Masaya, which is about 20 km NW of the Nicaragua’s capital of Managua, is one of the most active volcanoes in that country and has a caldera that contains a number of craters (BGVN 43:11). The Santiago crater is the one most currently active and it contains a small lava lake that emits weak gas plumes (figure 85). This report summarizes activity during February through May 2020 and is based on Instituto Nicaragüense de Estudios Territoriales (INETER) monthly reports and satellite data. During the reporting period, the volcano was relatively calm, with only weak gas plumes.

Figure 85. Satellite images of Masaya from Sentinel-2 on 18 April 2020, showing and a small gas plume drifting SW (top, natural color bands 4, 3, 2) and the lava lake (bottom, false color bands 12, 11, 4). Courtesy of Sentinel Hub Playground.

According to INETER, thermal images of the lava lake and temperature data in the fumaroles were taken using an Omega infrared gun and a forward-looking infrared (FLIR) SC620 thermal camera. The temperatures above the lava lake have decreased since November 2019, when the temperature was 287°C, dropping to 96°C when measured on 14 May 2020. INETER attributed this decrease to subsidence in the level of the lava lake by 5 m which obstructed part of the lake and concentrated the gas emissions in the weak plume. Convection continued in the lava lake, which in May had decreased to a diameter of 3 m. Many landslides had occurred in the E, NE, and S walls of the crater rim due to rock fracturing caused by the high heat and acidity of the emissions.

During the reporting period, the MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded numerous thermal anomalies from the lava lake based on MODIS data (figure 86). Infrared satellite images from Sentinel-2 regularly showed a strong signature from the lava lake through 18 May, after which the volcano was covered by clouds.

Figure 86. Thermal anomalies at Masaya during February through May 2020. The larger anomalies with black lines are more distant and not related to the volcano. Courtesy of MIROVA.

Measurements of sulfur dioxide (SO2) made by INETER in the section of the Ticuantepe - La Concepción highway (just W of the volcano) with a mobile DOAS system varied between a low of just over 1,000 metric tons/day in mid-November 2019 to a high of almost 2,500 tons/day in late May. Temperatures of fumaroles in the Cerro El Comalito area, just ENE of Santiago crater, ranged from 58 to 76°C during February-May 2020, with most values in the 69-72°C range.

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

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

Shishaldin is located near the center of Unimak Island in Alaska, with the current eruption phase beginning in July 2019 and characterized by ash plumes, lava flows, lava fountaining, pyroclastic flows, and lahars. More recently, in late 2019 and into January 2020, activity consisted of multiple lava flows, pyroclastic flows, lahars, and ashfall events (BGVN 45:02). This report summarizes activity from February through May 2020, including gas-and-steam emissions, brief thermal activity in mid-March, and a possible new cone within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) reports and various satellite data.

Volcanism during February 2020 was relatively low, consisting of weakly to moderately elevated surface temperatures during 1-4 February and occasional small gas-and-steam plumes (figure 37). By 6 February both seismicity and surface temperatures had decreased. Seismicity and surface temperatures increased slightly again on 8 March and remained elevated through the rest of the reporting period. Intermittent gas-and-steam emissions were also visible from mid-March (figure 38) through May. Minor ash deposits visible on the upper SE flank may have been due to ash resuspension or a small collapse event at the summit, according to AVO.

Figure 37. Photo of a gas-and-steam plume rising from the summit crater at Shishaldin on 22 February 2020. Photo courtesy of Ben David Jacob via AVO.

Figure 38. A Worldview-2 panchromatic satellite image on 11 March 2020 showing a gas-and-steam plume rising from the summit of Shishaldin and minor ash deposits on the SE flank (left). Aerial photo showing minor gas-and-steam emissions rising from the summit crater on 11 March (right). Some erosion of the snow and ice on the upper flanks is a result of the lava flows from the activity in late 2019 and early 2020. Photo courtesy of Matt Loewen (left) and Ed Fischer (right) via AVO.

On 14 March, lava and a possible new cone were visible in the summit crater using satellite imagery, accompanied by small explosion signals. Strong thermal signatures due to the lava were also seen in Sentinel-2 satellite data and continued strongly through the month (figure 39). The lava reported by AVO in the summit crater was also reflected in satellite-based MODIS thermal anomalies recorded by the MIROVA system (figure 40). Seismic and infrasound data identified small explosions signals within the summit crater during 14-19 March.

Figure 39. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show a bright hotspot (yellow-orange) at the summit crater of Shishaldin during mid-March 2020 that decreases in intensity by late March. Courtesy of Sentinel Hub Playground.

Figure 40. MIROVA thermal data showing a brief increase in thermal anomalies during late March 2020 and on two days in late April between periods of little to no activity. Courtesy of MIROVA.

AVO released a Volcano Observatory Notice for Aviation (VONA) stating that seismicity had decreased by 16 April and that satellite data no longer showed lava or additional changes in the crater since the start of April. Sentinel-2 thermal satellite imagery continued to show a weak hotspot in the crater summit through May (figure 41), which was also detected by the MIROVA system on two days. A daily report on 6 May reported a visible ash deposit extending a short distance SE from the summit, which had likely been present since 29 April. AVO noted that the timing of the deposit corresponds to an increase in the summit crater diameter and depth, further supporting a possible small collapse. Small gas-and-steam emissions continued intermittently and were accompanied by weak tremors and occasional low-frequency earthquakes through May (figure 42). Minor amounts of sulfur dioxide were detected in the gas-and-steam emissions during 20 and 29 April, and 2, 16, and 28 May.

Figure 41. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show occasional gas-and-steam emissions rising from Shishaldin on 26 February (top left) and 24 April 2020 (bottom left) and a weak hotspot (yellow-orange) persisting at the summit crater during April and early May 2020. Courtesy of Sentinel Hub Playground.

Figure 42. A Worldview-1 panchromatic satellite image showing gas-and-steam emissions rising from the summit of Shishaldin on 1 May 2020 (local time) (left). Aerial photo of the N flank of Shishaldin with minor gas-and-steam emissions rising from the summit on 8 May (right). Photo courtesy of Matt Loewen (left) and Levi Musselwhite (right) via AVO.

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

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/); 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).

