Stromboli, located in the northeastern Aeolian Islands, is composed of two active summit craters: the Northern (N) crater and the Central-South (CS) crater that are situated at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano (figure 187). The current eruption period began in February 1934 and has been recently characterized by Strombolian explosions at both summit craters, ash plumes, and SO₂ plumes (BGVN 45:09). This report covers activity consisting of dominantly Strombolian explosions, incandescent ejecta, and ash plumes from September to December 2020, with information primarily from daily and weekly reports by Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) and various satellite data.

Figure 187. Photo of the summit craters at Stromboli showing the North and Central-South crater areas with the location of each active vent: N1 and N2 in the N crater and S1, S2, and C in the CS crater. Photo was taken from the Pizzo sopa la Fossa during an expedition on 22 August by INGV-OE personnel. Courtesy of INGV (Rep. No. 37/2020, Stromboli, Bollettino Settimanale, 31/08/2020 - 06/09/2020, data emissione 08/09/2020).

Activity was consistent during this reporting period. Explosion rates typically ranged from 1-14 events per hour and varied in intensity that ejected material 80-250 m above the N crater and 150-250 m above the CS crater (table 10). An ash plume on 16 November rose 1 km above the crater, accompanied by a pyroclastic flow descending the Sciara del Fuoco to the NW as far as 200 m. As a result, some ash and lapilli fell in the town of Stromboli (2 km NE). Strombolian explosions were often accompanied by gas-and-steam emissions, occasional spattering that deposited material on the Sciara del Fuoco, small lava flows, and small pyroclastic flows. According to INGV, the daily SO₂ emissions measured 250-300 tons/day.

Table 10. Summary of activity at Stromboli during September-December 2020. Low-intensity activity indicates ejecta rising less than 80 m, medium-intensity is ejecta rising less than 150 m, and high-intensity is ejecta rising over 200 m above the vent. Data courtesy of INGV.

During September the frequency of the Strombolian explosions in the N crater typically ranged from 2-14 per hour; in the CS crater there were 1-10 explosions per hour. N1 consisted of three points of emissions that produced low- to high-intensity explosions, launching lapilli and bombs, sometimes mixed with fine ash, 80-200 m above the N crater and were distributed radially (figure 188); N2 typically showed low-intensity explosions (less than 80 m above the crater). Medium- to high-intensity explosions ejected mostly fine material mixed with some coarse tephra 250 m above the CS crater. On 28 September the number of explosive events reached a high of 22 per hour.

Figure 188. Webcam images of Strombolian activity at Stromboli in the N1 crater on 29 September (left) and in the CS crater on 4 October (right) 2020. Images captured by the SCV surveillance cameras. Courtesy of INGV (Rep. No. 41/2020, Stromboli, Bollettino Settimanale, 28/09/2020 - 04/10/2020, data emissione 06/10/2020).

Explosions with occasional spatter continued in October at a rate of 2-13 per hour in the N crater and 1-4 per hour in the CS crater. In the N crater, N1 consisted of 2-4 eruptive vents that produced explosions of variable intensity while N2 contained two vents that primarily produced low-intensity explosions. Lapilli and bombs, sometimes mixed with fine ash, were ejected 80-250 m above the N crater. Fine ash sometimes mixed with coarse-to-medium tephra rose 150-250 m above the CS crater. Spatter was reported from two hornitos that formed in the N1 crater (figure 189). On 11 October sporadic ash emissions and coarse ejecta were observed above the S2 crater, episodic ash emissions rose above the S1 crater, and occasional degassing with modest spattering were visible in the C crater.

Figure 189. Drone images showing gas-and-steam emissions and Strombolian activity at Stromboli during 8-9 October 2020. The white annotations label the craters and the red show the active hornitos (H). The N2H2 label shows a small explosion (right). Images from the HPHT Lab from INGV-Roma 1. Courtesy of INGV (Rep. No. 42/2020, Stromboli, Bollettino Settimanale, 05/10/2020 - 11/10/2020, data emissione 13/10/2020).

Strombolian explosions persisted into November. The N1 crater consisted of 2-3 vents, producing explosions of variable intensity; the N2 crater also consisted of 2-3 active vents that produced low- to medium-intensity explosions. The frequency of explosions ranged from 2-10 per hour in the N crater and 1-4 per hour in the CS crater. Lapilli and bombs, sometimes mixed with fine ash, rose 80-250 m above the N crater and fine material was ejected 150 m above the CS crater. On 10 November an explosion was detected at 2104 in the S2 crater of the CS area, producing pyroclastic material that was distributed radially along the Sciara del Fuoco, followed by an ash plume (figure 190). Within 30 seconds, another pulse of activity from the C crater in the northern part of the CS area produced intense lava fountaining that ejected coarse incandescent material 300 m above the crater, lasting about two minutes. At 2106 a small explosion was detected in the N2 crater, ending the explosive sequence.

Figure 190. Thermal (rows 1 and 3) and webcam (rows 2 and 4) images showing the evolution of the explosion at Stromboli on the evening of 10 November 2020 accompanied by an ash plume and incandescent ejecta. Images captured by the SCT and SQV surveillance cameras. Courtesy of INGV (Rep. No. 47/2020, Stromboli, Bollettino Settimanale, 09/11/2020 - 15/11/2020, data emissione 17/11/2020).

During an overflight by the 2nd Air Unit of the Coast Guard of Catania on 11 November, scientists identified degassing in the entire summit crater area; a small lava flow was observed in the S1 crater, originating from an intra-crater vent. Additional thermal anomalies were noted at the bottom of the C, N1, and N2 craters. Strong fumaroles were visible originating from a hornito located outside the S1 crater on the Sciara del Fuoco. A second hornito was visible on the slope of the Sciara del Fuoco near the N2 crater. On 16 November a major explosion was detected at 1017 in the N crater area and on the edge of the N2 crater. Thermal and visible images captured the resulting dense, gray ash plume that rose 1 km above the crater and the accompanying pyroclastic flow that descended the Sciara del Fuoco as far as 200 m (figure 191). Some ash and lapilli fell over the town of Stromboli, about 2 km away on the NE coast of the island. A sequence of explosive events at 0133 on 21 November was detected in three different craters: the first two events occurred in the N1 and N2 craters, and the third occurred in the C crater. Coarse material was ejected 300 m above the crater and was distributed radially, affecting the upper part of the Sciara del Fuoco. A small ash plume was also visible.

Figure 191. Thermal (top row) and webcam (bottom row) images showing the evolution of the explosion at Stromboli on the morning of 16 November 2020 accompanied by a significant gray ash plume. Images captured by the SCT and SCV surveillance cameras. Courtesy of INGV (Rep. No. 48/2020, Stromboli, Bollettino Settimanale, 16/11/2020 - 22/11/2020, data emissione 24/11/2020).

During December, similar Strombolian explosions were reported. There were two eruptive vents in the N1 crater and 2-4 in the N2 crater that produced explosions of low intensity and low-to-medium intensity, respectively. The frequency of explosions ranged from 1-13 per hour in the N crater and 1-5 per hour in the CS crater. Fine ash mixed with some coarse material (lapilli and bombs) was ejected 80-150 m above the N crater and mostly fine material rose 150 m above the CS crater. Some spattering activity was reported in the N2 crater, which contributed to the formation of hornitos that produced incandescent material. On 6 December an explosive sequence of events was detected in the CS crater area at 0612. An explosion ejected material 300 m above the crater that were distributed radially, depositing on the upper Sciara del Fuoco. In addition, two small lava flows formed (figure 192). A second explosion was recorded at 0613, characterized by lava fountaining in the CS crater that reached a height of 200 m. Similar activity in the N and CS craters were also captured by webcam images on 21 and 27 December, which showed lava fountaining, accompanied by a small pyroclastic flow (figure 193).

Figure 192. Thermal images of the explosion at Stromboli in the CS crater on 6 December 2020, accompanied by incandescent ejecta and two small lava flows. Some lava fountaining was visible in the bottom center image at 0513:47. Images captured by the SCT surveillance camera. Courtesy of INGV (Rep. No. 50/2020, Stromboli, Bollettino Settimanale, 30/11/2020 - 06/12/2020, data emissione 08/12/2020).

Figure 193. Webcam (top row) and thermal (bottom row) images of Strombolian activity in the N (left column) and CS (right column) crater areas at Stromboli on 21 December (top right) and 27 December (top left and bottom row) 2020. This activity included a small pyroclastic flow and lava fountaining. Images captured by the SCV and SCT surveillance cameras. Courtesy of INGV (Rep. No. 53/2020, Stromboli, Bollettino Settimanale, 21/12/2020 - 27/12/2020, data emissione 29/12/2020).

Intermittent and low-power thermal activity was detected during September through December, according to the MIROVA Log Radiative Power graph using MODIS infrared satellite information (figure 194). Though there were no detected MODVOLC thermal alerts during this reporting period, many thermal hotspots were visible in one or both summit craters on clear weather days using Sentinel-2 thermal satellite imagery, which is due to Strombolian activity (figure 195).

Figure 194. Intermittent, low thermal activity at Stromboli was recorded by the MIROVA graph (Log Radiative Power) during September through December 2020. The frequency of the thermal anomalies had decreased compared to the previous months of May through August; a total of eleven thermal anomalies were detected during this reporting period. Courtesy of MIROVA.

Figure 195. Weak thermal anomalies (bright yellow-orange) at Stromboli were visible in Sentinel-2 thermal satellite imagery from typically both summit craters during September through December 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The glaciated Saunders Island is located in the remote South Sandwich Volcanic Arc in the South Atlantic between Candlemas (to the north) and Montagu (to the south) islands. The main volcanic features are Mount Michael, lava flows on the northern Blackstone Plain, and the Ashen hills complex near the eastern Nattriss Point (figure 31). The Ashen Hills complex is a group of overlapping craters formed through phreatomagmatic activity, with the largest crater opening towards the NW (figure 32). Gas emissions have been remotely observed from the ice-filled Old crater to the SE, with reports of gas plumes extending back to 1820 (LeMasurier et al., 1990; Patrick and Smellie, 2013; Liu et al., 2021). The current eruption period, centered at the 500-m-diameter Mount Michael summit crater, has been ongoing since at least 12 November 2014, based on remote sensing analysis (Gray et al., 2019). Activity consists of a lava lake, persistent degassing, and intermittent explosions producing ash plumes (Patrick and Smellie 2013; Gray et al. 2019). Visits are infrequent due to the remote location, and cloud and plume cover often prevents satellite observations. This report summarizes activity during June 2019 through May 2020 primarily using satellite data, as well as observations from visiting scientists.

Figure 31. This 24 December 2019 satellite image (PlanetScope 3-Band scene) of Saunders Island shows the locations of the active Mount Michael summit crater and other features on the island. Courtesy of Planet Labs.

Figure 32. Images of the southeastern area of Saunders Island taken in January 2020. The top left image shows Nattriss Point with Ashen Hills in the background. The other photos show the crater and flanks of the Ashen Hills complex with rill and gully features from fluvial erosion. White and black speckled features in the images are penguins. Photos courtesy of Emma Liu and the 2020 Pelagic Australis expedition group.

Activity during June-December 2019. Ashfall deposits on the flanks were sometimes visible on the snow and ice (figure 33). MIROVA thermal anomaly data during June 2019 through June 2020 showed few days where high temperatures were detected by this sensor, but the active summit crater floor is often obscured by cloud cover or condensed gas-and-steam plumes. The TROPOspheric Monitoring Instrument (TROPOMI) detected frequent sulfur dioxide (SO₂) plumes of varying concentrations that are dispersed in different directions by wind (figure 34). Small condensed gas-and-steam plumes are often visible in satellite imagery within the crater, and some larger plumes are also imaged (figure 35). All satellite images where the summit crater was not obscured by either cloud cover or gas-and-steam plumes showed elevated temperatures within the summit crater, with three distinct areas visible possibly indicating multiple active vents (figure 36).

Figure 33. This satellite image of Saunders Island acquired on 15 September 2019 shows the snow and ice-covered island and a recent ashfall deposit on the NE flank towards Cordelia Bay, with a green sediment plume in the water. Sentinel-2 image with Natural color (bands 4, 3, 2) rendering. Courtesy of Planet Labs.

Figure 34. These images show data acquired by the TROPOspheric Monitoring Instrument (TROPOMI) that demonstrate detected SO2 (sulfur dioxide) from Mount Michael on Saunders Island on 2, 3, 25, and 29 September 2019. These are examples of gas plumes through the month with wind dispersing the plumes in different directions. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 35. This 10 October 2019 satellite image shows Saunders Island and the surrounding area with light cloud cover, and a condensed gas-and-steam plume from the summit crater drifting towards the E to SE. Sentinel-2 image with Natural color (bands 4, 3, 2) rendering. Courtesy of Planet Labs.

Figure 36. These two Sentinel-2 thermal satellite images of Saunders Island acquired on 2 and 24 December 2019 show three distinct areas of elevated temperature within the Mount Michael summit crater (yellow to red). While the locations of the thermal anomalies look different in these images, the angle of the view into the crater is not specified. Blue is Ice, black is ocean water. Sentinel-2 image with False color (Urban) (bands 12, 11, 4) rendering. Courtesy of Sentinel Hub Playground.

Activity during January-May 2020. During January through May 2020 various remote sensing data showed the same activity as the previous seven months, with abundant cloud cover over the island. The Sentinel-2 satellite imaged a vertical plume on 13 March rising then being dispersed NE (figure 37). Intermittent observations of SO₂ plumes continued through TROPOMI data analysis (figure 38). A clear view of the summit area on 29 May showed the ice-free active summit crater producing a weak gas-and-steam plume, and ash deposition on the NE to SE upper flanks (figure 39).

Figure 37. This Sentinel-2 satellite image of the Mount Michael summit area on Saunders Island with a gas-and-steam plume rising from the summit crater above the cloud cover, and dispersing NE. The plume and clouds are casting dark shadows below them. Sentinel-2 image with False color (Urban) (bands 12, 11, 4) rendering. Courtesy of Sentinel Hub Playground.

Figure 38. Examples of SO2 gas plumes originating from Saunders detected by the TROPOMI instrument on 14 and 18 March 2020. The plumes are dispersing N to NNE. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 39. This 29 May 2020 Planet Scope satellite image shows the summit area of Mount Michael above cloud cover with the active summit crater and the old crater to the SE. There is a weak gas plume rising from the crater and ashfall on the upper E flank. Courtesy of Planet Labs.

Research expedition in January 2020. The team of the 2020 Pelagic Australis expedition visited the island on 5-8 January 2020, with shore landings on the last three days, to quantify gas emissions from the island. The following information is from the published expedition results (Liu et al., 2021), with photos supplied by volcanologist Emma Liu.

Across the South Sandwich islands they used a combination of a ground-based and drone-mounted gas detectors (Multi-GAS), a UV imaging camera, sample collection, and NDIR spectrometer analyses to quantify gas output. They confirmed that the summit crater is a persistent source of gas emissions with 145 ± 59 tons per day of SO₂ and a CO₂ flux of 179 ± 76 tons per day. On the 5th they observed a vertical plume and on the 7th they observed the plume drifting down the E flank before rising (figure 40). They noted that the surface was steaming and was warm to the touch, suggesting widespread geothermal activity. The non-glaciated surfaces of the island contain tephra deposits, with units exposed by erosion and preserved within snow and ice (figure 41). Explosions have emplaced tephra layers across the island as well as ballistic blocks and bombs on the E flank (figure 42; Liu et al., 2021).

Figure 40. These images show the gas emissions from Mount Michael on Saunders Island in January 2020. The top right image is a vertical gas plume rising from the summit crater on the evening of the 5th. The two photos on the right are looking towards the E on the 7th. The bottom left image is a low-lying condensed gas plume on the 8th travelling down the E flank before rising. Courtesy of Emma Liu, and Liu et al. (2021).

Figure 41. Tephra layers are preserved within the stratigraphy of snow and ice on Saunders Island. Scale shown by penguins (top) and volcanologist Kieran Wood (right). Photos courtesy of Emma Liu.

Figure 42. Dense volcanic blocks up to a meter in size are widespread on Saunders Island. The block in the foreground has a height of approximately 35 cm; the Chinstrap penguin in the foreground is around 50 cm tall. Courtesy of Emma Liu and Liu et al. (2021).

