central edifice intersected by two seamount chains, as shown by bathymetric mapping (Leat et al., 2013). The young constructional Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Vapor emission is frequently reported from the summit crater. Recent AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater.

Information Contacts: 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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Chris Darby (URL: https://twitter.com/ChrisDDarby, image at https://twitter.com/ChrisDDarby/status/1100686838568812544).

Pacaya is one of the most active volcanoes in Guatemala, with activity largely consisting of frequent lava flows and Strombolian activity at the Mackenney crater. This report summarizes continued activity during February through July 2019 based on reports by Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) and Sistema de la Coordinadora Nacional para la Reducción de Desastres (CONRED), visiting scientists, and satellite data.

At the beginning of February activity included Strombolian explosions ejecting material up to 5 to 30 m above the Mackenney crater and a degassing plume up to 300 m. Multiple lava flows were observed throughout the month on the N, NW, and W flanks, reaching 350 m from the crater and resulting in avalanches from the flow fronts. Strombolian activity continued with sporadic to continuous explosions ejecting material 5-75 m above the Mackenney crater. Degassing produced plumes up to 300 m above the crater, and incandescence from the crater and lava flows were seen at night. Daniel Sturgess of Bristol University observed activity on the 24th, noting a 70-m-long lava flow with individual blocks from the front of the flow rolling down the flanks (figure 108). He reported that mild Strombolian explosions occurred every 10-20 minutes and ejected blocks, up to approximately 4 m in diameter, as high as 5-30 m above the crater and towards the northern flank.

Figure 108. An active lava flow on the NW flank of Pacaya on 24 February 2019 with incandescence visible in lower light conditions. Courtesy of Daniel Sturgess, University of Bristol.

Similar activity continued through March with multiple lava flows reaching a maximum of 200 m N and NW, and avalanches descending from the flow fronts. Ongoing Strombolian explosions expelled material up to 75 m above the Mackenney crater. Degassing produced a white-blue plume to a maximum of 900 m above the crater (figure 109) and incandescence was noted some nights.

Figure 109. A degassing plume at Pacaya reaching 350 m above the crater and dispersing to the S on 19 March 2019. Courtesy of CONRED.

During April lava flows continued on the N and NW flanks, reaching a maximum length of 300 m, with avalanches forming from the flow fronts. Degassing formed plumes up to 600 m above the crater that dispersed with various wind directions. Strombolian activity continued with explosions ejecting material up to 40 m above the crater. On the 2nd and 3rd weak rumbles were heard at distances of 4-5 km. Similar activity continued through May with lava flows reaching 300 m to the N, degassing producing plumes up to 600 m above the crater, and Strombolian explosions ejecting material up to 15 m above the crater.

Lava flows continued out to 300 m in length to the N and NW during June (figures 110 and 111). Strombolian activity ejected material up to 30 m above the crater and degassing resulted in plumes that reached 300 m. During July there were multiple active lava flows that reached a maximum of 300 m in length on the N and NW flanks (figure 112). Avalanches generated by the collapse of material at the front of the lava flows were accompanied by explosions ejecting material up to 30 m above the crater.

Figure 110. An active lava flow on Pacaya on 9 June 2019 with incandescent blocks rolling down the flank from the flow front. Courtesy of Paul Wallace, University of Liverpool.

Figure 111. Activity at Pacaya on 22 June 2019 with a degassing plume dispersed to the W and a 300-m-long lava flow. Photos by Miguel Morales, courtesy of CONRED.

Figure 112. Two lava flows were active to the N and NW at Pacaya on 20 July 2019. Photos courtesy of CONRED.

During February through July multiple lava flows and crater activity were detected in Sentinel-2 satellite thermal images (figures 113 and 114) and relatively constant thermal energy was detected by the MIROVA system with a slight decrease in the energy and frequency of anomalies during June (figure 115). The thermal anomalies detected by the MODVOLC system for each month from February through July spanned 6-30, with six during June and 30 during April.

Figure 113. Sentinel-2 thermal satellite images of Pacaya show lava flows to the N and NW during February through April 2019. There was a reduction in visible activity in early March. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 114. Sentinel-2 thermal satellite images of Pacaya showing lava flow and hot avalanche activity during June and July 2019. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 115. MIROVA log radiative power plot of MODIS thermal infrared at Pacaya during October 2018 through July 2019. Detected thermal energy is relatively stable with a decrease through June and subsequent increase during July. 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/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); 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/); Daniel Sturgess, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom (URL: http://www.bristol.ac.uk/earthsciences/); Paul Wallace, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, 4 Brownlow Street, Liverpool L69 3GP, United Kingdom (URL: https://www.liverpool.ac.uk/environmental-sciences/staff/paul-wallace/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Frequent historical eruptions at Volcán de Colima date back to the 16th century and include explosive activity, lava flows, and large debris avalanches. The most recent eruptive episode began in January 2013 and continued through March 2017. Previous reports have covered activity involving ash plumes with extensive ashfall, lava flows, lahars, and pyroclastic flows (BGVN 41:01 and 42:08). In late April 2019, increased seismicity related to volcanic activity began again. This report covers activity through July 2019. The primary source of information was the Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC).

On 11 May 2019, CUEIV-UdC reported an explosion that was recorded by several monitoring stations. A thermal camera located south of Colima captured thermal anomalies associated with the explosion as well as intermittent degassing, which mainly consisted of water vapor (figure 131). A report from the Unidad Estatal de Protección Civil de Colima (UEPCC), and seismic and infrasound network data from CUEIV-UdC, recorded about 60 high-frequency events, 16 landslides, and 14 low-magnitude explosions occurring on the NE side of the crater during 11-24 May. Drone imagery showed fumarolic activity occurring on the inner wall of this crater on 22 May (figure 132).

Figure 131. Gas emissions from Colima during the 11 May 2019 eruption as seen from the Naranjal station. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 17 mayo 2019 no 121).

Figure 132. A drone photo showing fumarolic activity occurring within the NE wall of the crater at Colima on 22 May 2019. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 24 mayo 2019 no 122).

Small explosions and gas-and-steam emissions continued intermittently through mid-July 2019 concentrated on the NE side of the crater. An overflight on 9 July 2019 revealed that subsidence from the consistent activity slightly increased the diameter of the vent; other areas within the crater also showed evidence of subsidence and some collapsed material on the outer W wall (figure 133). During the weeks of 19 and 26 July 2019, monitoring cameras and seismic data recorded eight lahars.

Figure 133. A drone photo of the crater at Colima on 8 July 2019 shows continuing fumarolic activity and evidence of a collapsed wall on the W exterior side. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 12 julio 2019 no 129).

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC), Colima, Col. 28045, Mexico; Centro Universitario de Estudios Vulcanologicos y Facultad de Ciencias de la Universidad de Colima, Avenida Universidad 333, Colima, Col. 28045, Mexico (URL: http://portal.ucol.mx/cueiv/); Unidad Estatal de Protección Civil, Colima, Roberto Esperón No. 1170 Col. de los Trabajadores, C.P. 28020, Mexico (URL: http://www.proteccioncivil.col.gob.mx/).

Masaya, in Nicaragua, contains a lava lake found in the Santiago Crater which has remained active since its return in December 2015 (BGVN 41:08). In addition to this lava lake, previous volcanism included explosive eruptions, lava flows, and gas emissions. Activity generally decreased during March-July 2019, including the number and frequency of thermal anomalies, lava lake levels, and gas emissions. The primary source of information for this report comes from the Instituto Nicareguense de Estudios Territoriales (INETER).

On 21 July 2019 a small explosion in the Santiago Crater resulted in some gas emissions and an ash cloud drifting WNW. In addition to the active lava lake (figure 77), monthly reports from INETER noted that thermal activity and gas emissions (figure 78) were decreasing.

Figure 77. Active lava lake visible in the Santiago Crater at Masaya on 27 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

Figure 78. Gas emissions coming from the Santiago Crater at Masaya on 29 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

On 15 May and 22 July 2019, INETER scientists used a FLIR SC620 thermal infrared camera to measure temperatures of fumaroles on the Santiago Crater. In May 2019 the temperature of fumaroles had decreased by 48°C since the previous month. Between May and July 2019 fumarole temperatures continued to decline; temperatures ranged from 90° to 136°C (figure 79). Compared to May 2019 these temperatures are 3°C lower. INETER reports that the level of the lava lake has been slowly dropping during this reporting period.

Figure 79. FLIR (forward-looking infrared) and visible images of the Santiago Crater at Masaya showing fumarole temperatures ranging from 90° to 136°C. The scale in the center shows the range of temperatures in the FLIR image. Courtesy of INETER (March 2019 report).

According to MIROVA (Middle InfraRed Observation of Volcanic Activity) data from MODIS satellite instruments, frequent thermal anomalies were recorded from mid-March through early May 2019, with little to no activity from mid-May to July 2019 (figure 80). Sentinel-2 thermal images show high temperatures in the active lava lake on 10 March 2019 (figure 81). Thermal energy detected by the MODVOLC algorithm showed 14 hotspot pixels with the most number of hotspots (7) occurring in March 2019.

Figure 80. Thermal anomalies were relatively constant at Masaya from early September 2018 through early May 2019 and then abruptly decreased until mid-June 2019 as recorded by MIROVA. Courtesy of MIROVA.

Figure 81. Sentinel-2 thermal satellite image showing a detected heat signature from the active lava lake at Masaya on 10 March 2019. The lava lake is visible (bright yellow-orange). Approximate diameter of the crater containing the lava lake is 500 m. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is 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 twin volcanoes of Nindirí and Masaya, 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 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. 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 cause 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/); 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); Sheila DeForest (URL: https://www.facebook.com/sheila.deforest).

The acid lake of Rincón de la Vieja's active crater has generated intermittent weak phreatic explosions regularly since 2011, continuing during the past year through at least August 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 4 March and 2 September 2019. Clouds often prevented webcam and satellite views. The current report describes activity from March through July 2019.

OVSICORI-UNA reported that weak events occurred on 19 March at 1851 and on 29 March 2019 at 2043. A two-minute-long phreatic explosion on 1 April at 0802 produced a plume that rose 600 m above the crater rim. Continuous emissions were visible during 3-4 April, rising 200 m above the crater rim. On 3 April, at 1437, a small explosion was detected. An explosion on 10 April at 0617 produced a gas-and-steam plume that rose 1 km above the crater rim and drifted SE. On 12 April at 0643, a plume rose 500 m. Another event took place at 0700 on 13 April, although poor weather conditions prevented visual observations. On 14 April, OVSICORI-UNA noted that aerial photographs showed a milky-gray acid lake at a relatively low water level with convection cells of several tens meters of diameter in the center and eastern parts of the lake.

According to an OVSICORI-UNA bulletin, a small phreatic explosion occurred on 1 May. Another explosion on 11 May at 0720 produced a white gas-and-steam plume that rose 600 m above the crater rim. Phreatic explosions were recorded on 14 May at 1703 and on 17 May at 0357, though dense fog prevented visual confirmation of both events with webcams. On 15 May a local observer noted a diffuse plume of steam and gas, material rising from the crater, and photographed milky-gray deposits on the N part of the crater rim ejected from the event the day before. A major explosion occurred on 24 May.

OVSICORI-UNA recorded a significant phreatic 10-minute-long explosion that began on 11 June at 0343, but plumes were not visible due to weather conditions. No further phreatic events were reported in July.

Seismic activity was very low during the reporting period, and there was no significant deformation. Short tremors were frequent toward the end of April, but were only periodic in May and June; tremor almost disappeared in July. A few long-period earthquakes were recorded, and volcano-tectonic earthquakes were even less frequent.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/, https://www.facebook.com/OVSICORI/).

Sakurajima rises from Kagoshima Bay, which fills the Aira Caldera near the southern tip of Japan's Kyushu Island. Frequent explosive and occasional effusive activity has been ongoing for centuries. The Minamidake summit cone has been the location of persistent activity since 1955; the Showa crater on its E flank has also been intermittently active since 2006. Numerous explosions and ash-bearing emissions have been occurring each month at either Minamidake or Showa crater since the latest eruptive episode began in late March 2017. This report covers ongoing activity from January through June 2019; the Japan Meteorological Agency (JMA) provides regular reports on activity, and the Tokyo VAAC (Volcanic Ash Advisory Center) issues tens of reports each month about the frequent ash plumes.

From January to June 2019, ash plumes and explosions were usually reported multiple times each week. The quietest month was June with only five eruptive events; the most active was March with 29 (table 21). Ash plumes rose from a few hundred meters to 3,500 m above the summit during the period. Large blocks of incandescent ejecta traveled as far as 1,700 m from the Minamidake crater during explosions in February and April. All the activity originated in the Minamidake crater; the adjacent Showa crater only had a mild thermal anomaly and fumarole throughout the period. Satellite imagery identified thermal anomalies inside the Minamidake crater several times each month.

Table 21. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater in Aira caldera, January-June 2019. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Data courtesy of JMA (January to June 2019 monthly reports).

There were eight eruptive events reported by JMA during January 2019 at the Minamidake summit crater of Sakurajima. They occurred on 3, 6, 7, 9, 17, and 19 January (figure 76). Ash plume heights ranged from 600 to 2,100 m above the summit. The largest explosion, on 9 January, generated an ash plume that rose 2,100 m above the summit crater and drifted E. In addition, incandescent ejecta was sent 800-1,100 m from the summit. Incandescence was visible at the summit on most clear nights. During an overflight on 18 January no significant changes were noted at the crater (figure 77). Infrared thermal imaging done on 29 January indicated a weak thermal anomaly in the vicinity of the Showa crater on the SE side of Minamidake crater. The Kagoshima Regional Meteorological Observatory (KRMO) (11 km WSW) recorded ashfall there during four days of the month. Satellite imagery indicated thermal anomalies inside Minamidake on 7 and 27 January (figure 77).

Figure 76. Incandescent ejecta and ash emissions characterized activity from Sakurajima volcano at Aira during January 2019. Left: A webcam image showed incandescent ejecta on the flanks on 9 January 2019, courtesy of JMA (Explanation of volcanic activity in Sakurajima, January 2019). Right: An ash plume rose hundreds of meters above the summit, likely also on 9 January, posted on 10 January 2019, courtesy of Mike Day.

Figure 77. The summit of Sakurajima consists of the larger Minamidake crater and the smaller Showa crater on the E flank. Left: The Minamidake crater at the summit of Sakurajima volcano at Aira on 18 January 2019 seen in an overflight courtesy of JMA (Explanation of volcanic activity in Sakurajima, March 2019). Right: Two areas of thermal anomaly were visible in Sentinel-2 satellite imagery on 27 January 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

Activity increased during February 2019, with 15 eruptive events reported on days 1, 3, 7, 8, 10, 13, 14, 17, 22, 24, and 27. Ash plume heights ranged from 600-2,300 m above the summit, and ejecta was reported 300 to 1,700 m from the crater in various events (figure 78). KRMO reported two days of ashfall during February. Satellite imagery identified thermal anomalies at the crater on 6 and 26 February, and ash plumes on 21 and 26 February (figure 79).

Figure 78. An explosion from Sakurajima at Aira on 7 February 2019 sent ejecta up to 1,700 m from the Minamidake summit crater. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, February 2019).

Figure 79. Thermal anomalies and ash emissions were captured in Sentinel-2 satellite imagery on 6, 21, and 26 February 2019 originating from Sakurajima volcano at Aira. Top: Thermal anomalies within the summit crater were visible underneath steam and ash plumes on 6 and 26 February (closeup of bottom right photo). Bottom: Ash emissions on 21 and 26 February drifted SE from the volcano. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

The number of eruptive events continued to increase during March 2019; there were 29 events reported on numerous days (figures 80 and 81). An explosion on 14 March produced an ash plume that rose 3,500 m above the summit and drifted E. It also produced ejecta that landed 800-1,100 m from the crater. During an overflight on 26 March a fumarole was the only activity in Showa crater. KRMO reported 14 days of ashfall during the month. Satellite imagery identified an ash plume on 13 March and a thermal anomaly on 18 March (figure 82).

Figure 80. A large ash emission from Sakurajima volcano at Aira was photographed by a tourist on the W flank and posted on 1 March 2019. Courtesy of Kratü.

Figure 81. An ash plume from Sakurajima volcano at Aira on 18 March 2019 produced enough ashfall to disrupt the trains in the nearby city of Kagoshima according to the photographer. Image taken from about 20 km away. Courtesy of Tim Board.

Figure 82. An ash plume drifted SE from the summit of Sakurajima volcano at Aira on 13 March (left) and a thermal anomaly was visible inside the Minamidake crater on 18 March 2019 (right). "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

A decline in activity to only ten eruptive events on days 7, 13, 17, 22, and 25 was reported by JMA for April 2019. An explosion on 7 April sent ejecta up to 1,700 m from the crater. Another explosion on 13 April produced an ash plume that rose 2,200 m above the summit. Most of the eruptive events at Sakurajima last for less than 30 minutes; on 22 April two events lasted for almost an hour each producing ash plumes that rose 1,400 m above the summit. Ashfall at KRMO was reported during seven days in April. Two distinct thermal anomalies were visible inside the Minamidake crater on both 12 and 27 April (figure 83).

Figure 83. Two thermal anomalies were present inside Minamidake crater at the summit of Sakurajima volcano at Aira on 12 (left) and 27 (right) April 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

There were 15 eruptive events during May 2019. An event that lasted for two hours on 12 May produced an ash plume that rose 2,900 m from the summit and drifted NE (figure 84). The Meteorological Observatory reported 14 days with ashfall during the month. Two thermal anomalies were present in satellite imagery in the Minamidake crater on both 17 and 22 May.

Figure 84. An ash plume rose 2,900 m above the summit of Sakurajima at Aira on 12 May 2019 (left); incandescent ejecta went 1,300 m from the summit crater on 13 May. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, May 2019).

During June 2019 five eruptive events were reported, on 11, 13, and 24 June; the event on 11 June lasted for almost two hours, sent ash 2,200 m above the summit, and produced ejecta that landed up to 1,100 m from the crater (figure 85). Five days of ashfall were reported by KRMO.