Krakatau, located in the Sunda Strait between Indonesia’s Java and Sumatra Islands, experienced a major caldera collapse around 535 CE, forming a 7-km-wide caldera ringed by three islands. On 22 December 2018, a large explosion and flank collapse destroyed most of the 338-m-high island of Anak Krakatau (Child of Krakatau) and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake (BGVN 45:02). Recently, volcanism has been characterized by occasional Strombolian explosions, dense ash plumes, and crater incandescence. This report covers activity from February through May 2020 using information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity during February 2020 consisted of dominantly white gas-and-steam emissions rising 300 m above the crater, according to PVMBG. According to the Darwin VAAC, a ground observer reported an eruption on 7 and 8 February, but no volcanic ash was observed. During 10-11 February, a short-lived eruption was detected by seismograms which produced an ash plume up to 1 km above the crater drifting E. MAGMA Indonesia reported two eruptions on 18 March, both of which rose to 300 m above the crater. White gas-and-steam emissions were observed for the rest of the month and early April.

On 10 April PVMBG reported two eruptions, at 2158 and 2235, both of which produced dark ash plumes rising 2 km above the crater followed by Strombolian explosions ejecting incandescent material that landed on the crater floor (figures 108 and 109). The Darwin VAAC issued a notice at 0145 on 11 April reporting an ash plume to 14.3 km altitude drifting WNW, however this was noted with low confidence due to the possible mixing of clouds. During the same day, an intense thermal hotspot was detected in the HIMAWARI thermal satellite imagery and the NASA Global Sulfur Dioxide page showed a strong SO₂ plume at 11.3 km altitude drifting W (figure 110). The CCTV Lava93 webcam showed new lava flows and lava fountaining from the 10-11 April eruptions. This activity was evident in the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data (figure 111).

Figure 108. Webcam (Lava93) images of Krakatau on 10 April 2020 showing Strombolian explosions, strong incandescence, and ash plumes rising from the crater. Courtesy of PVMBG and MAGMA Indonesia.

Figure 109. Webcam image of incandescent Strombolian explosions at Krakatau on 10 April 2020. Courtesy of PVMBG and MAGMA Indonesia.

Figure 110. Strong sulfur dioxide emissions rising from Krakatau and drifting W were detected using the TROPOMI instrument on the Sentinel-5P satellite on 11 April 2020 (top row). Smaller volumes of SO2 were visible in Sentinel-5P/TROPOMI maps on 13 (bottom left) and 19 April (bottom right). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 111. Thermal activity at Anak Krakatau from 29 June-May 2020 shown on a MIROVA Log Radiative Power graph. The power and frequency of the thermal anomalies sharply increased in mid-April. After the larger eruptive event in mid-April the thermal anomalies declined slightly in strength but continued to be detected intermittently through May. Courtesy of MIROVA.

Strombolian activity rising up to 500 m continued into 12 April and was accompanied by SO₂ emissions that rose 3 km altitude, drifting NW according to a VAAC notice. PVMBG reported an eruption on 13 April at 2054 that resulted in incandescence as high as 25 m above the crater. Volcanic ash, accompanied by white gas-and-steam emissions, continued intermittently through 18 April, many of which were observed by the CCTV webcam. After 18 April only gas-and-steam plumes were reported, rising up to 100 m above the crater; Sentinel-2 satellite imagery showed faint thermal anomalies in the crater (figure 112). SO₂ emissions continued intermittently throughout April, though at lower volumes and altitudes compared to the 11th. MODIS satellite data seen in MIROVA showed intermittent thermal anomalies through May.

Figure 112. Sentinel-2 thermal satellite images showing the cool crater lake on 20 March (top left) followed by minor heating of the crater during April and May 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Taal volcano is in a caldera system located in southern Luzon island and is one of the most active volcanoes in the Philippines. It has produced around 35 recorded eruptions since 3,580 BCE, ranging from VEI 1 to 6, with the majority of eruptions being a VEI 2. The caldera contains a lake with an island that also contains a lake within the Main Crater (figure 12). Prior to 2020 the most recent eruption was in 1977, on the south flank near Mt. Tambaro. The United Nations Office for the Coordination of Humanitarian Affairs in the Philippines reports that over 450,000 people live within 40 km of the caldera (figure 13). This report covers activity during January through February 2020 including the 12 to 22 January eruption, and is based on reports by Philippine Institute of Volcanology and Seismology (PHIVOLCS), satellite data, geophysical data, and media reports.

Figure 12. Annotated satellite images showing the Taal caldera, Volcano Island in the caldera lake, and features on the island including Main Crater. Imagery courtesy of Planet Inc.

Figure 13. Map showing population totals within 14 and 17 km of Volcano Island at Taal. Courtesy of the United Nations Office for the Coordination of Humanitarian Affairs (OCHA).

The hazard status at Taal was raised to Alert Level 1 (abnormal, on a scale of 0-5) on 28 March 2019. From that date through to 1 December there were 4,857 earthquakes registered, with some felt nearby. Inflation was detected during 21-29 November and an increase in CO₂ emission within the Main Crater was observed. Seismicity increased beginning at 1100 on 12 January. At 1300 there were phreatic (steam) explosions from several points inside Main Crater and the Alert Level was raised to 2 (increasing unrest). Booming sounds were heard in Talisay, Batangas, at 1400; by 1402 the plume had reached 1 km above the crater, after which the Alert Level was raised to 3 (magmatic unrest).

Phreatic eruption on 12 January 2020. A seismic swarm began at 1100 on 12 January 2020 followed by a phreatic eruption at 1300. The initial activity consisted of steaming from at least five vents in Main Crater and phreatic explosions that generated 100-m-high plumes. PHIVOLCS raised the Alert Level to 2. The Earth Observatory of Singapore reported that the International Data Center (IDC) for the Comprehensive test Ban Treaty (CTBT) in Vienna noted initial infrasound detections at 1450 that day.

Booming sounds were heard at 1400 in Talisay, Batangas (4 km NNE from the Main Crater), and at 1404 volcanic tremor and earthquakes felt locally were accompanied by an eruption plume that rose 1 km; ash fell to the SSW. The Alert Level was raised to 3 and the evacuation of high-risk barangays was recommended. Activity again intensified around 1730, prompting PHIVOLCS to raise the Alert Level to 4 and recommend a total evacuation of the island and high-risk areas within a 14-km radius. The eruption plume of steam, gas, and tephra significantly intensified, rising to 10-15 km altitude and producing frequent lightning (figures 14 and 15). Wet ash fell as far away as Quezon City (75 km N). According to news articles schools and government offices were ordered to close and the Ninoy Aquino International Airport (56 km N) in Manila suspended flights. About 6,000 people had been evacuated. Residents described heavy ashfall, low visibility, and fallen trees.

Figure 14. Lightning produced during the eruption of Taal during 1500 on 12 January to 0500 on 13 January 2020 local time (0700-2100 UTC on 12 January). Courtesy of Chris Vagasky, Vaisala.

