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).

This report extends our recent coverage of Bardarbunga (BGVN 39:10) by discussing activity between 7 January 2015 and 1 May 2015, although the eruption ceased on 28 February 2015. Most of the information below is based on reports from the Icelandic Met Office (IMO), with ancillary information from other agencies as noted. For sources other than the IMO reports shown in the reference list, see the websites provided in the "Information contacts" section at the end of this report. In general, the information sources there closely coincides with the date range of interest. The eruption began at Holuhraun on 31 August 2014 (BGVN 39:10).

IMO reports for January 2015 noted that activity at Bárdarbunga's Holuhraun lava field grew slightly along its N and NE margins. The lava field covered 84.1 km²on 10 January, 84.3 km² on 15 January, and 84.7 km² on 22 January. Seismicity remained strong, for example, an earthquake swarm occurred on 29 January 2015. (Specific numbers of earthquakes appear in some IMO reporting, although no plot has emerged with graphical depiction of earthquakes in this reporting interval such as figure 5 in BGVN 39:10.) Local air pollution from gas emissions persisted. GPS measurements showed that subsidence continued. As measured on the ice surface, total subsidence of the Bárdarbunga surface between mid-August 2014 and the end of January 2015 was 61 m. During this period, IMO maintained an Aviation Colour Code of Orange (the second highest on a five-color scale).

IMO noted that on 21 January, "Handheld meters, carried by scientist near the eruptive site . . . showed SO₂ concentrations of 29 ppm and 14 ppm. This is in concordance with the sulphur veils apparent from the aircraft and is reminiscent of the circumstances in SE Iceland [on] 28 October 2014. Since 1 ppm is about 3000 μg/m³ [micrograms per cubic meter ] this refers to concentrations of 87,000 μg/m³ and 42,000 μg/m³ respectively. For comparison, see values in the table compiled by the Environment Agency of Iceland and the Directorate of Health."

According to the Environmental Agency of Iceland, an SO₂ concentration above 14,000 μg/m³ is the most hazardous of six health hazard categories; the Agency advises that serious respiratory symptoms are to be expected. More specifically, the Agency states that when SO₂ concentrations exceed 14,000 μg/m³, residents should remain indoors, close the windows, and shut down air conditioning.

The Institute of Earth Sciences (IES) at the University of Iceland provided a map prepared on 21 January showing that the lava field was thickening and not spreading significantly; the volume of erupted lava was an estimated 1.4 km³ (15% uncertainty)(figure 11). An IMO report on 27 January stated that the average rate of lava emission during the previous three weeks had been just less than 100 m³ per second, taken by the report authors as a sign that the eruption intensity was slowly decreasing. On 27 January, a plume rose to an estimated height of 1.3 km above the plain.

Figure 11. Map of the new lava from Bardarbunga, prepared on 21 January 2015. During January, the lava thickened, without extending much further. Numbers indicate the thickness (m) which is also color-coded (legend on right). Courtesy of Institute of Earth Sciences (IES), University of Iceland.

On 6 February, IMO issued a statement that eruptive activity had decreased visibly during the previous two weeks, although seismicity was still strong. Lower seismicity continued during 11-19 February with many days of over a dozen earthquakes and seismic activity ranging up to M 4.3. On 14 February, the lava field covered 85 km²; measurements of the lava field's size on 4 and 12 February found no significant change.

An IES report issued on 20 February 2015 for 17-19 February 2015 noted "There is only one active vent inside the crater and the surface of the molten lava continues to sink. The lava channel has crusted over, except the 200-300 m nearest to the vent. The eruption column reaches no more than 1000 m above ground. The photos below show breakouts 15–16 km ENE of the vent, fed by the closed lava pathway which is inflating the lava field."

According to the IMO, a lava tube continued to feed the N and NE parts of Holuhraun, inflating the lava field. They also noted a reduced rate of effusion no longer sustained active breakouts in an area 17-18 km ENE from the vent.

A 24 February report noted that the rate of subsidence at Bardarbunga caldera was less than 2 cm per day. (IMO cautioned that care was needed with the interpretation of these data, given that GPS measurements are affected by ice flowing slowly into the caldera.) The eruption rate decreased substantially, and seismic activity continued to decrease although it was still considered strong.

IMO reported that a 27 February 2015 evening overflight found no visible incandescence at Holuhraun. According to FLIR thermal measurements, the radiant heat was greatest from the crater's rim, and lesser from the crater's depths. A gas detector in flight showed a maximum concentration of 0.5 ppm SO₂, and a maximum concentration of 0.4 ppm when tested on the ground at the SW edge of the lava field. Glowing areas were observed in the NE part of the lava field; the maximum temperature detected was 560°C (compared to 1,200°C earlier). Radar measurements showed that the extent of the lava field had not increased since mid-February. (Data from SENTINEL-1 radar image 0741 UTC 27 February 2015 and helicopter flight, 1515 UTC 27 February 2015). According to IMO, experience with other lava-bearing eruptions suggested that the Holuhraun lava field would continue to emit gas for a long time. Without buoyant rise, driven by thermal emission from an active vent, the gases would remain low (near the ground surface). Therefore, IMO expected even greater concentrations of gas than residents had previously seen.

IMO reported that the eruption at the fissure of Bárdarbunga's Holuhraun, which began on 31 August 2014 ended on 28 February 2015. The Aviation Colour Code was lowered to Yellow.

IMO scientists conducted a field study on 3-4 March 2015, and found no signs of activity, other than a diffuse bluish haze at ground level across the lava field (figure 12). The IMO scientists reported that the crater rim had several cracks at the very edge, and while standing close to the crater rim it was possible to hear rumbling due to movements of rocks/solidified lava inside the crater.

Figure 12. Photo of IMO geologists inside the Baugur crater on 4 March 2015. From the photo it appears that the vent discharging the lava is in the distance at the far end of the crater (area with white plume). According to the IMO caption, the photo was taken from the central part of Baugur crater as viewed looking along it to the N. The encrusted surface of the lava lake has collapsed, its remains seen as coarse, black rubble at the crater floor. On the crater floor, observers saw small vents sporadically discharging bluish gas. Part of the crater rim seen on the right side had broken, providing an outlet onto the lava field beyond. The resulting lava channel was about 50 m wide and 40 m deep. Courtesy of IMO (Ármann Höskuldsson; taken from IMO's March-April 2015 report).

In early March maximum CO (carbon monoxide) and SO₂ concentrations, measured with personal sensors near and at the crater rim, were 3 ppm and 2.5 ppm, respectively. A multiGAS instrument at the crater rim measured concentrations of SO₂, CO₂, H₂S, and H₂ for about 30 minutes, and provided ratios of CO₂/SO₂, H₂O/SO₂, and H₂O/CO₂ of 17, 101, and 6, respectively. The scientists noted that comparing the CO₂/SO₂ ratio with previous measurements showed a clear increase, consistent with the end of an eruption. The maximum concentrations measured with the MultiGAS instrument were at the level of 30 ppm for SO₂ (the concentration at which the instrument saturates). For CO₂ and H₂S, the respective measurements were 700 ppm and 5 ppm. The level of SO₂ was measured with an automatic gas detector, as reported by the Science Advisory Board of the Icelandic Civil Protection and disseminated by the Icelandic Commissioner of the Icelandic Police, as 500 µg/m³ (~0.5 ppm). Blönduós is a town and municipality in the North of Iceland situated on Route 1 at the mouth of the glacial river, Blanda. The report of the Police contained a links to a Gas Forecast and a Gas Model and involved scientists from the IMO and the IES along with representatives from the Icelandic Civil Protection, the Environmental Agency of Iceland and the Directorate of Health. The area to the SW and S of Blönduós was reported as possibly affected on the day following the measurement.

On 26 April, IMO lowered the Aviation Color Code to Green (the second lowest level), stating that no further signs of unrest had been noted since the end of the eruption on 28 February. Seismicity both within the caldera and the associated dyke intrusion continued to decline.