Figure 85. A large ash plume on 11 June 2019 rose 2,200 m above the summit of Sakurajima volcano at Aira. Courtesy of Aone Wakatsuki.

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

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); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Mike Day, Minnesota, Twitter (URL: https://twitter.com/MikeDaySMM, photo at https://twitter.com/MikeDaySMM/status/1083489400451989505/photo/1); Kratü, Twitter (URL: https://twitter.com/TalesOfKratue, photo at https://twitter.com/TalesOfKratue/status/1101469595414589441/photo/1); Tim Board, Japan, Twitter (URL: https://twitter.com/Hawkworld_, photo at https://twitter.com/Hawkworld_/status/1107789108754038789); Aone Wakatsuke, Twitter (URL: https://twitter.com/AoneWakatsuki, photo at https://twitter.com/AoneWakatsuki/status/1138420031258210305/photo/3).

After a large, deadly explosive and effusive eruption during 1963-64, Indonesia's Mount Agung on Bali remained quiet until a new eruption began in November 2017 (BGVN 43:01). Lava emerged into the summit crater at the end of November and intermittent ash plumes rose as high as 3 km above the summit through the end of the year. Activity continued throughout 2018 with explosions that produced ash plumes rising multiple kilometers above the summit, and the slow effusion of the lava within the summit crater (BGVN 43:08, 44:02). Information about the ongoing eruptive episode comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and multiple sources of satellite data. This report covers the ongoing eruption from February through May 2019.

Intermittent but increasingly frequent and intense explosions with ash emissions and incandescent ejecta characterized activity at Agung during February through May 2019. During February, explosions were reported three times; events on seven days in March were documented with ash plumes and ashfall in surrounding villages. Five significant events occurred during April; two involved incandescent ejecta that traveled several kilometers from the summit, and ashfall tens of kilometers from the volcano. Most of the five significant events reported in May involved incandescent ejecta and ashfall in adjacent villages; air traffic was disrupted during the 24 May event. Ash plumes in May reached altitudes over 7 km multiple times. Thermal activity increased steadily during the period, according to both the MIROVA project (figure 44) and MODVOLC thermal alert data. MAGMA Indonesia reported at the end of May 2019 that the volume of lava within the summit crater remained at about 25 million m³; satellite information indicated continued thermal activity within the crater. Alert Level III (of four levels) remained in effect throughout the period with a 4 km exclusion radius around the volcano.

Figure 44. Thermal activity at Agung from 4 September 2018 through May 2019 was variable. The increasing frequency and intensity of thermal events was apparent from February-May. Courtesy of MIROVA.

Steam plumes rose 30-300 m high daily during February 2019. The Agung Volcano Observatory (AVO) and PVMBG issued a VONA on 7 February (UTC) reporting an ash plume, although it was not visible due to meteoric cloud cover. Incandescence, however, was observed at the summit from webcams in both Rendang and Karangasem City (16 km SE). The seismic event associated with the explosion lasted for 97 seconds. A similar event on 13 February was also obscured by clouds but produced a seismic event that lasted for 3 minutes and 40 seconds, and ashfall was reported in the village of Bugbug, about 20 km SE. On 22 February a gray ash plume rose 700 m from the summit during a seismic event that lasted for 6 minutes and 20 seconds (figure 45). The Darwin VAAC reported the plume visible in satellite imagery moving W at 4.3 km altitude. It dissipated after a few hours, but a hotspot remained visible about 10 hours later.

Figure 45. An ash plume rose from the summit of Agung on 22 February 2019, viewed from the Besakih temple, 7 km SW of the summit. Courtesy of PunapiBali.

Persistent steam plumes rose 50-500 m from the summit during March 2019. An explosion on 4 March was recorded for just under three minutes and produced ashfall in Besakih (7 km SW); no ash plume was observed due to fog. A short-lived ash plume rose to 3.7 km altitude and drifted SE on 8 March (UTC) 2019. The seismic event lasted for just under 4 minutes. Ash emissions were reported on 15 and 17 March to 4.3 and 3.7 km altitude, respectively, drifting W (figure 46). Ashfall from the 15 March event spread NNW and was reported in the villages of Kubu (6 km N), Tianyar (14 km NNW), Ban, Kadundung, and Sukadana. MAGMA Indonesia noted that two explosions on the morning of 17 March (local time) produced gray plumes; the first sent a plume to 500 m above the summit drifting E and lasted for about 40 seconds, while the second plume a few hours later rose 600 m above the crater and lasted for 1 minute and 16 seconds. On 18 March an ash plume rose 1 km and drifted W and NW. An event on 20 March was measured only seismically by PVMBG because fog prevented observations. An eruption on 28 March produced an ash plume 2 km high that drifted W and NW. The seismic signal for this event lasted for about two and a half minutes. The Darwin VAAC reported the ash plume at 5.5 km altitude, dissipating quickly to the NW. No ash was visible four hours later, but a thermal anomaly remained at the summit (figure 47). Ashfall was reported in nearby villages.

Figure 46. Ash plumes from Agung on 15 (left) and 17 (right) March 2019 resulted in ashfall in communities 10-20 km from the volcano. Courtesy of PVMBG and MAGMA Indonesia (Information on G. Agung Eruption, 15 March 2019 and Gunung Agung Eruption Press Release March 17, 2019).

Figure 47. A thermal anomaly was visible through thick cloud cover at the summit of Agung on 29 March 2019 less than 24 hours after a gray ash plume was reported 2,000 m above the summit. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

The first explosion of April 2019 occurred on the 3rd (UTC); PVMBG reported the dense gray ash plume 2 km above the summit drifting W. A few hours later the Darwin VAAC raised the altitude to 6.1 km based on infrared temperatures in satellite imagery. The seismic signal lasted for three and a half minutes and the explosion was heard at the PGA Post in Rendang (12 km SW). Incandescent material fell within a radius of 2-3 km, mainly on the S flank (figure 48). Ashfall was reported in the villages of Telungbuana, Badeg, Besakih, Pempatan, Teges, and Puregai on the W and S flanks (figure 49). An explosion on 11 April also produced a dense gray ash plume that rose 2 km above the summit and drifted W. A hotspot remained about six hours later after the ash dissipated.

Figure 48. Incandescent ejecta appeared on the flanks of Agung after an eruption on 4 April 2019 (local time) as viewed from the observation post in Rendang (8 km SW). Courtesy of Jamie Sincioco.

Figure 49. Ashfall in a nearby town dusted mustard plants on 4 April 2019 from an explosion at Agung the previous day. Courtesy of Pantau.com (Photo: Antara / Nyoman Hendra).

PVMBG reported an eruption visible in the webcam early on 21 April (local time) that rose to 5.5 km altitude and drifted SW. The ash spread W and S and ash fell around Besakih (7 km SW), Rendang (8 km SW), Klungkung (25 km S), Gianyar (20 km WSW), Bangli (17 km WNW), Tabanan (50 km WSW), and at the Ngurah Rai-Denpasar Airport (60 km SW). About 15 hours later a new explosion produced a dense gray ash plume that rose to 3 km above the summit and produced incandescent ejecta in all directions as far as 3 km away (figure 50). The ash spread to the S and ashfall was reported in Besakih, Rendang, Sebudi (6 km SW), and Selat (12 km SSW). Both of the explosions were heard in Rendang and Batulompeh. The incandescent ejecta from the explosions remained within the 4-km exclusion zone. A satellite image on 23 April showed multiple thermal anomalies within the summit crater (figure 51). A dense gray plume drifted E from Agung on 29 April (30 April local time) at 4.6 km altitude. It was initially reported by ground observers, but was also visible in multispectral satellite imagery for about six hours before dissipating.

Figure 50. An explosion at Agung on 21 April 2019 sent incandescent eject 3,000 m from the summit. Courtesy of MAGMA Indonesia (Gunung Agung Eruption Press Release April 21, 2019).

Figure 51. Multiple thermal anomalies were still present within the summit crater of Agung on 23 April 2019 after two substantial explosions produced ash and incandescent ejecta around the summit two days earlier. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG reported an eruption on 3 May 2019 that was recorded on a seismogram with a signal that lasted for about a minute. Satellite imagery reported by the Darwin VAAC showed a growing hotspot and possible ash near the summit at 4.3 km altitude moving NE. A few days later, on 6 May, a gray ash plume rose to 5.2 km altitude and drifted slowly W before dissipating; it was accompanied by a seismic signal that lasted for about two minutes. Explosions on 12 and 18 May produced significant amounts of incandescent ejecta (figure 52). The seismic signal for the 12 May event lasted for about two minutes; no plume was observed due to fog, but incandescent ejecta was visible on the flanks and the explosion was heard at Rendang. The Darwin VAAC reported an ash plume from the explosion on 17 May (18 May local time) at 6.1 km altitude in satellite imagery moving E. They revised the altitude a short while later to 7.6 km based on IR temperature and movement; the plume drifted N, NE, and E in light and variable winds. A few hours after that it was moving NE at 7.6 km altitude and SE at 5.5 km altitude; this lasted for about 12 hours until it dissipated. Ashfall was reported in villages downwind including Cutcut, Tongtongan, Bonyoh (20 km WNW), and Temakung.

Figure 52. Explosions on 12 (left) and 18 (right) May (local time) 2019 produced substantial ejecta on the flanks of Agung visible from a distance of 10 km or more in PVMBG webcams. The ash plume from the 18 May event resulted in ashfall in numerous communities downwind. Courtesy of PVMBG (Information Eruption G. Agung, May 13, 2019, Information Eruption G. Agung, May 18, 2019).

The initial explosion on 18 May was captured by a webcam at a nearby resort and sent incandescent ejecta hundreds of meters down the NE flank within 20 seconds (figure 53). Satellite imagery on 3, 8, 13, and 18 May indicated multiple thermal anomalies growing stronger at the summit. All of the images were captured within 24 hours of an explosive event reported by PVMBG (figure 54).

Figure 53. The 18 May 2019 explosion at Agung produced an ash plume that rose to over 7 km altitude and large bombs of incandescent material that traveled hundreds of meters down the NE flank within the first 20 seconds of the explosion. Images taken from a private webcam located 12 km NE. Courtesy of Volcanoverse, used with permission.

Figure 54. Satellite images from 3, 8, 13, and 18 May 2019 at Agung showed persistent and increasing thermal anomalies within the summit crater. All images were captured within 24 hours of explosions reported by PVMBG. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG issued a VONA on 24 May 2019 reporting a new ash emission. They indicated that incandescent fragments were ejected 2.5-3 km in all directions from the summit, and the seismic signal lasted for four and a half minutes (figure 55). A dense gray ash plume was observed from Tulamben on the NE flank rising 2 km above the summit. Satellite imagery indicated that the plume drifted SW and ashfall was reported in the villages of Besakih, Pempatan, Menanga, Sebudi, Muncan, Amerta Bhuana, Nongan, Rendang, and at the Ngurah Rai Airport in Denpassar. Additionally, ashfall was reported in the districts of Tembuku, Bangli, and Susut (20 km SW). The Darwin VAAC reported an ash plume visible in satellite imagery at 4.6 km altitude along with a thermal anomaly and incandescent lava visible in webcam imagery. The remains of the ash plume were about 170 km S of the airport in Denpasar (60 km SW) and had nearly dissipated 18 hours after the event. According to a news article several flights to and from Australia were cancelled or diverted, though the International Gusti Ngurah Rai (IGNR) airport was not closed. On 31 May another large explosion produced the largest ash plume of the report period, rising more than 2 km above the summit (figure 56). The Darwin VAAC reported its altitude as 8.2 km drifting ESE visible in satellite data. It split into two plumes, one drifted E at 8.2 km and the other ESE at 6.1 km altitude, dissipating after about 20 hours.

Figure 55. A large explosion at Agung on 24 May 2019 produced incandescent ejecta that covered all the flanks and dispersed ash to many communities to the SW. Courtesy of PVMBG (Gunung Agung Eruption Press Release 24 May 2019 20:38 WIB, Kasbani, Ir., M.Sc.).

Figure 56. An explosion at Agung on 31 May 2019 sent an ash plume to 8.2 km altitude, the highest for the report period. Courtesy of Sutopo Purwo Nugroho, BNPB.

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

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.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); The Jakarta Post, Mount Agung eruption disrupts Australian flights, (URL: https://www.thejakartapost.com/news/2019/05/25/mount-agung-eruption-disrupts-australian-flights.html); PunapiBali (URL: http://punapibali.com/, Twitter: https://twitter.com/punapibali, image at https://twitter.com/punapibali/status/1098869352588288000/photo/1); Jamie S. Sincioco, Phillipines (URL: Twitter: https://twitter.com/jaimessincioco. Image at https://twitter.com/jaimessincioco/status/1113765842557104130/photo/1); Pantau.com (URL: https://www.pantau.com/berita/erupsi-gunung-agung-sebagian-wilayah-bali-terpapar-hujan-abu?utm_source=dlvr.it&utm_medium=twitter); Volcanoverse (URL: https://www.youtube.com/channel/UCi3T_esus8Sr9I-3W5teVQQ); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN ).

Frequently active, Indonesia's Mount Kerinci on Sumatra has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838. Intermittent explosions with ash plumes, usually multiple times per month, have characterized activity since April 2018. Similar activity continued during February-May 2019, the period covered in this report with information provided primarily by the Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), MAGMA Indonesia, notices from the Darwin Volcano Ash Advisory Center (Darwin VAAC), and satellite data. PVMBG has maintained an Alert Level II (of 4) at Kerinci for several years.

On 13 February 2019 the Kerinci Volcano Observatory (KVO), part of PVMBG, noted a brownish-white ash emission that was drifting NE about 400 m above the summit. The seismicity during the event was dominated by continuous volcanic tremor. A brown ash emission was reported on 7 March 2019 that rose to 3.9 km altitude and drifted NE. Ash also drifted 1,300 m down the SE flank. Another ash plume the next morning drifted W at 4.5 km altitude, according to KVO. On 10, 11, and 13 March KVO reported brown ash plumes drifting NE from the summit at about 4.0-4.3 km altitude. The Darwin VAAC observed continuous ash emissions in satellite imagery on 15 March drifting W at 4.3 m altitude that dissipated after about 3 hours (figure 10). A gray ash emission was reported on 19 March about 600 m above the summit drifting NE; local news media noted that residents of Kayo Aro reported emissions on both 18 and 19 March (figure 11). An ash emission appeared in satellite imagery on 25 March (figure 10). On 30 March the observatory reported two ash plumes; a brown emission at 0351 UTC and a gray emission at 0746 UTC that both drifted NE at about 4.4 km altitude and dissipated within a few hours. PVMBG reported another gray ash plume the following day at a similar altitude.

Figure 10. Sentinel-2 satellite imagery of Kerinci from 15 (left) and 25 (right) March 2019 showed evidence of ash plumes rising from the summit. Kerinci's summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Figure 11. Dense ash plumes from Kerinci were reported by local news media on 18 and 19 March 2019. Courtesy of Nusana Jambi.

Activity continued during April with a brown ash emission reported on 3 April by several different agencies; the Darwin VAAC and PVMBG daily reports noted that the plume was about 500 m above the summit (4.3 km altitude) drifting NE. KVO observed two brown ash emissions on 13 April (UTC) that rose to 4.2 km altitude and drifted NE. Satellite imagery showed minor ash emissions from the summit on 14 April; steam plumes 100-500 m above the summit characterized activity for the remainder of April (figure 12).

Figure 12. A dilute ash emission rose from the summit of Kerinci on 14 April 2019 (left); only steam emissions were present on a clear 29 April in Sentinel-2 imagery (right). "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Ashfall on the NE and S flanks within 7 km of the volcano was reported on 2 May 2019. According to a news article, at least five villages were affected late on 2 May, including Tanjung Bungo, Sangir, Sangir Tengah, Sungai Rumpun, and Bendung Air (figures 13 and 14). The smell of sulfur was apparent in the villages. Brown ash emissions were observed on 3 and 4 May that rose to 4.6 and 4.1 km altitude and drifted SE. The Darwin VAAC reported an emission on 5 May, based on a pilot report, that rose to 6.7 km altitude and drifted NE for about an hour before dissipating. A brown ash emission on 10 May rose 700 m above the summit and drifted SE. Satellite imagery captured ash emissions from the summit on 14 and 24 May (figure 15). For the remainder of the month, 300-700-m-high dense steam plumes were noted daily until PVMBG reported white and brown plumes on 26 and 27 May rising 500-1,000 m above the summit. Although thermal anomalies were not reported during the period, persistent weak SO₂ emissions were identified in TROPOMI instrument satellite data multiple times per month (figure 16).

Figure 13. Ashfall was reported from five villages on the flanks of Kerinci on 2 May 2019. Courtesy of Uzone.

Figure 14. An ash plume at Kerinci rose hundreds of meters on 2 May 2019; ashfall was reported in several nearby villages. Courtesy of Kerinci Time.

Figure 15. Ash emissions from Kerinci were captured in Sentinel-2 satellite imagery on 14 (left) and 24 (right) May 2019. The summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Figure 16. Weak SO2 anomalies from Kerinci emissions were captured by the TROPOMI instrument on the Sentinel-5P satellite multiple times each month from February to May 2019. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

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.vsi.esdm.go.id/); 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/); Nuansa Jambi, Informasi Utama Jambi: (URL: https://nuansajambi.com/2019/03/20/gunung-kerinci-semburkan-asap-tebal/); Kerinci Time (URL: https://kerincitime.co.id/gunung-kerinci-semburkan-abu-vulkanik.html); Uzone.id (URL: https://news.uzone.id/gunung-kerinci-erupsi-5-desa-tertutup-abu-tebal).