Figure 15. Lightning strokes produced during the first days of the Taal January 2020 eruption. Courtesy of Domcar C Lagto/SIPA/REX/Shutterstock via The Guardian.

In a statement issued at 0320 on 13 January, PHIVOLCS noted that ashfall had been reported across a broad area to the north in Tanauan (18 km NE), Batangas; Escala (11 km NW), Tagaytay; Sta. Rosa (32 km NNW), Laguna; Dasmariñas (32 km N), Bacoor (44 km N), and Silang (22 km N), Cavite; Malolos (93 km N), San Jose Del Monte (87 km N), and Meycauayan (80 km N), Bulacan; Antipolo (68 km NNE), Rizal; Muntinlupa (43 km N), Las Piñas (47 km N), Marikina (70 km NNE), Parañaque (51 km N), Pasig (62 km NNE), Quezon City, Mandaluyong (62 km N), San Juan (64 km N), Manila; Makati City (59 km N) and Taguig City (55 km N). Lapilli (2-64 mm in diameter) fell in Tanauan and Talisay; Tagaytay City (12 km N); Nuvali (25 km NNE) and Sta (figure 16). Rosa, Laguna. Felt earthquakes (Intensities II-V) continued to be recorded in local areas.

Figure 16. Ashfall from the Taal January 2020 eruption in Lemery (top) and in the Batangas province (bottom). Photos posted on 13 January, courtesy of Ezra Acayan/Getty Images, Aaron Favila/AP, and Ted Aljibe/AFP via Getty Images via The Guardian.

Magmatic eruption on 13 January 2020. A magmatic eruption began during 0249-0428 on 13 January, characterized by weak lava fountaining accompanied by thunder and flashes of lightning. Activity briefly waned then resumed with sporadic weak fountaining and explosions that generated 2-km-high, dark gray, steam-laden ash plumes (figure 17). New lateral vents opened on the N flank, producing 500-m-tall lava fountains. Heavy ashfall impacted areas to the SW, including in Cuenca (15 km SSW), Lemery (16 km SW), Talisay, and Taal (15 km SSW), Batangas (figure 18).

Figure 17. Ash plumes seen from various points around Taal in the initial days of the January 2020 eruption, posted on 13 January. Courtesy of Eloisa Lopez/Reuters, Kester Ragaza/Pacific Press/Shutterstock, Ted Aljibe/AFP via Getty Images, via The Guardian.

Figure 18. Map indicating areas impacted by ashfall from the 12 January eruption through to 0800 on the 13th. Small yellow circles (to the N) are ashfall report locations; blue circles (at the island and to the S) are heavy ashfall; large green circles are lapilli (particles measuring 2-64 mm in diameter). Modified from a map courtesy of Lauriane Chardot, Earth Observatory of Singapore; data taken from PHIVOLCS.

News articles noted that more than 300 domestic and 230 international flights were cancelled as the Manila Ninoy Aquino International Airport was closed during 12-13 January. Some roads from Talisay to Lemery and Agoncillo were impassible and electricity and water services were intermittent. Ashfall in several provinces caused power outages. Authorities continued to evacuate high-risk areas, and by 13 January more than 24,500 people had moved to 75 shelters out of a total number of 460,000 people within 14 km.

A PHIVOLCS report for 0800 on the 13th through 0800 on 14 January noted that lava fountaining had continued, with steam-rich ash plumes reaching around 2 km above the volcano and dispersing ash SE and W of Main Crater. Volcanic lighting continued at the base of the plumes. Fissures on the N flank produced 500-m-tall lava fountains. Heavy ashfall continued in the Lemery, Talisay, Taal, and Cuenca, Batangas Municipalities. By 1300 on the 13th lava fountaining generated 800-m-tall, dark gray, steam-laden ash plumes that drifted SW. Sulfur dioxide emissions averaged 5,299 metric tons/day (t/d) on 13 January and dispersed NNE (figure 19).

Figure 19. Compilation of sulfur dioxide plumes from TROPOMI overlaid in Google Earth for 13 January from 0313-1641 UT. Courtesy of NASA Global Sulfur Dioxide Monitoring Page and Google Earth.

Explosions and ash emission through 22 January 2020. At 0800 on 15 January PHIVOLCS stated that activity was generally weaker; dark gray, steam-laden ash plumes rose about 1 km and drifted SW. Satellite images showed that the Main Crater lake was gone and new craters had formed inside Main Crater and on the N side of Volcano Island.

PHIVOLCS reported that activity during 15-16 January was characterized by dark gray, steam-laden plumes that rose as high as 1 km above the vents in Main Crater and drifted S and SW. Sulfur dioxide emissions were 4,186 t/d on 15 January. Eruptive events at 0617 and 0621 on 16 January generated short-lived, dark gray ash plumes that rose 500 and 800 m, respectively, and drifted SW. Weak steam plumes rose 800 m and drifted SW during 1100-1700, and nine weak explosions were recorded by the seismic network.

Steady steam emissions were visible during 17-21 January. Infrequent weak explosions generated ash plumes that rose as high as 1 km and drifted SW. Sulfur dioxide emissions fluctuated and were as high as 4,353 t/d on 20 January and as low as 344 t/d on 21 January. PHIVOLCS reported that white steam-laden plumes rose as high as 800 m above main vent during 22-28 January and drifted SW and NE; ash emissions ceased around 0500 on 22 January. Remobilized ash drifted SW on 22 January due to strong low winds, affecting the towns of Lemery (16 km SW) and Agoncillo, and rose as high as 5.8 km altitude as reported by pilots. Sulfur dioxide emissions were low at 140 t/d.

Steam plumes through mid-April 2020. The Alert Level was lowered to 3 on 26 January and PHIVOLCS recommended no entry onto Volcano Island and Taal Lake, nor into towns on the western side of the island within a 7-km radius. PHIVOLCS reported that whitish steam plumes rose as high as 800 m during 29 January-4 February and drifted SW (figure 20). The observed steam plumes rose as high as 300 m during 5-11 February and drifted SW.

Sulfur dioxide emissions averaged around 250 t/d during 22-26 January; emissions were 87 t/d on 27 January and below detectable limits the next day. During 29 January-4 February sulfur dioxide emissions ranged to a high of 231 t/d (on 3 February). The following week sulfur dioxide emissions ranged from values below detectable limits to a high of 116 t/d (on 8 February).

Figure 20. Taal Volcano Island producing gas-and-steam plumes on 15-16 January 2020. Courtesy of James Reynolds, Earth Uncut.

