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).

According to the Sakurajima Volcano Research Center (SVRC) at Kyoto University, an eruption started on 4 June 2006 at the Showa crater, a spot that differs from vents active in recent decades at the summit of Minami-dake ("south mountain"; BGVN 31:06 and many previous reports). The Showa crater resides on the E slope of Minami-dake at an elevation of ~ 800 m (figures 23, 24, and 25). Showa crater was formed in a 1946 eruption; the 1946 vent was the source of lava flows that spread E and then branched to travel S and ENE (figure 25).

Figure 23. Map images showing Sakura-jima stratovolcano and environs on Japan's Kyushu island (~ 1,000 km S of Tokyo). (left) Image from Google Earth showing the S end of Kyushu Island. Population centers are labeled. Sakura-jima forms the dominant topographic feature in Kagoshima Bay. The Osumi Peninsula is to the E; the Satsuma Peninsula to the W. (right) Image from Google Earth showing terrain features looking NW towards the upper portions of Kagoshima Bay. Courtesy of Google Earth.

Figure 24. A sketch map focused on the geologic context of Sakura-jima, the Aira caldera, and adjacent calderas. The Kagoshima graben forms the Bay of the same name. The graben also lies coincident with several caldera margins. Sakura-jima resides at the S portion of Aira caldera. Modified slightly from Okuno and others (1998).

Figure 25. A geological map of Sakura-jima shown with several key features and eruptive dates labeled. Topographic highs from N to S include Kita-dake (K), Nika-dake (N), and Minami-dake (M). Craters at the summit of Minami-dake have been the active in past decades, but the eruption that started on 4 June eruption vented at Showa crater (S). An E flank lava flow (the Taisho Lava of 1914-1915) joined what had been an island's SE side to the shore (arrow at lower right labeled "j" aims at the zone of contact). Fringing the roughly circular former island are several areas of submarine volcanic and intrusive deposits (labeled here with the abbreviation "subm."). For example, the large area budding NE from the island consists of submarine and intrusive rocks of 1779-1780. Many of the Holocene eruptive deposits are dacites and andesites. They commonly bear pyroxene (and also sometimes, olivine). Besides lava flows, deposits include welded air-fall and pyroclastic-flow deposits (in some cases showing rheomorphosed textures indicative of movement downslope after forming a welded mass). From the Geologic Survey of Japan, AIST website (after Fukuyama and Ono, 1981 and Kobayashi, 1988).

Unfortunately, at press time many details still remained unavailable to Bulletin editors regarding the duration and character of the return of venting at Showa crater. It is also unclear to what extent the Minami-dake summit craters continued to participate in the emissions.

The 4 June 2006 eruption continued intermittently, including an evening eruption on 7 June which sent an ash column ~ 1 km above the crater. Figure 26 shows one such eruption on 6 June.

Figure 26. A photograph of Sakura-jima erupting at 1231 on 6 June 2006 from Showa crater. Courtesy of SVRC, Disaster Prevention Research Institute, Kyoto University.

A series of plots describe the short- and long-term seismicity and volume of magma supplied at Sakura-jima (figures 27 and 28). The number of shallow earthquakes had increased since the middle of March 2006 (figures 26 and 27), and small volcanic tremors with a duration shorter than 2 minutes had increased since the middle of May 2006. GPS data showed continued inflation in the N part of the Aira caldera, an observation attributed to incoming magma. Kazuhiro Ishihara, director of SVRC, commented that the present eruption was considered to be related to magma accumulating in the Aira caldera and searching for an exit.

Figure 27. A multi-year (1995 to mid-2006) view of Sakura-jima's activity: (top) monthly A-type earthquakes, (middle) monthly number of explosions (determined geophysically, exact method undisclosed), and (bottom) the cumulative volume of magma supplied. Courtesy of SVRC, Disaster Prevention Research Institute, Kyoto University.

Figure 28. Plot of the daily number of volcanic earthquakes at Sakura-jima for the period 1 January-7 June 2006. Courtesy of SVRC, Disaster Prevention Research Institute, Kyoto University.

Table 14 presents a chronology of ash-plume observations made since the previous Bulletin report (BGVN 31:06). The table is based primarily on reports from Tokyo Volcanic Ash Advisory Center (VAAC) and covers the interval 7 June 2006 to 20 March 2007. Most of the plumes described did not exceed 3 km altitude. The tallest plume recorded on the table, an ash plume on 20 March 2007, rose to 3.7 km altitude.

Table 14. Heights and drift of plumes and their character at Sakurajima from June 2006-March 2007. Some of the data during mid-June 2006 were previously reported, but new information has emerged. Courtesy of SVRC and Tokyo Volcanic Ash Advisory Center.

Volcanic hazards research. Lee and others (2005) reported the successful remote measurement of significant amounts of ClO (as well as BrO and SO₂) in a volcanic plume from Sakura-jima during May 2004. Near the volcano they also observed halogen-catalyzed, local surface ozone depletion. The investigators employed ground-based, multi-axis, differential optical absorption spectroscopy. Their results help document the presence of a wide range of chemical species that have potential health implications for populations living nearby.

The center of Kagoshima City (population ~ 550,000) sits ~ 10 km from Minami-dake's summit and ~ 4 km from Sakura-jima's E shore (just off figure 24, but along the trend of the arrow labeled KC). According to Durand and others (2001), "Since 1955 the city has been subjected to ashfall from Sakura-jima. Until 1990 ashfalls occurred up to twice per week, although this has decreased in frequency in recent years."

Durand and others (2001) comment that "[Kagoshima City] presents a good opportunity to study the impacts of volcanic ash on key services, or 'lifelines.' In addition, the city provides a chance to see how lifelines have been adapted to counter any problems presented by ashfalls." They also noted that, "The advice from Kagoshima would seem to be that during an ashfall event, people should bring in the washing and shut the doors and windows. People who have to go out and work in ashfall should wear goggles and a face mask. In Kagoshima, umbrellas are the only form of protection for many people going to work during ashfall events."

References. Durand, M.; Gordon, K .; Johnston, D. ; Lorden, R. ; Poirot ,T. ; Scott, J. ; and Shephard, B.; 2001; Impacts of, and responses to ashfall in Kagoshima from Sakurajima Volcano?lessons for New Zealand. Science report 2001/30, Institute of Geological & Nuclear Sciences; Lower Hutt, New Zealand, November 2001 53p. (ISSN 1171-9184, ISBN 0-478-09748-4).