Ethiopia's Erta Ale basaltic shield volcano has had an active lava lake since the mid 1960s, and possibly much earlier. The first confirmed historical observations were in 1906. Two active craters (Northern and Southern) within a larger oval-shaped caldera exhibit periodic fountaining of lava causing lava lake overflows; this creates spectacular incandescence as the pahoehoe lava flows into the larger caldera around the craters and occasionally beyond. Lava flows in the South Pit crater overflowed its rim in November 2010 (BGVN 36:06). This report discusses activity from 2011 through June 2017, including the South Pit crater overflows in January and November 2016, and a new fissure eruption on the SE flank that began in January 2017 and was continuing in June 2017. Information comes from satellite thermal and visual data (NASA Earth Observatory, MODIS), and photographs from expeditions (primarily from Volcano Discovery) that regularly visit this remote site.

The lava lake at the South Pit crater in the summit caldera remained active, with the lake level falling and rising to within a few meters of the rim, during 2011-2015. Intermittent lava flows were reported from the North Pit Crater as well during this time. Activity increased late in 2015, and the first overflows of the South Pit crater rim since late 2010 occurred in mid-January 2016. It overflowed again in November 2016, and covered a significant area of the surrounding caldera floor with pahoehoe. By late December, effusive activity was reported from both craters. Flow intensity and volume increased dramatically for several days beginning on 17 January 2017, followed by ash emissions and crater collapses on 20-21 January. A new fissure eruption on the SE flank about 4 km from the caldera appeared on 21 January 2017, and sent lava flows several kilometers to the NE and the SW. Activity at the fissure vent increased during subsequent months, and by June 2017 a substantial new lava field that contained at least one new lava lake and flows more than 1,500 m long covered the area. Effusive activity had also resumed at both craters in the summit caldera.

Activity during November 2011-December 2016. Visitors in November 2011 confirmed the continued presence of the lava lake (figure 32) at the South Pit crater in the summit caldera. On 16 January 2012, an attack by Eritrean rebels on tourists camping at the S crater rim left at least five European tourists dead and seven others wounded; four Europeans and their Ethiopian guides were also abducted, according to Volcano Discovery reports. News reported through Volcano Discovery suggested that the abducted tourists were released in March 2012.

Figure 32. The active lava lake at Erta Ale's South pit crater during November 2011. Photo by Reinhard Radke, courtesy of Volcano Discovery.

Visitors in January 2013 reported that the lava lake in the North Pit crater was active and about 10 m below the rim. Intermittent lava flows were observed from a hornito in the South Pit crater and were continuing to fill the crater floor. Members of an expedition in December 2013 observed that the active lava lake at the South Pit crater had risen considerably during previous months (figure 33). An expedition in February 2015 also documented continued lava fountaining (figure 34) at the South Pit crater.

Figure 33. The active lava lake at the South Pit crater of Erta Ale in December 2013. Photo copyright by Dominique Voegtli, courtesy of Volcano Discovery, used by permission.

Figure 34. The active lava lake at the South Pit crater at Erta Ale in February 2015. Upper image: lava fountaining up over the lake surface. Lower image: night time glow of lava seeping up through cracks in the lake surface. Photos by Dietmar Berendes, courtesy of Volcano Discovery.

During 19-21 November 2015, visitors on an expedition to Erta Ale observed significant changes in the lava lake level at the South Pit crater. On the morning of 19 November (figure 35) the lake surface was 2-3 m below the rim. A local guide reported that the lake had been very active during the previous weeks, rising to levels near overflowing similar to the event in late 2010. A second terrace of freshly cooled pahoehoe was visible less than 1 m below the rim, indicating the most recent maximum height of the lake. On 19 November, the lake rose to within 30 cm of the terrace rim, with occasional lava fountains splashing onto the terrace (figure 36), and Pele's hair forming continuously. The level had dropped several meters by the next morning. During 20 and 21 November, the activity was characterized by large, periodic "exploding bubbles" from the center of the lake creating waves across the surface; minor Strombolian activity and fountaining occurred around the edges. The lake level generally fluctuated between 0.5 and 1 m below the second terrace. On the evening of 21 November, the level rose rapidly from five to three meters below the second terrace; lava rapidly seeped out of the cracks in the cooling surface, overflowing onto the thin crust.

Figure 35. The lava lake at the South Pit crater of Erta Ale on the morning of 19 November 2015. The lake level was higher than it was in February 2015 (figure 34). Photo by Ingrid Smet, courtesy of Volcano Discovery.

Figure 36. Fountains from the lake at the South Pit crater of Erta Ale splatter lava onto the crater rim on 19 November 2015. Photo by Ingrid Smet, courtesy of Volcano Discovery.

Volcano Discovery reported that the lava overflowed the rim of the South Pit crater during the night of 15-16 January 2016, and covered the rim with a fresh crust of pahoehoe. An expedition leader reported that during 12-15 February 2016, the lake level had dropped 5-7 m. A visitor to the crater in April 2016 photographed the lake level several meters below the rim with active fountaining lava (figure 37).

Figure 37. The boiling lava lake at the Sout Pit crater of Erta Ale on 3 April 2016. Photo by V, courtesy of Flickr.

The southern pit crater began overflowing again at the beginning of November 2016, and covered significant parts of the surrounding caldera floor (figures 38 and 39). The overflow was observed at mid-day on 14 November by visitors from the Societe de Volcanologie Geneve (SVG).

Figure 38. The South Pit crater of Erta Ale began overflowing the rim in early November 2016. An expedition during the second half of November witnessed lava overflowing its newly constructed containment ring a number of times each day. Upper image: the perched lava lake sits above the recent flows. Lower Image: a closeup of the fresh pahoehoe flows that covered Erta Ale´s caldera floor from the overflow. Photos by Hans en Jooske, courtesy of Volcano Discovery.

Figure 39. The summit caldera of Erta Ale around the South Pit crater before and after the overflows of November 2016. Upper image: The South Pit Crater in November 2015 is surrounded by the lava flows from the 2010 overflow. Photo by Ingrid Smet. Lower image: A large volume of fresh pahoehoe from November 2016 covers the older flows. The active lake is center-left in the background with a gas plume. Views are from different places along the caldera rim. Photo by Hans en Jooske, courtesy of Volcano Discovery.

By late December 2016, effusive activity was reported from both the North and South Pit craters, including activity at the South Pit crater overflowing beyond the surrounding summit caldera. An expedition during 29 December 2016-1 January 2017 observed changing activity from both craters inside the summit caldera (figure 40). During 29-31 December, the lake level at the South Pit crater fluctuated between 0.5 and 1 m below the rim. During this time lava fountains 2-3 m high were frequent along the South Pit crater rim, but it did not overflow. The caldera floor around the crater was covered with 2-3 m of fresh pahoehoe, over an area about 150 m in diameter. Activity at the North Pit crater had formed three hornitos, one of which was emitting lava.

Figure 40. Erta Ale's lava lake at the South Pit crater on 29 December 2016. Photo by Jens Wolfram Erben, courtesy of Volcano Discovery.

Activity during January-June 2017. Observations on 16 January 2017 at the North Pit crater showed remnants of two large hornitos surrounded by fresh lava flows (figure 41). During 16-20 January 2017, the lava lake at the South Pit crater underwent rapid and large variations, producing massive overflows and intense spattering. During the morning of 16 January the lake overflowed the W rim of the crater (figure 42); in the afternoon two lava rivers, reaching 500 m in length, appeared on the SW flank.

Figure 41. The center of the less active North Pit crater of Erta Ale on 16 January 2017, with remnants of two large hornitos surrounded by fresh lava flows. This crater collapsed shortly after the expedition group left. Photo by Paul Reichert, courtesy of Volcano Discovery.

Figure 42. A vigorous overflow of the western rim of Erta Ale's South Pit crater started at 1030 on 16 January 2017 and produced a flood of lava that flowed SW. It was reported by Ethiopian geologist Enku Mulugeta as traveling at several meters per second. Photo by Paul Reichert, courtesy of Volcano Discovery.

On 17 January around 1300, two overflows began on the South Pit crater rim. Two hours later, overflows appeared on the NE and N flank; lava was flowing over about 70% of the rim according to visitors (figure 43). They reported the speed of the lava flowing on the flank at 50-70 km per hour, covering about 1 km² within the larger caldera. In the morning of 18 January, fresh, glowing lava covered the area around the South Pit crater 500-700 m in all directions (figure 44). Sporadic overflows occurred with lake levels fluctuating by 10-15 m for several days. During lower levels, Strombolian fountains reached 50-60 m above the lake.

Figure 43. The lava lake at the South Pit crater of Erta Ale overflowing on all sides on 17 January 2017. Photo by Enku Mulugeta, courtesy of Volcano Discovery.

Figure 44. Lava flows on the SW side of the South Pit crater at Erta Ale had covered much of the western caldera floor by the afternoon of 17 January 2017, and invaded the larger, gently dipping southern part of the oval-shaped NW-SE trending caldera. View is to the S, with the SW rim of the Summit caldera on the right. Photo by Paul Reichert, courtesy of Volcano Discovery.

On the evening of 20 January, explosions of very large gas bubbles were observed by Oliver Grunewald and reported by Culture Volcan, causing lava to spatter up to 30 m high. Parts of both of the craters in the Summit caldera began to collapse. At the North Pit crater, a new 20 m deep oval-shaped pit crater 150 x 30 m formed during the next 24 hours. A collapse at the South Pit crater doubled its size. This activity was accompanied by ash emissions that reached 700-800 m above the crater.

Volcano Discovery reported news from eyewitness reports of a fissure eruption beginning on 21 January 2017. Two fissure eruptions were visible on the SE flank, 3 and 4 km SE of the South Pit crater lava lake, in satellite imagery taken on 26 January 2017 (figure 45). The higher vent was located at about 650 m elevation, and the lower one around 400 m. The fissures created three distinct lava fields, one to the NE reaching about 3 km length, a smaller one to the W (about 1 km), and one to the SSE about 2 km long. The surface area covered by the first two (on either side on the northernmost fissures) was estimated to be about 1.5 km² (1,500,000 m²), while the southern flow covered about 0.35 km² (350,000 m²). As a result of the sudden draining of the magma into the new fissure zone, the lava lake in the South Pit crater was reported to have dropped by 80-100 m. Additional satellite imagery taken before and after the fissure eruptions began reveal the locations of the new flows on 23 and 27 January 2017 (figure 46).

Figure 45. Infrared hot spots and gas plumes are clearly visible from Erta Ale on 26 January 2017. The new fissure eruptions 3-4 km SE of the South Pit crater were first reported on 21 January. This led to a large drop in lake level at the South Pit crater. This image was captured by the Operational Land Imager (OLI) sensor on Landsat 8 on 26 January 2017. It is a composite of natural color (OLI bands 4-3-2) and shortwave infrared (OLI band 7). Shortwave infrared light (SWIR) is invisible to the naked eye, but strong SWIR signals indicate increased temperatures. Infrared hot spots representing two distinct lava flows are visible. Plumes of volcanic gases and steam drift from lava lakes at both summit craters. Courtesy of NASA Earth Observatory.

Figure 46. Satellite imagery showing changes in the lava flows from the flank eruption at Erta Ale during 16-27 January 2017. The flank eruption began on 21 January. On 16 January (top), the flank eruption has not yet begun. By 23 January (middle) the new lava flows and steam emissions are visible from several vents located 3-4 km SE of the South Pit crater. Additional new lava is visible in the lower center of the 27 January image (bottom). Images copyright by Planet Labs Inc., 3 m per pixel resolution, and used with permission under a Creative Common license.

After dropping about 100 m after the flank eruption began, the South Pit crater lake level rose again by mid-February to 40-50 m below its rim. By April 2017, activity still remained high; a new lava lake about 80 x 175 m in size had formed at the flank eruption site, and a growing lava field, about 1,500 m wide had reached 3.5 km NE of the original site. Geologists from Addis Abeba University who visited the site during 11-15 April 2017 noted two coalesced hornitos in the NE part of the South Pit crater, estimated to be 7 m high. The old lava lake was covered with cooled lava in a 200-m-diameter near-circular shape. Frequent surface collapse and lake-level changes occurred every 30 minutes, and lava fountains rose 25 m above the surface. The fresh lava surface around the crater rim had cooled enough to walk on it. The North Pit crater was still degassing, with several small hornitos growing in the center. The lake level at the new fissure (the SE Rift Zone) had dropped by about 10 m.

By early May 2017, the first lava lake at the SE Rift Zone had crusted over and a new lake was forming about 350 m E. A new breakout also started in early May, and was feeding a new flow field overlapping the previous one to the NE, more than 1,500 m long and over 500 m wide.

Satellite data. In addition to field observations of Erta Ale, valuable information is available from continuous satellite data. Thermal data from MODIS is processed by both the MIROVA and MODVOLC systems. The MIROVA thermal anomaly system recorded the high levels of heat flow and changes in location of the heat flow sources from late September 2015 through June 2017 (figure 47). The change in location and intensity of the heat flow in late January 2017 corresponds with the opening of the SE-flank fissure.

Figure 47. MIROVA thermal anomalies at Erta Ale from late September 2015 through early July 2017. The thermal anomaly signature has been strong and variable since late September 2015. The large spike in intensity and change in location of activity in late January 2017 coincides with the opening of the SE flank fissure vents. The black lines indicate heat sources more than 5 km from the summit crater, and correspond to the new fissure zone SE of the summit caldera. Courtesy of MIROVA.

The MODVOLC thermal alert system managed by the University of Hawaii has captured persistent thermal alerts from Erta Ale for at least 10 years. When activity is moderate to high at the lava lakes in the pit craters, the signal is concentrated in those areas (figure 48). The reports of lava overflowing the south crater rim in January 2016 correspond to increased heat flow visible in the MODVOLC data. The dramatic changes in heat flow with the new fissure flows from the SE rift zone and subsequent new lava lake formation are apparent in MODVOLC images from January-May 2017 (figure 49).

Figure 48. Selected MODVOLC thermal alert images from 2015 and 2016 for Erta Ale showing variations in heat flow when activity is concentrated at the North and South Pit craters in the Summit caldera. The increase in January 2016 corresponds to lava overflows at the South Pit Crater. Courtesy of MODVOLC.

Figure 49. The dramatic changes in heat flow with the new fissure flows from the SE rift zone and subsequent new lava lake formation are apparent in MODVOLC images from January-May 2017. On 20 January, only the Summit Caldera craters were active. On 27 January, a new lava lake was reported at the fissure on the SE flank. During the week of 17-24 February, lava flows were active at both the fissure and at the summit craters. By 29 April-5 May, the new SE Rift Zone is extending several kilometers to the NE. Courtesy of MODVOLC.

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

Information Contacts: NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Robert Simon, Sr. Data Visualization Engineer, Planet Labs Inc. (URL: http://www.planet.com/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); Societe de Volcanologie Geneve (SVG), Bulletin 161, January 2017.

Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on Reunion Island in the western Indian Ocean, for several thousand years. Recent eruptive episodes on 21 June 2014 and activity that started on 4 February 2015 have already been reported (BGVN 40:02). This report covers the remainder of the 2015 eruptive episode, and additional activity through May 2017. Information about Piton de la Fournaise is provided by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) and satellite instruments.

A one-day fissure eruption on the ESE side of the central cone of the summit caldera on 21 June 2014 created a 1.5-km-long flow. This was followed by seven months of quiet. There were four effusive eruption events during 2015. The 4-15 February event occurred on the W side of the Dolomieu summit cone and the lava flow traveled about 2.5 km S. Effusion during 17-30 May started outside and SE of the Dolomieu Crater and traveled 4 km before it ceased. The brief 30 July-2 August event erupted from a 1-km-long fissure in the NE part of the l'Enclos Fouqué caldera and produced dozens of lava fountains. During 24 August-31 October a more sustained eruption from a fissure on the S flank of Dolomieu Crater sent lava flows at least 3.5 km down the flank to the S. Piton de la Fournaise experienced two effusive episodes in 2016. The 26-27 May event caused lava fountains on the SE flank of Dolomieu Crater. During 11-18 September, several fissures opened in the N part of the l'Enclos Fouqué caldera and produced numerous lava fountains and a lava flow. An effusive event on the SE flank of the summit crater during 31 January-27 February 2017 sent lava through tubes and flowed several kilometers to the SE before subsiding.

Activity during June 2014 and February 2015. The one-day eruption on 21 June 2014 consisted of a fissure eruption that was entirely contained within the Enclos Fouqué (the summit caldera) on the ESE side of the central (Dolomieu) cone. A lava fountain at the fissure created a spatter rampart and two lava flows that traveled about 1.5 km to the SE (BGVN 40:02).

The next eruption began abruptly on 4 February 2015 at a fissure on the W side of the summit cone adjacent to Bory crater (see figure 87), and lava flowed generally S, reaching about 2.5 km in length by 8 February (figure 88). The MODVOLC thermal alert signal for this event was detected over 4-14 February, and indications of continuing activity ceased by 15 February. OVPF partially reopened access to the volcano on 21 February.

Figure 88. The eruptive cone from the 4-15 February 2015 eruption at Piton de la Fournaise. Upper image: 6 February 2015; lower Image: 12 February 2015. Courtesy of OVPF (Bulletin d'acitivité du Piton de la Fournaise du 15 février 2015 à 9h00 Locale).

Activity during May 2015. A brief increase in seismic activity, continued deformation, and increased magmatic gas emissions occurred on 29 April, but no effusive activity took place. A 90-minute seismic swarm of 200 volcano-tectonic (VT) events followed by significant deformation at the summit crater preceded a new effusive eruption at 1345 on 17 May. The eruption started outside and SE of Dolomieu crater in the Castle crater area. Volcanologists noted lava fountains from three fissures, and two lava flows. A very large gas plume emitted during the first few hours of the eruption rose 3.6-4 km above the summit and drifted NW. The fissure furthest W stopped issuing lava fountains before midnight.

On 18 May only one fissure was active and the SSW-drifting gas plume was much smaller. Hydrogen sulfide emissions continued to be high, and carbon dioxide emissions increased. Lava fountains from a single vent along the second fissure, further E, rose 40-50 m. The lava flow had traveled 4 km, reaching an elevation of 1.1 km. On 19 May, scientists observed lava fountains 20-30 m high, and noted the lava flow which had traveled 750 m in the previous day, reaching 1 km elevation. Lava-flow rates estimated by satellite data fluctuated but showed an overall decrease from 24.2 m²/s on 17 May to 2.5 m²/s on 21 May. During 21-22 May observers reported large variations in activity, including increasing heights of the lava fountain (over 50 m high), collapsing parts of the newly formed cinder cone, and a new very fluid lava flow adjacent to the main flow.