On 14 February PHIVOLCS lowered the Alert Level to 2, noting a decline in the number of volcanic earthquakes, stabilizing ground deformation of the caldera and Volcano Island, and diffuse steam-and-gas emission that continued to rise no higher than 300 m above the main vent during the past three weeks. During 14-18 February sulfur dioxide emissions ranged from values below detectable limits to a high of 58 tonnes per day (on 16 February). Sulfur dioxide emissions were below detectable limits during 19-20 February. During 26 February-2 March steam plumes rose 50-300 m above the vent and drifted SW and NE. PHIVOLCS reported that during 4-10 March weak steam plumes rose 50-100 m and drifted SW and NE; moderate steam plumes rose 300-500 m and drifted SW during 8-9 March. During 11-17 March weak steam plumes again rose only 50-100 m and drifted SW and NE.

PHIVOLCS lowered the Alert Level to 1 on 19 March and recommended no entry onto Volcano Island, the area defined as the Permanent Danger Zone. During 8-9 April steam plumes rose 100-300 m and drifted SW. As of 1-2 May 2020 only weak steaming and fumarolic activity from fissure vents along the Daang Kastila trail was observed.

Evacuations. According to the Disaster Response Operations Monitoring and Information Center (DROMIC) there were a total of 53,832 people dispersed to 244 evacuation centers by 1800 on 15 January. By 21 January there were 148,987 people in 493 evacuation. The number of residents in evacuation centers dropped over the next week to 125,178 people in 497 locations on 28 January. However, many residents remained displaced as of 3 February, with DROMIC reporting 23,915 people in 152 evacuation centers, but an additional 224,188 people staying at other locations.

By 10 February there were 17,088 people in 110 evacuation centers, and an additional 211,729 staying at other locations. According to the DROMIC there were a total of 5,321 people in 21 evacuation centers, and an additional 195,987 people were staying at other locations as of 19 February.

The number of displaced residents continued to drop, and by 3 March there were 4,314 people in 12 evacuation centers, and an additional 132,931 people at other locations. As of 11 March there were still 4,131 people in 11 evacuation centers, but only 17,563 staying at other locations.

Deformation and ground cracks. New ground cracks were observed on 13 January in Sinisian (18 km SW), Mahabang Dahilig (14 km SW), Dayapan (15 km SW), Palanas (17 km SW), Sangalang (17 km SW), and Poblacion (19 km SW) Lemery; Pansipit (11 km SW), Agoncillo; Poblacion 1, Poblacion 2, Poblacion 3, Poblacion 5 (all around 17 km SW), Talisay, and Poblacion (11 km SW), San Nicolas (figure 21). A fissure opened across the road connecting Agoncillo to Laurel, Batangas. New ground cracking was reported the next day in Sambal Ibaba (17 km SW), and portions of the Pansipit River (SW) had dried up.

Figure 21. Video screenshots showing ground cracks that formed during the Taal unrest and captured on 15 and 16 January 2020. Courtesy of James Reynolds, Earth Uncut.

Dropping water levels of Taal Lake were first observed in some areas on 16 January but reported to be lake-wide the next day. The known ground cracks in the barangays of Lemery, Agoncillo, Talisay, and San Nicolas in Batangas Province widened a few centimeters by 17 January, and a new steaming fissure was identified on the N flank of the island.

GPS data had recorded a sudden widening of the caldera by ~1 m, uplift of the NW sector by ~20 cm, and subsidence of the SW part of Volcano Island by ~1 m just after the main eruption phase. The rate of deformation was smaller during 15-22 January, and generally corroborated by field observations; Taal Lake had receded about 30 cm by 25 January but about 2.5 m of the change (due to uplift) was observed around the SW portion of the lake, near the Pansipit River Valley where ground cracking had been reported.

Weak steaming (plumes 10-20 m high) from ground cracks was visible during 5-11 February along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater. PHIVOLCS reported that during 19-24 February steam plumes rose 50-100 m above the vent and drifted SW. Weak steaming (plumes up to 20 m high) from ground cracks was visible during 8-14 April along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater.

Seismicity. Between 1300 on 12 January and 0800 on 21 January the Philippine Seismic Network (PSN) had recorded a total of 718 volcanic earthquakes; 176 of those had magnitudes ranging from 1.2-4.1 and were felt with Intensities of I-V. During 20-21 January there were five volcanic earthquakes with magnitudes of 1.6-2.5; the Taal Volcano network (which can detect smaller events not detectable by the PSN) recorded 448 volcanic earthquakes, including 17 low-frequency events. PHIVOLCS stated that by 21 January hybrid earthquakes had ceased and both the number and magnitude of low-frequency events had diminished.

Geologic Background. Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Disaster Response Operations Monitoring and Information Center (DROMIC) (URL: https://dromic.dswd.gov.ph/); United Nations Office for the Coordination of Humanitarian Affairs, Philippines (URL: https://www.unocha.org/philippines); James Reynolds, Earth Uncut TV (Twitter: @EarthUncutTV, URL: https://www.earthuncut.tv/, YouTube: https://www.youtube.com/user/TyphoonHunter); Chris Vagasky, Vaisala Inc., Louisville, Colorado, USA (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman); Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue, Singapore (URL: https://www.earthobservatory.sg/); 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/); Relief Web, Flash Update No. 1 - Philippines: Taal Volcano eruption (As of 13 January 2020, 2 p.m. local time) (URL: https://reliefweb.int/report/philippines/flash-update-no-1-philippines-taal-volcano-eruption-13-january-2020-2-pm-local); Bloomberg, Philippines Braces for Hazardous Volcano Eruption (URL: https://www.bloomberg.com/news/articles/2020-01-12/philippines-raises-alert-level-in-taal-as-volcano-spews-ash); National Public Radio (NPR), Volcanic Eruption In Philippines Causes Thousands To Flee (URL: npr.org/2020/01/13/795815351/volcanic-eruption-in-philippines-causes-thousands-to-flee); Reuters (http://www.reuters.com/); Agence France-Presse (URL: http://www.afp.com/); Pacific Press (URL: http://www.pacificpress.com/); Shutterstock (URL: https://www.shutterstock.com/); Getty Images (URL: http://www.gettyimages.com/); Google Earth (URL: https://www.google.com/earth/).

In the northern Tonga region, approximately 80 km NW of Vava’u, large areas of floating pumice, termed rafts, were observed starting as early as 7 August 2019. The area of these andesitic pumice rafts was initially 195 km² with the layers measuring 15-30 cm thick and were produced 200 m below sea level (Jutzeler et al. 2020). The previous report (BGVN 44:11) described the morphology of the clasts and the rafts, and their general westward path from 9 August to 9 October 2019, with the first sighting occurring on 9 August NW of Vava’u in Tonga. This report updates details regarding the submarine pumice raft eruption in early August 2019 using new observations and data from Brandl et al. (2019) and Jutzeler et al. (2020).