Fukuyama, H. and Ono, K., 1981, Geological Map of Sakura-jima, scale 1:25,000

Kobayashi, Tetsuo, 1988, Geological Map of Sakurajima Volcano, A Guidebook for Sakura-jima Volcano, in Kagoshima International Conference on Volcanoes, 1988 (1:50,000).

Lee, C., Kim, Y. J., Tanimoto, H., Bobrowski, N., Platt, U., Mori, T., Yamamoto, K., and Hong, C. S., 2005, High ClO and ozone depletion observed in the plume of Sakurajima volcano, Japan, Geophysical Research Letters, v. 32, L21809, doi:10.1029/2005GL023785.

Okuno, Mitsuru; Nakamura, Toshio, and Kobayashi, Tetsuo, 1998, AMS 14C dating of historic eruptions of the Kirishima, Sakura-jima and Kaimon-dake volcanoes, Southern Kyushu, Japan. Proceedings of the 16th International 14C Conference, edited by W. G. Mook and van der Plicht, RADIOCARBON, Vol. 40, No. 2, 1998, P. 825,832.

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

Information Contacts: Sakura-jima Volcano Research Center, Disaster Prevention Research Institute (DPRI), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan (URL: http://www.dpri.kyoto-u.ac.jp/~kazan/default_e.html); Tokyo Volcanic Ash Advisory Center (VAAC), Japan Meteorological Agency (JMA) (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

Brief periods of effusive activity took place during January to mid-April 2006 (BGVN 31:05), with ash-and-steam emissions reported as late as 18 June 2006. Activity has continued since that time through early June 2007, with evidence coming from either MODIS thermal satellite data, observations of glow, or plume observations from the ground or satellites (figure 8). It appears that there were three episodes of increased plume generation, two periods of frequent glow observations, and almost daily MODIS anomalies over that one-year time frame.

Figure 8. Summary of daily activity at Bagana, 18 June 2006-5 June 2007. Plumes are all varieties (steam or ash) reported by RVO or Darwin VAAC; glow as reported by RVO; MODIS data indicates days with at least one thermal pixel detected. Compiled from MODIS/HIGP data, Darwin VAAC reports, and RVO reports.

The Rabaul Volcano Observatory (RVO) noted that between 18 September and 4 December 2006 only white vapor was released; some of these emissions were forceful. Jet engine-like roaring noises were heard on 11 and 20 November. Variable glow was visible on 25-26 September, 15, 20, and 29 October, 15-21 November, and 4 December. The lava flow on the S flank was active only on 15 October.

There were no aviation warnings after June until a diffuse plume became visible on satellite imagery on 22 November. Based on satellite imagery, the Darwin Volcanic Ash Advisory Centre (VAAC) reported subsequent plumes on 5 December (ash), 21-22 December (ash-and steam), and 9 January 2007.

RVO reported that white vapor emissions from the summit crater continued during 10 January-21 May 2007. Emissions were occasionally forceful and were accompanied by ash clouds on 3 and 17 March, as well as 1 and 3-5 April. Summit incandescence was visible on 7, 8, 20, and 24 March, and 17 May. Based on satellite imagery, the Darwin VAAC reported diffuse plumes to altitudes of 2.4 and 3 km on 10 March and 20 May, respectively. Forceful, white emissions on 21 May produced plumes that rose to an altitude of 2.3 km and drifted W. Diffuse ash-and-steam plumes were seen in satellite images again on 22 and 28 May, rising to altitudes of 3.7 and 3 km, respectively.

Moderate Resolution Imaging Spectroradiometers (MODIS) satellite thermal anomaly data reported by the Hawai'i Institute of Geophysics and Planetology (HIGP) revealed frequent thermal anomalies during 20 June-24 July 2006, 16 August-3 October 2006, 9 November 2006-23 January 2007, and 13 February-2 June 2007.

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

Information Contacts: Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) Hot Spots System, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Activity declined at Bulusan in late June 2006 after a series of 10 explosions that began on 19 March 2006 (BGVN 31:09). Between 30 August and 1 September steam plumes reached up to 350 m above the summit; the plumes drifted NW and SE. This report summarizes Bulusan's activity from 10 October 2006 through 12 May 2007 (table 4). Hazard maps created by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) illustrate the risks to the large numbers of cummunities in the vicinity of the volcano (figure 7). Review of the available MODIS data indicates no thermal alerts during the year prior to 31 May 2007.

Table 4. An overview of Bulusan's activity, as noted by PHIVOLCS during 10 October 2006 through 12 May 2007. Courtesy of PHIVOLCS.

Figure 7. Hazards maps for Bulusan showing susceptibility to pyroclastic flows and surges (left), and lava flows and lahars (right). Courtesy of PHIVOLCS.

PHIVOLCS reported an explosion from Bulusan on 10 October that produced an ash-and-steam plume that rose to 4.5 km altitude and drifted mainly SE and SSW. Light ashfall (1.5-5.0 mm thick) was reported in neighboring towns downwind. Based on seismic data, the activity lasted for 9 minutes. On 11 and 12 October, steam plumes drifted SW and SSW. Another explosion occurred on 19 October. The following day, steam plumes drifted W and WSW. On 23 October, an explosion produced a brownish ash plume that rose to about 2.6 km and drifted SE and SW. Light ashfall (trace to 0.5 mm thick) from the 19 and 23 Cctober explosions was reported from neighborhoods in the municipality of Irosin, about 7 km S of the summit.

During 25-26 October, PHIVOLCS reported a lahar that deposited sediments 15 cm thick along a tributary leading to the Gulang-gulang River. According to news articles, the lahar mobilized boulders as large as trucks and caused at least 96 people to evacuate. During 30-31 October, ash explosions generated a light gray ash-and-steam plume that rose to 2.3 km and drifted NNE. Later field inspection revealed ashfall (trace to 1 mm) N of the volcano, as well as in the municipalities of Casiguran and Gubat, about 12 km SSE and 18 km NNE, respectively, from the summit. Two explosion-type earthquakes recorded late on 31 October were followed by ashfall in Casiguran, Malapatan, and Irosin.

News articles and wire services reported that Bulusan emitted ash accompanied by rumbling noises and lightning flashes on 20 December. Clouds hindered a view of the summit. Ash deposits up to 4 mm thick were noted in several villages in the foothills. A news report in News Balita noted a plume of gas and "white ash" on 22 December.