During an overflight on 23 May scientists observed a large blue sulfur dioxide plume above the vent, lower lava fountains, a smaller vent in the cone, and the presence of a lava tube about 200 m downstream of the vent. During 24-25 May activity remained unchanged; low lava fountains and low-level lava flows persisted (figure 89). OVPF reported that the eruption continued through 30 May 2015 after which tremor was no longer detected. The MODVOLC thermal alerts for this event agreed well with the observations of the volcanologists. Strong multi-pixel alerts were issued daily from 17-30 May.

Figure 89. Eruptive cone at Piton de la Fournaise on 24 May 2015. Courtesy of OVPF (Observations des 24 et 25 mai 2015).

Activity during 30 July-2 August 2015. A brief spike in seismicity on 6 July was the only notable activity after 30 May prior to a new eruptive episode that began on 30 July with a sharp increase in seismicity, increased gas emissions, and deformation near the summit. A fissure eruption began the next day at 0920, preceded by 90 minutes of high seismicity and 80 minutes of major deformation; it was confirmed by a hiker and then by observation of a gas plume. The 1-km-long fissure opened in the NE part of the l'Enclos Fouqué caldera and produced dozens of lava fountains (figure 90). Based on satellite images and gas data, the flow rate was estimated to be 28 m²/s initially and then 11 m²/s later that day. A gas plume rose to altitudes of 3.2-3.5 km. By the evening there were only five fountains, and a lava flow had traveled as far E as Plaine des Osmondes (NE part of the caldera). According to an AP news article, lava fountains were 40 m high, forming 20-m-high cones on 31 July. At 1115 on 2 August tremor stopped after several hours of fluctuating intensity, indicating the end of effusive activity.

Figure 90. Fountains of lava erupt from a 1-km-long fissure that opened in the NE part of the l'Enclos Fouqué caldera at Piton de la Fournaise on 1 August 2015. AP Photo by Ben Curtis, courtesy of the Associated Press.

Activity during 24 August-November 2015. The government reopened access to the caldera on 20 August; this was very short-lived, however, as a new eruption began on 24 August that continued through November 2015. Sulfur dioxide gas emissions increased at 1600, and the seismic and deformation network indicated a magmatic intrusion beginning at 1711 (figure 91). Lava fountains were visible at 1850 from a fissure on the S flank of Dolomieu Crater, at about 2,000 m elevation, near Rivals Crater. The fissure propagated towards the top of Rivals, and at around 2115 a fissure opened to the NW, below Bory Crater. The lava-flow rate was 30-60 m²/s . By the next morning fountains at higher elevations ceased, and were only active from a 100-m-long section near Rivals crater. The lava flow rate had significantly decreased to 10 m²/s . Near the top of the active fissure, a small cone had formed 140 m E of the sign to Rivals crater.

Figure 91. New lava flows at Piton de la Fournaise on the S flank of Dolomieu Crater, 24 August 2015. To create this image, OVPF superimposed a daytime image taken earlier the same day onto one showing the nighttime lava flows, which allows the location of the activity to be better identified. Images taken from the Piton de Bert webcam. Courtesy of OVPF (Localisation des coulees vers 21h00 le 24/08/2015).

OVPF reported that the eruption fluctuated during the rest of August, causing variations in the height of the lava fountains and emissions. One vent remained active, and lava flows from it traveled at least as far as 3.5 km during 27-28 August. During an overflight the next day, scientists observed two growing cinder cones with lava lakes and lava fountains. An 'a'a lava flow was active, and a large gas plume rose 3 km.

Scientists conducting fieldwork during 31 August-1 September observed an active cone (20 m high) filled with a lava lake. Fluctuating lava fountains rose 15-20 m above the surface and gas bubbles exploded. Lava traveled through a 50-m-long lava tube and extended a distance of 1 km. During 1-2 September, seismicity increased and the lava flow grew to 2 km long (figure 92). Lava was observed in two separate side-by-side vents on 4 September (figure 93), and lava fountains were lower compared to recent days. Five small lava flows were visible near the foot of the cone; four were 30 m long and the fifth was 1 km long.

Figure 92. Thermal measurements of an active lava flow on 3 September 2015 at Piton de la Fournaise. Courtesy of OVPF (Bulletin d'activité du vendredi 4 septembre 2015 à 09h00).

Figure 93. Side-by-side eruptive vents at Piton de la Fournaise on 4 September 2015. Courtesy of OVPF (Bulletin d'activité du samedi 5 septembre 2015 à 15h00).

The side-by-side vents remained active through 17 September, after which only one was active. Lava flows emerged from and were active beyond a 50-100 m lava tube; the largest lava flows were up to 1.5 km in length. During 22-23 September a new lava tube formed to the W of the lava field. By 24 September the active cone was 30 m high; lava fountains were lower and less frequently observed but lava flows continued to be active, traveling as far as 3 km S and E (figure 94). OVPF reported that seismicity at Piton de la Fournaise slowly increased during the last week of September, and deformation data showed a trend of deflation during the last few days of the month. During fieldwork on 27 September volcanologists noted continuous lava fountains. Small lava flows were active, though the fronts of the two larger ones were no longer advancing.

Figure 94. Map-view image showing lava flows created between 24 August and 28 September 2015 at Piton de la Fournaise. Contour extraction was performed using the coherence images (obtained in the interferogram production chain) produced by the OI2 observation service. Image courtesy of OVPF/IPGP and JL.Froger LMV/OPGC (Bulletin d'activité du vendredi 2 septembre 2015 à 07h00).

During the first two weeks of October, the lava lake remained active; bursting gas bubbles ejected lava onto the edges of the 30-35-m-high cone. Pahoehoe lava flows issued from ephemeral vents on lava tubes, and in many instances hornitos were built at these vents. Lava was active as far as 2.5 km from the base of the cone and burned vegetation near the base of Piton de Bert. The lava-flow rate peaked at 11 m²/s during 1-4 October then returned to the previous rate of 5-10 m²/s. On 7 October lava flowed out of a breach in the cone. The evolution of the morphology of the eruptive vent changed from a fissure to a single cone between late August and early October (figure 95).

Figure 95. Evolution of the morphology of the eruptive cone at Piton de la Fournaise, 25 August-10 October 2015. Courtesy of OVPF (Bulletin d'activité du vendredi 9 octobre 2015 à 19h00)

On 12 October there was a strong increase in tremor intensity, with values reaching or exceeding those detected during the first few hours of the eruption (24 August). Strain measurements showed continued deflation. A hornito SW of the cone ejected spatter during 13-14 October. Activity continued to increase on 16 and 17 October (figure 96). The cone continued to grow; the base was 100 m in diameter and it was about 40 m high. Parts of the cone rim continued to collapse, and a notch in the rim allowed for periodic lava-lake overflows. Increased SO₂ flux created bubbles in the lava that caused ejection and spattering of large amounts of lava around the vent rim.

Figure 96. Large amounts of lava spattered around the rim of the active vent at Piton de la Fournaise on 16 October 2015 (Bulletin d'activité du samedi 17 octobre 2015 à 08h00).

Tremor ceased abruptly on 19 October. Observers reported that a small explosion in the vent ejected spatter on 22 October, but lava flows were not observed. Lava fountains were visible from the main 24 August vent on 30 October for the last time (figure 97).

Figure 97. Lava fountains were observed for the last time in the early morning on 30 October 2015 from the vent of the 24 August 2015 eruption (Bulletin d'activité du vendredi 30 octobre 2015 à 07h00).

OVPF reported that based on the change in seismic and lava flow activity, the effusive phase of the eruption beginning on 24 August had ended by 31 October 2015. They noted that during a few days before 11 November, the networks had recorded geophysical and geochemical signs of pressurization within the volcano. They also observed during aerial reconnaissance on 11 November persistent white fumarolic activity reflecting the high temperature of the lava field. Indications of inflation ceased at the end of November. MODVOLC thermal alerts became sporadic during November and ceased altogether on 2 December 2015 for more than five months.

MODVOLC thermal alerts for 2015. The MODVOLC thermal alerts captured for Piton de la Fournaise during 2015 show the differing locations of the four effusive eruptions (figure 98). The 4-14 February episode was located on the W side of the summit cone adjacent to Bory crater, in the W side of the Enclos Fouqué summit caldera. The 17-30 May episode extended farther E than that of the February event. A 1-km-long fissure opened in the NE part of the l'Enclos Fouqué caldera for the brief 31 July-1 August episode. Activity was concentrated on the S flank of the Dolomieu Crater during the lengthier 24 August-31 October effusive episode.

Figure 98. MODVOLC thermal alerts for the four eruptive episodes of 2015 at Piton de la Fournaise. The 4-14 February activity was located on the W side of the summit cone adjacent to Bory crater, in the W side of the Enclos Fouqué summit caldera. The 17-30 May episode extended farther E than that of the February event. A 1-km-long fissure opened in the NE part of the l'Enclos Fouqué caldera during the 31 July-1 August. Activity was concentrated on the S flank of the Dolomieu Crater during the lengthier 24 August-31 October effusive period; only the first week of thermal activity is shown here. Courtesy of MODVOLC.

Sulfur Dioxide flux during 2015. Images captured by the OMI (Ozone Monitoring Instrument) on the Aura satellite showed significant SO₂ plumes during three of the 2015 eruptive episodes, especially at the onset of the activity (figure 99). Dobson Unit (DU) values greater than 2 are shown as red pixels in the images. The largest plumes of SO₂ captured during 2015 were after the effusive episodes had ended on 24 and 31 October 2015 (figure 100).

Figure 99. Images of SO2 flux at Piton de la Fournaise during three of the eruptive episodes during 2015. Dobson Unit (DU) values greater than two are shown as red pixels. On 19 May 2015, the SO2 plume drifts W (top left). The plume captured on 31 July 2015 is drifting E (top right). The lower two images are the second day (25 August) and the last day (17 October) that effusive activity was reported by OVPF for that eruptive episode. Courtesy of NASA Goddard Space Flight Center (NASA/GSFC).

Figure 100. Images of SO2 flux at Piton de la Fournaise on 24 and 31 October 2015. Courtesy of NASA GSFC. Top: The large, 7.88 DU plume drifts SE from Reunion Island on 24 October. Bottom: Another plume with 10.96 DU SO2 drifted W and N from the island on 31 October. Courtesy of NASA/GSFC.

Activity during 2016. Piton de la Fournaise experienced two effusive episodes in 2016, one occurred during 26-27 May, and the other during 11-18 September. The GPS networks detected evidence of inflation on 24 January 2016. This lasted until the second week of February when weak deflation was recorded. OVPF reported that CO₂ gas emission, deformation, and seismicity began to slowly increase on 16 May, and then seismicity significantly increased at 1140 on 25 May. Tremor began at 0805 on 26 May, characteristic of an ongoing eruption, likely from a new fissure near Château Fort crater. Bad weather prevented visual observations of the area at first, though at 0900 ground observers confirmed a new eruption. Later that day scientists and reporters saw about six lava fountains (some were 40-50 m high) during brief aerial surveys and a cinder cone being built on a flat area at 1850 m elevation about 1-1.5 km SE of Castle Crater. On 27 May, tremor levels significantly dropped at 0845 and then ceased at 1100. Signals indicative of degassing continued. The lava fountains on 26 May were located on the SE flank of the main Dolomieu Crater south of the locations of both the May and August 2015 episodes (figure 101).

Figure 101. The location of the highest elevation point of the 26 May 2016 effusive episode at Piton de la Fournaise is shown by the yellow pin (260515 should be 260516), as recorded that day by the Section Aerienne de la Gendarmerie (SAG, the French Air Force). In white and red, respectively, are the contours of the eruptions of May and August 2015 (Bulletin d'activité du jeudi 26 mai 2016 à 22h00).

Significant inflation continued after the 26-27 May eruption until mid-June (more than two centimeters between 27 May and 8 June) when it levelled off, and then began again in mid-July along with increased seismicity beginning on 13 July that lasted through the remainder of the month. OVPF reported that seismicity remained low during August. Gas emissions were also low and dominated by water vapor; CO₂ emissions had been elevated during 21-27 July. Inflation had stopped in early August and slight deflation was detected through 2 September.

Seismicity increased on 10 September, and elevated levels of SO₂ were detected at fumaroles. A seismic swarm occurred at 0735 on 11 September, characterized by several earthquakes per minute. Deformation suggested magma migrating to the surface. Volcanic tremor began at 0841, indicating the beginning of the eruption. Several fissures opened in the N part of the l'Enclos Fouqué caldera, between Puy Mi-côte and the July 2015 eruption site, and produced a dozen 15-30-m-high lava fountains distributed over several hundred meters. The eruption continued on the next day.

OVPF reported that volcanic tremor stabilized during 14-17 September. Field observations on 15 September revealed that the two volcanic cones that had formed on the lower part of the fissures had begun to coalesce (figure 102). Lava from the northernmost cone flowed N and NE, and by 0900 was active midway between Piton Partage and Nez Coupé de Sainte Rose. The height of the lava fountains grew in the afternoon, rising as high as 60 m, likely from activity ceasing at the southernmost cone and focusing at one main cone. On 16 September the main cone continued to build around a 50-m-high lava fountain; lava flows from this vent traveled NE. Tremor rose during the night on 17 September, and then fell sharply at 0418 on 18 September, indicating the end of surface activity. During 11-18 September, the erupted volume was an estimated 7 million cubic meters. By 26 September, earthquake frequency had decreased to less than five per day.

Figure 102. View of the eruptive site at Piton de la Fournaise on 15 September 2016 at 0930. The two cones are coalescing into one. Courtesy of OVPF/IPGP (copyright OVPF / IPGP; Bulletin d'activité du jeudi 15 septembre 2016 à 16h30).

Following the slight deflation observed during the eruption (11-18 September), inflation began again on 18 September, slowed significantly by 1 October and ceased by 6 October. Inflation resumed at the summit on 12 December, and increased summit seismicity was reported by OVPF on 22 December 2016.

Activity during January-May 2017. A return to background levels of seismicity (0-1 events per day) and a slowdown in inflation were reported on 9 January 2017. Inflation resumed on 22 January. This was interpreted by OVPF to represent the deep-seated magma supplies beginning to feed the surface reservoir about 1.5-2 km under the summit craters once again. Following a seismic swarm beginning at 1522 on 31 January, seismic tremor indicated that a new effusive eruption began at 1940 on 31 January.

Visual observations on 1 February confirmed that the active vent was located about 1 km SE of Château Fort and about 2.5 km ENE of Piton de Bert (figure 103). Lava fountains rose 20-50 m above the 10-m-high vent, and 'a'a lava flows branched and traveled 750 m (figure 104). Two other cracks had opened at the beginning of the eruption, but were no longer active. Tremor levels decreased in the early hours of the eruption; lava-fountain heights were variable (between 20-50 m).

Figure 103. Topographic map showing the location of the 1 February 2017 eruption vent. Piton de Bert is located in the lower left (SW) corner at the caldera edge. The plot of the lava flows at 0830 is shown. Smaller red areas NW of flow are eruptive cracks that opened briefly at the beginning of the eruption. Base map courtesy of IGN, data courtesy of OVPF/IPGP (copyright OVPF / IPGP; Bulletin d'activité du mercredi 1 février 2017 à 17h00).

Figure 104. The eruptive site at Piton de la Fournaise on 1 February 2017 at 0740. Courtesy of OVPF (copyright OVPF / IPGP; Bulletin d'activité du mercredi 1 février 2017 à 09h00).

On 2 February, two lava fountains at the vent were visible, and lava flows had traveled an additional 500 m E (figure 105). The vent was 128 m long and about 35 m high at the highest part. On 4 February OVPF noted that significant fluctuations of volcanic tremor were detected for more than 24 hours, with intensity levels reaching those observed at the onset of the eruption. Higher levels of seismicity continued through 7 February.

Figure 105. Thermal images of the Piton de la Fournaise eruptive site from 1 and 2 February 2017. Left and center are aerial views taken in on 2 February at 0845, and the right image is a ground view from 1 February at 1000. Courtesy of OVPF (copyright OVPF / IPGP; Bulletin d'activité du jeudi 2 février 2017 à 16h00).

OVPF reported that during 8-14 February volcanic tremor was high, with levels reaching those observed at the onset of the eruption on 31 January. The eruptive vent was perched on top of a cone that was 30-35 m high and 190 m wide at the base (figure 106). The lava level inside of the cone was low, or about half of cone's height, and incandescent material was ejected from the vent. Inflation stopped on 11 February. The lava flow reached its farthest extent on 10 February, almost 3 km SE of the vent (figures 107 and 108).

Figure 106. The eruptive cone at Piton de la Fournaise on 10 February 2017 at 0850. The lava is exiting the cone from the side and then flowing SE. Courtesy of OVPF (copyright OVPF / IPGP; Bulletin d'activité du vendredi 10 février 2017 à 17h00).

Figure 107. Approximate location of Piton de la Fournaise lava flows as of 10 February 2017 at 0850, interpreted from aerial photographs (IGN background map). Courtesy of OVPF (copyright OVPF / IPGP; Bulletin d'activité du vendredi 10 février 2017 à 17h00).

Figure 108. The front of the lava flow at Piton de la Fournaise on 10 February at 0730. View is looking SE, see flow location on topographic map in figure 107. Courtesy of OVPF (copyright OVPF / IPGP; Bulletin d'activité du vendredi 10 février 2017 à 17h00).

Volcanic tremor fluctuated during 14-21 February. Observations made on the ground on 16 February by the observatory teams indicated that activity continued mainly in lava tubes. Only a few flows were visible a hundred meters downstream of the eruptive cone. A resumption of inflation was confirmed on 20 February.