References: Liu E J, Wood K, Aiuppa A, Giudice G, Bitetto M, Fischer T P, McCormick Kilbride B T, Plank T, Hart T, 2021. Volcanic activity and gas emissions along the South Sandwich Arc. Bull Volcanol 83. https://doi.org/10.1007/s00445-020-01415-2

LeMasurier W E, Thomson J W, Baker P E, Kyle P R, Rowley P D, Smellie J L, Verwoerd W J, 1990. Volcanoes of the Antarctic Plate and Southern Ocean. American Geophysical Union, Washington, D.C.

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

Patrick M R, Smellie J L, 2013. Synthesis A spaceborne inventory of volcanic activity in Antarctica and southern oceans, 2000–10. Antarct Sci 25:475–500. https://doi.org/10.1017/S0954102013000436

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). Analysis of satellite imagery available since 1989 (Gray et al., 2019; MODVOLC) suggests frequent eruptive activity (when weatehr conditions allow), volcanic clouds, steam plumes, and thermal anomalies indicative of a persistent, or at least frequently active, lava lake in the summit crater. Due to this observational bias, there has been a presumption when defining eruptive periods that activity has been ongoing unless there is no evidence for at least 10 months.

Information Contacts: Emma Liu, University College London, Kathleen Lonsdale Building, 5 Gower Place, London, WC1E 6BS, United Kingdom; Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Volcán Popocatépetl is an active stratovolcano near Mexico City that has had frequent historical eruptions dating back to the 14th century. The current eruption has been ongoing since January 2005 and has more recently consisted of lava dome growth and destruction, frequent explosions, and emissions of ash plumes and incandescent ejecta. Activity through July 2020 was characterized by hundreds of daily low-intensity emissions that included gas-and-steam and small amounts of ash, and multiple daily minor and moderate explosions that sent ash plumes more than 1 km above the crater (BGVN 45:08). This report covers somewhat decreased activity from August 2020 through January 2021 using information from México's Centro Nacional de Prevención de Desastres (CENAPRED), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

Popocatépetl had ongoing water vapor, gas, and ash emissions throughout August 2020-January 2021, but far fewer minor and moderate explosions than during the period of the previous report. Ash emissions generally rose to 5.8-7.1 km altitude and drifted in many different directions. Ashfall was reported in multiple communities during August, October, and numerous times in January 2021. Thermal anomalies were recorded in satellite images inside the summit crater a few times each month. The MIROVA thermal anomaly data indicated persistent, low levels of activity throughout the reporting period (figure 162). CENAPRED reported the number of low-intensity emissions or ‘exhalations’ and the number of minutes of tremor in their daily reports (figure 163). Tremor activity was very high at the beginning of August, and then again during January 2021. The daily number of exhalations was highest during late October and November 2020.

Figure 162. MIROVA thermal anomaly data for Popocatépetl for the year ending on 3 February 2021 showed persistent low levels of activity from August 2020 through January 2021, the period covered in this report. Courtesy of MIROVA.

Figure 163. CENAPRED reported the number of exhalations (low-intensity emissions) and the number of minutes of tremor at Popocatépetl in their daily reports. Tremor activity was very high at the beginning of August, and then again during January 2021 (yellow columns). The daily number of exhalations was highest during late October and November 2020 (blue columns). Data courtesy of CENAPRED daily monitoring reports.

During August 2020 daily water vapor and gas emissions often contained small quantities of ash. In addition, low-intensity emissions or exhalations with larger quantities of ash occurred tens of times per day. The daily number of minutes of tremor was over 1,000 at the beginning of the month but dropped back to lower levels of a few tens or hundreds of minutes later in the month. Slight amounts of ashfall were reported in Amecameca and Ozumba in the State of Mexico on 1 August. On 2 August the 1159 minutes of tremor were sometimes accompanied by incandescent ejecta that fell into and a short distance from the summit crater. The Washington VAAC observed an ash emission drifting NE at 6.1 km altitude on 2 August that later rose to 7.6 km altitude. It fanned out from the summit to the N and E for about 15 km. Similar observations were made virtually every day of the month; ash or gas-and-ash emissions generally rose to 5.8-7.6 km altitude and drifted a few tens of kilometers in different directions before dissipating. Constant gas emissions and incandescence were reported at night during 10-23 August; an ash emission that rose to 600 m above the crater rim and drifted W on 14 August was captured in the webcam (figure 164). The largest SO₂ emissions during the period were captured by the TROPOMI instrument on the Sentinel-5P satellite during 2-5 August (figure 165).

Figure 164. An ash emission at Popocatépetl rose to 600 m above the crater rim and drifted W on 14 August 2020. Dense steam emissions also drifted just above the summit. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 14 de Agosto).

Figure 165. The largest SO2 emissions at Popocatépetl during the period were captured by the TROPOMI instrument on the Sentinel-5P satellite during 2-5 August 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Gas and occasional weak ash emissions accompanied the tens of daily low-intensity emissions during September 2020; thermal activity was very low with weak anomalies inside the summit present in satellite images on 3, 8, and 13 September. Ash emissions were visible from a webcam on 18 September and in satellite imagery on 23 September (figure 166). Weak incandescence above the crater was only reported by CENAPRED during 26 and 27 September. The Washington VAAC reported intermittent ash emissions throughout the month that commonly rose to 6-7 km altitude and drifted over 50 km downwind before dissipating.

Figure 166. Ash emissions were visible from a webcam at Popocatépetl on 18 September (left) and in satellite imagery on 23 September 2020 (right). Right image is from Sentinel-2 with natural color rendering (bands 4, 3, 2). Left image courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 18 de septiembre). Right image courtesy of Sentinel Hub Playground.

Water-vapor and gas emissions with small quantities of ash similar to those seen in September were also typical activity during October 2020. Tens or a few hundred daily low-intensity emissions often produced ash plumes visible in the webcams (figure 167). Ashfall was reported in Tetela del Volcano (20 km SW), in the state of Morelos, and in Amecameca (20 km NW), Atlautla (17 km W), Ayapango (22 km NW) and Ecatzingo (15 km SW), in the State of Mexico on 7 October; a small amount of ashfall was also reported in Amecameca on 13 October. The Washington VAAC issued multiple daily ash advisories throughout the month; many ash plumes were visible in satellite imagery. Incandescence appeared over the summit crater at night during 10-16 October, and was noted in satellite imagery on 3, 8, 18, 23, and 28 October. Incandescence and ash emissions were both captured in satellite imagery on 8 and 18 October (figure 168). Personnel from the Institute of Geophysics of the National Autonomous University of Mexico (UNAM) and the National Center for Disaster Prevention (CENAPRED) conducted an overflight on 16 October and verified that the inner crater at the summit was covered in tephra and about 360-390 m in diameter and 120-170 m deep (figure 169).

Figure 167. Ash plumes and steam rose hundreds of meters above Popocatépetl on 5 (left) and 10 (right) October 2020. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 5 de octubre y 10 de octubre de 2020).

Figure 168. Thermal anomalies at the summit of Popocatépetl and ash plumes drifting SW were both present in satellite imagery on 8 (left) and 18 (right) October 2020. Images are using Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 169. Personnel from the Institute of Geophysics of the National Autonomous University of Mexico (UNAM) and the National Center for Disaster Prevention (CENAPRED) conducted an overflight of Popocatépetl on 16 October 2020 and verified that the inner crater at the summit was covered in tephra, about 360-390 m in diameter, and 120-170 m deep. Courtesy of CENAPRED (Sobrevuelo al volcán Popocatépetl, 16 de octubre de 2020).

Activity during November 2020 consisted primarily of weak emissions of steam and gas with occasional small quantities of ash that rose a short distance above the summit crater (figure 170). The Washington VAAC reported ash emissions on 19 days during the month, most rising to 5.8-6.7 km altitude and drifting for a few tens of kilometers before dissipating. CENAPRED reported a few hundred low-intensity emissions daily, but only a few tens of minutes of tremor each day, significantly lower than previous months. Satellite imagery showed weak thermal anomalies inside the summit crater on 2, 7, 12, 22, and 27 November.

Figure 170. Activity during November 2020 at Popocatépetl consisted primarily of weak emissions of steam and gas with occasional small quantities of ash that rose a short distance above the summit crater such as this one on 2 November. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 02 de noviembre).

Emissions of steam and gas with occasional low quantities of ash continued during December 2020. Six explosions on 5 December produced small ash plumes that rose 500-1,000 m above the crater. The next day two explosions produced plumes that rose less than 1,500 m above the crater and drifted NE. Incandescent ejecta was captured in the webcam on 14 December (figure 171). The Washington VAAC issued multiple aviation alerts nearly every day of the month; ash plumes generally rose to 6-7 km altitude and drifted 30-50 km before dissipating. Activity increased during the second half of the month (figure 172). Visible ejecta was seen in webcams during low-energy emissions on 24 December, accompanied by an ash plume that rose 1,000 m above the crater. The next day an ash emission rose 300 m. Ejecta was noted on the SE flank after an explosion on 27 December, and ash plumes rose to 500-1,400 m above the crater each day through the end of December and into January 2021. Thermal anomalies appeared in satellite data inside the summit crater on 2, 17, 22, and 27 December.

Figure 171. Explosions at Popocatépetl produced dense ash emissions and incandescent ejecta. On 6 December the ash plume rose to 1,500 m above the crater and drifted NE (left). On 14 December 2020 incandescent ejecta rose a few hundred meters above the summit crater (right). Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl, 7 de diciembre y 15 de Diciembre de 2020).

Figure 172. Ash emissions occurred daily at Popocatépetl during December 2020. On 20 December the dense plume rose about one kilometer above the summit (left). On 31 December a thermal inversion was the likely reason that the ash from the summit flowed down the flank towards the webcam (right). Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl, 20 de diciembre y 31 de Diciembre de 2020).

Daily ash emissions were reported by the Washington VAAC during January 2021, rising to 5.8-7.0 km altitude and drifting tens or hundreds of kilometers before dissipating (figure 173). Ash plumes rose 500-600 m above the crater on 1 and 2 January; at least one explosion each of those days produced incandescent ejecta in and around the crater. The Washington VAAC reported the ash plume from 1 January as visible in the webcam and satellite imagery over 200 km NE from the summit before dissipating, and one on 6 January visible about 100 km E of the volcano (figure 174). Ashfall was reported each day during 4-6 January in Puebla to the NW. On 8 January ashfall occurred in Atlixco (23 km SE), San Andrés Cholula (35 km E), San Nicolás de los Ranchos (15 km ENE) and Domingo Arenas (22 km NE), all in the state of Puebla. The following day ashfall was reported in San Salvador el Verde (30 km NNE) and San Nicolás de los Ranchos. Multiple explosions with ash plumes rising 500-700 m were reported on 14 and 15 January followed the next day by ashfall in San Nicolás de los Ranchos. Trace amounts of ash were reported in Tetela del Volcán (18 km SW) in the State of Morelos on 22 January. An explosion on 26 January ejected ash 700 m high and sent incandescent fragments a short distance from the crater rim. Ashfall on 28 January was reported in Ixtlacuixtla de Mariano, Nativitas and part of the center of Tlaxcala (50 km NE). The circular inner crater rim at the summit was sharply defined in a satellite image taken on 31 January 2021; a thermal anomaly was also present inside the crater (figure 175).

Figure 173. Ash plumes were reported daily at Popocatépetl during January 2021, including on 19 (left) and 21 (right) January, some rising over a kilometer above summit and drifting for tens of kilometers before dissipating. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl, 20 y 21 de Enero de 2021).

Figure 174. The Washington VAAC reported an ash plume at Popocatépetl from 1 January 2020 as visible over 200 km NE from the summit before dissipating (left), and one on 6 January as visible about 100 km E of the volcano (right). Sentinel-2 satellite images are with Natural color (bands 4, 3, 2) and Atmospheric penetration (bands 12, 11, 8a) rendering. Courtesy of Sentinel Hub Playground.

Figure 175. A thermal anomaly inside the summit crater of Popocatépetl seen in this Sentinel-2 image was surrounded by a distinct gray circle that was the rim of the inner crater on a clear 31 January 2021. Image uses Atmospheric penetration rendering (bands 12, 11, 8A). 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/, Daily Report Archive https://www.gob.mx/cenapred/archivo/articulos); 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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA 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/).

Extensive lava flows, bomb-laden Strombolian explosions, and ash plumes emerging from Mackenney crater have characterized the persistent activity at Pacaya since 1961. The latest eruptive episode began with intermittent ash plumes and incandescence in June 2015; the growth of a new pyroclastic cone inside the summit crater was confirmed later that year. The pyroclastic cone has continued to grow, producing Strombolian explosions rising above the crater rim and frequent loud explosions. In addition, fissures on the flanks of the summit crater have produced an increasing number of lava flows traveling distances of over one kilometer down multiple flanks during 2019 and 2020 (figure 129). Increasing explosive and effusive activity during August-November 2020 is covered in this report with information provided by Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), multiple sources of satellite data, and numerous photographs from observers on the ground.

Figure 129. Lava flows traveled down the flank of Pacaya during July 2019 while ash emissions and incandescent ejecta marked the summit of Fuego located 30 km NW. The large edifice on the right is Agua, and the one between it and Fuego is Acatenango, which last erupted in the early 20th century. Photo courtesy David Rojas, used with permission.

After a brief pause in effusive activity at the end of July 2020, two lava flows appeared on the NW flank on 12 August. Another flow began on the NE flank ten days later, and multiple flows were active for the remainder of the month, some reaching 650 m long. Multiple lava flows issued from fissures on the N flank and elsewhere throughout September. A flow on the NE flank was reported as 1,200 m long and was visible from Guatemala City on 8 September. A new flow on the S flank was very active later in the month. Flows were persistent on most of the flanks throughout October; a flow appeared from a fissure on the W flank on 20 October and reached 1 km in length by 24 October. Block avalanches spalled off the front of the flows and generated small ash plumes. Multi-branched flows on the W and SW flanks from the W flank fissure remained active throughout November. The slowdown in effusive activity in late July and early August 2020 is apparent in the MIROVA thermal anomaly data, as is the significant increase in activity during September that persisted into November 2020 (figure 130).

Figure 130. Thermal activity at Pacaya decreased in late July and early August 2020 but then increased significantly in early September and remained high through November 2020; numerous lava flows were reported during the periods of increased thermal activity. Thermal data is shown from 3 February through November 2020. Courtesy of MIROVA.

The break in the lava flow activity that began on 25 July 2020 (BGVN 45:08) lasted until 12 August. During that time, steam plumes were reported rising 25-75 m above the summit and drifting generally S or SW as far as 6 km before dissipating. Strombolian explosions rose 25-150 m above the rim of Mackenney crater and ejecta reached 50 m from the rim; noises as loud as a train engine were heard in nearby communities. Incandescence was observed nearly constantly along with persistent seismic tremor activity. On 12 August two lava flows emerged on the NW flank, each reaching about 150 m long. Incandescence from the flows was visible each day through 21 August on the NW flank in the area just above Cerro Chino (figure 131). The active flows were 100-200 m long during this period. A new lava flow appeared on the NE flank and grew to 300 m in length on 22 August.

Figure 131. A thermal anomaly from a lava flow on the NNW flank of Pacaya was present in Sentinel-2 satellite imagery on 17 August 2020 in addition to a thermal anomaly at the center of the pyroclastic cone inside the summit crater. Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Multiple lava flows were active on the NW, N, and NE flanks for the rest of the August. Incandescence on 24 August from the NW-flank flow near Cerro Chino indicated it was 250-300 m long. During 27 and 28 August flows were reported on the N and NNE flanks, 600 and 300 m long, respectively (figure 132). Incandescent pulses were reported from the crater overnight on 28-29 August; the NW flank flow remained active and was 300 m long. MODVOLC reported three thermal alerts on 29 August. The next day, 30 August, incandescence from the 650-m-long N flank flow and 300-m-long NE flank flow continued. Constant crater incandescence accompanied dense gray ash emissions on 31 August; the lava flow on the N flank remained incandescent for 350-400 m, but there was no incandescence or degassing from the NE-flank flow on the last day of the month.

Figure 132. A 600-m-long lava flow was visible on the N flank of Pacaya as seen from Villa Nueva, part of Guatemala City, late on 27 August 2020. Courtesy of Sh!ft.

White and blue steam and gas plumes were present daily throughout September 2020. They drifted in multiple directions as far as 8 km from the summit before dissipating. Strombolian activity was constant, building up the pyroclastic cone inside of Mackenney crater and sending ejecta as far as 50 m from the rim. Ejecta rose 50-150 m on most days; it was reported at 200 m high on 3, 9, and 14 September and was heard loudly and rattled windows nearby on 17 and 27 September. Constant crater incandescence with prolonged degassing of dense gray ash plumes was reported on 5, 10, 15, 17, and 21 September.