In January 2007, PHIVOLCS reported that an explosion from the summit on 24 January lasted about 10 minutes, based on seismic interpretation. Observation was inhibited due to cloud cover. Ashfall was reported SW of the volcano.

On 15 March, news media reported that ash fell on Bulusan's SW slopes and nearby villages. A resident volcanologist stated that ashfall was caused by voluminous steaming during 12-15 March, not explosions. Other news articles stated that eruptions on 8 April produced ash plumes that rose to altitudes of 3.1-6.6 km.

PHIVOLCS reported another ash explosion on 12 May 2007 with an eruption column reaching a maximum height of 4 km above the summit before drifting to the WSW and WNW. The activity was accompanied by rumbling sounds and was recorded by the seismic network as an explosion type earthquake that lasted for about 35 minutes. Prior to the explosion, during 9-12 May, an increase in the daily number of volcanic earthquakes was noticed, with 42, 65 and 97 events recorded.

Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph); Tokyo Volcanic Ash Advisory Center, Tokyo, Japan (URL: http://www.jma.go.jp/jma/jma-eng/jma-center/vaac/index/html); Inquirer.net, Philippines (URL: http://www.inquirer.net/); Associated Press (URL: http://www.ap.org/); News Balita, Philippines (URL: http://news.balita.ph/).

The new island at Home Reef that was constructed by the 8-11 August 2006 felsic shallow marine explosive eruption (BGVN 31:09) was visited on 18 February 2007 by Scott Bryan (Kingston University, United Kingdom), Alex Cook (Queensland Museum, Australia), and Peter Colls (University of Queensland, Australia). The initial aim of field research was to map and describe the volcanic geology of the new island at Home Reef and to collect samples for comparison to floating pumice generated by the eruption (Bryan, 2007).

Island observations. Satellite imagery on 4 October 2006 showed an 800-m-long elongate island (0.23-0.26 km²), which was being rapidly modified by wave erosion (BGVN 31:10). An overflight by the RNZAF on 7 December 2006 revealed a roughly circular island, 450 m in diameter and up to 75 m above the water line (BGVN31:12). Upon arrival on 18 February 2007, the scientists found that only a small (50-75 m diameter) <5 m high low-relief wave-reworked "pumice mound" remained at the southern windward end of the Home Reef shoal (figure 23). Due to strong winds and large swells, landing on the tidally-exposed mound was not possible and it could only be viewed from a couple of hundred meters offshore. The location of the mound (18.993°S 174.758°W) is close to that reported for the circular island observed on 7 December 2006. Swells 2-m high or greater were strongly impacting the mound, with the largest waves almost completely engulfing and sweeping over the mound at half-tide.

Figure 23. View to the NW of the wave-reworked pumice mound at Home Reef, as seen on 18 February 2007. The diameter of the mound is ~ 75 m. Note the scattered large blocks on the upper surface of the mound. Late Island is in the background at right. Courtesy of Scott Bryan.

The morphology of the island suggests that no primary subaerial island-building deposits remain from the eruption and that complete reworking has occurred of the previously observed cone. On the southern side of the pumice mound were scattered large (>1 m diameter), outsized blocks (10-20 in number) on the mound surface (figure 23) that were largely immobile in the waves. Slopes of the mound reflected wave run-up and the pumiceous material comprising the mound appeared to be relatively coarse and well-sorted. There was little entrained particulate material in the water column downwind and downcurrent, but considerable amounts of material within the surf zone surrounding the island, coloring the water brown. A considerable area of discolored water (green, translucent milky) extended N of the mound for more than 500 m. Several smaller lobes or plumes extended off the W side of the main body of discoloration.

A strong sulfurous odor was detected downwind (NW) of the mound, indicating that magma was continuing to cool and degas at shallow levels in the seamount seven months after the eruption; no surface plume was visible. Surface water temperature measurements did not detect any thermal anomalies, recording ambient water temperatures (28-29°C).

Local pumice sightings. Downwind and downcurrent of the mound were small scattered pumice stringers forming orange-brown slicks a few meters to tens of meters long, characterized by low pumice clast abundance and size (usually 0.5-1 cm diameter). The pumice fragments were generally moderate to high sphericity grains, but some more platy pumice fragments were also sampled. Some clasts had orange to brown surface stains, reflecting hydrothermal alteration since the eruption. Most grains showed some signs of abrasion. Orange-brown algal clumps or coagulates floating on the ocean surface were associated with the stringers.

Small pumice rafts were also encountered around some of the islands at the SW end of the Vava'u Group during the week of 17-24 February (figure 24). The pumice rafts had lateral extents of tens of meters, but other flotsam (leaf, twig, sea grass and plastics) was also present. Pumice clast sizes ranged from ~ 2 mm up to 6 cm, and some of the gray pumice possessed orange-brown surface hydrothermal staining. Some rafts had abundant attached fauna, dominated bygoose barnacles (Lepas sp.) ~ 2-7 mm long. Much of these pumice rafts reflected remobilization of previously stranded material from neighboring beaches, and many SE-facing beaches had been stripped of pumice by strong SE trade winds.

Figure 24. Pumice slick from Home Reef found on the W side of Nuatapu Island, 21 February 2007. Note other flotsam (leaves, plastic) within the slick. Courtesy of Scott Bryan.

Many beaches had several pumice strandline deposits, the lowermost of which reflected tidal sorting. Dominantly lapilli-sized gray pumice formed the deposits, whereas a black glassy, moderately vesicular pumice of higher density was a notable feature of the highest strandlines. There were also abundant pumice clasts with an orange-brown staining on clast surfaces.

Floating pumice reaches Australia. Pumice rafts and beach strandings were reported previously as the pumice drifted westward past the Lau and Fiji islands and on to Vanuatu in November 2006. A major influx of pumice reached the E coast of northeastern Australia during March and April 2007, seven to eight months after the eruption. Pumice was first noticed passing the offshore islands of Willis Island (16.30°S, 149.98°E) in early February, and Lizard Island (14.66°S 145.47°E) the last week of February. Pumice strandings along the eastern Australian coast began in March in northern Queensland, with a substantial stranding occurring in mid-April corresponding to a change to easterly and northeasterly onshore wind conditions and king tides. This stranding event extended for more than 1,300 km along the Queensland and northern New South Wales coast.