References.IMO, 2015 (January), Bárðarbunga 2015-January events, Seismic and volcanic events, 1-31 January, Icelandic Meteorological Office Accessed on 31 March 2015 (URL: http://en.vedur.is/earthquakes-and-volcanism/articles/nr/3071 ) (accessed May 2015).

IMO, 2015 (February), Bárðarbunga 2015-February events, Seismic and volcanic events, 1-28 February, Icelandic Meteorological Office Accessed on 31 March 2015 (URL: http://en.vedur.is/earthquakes-and-volcanism/articles/nr/3087 ) (accessed May 2015).

Geologic Background. The large central volcano of Bárðarbunga lies beneath the NW part of the Vatnajökull icecap, NW of Grímsvötn volcano, and contains a subglacial 700-m-deep caldera. Related fissure systems include the Veidivötn and Trollagigar fissures, which extend about 100 km SW to near Torfajökull volcano and 50 km NE to near Askja volcano, respectively. Voluminous fissure eruptions, including one at Thjorsarhraun, which produced the largest known Holocene lava flow on Earth with a volume of more than 21 km3, have occurred throughout the Holocene into historical time from the Veidivötn fissure system. The last major eruption of Veidivötn, in 1477, also produced a large tephra deposit. The subglacial Loki-Fögrufjöll volcanic system to the SW is also part of the Bárðarbunga volcanic system and contains two subglacial ridges extending from the largely subglacial Hamarinn central volcano; the Loki ridge trends to the NE and the Fögrufjöll ridge to the SW. Jökulhlaups (glacier-outburst floods) from eruptions at Bárðarbunga potentially affect drainages in all directions.

Information Contacts: Icelandic Met Office (IMO) (URL: http://en.vedur.is/); Institute of Earth Sciences (IES), University of Iceland (URL: http://earthice.hi.is); National Commissioner of Police, Department of Civil Protection and Emergency Management (URL: http://avd.is/en/); and The Environmental Agency of Iceland (URL: http://www.ust.is/the-environment-agency-of-iceland).

A submarine eruption began here by 19 December 2014 and ended by 28 January 2015. Hunga Tonga and Hunga Ha'apai are small islands situated on the rim of a submarine caldera known by the names of the two islands (Hunga Tonga and Hunga Ha'apai) (figure 12). The 2014-2015 surtseyan eruption added a circular area of land over 100 m in elevation at a spot S of and about midway along Hunga Ha'apai island's length. The new island initially grew as an isolated third new island, but subsequently connected and joined with Hunga Ha'apai. The area of new land surface eventually reached about 1.5 to 2 km in diameter. The new island also grew to come as close a few hundred meters from Hunga Tonga island. The eruption issued dense ash plumes that generally rose less than about a kilometer in altitude but preliminary estimates on the associated higher, ash poor steam plumes rose to 7-10 km altitude.

Figure 12.(Inset) A map showing a large scale view of the South Pacific with the Kingdom of Tonga highlighted in purple. (Main map) Hunga Tonga and Hunga Ha'apai lie on the rim of a submarine caldera located 65 km N of a wharf in the harbor at Nuku'alofa, Tongatapu island (the main island of the archipelago). Nuku'alofa is a deep-water port, the nation's capital, and Tonga's economic hub. Tongatapu island also hosts an international airport, which sits to the S of the capital. (The word "Ha'apai" is also used as the name of a region of islands and reefs well N of Hunga Tonga-Hunga Ha'apai.) The volcano also lies ~70 km SW of Normuka island. Courtesy of USGS.

This 2014-2015 eruption followed 5 years of quiescence, the previous eruption having occurred in 2009 (BGVN 34:03). That 2009 eruption formed new land above water and deposits destroyed vegetation on neighboring Hunga Tonga and Hunga Ha'apai islands (BGVN 34:03). The 2009 eruption added land at the S end of Hunga Ha'apai island. New research has been published discussing the 2009 eruption since our earlier report (BGVN 34:03). For example, Allen and Riebeek (2009) issued a 28 March 2009 Earth Observatory picture of the day that featured Hunga Tonga-Hunga Ha'apai images depicting the island morphology before and after the eruption. For another example, Vaughan and Webley (2010) discussed satellite observations associated with the 2009 eruption. Bohnenstiehl and others (2013) also discussed marine acoustic signatures from the 2009 eruption.

A key source used to create this report on the 2014-2015 eruption consists of four reports created by the Tongan Ministry of Information and Communications (MIC) and released during 14-28 January 2015. Those four MIC Advisories (numbers 3, 4, 5, and 6) are hereafter referred to as MIC (2015 a, b, c, and d). MIC 3 (2015a) was issued 14 January looking back in time at key aspects of the eruption. Discussions included the location and behavior of the first seen early observations on 20 December 2014, a site visit by the Tongan Navy on 6 January, and a pilot report on 13 January 2015. MIC 4 (2015b) was issued on 19 January describing a visit made on 14 January. This was the first report of the existence of a new island. By this time the new island had attached to Hunga Ha'apai island, roughly doubling the size of that island. MIC 5 (2015c) was also issued on 19 January. It described observations made from a visit aboard a ship (the VOEA Neiafu) on 17 January. MIC 6 (2015b) issued on 28 January describing for a visit on 24 January 2015. The report noted a lack of ash, gas, or steam coming from the vent that formed the new island. The authors concluded that the eruption "appears to be over." They provided a sketch map of the new island.

There were no new MIC reports during February-March 2015. The visits and reporting drew on support that included the Tonga Meteorological Services, NZ-Meteorological Services, the Tongan Navy, National Emergency Management Office, Tonga Broadcasting Commission, the New Zealand High Commission, and Ministry of Lands and Natural Resources, Tonga Airport Limited, Tonga Meteorological Services, GNS-NZ, NZ-Meteorological Services, and possibly others.

Eruption, December 2014. The online newspaper Matangi Tonga on 30 December noted that fishermen observed an eruption near Hunga Tonga-Hunga Ha'apai on 19 December 2014 (Matangi Tonga, 2014). An editor from that publication, Mary Lyn Fonua, notified GVP of the eruption. The same publication issued over 10 reports during 30 December 2014 through at least 9 March 2015 (Matangi Tonga, 2014, 2015a, b, c).

MIC (2015a) was released at 0943 on 14 January; it reported the position of the vent that was active on 20 December. Figure 13 is a later version of their figure, made at higher resolution. MIC (2015a) described this particular area as venting steam and sulfurous-gas at the sea surface. Emissions here did not persist during the later stages of the eruption.

Figure 13. A map (N to top) showing the location of steaming at Hunga Tonga-Hunga Ha'apai volcano (orange icon) on 20 December 2014. Each of the two islands are about 2 km long and lie on margins or rim of the mostly submarine caldera, with Hunga Tonga island to the N, and Hunga Ha'apai island to the W of the caldera's center. The area circled in red is the approximate location of the vent that later formed a new rapidly growing island. Taken from Culture Volcan (2015).

Klemetti (2014) showed an image from a MODIS instrument aboard the Aqua satellite that captured of the area of the eruption on 29 December 2014 (figure 14). A small white plume was in evidence at the volcano in the image. He commented that the area of discolored water stretching to the S could be due to the eruption.

Figure 14. The eruption plume from Hunga Tonga-Hung Ha'apai seen on 29 December 2014 by Aqua's MODIS Imager. Image by NASA with annotations by Erik Klemetti (Klemetti, 2014).

According to Metangi Tonga (2014) on 30 December 2014, "A continuing eruption from Tonga's active undersea volcano, Hunga Ha'apai, was clearly visible on the horizon northwest of Tongatapu today."

Activity during January 2015. During the 6 January visit (MIC, 2015a), observers nearing the volcano saw vigorous venting at a new location. MIC (2015a) did not disclose whether a new island had yet emerged but later reporting mentioned below did clearly document an island. The sea (or perhaps a very low island) discharged vigorous emissions of black ash and white billowing clouds. The new location was situated farther N, much closer to the preexisting islands, than the vent indicated in figure 13. That submarine vent to the S lacked further indications of steam emission during the course of the eruption. Neither of the preexisting islands appeared to contain active vents.