Multiple lava flows issued from fissures on the N flank and elsewhere throughout the month. Two lava flows on 1 September on the N flank were 50 and 350 m long. The next day three flows on the same flank were 300, 350, and 650 m long. On 3 September a new flow appeared on the E flank and extended 600 m from its source in addition to two flows on the N flank. For the next several days multiple flows were active on the N and NE flanks, reaching 450 m on the NE flank on 7 September. The next day the flow on the NE flank reached 1,200 m in length and was visible from Guatemala City. Activity continued with multiple flows 150-300 m long through 12 September (figure 133).

Figure 133. Lava flows at Pacaya were active on multiple flanks on 11 September 2020, including one that reached over a kilometer in length on the NE flank. Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

On 13 September 2020 the flows on the N and NE flanks reached 600 and 300 m long, while a third flow reached 150 m down the S flank. The flow on the S flank was the most active during 14-23 September, extending 550 m from its source and producing numerous block avalanches from the flow front (figure 134). During the last week of the month the focus of the flow activity returned to the NE, N, and NW flanks where multiple flows were reported, some up to 550 m long, along with constant Strombolian activity (figures 135). Increased thermal activity resulted in MODVOLC thermal alerts reported on seven days during the second half of the month.

Figure 134. A large lava flow on the S flank of Pacaya during 14-23 September 2020 produced block avalanches from the flow front. It was seen here in Sentinel-2 satellite imagery on 21 September 2020 using atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 135. Strombolian explosions sent ejecta 40-70 m above the crater at Pacaya on 26 September 2020. In addition, a lava flow 200 m long descended the N flank. Courtesy of CONRED.

Gas and steam plumes persisted throughout October 2020. They generally rose a few hundred meters above the summit and usually drifted S or W up to 10 km. Strombolian explosions continued daily, reported at 75-150 m high for most of the month. In a special report on 8 October INSIVUMEH noted increased Strombolian activity that sent bombs and fine ash 200-300 m above the crater, with ash emissions drifting 12 km W. During the last week of the month the ejecta reached 250 m high on several days. Loud noises and shock waves were periodically reported; vibrations were felt in San Francisco de Sales on 23 October and in areas to the S of Guatemala City on 27 October. INSIVUMEH reported ash emissions that drifted 8-10 km S and W from the summit on 23 October. The Washington VAAC reported ash emissions seen in satellite imagery drifting 15 km NE at 3.7 km altitude on 28 October. Weak sulfur dioxide emissions were recorded by the TROPOMI instrument on 6, 20, and 26 October (figure 136).

Figure 136. Weak SO2 emissions from Pacaya were recorded by the TROPOMI instrument on the Sentinel 5P satellite on 6, 20, and 26 October 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Numerous lava flows were active throughout the month of October 2020 on multiple flanks (figure 137). During 1-4 October INSIVUMEH reported one or two flows active on the N and NE flanks that were 100-500 m long (figure 138). On 4 October there was a 200-m-long flow on the S flank, and another flow on the W flank. The S-flank flow grew to 250 m long by 8 October, had block avalanches spalling off the front, and fine ash that was stirred up by the wind. The next day three flows were active; they were 400 m long on the NE flank, 300 m on the N flank, and 200 m on the W flank. The N-flank flow was the most active during 11-15 October, reaching 650 m long. The W-flank flow was very active from 20 October through the end of the month, issuing from a fissure at mid-flank. It reached 1 km in length by 24 October and burned vegetation at the flow front (figures 139). A flow on the NE flank was 350 m long on 26 October (figure 140). MODVOLC issued thermal alerts on 7 days of the month, including seven alerts on 5 October.

Figure 137. Numerous lava flows were active throughout the month of October 2020 on multiple flanks of Pacaya. On 1 October the flows were concentrated on the N flank (left), and on 31 October a long flow was active on the W flank in addition to strong thermal activity at the summit crater (right). Atmospheric penetration rendering (bands 12, 11, and 8a) of Sentinel-2 satellite data. Courtesy of Sentinel Hub Playground.

Figure 138. A lava flow 125 m long on the N flank of Pacaya was active on 1 October 2020. Courtesy of CONRED.

Figure 139. A flow on the W flank of Pacaya was over 1 km long by 24 October 2020 when it was burning vegetation as it traveled downslope. Courtesy of Noti7.

Figure 140. An active flow on the SW flank of Pacaya issuing from a fissure on the W flank was over 1 km long on 26 October 2020 and had multiple branches flowing down the slope. Numerous people were camped on the slope below the flow. Photo by Mariana Lemus.

Although the weather was cloudy for much of November 2020, white steam and blue gas plumes were visible drifting S or W from the summit on many days, some reaching 10 km from the volcano before dissipating. Sporadic Strombolian explosions rose 100-200 m above the pyroclastic cone inside Mackenney crater; the explosions were often accompanied by small ash plumes that rose a few hundred meters and drifted downwind 8-10 km before dissipating. A small SO2 plume was recorded in the TROPOMI satellite data on 8 November, the same day that INSIVUMEH and the Washington VAAC reported an ash emission drifting NE at 3.4 km altitude over the village of Los Llanos and others in the area (figure 141). An increase in activity reported by INSIVUMEH on 15 November consisted of Strombolian explosions sending material up to 300 m above the summit and ejecting bombs up to 100 m outside the crater.

Figure 141. Ash and steam emissions were observed at Pacaya on 8 November 2020. Courtesy of CONRED.

Lava flows were still very active on the SW flank throughout November, emerging from a fissure a few hundred meters down from the summit that initially opened on 20 October. The main flow was 600 m long on 1 November and grew to 1,200 m long by 11 November (figure 142). On 5 November there were four separate branches of the SW-flank flow that were active. Block avalanches were common at the flow front. On 14 November a second flow was observed emerging from a fissure higher up on the SW flank from the earlier flow; they both were active for several days. INSIVUMEH issued a special report indicating increased effusion on 15 November from the SW-flank fissure. Block avalanches were occurring from the front of the 1-km-long flow, which had several branches. The blocks were 1-3 m in diameter and created small plumes of ash when moving as far as 500 m down the slope. An explosion during the night of 14-15 November at the SW-flank fissure created incandescent ejecta and ash emissions for several hours (figure 143). The flow remained active throughout the rest of November; on 26 November two flows were active from the main fissure, 500 and 400 m long (figure 144). On 30 November the main flow on the SW flank had three branches and extended 600 m from the mid-flank fissure.

Figure 142. A fissure on the W flank of Pacaya that opened on 20 October 2020 sent multiple flows down the W and SW flanks during November. The flow extended more than a kilometer on 10 November (left). It had moved in a SW direction by 20 November (center) and had three major branches active on 25 November (right). Atmospheric penetration rendering (bands 12, 11, and 8a) of Sentinel-2 satellite data. Courtesy of Sentinel Hub Playground.

Figure 143. An explosion at the fissure on the W flank of Pacaya during the night of 14-15 November 2020 produced incandescent ejecta almost as bright as that coming from the Strombolian activity inside the summit crater. For several hours dense ash emissions were visible at the fissure vent (inset). Large copyrighted photo courtesy of David Rojas, used with permission; inset courtesy of Prensa Objetiva.

Figure 144. Two flows with multiple branches were active on the W and SW flanks of Pacaya on 26 November 2020. Both copyrighted photos courtesy of David Rojas, used with permission.

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/ ); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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) (URL: https://twitter.com/ConredGuatemala/status/1310057080162844673, https://conred.gob.gt/monitoreo-a-flujo-de-lava-en-el-volcan-pacaya/) ; NASA 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/); 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/); David Rojas, Guatemala (URL: https://www.instagram.com/davidrojasgtfoto/, https://twitter.com/DavidRojasGt/); Mariana Lemus, Guatemala (URL: https://www.instagram.com/marianalemusgt/); Noti7 (URL: https://twitter.com/Noti7Guatemala/status/1320169410833883136); Sh!ft (URL: https://twitter.com/kevingt_/status/1299204020662304768); Prensa Objetiva (URL: https://twitter.com/noticiasprensa/status/1328102695832612865).

Santa Maria is one of the most active volcanoes in Guatemala. Major features are the Santa Maria edifice with the large crater that formed in the 1902 eruption, and the Santiaguito dome complex about 2.5 km down the SW flank that includes the currently active Caliente dome (figure 113). Activity typically includes ash plumes, gas emissions, lava extrusion, and avalanches. This report summarizes activity during August 2020 through January 2021 and is based on reports by Instituto Nacional de Sismología, Vulcanología, Meteorología e Hidrología (INSIVUMEH), Coordinadora Nacional para la Reducción de Desastres (CONRED), and satellite data.

Figure 113. Main features of the Santa Maria complex are shown in this March 2021 Planet Labs satellite image monthly mosaic. The large scarp is the wall of the crater produced during the 1902 eruption. Within that the El Brujo, El Monje, La Mitad domes, and the currently active Caliente dome, are from W to E. Courtesy of Planet Labs.

Throughout August weak to moderate explosions were reported most days, some days occurring 2-4 times per hour. These produced ash plumes to an altitude of 3.5 km, typically reaching 3.4 km. The plumes were dispersed mostly W and SW, sometimes S, SE, and NW. Degassing was reported throughout the month, with plumes reaching 3.5 km, but most often 3-3.1 km altitude. On the 3rd, ashfall was reported in San Marcos Palajuno (8 km SW), Loma Linda (6 km WSW) and others in that direction, and again on the 29th. It was also reported in Monte Claro (S of the summit) on the 12th and light ashfall occurred on the flanks through the month. Explosions on the 23rd produced weak pyroclastic flows that traveled down the SW flank of the dome. The activity produced frequent avalanches on the S, SW, and SE flanks of the dome, some reaching the base of the dome and some depositing fine ash onto the flanks. The sound of explosions and degassing were reported most days and incandescence was frequently seen at the crater at night.

This activity continued through September, maintaining the same eruptive pattern of weak and moderate explosions, gas emission, lava extrusion, and avalanches. Incandescence continued to be visible at the crater. There was ashfall reported in Monte Claro, Aldea San Marcos Palajunoj and other surrounding communities on the 7th, Monte Claro on the 11th, and across the Palajunoj area on the 28th. On the afternoon of 25 September lahars occurred in the Cabello de Ángel and Nimá I drainages. Lava extrusion was reported on the morning of the 29th along with resulting block-and-ash flows.

Throughout October explosions, gas emission, avalanches, and elevated crater temperatures producing nighttime incandescence (figure 114) continued in the same manner as the previous months. From the 9th the extrusion of lava was observed over the dome, generating block-and-ash flows mainly down the W flank. Ashfall was reported in of Loma Linda and El Rosario Palajunoj and others in the area on the 13th, 7 km SW on the 18th, and in San Marcos Palajunoj and nearby areas on the 23rd. Lava extrusion generated constant avalanches down multiple flanks from the 23rd, with some producing small ash plumes as they descended.

Figure 114. This Shortwave Infrared (SWIR) image of Santa Maria acquired on 19 October by the Landsat 8 satellite shows elevated temperatures at the Caliente dome. The contour intervals are 30 m. Courtesy of USGS and INSIVUMEH.

Throughout November gas emissions and explosions continued to produce gas-and-steam and ash plumes that rose up to 3.4 km altitude. Lava extrusion also continued down the W flank, producing incandescence and frequent avalanches down the SE, S, SW, and W flanks, as well as less frequent block-and-ash flows (figure 115). An increase in thermal energy detected towards the end of the month resulted from this extrusion (figure 116). Ashfall occurred around the volcano from explosions and avalanches. Ashfall was reported SE within the villages of Las Marías, Calaguache and others nearby on the 12th and 22nd, and SSW over the village of San Marcos Palajunoj, Loma Linda and Fincas in the Palajunoj area on the 27th. Degassing and explosions were intermittently heard in nearby communities with reports of sounds similar to an airplane turbine. An explosion on the 16th produced an ash plume up to 3.6 km altitude and pyroclastic flows down the flanks (figure 117).

Figure 115. This nighttime Landsat 8 Shortwave Infrared (SWIR) satellite image of Santa Maria with the contours of the Caliente dome overlain was acquired on 20 November 2020. There are elevated temperatures within the summit crater and lava is flowing down a channel on the western flank. The contour intervals are 20 m. Courtesy of USGS and INSIVUMEH.

Figure 116. This MIROVA log radiative power plot shows the thermal energy released at Santa Maria between April 2020 to February 2021. There was a decrease in energy emitted from May to November, followed by an increase in the frequency and the energy released on some days. The black vertical lines like the two in January-February are more than 5 km from the summit and are likely not a result of volcanic activity. Courtesy of MIROVA.

Figure 117. An explosion from the Caliente dome of Santa Maria is seen here at 0715 on 16 November 2020. The photo shows the ash plume that rose to 3.6 km altitude and pyroclastic flows descending the flanks. The seismogram shows the explosion in the center of the bottom line (the times on the left are given in UTC). Courtesy of INSIVUMEH.

Gas emissions and weak to moderate explosions continued throughout December, producing plumes reaching 3.4 km altitude along with ongoing lava extrusion producing avalanches (figures 118 and 119). Ash from explosions and avalanches was intermittently emplaced onto the flanks, and ashfall was reported in the villages of San Marcos and Loma Linda Palajunoj on the 7th, and in Loma Linda and Finca Montebello on the 11th. Activity increased from 0430 on 11 December 2020 with the generation of moderate to powerful avalanches as well as block-and-ash flows from lava extrusion and accumulation, with 13 events recorded between that time and when a report was released at 0900. The intensity continued with block-and-ash flows and pyroclastic flows moving down the W and SW flanks that generated ash plumes which extended 20 km downwind.

Figure 118. Plumes rise from the Caliente dome at Santa Maria on 9 (top left) and 15 (top right) December 2020. A faint plume rises from the summit of the Caliente dome and another plume rises from a possible avalanche down the SW flank (bottom). Courtesy of INSIVUMEH (Fotografías Recientes de Volcanes).

Figure 119. A gas-and-steam plume rises from the degassing Caliente dome at Santa Maria on 30 December 2020. Around this time weak and moderate explosions produced ash plumes up to 3-3.4 km altitude, resulting in ashfall on the flanks. Courtesy of CONRED.

The high level of background activity associated with lava extrusion continued through January. Satellite images show the lava flow advancing down the W-flank channel (figure 120), reaching approximately 250 m by the 11th. Avalanches also continued, producing ash that was emplaced nearby (figure 121). On the 22nd the collapse of dome material produced a pyroclastic flow to the E and SE. Explosions ejected ash to 3.4 km altitude, with ashfall that was reported in the Aldeas de San Marcos and Loma Linda Palajunoj on the 1st, Aldeas de San Marcos and Loma Linda Palajunoj on the 11th, Aldeas de San Marcos y Loma Linda Palajunoj, Fca. El Patrocinio during the 20-21st. Ashfall was again reported on the 31st to the west on farms, in Aldeas de San Marcos, and in Loma Linda Palajunoj. Sounds generated by explosions were sometimes heard around 10 km away.

Figure 120. PlanetScope satellite images of Santa Maria acquired on 20 December 2020 and 10 and 11 January 2021 show the development of a lava flow down a channel on the W flank (white arrows). In the latest image the flow is approximately 250 m long. Courtesy of Planet Labs.

Figure 121. Thermal infrared satellite images of Santa Maria acquired on 12 and 22 January 2021 show higher temperatures on the Caliente dome. Top: Elevated thermal areas are detected at the summit and hot material is emplaced down the W-flank channel. Bottom: Elevated temperatures at the summit of the lava dome, with a possible avalanche on the E flank. Sentinel-2 thermal satellite images with false color (urban) (bands 12, 11, 4) rendering. Courtesy of Sentinel Hub Playground.

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/); 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/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Activity at Bromo, the youngest and only active cone within the 16-km-wide Tengger caldera in East Java, is characterized by occasional explosions with ash plumes followed by periods of relative quiet with only gas-and-steam emissions (BGVN 44:05). There have been more than 30 eruptive periods since 1900. During the first seven months of 2019, ash explosions occurred on 18 February 2019 and became especially numerous in March and April, with more explosive activity in July 2019 (BGVN 44:05, 44:08). 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 by the Darwin Volcanic Ash Advisory Centre (VAAC).