During 25-26 February OVPF observers noted ejections of material from the active vent. A few skylights in the lava tubes were spotted. Late at night on 26 February tremor began to decline, and ceased at 1010 the next morning. Mid-day on 27 February observers confirmed that no material was being ejected from the vent, and that only white plumes were rising; gas emissions ceased at 1930. OVPF reported that the 28-day eruption at Piton de la Fournaise, beginning on 31 January and ending on 27 February, was estimated to have produced between 8 and 10 million cubic meters of lava. Although the eruption had ended on 27 February, inflation at the summit continued until about 7 March. It resumed at a low rate in mid-April, along with minor seismicity.

A new seismic swarm began at 1340 on 17 May and was accompanied by rapid deformation that suggested rising magma; volcanic tremor was recorded at 2010. The seismic and deformation activity was located in the NE part of l'Enclos Fouqué caldera. During an overflight at 1100 on 18 May scientists observed no surface activity at the base of the Nez Coupé de Sainte Rose rampart (on the N side of the volcano) nor outside of l'Enclos Fouqué caldera, and suggested that fractures opened but did not emit lava.

Seismicity increased again at 0400 on 18 May. The number of shallow (2 km depth) volcano-tectonic earthquakes progressively decreased over the next three days. During a field visit on 22 May scientists mapped the deformation associated with the 17 May event and measured displacements which did not exceed 35 cm. The 17-18 May activity resulted in two new zones of fumaroles that followed the trends seen in seismic and deformation data. Inflation stopped around mid-June, and seismicity was minimal for the remainder of the month.

MIROVA thermal data for 2016 and January-May 2017. Plots of thermal anomaly data by the MIROVA system correlated with the eruptive activity of 26-27 May 2016, 11-18 September 2016, and 31 January-27 February 2017 (figure 109). The thermal signatures of the September 2016 and February 2017 episodes show continued cooling of the new lava flows for several weeks after the effusive activity ceased.

Figure 109. MIROVA data for Piton de la Fournaise from March 2016 through May 2017. The thermal signatures of the September 2016 and February 2017 events show continued cooling of the new lava flows for several weeks after the effusive activity ceased. Courtesy of MIROVA.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: 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/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Associated Press (URL: http://www.ap.org/); U.S. News (URL: https://www.usnews.com/news/world/articles/2015/08/01/highly-active-volcano-erupts-on-reunion-amid-media-frenzy).

The last major eruption at Kambalny volcano was around 1350, although younger undated tephra layers have been found; there are also five Holocene cinder cones on the W and SE flanks. According to the Kamchatkan Volcanic Eruption Response Team (KVERT), a new eruption began began at about 2120 UTC on 24 March 2017. Satellite data showed an initial ash plume at about 5-6 km altitude drifting about 35 km SW from the volcano.

Explosive activity was strong during 24-27 March, generating ash plumes up to 7 km high that drifted downwind as far as 2,000 km (table 1). Activity then decreased, with only minor ash emissions through 6 April, followed by ash plumes that drifted 50 and 170 km on 9 and 10 April, respectively. Only gas-and-steam plumes were reported after that time.

Table 1. Chronological details of the March-April 2017 eruption of Kambalny. Data from KVERT reports.

On 25 March satellite imagery showed an ash plume stretching about 100 km SW of the Kamchatka Peninsula (figure 1). A dark stain is visible to the W of the plume, where ash has covered the snow. By 26 March ashfall had covered the ground on both sides of the volcano. The eruption was also observed on the ground by staff at the South Kamchatka Federal Wildlife Sanctuary (figure 2). The Ozone Monitoring Instrument on the Aura satellite observed an airborne plume of sulfur dioxide (SO2) trailing S of Kamchatka on 26 March 2017 (figure 3).

Figure 1. The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite captured a natural-color image of Kambalny and its plume on 25 March 2017, the day after it began to erupt (N to top of photo.) By 0134 UTC (1334 local time) that day, the plume stretched about 100 km SW. Courtesy of NASA Earth Observatory; image prepared by Jeff Schmatlz and Joshua Stevens using MODIS data from LANCE/EOSDIS Rapid Response, and caption by Pola Lem.

Figure 2. Eruption of Kambalny on 25 March 2017. Photo by Liana Varavskaya, South Kamchatka Federal Wildlife Sanctuary (URL: http://www.kronoki.ru/news/1187).

Figure 3. Sulfur dioxide in the 26 March 2017 plume from Kambalny eruption. Courtesy of NASA Earth Observatory; map by Joshua Stevens using data from the Aura OMI science team.

On 28 March 2017, the Operational Land Imager (OLI) on the Landsat 8 satellite acquired a natural-color image of an ash plume from Kambalny (figure 4), including a large area of ash-covered snow. When photographed by scientists on 12 April (figure 5), the entire edifice was covered by ash and there was a gas-and-steam plume rising from a crater fumarole.

Figure 4. Ash plume from Kambalny moving WNW on 28 March 2017. A large area of ash-covered snow is visible across the southern portion of the image. Courtesy of NASA Earth Observatory; image by Joshua Stevens using Landsat 8 OLI data from the U.S. Geological Survey.

Figure 5. A small gas-and-steam plume rises from a fumarole in the Kambalny crater on 12 April 2017. View is from the S. Photo by A. Sokorenko; courtesy of IVS FEB RAS.

Geologic Background. The southernmost major stratovolcano on the Kamchatka peninsula, Kambalny has a summit crater that is breached to the SE. Five Holocene cinder cones on the W and SE flanks have produced fresh-looking lava flows. Beginning about 6,300 radiocarbon years ago, a series of major collapses of the edifice produced at least three debris-avalanche deposits. The last major eruption took place about 600 years ago, although younger tephra layers have been found, and an eruption was reported in 1767. Active fumarolic areas are found on the flanks of the volcano, which is located south of the massive Pauzhetka volcano-tectonic depression.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences, (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); South Kamchatka Federal Wildlife Sanctuary, Ministry of Natural Resources and Ecology of the Russian Federation, Kamchatka Territory 684000, Russia (URL: http://www.kronoki.ru/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The six overlapping summit craters of northern Chile's Lascar volcano have produced numerous lava flows down the NW flanks. Frequent small-to-moderate explosive eruptions since the mid-19th century, and infrequent larger eruptions, have produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires. An explosion on 30 October 2015 produced an ash plume that rose 2.5 km above the 5.6 km high summit and drifted NE; this event also initiated a distinct thermal anomaly signal recorded by MIROVA that continued through June 2016 (BGVN 41:07). Continuous incandescence from the crater was seen for the next two months. The thermal anomaly did not begin to diminish until February 2017; details of activity through June 2017 are reported here with information primarily from Chile's Servicio Nacional de Geología y Minería, (SERNAGEOMIN), and the Italian MIROVA project.

After the 30 October 2015 explosion, a persistent thermal anomaly appeared in the MIROVA data that maintained a near-constant level of activity through June 2016 (figure 49, BGVN 41:07). The MIROVA VRP (Volcanic Radiative Power) values remained steady with multiple weekly anomalies through January 2017 when they began to taper off in both frequency and intensity (figure 50). They were intermittent during February, persistent but at a lower level during March and into the first few days of April. A few anomalies appeared later in April, and one during mid-May 2017; there is no evidence to determine exactly when eruptive activity ended or the cause of the anomalies.

Figure 50. Thermal anomaly data from MIROVA (Log Radiative Power) at Lascar for the year ending on 12 June 2017. The thermal anomalies persisted at a steady rate and intensity from November 2015 (see figure 49, BGVN 41:07) through January 2017 when they began to decrease in both frequency and intensity, until they ceased in May 2017. Courtesy of MIROVA.

Throughout July 2016-June 2017, the local webcam showed persistent degassing of mostly steam plumes from the main crater, with plume heights ranging from 500-1,500 m above the summit (table 6). Although there were three pilot reports of ash emissions from Lascar on 22 and 25 September and 29 December 2016, in each case the Buenos Aires VAAC noted that there was no indication of volcanic ash in satellite images under clear skies; the webcam did show continuous emissions of steam and gas dissipating rapidly near the summit. Seismicity during this period varied from a low of three events during October 2016 to a high of 122 events during June 2017. Although there was an increase in the number of seismic events during April 2017, the total energy released remained low. Continuous incandescence at the crater was observed during October-December 2016.

Table 6. Seismic events, degassing information, and incandescence observed at Lascar from July 2016-June 2017. Information provided by SERNAGEOMIN monthly reports. Maximum height is meters above the 5,592 m elevation summit.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: Servicio Nacional de Geología y Minería, (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile ( URL: http://www.sernageomin.cl/); 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/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php?lang=es).

Frequent historical eruptions, first recorded in Aztec codices, have occurred since pre-Columbian time at México's Popocatépetl, the second highest volcano in North America. More recently, activity picked up in the mid-1990s after about 50 years of quiescence. The current eruption, which has been ongoing since January 2005, has included frequent ash plumes rising generally 1-4 km above the 5.4-km-elevation summit, and numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple ash emissions generally occur daily, with larger, more explosive events that generate ashfall in neighboring communities occurring several times each month. Information about Popocatépetl comes primarily from daily reports provided by México's Centro Nacional de Prevención de Desastres (CENAPRED). Many ash emissions are also reported by the Washington Volcanic Ash Advisory Center (VAAC). Satellite visible and thermal imagery and SO₂ data also provide important information about the character of the eruptive activity. Our last report covered activity through December 2014 (BGVN 40:02); this report covers 2015 and the first six months of 2016.

CENAPRED reported near-constant emissions of water vapor, gas, and minor ash during 2015 and January-June 2016. Ash plumes from larger explosions regularly occurred several times per day during the more active months, and a few times a week during the quieter months. Ashfall is sometimes reported within 40 km of the summit. The plumes generally rose to altitudes of 6.1-7.9 km, and occasionally higher. The prevailing winds most often sent the ash NE or E, but multi-direction plumes at different altitudes were also common. Incandescent tephra was ejected onto the flank within 1 km of the summit every month, and was reported 3.5 km from the summit after stronger activity on 3 April 2016. Sulfur dioxide emissions are persistent, with plumes drifting a hundred or more kilometers from the volcano observed regularly in satellite data. Two episodes of dome growth were reported in February and April 2015, and dome destruction was inferred during January 2016.

Activity during January-June 2015. During January 2015 CENAPRED reported at least 13 explosions with ash-bearing plumes, as well as near-constant emissions of water vapor and gas that sometimes contained ash. The ash plumes generally rose to 600-1,500 m above the summit crater (up to 6.9 km altitude) and drifted either E or NE. Incandescence from the crater was visible on most clear nights. The Washington VAAC issued two series of reports; ash emissions on 4 January were not observed in satellite imagery due to weather clouds, but the 17 January emission was observed via webcam and satellite images at 5.8 km altitude drifting E. There were 58 MODVOLC thermal alerts issued in January, all from the immediate vicinity of the summit crater; most days had multiple-pixel alerts. NASA's Global Sulfur Dioxide monitoring system captured nine days of SO₂ emissions with values greater than two Dobson Units (DU), a measure of the molecular density of SO₂ in the atmosphere. Values greater than 2 show as red pixels on the imagery created from the OMI on the Aura satellite (figure 69).

Figure 69. Sulfur dioxide plume from Popocatépetl on 15 January 2015 extending ENE from the summit over the Gulf of México. The gas is measured in Dobson Units (DU), the number of molecules in a square centimeter of the atmosphere. If you were to compress all of the sulfur dioxide in a column of the atmosphere into a flat layer at standard temperature and pressure (0° C and 1013.25 hPa), one Dobson Unit would be 0.01 millimeters thick and would contain 0.0285 grams of SO2 per square meter. The red pixels represent values >2 DU. Courtesy of NASA Goddard Space Flight Center (GSFC).

The volcano was very active during February 2015. CENAPRED reported that their seismic network recorded several hundred low-intensity events that were accompanied by steam-and-gas-emissions and usually contained ash. Numerous explosions were attributed to lava-dome growth. Ash plumes rose 1-2 km above the crater, generally drifting NE. Ashfall was reported a number of times in communities up to 50 km away, and incandescence at the summit was observed on many nights.

On 11 February, ashfall was reported in the city of Puebla (~50 km to the E) and in the municipalities of Juan C. Bonilla (30 km ENE), Domingo Arenas (22 km NE), Huejotzingo (27 km NE), and at the airport to the E. On 15 February, explosions generated ashfall in Huejotzingo, Domingo Arenas, Salvador el Verde (30 km NNE), San Felipe Teotlalcingo (26 km NNE), and Puebla. Five explosions generated ash plumes on 18 February (figure 70). On 21 February, there were 22 small explosions, some of which ejected tephra 200 m onto the NE flank. A series of explosions on 24 February ejected incandescent material as far as 700 m onto the NE and SE flanks.

Figure 70. Ash explosion from Popocatépetl on 18 February 2015. Webcam image courtesy of CENAPRED.

Additional explosions (19) detected on 25 February resulted in ashfall 20-37 km to the NE in San Martín Texmelucan (35 km NE), San Matías Tlalancaleca (35 km NE), San Salvador el Verde (29 km NE), Santa Rita Tlahuapan (34 km NNE), Tlaltenango, Huejotzingo, San Miguel Xoxtla (37 km NE), Domingo Arenas, Santa María Atexcac (20 km NE), and the Puebla airport (30 km NE). Explosions on 26 February ejected incandescent tephra 700 m onto the N and NE flanks; ashfall was again noted in Domingo Arenas, San Martín Texmelucan, and Huejotzingo in the state of Puebla. The international airport in Huejotzingo suspended operations to clean up the ash. On 27 February explosions generated ash emissions and again ejected incandescent tephra 300 m onto the flanks. Ashfall was reported in Huejotzingo, Domingo Arenas, Tlaltenango, San Andrés Cholula (33 km E), and Puebla. Two separate series of explosions were detected on 28 February, and more incandescent tephra was ejected 300 m onto the flanks.

During an overflight on 17 February, volcanologists observed a dome at the bottom of the inner crater, which formed in July 2013 and extends 100 m below the floor of the main crater. They identified this as dome number 55; it was 150 in diameter. On a second overflight on 27 February, volcanologists observed that the dome had grown and was filling the bottom of the inner crater (figure 71). The dome was 250 m in diameter and at least 40 m high, putting the top about 60 m above the bottom of the main crater floor. The volume was an estimated 1.96 million cubic meters. They also witnessed a small ash explosion from the inner crater (figure 71).

Figure 71. The summit crater with dome 55 at Popocatépetl on 27 February 2015. The dome at the bottom of the inner crater was estimated to be 250 m in diameter and at least 40 m high (upper). CENAPRED scientists witnessed a small ash explosion from the inner crater during the overflight (lower). Courtesy of CENAPRED.

The Washington VAAC issued reports of ash emissions on 3 February, and during 11-16 and 24-28 February. Ash plumes identified in satellite imagery rose to altitudes of 6.1-6.7 km during 11-13 February and drifted as far as 5 km NE. On 24 February, a plume was seen extending about 15 km ENE from the summit at 6.7 km altitude. The next day an ash plume was observed in satellite imagery at 9.1 km altitude extending NE about 12 km from the summit. Later that day (25 February) it extended 300 km NE at 6.7 km altitude, out over the Gulf of México, before it dissipated. Additional emissions on 25 February occurred about every 60-90 minutes and drifted 130 km ENE at 8.2 km altitude. These bursts of ash continued moving ENE and finally dissipated about 170 km from the volcano. Plumes observed on 27 and 28 February in multispectral satellite images rose to 7-7.9 km altitude. A small area of faint ash from the 27 February emission was visible in images in the Gulf of México about 390 ENE of the summit late on 28 February, while a new emission was visible extending NE about 25 km. Twenty-five MODVOLC thermal alerts were issued most days during February (except 12-17). The OMI instrument on the AURA satellite captured 14 days of SO₂ emissions with DU>2.

Activity continued at a high rate during March 2015, again with hundreds of emission events with gas, steam, and small quantities of ash (figure 72). Larger quantities of ash from multiple-per-week explosions rose 1-3 km above the summit and drifted N or NE. Incandescent tephra was ejected 100-800 m onto the N, NE, and SE flanks at least four times. A series of explosions on 7 March led to ashfall reported in Ecatzingo (15 km SW). On 9 March ashfall was reported in Amecameca (20 km NW), Ecatzingo (15 km SW), and Tepextlipa from explosions the previous day. A four-hour series of explosions on 24 March produced steam, gas, and ash emissions that rose 3 km.

Figure 72. Ash emission from Popocatépetl on 2 March 2015. Webcam image courtesy of CENAPRED.

The Washington VAAC reported ash emissions every day during 1-5, 7-10, 19-21, and 24-26 March. During the first week, the plumes rose 6.1-7.6 km altitude, drifted NE, N, and NW, and were usually visible for about 100 km from the summit before dissipating. On 8 March, two plumes drifted in opposite directions: one went 15 km ENE at 7 km altitude and one drifted 45 km W at 5.6 km altitude. During the second half of March, the plumes drifted generally NE, at altitudes of 6.1-7.3 km, tens of kilometers before dissipating. Only 11 MODVOLC thermal alerts were issued in March; SO₂ data showed four days with DU>2, although SO₂ plumes were visible in satellite data almost every day.

Hundreds of daily ash emissions were noted by CENAPRED during April 2015. Ash plumes generally drifted N or NE at 1-3 km above the summit crater, but occasionally they drifted W or SW. Incandescence was often noted at night. Incandescent tephra was ejected several hundred meters onto the flanks during 4-6 April, and again on 18 and 20 April. The only ashfall reported during the month was in Tetela and Ocuituco (both about 22 km SW) after ash-bearing explosions during 3-4 April.

During an overflight on 10 April (figure 73), scientists confirmed that a lava dome had been emplaced in the bottom of the crater between 24 March and 4 April. The lava dome was at least 250 m in diameter and 30 m high. The surface of the dome had concentric fractures and the central part was collapsed from deflation.

Figure 73. During an overflight on 10 April 2015, CENAPRED scientists confirmed that a lava dome had been emplaced in the bottom of the inner summit crater at Popocatépetl between 24 March and 4 April. Courtesy of CENAPRED.