MIC (2015a) contained 11 captioned photos, but most are somewhat hazy and with limited contrast, conditions explained later (MIC, 2015b) as due to rain. Plumes on the 6th rose up to 2 km, but almost all the plumes in the photos were under 1.3 km altitude. At least one photo appeared to capture two low, vertical and parallel plumes. The photos documented some highly non-vertical black plumes, some peculiar low white plumes that seem to rise suddenly at distance, black plumes that appear to contain abundant clasts in their leading edge, low billowing clouds that encircle the darker ones and hug the water surface. In one case (figure 9 of MIC, 2015a) they reported that a white plume with its basal portion hugging the sea surface extended E over 3 km. The captions to their figures 10 and 11 indicated pulsing phenomena..

On 12 January 2015, Wellington VAAC reported ash from Hunga Tonga-Hunga Ha'apai reached an altitude of 6 km. They reported that fallout from the plume turned the sea surface red. Brief discussion of red colored sea surface is again mentioned below, both associated with observations on 14 January 2015 and briefly in a quote in an article by Field (2015).

The Wellington VAAC issued graphics to illustrate observed plume location and possible plume dispersal (figures 15 and 16). On figure 15 they labeled the altitude of the plume as SFC/FL200 (20,000 feet, ~6 km). The label "10/0500Z OBS" refers to the coordinated universal time (UTC) when the plume was observed. The next three cartoons represent movement of the ash plume at 6-hour intervals. The VAA graphic in figure 16 is based on the ash advisory mapping shows the recommended area of avoidance and several flight routes in the area.

Figure 15. Wellington VAAC Ash Advisory maps produced to describe the Hunga Tonga-Hunga Ha'apai plume and its trajectory. Times and dates are UTC (e.g., "10/0500Z" corresponds to 10 January 2015 at 0500 UTC). (Upper left) This is the observed ("OBS") ash plume's margin, which was traced onto this map from satellite image. This is the starting point for the subsequent forecasts. (Upper right) The forecast ("FCST") plume after 6 hours. (Lower left) The forecast plume after 12 hours. (Lower right) The forecast plume after 18 hours. Courtesy of the Wellington VAAC. [Maps extracted from NZ Met Service website (OBS-Observed; FCST, Forecasted) (http://vaac.metservice.com/vag/243040-2015_19)].

Figure 16.Wellington VAAC graphic showing the Hunga Tonga-Hunga Ha'apai ash plume boundararies for 12-13 January 2015 as an area enclosed in a blue polygon. The curved black lines in the center and at right are flight paths. Taken from the Wellington VAAC graphic for 12-13 January 2015.

MIC (2015a) noted that all international flights on 13 January 2015 were cancelled, though the domestic airline was operational. A Tongan government daily media release on 13 January described the ongoing eruption and cancellation of flights: "Activity continues at the Hunga Ha'apai-Hunga Tonga region and the emission of ash is reported to have escalated. Volcanic ash is forecasted to reach 870 km in 80 km wide toward the ESE from the Hunga Ha'apai-Hunga Tonga Region. By 11 January 2015, Real Tonga Airlines cancelled their flights for the day." Similar discussions of flight cancellation occurred around this time in Matangi Tonga, in their reports for 9, 13, 14 January.

On 13 January 2015 the Australian Aviation blog reported numerous flight cancellations, including Air New Zealand, Fiji Airways, and Virgin Australia. They also reported resumed service on 14 January 2015. According to Matangi Tonga (2015a) flights resumed on 15 January.

MIC (2015b, one of two reports issued on 19 January) discussed a site inspection on 14 January using a Tongan Navy vessel. The 14 January observations conveyed in MIC (2015b) noted that continuous volcanic eruptions had created a new island (figure 17). On 14 January the volcano was erupting about every five minutes. Ash and rock were ejected to a height of about 400 m above the sea surface. Wet ash was deposited close to the vent, building up the new island. Hazardous surges of ash and steam spread out horizontally during eruptions, and extended more than 1 km from the erupting vent (figure 18). Ash and acid rain fell in an area of ~10 km surrounding the eruption.

Figure 17. Sketch map of Hunga Tonga-Tonga Ha'apai as seen during a 14 January 2015 site inspection. The arrow points to the initial vent seen on 20 December 2014. The red circle indicates the location of the later vent that erupted for about a month, constructing an island with above water extent on 14 January 2015 in the area within the yellow circle. The circle is roughly 2 km in longest dimension. On the basis of this map, the minimum distance between Hunga Tonga island and the new land scales to ~300 m. Modofied from MIC (2015b).

Figure 18. The new island amid eruption on 14 January 2015. The view is looking NE and the steep high area is Hunga Ha'apai island, which resides in behind the new island. The plume was made up of discrete white and dark components. From this perspective the vent appears to sit in the midst of the new low island. Photo taken on 14 January 2015 from the Tongan naval vessel ~300 m offshore (MIC, 2015b).

MIC (2015b) noted that on 14 January steam rose over 1 km and was noted by pilots. The eruption continued to emit ash but in recent days the presence of ash has been limited to low elevations. An early summary section in the report also include the following.

"The new island is more than 1 km wide, ~2 km long and about 100 m high. During our observations the volcano was erupting about every 5 minutes. Dense ash was being erupted to a height of about 400 m, accompanied by some large rocks. Higher we observed mostly steam, but with some ash. Above about 1000 m, the eruption plume was almost exclusively steam. As the ash is very wet, most is being deposited close to the vent, building up the new island.

"Hazardous surges of ash and steam were seen to spread out horizontally during eruptions, and these extended more than 1 km from the erupting vent.

"Ash fall and acidic rain was observed within 10 km of the eruption. Leaves on trees on Hunga Tonga and Hunga Ha'apai have died, probably caused by volcanic ash and gases.

"No large rafts of pumice or other floating volcanic debris were observed. Strong smells of volcanic gases were noticed on a few occasions.

"This eruption is similar to that at Hunga Ha'apai in 2009, but only producing larger volume of materials resulting in the size of the island.

"It is unclear at this stage if there is any relationship between the eruption and a red algal bloom observed in seawaters around Tonga recently."

Field (2015) contained an image from the 14 January site inspection (figure 19).

Figure 19. Hunga Tonga-Hunga Ha'apai eruption viewed from a Tongan naval vessel N of the island on 14 January 2015. Taken from Field (2015) with photo credit there given to the New Zealand High Commission in Tonga.

On 14 January Matangi Tonga (2015b) reported more details on the algal bloom mentioned above (the cause of which remains uncertain). Matangi Tonga (2015b) also reported unusual optical effects seen on the E facing side at the NE end of Tongatapu island (Kanokupolu beach) around that time. The article said the bloom "...turned the seas frothy white, chocolate and red..." and "...the sun shone through a champagne sky." The article contained photos by Shane Egan documenting these effects. Algal blooms can in some cases be detected and tracked by remote sensing as exemplified by Mantas and others (2011), who discuss remote sensing of algal communities as a possible cause of discolored water associated with the Home Reef eruption of 2006.

MIC (2015c) discussed a site visit conducted aboard a naval vessel on 17 January 2015. The authors noted that the eruption still continued at the new island during the visit. MIC (2015c) further stated the following. "During most of our time near the island, strong emission of steam to heights of 7–10 km was observed, but with only limited amounts of ash. Later, some eruptions that threw dense, wet ash, and small rocks 200-300 m into the air, accompanied by further strong emissions of steam. Hunga Tonga and Hunga Ha'apai islands were covered by ash from the eruption over the last month. The eruptions observed today were too small to deposit ash on those islands, suggesting that the eruptions a week or two ago were probably substantially stronger than those observed [on the 17 January site visit]. No trace of rafts of pumice or other floating volcanic debris was observed. No strong smells of volcanic gases were noticed within 3.7 km of the site, it was noticed however 27-47 km on the way to the site. The style of this eruption is similar to that at Hunga Ha'apai in 2009, but the volume of material erupted this time is much greater. International and domestic flights have operated without interruption in the last few days."