Following the ash explosion on 28 July 2019, satellite observations frequently showed a white gas-and-steam plume in the Bromo crater (figure 19). No additional eruptive activity was reported until 26-27 December 2020 when PVMBG reported white-and-gray plumes rose 50-700 m above the summit of Bromo’s cone. The next day, at 0550 on 28 December, an observer spotted a gas-and-ash emission rising at least 500 m above the summit. The Darwin VAAC was unable to confirm if there was ash in the plume based on satellite data, but ashfall was reported in the Ngadirejo area, about 5 km NE. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to stay outside a 1-km radius of the crater.

Figure 19. Satellite image of the Tengger Caldera on 12 September 2020, with a typical white plume visible in the Bromo crater. Sentinel-2 image with natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Lewotolok (also known as Lewotolo) is located on the eastern end of a peninsula connected to Lembata (formerly Lomblen) that extends north into the Flores Sea. Eruptions date back to 1660, characterized by explosive activity in the summit crater. Typical activity has consisted of seismicity and thermal anomalies near the summit crater (BGVN 36:12 and 41:09). A new eruption that began in late November 2020 was characterized by increased seismicity, dense, gray ash plumes, nighttime crater incandescence, and ashfall. This report covers activity through January 2021 using information primarily from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and satellite data.

Summary of activity during February 2012-October 2020. Activity from February 2012 to November 2020 was relatively low and consisted primarily of a persistent thermal anomaly in the summit crater since at least March 2016 and occasional white gas-and-steam emissions. During January 2012 intermittent white gas-and-steam plumes rose 15-500 m above the crater, accompanied by crater incandescence; no thermal anomalies were reported during 16-24 January. On 6 January there were 500 people in the Lembata district evacuated due to reports of ash plumes that were observed by local residents, the smell of sulfur, and the sound of rumbling (BGVN 36:12).

Thermal activity dates back to 13 October 2014 using MODIS data in MODVOLC satellite data (BGVN 41:09; figure 3). According to the MODVOLC algorithm, a total of seven thermal alerts were detected on 13 October 2014 (1), 27 September 2015 (1), 2, 3, and 4 (2) October 2015, and 5 November 2017 (1). The number of thermal alerts in both MODVOLC and Sentinel-2 satellite data had increased slightly in 2020 compared to 2018 and 2019, though cloud cover often prevented visual confirmation for the latter (figure 3). Sentinel-2 thermal satellite imagery captured occasional thermal anomalies in the summit crater during 2016-2019 (figure 4). White gas-and-steam plumes were intermittently reported from September 2017 through 2 March 2018 that rose as high as 500 m above the crater and drifted dominantly E and W, according to PVMBG.

Figure 3. Graph comparing the number of thermal anomalies using MODVOLC alerts and Sentinel-2 satellite data for Lewotolok during January 2014-January 2021 for MODVOLC and 20 March 2016-January 2021 for Sentinel-2 thermal satellite data. Data courtesy of HIGP - MODVOLC Thermal Alerts System and Sentinel Hub Playground.

Brief seismicity, which included shallow and deep volcanic earthquakes was detected during October 2017. On 9 October 2017 PVMBG issued a VONA (Volcano Observatory Notice for Aviation) reporting that white gas-and-steam emissions rose 500 m above the crater. On 10 October BNPB (Badan Nacional Penanggulangan Bencana) reported that five earthquakes 10-30 km below Lewotolok and ranging in magnitude of 3.9-4.9 as recorded by Badan Meteorologi, Klimatologi, dan Geofisika (BMKG). These seismic events were felt by local populations and resulted in an evacuation of 723 people. The only activity reported between January 2018 and October 2020 was white gas-and-steam plumes that rose 5-100 m above the crater drifting primarily E and W and an occasional thermal anomaly in the summit crater (figure 4).

Figure 4. Sentinel-2 thermal satellite imagery shows a thermal anomaly in the summit crater of Lewotolok during 20 March 2016 (top left), 8 July 2017 (top right), 13 July 2018 (bottom left), and 12 August 2019 (bottom right). Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

New eruption starting in November 2020. On 26 November 2020 a continuous tremor began at 1943, followed by a series of volcanic earthquakes at 1947 and deep volcanic earthquakes at 1951, 1952, 1953, and 2255; white gas-and-steam emissions rose 20 m above the crater. Deep volcanic earthquakes were again recorded at 0242, 0537, 0556 on 27 November. At 0557 an explosion produced a gray ash plume that rose 500 m above the crater and drifted W; by 0630 the plume turned white, according to PVMBG (figure 5). Seismicity decreased slightly after the explosion, but tremor continued. During 27-28 November dense white gas-and-steam plumes rose as high as 500 m above the crater and nighttime crater incandescence was observed.

Figure 5. Webcam image of a dense gray ash plume rising 500 m above the crater of Lewotolok on 27 November 2020. Courtesy of MAGMA Indonesia.

During the morning of 29 November seismicity increased again and consisted of six deep volcanic earthquakes, continuous tremor occurred around 0930. A second explosion was recorded at 0945 that produced an ash plume 4 km above the crater, accompanied by incandescent material that was ejected above the crater (figure 6). The ash plume consisted of two levels: the lower-level drifted W and NW and the upper-level drifted E and SE. The large, gray ash plume was captured in a satellite image as it spread generally E and W (figure 7). Ashfall and a sulfur odor was reported in several surrounding villages; videos from social media showed tephra falling onto the roofs of residential areas. BPBD evacuated residents in 28 villages in two sub-districts; by 29 November at 1300 about 900 people had been evacuated. At 1900 Strombolian activity was observed and during the night, crater incandescence was visible.

Figure 6. Photos of the eruption at Lewotolok on 29 November 2020 that produced a dense, gray ash plume 4 km above the crater. Courtesy of Devy Kamil Syahbana, PVMBG (left) and MAGMA Indonesia (right).

Figure 7. Satellite image showing a strong gray ash plume above Lewotolok on 29 November 2020, expanding roughly E and W. Courtesy of Sentinel Hub Playground and the European Space Agency, Copernicus.

The eruption continued from 29 November into 1 December, where the white-and-gray ash plumes rose 700-2,000 m above the crater and drifted SE and W, accompanied by incandescent material that was ejected above the crater and the smell of sulfur, according to PVMBG (figure 8). A large sulfur dioxide plume was reported drifting SE and extending over the N half of Australia by 30 November (figure 9). By 1300 that day, 4,628 people had been evacuated. Incandescent lava flows near the summit were visible and incandescent material traveled down the flanks during 30 November and 1 December.

Figure 8. Webcam image of the continuous eruption at Lewotolok showing a dense gray ash plume rising above the cloud-covered summit on 30 November 2020. Courtesy of MAGMA Indonesia.

Figure 9. SO2 plume from Lewotolok captured by the Sentinel-5P/TROPOMI instrument on 30 November 2020 drifting SE and along the N part of Australia. Courtesy of Simon Carn and the NASA Global Sulfur Dioxide Monitoring Page.

White-and-gray plumes continued frequently through January 2021, rising 100-1,500 m above the crater, drifting in multiple directions, accompanied by nighttime crater incandescence and occasional incandescent ejecta (figure 10). During 1-8 December gray plumes rose 100-1,000 m above the crater and drifted E, W, and SW accompanied by nightly crater incandescence and incandescent material ejected as high as 20 m above the crater. By 5 December at 2200 about 9,028 residents had been evacuated to 11 evacuation centers, according to BNPB. Black, gray, and brown ash plumes were visible daily during 9-15 December, rising 1 km above the crater, accompanied by nightly Strombolian explosions that ejected material above the crater. More Strombolian explosions on most nights over 16-29 December ejected material 100-300 m above the crater; in addition, the sounds of rumbling and banging could be heard. The material was deposited as far as 1 km from the crater E and SE during 24-25 and 27-31 December and 4-7 January 2021. Strombolian activity continued into January, accompanied by frequent gray-and-white ash plumes, rumbling and banging sounds, and incandescent ejecta up to 600 above the crater that extended as far as 500 m E, SE, and W. Crater incandescence was visible up to 600 m above the crater.

Figure 10. Webcam images showing continuing dense gray ash plumes from Lewotolok on 1 December 2020 (top) and 8 January 2021 (bottom). Courtesy of MAGMA Indonesia.

A consistent level of thermal activity was recorded in the Sentinel-2 MODIS Thermal Volcanic Activity from February 2019 through October 2020; in early December 2020 a slight increase in thermal anomalies were detected (figure 11). This data reflects the start of the new eruption in late November 2020. According to the MODVOLC thermal algorithm, five thermal hotspots were detected between January 2020 and January 2021 on 3 September (1), 29 November (2), 24 December (1), and 5 January 2021 (1). Some of this thermal activity was also observed in Sentinel-2 thermal satellite imagery in the summit crater (figure 12).

Figure 11. Sentinel-2 MODIS Thermal Volcanic Activity data (bands 12, 11, 8A) shows consistent thermal activity (red dots) at Lewotolok during February 2020 through December 2020. Stronger thermal anomalies in early December is likely due to the new eruption that began in late November 2020. Courtesy of MIROVA.

Figure 12. Sentinel-2 thermal satellite imagery showing a thermal anomaly in the summit crater of Lewotolok on 25 October (top left), 9 November (top right), and 3 January 2021 (bottom right). On 14 December (bottom left) a Natural Color image showed a gray ash emission above the clouds and drifted E. On 3 January 2021 (bottom right) two thermal anomalies were visible in the summit crater accompanied by gas-and-steam emissions drifting NE. Sentinel-2 satellite images with “Natural Color” rendering (bands 4, 3, 2) on 14 December 2020, all other images use “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); 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/); 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); European Space Agency (ESA), Copernicus (URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus); NASA 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/); Simon Carn, Dept of Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA (URL: https://so2.gsfc.nasa.gov/).

Soufrière St. Vincent is the northernmost stratovolcano on St. Vincent Island in the southern part of the Lesser Antilles. The NE rim of the 1.6-km-wide summit crater is cut by a crater (500 m wide and 60 m depth) that formed in 1812. Recorded eruptions date back to 1718, with notable eruptions occurring in 1812, 1902, and 1979. The eruption of 1979 was characterized by ashfall, pyroclastic flows, and lahars, in addition to a series of Vulcanian explosions during 13-26 April 1979 that destroyed the lava dome in the summit crater, which had formed during a 1971 effusive eruption (SEAN 04:04). As a result, more than 20,000 people were evacuated. Beginning around 3 May 1979 another lava dome began to form in the main crater (SEAN 04:05; Shepherd et al., 1979) that continued to grow until the end of October 1979, expanding to 850 m in diameter and 120 m high (SEAN 04:11; Cole et al., 2019).

No further eruptive activity took place until December 2020, when a new lava dome began to grow SW of the pre-existing 1979 lava dome, accompanied by increased seismicity, crater incandescence, and gas-and-steam emissions. This report reviews information through February 2021 using bulletins from the University of the West Indies Seismic Research Centre (UWI-SRC), the National Emergency Management Organisation (NEMO), and various satellite data. Soufrière St. Vincent is monitored by the SRC assisted by the Soufrière Monitoring Unit (SMU) from the Ministry of Agriculture in Kingstown. As of 2004, the monitoring network had consisted of five seismic stations, eight GPS stations, and several dry tilt sites. Seismic data are transmitted from field sites to the Belmont Observatory (9 km SSW), which is operated by the SMU (figure 4). On 1 January 2021 a new seismic station was installed at Georgetown, on 10 January one was installed in Owia, followed on 15 January by another on the upper S flank, station SSVA at the summit on 18 January, and in Fancy on 21 January. In February 2021 the USGS-USAID (US Geological Survey-US Agency for International Development), through the Volcano Disaster Assistance Program (VDAP), donated equipment to build four more seismic stations.

Figure 4. Location map of the Belmont Observatory (yellow star) located in Rosehall, St. Vincent, 9 km SSW from the Soufrière St. Vincent summit crater (red triangle). Base map satellite imagery courtesy of Google Earth.

A spike in seismicity was recorded during June-July 2019 (figure 5), though no cause was reported. The number of events sharply declined after July but continued intermittently through November 2020. Seismicity began to increase in early November through 23 December 2020, which included 126 earthquakes described as volcano-tectonic events and rockfall signals that were captured on one reliable seismic station (SVB) located 9 km from the volcano. The maximum daily count was 11 events on 16 November. After 23 December a total of eight events were detected before seismicity briefly subsided.

Figure 5. Daily count of volcanic earthquakes recorded at Soufrière St. Vincent during 1 January 2019 through February 2021. Increased seismicity was detected during June-July 2019 and mid-October 2020 through February 2021. An installation of station SVV on 6 January 2021 at Wallibou is annotated on this graph. Data courtesy of UWI-SRC.

Activity during December 2020. Staff members of the Soufrière Monitoring Unit (SMU) made visual observations of the crater on 16 December and reported minor changes in fumarolic activity and a small lake on the E side of the crater floor. On 27 December UWI-SRC and NEMO reported that an effusive eruption had begun, which was characterized by a new lava dome in the main crater on the SW perimeter of the 1979 dome (figures 6 and 7). A thermal hotspot in the crater was also detected that day using satellite data by NASA FIRMS. As a result, the Volcanic Alert Level (VAL) was raised to Orange (the second highest level on a four-color scale) on 29 December (figure 8). The Volcano Ready Communities Project, a collaboration between NEMO SVG and UWI Seismic Research Centre, distributed their volcano hazard map for the surrounding communities, in preparation for a potential evacuation (figure 9).

Figure 6. Photo of the first documented observation of the new lava dome at Soufrière St. Vincent on 27 December 2020 taken from the E side of the summit. Courtesy of Melanie Grant, IG, UWI-SRC.

Figure 7. Photo of an early observation of the new lava dome at Soufrière St. Vincent on 29 December 2020 growing WSW of the 1979 lava dome on the SW edge of the summit crater, accompanied by gas-and-steam emissions. The dome was estimated to be 60 m high on 30 December. Courtesy of Kemron Alexander (color corrected), SMU, UWI-SRC.

Figure 8. Volcanic Hazard Alert Level System for Soufriere St. Vincent. Courtesy of UWI-SRC.

Figure 9. Volcanic hazard map for Soufrière St. Vincent, showing different areas that are likely to experience hazardous volcanic events which would require evacuations. The hazard map is divided into four zones: Zone 1 (Red), which is a very high hazard location; Zone 2 (Orange), which is a high hazard location; Zone 3 (Yellow), which is a moderate hazard location; and Zone 4 (Green), which is a low hazard location. This poster was created prior to the current eruption as part of the Volcano Ready Communities Project, a collaboration between NEMO SVG and UWI Seismic Research Centre. Courtesy of UWI-SRC and NEMO.

Activity during January-February 2021. Observations made during a field visit on 5 January, during a helicopter overflight on 6 January, and based on 9 January drone video noted that the new dome was expanding to the W on the WSW edge of the 1979 lava dome and continued to gradually grow through February 2021 (figure 10). Growth of the 2020/21 lava dome produced small, hot rockfalls and gas-and-steam emissions that were visible from the Belmont Observatory. The gas emissions were most notable from a small depression at the top of the dome. Two seismic stations were installed on the flank of the volcano at Wallibou (SVV) and at the summit (SSVA) on 6 and 18 January, respectively.

Figure 10. Map showing the growth of the new 2020/21 lava dome at Soufrière St. Vincent from 27 December 2020 to 12 February 2021. The dome is located on the SW edge of the crater rim and WSW of the 1979 lava dome that is covered in vegetation. Courtesy of UWI-SRC.

Seismic stations recorded 573 events through 0730 on 30 January; this number continued to grow into February (up to 703 events by 0830 on 4 February) (figure 5). Observations on 14 January showed that the dome was growing taller and expanding to the E and W. An overflight on 15 January showed extensive vegetation damage on the E, S, and W inner crater walls; damage previously noted on the upper SW crater rim had expanded downslope (figure 11). Scientists visited on 16 January and recorded temperatures of 590°C at the dome surface (figure 12). During 15-17 January residents to the W of the volcano reported nighttime crater incandescence. Persistent gas-and-steam emissions were observed rising above the dome, as well as from the contact between the 2020/21 and 1979 domes during the rest of the month and through February.

Figure 11. Oblique aerial view of the lava dome at Soufrière St. Vincent between the 1979 dome and the SW crater rim on 15 January 2021, accompanied by gas-and-steam emissions. On this day, the dome was 340 m long, 160 m wide, and 80 m high. Courtesy of Adam Stinton, MVO, UWI-SRC.