The NoToVE-2004 (Northern Tonga Vents Expedition) research cruise on the RV Southern Surveyor (SS11/2004) from the Australian CSIRO Marine National Facility traveled to the northern Tonga Arc and discovered several submarine basalt-to-rhyolite volcanic centers (Arculus, 2004). One of these volcanic centers 50 km NW of Vava’u was the unnamed seamount (volcano number 243091) that had erupted in 2001 and again in 2019, unofficially designated “Volcano F” for reference purposes by Arculus (2004) and also used by Brandl et al. (2019). It is a volcanic complex that rises more than 1 km from the seafloor with a central 6 x 8.7 km caldera and a volcanic apron measuring over 50 km in diameter (figures 19 and 20). Arculus (2004) described some of the dredged material as “fresh, black, plagioclase-bearing lava with well-formed, glassy crusts up to 2cm thick” from cones by the eastern wall of the caldera; a number of apparent flows, lava or debris, were observed draping over the northern wall of the caldera.

Figure 19. Visualization of the unnamed submarine Tongan volcano (marked “Volcano F”) using bathymetric data to show the site of the 6-8 August 2020 eruption and the rest of the cone complex. Courtesy of Philipp Brandl via GEOMAR.

Figure 20. Map of the unnamed submarine Tongan volcano using satellite imagery, bathymetric data, with shading from the NW. The yellow circle indicates the location of the August 2019 activity. Young volcanic cones are marked “C” and those with pit craters at the top are marked with “P.” Courtesy of Brandl et al. (2019).

The International Seismological Centre (ISC) Preliminary Bulletin listed a particularly strong (5.7 Mw) earthquake at 2201 local time on 5 August, 15 km SSW of the volcano at a depth of 10 km (Brandl et al. 2019). This event was followed by six slightly lower magnitude earthquakes over the next two days.

Sentinel-2 satellite imagery showed two concentric rings originating from a point source (18.307°S 174.395°W) on 6 August (figure 21), which could be interpreted as small weak submarine plumes or possibly a series of small volcanic cones, according to Brandl et al. (2019). The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. By 8 August volcanic activity had decreased, but the pumice rafts that were produced remained visible through at least early October (BGVN 44:11). Brandl et al. (2019) states that, due to the lack of continued observed activity rising from this location, the eruption was likely a 2-day-long event during 6-8 August.

Figure 21. Sentinel-2 satellite image of possible gas/vapor emissions (streaks) on 6 August 2019 drifting NW, which is the interpreted site for the unnamed Tongan seamount. The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. Image using False Color (urban) rendering (bands 12, 11, 4); courtesy of Sentinel Hub Playground.

The pumice was first observed on 9 August occurred up to 56 km from the point of origin, according to Jutzeler et al. (2020). By calculating the velocity (14 km/day) of the raft using three satellites, Jutzeler et al. (2020) determined the pumice was erupted immediately after the satellite image of the submarine plumes on 6 August (UTC time). Minor activity at the vent may have continued on 8 and 11 August (UTC time) with pale blue-green water discoloration (figure 22) and a small (less than 1 km²) diffuse pumice raft 2-5 km from the vent.

Figure 22. Sentinel-2 satellite image of the last visible activity occurring W of the unnamed submarine Tongan volcano on 8 August 2019, represented by slightly discolored blue-green water. Image using Natural Color rendering (bands 4, 3, 2) and enhanced with color correction; courtesy of Sentinel Hub Playground.

Continuous observations using various satellite data and observations aboard the catamaran ROAM tracked the movement and extent of the pumice raft that was produced during the submarine eruption in early August (figure 23). The first visible pumice raft was observed on 8 August 2019, covering more than 136.7 km² between the volcanic islands of Fonualei and Late and drifting W for 60 km until 9 August (Brandl et al. 2019; Jutzeler 2020). The next day, the raft increased to 167.2-195 km² while drifting SW for 74 km until 14 August. Over the next three days (10-12 August) the size of the raft briefly decreased in size to less than 100 km² before increasing again to 157.4 km² on 14 August; at least nine individual rafts were mapped and identified on satellite imagery (Brandl et al. 2019). On 15 August sailing vessels observed a large pumice raft about 75 km W of Late Island (see details in BGVN 44:11), which was the same one as seen in satellite imagery on 8 August.

Figure 23. Map of the extent of discolored water and the pumice raft from the unnamed submarine Tongan volcano between 8 and 14 August 2019 using imagery from NASA’s MODIS, ESA’s Sentinel-2 satellite, and observations from aboard the catamaran ROAM (BGVN 44:11). Back-tracing the path of the pumice raft points to a source location at the unnamed submarine Tongan volcano. Courtesy of Brandl et al. (2019).

By 17 August high-resolution satellite images showed an area of large and small rafts measuring 222 km² and were found within a field of smaller rafts for a total extent of 1,350 km², which drifted 73 km NNW through 22 August before moving counterclockwise for three days (figure f; Jutzeler et al., 2020). Small pumice ribbons encountered the Oneata Lagoon on 30 August, the first island that the raft came into contact (Jutzeler et al. 2020). By 2 September, the main raft intersected with Lakeba Island (460 km from the source) (figure 24), breaking into smaller ribbons that started to drift W on 8 September. On 19 September the small rafts (less than 100 m x less than 2 km) entered the strait between Viti Levu and Vanua Levu, the two main islands of Fiji, while most of the others were stranded 60 km W in the Yasawa Islands for more than two months (Jutzeler et al., 2020).

Figure 24. Time-series map of the raft dispersal from the unnamed submarine Tongan volcano using multiple satellite images. A) Map showing the first days of the raft dispersal starting on 7 August 2019 and drifting SW from the vent (marked with a red triangle). Precursory seismicity that began on 5 August is marked with a white star. By 15-17 August the raft was entrained in an ocean loop or eddy. The dashed lines represent the path of the sailing vessels. B) Map of the raft dispersal using high-resolution Sentinel-2 and -3 imagery. Two dispersal trails (red and blue dashed lines) show the daily dispersal of two parts of the raft that were separated on 17 August 2019. Courtesy of Jutzeler et al. (2020).

References: Arculus, R J, SS2004/11 shipboard scientists, 2004. SS11/2004 Voyage Summary: NoToVE-2004 (Northern Tonga Vents Expedition): submarine hydrothermal plume activity and petrology of the northern Tofua Arc, Tonga. https://www.cmar.csiro.au/data/reporting/get file.cfm?eovpub id=901.