Most stranded pumice clasts ranged in size from 1-4 cm diameter, with the largest clasts up to 17 cm diameter. Pumice clasts were fouled by a variety of organisms, primarily goose barnacles (Lepas sp.) up to 2.7 cm long, molluscs, bryozoa, and dark green algae (figure 25), with serpulids, oysters and other species of algae (e.g., Halimeda) less abundant. A substantial proportion of stranded pumice material remains on beaches inshore from the Great Barrier Reef. However, little stranded material has remained on exposed beaches south of 25°S, to the extent that some beaches still have more pumice preserved from the 2001 eruption of an unnamed Tongan seamount about 85 km NW of Home Reef.

Figure 25. Closeup of a pumice clast from Home Reef that reached Marion Reef (19.095°S, 152.390°E), Australia, fouled by goose barnacles (Lepas sp.), bryozoa, and mollusc. Coin is 2 cm in diameter. Courtesy of Scott Bryan.

Seismicity. Although no seismicity has been reported that was detected during the eruption, Robert Dziak identified seismic signals from Home Reef in March 2006. The East Pacific hydrophone array maintained by NOAA recorded 52 earthquakes over a 12-hour period beginning at 1700 UTC on 12 March 2006. The arrivals were all very clear and had medium to low T-wave amplitudes.

Reference. Bryan, S.E., 2007, Preliminary Report: Field investigation of Home Reef volcano and Unnamed Seamount 0403-091: Unpublished Report for Ministry of Lands, Survey, Natural Resources and Environment, Tonga, 9 p.

Geologic Background. Home Reef, a submarine volcano midway between Metis Shoal and Late Island in the central Tonga islands, was first reported active in the mid-19th century, when an ephemeral island formed. An eruption in 1984 produced a 12-km-high eruption plume, copious amounts of floating pumice, and an ephemeral island 500 x 1500 m wide, with cliffs 30-50 m high that enclosed a water-filled crater. Another island-forming eruption in 2006 produced widespread dacitic pumice rafts that reached as far as Australia.

Information Contacts: Scott Bryan, School of Earth Sciences & Geography, Kingston University, Kingston Upon Thames, Surrey KT1 2EL, United Kingdom; Peter Colls, School of Physical Sciences, University of Queensland, St Lucia, Queensland 4072, Australia; Robert Dziak, NOAA Pacific Marine Environmental Laboratory (PMEL), Hatfield Marine Science Center, 2115 SE Oregon State University Drive, Newport, OR 97365, USA.

Eruptive activity at Manam has generally been low following a significant explosion in late February 2006 (BGVN 31:02). Between March and July 2006 the Rabaul Volcano Observatory (RVO) reported intermittent, milder, ash explosions (BGVN 31:06). Similar variable activity has continued into early May 2007, with plumes frequently identified on satellite imagery by the Darwin Volcanic Ash Advisory Centre (VAAC).

RVO received a report that four people were swept away by a mudflow in the early hours of 13 March following heavy rainfall on the northern part of the island. A 5th person was reportedly critically wounded and in a hospital.

Activity during August-December 2006. On 4 and 5 August, an ash plume was visible on satellite imagery extending 30 km NW. Ash plumes were emitted again during 14-15August. Over the next couple of days, the emissions became more diffuse and weak incandescence was observed at night. Based on pilot reports and satellite imagery, continuous emissions during 17-21 August eached altitudes of 3.7 km and drifted NW. Eruptive activity from Main Crater during 22-23 August consisted mainly of dark brown-to-gray ash plumes that rose 1-2 km above the summit and drifted W and NW. The Darwin VAAC reported that eruption plumes were visible on satellite imagery on 23 and 26 August, extending NW. Southern Crater continued to release only diffuse white vapor.

From the end of August to 5 September 2006, the Darwin VAAC reported that ash-and-steam plumes reached altitudes of 4.6 km and drifted W. Steam plumes with possible ash were visible on imagery below 3 km and drifted NE. RVO reported mild eruptive activity during 15-17 October that consisted of steam and ash plumes. White vapor plumes were visible from Southern Crater and intermittently from Main Crater. Main Crater produced gray ash plumes on 19 October. Weak incandescence was seen during 15-17 and 29 October.

During 1-13 November, white vapor plumes rose from Southern and Main craters. Incandescence was noted from both craters during 8-10 November and from Main Crater on 12 November. On 13 November a diffuse plume seen on satellite imagery drifted W. Steady incandescence was again observed from Main Crater during 8-10 December and bluish white vapor emissions during 6-9 December changed to a darker gray on 10 December. Weak glow continued from Main Crater during 14-18 December and a white vapor plume rose just above 2 km altitude. Based on satellite imagery, diffuse plumes drifted mainly W during 13-15 December. The daily number of volcanic earthquakes fluctuated between 700 and 1,000.

Activity during January-May 2007. RVO reported that mild eruptive activity and emissions of white vapor plumes from Main Crater were observed during 1-14 January. Brown-to-gray ash plumes accompanied emissions on 6 and 9-11 January; and nighttime incandescence was observed intermittently. White vapor clouds were occasionally released from Southern Crater. Seismic activity was at low to moderate levels; the daily number of low-frequency earthquakes fluctuated between 500 and 1,000.

Satellite imagery showed diffuse plumes drifting WSW on 15 February. Southern Crater emitted gray ash plumes during 15-19 February and white vapor plumes on 21 February. Continuous gray ash plumes from Main Crater rose to an altitude of 2.3 km and drifted SE during 19-21 February. The daily number of low-frequency earthquakes fluctuated between 400 and 500 during 22-24 February before the seismograph developed technical problems.

Mild eruptive activity continued during 22 February-10 March. Main Crater forcefully released variable gray ash clouds on 22 February that rose less than 1 km above the summit before being blown SE. Incandescence was also visible that day. Poor weather prevented observations for the remainder of the month. When the clouds cleared on 3 March, Main Crater was seen sending ash clouds less than 500 m high. Glow was visible during 2-5 and 9-10 March. Southern Crater released occasional diffuse gray ash clouds on 3-4 and 6 March, but only white vapor on 5 and 7-11 March.