Figure 12. Thermal measurements were taken at the base of the freshly extruded lava dome at Soufrière St. Vincent on 16 January 2021. Top: Photo (color corrected) of the base of the new lava dome. Bottom: Thermal FLIR (Forward-Looking InfraRed) image of the base of the new lava dome showing a maximum temperature of 590.8°C. Courtesy of Adam Stinton, MVO, UWI-SRC.

Sulfur dioxide emissions were first detected on 1 February using a Multi-Gas Instrument and a filter pack; the dome had reached an estimated volume of 5.93 million cubic meters. Vegetation on the NW part of the crater (N of the dome) was damaged, likely due to fire. The dome continued to expand laterally to the N and S, according to reports issued on 6 and 8 February. After that it grew about 15 m to the NW and SE, according to 11 and 15 February reports (figure 13). NEMO reported that the growth rate of the lava dome ranged from 1.9 to 2.13 m³/s (figure 14). Active gas-and-steam emissions originated dominantly at contact areas between the pre-existing 1979 dome and the 2020/21 dome, as well as at the top of the new dome.

Figure 13. Photo of the 2020/21 lava dome (dark mass at left) at Soufrière St. Vincent on 12 February 2021 showing continuous gas-and-steam emissions and damaged vegetation on the 1979 lava dome (right). On this day, the dome was 618 m long, 232 m wide, 90 m high, and an estimated volume of 6.83 million cubic meters. Courtesy of Kemron Alexander, SMU, UWI-SRC.

Figure 14. Estimated lava extrusion rates and added volume of material at Soufrière St. Vincent’s 2020/21 lava dome during 27 December 2020 through 3 February 2021. Calculations were based on UAV photography and photogrammetry. Data courtesy of UWI-SRC.

Thermal satellite data. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows the beginning of thermal activity in late December 2020 and continuing at a lower power into early February (figure 15). A single MODVOLC thermal alert was detected on 29 December. This activity marks the beginning of the effusive eruption and the formation of the new lava dome. Sentinel-2 thermal satellite imagery detected a thermal anomaly on the SW side of the main crater during clear weather days in January 2021, which represents the active 2020/21 lava dome (figure 16). Fresh, hot material is also visible surrounding the thermal anomaly, which demonstrates the growth of the lava dome over time.

Figure 15. Thermal activity at Soufrière St. Vincent was detected beginning in late December 2020 and continued through early February 2021, as reflected in the MIROVA data (Log Radiative Power). The power of the thermal anomalies had slightly decreased after December. Courtesy of MIROVA.

Figure 16. Sentinel-2 thermal satellite imagery showing a persistent thermal anomaly (bright yellow-orange) in Soufrière St. Vincent’s growing lava dome on the WSW edge of the main crater during 3 January through 28 January 2021. The dark black color is the freshly cooled material from the effusive activity, which also demonstrates the increasing size of the lava dome. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Field work during mid-January 2021. SRC collected rock samples from the new lava dome and sent them to scientists from the University of East Anglia, University of Plymouth, and University of Oxford on 16 January 2021 as a collaborative project to analyze their composition and compare them with the composition of rocks erupted in 1902, 1971, and 1979. Analyses showed that the new 2020/21 lava dome was basaltic andesite, similar in composition to the earlier domes (figure 17).

Figure 17. Backscattered electron image of a sample from the 2020/21 lava dome showing groundmass texture. Low-contrast dark gray crystals are feldspar microlites in glass (darkest gray). Some of the larger feldspar crystals have Ca-rich cores (paler gray). Clinopyroxenes also make up the groundmass (brighter gray) and some are breaking down to Fe-oxides (small oxides at edges of clinopyroxene bottom center and bottom right). In some areas dark glass is devitrifying (paler gray irregular shapes within dark gray glassy patches). Fe-Ti oxides are also common (bright white crystals). Total image width is about 0.3 mm. Image and description courtesy of Bridie Davies, UEA.

References: Cole P D, Robertson R E A, Fedele L, Scarpati C, 2019. Explosive activity of the last 1000 years at La Soufrière, St Vincent, Lesser Antilles. J. Volcanol. Geotherm. Res., 371:86-100.

Shepherd, J. B., Aspinall, W. P., Rowley, K. C., Pereira, J., Sigurdsson, H., Fiske, R. S., Tomblin, J. F., 1979. The eruption of Soufrière volcano, St Vincent April–June 1979. Nature, 282 (5734), 24–28. doi:10.1038/282024a0.

Geologic Background. Soufrière St. Vincent is the northernmost and youngest volcano on St. Vincent Island. The NE rim of the 1.6-km wide summit crater is cut by a crater formed in 1812. The crater itself lies on the SW margin of a larger 2.2-km-wide caldera, which is breached widely to the SW as a result of slope failure. Frequent explosive eruptions after about 4,300 years ago produced pyroclastic deposits of the Yellow Tephra Formation, which cover much of the island. The first historical eruption took place in 1718; it and the 1812 eruption produced major explosions. Much of the northern end of the island was devastated by a major eruption in 1902 that coincided with the catastrophic Mont Pelée eruption on Martinique. A lava dome was emplaced in the summit crater in 1971 during a strictly effusive eruption, forming an island within a lake that filled the crater. A series of explosive eruptions in 1979 destroyed the 1971 dome and ejected the lake; a new dome was then built.

Information Contacts: University of the West Indies Seismic Research Centre (UWI-SRC), University of the West Indies, St. Augustine, Trinidad & Tobago, West Indies (URL: http://www.uwiseismic.com/); National Emergency Management Organisation (NEMO), Government of Saint Vincent and the Grenadines, Biseé, PO. Box 1517, Castries, Saint Lucia, West Indies (URL: http://nemo.gov.lc/); 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); Google Earth (URL: https://www.google.com/earth/); Bridie Davies, University of East Anglia, Norwich Research Park, Norwich, Norfolk, NR4 7TJ, UK (URL: https://people.uea.ac.uk/bridie_davies).

Erta Ale, located in Ethiopia, is a highly active volcano that contains a 0.7 x 1.6 km, elliptical summit caldera with multiple pit craters that frequently host active lava lakes. Another larger 1.8 x 3.1 km wide depression SE of the summit is bounded by curvilinear fault scarps on the SE side. Recent activity has been characterized by lava flow outbreaks (BGVN 45:05) and thermal anomalies detected from pit craters in the summit caldera (BGVN 45:05 and 45:10). This report covers activity from October 2020 through February 2021 and is characterized by a brief period of strong thermal anomalies in late November, which sharply declined in December. Information primarily comes from satellite data.

Activity at Erta Ale had gradually decreased compared to previous months; thermal activity during this reporting period remained primarily in the N summit caldera. MIROVA (Middle Infrared Observation of Volcanic Activity) analysis of MODIS satellite data shows a total of four low-power thermal anomalies from October through most of November. At the end of November, a brief surge of strong thermal activity was detected in the S pit crater of the summit caldera, followed by a sharp decrease the following days (figure 102). Similarly, the MODVOLC system detected a total of eight thermal alerts; two were detected on 29 November and six were detected on 30 November, primarily focused in the summit caldera. Only two thermal anomalies were recorded in the MIROVA graph after this surge of activity; one in mid-December and one in early January. Thermal data from NASA VIIRS detected hotspots on 28-30 November, 1-3 December, and 8 December.

Figure 102. A total of four low-power thermal anomalies were recorded at Erta Ale during October through most of November 2020. Beginning in late November into early December a strong but brief surge of thermal activity was detected according to the MIROVA system (Log Radiative Power). Only two low-power thermal anomalies were recorded after the activity in early December; one in mid-December and one in early January 2021. Courtesy of MIROVA.

According to Sentinel-2 thermal satellite images, a weak thermal anomaly was first visible on 20 October in the summit caldera. Intermittent, weak anomalies were also detected in the summit caldera on 25 and 30 October and 4, 9, 19, and 24 November. On 29 November the thermal activity increased significantly, detected as a strong hotspot in the S pit crater of the summit caldera (figure 103). This brief increase in power was also recorded in the MIROVA graph and by the MODVOLC thermal algorithm. By 4 December the size and power of this thermal activity decreased significantly, though it was still visible in the summit caldera. Thermal activity was no longer observed after 4 December until clear weather days on 2 and 12 February when a faint anomaly was detected.

Figure 103. Sentinel-2 thermal satellite images of Erta Ale during 30 October 2020 to 12 February 2021 showing a single thermal anomaly (bright yellow-orange) in the S pit crater of the summit caldera that varies in strength. Top left: 30 October 2020 shows a faint thermal anomaly in the S pit crater. Top right: 29 November 2020 shows the strongest thermal anomaly in the S pit crater during the reporting period and is also reflected in the MIROVA graph and detected by the MODVOLC system. Bottom left: 4 December 2020 shows that the thermal anomaly from activity in late November remains hot but begins to decrease in strength. Bottom right: 12 February 2021 again shows thermal activity from the S pit but weaker than the previous November and December. Sentinel-2 images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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: 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); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/).

Bagana is a remote volcano located in central Bougainville Island in Papua New Guinea with eruptions dating back to 1842. The current eruption period began in February 2000, with more recent activity characterized by thermal anomalies along with gas-and-steam and ash plumes (BGVN 44:12 and 45:07). Typical activity consists of episodes of lava flows and intermittent strong passive degassing, especially sulfur dioxide. This report covers activity from May-December 2020 using primarily thermal data and satellite imagery.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed a cluster of intermittent low-power thermal anomalies during June through early August, followed by a period of quiescence during August to mid-October, with the exception of two anomalies detected in early September (figure 44). Thermal activity slightly increased again by mid-October and continued infrequently through December at low levels. This pattern of thermal activity is also reflected in three Sentinel-2 thermal satellite images that showed faint, roughly linear, thermal anomalies, indicative of lava flows trending NE and NW on 21 June, NE on 1 July, and W on 23 November (figure 45). On clear weather days, gas-and-steam emissions could be seen in satellite imagery on 30 August, 4 October, and 23 November, each of which drifted W (figure 45). Gas-and-steam emissions on 13 December drifted E.

Figure 44. Intermittent low-power thermal anomalies were detected at Bagana during late May-December 2020 as recorded by the MIROVA system (Log Radiative Power). Relatively higher power and frequency anomalies were detected during June-early August. Thermal activity declined after early August into mid-October, with the exception of two thermal anomalies in early September. Activity increased again slightly by mid-October and continued through December, but at a lower power and frequency. Courtesy of MIROVA.

Figure 45. Sentinel-2 thermal satellite imagery showing weak thermal anomalies at Bagana during June through December 2020. Top left: Faint, linear thermal anomalies on 21 June 2020 on the NE and NW flanks, which could represent lava effusion, though clouds covered much of the area. Top right: Hot material traveling down the NE flank on 1 July 2020. Middle left and right: Gas-and-steam emissions rising from the summit crater and drifting W on 30 August and 4 October 2020; very faint thermal anomalies can be observed in the crater. Bottom left: Gas-and-steam emissions in the summit crater drifted W on 23 November 2020, and a probable lava flow is visible extending down the NW flank. Bottom right: Gas-and-steam emissions rose above the summit crater on 13 December 2020 and drifted E. Sentinel-2 images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Kadovar is located in the Bismark Sea offshore from the mainland of Papua New Guinea about 25 km NNE from the mouth of the Sepik River. Its first confirmed eruption began in early January 2018, characterized by ash plumes and a lava extrusion that resulted in the evacuation of around 600 residents from the N side of the island (BGVN 43:03). Activity has recently consisted of intermittent ash plumes, gas-and-steam plumes, and thermal anomalies (BGVN 45:07). Similar activity continued during this reporting period of July-December 2020 using information from the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

RVO issued an information bulletin on 15 July reporting minor eruptive activity during 1-5 July with moderate light-gray ash emissions rising a few hundred meters above the Main Crater. On 5 July activity intensified; explosions recorded at 1652 and 1815 generated a dense dark gray ash plume that rose 1 km above the crater and drifted W. Activity subsided that day, though fluctuating summit crater incandescence was visible at night. Activity increased again during 8-10 July, characterized by explosions detected on 8 July at 2045, on 9 July at 1145 and 1400, and on 10 July at 0950 and 1125, each of which produced a dark gray ash plume that rose 1 km above the crater. According to Darwin VAAC advisories issued on 10, 16, and 30 July ash plumes were observed rising to 1.5-1.8 km altitude and drifting NW.

Gas-and-steam emissions and occasional ash plumes were observed in Sentinel-2 satellite imagery on clear weather days during August through December (figure 56). Ash plumes rose to 1.2 and 1.5 km altitude on 3 and 16 August, respectively, and drifted NW, according to Darwin VAAC advisories. On 26 August an ash plume rose to 2.1 km altitude and drifted WNW before dissipating within 1-2 hours. Similar activity was reported during September-November, according to several Darwin VAAC reports; ash plumes rose to 0.9-2.1 km altitude and drifted mainly NW. VAAC notices were issued on 12 and 22 September, 4, 7-8, and 18 October, and 18 November. A single MODVOLC alert was issued on 27 November.

Figure 56. Sentinel-2 satellite data showing a consistent gas-and-steam plume originating from the summit of Kadovar during August-December 2020 and drifting NW. On 21 September (top right) a gray plume was seen drifting several kilometers from the island to the NW. Images with “Natural color” (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows intermittent low-power anomalies during July through December 2020 (figure 57). Some of this thermal activity in the summit crater was observed in Sentinel-2 thermal satellite imagery, accompanied by gas-and-steam emissions that drifted primarily NW (figure 58).

Figure 57. Intermittent low-power thermal anomalies at Kadovar were detected in the MIROVA graph (Log Radiative Power) during July through December 2020. The island location is mislocated in the MIROVA system by about 5.5 km SE due to older mis-registered imagery; the anomalies are all on the island. Courtesy of MIROVA.

Figure 58. Sentinel-2 satellite data showing thermal anomalies at the summit of Kadovar on 23 July (top left), 7 August (top right), 1 September (bottom left), and 21 September (bottom right) 2020, occasionally accompanied by a gas-and-steam plume drifting dominantly NW. Two thermal anomalies were visible on the E rim of the summit crater on 23 July (top left) and 7 August (top right). Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; 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).

Klyuchevskoy, located in northern Kamchatka, has had historical eruptions dating back 3,000 years characterized by major explosive and effusive eruptions from the flank craters. The current eruption began in April 2019 and has recently consisted of Strombolian activity, ash plumes, and an active lava flow descending the SE flank (BGVN 45:09). This report covers September-December 2020 and describes similar activity of Strombolian explosions, ash plumes, and active lava flows beginning in early October. Information primarily comes from weekly and daily reports from the Kamchatkan Volcanic Eruption Response Team (KVERT), the Tokyo Volcanic Ash Advisory (VAAC), and satellite data.

Activity from July through September was relatively low, with no thermal activity detected during August-September. On 2 October renewed Strombolian explosions began at 1003, ejecting ash 300-400 m above the summit and producing gas-and-steam plumes with some ash that drifted down the E flank (figure 48). That night, crater incandescence was visible. On 5 October KVERT reported that a lava flow began to effuse along the Apakhonchich chute at 0100. During 7-8 October activity intensified and was characterized by strong explosions, collapses of the sides of the drainage, strong thermal anomalies, and ash plumes that extended over 200 km SE from the crater; the lava flow remained active and continued to descend the SE flank. A Tokyo VAAC advisory issued on 7 October reported that an ash plume rose to 8.8 km altitude and drifted E and SE; during 8-9 October ash plumes rose to 5.5 km altitude and drifted as far as 270 km SE. A strong, bright, thermal anomaly was observed daily in satellite imagery, which represented the new lava flow. Strombolian explosions continued throughout the month, accompanied by gas-and-steam plumes containing some ash and an active lava flow advancing down the Apakhonchich chute on the SE flank (figure 49).

Figure 48. Photos of a gray ash plume (left) and the beginning of the lava flow (right), represented as summit crater incandescence at Klyuchevskoy on 2 October 2020 at 1030 and 2100, respectively. Photos by Y. Demyanchuk; courtesy of Volkstat.

Figure 49. Photo of Strombolian explosions at the summit of Klyuchevskoy accompanied by ash emissions and a lava flow advancing down the SE-flank Apakhonchich chute on 25 October 2020. Photo by Y. Demyanchuk (color corrected); courtesy of Volkstat.