The Washington VAAC issued aviation alerts during 1, 3-8, 13, and 18-21 April. On 3 April volcanic ash was observed moving SE from the summit at 8.2 km altitude. The plume extended over 150 km before dissipating later in the day. Another plume the same day rose to 9.1 km altitude and drifted 55 km NE. During 4 and 5 April, ongoing emissions at various altitudes from 6.1 to 9.1 km drifted in multiple directions for tens of kilometers before dissipating. Most of the alerts were for brief, intermittent emissions that dissipated within 20 km of the summit after a few hours. On 7 April one ash cloud drifted 45 km SSE and another drifted 100 km SE, both at 7.6 km altitude. An ash emission on 13 April traveled around 260 km E at 7.3 km altitude before dissipating. The plumes observed during 18-21 April ranged from 6.7 to 9.7 km in altitude, and mostly drifted NE or E. There were 20 MODVOLC thermal alerts issued during April, scattered throughout the month. Most days during April had SO₂ plumes with values >2 DU in the satellite data.

Ashfall was reported in San Pedro Benito Juárez (10-12 km SE), in the municipality of Atlixco Puebla on 2 May 2015, and in Ocuituco (24 km SW) on 22 May. On 26 May ashfall was reported in Tetela del Volcán (20 km SW) and slight ashfall was recorded in Amozoc, Puebla (60 km E) on 31 May. The ongoing explosions generated ash emissions that generally rose 0.5-2.5 km above the crater rim and sent plumes to the SW, SE, and E (figure 74). Nighttime crater incandescence was observed on most clear nights.

Figure 74. Ash emission at Popocatépetl on 30 May 2015. Webcam image courtesy of CENAPRED.

Although aviation alerts from the Washington VAAC were issued during 9 days of May (2, 10, 20-21, 25-26, 28, and 30-31), plumes were only visible in satellite images a few times. The highest plume was on 20 May, at 8.2 km altitude drifting SSW. The plume on 26 May was observed drifting NW at 6.1 km, extending 150 km from the summit. Only four MODVOLC thermal alerts were issued during 10, 19, 21 and 30 May, but strong SO₂ plumes (>2 DU values) were recorded 12 times, with just as many days showing smaller-magnitude plumes.

Activity was much quieter at Popocatépetl during June 2015. Only six VAAC reports were issued (during 7-8, 12, and 21-22), and only two were identified in satellite images. The plume on 7 June rose to 8.2 km altitude and drifted SW. The larger plume on 12 June came from multiple small emissions; it rose to 6.1 km altitude and was last seen at 55 km SW of the summit before dissipating. There were seven MODVOLC thermal alerts on seven different days during June, and 17 different days with SO₂ plumes with recorded values >2 Dobson Units.

Activity during July-December 2015. Multiple daily emissions, nighttime incandescence, and intermittent explosions continued during July 2015 (figure 75). Nine MODVOLC thermal alerts were issued, but they were concentrated during 6-8 and 26-31 July. The Washington VAAC issued alerts on 8, 10, and 11 July, and then during a second period from 24 to 28 July. The report on 8 July noted an ash emission at 7.6 km altitude extending 15 km SW from the summit. The report on 10 July noted that ashfall had been reported about 10 km NW of the summit, but cloudy skies prevented satellite observations. Reports issued during 24-28 July included satellite observations of emissions at 6.1 to 7.6 km altitude extending 25-45 km NE or W from the summit before dissipating. The SO₂ emissions during July were visible nearly every day in the satellite data, with 16 days having values >2 DU.

Figure 75. Ash emission on 17 July 2015 from Popocatépetl. Webcam image courtesy of CENAPRED.

Sulfur dioxide emissions during August 2015 were also visible in satellite imagery nearly every day. Six days had values >2 DU. There were no Washington VAAC reports during August, but there were ten MODVOLC thermal alerts issued throughout the month.

The number of daily emissions during September 2015 were far fewer than during January-July 2015, although crater incandescence was still observed. The Washington VAAC only issued three reports, all during 19-20 September. They observed an ash emission on 19 September at 6.7 km altitude that extended 45 km WNW from the summit for a few hours before dissipating (figure 76). Ten MODVOLC thermal alerts were issued in September, and SO₂ plumes were visible daily with values >2 DU on half the days of the month.

Figure 76. Ash emission from Popocatépetl on 19 September 2015. Webcam image courtesy of CENAPRED.

Ash emissions increased again during October 2015. Ash-bearing plumes rose as high as 2 km above the crater. The Washington VAAC issued reports of ash plumes on 12 different days. An ash plume observed on 2 October at 7.6 km altitude extended 185 km SW before dissipating; another plume on 20 October was identified in satellite images at 8.5 km altitude drifting NW, and was visible from México City. Eighteen MODVOLC thermal alerts were issued throughout the month, and strong SO₂ plumes were detected nearly every day in OMI satellite data.

Activity during November 2015 was similar to that during October. CENAPRED recorded tens of daily emissions of water vapor, gas, and minor amounts of ash. Explosions at regular intervals sent ash plumes 1-3 km above the summit, and incandescent material was deposited on the flanks within 1 km of the crater a number of times (figure 77). The Washington VAAC issued aviation alerts almost daily during 1-17 November, but none after that for the rest of the year. Most of the ash plumes reached 6.1-7.3 km altitude and drifted N, NE, SW, W, and S for a few tens of kilometers before dissipating. The plume on 7 November rose to 9.1 km and was visible as a dark feature above the weather clouds before it dissipated.

Figure 77. Incandescent material showers the flanks of Popocatépetl from an explosion during the early morning hours of 17 November 2015. Webcam image courtesy of CENAPRED.

While ash plume observations decreased during the second half of November and during December, MODVOLC thermal alerts increased in number. Thirty-three appeared during November, and 35 during December. Plumes of SO₂ were persistently visible in Aura/OMI satellite data both months.

Activity during January-June 2016. A series of explosive events during 2-8 January 2016 resulted in 13 aviation alerts from the Washington VAAC. An ash plume first reported in satellite data early on 6 January was drifting E at 6.4 km altitude. By late the next day, VAAC reports indicated that the plume was still visible over 1,000 km E before it finally dissipated. A new series of explosive events began on 20 January (figure 78) and lasted through 26 January.

Figure 78. Ash explosion at Popocatépetl on 20 January 2016. Webcam image courtesy of CENAPRED.

CENAPRED reported that on 23 January 2016 an increase in activity was characterized by continuous gas-and-ash emissions, likely related to the destruction of a recently-formed lava dome. Later that night cameras recorded incandescent fragments ejected during periods of emissions. The constant steam-and-ash emissions drifted E and ENE for more than 48 hours at altitudes from 6.1 to 8.2 km. By 25 January, an ash plume was still visible over 900 km E. NASA Earth Observatory posted a satellite image of the plume around 1930 UTC (1330 local time) (figure 79). NASA's Goddard Space Flight Center also captured an image of a strong SO₂ plume drifting NE from Popocatépetl at the same time (figure 80). Twenty-six MODVOLC thermal alerts were issued on 15 days of January. Especially strong SO₂ plumes were visible on 6, 7, 23, and 25 January.

Figure 79. Popocatépetl emits an ash plume on 25 January 2016 that extends over 300 km E over the Gulf of México. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this image at 1930. Image prepared by Jeff Schmaltz, LANCE/EOSDIS Rapid Response using VIIRS data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Courtesy of NASA Earth Observatory.

Figure 80. A strong SO2 plume drifting over 500 km NE from Popocatépetl was captured by the OMI instrument on the AURA satellite during 1918-2015 UTC on 25 January 2016. A visible infrared image was acquired within this same period (see figure 79). Courtesy of NASA GSFC.

Tens of daily emissions of water vapor, gas, and ash were reported during February 2016, along with multiple daily explosions generating ash plumes and occasionally sending tephra onto the flank. The Washington VAAC issued aviation alerts on twelve days during the month. They were discrete events that sent ash plumes generally E or SE at altitudes between 6 and 7 km, and generally dissipated within 6 hours, tens of kilometers from the summit. An ash plume reported on 15 February was still visible 500 km E of the summit before it dissipated. MODVOLC thermal alerts were reported on 10 days during the month, SO₂ plumes were more intermittent and only exceeded 2 DU on four days.

The largest ash explosion events during March 2016 took place at the end of the month. On 27 March, an ash plume was spotted by the Washington VAAC extending about 100 km NE at 6.4 km altitude. Explosions on 29 March created an ash plume at 9.1 km altitude moving rapidly ESE (figure 81). Ashfall from the plume caused Puebla's airport to close from 2000 on 29 March to 0600 on 30 March. The plume fanned out and extended tens of kilometers to both the S and SE before dissipating. On 31 March an explosion produced an ash plume that rose 1.8 km and drifted ENE; incandescent fragments fell 1 km away on the ESE flank. Thermal alerts were issued by MODVOLC on 13 days of March, and SO₂ plumes were visible about the same number of days, but values did not exceed 2 DU.

Figure 81. An ash plume at Popocatépetl on 29 March 2016. Webcam image courtesy of CENAPRED.

On 2 April 2016 CENAPRED scientists conducted an overflight of the crater and observed the inner crater which was 325 m in diameter and 50 m deep (figure 82). The crater had previously been filled with a lava dome, destroyed in January, which had grown to an estimated volume of 2,000,000 cubic meters. Small landslides had occurred on the E wall of the inner crater. During 3 April, incandescent fragments were ejected as far as 3.5 km onto the E and SE flanks, generating fires in that part of the forest; authorities noted that the event was the largest explosion in three years. Ash fell in the towns of Juan C. Bonilla (32 km ENE) and Coronango (35 km ENE), both in the state of Puebla. The Washington VAAC reported numerous ash plumes during 1-9 April. The highest, on 1 April, was observed in satellite data at 9.7 km altitude, extending over 300 km NE over the Gulf of México. The other plumes were mostly observed between 6.4 and 8.5 km altitude, drifting E or NE.

Figure 82. The inner crater at Popocatépetl on 2 April 2016. CENAPRED scientists estimated that it was 325 m in diameter and 50 m deep. The previous lava dome was destroyed during January 2016. Courtesy of CENAPRED.

Strombolian activity on 18 April ejected incandescent fragments 1.6 km onto the NE flank, and ash plumes rose 3 km above the crater and drifted ENE. Ashfall was reported in San Pedro Benito Juárez (12 km SE), San Nicolás de los Ranchos (15 km ENE), Tianguismanalco (17 km E), San Martín Texmelucan (35 km NNE), and Huejotzingo (27 km NE). According to a news article, the airport in Puebla closed again due to the ash plumes. Thermal alerts from MODVOLC were recorded on 13 days during the month, and SO₂ plumes were visible in the Aura/OMI data almost every day.

Activity continued at slightly lower levels during May 2016 with VAAC reports issued on nine days. The ash plumes reported all dissipated quickly within a few tens of kilometers of the summit after drifting E at altitudes generally around 6.4 to 6.7 km. Single MODVOLC alerts were reported on only six days during the month, and except for a large SO₂ plume on 3 May, small plumes were visible about 8 days of the month.

An increase in the number of daily explosions with ash emissions was reported by CENAPRED during June 2016. As many as six a day were reported during the second week of the month. An explosion on 12 June produced an ash plume that rose 2.5 km and drifted W (figure 83). Minor amounts of ash fell in Ozumba (18 km W). Aviation alerts were issued by the Washington VAAC on 13 days. Most of the ash plumes dissipated within six hours a few tens of kilometers from the summit due to high winds. The plumes rose to altitudes between 6.1 and 7.9 km, and drifted NE, W and SW. The ash plume reported on 23 June extended NE 16 km at 7.3 km altitude, and 26 km SW at 5.8 km altitude simultaneously. Thermal alerts from the MODVOLC system were reported on 1, 8, and 25 June. SO₂ satellite data was only available for the second half of the month, and showed two days with significant SO₂ plumes.

Figure 83. Explosion with ash plume at Popocatépetl on 12 June 2016. Webcam image courtesy of CENAPRED.

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

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: https://www.gob.mx/cenapred/); 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: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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 Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The andesitic Volcán El Reventador lies well east of the main volcanic axis of the Cordillera Real in Ecuador and has historical observations of eruptions with numerous lava flows and explosive events going back to the 16th century. The largest historical eruption took place in November 2002 and generated a 17-km-high eruption cloud, pyroclastic flows that traveled 8 km, and several lava flows. From June 2014-December 2015, monthly eruptive activity included ash plumes, lava flows, pyroclastic flows, and ejected incandescent blocks (BGVN 42:06). Similar activity during January-April 2016 is described below with information provided by the Instituto Geofisico-Escuela Politecnicia Nacional (IG) of Ecuador, and the Washington Volcanic Ash Advisory Center (VAAC).

Almost daily eruptive activity continued during January-April 2016. Steam and gas emissions, usually containing minor amounts of ash, were visible at the summit crater on most clear days rising 500-1,000 m above the 3.6-km-high summit. Explosions sent incandescent blocks 500-1,500 m down all flanks several times each month. Pyroclastic flows also traveled similar distances down the flanks a few times each month. A lava flow was observed descending the N flank of the summit cone on 28 January 2016.

Steam and gas emissions, usually with minor amounts of ash, rose daily from the summit crater during January 2016. Plumes generally rose 500-1,000 m and drifted NW or W. A pyroclastic flow descended 1,000 m down the NE flank on 5 January. Loud explosions were heard in the community of El Reventador (15 km E) on 6 and 7 January, and plumes were observed 1.5 km above the crater. The Washington VAAC reported an ash emission moving SW on 9 January at 4.6 km altitude; it extended 65 km SW before dissipating. The Guayaquil Meteorological Weather Office (MWO) reported an ash emission on 12 January at 6.7 km altitude, but extensive cloud cover prevented satellite observation.

The Washington VAAC observed emissions in satellite imagery moving 25 km NW on 15 and 16 January at about 4.9 km altitude. Technical crews performing maintenance on 15 January observed and documented several explosions with ash plumes that reached 2 km above the summit (about 5.5 km altitude) and observed a pyroclastic flow that moved 500 m down the N flank (figure 53). They also noted pyroclastic deposits that had been emplaced during recent weeks along the N flank. Small pyroclastic flows during the night of 18 January descended the flanks of the cone for 1,000 m. Additional explosions the next day sent blocks down the SW flank. On 21 January, incandescent blocks traveled 1,200 m down the W flank; on 27 January, they were observed 500 m below the summit crater. The Washington VAAC observed a hotpot in infrared imagery on 24 January.

Figure 53. Activity at Reventador on 15 January 2016 was documented by technicians working on monitoring equipment. Top: an ash column reached 1.5 to 2 km above the summit during the afternoon. Bottom: A pyroclastic flow traveled 500 m down the flank as seen in this thermal image. Top photo by J. Córdoba, courtesy of IG-EPN (Actualization de la Actividad eruptive del volcán Reventador Informe 2016-1).

On 28 January 2016, IG conducted an overflight and observed pulsing fumarolic activity producing plumes with low to moderate ash emissions drifting W. They noted pyroclastic flow deposits on all the flanks that did not go beyond the foot of the active cone. They also witnessed an active lava flow descending the N flank, emerging from a vent on the N side of the summit of the cone (figure 54). Thermal measurements were taken at the N vent (501°C ), the central vent (372.8°C), and the base of the flow (324.6°C) (figure 55). MODVOLC thermal alerts were reported on eight days during January (6, 9 (4), 14, 16 (3), 18 (3), 25 (2), 27 (3), 29, 31).

Figure 54. A lava flow descends the N flank of the summit cone at Reventador on 28 January 2016 as seen during an overflight by IG. The lava is emerging from a vent on the N side of the summit 'Vento Norte,' distinct from the vent at the center of the summit 'Vento Central.' Photo by M Almeida, courtesy of IG-EPN (Resumen de las Observaciones efectuadas durante el vuelo efectuado el 28 de enero de 2016).

Figure 55. Closeup view of the 28 January 2016 lava flow at Reventador showing the temperature values from three different locations. The temperature at the central vent was 372.8°C, at the N vent from which the flow emerged it was 501°C, and 324.6°C at the base of the flow. The points of thermal measurement are shown in the corresponding photograph on the right. Minor gas emissions drifted W. Thermal image by P. Ramón, photograph by M. Almeida, courtesy of IG-EPN (Resumen de las Observaciones efectuadas durante el vuelo efectuado el 28 de enero de 2016).

Reventador was quieter during February 2016 than in January. Steam and gas emissions with minor ash were observed often, with emissions generally below 500 m above the crater. Incandescent blocks observed on 4 February were 1,000 m below the summit crater. The Washington VAAC reported ash emissions visible in satellite imagery on 5 February moving SSW, extending about 25 km at 4.3 km altitude (about 700 m above the summit crater); they also observed incandescence at the crater. Incandescence was again observed on 6 and 7 February; blocks traveled 700 m down the SW flank on 13 February. A diffuse, narrow plume of ash was drifting NW from the summit on 14 February at 4.6 km altitude. The Guayaquil MWO reported an ash plume at 6.1 km altitude moving W on 23 February, but weather clouds obscured views in satellite imagery. Although it was cloudy on 27 February, loud explosions were heard during the night. MODVOLC thermal alerts were reported on seven days of the month; 1 (3), 3 (5), 5 (4), 6, 14 (3), 19, and 26 (3).

Tourists visiting the Hostería el Reventador observed steam, gas, and ash emissions on 2 March 2016. On many clear days during March, emissions of steam with minor ash were observed rising 1 km above the summit crater, drifting NW, W or SW. Incandescence and pyroclastic flows were seen much more frequently than during February. A pyroclastic flow traveled down the SE flank on 5 March. Explosions that afternoon sent incandescent blocks 1,200 m down the E and SE flanks. This activity continued through 9 March with blocks traveling daily 500-1,000 m down the flanks. On 9 March, ash emissions rose to 1 km above the crater and drifted NW; morning explosions sent blocks 1,200 m down the flanks and a small pyroclastic flow was observed that night. Explosions with steam and ash rising 1 km above the summit were observed on 10 March. Incandescence at the summit, and blocks rolling up to 1,500 m down the flanks were observed on most clear nights during the second half of March. A pyroclastic flow on 20 March descended 2 km down the SW flank. Steam and ash were reported drifting W 1 km above the crater on 21 March.