Main Crater continued to release occasional low-level ash clouds through 6 April. Incandescence was visible during clear weather on the nights of 11-12 and 16-18 March. Southern Crater released diffuse white vapor on 11-12 and 15 March; however, diffuse ash clouds were reported on 16-20 March. Weak roaring noises were heard on 24 March, and on 7, 12, and 26 April. Low-level plumes were seen during 25-26 April, and a small plume was blowing W on 28 April. Weak incandescence was again visible from Main Crater on 2 and 4 May. Diffuse plumes were seen in satellite imagery on 6 and 23 May. Seismic activity was at a low level, with the daily number of volcanic earthquakes between 800 and 1,000 events.

Thermal satellite data. Thermal anomalies were not detected by Moderate Resolution Imaging Spectroradiometers (MODIS) for 9 months after events related to the 27-28 February 2006 explosion. Anomalies reappeared in December, with hot pixels detected on 5, 7, 9, 10, 12, and 14 December 2006. Another anomaly was recorded on 19 April 2007. Additional thermal anomalies were present on 16 and 23 May 2007. Most of the pixels were located near the summit, or slightly towards the NE. The May anomalies were the furthest down the NE Valley.

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Herman Patia and Steve Saunders, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) Hot Spots System, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).

Centro Nacional de Prevencion de Desastres (CENAPRED) reported only sporadic, modest activity at Popocatépetl during early 2006 through April 2007. Based on information from the Mexico City Meteorological Watch Office (MWO), and the Washington Volcanic Ash Advisory Center (VAAC), there were five occasions when ash plumes rose substantially. On 25 and 27 July 2006 ash plumes rose to an altitude of ~ 9.8 km. On 18 and 20 December 2006, ash plumes rose to an altitude of ~ 6.7 km and 7.9 km, respectively. In April 2007, ash plumes rose to ~ 7.6 km on the 1st, and to ~ 7.3 km on the 3rd.

In August 2006, the lava dome that had been irregularly growing since July 2005 covered the floor of the internal crater and began a piston-like growth on the top of the previous dome. The enlarged dome can be seen in an aerial photography taken in 24 November 2006 (figure 51). This formation of the dome was the twenty-sixth such event since 1996.

Figure 51. Aerial photo taken 24 November 2006 showing the growing lava dome at Popocatépetl.The dashed white line defines the dome edge. The lava dome that started growing in July 2005 has covered the floor of the internal crater and began growing on the top of the previous dome. The white areas outside the inner-crater rim are snow cover. Courtesy of the government of the State of Puebla, Mexico.

On 4-5 August and 1-3 November 2006 episodes of large-amplitude harmonic tremor (figure 52) were believed to reflect an increased rate of dome growth. The accumulated volume of the lava dome between November of 2005 and November of 2006 was estimated to be 1,299,000 m³. The average rate growth over that interval is around 0.04 m?/s. Assuming that the dome grows only during the tremor episodes, the rate would be ~ 6.75 m³/s.

Figure 52. Evidence of a large-amplitude, multiband harmonic tremor, showing clear frequency peaks in its spectrum detected in August 2006 at Popocatépetl. The combination of the frequencies appear as moiré shadows in the paper recording.Courtesy of CENAPRED.

Incandescence at the summit was recorded by the CENAPRED camera on 3 August and 4-5 September 2006. Over 27-29 October 2006, eigth small explosions ejected incandescent debris on the slopes surrounding the crater. During November and December 2006, more episodes of low amplitude tremors were recorded. From August to December 2006, 77 volcano-tectonic micro-earthquakes were detected, with magnitudes ranging between 2.0 and 3.0. From these, 66 were located below the crater at depths ranging between 3 and 7 km (figure 53).

Figure 53. Location and depth of micro-earthquakes on Popocatépetl recorded during August to December 2006. Courtesy of CENAPRED.

Hot spots at the summit were detected on satellite imagery by the Washington Volcanic Ash Advisory Center (VAAC) on 7-8 January 2007. According to the Washington VAAC, a puff with little ash content emitted from Popocatépetl was reported from the MWO and visible from the camera operated by CENEPRED on 14 February 2007. A very diffuse plume was seen drifting to the E on satellite imagery. Base on an aerial photograph taken on 24 January 2007, CENEPRED reported that the lava-dome dimensions have slightly increased since 24 November 2006.

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

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: https://www.gob.mx/cenapred/); Alicia Martinez Bringas and Angel Gómez Vázquez, CENAPRED; Servando de la Cruz Reyna, Insituto de Geofisica UNAM. Ciudad Universitaria, s/n. Circuito Institutos . Coyoacan México D.F. México; Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

This report discusses evidence for the end of the March 2006 eruption, and press releases announcing newly acquired multibeam bathymetry that disclosed submarine calderas on the flanks of Raoul Island and some adjacent volcanoes.

End of the March 2006 eruption. After the 17 March 2006 eruption (BGVN 31:03), volcanic activity decreased significantly. On 18 September 2006 the Alert Level was lowered to 0.

GeoNet Science (GNS) summarized the decreased activity in their Volcano Alert Bulletin of 18 September 2006. The report noted an absence of significant earthquakes within ~ 30 km of Raoul Island. The water level in Green Lake had continued to drop and was close to the pre-eruption level by 18 September. On 27 August the lake temperature was 20.3°C, well within the seasonal range. The level of ongoing hydrothermal activity (upwelling in Green Lake, nearby hot pools, and steaming ground) was commensurate with that expected six months after an eruption like that seen in March. Chemical analyses of samples recently collected from some of the thermal features were typical of volcano-hydrothermal features in this environment.

GNS reported that the water level in Green Lake, which had risen significantly during the week after the March 2006 eruption and had drowned several new steam vents, still remained above pre-eruption levels as of July 2006, but thereafter dropped slowly. Upwelling and bubbling of springs indicated the volcanic-hydrothermal system was still weakly active 3 months after the eruption. The water temperature, obtained from a thermal infrared satellite image taken on 11 April 2006, was 39.2°C, was 7°C above the average water temperature in April, but had returned to seasonal temperatures by August 2006.

Only 1 to 5 earthquakes were recorded per day in the months following the eruption. The number of earthquakes 30-40 km offshore was slightly higher than normal.

New submarine volcanoes discovered. Marine geologists who had investigated two volcanoes in the Kermadec Arc during May 2007, discovered two new submarine volcanoes near Raoul Island. The geologists were on a scientific expedition mounted by New Zealand's National Institute of Water & Atmospheric Research (NIWA) and the University of Auckland aboard NIWA's deepwater research vessel Tangaroa. They investigated volcanoes on the two largest Kermadec Islands (Raoul and Macauley) and their submerged flanks.