On 19 January 2015, the Pléiades satellite captured the Hunga Tonga-Hunga Ha'apai eruption. France's Centre National d'Etudes Spatiales (CNES) issued the resulting 50 m resolution images of the new land created by Hunga Tonga-Hunga Ha'apai's latest eruptions (figure 20). Hunga Tonga island in on the upper right; and Hunga Ha'apai, center left. In the center of the image is a nearly circular, gray colored area, which is the newly created land attached to Hunga Ha'apai island. The vent area on the new island was filled with water (green). Ash from the eruption covered extensive areas of the vegetation on both islands. This and other Images were featured in the article Airbus Defense and Space (2015).

Figure 20. CNES Pléiades satellite image (50-m resolution, optical band) taken on 19 January 2015. Ejecta from the new crater connects it to the E side of Hunga Ha'apai (island at left). Taken Airbus Defense and Space (2015) with data acquisition credit to CNES.

MIC (2015d) was issued on 28 January 2015 summarizing a 24 January site visit, which found the eruption over by this time. Figure 21 shows where the new land surface joins the preexisting Hunga Ha'apai island. Rough seas prevented landing and limited the trip to observations from the naval vessel. The scientists stated, "The eruption from the new island that started growing over a month ago appears to be over. There were no sign of any emissions of ash, gas or steam observed coming out from the vent of the newly formed island."

Figure 21. The point where new land adjoins the older island as seen in January 2015 after the Hunga Tonga Hunga Ha'apai eruption was over. The steep sea cliff forming the old margin of Hunga Ha'apai island is on the left. In the center and right parts of the image lie a low area of gently sloping gray material, which is an outer portion of the newly created land. Besides creating the new land, ash from the eruption covered vegetation over extensive areas on both the older islands. Taken from MIC (2015d).

On 13 March 2015, Luntz (2015) reported that on 6 March 2015 GP Orbassano and two other residents of Tonga landed on one of the new land's three beaches. With his son, he climbed to the highest point of the island's crater, which was ~250 m high. According to Luntz (2015), Tonga's lands and Natural Resources Ministry said the newly formed island was 1.3 km long and 800 m wide.

Orbasano smelled sulfurous and other chemical odors. The vent had filled with opaque green water (figure 22). Matangi Tonga (2015c) also reported on this same topic and featured numerous photos.

Figure 22. The crater lake in the vent area located in the central area of new land as seen on 6 March 2015. Courtesy of Luntz (2015) with photo credit to GP Orbassano.

Luntz (2015) quoted Orbassano as saying "the ash and rock surface was difficult to walk on due to the channels cut in it" (figure 23).

Figure 23. The highest peak on the new land as seen as seen on 6 March 2015. Note extensive rills and gullies. Taken from Luntz (2015) with photo credit to GP Orbassano.

"There are thousands of seabirds--all kinds, laying eggs on the island," Orbassano said (figure 24).

Figure 24. On the new land surface at Hunga Tonga-Hunga Ha'apai, these sea bird eggs were found laid directly upon the fragmental deposits. Taken on 6 March 2015. Courtesy of Iflscience and GP Orbassano.

References. Allen, J, and Riebeek, H, 2009, Submarine Eruption in the Tonga Islands NASA image, (28 March 2009, NASA Earth Observatory, Image of the Day) NASA (URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=37657) (accessed May 2015)

Australian Aviation, 2015, Volcano ash cloud disrupts Tonga flights, Australianaviation.com.au (posted 13 January 2015) (accessed May 2015) (URL: http://australianaviation.com.au/2015/01/volcano-ash-cloud-disrupts-tonga-flights/ )

Airbus Defense and Space, 2015, Eruption of a volcano in the Tonga archipelago, Pléiades captures the birth of a new island (accessed March 2015) (URL: http://www.geo-airbusds.com/en/6322-eruption-of-a-volcano-in-the-tonga-archipelago-pleiades-captures-the-birth-of-a-new-island)

Bohnenstiehl D.R., Dziak R.P., Matsumoto H., Lau T.K. Underwater acoustic records from the March 2009 eruption of Hunga Ha'apai–Hunga Tonga volcano in the Kingdom of Tonga. J. Volc. Geotherm. Res. 2013;249:12-24.

Culture Volcan (Journal d'un volcanophile), 2015, L'activité du volcan Hunga Tonga Hunga Ha'apai a-t-elle changé de style? (posted 14 January 2014) (URL: http://laculturevolcan.blogspot.com/2015/01/lactivite-du-volcan-hunga-tonga-hunga.html)

Field, M, 2015, Tonga volcanic eruption creates new island, Stuff.co, posted 16 January 2015 (URL: http://www.stuff.co.nz/world/south-pacific/65103454/tonga-volcanic-eruption-creates-new-island ).

Klemetti, E, 2014, New Eruption at Hunga Tonga-Hunga Ha'apai, Wired (online), posted 30 December 2014 (accessed 6 June 2015).

Luntz, S, 2015, Newly emerged Pacific "Island" photographed for the first time, IFLSCIENCE (posted 13 March 2015. Accessed March 2015 (URL: http://www.iflscience.com/physics/newly-emerged-pacific-peak-photographed-first-time).

Mantas, V M, Pereira, AJSC., and Morais, PV, 2011, Plumes of discolored water of volcanic origin and possible implications for algal communities. The case of the Home Reef eruption of 2006 (Tonga, Southwest Pacific Ocean). Remote Sensing of Environment, v. 115, no. 6, p. 1341-1352.

Matangi Tonga, 2014, Hunga Ha'apai eruption continues, Matangi Tonga (Posted 30 December 2014; free content accessed in May 2015) (URL: http://matangitonga.to/2014/12/30/hunga-haapai-eruption-continues).

Matangi Tonga, 2015a, Fua'amotu airport's busiest day, as flights resume, Matangi Tonga (Posted 15 January 2015; free content accessed in May 2015) (URL: https://matangitonga.to/2015/01/15/fuaamotu-airports-busiest-day-flights-resume).

Matangi Tonga, 2015b, Nature plays with the sea and sky in Tonga, Matangi Tonga (Posted 15 January; free content accessed in May 2015) (URL: http://matangitonga.to/2015/01/15/nature-plays-sea-and-sky-tonga).

Matangi Tonga, 2015c, New volcanic island attracts sightseers, Matangi Tonga (Posted 9 March 2015; free content accessed in May 2015) (URL: http://matangitonga.to/2015/03/09/new-volcanic-island-attracts-sightseers).

MIC, 2015a, Government of Tonga Ministry of Information and Communication 3 (issued 14 January 2015) (URL: http://www.mic.gov.to/news-today/press-releases/5180-advisory-of-volcanic-activity-no3) (Accessed April 2015).

MIC, 2015b, Government of Tonga Ministry of Information and Communication 4 (issued 19 January 2015) (URL: http://www.mic.gov.to/news-today/press-releases/5185-volcanic-advisory-4) (Accessed April 2015).

MIC, 2015c, Government of Tonga Ministry of Information and Communication 5 (issued 19 January 2015) URL: http://www.mic.gov.to/news-today/press-releases/5183-volcanic-advisory-5) (Accessed April 2015).

MIC, 2015d, Government of Tonga Ministry of Information and Communication 6 (issued 28 January 2015) (URL: http://www.mic.gov.to/news-today/press-releases/5197-volcanic-advisory-6) (Accessed April 2015).

Vaughan, RG, Webley, P, 2010, Satellite observations of a surtseyan eruption: Hunga Ha'apai, Tonga, Journal of Volcanology and Geothermal Research. 12/2010; 198(1-2):177-186. DOI: 10.1016/j.jvolgeores.2010.08.017.