The Guayaquil MWO reported ash emissions on 7 March to 4.9 km, but weather clouds prevented observations by the Washington VAAC. On 10 March, ash emissions were confirmed in satellite imagery at 6.1 km altitude drifting W. The MWO reported ash emissions at 6.4 km altitude on 15 March, but weather clouds again prevented satellite observation. Webcam images showed ash emissions on 18 March at 4.3 km altitude drifting NW. The next day, the Washington VAAC was able to observe emissions in both satellite imagery and the webcam drifting W at 5.5 km altitude. Possible emissions on 31 March were also obscured by weather clouds. MODVOLC thermal alerts were reported on 7 days during March; 6, 15 (2), 16 (2), 22 (4), 26 (4), 29, 31.

Explosions that sent incandescent blocks down the flanks were observed nine times during April 2016, on days 3, 4, 7, 9, 12, 19, 23, 25, and 26. They generally travelled 1,000 m or more down various flanks. They were observed 2,000 m down the SW flank after a large explosion on 23 April. Pyroclastic flows were observed three times. On 6 April they traveled 1,500 m down the NW flank; on 13 and 21 April they traveled 1,000 m down the E flank. Steam and gas emissions were observed on most clear days, and generally contained minor amounts of ash. The plumes usually rose 300 to 800 m above the summit and drifted W, but on 13 and 18 April they rose 2 km above the summit, according to INSIVUMEH.

The Washington VAAC reported a possible ash emission on 4 April drifting NW at 4.3 km altitude based on a brief emission witnessed from the webcam. Weather clouds prevented satellite imagery views. There were also reports of volcanic ash at 6.7 km altitude drifting SE on 12 April, but both the webcam and satellite imagery were obscured by clouds. Observers reported an ash plume moving NE at 5.5 km altitude the next day. Ash emissions were reported moving NW at 5.8 km altitude on 29 April, but weather clouds again obscured satellite imagery. MODVOLC thermal alerts were reported on 8 days of April: 3, 11 (2), 14 (2), 19 (2), 20, 25 (4), 26 (3), 30.

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 (IG), Escuela Politécnica Nacional, 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: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/).

Volcán de San Miguel (Chaparrastique), in southern El Salvador, was active with several flank lava flows during the 17th-19th centuries, but recent activity has consisted of occasional ash eruptions from the summit crater. The beginning of the most recent eruption on 29 December 2013 resulted in a large ash plume that rose to 9.7 km altitude, and dispersed ash to many communities within 30 km of the volcano (BGVN 40:08). Intermittent ash plumes lasted through 28 July 2014. This report covers activity from January 2015 through June 2017, and describes six small ash emission events during this time. Information about San Miguel comes from the the Ministero de Medio Ambiente y Recursos Naturales (MARN) of El Salvador, and the Washington Volcanic Ash Advisory Center (VAAC).

Six ash-bearing explosions occurred at San Miguel between January 2015 and June 2017. Otherwise, minor seismicity and pulses of gas-and-steam emissions were the primary type of activity. The explosion on 26 January 2015 sent a plume 300 m above the crater, drifting SW. An explosion on 11 April 2015 resulted in an ash plume rising about 800 m above the crater that also drifted SW. Trace amounts of ash were emitted on 13 August 2015. The largest explosion of the period took place on 12 January 2016, when an ash plume drifting W caused ashfall as far as 25 km away, and the plume was ultimately visible as far as 300 km from the volcano. Incandescence was observed at the base of the 900-m-high eruptive column that appeared on 18 June 2016. Minor ash emissions were reported on 7 January 2017 drifting 130 km SW from San Miguel. Minor seismic swarms and steam-and-gas plumes were reported during February-June 2017.

Activity during 2015. After very little activity other than slightly elevated RSAM values since July 2014, a small ash-bearing explosion occurred on 26 January 2015 (figure 18). The ash plume rose about 300 m above the crater and drifted SW, dissipating quickly. Trace amounts of ash fell in the Piedra Azul area about 6 km SW of the crater.

Figure 18. Gas-and-steam emissions at San Miguel on 26 January 2015, after an ash-bearing explosion that occurred earlier in the day. Courtesy of MARN (Informe Especial No. 8. Continúa constante emanación de gases del volcán Chaparrastique January 27, 2015 at 11:21 am).

Another emission lasting for 20 minutes on 22 February 2015 sent a column of gas 300 m above the crater that dispersed to the SSW; no ash was observed. Occasional pulses of gas were reported during March rising 200 m above the summit crater. An explosion on 11 April 2015 resulted in an ash plume rising about 800 m above the crater and drifting SW. Local observers reported a millimeter of ashfall in the areas of La Piedra, Morita, and San Jorge, less than 10 km to the SW.

Occasional small pulses of gas that rose to about 200 m above the crater were typical behavior during May-July (figure 19). On 13 August 2015, the webcam captured a gas plume emission that contained minor amounts of ash and rose 200-300 m above the crater. A millimeter of ashfall was reported in San Jorge, and near the communities of Moritas and Piedrita to the SW. No emissions were reported during September, and the small pulses of gas observed during October did not exceed 200 m above the summit crater. No anomalous activity was reported during November, and small discrete pulses of gas were the only activity reported for December 2015.

Figure 19. Diffuse degassing from the summit crater at San Miguel on 24 June 2015. Courtesy of MARN (Informe Mensual de Monitoreo Volcánico Junio, 2015).

Activity during 2016. San Miguel began the year with what MARN described as a VEI 1 eruption of ash and gas on 12 January 2016 (figure 20). Periodic pulses of ash and gas lasting 3-5 minutes rose to less than 1,000 m above the crater and drifted WSW. Ashfall was reported from La Piedra, Moritas, La Placita, San Jorge, (all less than 10 km SW), San Rafael Oriente (10 km SW), Alegría (25 km NW) and Berlin in Usulután (21 km SW).

Figure 20. Ash eruption at San Miguel in the early morning of 12 January 2016. Image from the MARN webcam on the N side of the volcano. Courtesy of MARN (Informe Mensual de Monitoreo Volcánico Enero, 2016).

NASA Earth Observatory captured images of two pulses of ash from the 12 January eruption that show the changing direction of the plume (figure 21). The first image, taken at 1635 (UTC) shows the ash plume headed directly W. The second image, taken three hours later at 1935 shows the active plume drifting SW, with the earlier plume segment farther to the W over the Pacific Ocean. The Washington VAAC reported the ash emission at 2.4 km altitude (300 m above the summit crater) drifting WSW at 1745 (UTC). At that time, the denser part of the plume extended 45 km from the volcano and the diffuse, wispy plume extended 130 km WSW. By midday on 13 January, the Washington VAAC reported ongoing emissions and that the plume extended 300 km SW. The plume was no longer visible in satellite images by the end of the day.

Figure 21. Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on NASA's Aqua and Terra satellites acquired these natural-color images of ash streaming from San Miguel on 12 January 2016. Terra captured the upper image at 1035 local time (1635 UTC) which shows the ash plume drifting W; Aqua captured the lower image three hours later at 1335 local time (1935 UTC), and it shows the SW drift of the plume with the older remnant to the W over the Pacific Ocean. Courtesy of NASA Earth Observatory.

Seismicity declined during 12-14 January 2016. On 15 January, local observers reported a millimeter of ash deposited in Las Cruces on the N flank. Gas emissions during 17-18 January were weak, only rising 150 m. At 0900 on 18 January, the emission plume became dark and drifted SW. By the next crater inspection on 19 February, MARN scientists noted only minor degassing from the summit crater.

Although a period of volcanic tremor occurred on 8 March 2016, only short pulses of gas were observed that did not rise more than 150 m above the crater. Another spike in seismicity occurred on 3 April, but no gas or ash emissions were observed. Otherwise, only minor pulses of gas issued from the crater during February through May. A seismic swarm indicating rock fracturing at depth on 31 May could have resulted in trace amounts of ash deposited within the crater, but cloudy weather prevented observations. A few pulses of gas were observed from the webcam other times during May.

Seismic activity increased significantly during the second week in June. An explosion in the early morning of 18 June 2016 lasted about 60 seconds, and sent an ash emission to about 900 m above the crater (figure 22). Incandescence was observed within the eruptive column, and the debris fell about 100 m down the N flank. Ashfall of less than half a millimeter was reported in the El Volcan area about 7 km NE of the crater. The volcanologist who examined the ash determined that it was juvenile material from a magmatic explosion. A continuous column of steam-and-gas issued from the crater until 29 June (figure 23). During this time, local observers and officials from the Civil Protection of San Jorge reported sulfur odors and slight acid rain damage to the vegetation in the La Morita, La Piedrita, La Ceiba, and LACAYO farms, located about 4 km W of the crater.

Figure 22. The pre-dawn eruption of 18 June 2016 at San Miguel photographed from the MARN webcam. The ash emission rose to about 900 m above the summit crater. Courtesy of MARN (Informe Mensual de Monitoreo Volcánico Junio, 2016).

Figure 23. Gas plumes from San Miguel during the second half of June 2016 caused acid rain damage to vegetation W of the volcano. Upper image from the MARN webcam taken on 24 June 2016. The lower image was taken at 0800 on 27 June near Las Moritas, about 5 km WSW of the crater by Antonio Saravia. Courtesy of MARN (Informe Mensual de Monitoreo Volcánico Junio, 2016).

Seismic activity was slightly elevated during the first half of July 2016, but otherwise only small pulses of gas were observed from the crater. Low-level activity continued from the summit crater during August. On 29 August, however, a seismic signal indicative of a lahar was noted near the VSM (Santa Isabel) seismic station, but no damage was reported. Periodic pulses of gases were noted during September 2016. A 20-minute-long seismic signal on 5 September indicated another lahar passing near seismic station VSM, but no damage was reported. GPS measurements during September indicated deformation of a few millimeters on the N flank. No explosions were reported during October-December 2016, only small plumes of steam and gas were observed (figure 24).

Figure 24. Steam-and-gas plumes blowing SW from San Miguel during December 2016. Image taken by the webcam located at the El Pacayal (Chinameca) volcano about 8 km S. Courtesy of MARN (Informe Mensual de Monitoreo Volcánico Diciembre, 2016).

Activity during January-June 2017. On 7 January 2017, the Washington VAAC reported minor volcanic ash emissions from San Miguel at 2.6 km altitude extending SW about 130 km from the summit. Mild degassing continued during February and March. A brief seismic swarm occurred on 17 April 2017, but no explosions of gas or ash were observed in the webcam. A strong gas plume rose 1.2 km above the crater rim on 27 April. Seismicity decreased during May. Other than small gas plumes, the only activity reported during June 2017 was a slight increase in seismicity beginning on 12 June and lasting to the end of the month.

Geologic Background. The symmetrical cone of San Miguel volcano, one of the most active in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. The unvegetated summit rises above slopes draped with coffee plantations. A broad, deep crater complex that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit, also known locally as Chaparrastique. Radial fissures on the flanks of the basaltic-andesitic volcano have fed a series of historical lava flows, including several erupted during the 17th-19th centuries that reached beyond the base of the volcano on the N, NE, and SE sides. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. The location of flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Information Contacts: Ministero de Medio Ambiente y Recursos Naturales (MARN), Km. 5½ Carretera a Nueva San Salvador, Avenida las Mercedes, San Salvador, El Salvador (URL: http://www.snet.gob.sv/ver/vulcanologia); 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: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

The dacitic Santiaguito lava-dome complex on the W flank of Guatemala's Santa María volcano has been growing since 1922. The youngest of the four vents in the complex, Caliente, has been actively erupting with ash explosions, pyroclastic flows, and lava flows for more than 40 years. Constant steam and magmatic gases during January-June 2016 were accompanied by some of the largest explosive events of the last few years in April and May. Ash plumes rose to over 5 km altitude and spread ash regularly over communities within 30 km (BGVN 41:09). Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and the Washington VAAC (Volcanic Ash Advisory Center) provided regular updates on the continuing activity during the second half of 2016, and are the primary sources of information for this report.

Constant emission of both steam and magmatic gas were observed from the summit of Caliente dome throughout July-December 2016. Overall, eruptive activity decreased during this period compared with the previous six months. During July-September, INSIVUMEH reported 3-5 daily weak or moderate explosions with ash plumes that rose to 3.3-3.5 km altitude and dispersed ash over communities generally to the SW within 30 km. Stronger explosions took place 5-10 times each month from July-September. The ash plumes from these larger explosions usually rose to 5-5.5 km altitude. The highest plume was reported by the Washington VAAC at 6.1 km altitude during August. Ash plumes drifted more than 100 km from the volcano on several occasions, and ashfall was reported more than 50 km away more than once. These larger explosions also produced numerous pyroclastic flows that descended into the drainages on the SE, S, and SW flanks of Caliente dome. Heavy rains resulted in substantial lahars generated from the ash and debris several times each month.

INSIVUMEH observed the growth of a new lava dome inside the summit crater of Caliente beginning in October. By the end of the year, it had filled more than half of the summit crater with new material. During October, November, and the first part of December, the number of smaller explosions to around 3.5 km altitude increased to 25-35 daily events.

Activity during July-August 2016. Eruptive activity at the Santiaguito dome complex decreased from previous months during July 2016. Constant degassing from the Caliente dome, weak and moderate daily explosions, and ashfall in nearby (5-20 km) communities to the W and SW were typical. Steam and magmatic gases generally rose 300-400 m above the summit crater. Three or four weak to moderate explosions per day generally created diffuse ash plumes that rose to altitudes of 3.3-3.5 km. Ashfall from the smaller explosions generally affected the villages of San Marcos Palajunoj, Loma Linda, Monte Bello, and a few others located 10-20 km SW. Four stronger explosions on 1 (2), 3, and 10 July sent ash plumes to altitudes of 5-5.5 km (figure 48) and generated pyroclastic flows that descended the SW, S, and SE flanks (figure 49).

Figure 48. A strong explosion with a mushroom-cloud-shaped ash plume rising to 5.5 km on 1 July 2016 at Santa María. View is from the NW. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Julio 2016).

Figure 49. A strong explosion with pyroclastic flows traveling down the SW, S, and SE flanks of Caliente dome at Santa María during July 2016. View is from the SE. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Julio 2016).

Ash from the larger explosions was reported at least once in Columba, about 20 km SW (figure 50), Malacatán (about 55 km NW), and also from the Chiapas regions of Mexico, 70 km W. The Washington VAAC reported a plume on 1 July at 5.2 km altitude with ash extending about 35 km WNW. On 10 July, they observed an ash plume in multispectral imagery moving NW about 45 km from the summit. They also observed a bright hotspot at the summit. On 11 July, they reported an ash plume at 6.4 km altitude extending over 80 km NW. Dissipating ash was visible in imagery about 275 km NW later in the day.

Figure 50. Ash fall covered vehicles in Colomba, about 20 km SW, from one of the larger explosions at Santa María during July 2016. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Julio 2016).

A lahar descended the Cabello de Ángel river drainage on 3 July 2016 after a large explosion (figure 51). It was up to 30 m wide in places, and 1.5 m deep with blocks up to 1.5 m in diameter. The Cabello de Ángel flows into the Nimá I and Samala River drainages.

Figure 51. A lahar descends the Nimá I drainage on 3 July 2016 at Santa María after a large explosion created a pyroclastic flow down the S flank. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Julio 2016).

Constant degassing of steam and bluish magmatic gases continued during August 2016, rising 100-400 m above the summit of Caliente dome. Three to five weak or moderate explosions occurred daily, sending ash plumes to altitudes of 3.3-3.5 km (800-1,000 m above the dome). The STG3 seismic station recorded nine larger explosions in August (4, 14, 16, 18, 20, 21, 23, 28) that sent ash emissions to 4-5.5 km altitude, and generated pyroclastic flows that descended up to 2.5 km down the flanks (figure 52). The incandescent rock and ash descended the Nimá I, Nimá II, and San Isidro drainages on the SW, S, and SE flanks.

Figure 52. Pyroclastic flows descend several drainages on the S, SW, and SE flanks of Caliente at Santa María during one of the large explosions of August 2016. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Agosto 2016).

Communities and fincas (farms) affected by ashfall from these explosions included San Marcos Palajunoj, Loma Linda, Monte Bello, San Felipe (15 km SSW), Mazatenango (25 km SSE), Retalhuleu (27 km SW), El Faro, La Florida (5 km S), Patzulin (SW flank), and El Patrocinio. Tephra particles as large as 8 mm were collected in Loma Linda (figure 53). A few of the explosions resulted in ashfall more than 50 km from the volcano, including into Mexico. The Washington VAAC reported ash plumes rising to 5.8 km on 1 August; they were later visible 175 km W of the Mexico coast, W of Tapachula, Mexico. Two emissions on 12 August were seen at 5.2 km altitude drifting W. Ongoing emissions were reported at 6.1 km altitude on 16 August moving WNW and extending about 80 km. The plume observed on 19 August was 65 km NW at 5.5 km altitude. A plume observed in multispectral imagery on 25 August was moving NW at 6.1 km altitude over 185 km from the summit.

Figure 53. Lapilli fragments as large as 8 mm diameter were collected in Loma Linda on 16 August 2016 from an explosion at Santa María. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Agosto 2016).

Increased precipitation during August 2016 led to lahars on 8, 13, and 29 August 2016 that descended the Cabello de Ángel , Nimá I, and Samalá drainages. They ranged from 18 to 25 m wide and were 1.5 m deep containing blocks up to 1.5 m in diameter. Flooding was reported downstream near the Castillo Armas bridge on the Samalá River.