A 22 May 2007 press release by NIWA reported that new seafloor observations revealed for the first time the presence of two submerged calderas. Both calderas were relatively small, ~ 4 km in diameter. One caldera was very deep, measuring ~ 1 km from the rim to the crater floor. Both volcanoes appeared geologically young, on the order of thousands of years old, but laboratory analysis of sediments will be needed to better quantify their age.

The expedition took sediment samples and mapped the contours of the volcanoes both above and below sea level (the latter using multibeam sonar). A series of sediment cores taken from E and W of both islands revealed at least six eruptions from the two islands, recorded as centimeter-thick layers up to 100 km from the islands.

Geologic Background. Anvil-shaped Raoul Island is the largest and northernmost of the Kermadec Islands. During the past several thousand years volcanism has been dominated by dacitic explosive eruptions. Two Holocene calderas exist, the older of which cuts the center the island and is about 2.5 x 3.5 km wide. Denham caldera, formed during a major dacitic explosive eruption about 2200 years ago, truncated the W side of the island and is 6.5 x 4 km wide. Its long axis is parallel to the tectonic fabric of the Havre Trough that lies W of the volcanic arc. Historical eruptions during the 19th and 20th centuries have sometimes occurred simultaneously from both calderas, and have consisted of small-to-moderate phreatic eruptions, some of which formed ephemeral islands in Denham caldera. An unnamed submarine cone, one of several located along a fissure on the lower NNE flank, has also erupted during historical time, and satellitic vents are concentrated along two parallel NNE-trending lineaments.

Information Contacts: Steve Sherburn, GeoNet Science (GNS), Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; Ian Wright, Ocean Geology group, National Institute of Water & Atmospheric Research (NIWA), PO Box 14901, Wellington, New Zealand (URL: http://www.niwascience.co.nz); Roger Matthews, North Shore City Council, 1 The Strand, Takapuna Private Bag 93500, Takapuna, North Shore City, New Zealand (URL: http://www.northshorecity.govt.nz/).

Our last report (BGVN 31:01) discussed post-eruption lahars following the sudden 1 October 2005 eruption (BGVN 30:09). This report contains two sections. The first section addresses regional processes such as vegetation loss, ash accumulation, and lahars on and beyond the E flank of Santa Ana (also known as Ilamatepec) to the shores of Lake Coatepeque. Those lahars began soon after the 1 October 2005 eruption. The information on these lahars chiefly came from a report (SNET, 2006) authored by El Salvador's Servicio Nacional de Estudios Territoriales (SNET).

The second section addresses monitoring and observations such as extensive steaming and drop in the surface elevation of the lake in the summit crater. Material for this section, primarily found on the SNET website, covers January-April 2006, when activity was fumarolic with no large eruptions. The 1 October 2005 eruption was possibly followed by a second one two days later on 3 October (SNET, 2006). A 3 October eruption was not mentioned in previous Bulletin reports.Carlos Pullinger explained that the evidence for the second eruption was tremor that day, but that could stemmed from other causes such as geysers in the summit crater lake, so the evidence for a 3 October eruption remains equivocal.

E-flank issues. October 2005 volcanism took place coincident with unusually high rains during tropical storm Stan (1-10 October 2005). On the E flank, the October 2005 eruptive episode killed extensive vegetation and left loose ash deposits covering the upper slopes (figure 7).

Figure 7. A November 2005 photo looking southward showing Santa Ana in the foreground, along with denuded, ash-laden vegetation. A wisp of steam escapes the summit crater, a basin hosting an acidic crater lake. Santa Ana's plumes and October 2005 ash deposits, coupled with other factors such as steep slopes, stress to vegetation, the lack of surviving permeable soils, and regional rainfall have led to a rash of new E-flank lahars. Peaks beyond Santa Ana include its satellitic cone Cerro Verde and then Izalco (sharp peak beyond the notch). Photo from SNET (2006).

Based on a rain gauge 5 km W of the crater (national meteorological station Los Naranjos), rainfall in October averages 193 mm; the yearly average is 2,155 mm. In the months prior to October 2006, rainfall at that station remained at normal values, always below 460 mm per month. In contrast, rainfall reached 865 mm during October 2006. During the peak of the storm, 3-6 October 2005, the Los Naranjos rain gauge collected more than 100 mm per day; the highest reading of 320 mm was on 5 October.

The lahars on Santa Ana's E slope consisted of both material from the October 2005 eruption as well as previous deposits. The first lahar seen by local witnesses took place on the night of 2 October 2005. It carried material up to 2 m in diameter. The lahars that produced most of the damage were those that occurred immediately after the eruption and reached a maximum thickness of 1.5 m. Other lahars descended later in the storm, persisting well into 2006.The 2006 rainy season did not generate damaging lahars, just heavy runoff with minor sediment. In all, SNET seismically registered 22 lahar events, all of which were confirmed by local residents. The communities used tractors used to keep the main drainages open and to build levees, which confined the lahars inside main drainage areas. The SNET website mentioned several lahar episodes during 2006. Some of these episodes occurred in May, June, and July 2006.

A large scallop in the topographic margin of Coatepeque caldera results in Planes de la Laguna (an area of ~ 10 km²), which was where lahars eventually deposited (figures 8 and 9). This area of less steeply sloped, and in places comparatively level, ground contains numerous coffee plantations and small settlements. The largest settlement is El Javillal (figure 8, adjacent Lake Coatepeque).

Figure 8. Lahars displayed as trains of heavy dots on a topographic base map of the E-central side of Santa Ana and the adjacent W side of Lake Coatepeque. (N is towards the top; light grid-lines are 1 km apart, so the distance from the summit on the W to the large lake on the E is ~ 6.5 km.) In general, the lahars descended from W to E. Coatepeque is a 7 x 10 km caldera and the series of dashed lines across the map indicate the caldera's steep-sided topographic margin in. Several caldera domes are labeled, including Cerro Pacho and Cerro Afate. Note the lahar entering the settlement adjacent Lake Coatepeque ("Caserío El Javillal"). From SNET (2006).

Figure 9. An E-W topographic profile with Santa Ana on the W across to the E side of Lake Coatepeque on the E. Dashed lines indicate the location of Coatepeque's caldera wall. From SNET (2006).