Geologic Background. The small islands of Hunga Tonga and Hunga Ha'apai cap a large seamount located about 30 km SSE of Falcon Island. The two linear andesitic islands are about 2 km long and represent the western and northern remnants of the rim of a largely submarine caldera lying east and south of the islands. Hunga Tonga reaches an elevation of about 114 m above sea level, and both islands display inward-facing sea cliffs with lava and tephra layers dipping gently away from the submarine caldera. A rocky shoal 3.2 km SE of Hunga Ha'apai and 3 km south of Hunga Tonga marks a historically active vent. Several submarine eruptions have occurred at Hunga Tonga-Hunga Ha'apai since the first historical eruption in 1912. An eruption that began in mid-December 2014 built a new island between the other two large islands.

Information Contacts: Tonga’s Ministry of Information and Communications (URL: http://www.mic.gov.to); Tonga’s Natural Resources Division of the Ministry of Lands and Natural Resources (URL: http://www.mic.gov.to/ministrydepartment/14-govt-ministries/lands-survey-nat-res/); Mary Lyn Fonua, Matangi Tonga online (URL: http://matangitonga.to/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/); Wellington Volcanic Ash Advisory Centre, NZ Meteorology Service (URL: http://vaac.metservice.com/); Tonga Meteorological and Coastal Radio service (URL: http://www.met.gov.to); GNS Science (formerly New Zealand’s Institute of Geological and Nuclear Sciences Limited), Taupo, New Zealand (URL: http://www.gns.cri.nz/); and GP (Gianpiero(?)) Orbassano, Waterfront Lodge, Vuna Road, Ma'ufanga, PO Box 1001, Nuku'alofa, Tonga (URL: http://www.waterfront-lodge.com/).

This report covers activity at Nyamuragira (aka Nyamulagira), primarily from April 2014 to January 2015, during which time there were intervals with lava fountains, high SO₂ fluxes, elevated thermal infrared emissions, and high seismicity. A lava lake was in clear evidence starting in November 2014 and into 2015. More fragmentary data beyond the scope of this report as late as at least April 2015 suggests ongoing emissions if not a lava lake.

In the previous reporting interval (BGVN 39:03), an eruption occurred on 6 November 2011 and continued through April 2012. The reporting below begins with a report sent to Bulletin editors on 4 May 2015 by Benoît Smets and scientific colleagues including Nicolas d'Oreye, Nicolas Theys, and Julien Barriere. These and other data providers are listed in the "Information contacts" section at the bottom. Some further information after the material by Smets' team is largely tied to cited references. At present, there is a gap in data in the reporting stream that includes the year 2013.

Geographic background. Nyamuragira is located in the Virunga Volcanic Province (VVP) in the DRC, as depicted in figure 54. Part of the western branch of the East African Rift System (EARS), Nyamuragira includes a lava field that covers over 1,100 km² and contains more than 100 flank cones (figure 54).

Figure 54. 3D perspective view of the Virunga Volcanic Province, located between D.R. Congo and Rwanda. During the project TanDEM-X, radar interferometry was used to calculate a Digital Elevation Model (5-m resolution). This topographic data were 18 times better in terms of resolution than those delivered by NASA during the SRTM mission. Courtesy of F. Albino.

2012 to early 2015. What follows is the report that Smets' team submitted with some of the early figures discussing 2011-2012 omitted. Minor changes were made to some of the quoted material (e.g., date formats; with additions in square or hard brackets, [ ]).

"Starting from early March 2012, i.e. in the final stage of the five month-long eruption on the NE flank of Nyamulagira, SO₂-rich gas fumaroles were observed in the summit caldera of the volcano (D. Tedesco, Pers. Comm.). These fumaroles escaped from several fractures and from the 400-m-wide, 50-80-m-deep pit crater located in the NE part of the caldera.

"The 2011-2012 eruption of Nyamulagira marked the beginning of the progressive collapse and southward extension of the pit crater from which the fumarole escaped. During the second half of April 2012, a larger and permanent SO₂-rich gas plume started to escape from that pit crater.

"In April 2014, local testimonies reported red glow on top of Nyamulagira. This was accompanied by unusual seismic activity recorded by the Goma Volcano Observatory (GVO). Because of intense degassing, helicopter flights at day and night did not allow detecting any fresh lava at ground surface.

"This kind of event reappeared on 22 June 2014. This time, helicopter flights and field surveys on 1 and 5 July 2014 did allow observing lava fountains escaping from the lowest inner flanks of the now ~500 m-deep and ~400 x 600 m-wide pit crater [figure 55]. At that time, lava fountains were not vigorous enough to create and sustain a basin of molten lava in the pit crater. This [lava fountaining] activity was also characterized by large amounts of SO₂-rich gas emissions.

Figure 55. A lava fountain in the deep crater at Nyamuragira, as seen by Smets from a helicopter on 1 July 2014. In addition, he posted a video of the helicopter flyby to YouTube (see Benoît Smets, 2015, in the References section). A lava lake was not indicated. Courtesy of Benoît Smets.

"This [lava fountaining] activity stopped mid-September 2014 and, on 1 November 2014, a small lava lake, i.e. a small bubbling lava basin, appeared in the deepest section of the pit crater (GVO, Pers. Comm.). The related SO₂ emissions appeared lower than during lava fountain activity.

"The lava lake activity at Nyamulagira seems to continue since [1 November 2014 through at least January 2015].

"SO₂ gas emissions, radiated energy, and seismic activity during the April-December 2014 period illustrate very well the evolution of this new activity and the transition from lava fountaining activity to long-lived lava lake activity [figure 56]."

Figure 56. Graphs illustrating (top panel) seismicity, and (bottom panel) SO2 flux and radiated infrared energy at Nyamuragira during April to December 2014; (Green) seismicity in terms of Realtime Seismic Amplitude Measurement (RSAM), calculated using broadband seismometers at the Rumangabo station, ~20 km NE of the crater (installed in the RESIST and RGL-GEORISK projects); (Blue) SO2 emissions in the Virunga region, calculated using OMI measurements; (Red) radiated energy over Nyamuragira, calculated using MODIS imagery and the MODVOLC algorithm (Wright and others, 2004). Courtesy of Smets, d'Oreye, Nicolas Theys, and Julien Barriere.

Labels at the top of figure 56 represent behavior that Smets' team inferred on the basis of field observations. The intervals of quiet are unlabeled. The intervals with lava fountaining correspond with some intervals of high seismicity, high radiance, and pronounced SO₂ emissions. The intervals with the lava lake are somewhat similar to the fountaining in terms of seismicity and radiance but the SO₂ emissions were subdued.

According to the NASA MEASURES dataset, total atmospheric column SO₂ spiked during 19 to 26 June 2014. There was a period of low values during late September to early November 2014. After that and during the rest of the reporting interval, SO₂ was often elevated.

Lava lake. Observations of a lava lake were infrequent during much of 2014. Landsat 8 satellite images taken on 30 June 2014 and 29 July 2014 were interpreted by NASA Earth Observatory analysts Jesse Allen and Robert Simmon. They found "very hot surfaces" they interpreted as representing "the lava lake within the summit crater."

Smets' team did not observe a lava lake during helicopter missions and an expedition to the volcano in July 2014 (e.g. figure 55, which showed fountains but not a large glowing mass that would have clearly signified the presence of a lava lake). Smets' team noted that by 1 November 2014 GVO had seen a small lava lake in the deepest part of the crater. Exactly when this lake was first established and whether it was sustained or ephemeral remains equivocal (Campion, 2014; Oskin, 2014).

According to Bobrowski and others (2015) during 25 October to 5 November 2014 the lava lake was "still under formation" and field surveys carried out failed to find evidence for it. On the other hand, lava fountains were clearly observable in a ~350-m-wide crater, originating from an area of ~20 to 40 m². These fountains ejected materials and exhibited activity that the authors said might evolve into a new lava lake.