Similar activity continued to be reported in November, consisting of Strombolian explosions, ash plumes, and a lava flow advancing down the SE flank. A bright thermal anomaly was observed in thermal satellite imagery each day during the month. During 16-19 November explosions recorded in satellite and video data showed ash plumes rising to 7.5 km altitude and drifting as far as 108 km to the NE, E, SE, and S (figure 50). On 19 November an ash cloud 65 x 70 km in size drifted 50 km SE, according to a KVERT VONA (Volcano Observatory Notice for Aviation). During 26-30 November video and satellite data showed that gas-and-steam plumes containing some ash rose to 7 km altitude and extended as far as 300 km NW and E, accompanied by persistent moderate explosive-effusive activity (figure 51).

Figure 50. Photo of the Strombolian and Vulcanian explosions at Klyuchevskoy on 18 November 2020 which produced a dense gray ash plume. Photo by Yu. Demyanchuk, IVS FEB RAS, KVERT

Figure 51. Photo of the summit of Klyuchevskoy (right foreground) showing incandescent Strombolian explosions, the lava flow descending the Apakhonchich chute on the SE flank, and a gray ash plume on 29 November 2020. Kamen volcano is the cone at back left. Photo by Y. Demyanchuk (color corrected); courtesy of Volkstat.

Moderate explosive-effusive activity continued through December; a strong daily thermal anomaly was visible in satellite images. During 2-3 December gas-and-steam plumes containing some ash rose to 7 km altitude and extended 300 km NW and E. Intermittent gas-and-ash plumes continued through the month. On 7 December KVERT reported that a new lava flow began to advance down the Kozyrevsky chute on the S flank, while the flow on the SE flank continued. Strombolian explosions in the crater ejected incandescent material up to 300 m above the crater on 8 December while hot material was deposited and traveled 350 m below the crater. A cinder cone was observed growing in the summit crater and measured 75 m tall.

Strombolian and Vulcanian activity continued during 11-25 December, accompanied by the lava flow on the S flank; according to Sentinel-2 thermal satellite images, the effusion on the SE flank had stopped around 13 December and had begun to cool. The lava flow in the Kozyrevsky chute spalled off incandescent material that continued to travel an additional 350 m. Gas-and-steam plumes that contained some ash rose to 6 km altitude and drifted up to 350 km generally E. On 24 December the Kamchatka Volcanological Station field team visited Klyuchevskoy to do work on the field stations. The scientists observed explosions that ejected incandescent material 300 m above the crater and the S-flank lava flow (figure 52). On 28 December KVERT reported that the moderate explosive-effusive eruption continued, but the intensity of the explosions had significantly decreased. The lava flow on the S flank continued to effuse, but its flow rate had already decreased.

Figure 52. Photos of a dense ash plume (left) and a color corrected photo of the lava flow advancing on the S flank (right) of Klyuchevskoy on 24 December 2020, accompanied by incandescent Strombolian explosions and a gray ash plume. Photos by Y. Demyanchuk; courtesy of Volkstat.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows frequent and strong thermal activity beginning in early October and continuing through December 2020, which is represented by the active lava flows reported in the summit crater (figure 53). According to the MODVOLC thermal algorithm, a total of 615 thermal alerts were detected at or near the summit crater from 1 October to 31 December; none were reported in September. Sentinel-2 thermal satellite imagery frequently showed the progression of the active lava flows as a strong thermal anomaly descending the SE flank during October through late November and the SW flank during December, sometimes even through weather clouds (figure 54). The thermal anomalies were commonly accompanied by a gas-and-steam plume that drifted mainly E and NE. A total of 164 VAAC advisories were issued from 2 October through 31 December.

Figure 53. Strong and frequent thermal anomalies were detected in early October at Klyuchevskoy and continued through December 2020, as recorded by the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 54. Sentinel-2 thermal satellite images showing the progression of two lava flows (bright yellow-orange) originating from the summit crater at Klyuchevskoy from 4 October through December 2020. Crater incandescence was visible on 4 October (top left), which marked the beginning of the lava flow. By 31 October (top right) the active flow had traveled down the Apakhonchich chute on the SE flank, accompanied by a gas-and-steam plume that drifted NE. On 10 November (bottom left) the lava flow continued down the SE flank; the darker black color represents parts of the lava flow that began to cool. The gas-and-steam plume drifted E from the summit. On 25 December (bottom right) a new lava flow was observed descending the SW flank, also accompanied by a strong gas-and-steam plume. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

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/); Kamchatka Volcanological Station, Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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).

Introduction. The Associated Press reported a sudden explosion had occurred at Mount Cameroon on 3 February 2012 (see subsection below). A review of MODVOLC thermal alerts based on satellite infrared data during 2001 to mid-2014 found few if any of the highest-level alerts. In contrast, there were numerous stronger alerts during 3 March to 17 July 2000 (activity described in BGVN 24:09, 25:06).

In (BGVN 26:11) we reported that during 26-27 June 2001, Limbe, an economically important coastal town with ~85,000 residents located on the S foot of the steep sided stratovolcano Mt. Cameroon (figure 4), was struck by a series of heavy rains leading to deadly floods and landslides. Figure 5 shows a photo taken in Limbe during the flood. Although many would classify the flood as a meteorological disaster and not a volcanological one, Mt. Cameroon is the tallest peak in Western Africa and orogenic uplift of warm most air over the massive edifice is a factor affecting the amount of rainfall. Limbe sits at the mouth of drainages coming down this side of the edifice. During July 2014, heavy rains again resulted in floods in Limbe (Ndaley, 2014). In strict eruptive-hazard terms, Mount Cameroon is the only volcanic peak in Western Africa with recent ongoing eruptions.

Figure 4. (Inset) Indicating the location of the Republic of Cameroon in Africa. (Main map) The location of Mount Cameroon, the main bulk of which is centered ~25 km from the coastline. Some other regional volcanic features and their ages are also indicated. Etinde is a prominent conical volcanic center on the SW flank of the larger structure of Mount Cameroon. The town of Limbe resides along the coast just S of the volcano. Taken from Suh and others (2008).

Figure 5. Flooding that inundated Clerks quarter, Limbe in 2001. The volcanic topography feeds a number of catchment basins into Limbe, which is also why the same town is also highly vulnerable to lava flows (Wantim and others, 2011). Photo taken from MIA-VITA literature.

This report discusses recent research on the 2000 eruption of Mount Cameroon and then summarizes news articles on a smaller 2012 explosion. After that, this report discusses vulnerability studies, including a United Nations project that examined and attempted to mitigate the risk to local communities.

The 2000 eruption. On the basis of first-hand knowledge of some of their co-authors, Wantim and others (2011) stated that the eruption occurred during 28 May and 20 July 2000. MODVOLC satellite-based thermal alerts were found during the interval 3 March 2000 to 17 July 2000. The seismic activity for this eruption lasted 3 months, up to September 2000 (Ateba and others, 2009). Multiple fissure segments produced lava that built four different lava flow fields at three sites they specify in their paper (Wantim and others, 2011).

Eruptions at site 1 (~ 3,930 m a.s.l) began in the night of 28 May 2000 with an explosive phase that produced only tephra and ballistic blocks (Suh and others, 2003 and Wantim and others, 2011). A ~850 m-long ′a′a flow field was emplaced at this site a month later, an observation supported by data from MODVOLC and multispectral images (Landsat ETM + and ASTER) analyzed in this study. The upper 2000 flow is one of the shortest (850 m) recorded for historical lava flows here despite having descended steep slopes (10-25°). Late emission of the lava and field observations of cone breach at the lava source suggest that the lava flow was fed by the drainage of a transient lava lake. That lake was presumably formed by lava fountaining in the eruptive cone (Wantim and others., 2011). The lava flow field covers a total surface area of (8 ± 2) × 104 m² with a total volume of (3.4 ± 0.8) × 105 m³. There were two lobes, ~4.5 m and ~8.7 m thick (Wantim and others., 2011).

Brief explosion--2012 news reports. Cameroon state radio and television reports stated that Mount Cameroon sent "ashes and flames" into the air in a brief explosion on 3 February 2012. A violent explosion lasted a couple of seconds and lightly injured two of the porters and guides on the mountain, according to a 6 February 2012 Associated Press report.

Lava flow hazard and risk, and weathering studies. According to Favalli and others (2010), Mt. Cameroon is one of the most active effusive volcanoes in Africa. About 500,000 people living or working around its fertile flanks are subject to significant threat from lava flow inundation. Therefore, this group initiated a scientific project to assess the hazards/risks associated with the volcano by simulating probable lava flow paths using the DOWNFLOW code, a routine that for lava-flow-hazard mapping that defines areas susceptible to inundation.

According to Wantim and others (2013), as for many other effusive volcanoes, only limited information exists on the relevant lava flow properties and emplacement dynamics for recent eruptions. This study provides new quantitative constraints for rheological and dynamic characteristics of lava flow effusion at Mount Cameroon during the 1982 and 2000 eruptions. These constraints were used to calibrate the FLOWGO thermo-rheological model for these lava flows. FLOWGO (Harris and Rowland, 2001) was the only model that enables full inversion of the thermo-rheological properties of lava flows. It can be constrained from channel morphology and down-flow evolution of crystal content.

Lava flow hazard and risk were assessed by simulating probable lava flow paths using the DOWNFLOW code (Tarquini and Favalli, 2011). That code incorporates digital elevation data and allows the definition of areas that are susceptible to inundation by lava flows originating from each vent; it has been used extensively to simulate lava flows at Mt. Etna and Nyiragongo volcanoes ( Favalli and others, 2005, 2006, 2009; Chirico and others 2009). The details of the modeling and the resulting maps they produced can be found in the cited references. Simulated lava flows from about 80,000 possible vents were used to produce a detailed lava flow hazard map. The lava flow risk in the area was mapped by combining the hazard map with digitized infrastructures (i.e., human settlements and roads).

Results show that the risk of lava flow inundation is greatest in the most inhabited coastal areas, specifically the town of Limbe (which constitutes the center of Cameroon's oil industry and an important commercial port). Buea, the second most important town in the area, has a much lower risk although it is significantly closer to the summit of the volcano. Non-negligible risk characterizes many villages and most roads in the area surrounding the volcano. In addition to the conventional risk mapping described above, the authors also present (1) two reversed risk maps (one for buildings and one for roads), where each point on the volcano is classified according to the total damage expected as a consequence of vent opening at that point; (2) maps of the lava catchments for the two main towns of Limbe and Buea, illustrating the expected damage upon venting at any point in the catchment basin. The hazard and risk maps provided here represent valuable tools for both medium/long-term land-use planning and real-time volcanic risk management and decision making.

The largely geochemical study of Che and others (2012), analyses the behavior and mobility of major and some trace elements during the physical and chemical development of landslide-prone soil profiles in Limbe, SW Cameroon. The soils result from in situ weathering of Tertiary basaltic and picrobasaltic rocks. Textural and chemical characterizations, together with two mass balance models are applied to understand the mobility and redistribution of elements during the weathering of pyroclastic cones and lava flows in the setting of Mt. Cameroon. This weathering is a major factor in the cohesion of steep slopes, and thus these studies address slope stability, another kind of volcano-related hazard that could occur even in times of volcanic quiescence.

Socio-economic vulnerability study. A United Nations project, MIA-VITA (Mitigate and Assess risk from Volcanic Impact on Terrain and human Activities) was started in Cameroon during 2011 (Apa and others, 2007; Bosi and others, 2011; European Commission, 2010). (The phrase 'Mia Vita' comes from the Italian, "My Life"). The project was based on the UN International Strategy for Disaster Reduction and a key expected outcome was to finding the best means to help local populations and authorities better perceive risks and thus reduce community vulnerability.

The program in Cameroon, as well in three other developing countries with active volcanoes, had several goals: (1) to assess the natural risk to local communities from the selected volcano, based on risk mapping and damage scenarios; (2) to improve crisis management, based on early warning systems and improved communications between government officials and the local populations, and (3) to reduce the vulnerability of populations in the wake of an eruption.

Besides Mount Cameroon, MIA-VITA also contributed to similar goals at Mount Merapi in Indonesia, Mount Kanlaon in Philippines, and Mount Fogo in Cape Verde. In the service of local citizens facing volcanic hazards, the MIA-VITA study also aimed to improve civil-defence, planning, and coordination and to reduce rumors and alarmist information.

MIA-VITA also integrates GIS capability with an analytic hierarchy method that yields volcanic risk maps. The approach is designed to solve complex multiple criteria problems using relative pairwise comparisons (Saaty, 1996; Wikipedia, 2014). To apply this approach, it is necessary to break down a complex unstructured problem into its component factors. The method incorporates both qualitative and quantitative criteria in the evaluation.

References. Apa, M.I., Kouokam, E:, Akoko, R.M, Thierry, P., and Buongiorno, M.F., 2007, Mt. Cameroon Socio-Economic Vulnerability and Resilience Assessment Through Traditional Survey Methods[FP7-ENV-2007-1] (URL: http://meetingorganizer.copernicus.org/EGU2011/EGU2011-3402.pdf http://meetingorganizer.copernicus.org/EGU2011/EGU2011-3402.pdf )

Bosi, V., Cristiani C. and Costantini, L., 2011, 3rd MIA-VITA Newsletter (Sept. 2011), MIA-VITA (URL: www.spinics.net/lists/volcano/msg02475.html )

Che, V.B., Fontijin, K., Ernst, G.G.J., Kervyn, M., Elburg, M, Van Ranst, E., Suh, C.E., 2012, Evaluating the degree of weathering in landslide-prone soils in the humid tropics: The case of Limbe, SW Cameroon; Geoderma, Vol. 170, pp. 378-389

Chirico G.D., Favalli, M., Papale, P., Pareschi, M.T., Boschi, E., 2009, Lava flow hazard at Nyiragongo volcano, D.R.C. 2. Hazard reduction in urban areas. Bull Volcanol 71:375-387. doi:10.1007/s00445-008-0232-z

European Commission, 2010 (31 March 2010), MIA-VITA--1st newsletter (URL: http://images.nationmaster.com/images/motw/africa/calabar_tpc_1996.jpg )

Favalli, M., Chirico, G.D., Papale, P., Pareschi, M.T., Boschi, E. (2009a) Lava flow hazard at Nyiragongo volcano, D.R.C. 1. Model calibration and hazard mapping. Bull Volcanol 71:363-374. doi:10.1007/s00445-008-0233-y

Favalli, M., Tarquini, S., Papale, P, Fomacai, A, and Boschi, E., 2011, Lava flow hazard and risk at Mt. Cameroon volcano, _Journal of Volcanology 2012 74:433-439. adsabs.harvard.edu/abs/2012BVol...74..423F

Favalli, M., Mazzarini, F., Pareschi, M.T., Boschi E (2009b) Topographic control on lava flow paths at Mount Etna, Italy: Implications for hazard assessment. J Geophys Res 114:F01019. doi:10.1029/2007JF000918

Favalli, M., Tarquini, S., Fornaciai, A., Boschi, E., 2009c, A new approach to risk assessment of lava flow at Mount Etna, Geology, 37(12):1111-1114. doi:10.1130/G30187A

Harris, AJL and Rowland, SK, 2001, FLOWGO: A kinematic thermorheological model for lava flowing in a channel. Bull Volcanol., . 63:20-44. doi:10.1007/s004450000120

Ndaley, Yannick Fonki, 2014, Heavy Rains Beat Limbe, Floods Put Residents In Distress. Eden Newspaper, 12 July 2014, (URL: http://edennewspaper.net/)

Saaty, T. L. (1996). Multicriteria decision making: The analytic hierarchy process. Pittsburgh, PA: RWS Publications, 479 pp. (ISBN 0962031712, 9780962031717)

Suh, C.E., Luhr, J.F., and Njome, M.S., 2008, Olivine-hosted glass inclusions from Scoriae erupted in 1954-2000 at Mount Cameroon volcano, West Africa, Journal of Volcanology and Geothermal Research, Volume 169, Issues 1-2, 1 January 2008, pp. 1-33, ISSN 0377-0273, http://dx.doi.org/10.1016/j.jvolgeores.2007.07.004.