The upslope areas contained numerous channels carrying lahars (figure 8). Several kilometers into the caldera the channels merge as they cross the less steeply sloped Planes de Laguna. The channels eventually grow into two primary channels, La Mina on the S and El Javillal on the N (figure 10). The La Mina channel led directly towards the Cerro Pacho dome, where the lahars proceeded to branch into multiple routes (A, B, C, and D) before entering El Javillal (figure 11).

Figure 10. Annotated aerial photo at unknown date showing part of Coatepeque's Planes de Laguna, W of Santa Ana, taken looking roughly S. The view illustrates lahars in and around El Javillal.The lahars entered the area along two drainages (Quebradas La Mina and El Javillal), both flowing from right to left (arrows). Adjacent to the domes and settlements, the flow patterns become quite complex (as indicated by flow directions A, B, C, and D). Lake Coatepeque appears at the upper left. The steep caldera wall lies along the photo's margin from the upper center to right corner. The large circular dome is Cerro Pacho; the smaller dome to the right is Cerro Guacamayero. Photo from SNET (2006).

Figure 11. Photos showing October 2005 lahar deposits from Santa Ana in El Javillal. Deposits included lava blocks of differing sizes, and a mixture of soil, tree parts, mud, and water. Photos from SNET (2006).

Given the lack of soils and the state of vegetation, lahars were viewed as a potential ongoing hazard. To control lahars, SNET (2006) proposed excavating two channels from the vicinity of the domes to Lake Coatepeque, to carry sediment farther towards the lake. The proposed artificial channels are 2 m deep, with sides that slope at 45° outwards, and with a flat floor 5 m across. One proposed channel follows the S margin of the Cerro Pacho dome, the other follows a path similar to arrow A on figure 10.

Pullinger noted that the jocote de corona crop harvest was not affected because it came out just after the eruption. However, coffee was damaged wherever ash fell. Lahars did not directly hurt coffee plantations, but access roads were damaged and labor for harvesting was minimal, after much of the population had fled.

Monitoring. Moderate seismic activity and steam emissions continued during 2006. During 2006, seismicity was slightly above normal levels. Small earthquakes were interpreted as being associated with gas pulses.

Degassing continued in January 2006 with sporadic gas-and-steam emissions which rose approximately 200 m before dispersing. The SO₂ flux ranged between 163 and 1,578 metric tons/day.

On 2 February, there was an increase in seismicity, possibly related to an earthquake on the coast of Guatemala. From 1-7 February the SO₂ flux averaged 2,000 metric tons per day. A drop in the water level of the steaming, green-colored acidic lake in the summit crater revealed a local topographic high in the lake's center, which took the form of an irregular island (figure 12).

Figure 12. Photo showing the crater lake at Santa Ana volcano. The decrease in the water level has revealed an island of rocks and sediments that was previously covered by the crater lake. Photo taken on 17 February 2006 and provided courtesy of SNET.

Intense bubbling and fumarole activity during 27 February-23 March disturbed the lake's surface and made it difficult to assess the level of the water. During April, instability in the crater led to periodic landslides. One significant landslide deposited material in the SW section of the beach of the crater lake.

Reference. Servicio Nacional de Estudios Territoriales (SNET), 2006, Flujos de escombros en la Ladera Oriente del Volcán Ilamatepec, Departamento de Santa Ana: Perfil de Obras de Mitigacion, Enero de 2006, 12 p.

Geologic Background. Santa Ana, El Salvador's highest volcano, is a massive, dominantly andesitic-to-trachyandesitic stratovolcano that rises immediately W of Coatepeque caldera. Collapse of Santa Ana (also known as Ilamatepec) during the late Pleistocene produced a voluminous debris avalanche that swept into the Pacific Ocean, forming the Acajutla Peninsula. Reconstruction of the volcano subsequently filled most of the collapse scarp. The broad summit is cut by several crescentic craters, and a series of parasitic vents and cones have formed along a 20-km-long fissure system that extends from near the town of Chalchuapa NNW of the volcano to the San Marcelino and Cerro la Olla cinder cones on the SE flank. Historical activity, largely consisting of small-to-moderate explosive eruptions from both summit and flank vents, has been documented since the 16th century. The San Marcelino cinder cone on the SE flank produced a lava flow in 1722 that traveled 13 km E.

Information Contacts: Carlos Pullinger, Servicio Nacional de Estudios Territoriales (SNET), Alameda Roosevelt y 55 Avenida Norte, Edificio Torre El Salvador, Quinta Planta, San Salvador, El Salvador (URL: http://www.snet.gob.sv).

Activity returned to normal levels following the strong explosive episode of 10 September 2006 (BGVN 31:09). Activity after September included an occasional minor explosions, rockfalls, minor pyroclastic flows, venting of ash and gases and steam with emissions reaching up to 3 km altitude, minor ashfalls, and mudflows during heavy rains. In September and October, the minor pyroclastic flows primarily moved down the N and NE flanks of the dome. In January, pyroclastic flows traveled down the Gages Valley, Tyres Ghaut, Belham Valley, Tuits Ghaut, Farrells Plain, and especially the lower Tar River Valley E of the volcano.

Lava-dome growth slowed in March, and by the end of April it appeared to have ceased. On 1 June Montserrat Volcano Observatory (MVO) (figure 75) warned that, while the lava extrusion had ceased and the dome may not be actively growing, it remains as a large mass of partially molten lava capable of collapsing or exploding. According to MVO, the amount of material above Tyres Ghaut to the NW was sufficient to generate pyroclastic flows and surges capable of affecting the lower Belham Valley and other areas.

Figure 75. Map of Montserrat showing the pre-eruption topography of Soufrière Hills. The black circle shows the location of the MVO. The approximate outline of the Tar River delta in July 2004 is shown. Courtesy of Wadge and others (2005).

Data provided by MVO (table 64) shows the elevated seismicity (hybrid earthquakes and rockfall signals) related to the increased activity in late August and early September (BGVN 31:09). The high number of long-period earthquakes in late June reflects the dome collapse at that time (BGVN 31:05). The dramatic decrease in long-period events and rockfalls in mid-March corresponds to the observed reduction in dome growth.

Table 64. Seismicity at Soufrière Hills between 16 June 2006 and 25 May 2007. * Data for the first 4 days only. VT: volcanic tectonic; LP: long-period. Courtesy of MVO.