Once formed (by 1 November 2014), the lava lake was described as deep-seated and formed in a pit within the caldera's central N to NE area (Campion, 2014; Smets and others, 2014). As mentioned at the top of this report, Smets also noted that the lava lake continued to exist through and beyond January 2015 (the end of this reporting interval).

MIROVA stands for Middle InfraRed Observation of Volcanic Activity, where middle infrared is defined as 0.4-14.4 micrometer wavelengths. The infrared processing system uses source data that comes from the MODIS instrument that flies on the Aqua and Terra satellites. MIROVA makes plots of Volcanic Radiative Power (VRP). These are measurements of the heat radiated by hot volcanic products at the time of satellite acquisition. The VRP is calculated in Watts (W) and represents a combined measurement of the area of the volcanic emitter and its effective radiating temperature. MIROVA calculates the Volcanic Radiative Power (VRP) by using the "MIR method", an approach which was initially introduced by in order to estimate the heat radiated by active fires using satellite data (Wooster et al., 2003).

This approach (also known as Middle InfraRed method) relies on the fact that whenever a hot emitter has an effective radiating temperature higher than 600 K, the excess radiance detected in the MIR region (DLMIR), can be linearly related to the radiative power. Hence, for any individual hot-spot contaminated MODIS pixels, MIROVA calculates the VRP. (VRP = 18.9 x APIX x DLMIR where 18.9 is a best-fit regression coefficient (Wooster and others, 2003), APIX is the pixel size (1 km² for the MODIS pixels) and DLMIR is the above background MIR radiance of the pixel.) When a hot-spot is detected in more than one pixel, the total VRP is calculated as the sum of all pixels detecting a hot-spot.

Figure 57 is a time-series plot for Nyamuragira compiled by the MIROVA infrared processing system. All of the events on the plot that correspond to thermal anomalies are in the categories labeled low, moderate, and high. All of the events in the range moderate to high came from sources within 5 km of the crater (blue data points). Thermal emissions on figure 57 increased in June 2014, were minor for a period from late September to early November 2014, and increased once again for an interval extending through January 2015. Note the continuity of more elevated anomalies starting in November 2014, when there was clear evidence of the lava lake.

Figure 57. MODIS infrared data using MIROVA for the interval May 2014 through January 2015. The vertical scale shows 'Volcanic Radiative Power' (VRP, in Watts on a log scale, see text). Time is on the horizontal scale. As seen in the key at upper left, the blue data points represent those that occurred within 5 km of Nyamuragira's active crater, and the dark gray ones, over 5 km away. Courtesy of MIROVA.

MODIS instrument infrared data is automatically analyzed with the MODVOLC algorithm, creating alerts for cases with above-threshold thermal emissions. During April-May 2014, there were only six days with thermal alerts. Subsequently, the number of alerts increased in June 2014, in concurrence with the lava fountains. There were heightened periods of activity during 22–29 June and 1–3, 10–12, and 28 July. During August and September 2014, thermal events were once again sparse with occurrences only on three days. No events were observed in October. Consistent with other observations of the formation of a lava lake, alerts increased on 1 November and continued during 6–10 and 22–26 November. Thermal events occurred during 10–15 December and on 22, 24, and 31 December 2014. In January 2015, thermal activity was detected regularly during 9–18 and 25–30 January.

Impacts and risks. Virunga Team (2014) posted an article on 18 October 2014 about how a population of twelve chimpanzees took up a new residence at the Virunga National Park headquarters in Rumangabo. The chimpanzees were originally part of the main Tongo group across the valley, but were cut off from them by a lava flow during the Nyamulagira's 2012 eruption. Although the lava flow has cooled, the group has remained, and in the new location is much safer from poachers.

Fighting between the Democratic Republic of Congo (DRC) government and several rebel groups displaced 2-3 million people within that country by February 2014 (UN News Centre, 2014). According to the article, more than 60% of those displaced settled in the Kivu region, including some near to Nyamuragira although the population distribution was not specified for this area alone.

The authors of this article did not mention the situation at the volcano. It may be worth emphasizing that the increased number of people could signify an increased human vulnerability in the event of escalating volcanic activity (Dario Tedesco, Pers. Comm.). Even without a crisis, ongoing strong passive degassing contaminates rainwater, which is the primary water source in parts of the region (Cuoco and others, 2013).

References. Bobrowski, N., Calabrese, S., Giuffrida, G., Scaglione, S., Liotta, M., Brusca, L., D'Alessandro, W., Yalire, M., Arellano, S., Galle, B., Tedesco, D, 2015, Intercomparison of gas emissions from the lava lakes of Nyiragongo and Nyamulagira, DR Congo/ Plume composition and volatile flux from Nyamulagira volcano, (abstract) Geophysical Research Abstracts, 2015 European Geophysical Union Meeting, Vienna, Austria (URL: http://meetingorganizer.copernicus.org/EGU2015/EGU2015-6540.pdf; http://meetingorganizer.copernicus.org/EGU2015/EGU2015-13100-1.pdf)

Campion, R., 2014, New lava lake at Nyamuragira volcano revealed by combined ASTER and OMI SO₂ measurements, 7 November 2014, Geophysical Research Letters (URL: http://onlinelibrary.wiley.com/doi/10.1002/2014GL061808/full)

Calabrese, S., Scaglione, S., Milazzo, S., D'Alessandro, W., Bobrowski, N., Giuffrida, G. B., and Yalire, M., 2014, Passive degassing at Nyiragongo (DR Congo) and Etna (Italy) volcanoes. Annals of Geophysics.

Cuoco, E., Tedesco, D., Poreda, R. J., Williams, J. C., De Francesco, S., Balagizi, C., and Darrah, T. H., 2013, Impact of volcanic plume emissions on rain water chemistry during the January 2010 Nyamuragira eruptive event: implications for essential potable water resources. Journal of hazardous materials, 244, 570-581.

ESA Eduspace, date unknown, Nyiragongo and Nyamuragira, based on USGS, European Science Agency (URL: http://www.esa.int/SPECIALS/Eduspace_Disasters_EN/SEMDGLNSNNG_0.html) [accessed in May 2015]

Oskin, B., 2014, World's Newest Lava Lake Appears in Africa, based on Smets, Campion, etc., 26 November 2014, Live Science (URL: http://www.livescience.com/48914-new-lava-lake-nyamuragira-volcano.html) [accessed in May 2015]

Smets, B., 2015, Renewing activity at Nyamulagira volcano, 30 April 2015, Youtube (URL: https://www.youtube.com/watch?v=w1IHSjsgL48) [accessed in May 2015]

Smets, B., d'Oreye, N., Kervyn, F., 2014, Toward Another Lava Lake in the Virunga Volcanic Field?, 21 October 2014, EOS, Transactions American Geophysical Union (URL: http://onlinelibrary.wiley.com/doi/10.1002/2014EO420001/pdf)

UN News Centre, 2014, Journey to the centre of the earth: UN peacekeepers aid volcanologists in DR Congo, 25 February 2014, United Nations (URL: http://www.un.org/apps/news/story.asp?NewsID=47227&Cr=democratic&Cr1=congo#.VVjdhpPsatB) [accessed in May 2015]

Virunga Team, 2014, The Chimpanzees of Rumangabo, 18 October 2014, Virunga National Park (URL: https://virunga.org/news/the-chimpanzees-of-rumangabo/) [accessed in May 2015]

Wooster, MJ, Zhukov, B, Oertel, D, 2003, Fire radiative energy for quantitative study of biomass burning: derivation from the BIRD experimental satellite and comparison to MODIS fire products. Remote Sensing Of Environment, 86(1), 83-107.