Brandl P A, Schmid F, Augustin N, Grevemeyer I, Arculus R J, Devey C W, Petersen S, Stewart M , Kopp K, Hannington M D, 2019. The 6-8 Aug 2019 eruption of ‘Volcano F’ in the Tofua Arc, Tonga. Journal of Volcanology and Geothermal Research: https://doi.org/10.1016/j.jvolgeores.2019.106695

Jutzeler M, Marsh R, van Sebille E, Mittal T, Carey R, Fauria K, Manga M, McPhie J, 2020. Ongoing Dispersal of the 7 August 2019 Pumice Raft From the Tonga Arc in the Southwestern Pacific Ocean. AGU Geophysical Research Letters: https://doi.orh/10.1029/2019GL086768.

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

Information Contacts: Jan Steffen, Communication and Media, GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Klyuchevskoy is part of the Klyuchevskaya volcanic group in northern Kamchatka and is one of the most frequently active volcanoes of the region. Eruptions produce lava flows, ashfall, and lahars originating from summit and flank activity. This report summarizes activity during October 2019 through May 2020, and is based on reports by the Kamchatkan Volcanic Eruption Response Team (KVERT) and satellite data.

There were no activity reports from 1 to 22 October, but gas emissions were visible in satellite images. At 1020 on 24 October (2220 on 23 October UTC) KVERT noted that there was a small ash component in the ash plume from erosion of the conduit, with the plume reaching 130 km ENE. The Aviation Colour Code was raised from Green to Yellow, then to Orange the following day. An ash plume continued on the 25th to 5-7 km altitude and extending 15 km SE and 70 km SW and reached 30 km ESE on the 26th. Similar activity continued through to the end of the month.

Moderate gas emissions continued during 1-19 November, but the summit was obscured by clouds. Strong nighttime incandescence was visible at the crater during the 10-11 November and thermal anomalies were detected on 8 and 10-13 November. Explosions produced ash plumes up to 6 km altitude on the 20-21st and Strombolian activity was reported during 20-22 November. Degassing continued from 23 November through 12 December, and a thermal anomaly was visible on the days when the summit was not covered by clouds. An ash plume was reported moving to the NW on the 13th, and degassing with a thermal anomaly and intermittent Strombolian activity then resumed, continuing through to the end of December with an ash plume reported on the 30th.

Gas-and-steam plumes continued into January 2020 with incandescence noted when the summit was clear (figure 33). Strombolian activity was reported again starting on the 3rd. A weak ash plume produced on the 6th extended 55 km E, and on the 21st an ash plume reached 5-5.5 km altitude and extended 190 km NE (figure 34). Another ash plume the next day rose to the same altitude and extended 388 km NE. During 23-29 Strombolian activity continued, and Vulcanian activity produced ash plumes up to 5.5 altitude, extending to 282 km E on the 30th, and 145 km E on the 31st.

Figure 33. Incandescence and degassing were visible at Klyuchevskoy through January 2020, seen here on the 11th. Courtesy of KVERT.

Figure 34. A low ash plume at Klyuchevskoy on 21 January 2020 extended 190 km NE. Courtesy of KVERT.

Strombolian activity continued throughout February with occasional explosions producing ash plumes up to 5.5 km altitude, as well as gas-and-steam plumes and a persistent thermal anomaly with incandescence visible at night. Starting in late February thermal anomalies were detected much more frequently, and with higher energy output compared to the previous year (figure 35). A lava fountain was reported on 1 March with the material falling back into the summit crater. Strombolian activity continued through early March. Lava fountaining was reported again on the 8th with ejecta landing in the crater and down the flanks (figure 36). A strong persistent gas-and-steam plume containing some ash continued along with Strombolian activity through 25 March (figure 37), with Vulcanian activity noted on the 20th and 25th. Strombolian and Vulcanian activity was reported through the end of March.

Figure 35. This MIROVA thermal energy plot for Klyuchevskoy for the year ending 29 April 2020 (log radiative power) shows intermittent thermal anomalies leading up to more sustained energy detected from February through March, then steadily increasing energy through April 2020. Courtesy of MIROVA.

Figure 36. Strombolian explosions at Klyuchevskoy eject incandescent ash and gas, and blocks and bombs onto the upper flanks on 8 and 10 March 2020. Courtesy of IVS FEB RAS, KVERT.

Figure 37. Weak ash emission from the Klyuchevskoy summit crater are dispersed by wind on 19 and 29 March 2020, with ash depositing on the flanks. Courtesy of IVS FEB RAS, KVERT.

Activity was dominantly Strombolian during 1-5 April and included intermittent Vulcanian explosions from the 6th onwards, with ash plumes reaching 6 km altitude. On 18 April a lava flow began moving down the SE flank (figures 38). A report on the 26th reported explosions from lava-water interactions with avalanches from the active lava flow, which continued to move down the SE flank and into the Apakhonchich chute (figures 39 and 40). This continued throughout April and May with sustained Strombolian and intermittent Vulcanian activity at the summit (figures 41 and 42).

Figure 38. Strombolian activity produced ash plumes and a lava flow down the SE flank of Klyuchevskoy on 18 April 2020. Courtesy of IVS FEB RAS, KVERT.

Figure 39. A lava flow descends the SW flank of Klyuchevskoy and a gas plume is dispersed by winds on 21 April 2020. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Figure 40. Sentinel-2 thermal satellite images show the progression of the Klyuchevskoy lava flow from the summit crater down the SE flank from 19-29 April 2020. Associated gas plumes are dispersed in various directions. Courtesy of Sentinel Hub Playground.

Figure 41. Strombolian activity at Klyuchevskoy ejects incandescent ejecta, gas, and ash above the summit on 27 April 2020. Courtesy of D. Bud'kov, IVS FEB RAS, KVERT.

Figure 42. Sentinel-2 thermal satellite images of Klyuchevskoy show the progression of the SE flank lava flow through May 2020, with associated gas plumes being dispersed in multiple directions. 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/); 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).

Nyamuragira (also known as Nyamulagira) is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo and consists of a lava lake that reappeared in the summit crater in mid-April 2018. Volcanism has been characterized by lava emissions, thermal anomalies, seismicity, and gas-and-steam emissions. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

According to OVG, intermittent eruptive activity was detected in the lava lake of the central crater during December 2019 and January-April 2020, which also resulted in few seismic events. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows thermal anomalies within the summit crater that varied in both frequency and power between August 2019 and mid-March 2020, but very few were recorded afterward through late May (figure 88). Thermal hotspots identified by MODVOLC from 15 December 2019 through March 2020 were mainly located in the active central crater, with only three hotspots just outside the SW crater rim (figure 89). Sentinel-2 thermal satellite imagery also showed activity within the summit crater during January-May 2020, but by mid-March the thermal anomaly had visibly decreased in power (figure 90).