Tarquini, S and Favalli, M, 2011, Mapping and DOWNFLOW simulation of recent lava flow fields at Mount Etna. Journal of Volcanology and Geothermal Research, 204:27-39. doi:10.1016/j.jvolgeores.2011.05.001

Wantim, M.N. , Kervyn, M., Ernst, G.G.J, del Marmol, M.A., Suh, C.E.. and Jacobs, P., 2013, Numerical experiments on the dynamics of channelised lava flows at Mount Cameroon volcano with the FLOWGO thermo-rheological model, Journal of Volcanology and Geothermal Research, Volume 253, pp. 35-53, ISSN 0377-0273

Wikipedia, 2014, Multi-criteria decision analysis (URL: http://en.wikipedia.org/wiki/Multi-criteria_decision_analysis ).

Geologic Background. Mount Cameroon, one of Africa's largest volcanoes, rises above the coast of west Cameroon. The massive steep-sided volcano of dominantly basaltic-to-trachybasaltic composition forms a volcanic horst constructed above a basement of Precambrian metamorphic rocks covered with Cretaceous to Quaternary sediments. More than 100 small cinder cones, often fissure-controlled parallel to the long axis of the 1400 km3 edifice, occur on the flanks and surrounding lowlands. A large satellitic peak, Etinde (also known as Little Cameroon), is located on the S flank near the coast. Historical activity was first observed in the 5th century BCE by the Carthaginian navigator Hannon. During historical time, moderate explosive and effusive eruptions have occurred from both summit and flank vents. A 1922 SW-flank eruption produced a lava flow that reached the Atlantic coast, and a lava flow from a 1999 south-flank eruption stopped only 200 m from the sea. Explosive activity from two vents on the upper SE flank was reported in May 2000.

Information Contacts: MODVOLC Thermal Alert System, Hawai'i Instiute of Geophysics and Planetology (HIGP), (Univ. of Hawai'i, 2525 Corrrea Road, Honolulu, HI 96822 USA (URL: http://modis.higp.hawaii.edu/); Mary-Ann del Marmol, Department of Geology and Soil Science, Ghent University, Krijgslaan 281 S8, 9000 Gent, Belgium; Associated Press, and Cameroon Radio Television, CRTV Siège, CRTV Mballa II B.P. 1634, Yaounde, Cameroon (URL: http://crtv.cm/).

Our last report (BGVN 35:08) described a flank eruption at Nyamuragira during 2-27 January 2010 that produced a new cone and 12-km-long lava flows. The final report of the GORISK Scientific Network (Kervyn and others, 2010) stated that this eruption ended by 27 January 2010. At this stage we lack reporting from the field on Nyamuragira's behavior during February 2010 through early November 2011. That said, MODVOLC thermal alerts occurred regularly at Nyamuragira through 2 February 2010 and then ceased until early November 2011. We discuss the longer-term MODVOLC data at the end of the main body of this report.

Nyamuragira began to erupt again on its flanks at 1755 on 6 November 2011, according to GORISK, after two days of unspecified "intense seismic activity." GORISK inferred that the eruption lasted through April 2012. This report conveys information from a variety of sources credited below, but largely from Dario Tedesco and the GORISK Scientific Network. GORISK was an initiative of both the National Museum of Natural History (Luxembourg) and the Royal Museum for Central Africa (Belgium).

An early synopsis of the eruption that began on 6 November 2011 came from the Virunga National Park. The eruption was visible at Park headquarters. Park staff described the 6 November eruption as coming from a fissure on the volcano's NE flank. It produced slow-moving lava flows that advanced into unpopulated areas to the N. Park staff also took a (1080p) video of fountaining at night. On 7 November the Park uploaded 39 seconds of their footage on Youtube.

During the first week of the eruption the Park staff hiked cross country through the bush, in places having to cut vegetation, crossing young forest and irregular lichen-covered volcanic topography on a 4 hour hike that enabled them to take a closer view. This also established a narrow access route for later use.

The hikers described airfall scoria covering the landscape as they approached closer. Their log said that the ". . . eruption finally came into view, along with the roar of intensely spewing fire and lava, as well as lightning and thunder." The Park noted that the vent area was located 12 km ENE of the crater, close to one of the 1989 eruptive sites. The first fissure was oriented E-W, perpendicular to the rift, and emitted lava fountains up to 300 m high. The eruption site was described as a flat area cut by a 500- to 1,000-m-long fissure. Figure 39 shows a photo from around this time but a topographic high of new material had already grown. NASA Earth Observatory reported that lava flows had advanced as far as 11.5 km by 12 November 2011 (figure 40). On 12 November, the lava flow front was located 5 km from the Kelengera-Tongo road.

Figure 39. Lava fountaining at Nyamuragira during early November 2011. The venting fissure is also seen in the distance at left; tephra created the topographic high seen here, rising from a comparatively flat area. Exact date and look-direction unknown. Courtesy Dario Tedesco and the GORISK Scientific Network.

Figure 40. Satellite image of Nyamuragira on 15 November 2011 showing lava flowing away from the rift. The imager combines infrared and visible light; hot lava appears orange, and cooled lava appears black. Cooler clouds appear blue, and warm steam appears white and orange. Nyiragongo's lava lake is visible to the S. Image created by Jesse Allen, using EO-1 ALI data provided by the NASA EO-1 team. Courtesy NASA Earth Observatory.

For about a month, the park allowed overnight treks to the eruption site. A video featured on Youtube ) by Piet Schutter contains footage taken on 12 November. Some scenes are at close range (looking up towards the eruption). That (720p) video shows both daylight and night scenes, features sound, and has people in the foreground, which helps establish scale.

The GORISK Scientific Team reported that satellite radar (InSAR) images acquired on 11 November 2011 revealed major ground deformation features associated with the eruption—the largest deformation detected by that method (InSAR) since the early 1990s at Nyamuragira. Preliminary estimation of the observed deformation signal suggested an affected area spreading over 250 km². Pressure from the ascending magma caused the ground to rise more than 50 cm at the eruptive site where a spatter cone developed. Another 15 cm deformation was detected within the Nyamuragira caldera, which was accompanied by deflation observed on the flanks.

An elongated spatter-and-scoria cone, referred to by scientists as the western cone and by locals as "Umoja," formed along the first fissure (figure 41). In early December 2011, a new cone formed on a new eruptive fracture to the E; this cone was referred to by scientists as the eastern cone and by locals as "Tuungane" (figure 41). During the next few days, the eruptive activity migrated to this new edifice. Satellite images acquired on 3 January 2012 showed fresh lava flowing to the N-NE (figures 42 and 43).

Figure 41. Panoramic view of Nyamuragira and the two new cones of the November 2011-April 2012 eruption. Date of photo unknown (sometime between November 2011 and early June 2012). Photo courtesy Benoit Smets, GORISK Scientific Network.

Figure 42. False-color satellite image of Nyamuragira on 3 January 2012. The hot active lava was detected in shortwave and near-infrared light (bright red-orange). Nyiragongo's crater lava lake is visible to the S. Image acquired by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite. Courtesy Jesse Allen, Robert Simmon, and EO-1 Team, NASA Earth Observatory.

Figure 43. Natural-color satellite image of Nyamuragira on 3 January 2012 showing close-up of outlined area in Figure 42 of this report. Active lava is visible flowing N-NE, with older flows also visible to the N and NE. A sulfur-dioxide-rich plume extends to the SW from the central vent. Undisturbed vegetation is also visible. Image acquired by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite. Courtesy Jesse Allen, Robert Simmon, and EO-1 Team, NASA Earth Observatory.

According to scientists from the Afar Consortium Project visiting the 2011 fissure eruption, activity continued on 8 January 2012. The initial scoria cone appeared inactive and second cone formed to the N of the first cone. Both cones were about 300 m high. The second cone was extremely active for the duration of the observations (about 15 hours) with fire fountains over twice the height of the cone; lava flowed N. The observers, about 1.5 km away, felt the heat from the eruption and noted lapilli fall.

A team from Volcano Discovery observed the ongoing fissure eruption during 22-25 January 2012 from the newly formed cinder cones near the fissure. They reported three coalescent cones, the largest cradling a small lava lake. The lake ejected spatter every few seconds, rising as high as 200 m above the summit. Some bombs reached the base of the cone. Lava flows from the vent extended several kilometers N. Numerous small breakouts formed secondary flows, and a large breakout ~2 km N of the cone fed a large lava flow ~20 m wide. Burning forests were reported to the NNE.

A lava lake was present within the eastern cone during February 2012 through the end of the eruption in April 2012. Lava flows were fed through lava tubes, with fresh lava mainly visible at night.

Preliminary estimates by the GORISK Scientific Team for the 2011-2012 eruption indicated a volume of emitted lavas of at least 81.5 x 106 m³. The lava flows did not reach inhabited areas and only affected vegetation in Virunga National Park. The 2011-2012 eruption was the biggest event at Nyamuragira since the 1991-1993 eruption, which lasted nearly 1.5 years and emitted an estimated ~131 x 106 m³ of lava (Smets and others, 2010).

Beginning in late February 2012 through at least June 2012, degassing occurred in the Nyamuragira's caldera. The emission site was located inside the pit crater, but degassing occurred from all fractures inside the caldera. On several occasions, meteorological conditions caused sulfur odors to reach the city of Goma (~30 km S from Nyamuragira's crater).

A report by Dario Tedesco stated that in March 2012, a series of explosion earthquakes were recorded by the seismic network of the Goma Volcano Observatory. Following this activity, the fissure eruptions suddenly stopped. Also in March 2012, the morphology of the pit crater began to change (figures 44 and 45).

Figure 44. View of Nyamuragira's pit crater on 20 January 2012. Direction unknown. Courtesy Dario Tedesco, International Organization of Migrants and Second University of Naples.

Figure 45. View of Nyamuragira's pit crater on 16 April 2012. Direction unknown. Courtesy Dario Tedesco, International Organization of Migrants and Second University of Naples.

MODVOLC thermal alerts were accessed online in late July 2014. The alerts had waned at the fissure area in late March 2012 suggesting the end of the fissure eruption in that time frame. The last alerts around the summit area had occurred on 2 February 2010. The next alerts in the summit area appeared on the NE rim on 5 March 2014 and again on 30 May 2014. A sequence of several alerts took place in the same spot during 22-29 June and on 12 and on 28 July 2014.

References. Kervyn, F, d'Oreye, N, van Overbeke, A-C, 2010, GORISK: The combined use of Ground-Based and Remote Sensing techniques as a tool for volcanic risk and health impact assessment for the Goma region (North Kivu, Democratic Republic of Congo). Final Report. [Project SR/00/113] (URL: http://www.ecgs.lu/gorisk/wp-content/uploads/2010/11/GORISK_Final_Report_DISSEMINATION.pdf )

Smets, B., Wauthier, C., d'Oreye, N. (2010). A new map of the lava flow field of Nyamulagira (D.R. Congo) from satellite imagery. Journal of African Earth Sciences, 58 (5), 778-786. DOI:10.1016/j.jafrearsci.2010.07.005

Geologic Background. Africa's most active volcano, Nyamulagira (also known as Nyamuragira), is a massive high-potassium basaltic shield about 25 km N of Lake Kivu and 15 km NE of the steep-sided Nyiragongo volcano. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from the numerous flank fissures and cinder cones. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Recent lava flows extend down the flanks more than 30 km from the summit as far as Lake Kivu; extensive lava flows from this volcano have covered 1,500 km2 of the western branch of the East African Rift.

Information Contacts: Dario Tedesco, International Organization of Migrants (I.O.M.), Goma, DRC, and Second University of Naples, DISTABIF, Caserta, Italy; GORISK Scientific Team [an International scientific team for the study and monitoring of active volcanoes and their corresponding hazards in the Virunga Volcanic Province] (URL: http://terra.ecgs.lu/rnvt/); Virunga National Park, Democratic Republic of Congo (URL: http://virunga.org/); Jesse Allen and Robert Simmon, NASA Earth Observatory (URL: http://earthobservatory.nasa.gov); Volcano Discovery (URL: http://www.volcanodiscovery.com/); and Afar Consortium Project (URL: http://www.see.leeds.ac.uk/afar/).

A recent partial survey conducted by David K. Lynch and Paul M. Adams of Red Island, previously known as Red Hill, in Southern California, USA, has resulted in the discovery of five steaming hot vents on the SW flank of the northern Salton Buttes volcanic field. Lynch and Adams sent us a report, which follows. We also include some remarks from related literature and note geothermal power plants in the region.

Background. Red Island is part of the Salton Buttes, a collection of five late Quaternary rhyolitic volcanic necks in the Salton Sea Geothermal Field (SSGF) (figure 1). The SSGF rests within a topographic low, and has a geothermal gradient that averages ~0.3°C/m, reaching a maximum of 4.3°C/m (Lynch and others, 2013). This high geothermal gradient results from the shallow magma body of the spreading center between the San Andreas and Imperial faults. As shown in figure 2, the SSGF lies at the head of the Gulf of California, on the boundary of the Pacific and North American plates (Elders and Sass, 1988). Consequently, the SSGF's unique geology creates the perfect setting for hot geothermal fluids to seep to the surface, and has been slated as a site for geothermal electricity-generating plants. There are no previous Bulletin reports on the Salton Buttes.

Figure 1. The Salton Trough is a result of crustal stretching and sinking associated with regional extensional tectonics including the San Andreas Fault (SAF) and the East Pacific Rise (EPR, the spreading center shown at the bottom of the map).This sketch shows the boundary between the Pacific and North American plates, with the rectangle indicating the Salton Trough. The S end of the Salton Trough (as defined by the box) begins adjacent to the Sea of Cortez, the body of water separating the Baja California peninsula from mainland Mexico. The SSGF is within the Salton Trough. Other abbreviations include Gorda Rise, GR; Mendocino Triple Junction, MTJ; and Rivera Triple Junction, RTJ. Taken from Elders and Sass (1988).

Figure 2. Sketch map showing location of Salton Sea and the Salton Buttes volcanic area study area. For scale, the N-S distance from the S end of the Salton Sea to the USA-Mexico border is ~100 km. The lake is receding but its 2014 surface elevation is close to -69 m. Courtesy of Lynch and others (2013).

The Salton Buttes reside near the SE end of the Salton Sea. The Sea resides on the floor of the Salton Trough, chiefly in Imperial County, California. This briny water body is about 56 x 10 km. The Buttes lie along a NNE trending line spanning a distance of 7 km. The Salton Trough was filled, in part, by sediments carried by the Colorado River, which eventually built up and blocked the river's flow. The river was diverted away from the Salton Trough, yet, in 1905, heavy rainfall caused nearby levees to collapse, creating the Salton Sea (Morris, 2008).

Until recent work by Lynch and others (2011) and Schmidt and others (2013), the Salton Buttes were thought to have been formed by extruded magma during the late Pleistocene, ~16,000 BP. Age dates for some lavas are now dated to closer to 2,000 BP, much younger than originally understood, bringing closer scrutiny of the Buttes by the U.S. Geological Survey (USGS) California Volcano Observatory and other agencies concerned with geological threats in California (Lynch and Adams, unpublished draft).

Red Island consists of two conjoined volcanoes of related, yet distinctly different, geology. They are 2.5 km SSW of the Mullet Island fumaroles, an area discussed further by Lynch and others (2013).

Mullet Island fumaroles: As the briny water level of the Salton Sea began dropping in 1983, a number of fumarole fields were exposed subaerially for the first time since 1945. The Salton Sea overlaps the SSGF and, as a result, an interaction of rising gas and hot water with sediments has produced a number of hot, fumarolic gryphons (mud volcanoes) and salses (bubbling water in calderas of gryphons) (Lynch and others, 2013). Over-pressured subsurface gas cause the upward migration of fluidized sediment, creating these gryphons, as seen in figure 3.

Figure 3. View of a steaming spatter cone, one of the first stages of a gryphon's development. Once the rising mud becomes more viscous and covers the spatter cone completely, a composite gryphon is formed. The height of these gryphons can range from a few centimeters to ~2 m. Mullet Island can be seen at the top left of the image. Taken from Lynch and others (2013).

The NW trending alingment of these geothermal features is suggestive of a fault, most likely the Calipatria fault. Other fumarole fields are still below water level or are being exposed as the lake recedes.

Red Island vents. Before the work on Mullet Island fumaroles was published, Michael McKibben, while on a 2008 Desert Symposium field trip (Reynolds and others, 2008), mentioned a 'volcanic hotspot' on the SW flank of the N volcano at Red Island in a private communication to Lynch and Adams. However, a swift search of the area during the field trip did not reveal its location. As a result of this observation, Lynch and Adams performed a partial survey of the SW flank of the N volcano on 6, 7, and 29 November 2013, which resulted in the discovery of the five hot steaming vents on the summit of the south-facing slope. Lynch and Adams found that the vents were distributed along an ~80 m long line trending N65E, which they recognized as a possible fault.