Wright, R., Flynn, L.P., Garbeil, H., Harris, A.J.L., Pilger, E., 2004. MODVOLC: near-real-time thermal monitoring of global volcanism. Journal of Volcanology and Geothermal Research 135, 29–49. doi:10.1016/j.jvolgeores.2003.12.008

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: Benoît Smets, (a) Center for Geodynamics and Seismology, Walferdange, Luxembourg; (b) Vrije Universiteit Brussel, Department of Geography; Earth System Science, Brussels, Belgium; (c) Royal Museum for Central Africa, Department of Earth Sciences, Natural Hazards and Cartography Service, Tervuren, Belgium; Nicolas d’Oreye, European Center for Geodynamics, and Seismology, Walferdange, Luxembourg and National Museum of Natural History, Geophysics/Astrophysics Department, Walferdange, Luxembourg; Nicolas Theys, Belgian Institute for Space Aeronomy, Brussels, Belgium; and Julien Barriere, European Center for Geodynamics and Seismology, Walferdange, Luxembourg and National Museum of Natural History, Geophysics/Astrophysics Department, Walferdange, Luxembourg; Goma Volcanological Observatory (GVO, aka Observatoire Volcanologique de Goma), Mt. Goma, Goma, Democratic Republic of Congo; Jesse Allan and Robert Simmon, NASA Earth Observatory (URL: http://earthobservatory.nasa.gov); NASA MEASURES (URL: https://so2.gsfc.nasa.gov/); MODVOLC alerts team, Hawai’i Institute of Geophysics and Planetology (HIGP), University of Hawai’i at Manoa, 1680 East-West Road, Post 602, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); and MIROVA, Universities of Turin and Florence, Italy, Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Shishaldin, located on Unimak Island, is one of the most active volcanoes within the Aleutian Islands (figure 6). It is also the tallest volcano within the Aleutians, and has a symmetric cone and a basal diameter of 16 km.

In this Bulletin report, we summarize activity at Shishaldin from January to December 2009 and from January 2014 to March 2015. During 2009, Shishaldin emitted steam plumes, generated thermal anomalies, and underwent several episodes of tremor in what was considered to be a questionable eruption. From 2014 through March 2015, Shishaldin experienced elevated surface temperatures, steam emissions, and starting in March 2014, an ongoing low-level lava eruption within the summit crater that occasionally deposited ash on the upper flanks. As of March 2015, this low-level eruption continued.

Considerable information in this report was found in material released by the Alaska Volcano Observatory (AVO). For activity in 2009, we drew heavily on McGimsey and others (2014). Our last Bulletin report (BGVN 33:08) discussed activity at Shishaldin in February 2008, when a pilot reported a 3 km altitude ash plume.

Figure 6. Map showing the location of Shishaldin. The volcano is located near the center of Unimak Island, and is the tallest peak and one of the most active volcanoes within the Aleutians Islands. False Pass, located 38 km to the NE, is the closest town. Map is courtesy of Alaska Volcano Observatory and Alaska Division of Geological & Geophysical Surveys.

January-December 2009. This section of the report summarizes activity at Shishaldin throughout 2009. According to AVO's web page, activity began on 5 January (± 1 month) and ended on 16 August and was characterized as a questionable eruption. According to McGimsey and others (2014, a report cited by the AVO), increased seismicity, small steam plumes as well as thermal anomalies characterized activity during 2009. Steam plumes are considered normal at Shishaldin according to McGimsey and others (2014).

McGimsey and others (2014), stated that there was an increase in observed thermal anomalies at Shishaldin in early January 2009. On 5-6 January, an AVHRR satellite image of Unimak Island showed a thermal anomaly centered on Shishaldin's summit crater. The anomaly reached a 2-pixel size on 6 January. There was also a slight increase in seismicity. These observations indicated a clear departure from background conditions. On 6 January, AVO increased Shishaldin's Aviation Color Code (ACC) from Green to Yellow and the Volcano Alert Level from Normal to Advisory. That day, pilots and ground observers reported a constant steam plume rising ~300 m above the summit and drifting 16-25 km SE (McGimsey and others, 2014).

Over the next few days, AVO continued observing a thermal anomaly in satellite images. On 7 January 2009, AVO received both a pilot report and observations from Cold Bay (93 km to the NE, figure 6) noting a vigorous steam plume rising from Shishaldin. On 8 January, satellite images showed a steam-filled crater with no ash on the flanks (McGimsey and others, 2014). AVO's 9 January 2009 Weekly Update stated "Although detection of a thermal anomaly is rare at this volcano, it is not certain that this unrest will lead to an eruption. A thermal anomaly was observed in the months leading up to the last significant eruption at Shishaldin [that occurred] in 1999; this fact, combined with the likelihood that an eruption at Shishaldin could occur with little or no seismic precursors, drove AVO's decision to raise the Color Code and Alert Level."

On 11 January 2009, a photo captured by a pilot showed pulsing steam plumes. Two days later, AVO seismologists identified a minor, low-amplitude tremor that persisted for a few weeks. According to McGimsey and others (2014), during the next few weeks, seismicity remained low, a few thermal anomalies were detected, and steaming was observed.

According to AVO's 13 February 2009 Weekly Update, a very weak thermal anomaly was detected on 3 February. The Update went onto say that on 11 February, the ACC was downgraded to Green and the Volcano Alert Level lowered to Normal, due to Shishaldin's return to background conditions. That Update also mentioned that seismic activity had remained low, since decreasing to background levels in late December 2008.

McGimsey and others (2014) reported that over the next seven weeks (mid-February to early April 2009) occasional thermal anomalies were observed along with continuous low-level tremor, which was not considered unusual. On 7 April, a pilot reported that he saw Shishaldin steaming more vigorously than he had previously observed during his weekly flights past Shishaldin over the last 16 months. That day, a thermal anomaly was also observed in satellite imagery (McGimsey and others, 2014).

On 20 April 2009, thermal activity at Shishaldin's summit spiked based on multiple thermal anomalies containing saturated pixels observed in satellite imagery (McGimsey and others, 2014). According to McGimsey and others (2014), these anomalies indicated high ground temperatures (greater than 300°C). This level of thermal activity was last seen before Shishaldin's eruption in 1999. On 5 May, a pilot reported steaming from Shishaldin and a passenger on a different flight reported dark-colored linear features on the N side of the summit. According to McGimsey and others (2014), these linear features were later interpreted as minor streams of dirty water trailing downslope.

McGimsey and others (2014) reported that throughout June 2009, thermal anomalies were detected on about one third of days, with a particularly strong anomaly being recorded on 9 June. No unusual seismic activity was noted. On the night of 25 June, an ASTER thermal infrared satellite image captured a thermal anomaly and a 22 km-long steam plume extending E-NE from Shishaldin. Then on 29 June, an observer in Cold Bay (93 km NE) reported increased steaming at Shishaldin over the past few days.

In the first week of July 2009, thermal anomalies at Shishaldin increased in intensity, with a return of saturated pixels, indicating high ground temperatures. On 10 July, AVO increased the ACC from Green to Yellow and the Volcano Alert Level from Normal to Advisory, due to the increase and continued presence of thermal anomalies. Seismicity and deformation did not change significantly during this time and satellite data did not show any noteworthy SO2 emissions. On 13 July, emissions were detected in satellite imagery and a pilot reported a steam plume rising 600 m above Shishaldin and moving NW. On 15 July, the satellite-based Ozone Monitoring Instrument (OMI) detected a small cloud rich in SO2 that originated from Shishaldin.

For the rest of July and the first half of August 2009, steaming was observed from Shishaldin's summit, when weather permitted. Thermal anomalies were also detected in satellite images during August; one example was on 16 August.

In mid-September 2009, pressure sensors at Shishaldin detected anomalous airwaves. According to McGimsey and others (2014), the airwaves could be indicative of minor explosions; however, in retrospective analysis of the data collected by the pressure sensors, the airwaves were found to be a common occurrence and linked to episodic gas bursts (examples of which were seen during 2003-2004).

On 19 October 2009, due to the continued absence of thermal anomalies, a decrease in steam emissions and seismicity considered within background levels, AVO lowered the ACC to Green and the Volcano Alert Level to Normal. Besides a weak thermal anomaly detected on 2 November, Shishaldin remained quiet for the remainder of 2009.