Figure 88. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 27 July through May 2020 shows variably strong, intermittent thermal anomalies with a variation in power and frequency from August 2019 to mid-March 2020. Courtesy of MIROVA.

Figure 89. Map showing the number of MODVOLC hotspot pixels at Nyamuragira from 1 December 2019 t0 31 May 2020. 37 pixels were registered within the summit crater while 3 were detected just outside the SW crater rim. Courtesy of HIGP-MODVOLC Thermal Alerts System.

Figure 90. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright yellow-orange) at Nyamuragira from February into April 2020. The strength of the thermal anomaly in the summit crater decreased by late March 2020, but was still visible. Courtesy of Sentinel Hub Playground.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Information contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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/exp.

Nyiragongo is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo, part of the western branch of the East African Rift System and contains a 1.2 km-wide summit crater with a lava lake that has been active since at least 1971. Volcanism has been characterized by strong and frequent thermal anomalies, incandescence, gas-and-steam emissions, and seismicity. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

In the December 2019 monthly report, OVG stated that the level of the lava lake had increased. This level of the lava lake was maintained for the duration of the reporting period, according to later OVG monthly reports. Seismicity increased starting in November 2019 and was detected in the NE part of the crater, but it decreased by mid-April 2020. SO₂ emissions increased in January 2020 to roughly 7,000 tons/day but decreased again near the end of the month. OVG reported that SO₂ emissions rose again in February to roughly 8,500 tons/day before declining to about 6,000 tons/day. Unlike in the previous report (BGVN 44:12), incandescence was visible during the day in the active lava lake and activity at the small eruptive cone within the 1.2-km-wide summit crater has since increased, consisting of incandescence and some lava fountaining (figure 72). A field survey was conducted on 3-4 March where an OVG team observed active lava fountains and ejecta that produced Pele’s hair from the small eruptive cone (figure 73). During this survey, OVG reported that the level of the lava lake had reached the second terrace, which was formed on 17 January 2002 and represents remnants of the lava lake at different eruption stages. There, the open surface lava lake was observed; gas-and-steam emissions accompanied both the active lava lake and the small eruptive cone (figures 72 and 73).

Figure 72. Webcam image of Nyiragongo in February 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG February 2020).

Figure 73. Webcam image of Nyiragongo on 4 March 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG Mars 2020).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continued to show frequent strong thermal anomalies within 5 km of the summit crater through May 2020 (figure 74). Similarly, the MODVOLC algorithm reported multiple thermal hotspots almost daily within the summit crater between December 2019 and May 2020. These thermal signatures were also observed in Sentinel-2 thermal satellite imagery within the summit crater (figure 75).

Figure 74. Thermal anomalies at Nyiragongo from 27 July through May 2020 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.

Figure 75. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed ongoing thermal activity (bright yellow-orange) in the summit crater at Nyiragongo during January through April 2020. Courtesy of Sentinel Hub Playground.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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).

Kavachi is a submarine volcano located in the Solomon Islands south of Gatokae and Vangunu islands. Volcanism is frequently active, but rarely observed. The most recent eruptions took place during 2014, which consisted of an ash eruption, and during 2016, which included phreatomagmatic explosions (BGVN 42:03). This reporting period covers December 2016-April 2020 primarily using satellite data.

Activity at Kavachi is often only observed through satellite images, and frequently consists of discolored submarine plumes for which the cause is uncertain. On 1 January 2018 a slight yellow discoloration in the water is seen extending to the E from a specific point (figure 20). Similar faint plumes were observed on 16 January, 25 February, 2 March, 26 April, 6 May, and 25 June 2018. No similar water discoloration was noted during 2019, though clouds may have obscured views.

Figure 20. Satellite images from Sentinel-2 revealed intermittent faint water discoloration (yellow) at Kavachi during the first half of 2018, as seen here on 1 January (top left), 25 February (top right), 26 April (bottom left), and 25 June (bottom right). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Activity resumed in 2020, showing more discolored water in satellite imagery. The first instance occurred on 16 March, where a distinct plume extended from a specific point to the SE. On 25 April a satellite image showed a larger discolored plume in the water that spread over about 30 km², encompassing the area around Kavachi (figure 21). Another image on 30 April showed a thin ribbon of discolored water extending about 50 km W of the vent.

Figure 21. Sentinel-2 satellite images of a discolored plume (yellow) at Kavachi beginning on 16 March (top left) with a significant large plume on 25 April (right), which remained until 30 April (bottom left). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

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

Kuchinoerabujima encompasses a group of young stratovolcanoes located in the northern Ryukyu Islands. All historical eruptions have originated from the Shindake cone, with the exception of a lava flow that originated from the S flank of the Furudake cone. The most recent previous eruptive period took place during October 2018-February 2019 and primarily consisted of weak explosions, ash plumes, and ashfall. The current eruption began on 11 January 2020 after nearly a year of dominantly gas-and-steam emissions. Volcanism for this reporting period from March 2019 to April 2020 included explosions, ash plumes, SO₂ emissions, and ashfall. The primary source of information for this report comes from monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Volcanism at Kuchinoerabujima was relatively low during March through December 2019, according to JMA. During this time, SO₂ emissions ranged from 100 to 1,000 tons/day. Gas-and-steam emissions were frequently observed throughout the entire reporting period, rising to a maximum height of 1.1 km above the crater on 13 December 2019. Satellite imagery from Sentinel-2 showed gas-and-steam and occasional ash emissions rising from the Shindake crater throughout the reporting period (figure 7). Though JMA reported thermal anomalies occurring on 29 January and continuing through late April 2020, Sentinel-2 imagery shows the first thermal signature appearing on 26 April.

Figure 7. Sentinel-2 thermal satellite images showed gas-and-steam and ash emissions rising from Kuchinoerabujima. Some ash deposits can be seen on 6 February 2020 (top right). A thermal anomaly appeared on 26 April 2020 (bottom right). Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

An eruption on 11 January 2020 at 1505 ejected material 300 m from the crater and produced ash plumes that rose 2 km above the crater rim, extending E, according to JMA. The eruption continued through 12 January until 0730. The resulting ash plumes rose 400 m above the crater, drifting SW while the SO₂ emissions measured 1,300 tons/day. Ashfall was reported on Yakushima Island (15 km E). Minor eruptive activity was reported during 17-20 January which produced gray-white plumes that rose 300-500 m above the crater. On 23 January, seismicity increased, and an eruption produced an ash plume that rose 1.2 km altitude, according to a Tokyo VAAC report, resulting in ashfall 2 km NE of the crater. A small explosion was detected on 24 January, followed by an increase in the number of earthquakes during 25-26 January (65-71 earthquakes per day were registered). Another small eruptive event detected on 27 January at 0148 was accompanied by a volcanic tremor and a change in tilt data. During the month of January, some inflation was detected at the base on the volcano and a total of 347 earthquakes were recorded. The SO₂ emissions ranged from 200-1,600 tons/day.