All attempts at identifying vents were made before sunrise, when the air temperature was at its lowest diurnal value (~8°C). This provided a recognizable thermal contrast between cold and hot rocks. Lynch and Adams noted that it was unlikely that warm air coming from the vents could have been felt on a hot or windy day, as the vents appeared unremarkable from a relatively close distance (a few meters), "among the uneven field of loose, jutting volcanic rocks." To locate the vents, Lynch and Adams employed the following three tactics:

1. An Agena ThermoVision 470 infrared camera was used to look for areas that were warmer than the background (e.g., figure 4, lower). Absolute temperatures from the camera may have been off by 3-4°C due to systematic errors, but the image records relative temperatures between different parts of scene. were preserved. The vent seen in figure 4 may have been deliberately covered with a pile of rocks.

2. They reached into holes and crevasses to check for heat.

3. They measured rock temperatures using a Martin P. Jones & Associates, Inc., Model 9910 TE Infrared Thermometer. Because it was small enough to be placed deeper in the vents, the temperatures from this thermometer were higher than the IR camera temperatures.

Figure 4. (Top) Image of a hotspot (designated H3) seen in visible wavelength light. (Bottom) Image of the same spot taken with an Agena ThermoVision 470 IR camera. Yellow patches in the center and lower right of the image indicate bad pixels in the IR camera. Taken from Lynch and Adams (2013).

Lynch and Adams found one vent "by feeling hot air coming from it," one "by noticing wet rock," one "by seeing its steam cloud," and two by locating them with the IR camera. Once located, all vents were found to be steaming (figure 5) and surrounded by rocks wet from condensation.

Figure 5. Steam cloud from H1; still taken from a video of the hotspot at Red Island, Salton Buttes. Taken from Lynch and Adams (2013).

No surface deposits (e.g., sulfur) were seen, aside from water and greenish algae. The temperatures 1-2 m within the vents were 35-38°C. According to Lynch and Adams, these hotspots may "represent heat from original volcanism, or recent magma intrusions that have not reached the surface." The distribution of these vents, distinguished as H1, H2, H3, H4, H5, is shown in figure 6.

Figure 6. Vent locations marked on an image of Red Island, Salton Buttes, from Google Earth. Taken from Lynch and Adams (2013).

The team was relatively confident that no additional vents were located within the area extending 225 m to the S and W, although a more complete survey must be undertaken to investigate seismicity and movement/deformation of the area from GPS networks. However, other "warm spots" not associated with venting or outgassing were found on the SW flank of the N volcano. They were ~5-10°C warmer than ambient temperatures and may represent weak signals from the warm interior of the volcano. More likely, however, the warmer temperatures are due to emissivity variations in rock layers, or normal temperature distributions that occur in crevasses where rocks are not able to radiate heat into the cold night sky.

Geothermal electricity-generating plants. According to the Geothermal Energy Association, currently there are three major geothermal production sites in the Imperial Valley, totaling in 16 plants. Figure 7 shows one of these sites, which hosts seven geothermal plants with running capacities ranging from 5-45 MW (Geothermal Energy Association). Despite the fact that this site alone has contributed enough electricity to power ~100,000 homes, geothermal energy only accounts for 4.4% of all system power in California (Matek and Gawell, 2014). The SSGF is considered the best opportunity for increasing the production of geothermal energy in California. The unique geology of the Salton Sea area allows geothermal fluids to seep to the surface, allowing a range of capacity from 1,700 to 2,900 MW.

Figure 7. This CalEnergy geothermal site is located on the edge of the Salton Sea, and currently has seven running geothermal power plants. Taken from The Center for Land Use Interpretation.

References. Elders, W and Sass, J, 10 November 1988, The Salton Sea Scientific Drilling Project; Journal of Geophysical Research, v. 03, no. B11, pp. 12,953-12,968.

Lynch, D., Hudnut, K., and Adams, P., 2013, Development and growth of recently-exposed fumarole fields near Mullet Island, Imperial County, California; Geomorphology, v. 195, pp. 27-44.

Lynch, D.K., Schmitt, A.K.., Rood, D., and Akciz, S, 2011, Radiometric Dating of the Salton Buttes, Proposal to the Southern California Earthquake Center.

Matek, B., and Gawell, K., February 2014, Report on the State of Geothermal Energy in California; Geothermal Energy Association, 2014.

Morris, R., 2008, Welcome to the Salton Trough, California State University Long Beach Geology.

Reynolds, R., Jefferson, G., Lynch, D., 2008, Trough to Trough: The Colorado River and the Salton Sea, Proceedings of the 2008 Desert Symposium, Robert E. Reynolds (ed.), California State University, Desert Studies Consortium and LSA Associates, Inc.

Schmitt, A, Martin, A, Stockli, D, Farley, K, Lovera, O, 2013, (U-­-Th)/He zircon and archaeological ages for a late prehistoric eruption in the Salton Trough (California, USA), Geology, January 2013, v. 41, pp. 7-10.

Geologic Background. The Salton Buttes consist of five small rhyolitic lava domes extruded onto Quaternary sediments of the Colorado River delta at the SE margin of the Salton Sea. The age of the Salton Buttes has variously been considered to be late Pleistocene or early Holocene based on different dating techniques. Recent paleomagnetic dating calibrated by radiocarbon ages suggests that the Salton Buttes domes were erupted during an interval of about 500 years between about 2300 and 1800 years ago, with the possible exception of Mullet Island at the northern end of the field, which could be as much as 5000 years older. The present-day saline Salton Sea was formed in the early 20th century by unintended flooding into the basin formerly occupied by Pleistocene Lake Cahuilla Lake during diversion of the Colorado River for irrigation purposes. The Salton Sea geothermal field produces saline brines.

Information Contacts: David Lynch, Earthquake Science Center, USGS- Pasadena; Paul Adams, Thule Scientific, Topanga, CA (URL: http://thulescientific.com/Research.html); The Center for Land Use Interpretation, Culver City, CA (URL: http://clui.org/); and Geothermal Energy Association, Washington, D.C. (URL: http://geo-energy.org/).

This report summarizes activity from Santa María's active cone, Santiaguito, during October 2011-June 2014. Ash explosions, ashfall, and incandescent avalanches were observed throughout this time period. During the rainy season (April-September), lahars were frequently reported within the major drainages in the southern sector of the volcano. The sources for this report were Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), Washington Volcanic Ash Advisory Center (VAAC), and Coordinadora Nacional para la Reducción de Desastres (CONRED).

Recurrent ash explosions. INSIVUMEH and the Washington VAAC reported frequent ash explosions from Santiaguito's active dome, Caliente, during October 2011-June 2014 (figure 35). Ash plumes were typically in the range of 500 m above the dome with exceptional cases in the range of 4,000 m, such as the explosive event on 9 May 2014. Significant ash plumes were known to drift as far as the Guatemala-Mexico border (such as activity during 5-6 November 2011 when ash extended 18-28 km SE of the summit). Degassing from the Caliente dome also generated frequent, diffuse, white plumes that rose to heights around 200 m above the summit.

Figure 35. The Santiaguito dome complex of Santa María includes four major domes: El Brujo, El Monje, La Mitad, and Caliente (active since 1922). This photo was taken from the INSIVUMEH observatory located on Finca El Faro, ~6 km S of the active dome. Modified from Ball and others (2013).

Ashfall from explosions and rumbling noises from explosions and avalanches were frequently reported in communities nearby (table 5). Following activity on 9 May 2014, ashfall triggered evacuations affecting ~130 people. CONRED and INSIVUMEH reported that ash had extended up to 20 km from the summit reaching the communities of Las Marías, San Marcos (10 km SW), Palajunoj (18 km SSW), El Faro (SW flank), La Florida (5 km S), Patzulín, and Quetzaltenango (18 km WNW).

Table 5. Ashfall from explosions at Santa María's active dome, Santiaguito, was reported in numerous communities during November 2011-June 2014. Courtesy of INSIVUMEH.

Avalanches and pyroclastic flows originating from Caliente dome were reported throughout late 2011 through June 2014 (table 6). A pyroclastic flow observed on 9 May 2014 traveled ~7 km from the active lava dome (figure 35). Approximately 1 million cubic meters of tephra was deposited within the Nimá I drainage. Secondary explosions occurred along the flowpath associated with hot deposits in contact with river water.

Table 6. A summary of significant pyroclastic flows from Santa María's Santiaguito occurred during February 2012-May 2014. Courtesy of INSIVUMEH.

Figure 36. Looking approximately N toward Santa María's Santiaguito cone, this photo has been annotated to show surveyed distance measurements (in meters, here "mts.") measured along the slope between the summit and base of Santiaguito as well as the main pathway along the Nimá I drainage. The pyroclastic flow from 9 May 2014 traveled more than 6 km from the active dome (red dotted line). The length of the active lava flow on 11 May 2014 was 152 m. Courtesy of Gustavo Chigna, INSIVUMEH, and the International Volcano Monitoring Fund (IVM Fund).

Lahars. During 2012-2014, lahars began flowing down Santa María's SE drainages during the onset of the rainy season (table 7). INSIVUMEH reported that many of these events were triggered by heavy rainfall and were frequently contained within the Nimá I drainage (figure 37). Lahars following the nearby rivers Nimá II, San Isidro, and Tambor and merged with the larger river, Samalá. These primary drainages are located S and SW of the active dome (see map in figure 28 of BGVN 24:03; note that Río San Isidro is an intermittent stream located between the Tambor and Nimá II rivers), three of which were included in a hazard map prepared by INSIVUMEH in collaboration with Japan International Cooperation Agency (JICA) in 2003 (figure 38). INSIVUMEH and CONRED released public announcements when Río Samalá was threatened by lahars (for example: 21 May 2012, 23 June 2012, and 6 June 2014) that included specific warnings for the Castillo de Armas bridge; the bridge supports the Interamerican Highway where it passes through the town of San Sebastián.

Table 7. During April 2012- June 2014, weak-to-strong flowing lahars were frequently triggered by heavy rainfall, mainly during April-September each year. Courtesy of INSIVUMEH.

Figure 37. This set of two images of the Nimá I drainage shows a small-sized lahar that flowed from Santiaguito cone at 1615 on 7 October 2013 (left image was before (Antes); right image was during (Durante) the lahar flow). Looking upstream, this view is focused on a narrow section of Nimá I that was filled by a 12-m-wide and 1.5-m-high lahar. The rock wall on the right-hand side of the drainage (~3 m high) became a ramp for the lahar and was half-covered by the flow as the gray mass wrapped around the narrow corner in a fast and turbulent flow. Courtesy of Gustavo Chigna, INSIVUMEH and the IVM Fund.

Figure 38. Volcanic hazard map (#3 of 5 published in a series) for Santa María focused on the region S of Santiaguito dome. The basemap is from 2001-2002 aerial survey photos and the hazard assessments conducted during 2001-2003 in collaboration with the Japan International Cooperation Agency (JICA). The three drainages (Río Nimá I, Río Nimá II, and Río Samalá labeled in red text) were added by GVP staff. Major towns, farms, and the INSIVUMEH observatory (OVSAN) are labeled; hazard zones are indicated with color coding; the blue semicircle and linear corridor indicates the extent of the study area; the area encompassed by the red semi-circle is at risk for volcanic ballistics. Other hazards include pyroclastic flows (orange shading), lava flows (pink), lahars (blue), ashfall (orange outline), and debris avalanches (yellow and green outlines). Courtesy of INSIVUMEH.

The most damaging lahar during this reporting period occurred on 6 June 2014. The lahar flowed in pulses down the Nimá I drainage with crests 5-9 m high reaching a maximum width of 80 m. The Santiaguito Observatory (OVSAN) was forced to evacuate when the lahar overflowed the banks and spread across the facility grounds; important scientific equipment was damaged and also washed away. The lahar also flowed into a nearby farm.

Reference. Ball, J.L., Calder, E.S., Hubbard, B.E., and Bernstein, M.L., 2013, An assessment of hydrothermal alteration in the Santiaguito lava dome complex, Guatemala: implications for dome collapse hazards, Bulletin of Volcanology, 75:676.

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/inicio.html); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié; 21-72, Zona 13, Guatemala City, Guatemala (URL: http://www.conred.org/); and Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20748, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

The year 2014 marks the 3rd decade of largely non-explosive activity at Villarrica, historically one of the most active volcanoes in the Andes. Villarrica has been relatively quiet since our last report, which discussed events from April 2010 to October 2010 (BGVN 35:10). This report covers the time period from November 2010 to December 2013.

During this reporting period, comparative quiet prevailed. There were occasional cases reported of spattering lava, small white plumes, minor ash emissions (up to 50 m above the crater rim), and nighttime incandescence reflected off of the plumes according to Proyecto Observación Villarrica Internet (POVI) and Observatorio Volcanológico de los Andes del Sur (OVDAS-SERNAGEOMIN). Satellite thermal radiance during the reporting interval suggested often low radiance, with rare cases of high incandescence consistent with turbulence and fountaining in the deep, 40 m wide lava lake.

On 17 September 2011 remobilized tephra rose ~500 m above the crater, which according to POVI, was likely caused by a sudden impact when a snow cornice detached and fell into the crater. On 19 September 2011, a rapid rise in the level of the lava lake caused much of the snow and ice to melt, especially on the southern inner wall. Strombolian explosions from the crater were observed on 26 September 2011, and tephra deposits on the E edge of the crater were noted. On 27 September 2011 incandescence from the lava lake was reflected in the cloud cover above.

The period from November 2011 to March 2012 saw very little explosive activity. Two small ash emissions occurred on 7 March. Incandescence from the crater was observed from the town of Pucon (16 km N) during 7-8 March. During 7-9 March, lava spattering from the lava lake was observed for the first time that year. Four small ash emissions were observed during 13-14 March. On 20 March a large, white plume was visible above the crater. The observer postulated that due to the humid atmospheric conditions that day, the steam condensate in the visible plume remained conspicuous both to a height of 1,500 m above the crater as well as 20 km SW of the crater.

According to POVI, an ash plume rose 50 m above Villarrica on 19 April 2012. Incandescence from Villarrica's crater subsided in mid-April and was undetected by satellite and ground observations at least through 10 November 2012.

On 30 January 2013, weak incandescence was observed in the near-infrared spectrum from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument on the Terra satellite. POVI reported that satellite images of Villarrica acquired on 25 July revealed a weak thermal anomaly. On 29 July 2013 observers photographed the crater and described a thermal anomaly on the S edge of the crater rim, in the same area from which a lava flow originated on 29 December 1971. They also heard deep degassing sounds. A second photograph showed a diffuse gas plume rising from the bottom of the crater, and ash and lapilli on the snow on the inner crater walls.

Analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) band 21 (3.929-3.989 μm) satellite images from 2003 to 2013 highlights three main cycles of activity. These were characterized by convective lava fountains and Strombolian explosions from the lava pit, located ~ 40-150 m below the rim of the crater, according to POVI. The last time MODIS infrared sensors detected elevated thermal radiance was in early 2012 (figure 8).

Figure 28. Elevated thermal radiance in Watts per square meter detected at Villarrica using MODIS band 21 (3.929-3.989 μm) from 2003 through 2013. Courtesy of POVI and NASA MODIS.

In accord with the thermal radiance data seen in figure 28, OVDAS-SERNAGEOMIN maintained an Alert Level of Green for Villarrica from the period of 5 March 2012 to 30 December 2013, characterizing Villarrica as active but stable with no immediate threat. The seismicity reports from OVDAS-SERNAGEOMIN during the period of July 2013 to December 2013 showed the monthly number of earthquakes recorded ranged from 439 to 1,433. The reduced displacement of the tremors recorded fluctuated throughout July 2013- December 2013 from 0.6 cm² to 9.9 cm². During this period of time, the amount of SO₂ emissions recorded by a scanning DOAS spectrometer OVDAS-SERNAGEOMIN varied from 156 tons/day to 888 tons/day. The height above the crater rim of the steam-gas plumes ranged from 150 m to 1,500 m. MODIS did not record any thermal anomalies during this period of time.

Figure 29. Aerial image of the Villarrica crater at dawn on 14 October 2013. Copyrighted image taken by Diego Spatafore.

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/); and Observatorio Volcanológico de los Andes del Sur Servicio Nacional de Geologia y Mineria (OVDAS SERNAGEOMIN), Santiago, Chile (URL: http://www2.sernageomin.cl/ovdas).