Non-eruptive interval during 2010-2013. AVO reported no unusual activity at Shishaldin between the years 2010 and 2013. In 2010, 2012 and 2013, AVO uploaded photos of Shishaldin, some of which showed the volcano emitting steam (figure 7).

Figure 7. Photograph of Shishaldin emitting a steam plume on 14 September 2013. The photograph was taken from Korpiewski (2013).

Activity during January 2014-March 2015. According to AVO's website, increased activity was detected on 28 January 2014 at Shishaldin. A low-level lava eruption within the summit crater then began in March 2014 and continued through March 2015. In addition to the ongoing eruption, there were also instances of heightened activity, one such example occurring around 28 October 2014, after AVO noted several days of elevated tremor and stronger thermal anomalies.

AVO provides a description that synthesizes Shishaldin activity from late January 2014 through March 2015 on their website (as accessed on 1 May 2015). What follows is a quote of that description. For greater detail on activity during this interval, please see AVO's Weekly and Daily reports. Any information added to the quote by Bulletin editors has been [bracketed]. Bulletin editors also included pictures, depicting certain events that were described in the quote.

"On January 30, 2014, the Alaska Volcano Observatory raised the Volcano Alert Level to ADVISORY and the Aviation Color Code to YELLOW for Shishaldin, based on satellite observations of the previous days [figure 8]. Satellite observations included increased surface temperatures in the summit crater, as well as increased emissions of steam. Similar levels of unrest were last observed during 2009, and did not result in an eruption."

Figure 8. Satellite image of Shishaldin on Unimak Island captured at 0838 UTC on 30 January 2014. The image shows the elevated surface temperatures in the summit crater of Shishaldin. According to the AVO caption for this image, "This mid-infrared image is scaled so that warm values are bright white and cold values (like high clouds are dark). The elevated surface temperatures are visible as the white pixels within the yellow circle that indicates the location of Shishaldin." Image was created by Dave Schneider and is courtesy of Alaska Volcano Observatory/ U.S. Geological Survey.

The quote of AVO's description of Shishaldin during January 2014 and March 2015 continues here:

"For the next week, persistent elevated surface temperatures were visible in satellite imagery of the summit crater during clear-weather intervals. On February 7, a possible volcanic cloud was observed in satellite images beginning around 1545 UTC (6:45 AKST). This cloud may have resulted from a small explosive event at the volcano. The event was small enough that it was not detected by the one working seismic station near the volcano, but it appears to coincide with a signal recorded by a nearby tiltmeter. Satellite images suggest that the cloud may have reached as high as [7.6 km above sea level], was ash-poor, and short-lived. There was no evidence of elevated surface temperatures observed in satellite data immediately following this event, suggesting it was primarily a gas event and very little to no hot material was produced or deposited on the flanks of the volcano.

"On March 19, elevated surface temperatures were again detected in satellite data, accompanied by ground-coupled airwaves seen in the seismic data. On March 28, after seeing persistent elevated surface temperatures since March 19, and continuing ground-couple airwaves, AVO data analysis showed temperatures in satellite images consistent with the eruption of lava within the summit crater. [The 28 March 2014 Volcanic Activity Notification (VAN) stated, 'The current activity appears to be confined to the deep summit crater and there have been no observations of lava on the flanks of the volcano or surrounding the summit crater.']

"During the week of April 11, minor ash deposits extending several hundreds of meters from the summit crater were observed in satellite imagery. Infrasound signals from Shishaldin were occasionally detected at sensors located at Dillingham [585 km to the NE] and Akutan Island [145 km to the SW].

"Throughout April, May, June, and July, elevated surface temperatures consistent with low-level eruptive activity in the summit crater were observed in satellite data, and small explosion signals were detected in seismic data. Occasional clear webcam views often showed minor steaming. An AVO overflight on August 10 showed hot, glowing material in the crater [figure 9]. On August 13, AVO received a pilot report of a low-level plume. [On 23 August, a pilot reported a steam-and-ash plume rose ~300 m above the summit and drifted NE.] Similar levels of activity continued throughout August, September, and October."

Figure 9. Photograph of incandescent material within Shishaldin's steaming summit crater and steam being emitted. This aerial photograph was captured on 10 August 2014 and shows ash deposited on the snow (in the left of the photo). Photo was captured by Cyrus Read and is courtesy Alaska Volcano Observatory/ U.S. Geological Survey.

The final paragraphs of our quote of AVO's description of Shishaldin activity during January 2014 and March 2015 are below:

"On October 28, 2014, AVO noted an increase in intensity over the past several days, including elevated seismic tremor and stronger thermal anomalies. New deposits of ash and ballistics darkened the summit area, and the activity was also recorded on infrasound stations at Akutan and Dillingham. [On 26 October, clear webcam images revealed tephra deposits at the summit. The 28 October 2014 VAN stated that these new deposits indicated, '…the activity was energetic enough to eject material from a depth of several hundred meters (~600 ft) within the summit crater.'] This period of increased tremor lasted for several further days.

"On November 24, seismic activity at Shishaldin again increased, . . .. This increased seismicity declined by November 27, but remained above background. [AVO's 28 November 2014 Weekly Update said, 'Although the level of seismic activity has declined during the week, it is likely that a low-level lava eruption is ongoing within the summit crater of the volcano.'] Weak, but above background seismicity, along with weakly elevated crater surface temperatures, continued in December 2014 and January 2015.

"In late January 2015, strongly elevated temperatures were observed in satellite images, consistent with active lava within the crater. [AVO's 23 January 2015 Weekly Update stated, 'Activity [over the past week was] consistent with what we have observed at Shishaldin during the past several months, which includes lava effusion in the crater with occasional production of small amounts of ash restricted to the volcano's upper flanks.'] A wispy, low-level ash emission was observed in webcam images on February 2, 2015.

"Throughout February and March 2015, clear satellite views often show elevated surface temperatures at the crater, seismicity remained above background, and low-level steam emissions were frequently seen in webcam images. It is likely that low-level eruptive activity continued within the summit crater."

References. Alaska Volcano Observatory (AVO), Shishaldin reported activity, URL: https://www.avo.alaska.edu/volcanoes/volcact.php?volcname=Shishaldin, date accessed: 1 May 2015

Alaska Volcano Observatory (AVO), Shishaldin reported activity, Event specific information [for 2009], URL: https://www.avo.alaska.edu/volcanoes/activity.php?volcname=Shishaldin&page=basic&eruptionid=76, date accessed: 1 May 2015

Alaska Volcano Observatory (AVO), Shishaldin reported activity, Event specific information [for 2014], URL: https://www.avo.alaska.edu/volcanoes/activity.php?volcname=Shishaldin&page=basic&eruptionid=77, date accessed: 1 May 2015

Alaska Volcano Observatory/Alaska Division of Geological & Geophysical Surveys, 2009, URL: http://www.avo.alaska.edu/images/image.php?id=16190, date accessed: 1 May 2015

Korpiewski, J., U.S. Coast Guard, 2013, URL: http://www.avo.alaska.edu/images/image.php?id=57087, date accessed: 13 May 2015

McGimsey, R.G., Neal, C.A., Girina, O.A., Chibisova, Marina, and Rybin, Alexander, 2014, 2009 Volcanic activity in Alaska, Kamchatka, and the Kurile Islands - summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Scientific Investigations Report 2013-5213, 125 p., URL: http://pubs.usgs.gov/sir/2013/5213/

Read, C., Alaska Volcano Observatory/ U.S. Geological Survey, 2014, URL: http://www.avo.alaska.edu/images/image.php?id=66771, date accessed: 13 May 2015

Schneider, D., Alaska Volcano Observatory/ U.S. Geological Survey, 2014, URL: http://www.avo.alaska.edu/images/image.php?id=57691, date accessed: 13 May 2015.

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 the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), the Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and the Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, and NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845, USA (URL: http://vaac.arh.noaa.gov/).