An eruption on 1 February 2020 produced an eruption column that rose less than 1 km altitude and extended SE and SW (figure 8), according to the Tokyo VAAC report. On 3 February, an eruption from the Shindake crater at 0521 produced an ash plume that rose 7 km above the crater and ejected material as far as 600 m away. As a result, a pyroclastic flow formed, traveling 900-1,500 m SW. The previous pyroclastic flow that was recorded occurred on 29 January 2019. Ashfall was confirmed in the N part of Yakushima Island with a large amount in Miyanoura (32 km ESE) and southern Tanegashima. The SO₂ emissions measured 1,700 tons/day during this event.

Figure 8. Webcam images from the Honmura west surveillance camera of an ash plume rising from Kuchinoerabujima on 1 February 2020. Courtesy of JMA (Weekly bulletin report 509, February 2020).

Intermittent small eruptive events occurred during 5-9 February; field observations showed a large amount of ashfall on the SE flank which included lapilli that measured up to 2 cm in diameter. Additionally, thermal images showed 5-km-long pyroclastic flow deposits on the SW flank. An eruption on 9 February produced an ash plume that rose 1.2 km altitude, drifting SE. On 13 February a small eruption was detected in the Shindake crater at 1211, producing gray-white plumes that rose 300 m above the crater, drifting NE. Small eruptive events also occurred during 20-21 February, resulting in gas-and-steam emissions that rose 200 m above the crater. During the month of February, some horizontal extension was observed since January 2020 using GNSS data. The total number of earthquakes during this month drastically increased to 1225 compared to January. The SO₂ emissions ranged from 300-1,700 tons/day.

By 2 March 2020, seismicity decreased, and activity declined. Gas-and-steam emissions continued infrequently for the duration of the reporting period. The SO₂ emissions during March ranged from 700-2,100 tons/day, the latter of which occurred on 15 March. Seismicity increased again on 27 March. During 5-8 April 2020, small eruptive events were detected, generating ash plumes that rose 900 m above the crater (figure 9). The SO₂ emissions on 6 April reached 3,200 tons/day, the maximum measurement for this reporting period. These small eruptive events continued from 13-20 and 23-25 April within the Shindake crater, producing gray-white plumes that rose 300-800 m above the crater.

Figure 9. Webcam images from the Honmura Nishi (top) and Honmura west (bottom) surveillance cameras of ash plumes rising from Kuchinoerabujima on 6 March and 5 April 2020. Courtesy of JMA (Weekly bulletin report 509, March and April 2020).

Geologic Background. A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km W of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. All historical eruptions have occurred from Shindake, although a lava flow from the S flank of Furudake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shindake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Soputan is a stratovolcano located in the northern arm of Sulawesi Island, Indonesia. Previous eruptive periods were characterized by ash explosions, lava flows, and Strombolian eruptions. The most recent eruption occurred during October-December 2018, which consisted mostly of ash plumes and some summit incandescence (BGVN 44:01). This report updates information for January 2019-April 2020 characterized by two ash plumes and gas-and-steam emissions. The primary source of information come from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and the Darwin Volcanic Ash Advisory Center (VAAC).

Activity during January 2019-April 2020 was relatively low; three faint thermal anomalies were observed at the summit at Soputan in satellite imagery for a total of three days on 2 and 4 January, and 1 October 2019 (figure 17). The MIROVA (Middle InfraRed Observation of Volcanic Activity) based on analysis of MODIS data detected 12 distal hotspots and six low-power hotspots within 5 km of the summit during August to early October 2019. A single distal thermal hotspot was detected in early March 2020. In March, activity primarily consisted of white to gray gas-and-steam plumes that rose 20-100 m above the crater, according to PVMBG. The Darwin VAAC issued a notice on 23 March 2020 that reported an ash plume rose to 4.3 km altitude; minor ash emissions had been visible in a webcam image the previous day (figure 18). A second notice was issued on 2 April, where an ash plume was observed rising 2.1 km altitude and drifting W.

Figure 17. Sentinel-2 thermal satellite imagery detected a total of three thermal hotspots (bright yellow-orange) at the summit of Soputan on 2 and 4 January and 1 October 2019. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Figure 18. Minor ash emissions were seen rising from Soputan on 22 March 2020. Courtesy of MAGMA Indonesia.

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Heard Island is located on the Kerguelen Plateau in the southern Indian Ocean and contains Big Ben, a snow-covered stratovolcano with intermittent volcanism reported since 1910. Due to its remote location, visual observations are rare; therefore, thermal anomalies and hotspots detected by satellite-based instruments are the primary source of information. This report updates activity from October 2019 to April 2020.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed three prominent periods of strong thermal anomaly activity during this reporting period: late October 2019, December 2019, and the end of April 2020 (figure 41). These thermal anomalies were relatively strong and occurred within 5 km of the summit. Similarly, the MODVOLC algorithm reported a total of six thermal hotspots during 28 October, 1 November 2019, and 26 April 2020.

Figure 41. Thermal anomalies at Heard from 29 April 2019 through April 2020 as recorded by the MIROVA system (Log Radiative Power) were strong and frequent in late October, during December 2019, and at the end of April 2020. Courtesy of MIROVA.

Six thermal satellite images ranging from late October 2019 to late March showed evidence of active lava at the summit (figure 42). These images show hot material, possibly a lava flow, extending SW from the summit; a hotspot also remained at the summit. Cloud cover was pervasive during the majority of this reporting period, especially in April 2020, though gas-and-steam emissions were visible on 25 April through the clouds.

Figure 42. Thermal satellite images of Heard Island’s Big Ben showing strong thermal signatures representing a lava flow in the SW direction from 28 October to 17 December 2019. These thermal anomalies are located NE from Mawson Peak. A faint thermal anomaly is also captured on 26 March 2020. Satellite images with atmospheric penetration (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben because of its extensive ice cover. The historically active Mawson Peak forms the island's high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported at this isolated volcano, but observations are infrequent and additional activity may have occurred.

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).

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, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

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).