Activity during September 2016. Most of the steam and magmatic gases emitting daily from Caliente during September 2016 rose 100-400 m above the dome and generally drifted SW or W (figure 54). Small to moderate ash-bearing explosions occurred 3-5 times daily; ash plumes generally rose to 3.3-3.5 km altitude during these events. Several stronger explosions during September (1, 4, 11, 17, 19, 24, 25, 30) generated ash plumes that rose to 4.5 or 5 km altitude and drifted W, SW, S, SE and E. The Washington VAAC also reported an ash plume observed in multispectral imagery on 20 September at 5.2 km altitude drifting 45 km W. A few hours later, they reported two plumes, one at 4.6 km drifting 75 mi W, and a second at 5.2 km altitude moving WSW over 80 km from the summit.

Figure 54. A magmatic gas plume drifts W from the Caliente dome in this view from the summit of Santa María during September 2016. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Septiembre 2016).

Near-daily ashfall was reported from many of the communities 10-20 km SW including San Marcos Palajunoj, Loma Linda, Monte Bello, Santa María de Jesús, El Nuevo Palmar, and Las Marías (figure 55) during September 2016. Lapilli as large as 15 mm diameter was collected in the neighborhoods of San Marcos Palajunoj (figure 56).

Figure 55. Vegetation near Loma Linda was covered with ash almost daily from Santa María during September 2016. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Septiembre 2016).

Figure 56. Lapilli from Santa María up to 15 mm in diameter fell in the village San Marcos Palajunoj during September 2016. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Septiembre 2016).

The larger explosions also resulted in pyroclastic flows that travelled 2.0-2.5 km down the SW, S, and SE flanks in the Nimá I, Nimá II, and San Isidro drainages. Areas of vegetation burned from the heat of the pyroclastic flows (figure 57).

Figure 57. Several areas of burned vegetation from the pyroclastic flows that descended the drainages on the SE flank of Caliente dome at Santa María during September 2016 are highlighted in yellow. The view is from the summit of Santa María looking S. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Septiembre 2016).

Lahars or heavy mudflows were recorded on ten days during September, primarily in the Cabello de Ángel and Nimá I drainages (figure 58). Channels of debris worked their way over the 2015 lava flows in the Nimá I drainage and continued downstream. The lahars were 13-20 m wide and 1.5 m high and carried clay, volcanic ash, and blocks up to 1.5 m in diameter.

Figure 58. The active channels of the Cabello de Ángel and Nimá I drainages (in yellow) on the SE flank of the Caliente dome at Santa María hosted numerous pyroclastic flows and lahars. The many lahars of September 2016 traveled over parts of the channel covered by the 2015 lava flows in the Nimá I drainage. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Septiembre 2016).

The constant explosive activity at Caliente dome during 2016 enlarged the summit crater significantly between January and the end of September 2016. In January 2016, it was about 260 m wide and 20 m deep; by 21 September, it was 340 m wide and 175 m deep according to INSIVUMEH (figure 59).

Figure 59. The summit crater at Santa María's Caliente dome enlarged substantially between 9 January (left) and 21 September (right) 2016 from numerous explosions. In January 2016, it was about 260 m wide and 20 m deep; by 21 September, it was 340 m wide and 175 m deep. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Septiembre 2016).

Activity during October-December 2016. INSIVUMEH reported that a new lava dome began growing inside the summit crater of Caliente on 1 October 2016. The number of weak to moderate ash-bearing explosions increased during October, but the overall amount of energy from the explosions decreased. The STG3 seismic station recorded 25-35 weak to moderate explosions per day and the ash plumes they created generally rose to 3.3-3.5 km altitude (figure 60). There were no strong explosions reported by INSIVUMEH. The Washington VAAC reported larger ash plumes at 5.5 km altitude on 3 and 4 October that drifted a few tens of kilometers SSW from the summit before dissipating. Ashfall from these plumes was reported in the villages of San Marcos Palajunoj, Loma Linda, Monte Bello, El Faro, Patzulin and others to the S and SW. Lahars up to 20 m wide descended the Cabello de Ángel drainage on 4, 27, and 28 October.

Figure 60. An ash-bearing emission from the Caliente dome at Santa María on 5 October 2016 rises into the sunset glow. The plume rose to an altitude of about 3.5 km before drifting SW. View from the SE. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Octubre 2016).

The same eruptive pattern as October continued during November 2016 with 25-35 daily weak to moderate explosions that were responsible for ashfall in the villages to the SW, including Monte Claro, San José, and La Quinta and others. Steam and magmatic gasses continued to rise 100-500 m above the Caliente dome. A 15-m-wide lahar descended the Cabello de Ángel drainage on 9 November that was one meter deep, and carried material several kilometers down the Nimá and Samala drainages. The Washington VAAC reported some of the ash plumes visible up to 50 km from the dome. On 14 November, they noted two ash emissions at 4.6 km altitude. One was dissipating about 40 km SW while the second was within 15 km headed in the same direction. They also noted a small ash emission at 4.6 km altitude on 25 November drifting 20 km W.

Eruptive activity continued at a similar level during the first half of December 2016 with many weak and a few moderate explosions. During the second half of the month, the number of moderate explosions increased, but the overall number of explosions decreased. Twenty-five to thirty weak to moderate explosions per day were responsible for ash plumes rising to 3.0-3.5 km altitude. The Washington VAAC reported plumes on 24 and 30 December visible in satellite imagery at 4.6 km altitude drifting W. INSIVUMEH reported that the explosion on 30 December generated a pyroclastic flow that traveled for 2 km.

The growth of the new lava dome within the summit crater of Caliente first observed in October continued during November and December. By 18 December 2016 the new, growing dome had filled about two-thirds of the summit crater (figure 61). Heat flow at Caliente steadily declined during the second half of 2016, especially as compared with values during the first half of the year (see figure 47, BGVN (41:09). Only two MODVOLC thermal alerts were recorded after June 2016, on 29 July and 1 August. The MIROVA signal also showed a steady decrease in heat flow during this period (figure 62).

Figure 61. Growth of the new lava dome at the summit crater of Caliente dome at Santa María during November and December 2016. The upper image was taken by Barbara Garcia during November 2016. The lower image is dated 18 December 2016. Courtesy of INSIVUMEH (Informe Mensual de Actividad Volcánica, Noviembre and Diciembre 2016).

Figure 62. MIROVA graph of Log Radiative Power from Santa María from early June through December 2016 shows steadily declining heat flow. Courtesy of MIROVA.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

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/); 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: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Confirmed historical eruptions at Italy's Stromboli volcano go back 2,000 years as this island volcano in the Tyrrhenian Sea has been a natural beacon for eons with its near-constant fountains of lava. Explosive activity during 2014 generated numerous lava flows that traveled down the flanks, including several that reached the ocean during August (BGVN 42:01). The volcano was quieter during 2015 and 2016 as reported by the Instituto Nazionale de Geofisica e Vulcanologia (INGV), Sezione de Catania, who monitors the gas geochemistry, deformation, and seismology, as well as the surficial activity at Stromboli. Their weekly reports are summarized briefly below. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N Area) and a southern crater group (S Area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the island. Thermal and visual cameras placed on the nearby Pizzo Sopra La Fossa monitor activity at the Terrazza Craterica.

No reports were issued by INGV after a report of 16 October 2014. The last activity at Stromboli in 2014 captured remotely was a MODVOLC thermal alert on 8 November 2014. Low- to medium-intensity explosions from the active vent areas at the summit characterized activity throughout 2015 and 2016. Occasional bursts of higher-intensity activity sent ash, lapilli, and bombs across the Terrazza Craterica and onto the head of the Sciara del Fuoco.

Activity during 2015. While no thermal anomalies were identified in MODIS data during 2015 or 2016, the eruptive activity continued at low-to-moderate levels. Strombolian explosions were frequent from both crater areas during January 2015. Six explosions accompanied by abundant ash emissions erupted from the N Area on 12 and 13 January. In the S Area, vents also produced tephra containing lapilli and small bombs. A high-intensity burst from the S Area on 23 January contained ash and a few lapilli and bombs.

Intermittent explosive activity continued at both crater areas during February 2015. Medium-to-low intensity explosive activity during the first week characterized the N Area, with the ejection of bombs mixed with ash. Strombolian activity increased on 7 February. In the S Area, explosions were characterized by the ejection of fine ash with lesser coarse material (lapilli and bombs). An energetic explosive event took place at the S Area on 15 February (figure 92). It was the strongest event since the activity of August 2014, and was followed by several explosions over the following 12 hours that contained abundant tephra.

Figure 92. The explosive sequence of 15 February 2015 at the S Area crater of Stromboli. Images captured by the thermal and visual cameras located on the Pizzo Sopra La Fossa span a two-minute interval that starts at 1109:08 on 15 February (A) and goes through 1110:52 (D). Image E is from the same moment as image D. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 17/2/2015).

Low-intensity explosions characterized both the N and S Areas during March and early April 2015. Beginning on the afternoon of 15 April, the intensity and number of explosions increased significantly in the N Area for about 48 hours. Low- to medium-intensity explosions continued at both crater areas during May. On the evening of 11 May, and again during 13-15 May, a continuous glow was observed from the S Area caused by significant spattering activity. Strombolian activity was also noted from both crater areas on 20 and 21 May, and was more frequently observed during June 2015 (figure 93).

Figure 93. Images from the Pizzo Sopra La Fossa visual camera show the increased Strombolian activity of June 2015 at Stromboli. On 11 June a double explosion of medium intensity from the two vents located in the S Area occurred just 10 seconds apart (top). The morphology of the terrace is visible in the lower left image, and the only explosion observed from the N Area was simultaneous with an explosion from the S Area (bottom right). Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 16/6/2015).

Members of an expedition to the summit on 1 July 2015 observed explosive activity from the S Area vents (figure 94). Activity continued at low-to-moderate levels during July. On 16 July, a strongly intense explosive sequence occurred at both crater areas (figure 95). The first explosion occurred in the S Area at 0103. A larger explosion a few seconds later produced a jet of bombs and lapilli that lasted for about 15 seconds and rose about 300 m into the air, depositing material across the Terrazza Craterica area and the upper part of the Sciara del Fuoco. A third explosion, this time from the N Area, occurred about one minute later, ejecting bombs and lapilli 200 m into the air. Intense spattering continued from both crater areas for the next hour, after which activity resumed at lower levels.

Figure 94. Explosive activity from the S Area photographed from the Pizzo Sopra La Fossa at Stromboli on 1 July 2015. Photo by B. Behncke, courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 7/7/2015).

Figure 95. The explosive sequence of 16 July 2015 at Stromboli. A) the first explosion from the S Area; B) the second and strongest explosion from another S Area vent; C) bombs ejected across the Terrazza Craterica; D) maximum height of the eruptive column; E) the third explosion rises from the N Area; F) glowing bombs and lapilli are ejected during the third explosion. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 21/7/2015).

Low-intensity explosions accompanied by weak and discontinuous spattering with ash, lapilli, and bombs characterized activity from both areas for most of August except for a short-lived (2-hour) vigorous explosive event at the S Area beginning around 2300 on 8 August 2015. Activity was more vigorous at the N Area from 23 August through the end of the month. Low- and medium-low intensity explosions were typical during September with only a few days of medium- to medium-high intensity explosive events. Activity during October was difficult for INGV to monitor due to difficulty with their equipment, but it appeared to continue at low-to-moderate levels.

A series of medium- and medium-high intensity events occurred during 7-9 November 2015 from the N Area and were captured by the thermal camera on the Pizzo Sopra La Fossa (figure 96). Two vents in the N Area produced strong explosions at the same time generating plumes with fine ash and lapilli that likely reached over 200 m above the Terrazza Craterica. Another strong explosion from the N Area occurred on 19 November, sending coarse ejecta onto the top of the Sciara del Fuoco.

Figure 96. A strong explosion on 8 November 2015 from the N Area from 2053:26 to 2053:40 (14 seconds). Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 10/11/2015).

Explosions during 12 and 14 December ejected bombs and lapilli onto the Sciara del Fuoco. During an overflight on 16 December thermal imagery showed hot explosive material from the N Area deposited on the Sciara del Fuoco, and freshly erupted material surrounding the S Area as well.

Activity during 2016. During January 2016 windy and cloudy weather conditions and technical equipment problems made observations difficult for INGV, but activity was generally low to moderate at both crater areas. A strong Strombolian explosion from the N Area on 14 January was one of the larger events of the month, sending lapilli and bombs to the top of the Sciara del Fuoco. Numerous explosions from the N Area of medium-to-medium-high intensity were typical during February. Explosions at the S Area were generally low intensity. Clear weather on 15 February provided an excellent view of the two crater areas on the Terrazza Craterica (figure 97). A brief event on 21 February at the S Area caused weak spattering around the vent.

Figure 97. The Terrazza Craterica at Stromboli as seen on a clear day from the Pizzo Sopra La Fossa on 15 February 2016, showing the two crater areas (AREA N, AREA S). Photo by F. Ciancitto, courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 16/2/2016).

During March 2016, two vents were active in the S Area, and one in the N Area until 16 March, when a second vent began activity (figure 98). The typical frequency of events during low-level activity is 0-1 explosions per hour. Rarely, higher energy events will deposit material on the Sciara del Fuoco. After a month of low-intensity activity at both crater areas, there was a rapid intensification of explosive activity at the S Area at around 2130 on 28 April, which continued through 1 May (figure 99).

Figure 98. The Terrazza Craterica as viewed from the thermal camera on the Pizzo Sopra La Fossa at Stromboli during 16 March 2016. In (A) and (B), the vents of the S Area (Area S) (1, 4) are active with occasional spattering from vent 3. In C), vent 2 of the N Area (Area N) is active; the arrow marks the new vent triggered on 16 March, in conjunction with an explosion from vent 2. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 22/3/2016).

Figure 99. The Terrazza Craterica as viewed from the visible camera on the Pizzo Sopra La Fossa at Stromboli during 29-30 April 2016. On 29 April (A), simultaneous explosive activity was observed at two vents in the S Area (yellow and white arrows) and one the N Area (red arrow). On 30 April (B), daylight illuminates the profile of the Terrazza Craterica and the position of the three vents shown in (A). Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 3/5/2016).

Generally low-level activity during most of May was interrupted during 6-11 May with persistent incandescence and pulsating spattering at the S Area vents. Occasional medium-to-high-intensity explosions from the S Area produced significant ash emissions during the second half of May, and often sent lapilli and bombs on to the Terrazza Craterica, and occasionally onto the Sciara del Fuoco.

Events with medium-to-high intensity levels continued at the S Area during June 2016, which resulted in ash emissions covering much of the Terrazza Craterica. Intensity increased in the N area by the third week of June. Two site inspections on 6 and 7 July by INGV provided details of the ongoing changes in morphology at the Terrazza Craterica (figure 100). At the N Area, they noted two distinct vents, while in the S area they observed a large crater depression with subvertical walls that had many deep vents on the S side. Episodic explosive activity from the N Area was accompanied by small ash plumes. In the S Area, landslides occurred along the southernmost wall, lasting for tens of seconds and producing small ash clouds.

Figure 100. The Terrazza Craterica at Stromboli on the morning of 6 July 2016. The S Area (on the left) is a large crater depression with subvertical walls that has many deep vents on the S side; two distinct vents are visible from the N Area on the right. Photo by D. Andronico, courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 12/7/2016).

During late July, persistent incandescence was visible at night from the Pizzo Sopra La Fossa coming from the northernmost vent of the S Area, which continued until 19 August. Activity diminished from this vent and appeared at the southernmost vent of the S Area on 20 August. Explosions of incandescent lava were observed about ten meters above the crater rim. Occasional high-intensity explosions from the N Area resulted in coarse ash emissions during August, especially during 27 and 28 August when two vents were active at the N area, sending bombs, lapilli, and ash onto the Sciara del Fuoco.

By the end of August activity was concentrated mostly in the N Area where two active vents ejected lapilli, bombs, and abundant ash in explosions that occurred at a rate of 2-3 per hour. On 29 September, a nighttime pulsating glow was observed from the Pizzo Sopra La Fossa visible camera emanating from the southernmost vent of the S area. Observations of the glow persisted until 6 October. INVG inferred the glow was related to deep explosive activity. Typical low-to-moderate activity during October included Strombolian activity several tens of meters above the crater rim and frequent ash emissions, primarily from the S Area.

During November and December 2016, low- and moderate-level activity continued, with persistent incandescence observed at northern vent of the S Area for most of December, and rare low-and-medium-intensity explosions observed at the N Area (figure 101).

Figure 101. Typical activity during November and December 2016 at Stromboli is represented in images captured by the visible camera located on the Pizzo Sopra La Fossa on 6 and 7 November. A) the main vents active on the Terrazza Craterica. The yellow and white arrows point respectively to the southern and northern vents of the S Area; the green and red arrows point respectively to the southern and northern vents of the N Area. B) bomb-laden explosion from the southern vent (yellow arrow) of the S Area. C) an explosion from the southern vent (green arrow) of the N Area. D) the northern vent (red arrow) of the N Area explodes and sends a bomb outside the crater. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 8/11/2016).

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/en/).

The almost continuous eruption at Yasur, possibly over the previous 800 years, remained active through October 2016 (BGVN 41:12). The Vanuatu Geohazards Observatory (VGO) has maintained the hazards status at Volcano Alert Level 2 (major unrest - danger around the crater rim and specific area, notable/large unrest, considerable possibility of eruption and also chance of flank eruption) through mid-June 2017.

Volcano Alert Bulletins posted by the VGO on 19 April, 22 May, and 22 June 2017 indicated ongoing strong explosive activity. Satellite-detected MODIS thermal anomalies identified by MODVOLC were numerous during the reporting period, with at least one every month except during November 2016. The MIROVA system also detected nearly continuous thermal anomalies during the year ending on 12 June 2017 (figure 46), though activity decreased in the last few months of 2016 and was somewhat more intermittent in the first half of 2017 compared to July-September 2016.

Figure 46. Thermal anomalies detected in MODIS data by the MIROVA system (log radiative power) at Yasur for the year ending 12 June 2017. Courtesy of MIROVA.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Vanuatu Geohazards Observatory, Department of Geology, Mines and Water Resources of Vanuatu (URL: http://www.vmgd.gov.vu/vmgd/, http://www.vmgd.gov.vu/vmgd/index.php/geohazards/volcano); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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