Strong activity during mid-September 2006. On 9 and 10 September, vigorous ash venting from the Gages Wall was accompanied by small explosions. Pyroclastic flows from fountain collapse occurred on all sides of the dome and reached 1 km W down Gages valley. On 11 September, the collapse of an overhanging lava lobe produced pyroclastic flows NE down the Tar River valley. One pyroclastic flow in the same area on 13 September reached the sea. On 14 September, vigorous ash venting resumed. Continuous ash and gas emissions during 13-19 September produced plumes that reached altitudes of 2.4-3.7 km. The Gages Wall vent continued to produce ash and gas emissions into mid-October.

Activity during September-December 2006. During 15 September-6 October the lava dome continued to grow at a moderate rate in the summit area and on the S and E sides of the dome. On 22 September the volume of the dome was about 80 million cubic meters. Lava-dome growth was concentrated on the NE part of the edifice from 6 October until 15 December, when growth moved to the SW part of the dome. A new E-facing shear lobe with a smooth, curved back enlarged during 13-20 October.

During 24 November-1 December, the two cracks in the curved back of the shear E-facing lobe on the summit propagated downward and divided the lobe into three blocks. The dome overtopped the NE crater wall and fresh rock and boulder deposits were observed in that region. During 22-29 December, lava-dome growth was focused on the W, where gas-and-ash venting occurred. A high whaleback lobe directed SW was observed on 26 December.

Aviation notices reported continuous ash and gas emissions almost every day from 15 September through 14 November, with plumes rising above 2 km to a maximum of 4.6 km altitude. Plumes extended 140 km W on 2-3 October. During 17-24 November, ash venting originated from the westernmost of two cracks in the curved back of the shear E-facing lobe on the summit. An explosion produced an ash plume that rose to altitudes of 1.5-1.7 km.

Pyroclastic flows occurred regularly as collapses from the dome sent material in all directions. Pyroclastic flows reached both the upper region of Tuitts Ghaut (N) and the sea via the Tar River Valley (E) on 23 November.

Activity during January-March 2007. Rapid lava-dome growth, pyroclastic flows, and ash venting increased during 3-9 January. Dome growth was concentrated in the NW, the highest part of the dome. Pyroclastic flows were observed in Tyres Ghaut (NW), Gages Valley (W), and N, behind Gages Mountain and accompanied by ash venting. On 4 January, simultaneous pyroclastic flows descended Tyres Ghaut and Gages Valley, and a resultant ash cloud reached an altitude of 2.5 km. The maximum distance for the Gages Valley flow was 4 km. During 6-9 January, distances of pyroclastic flows increased in Tyres Ghaut and possibly exceeded 1.5 km.

During 10-16 January, lava-dome growth was focused on the NW quadrant. During 10-11 January, one pyroclastic flow was observed to the W in Gages Valley and one to the NW in Tyres Ghaut. On 15 January, a relatively large pyroclastic flow traveled E down the Tar River Valley. After 15 January, measurable activity was low. Gas and ash venting that originated from the W side of the dome continued. A clear view on 22 January revealed that the collapse scar from the 8 January event was filled in. A small spine was noted on the W side. On 23 January, a large pyroclastic flow traveled down Gages Valley. The Washington VAAC reported that ash plumes were visible during 26-27 January. On 28 January, a large pyroclastic flow traveled down the Tar River Valley and reached the sea. A diffuse plume rose to an altitude of 1.5 km on 31 January.

During 7-13 February, growth of the lava dome continued on the W side, then was concentrated on the E and N sides for the rest of the month. The lava-dome volume in mid-February was estimated at 200 million cubic meters based on LIDAR data. Previous measurements over-estimated the lava-dome volume due to the perceived location of the dome and the lack of data from inside the crater. Small pyroclastic traveled in multiple directions throughout February. Moderate pyroclastic flows traveled down the Tar River Valley during 24-25 and 27 February. Continuous ash emissions were reported during 14 February-6 March, with plumes to altitudes of 2.1-6.1 km.

Lava-dome growth during 2-9 March was concentrated on an E-facing lobe topped with blocky, spine-like protrusions. Rockfalls affected the E and NE flanks. Pyroclastic flows traveled 2 km in the Tar River Valley. Heightened pyroclastic activity on 7 March resulted in an ash plume that rose to an estimated 2.4 km. On 11 March, a pyroclastic flow traveled down the NE flank into White's Ghaut.

During 9-26 March, lava-dome growth was concentrated on the NE side. Intermittent pyroclastic flows traveled E down the Tar River valley and produced ash plumes. One plume on 12 March rose to 3 km altitude. Pyroclastic flows were observed NW in Tyre's Ghaut and ashfall was reported from the Salem /Old Towne areas. During 23 March-3 April, dome growth apparently stopped.

MODIS thermal data indicated hot pixels at the dome and from pyroclastic flows on 24 March. Another thermal anomaly from a pyroclastic flow Tar River was detected on 29 March. No futher anomalies had been recorded by the HIGP Hotspot system through May. However, the Washington VAAC reported that a SW-drifting, diffuse plume and a hotspot were visible on satellite imagery on 2 April.

During 30 March-13 April, small, intermittent pyroclastic flows from the E-facing shear lobe occurred in the Tar River valley (figure 76). Incandescent rockfalls were seen at night during 5-9 April. On 17 April, a small pyroclastic flow was observed to the NW in the upper part of Tyres Ghaut. In mid-April MVO estimated that the lava-dome volume was about 208 million cubic meters.

Figure 76. Photograph taken 4 April 2007 of southern Montserrat and Soufrière Hills from the NE, showing from left the Tar River Delta and the debris fans spilling from Tuitts and Whites Ghauts. Courtesy MVO.

The sulfur dioxide (SO₂) flux rate during 6-13 April was high, with an average value of 3,114 metric tons per day (t/d), well above the long-term average for the eruption. The previous week averaged 1,035 t/d, from a low of 71 to a high of 3,818 t/d. The three days from 8 to 10 April showed markedly elevated emissions: 3,550, 7,396 peaking at 7,471 t/d, whereas the remaining days' emissions were extremely low, some below 100 t/d.

During 13-20 April, material originating from the lava dome's E-facing shear lobe was shed down the Tar River Valley. A bluish haze containing sulfur dioxide was observed flowing down the N flanks on 18-20 April. Pyroclastic activity was ongoing on the E and NE sides of the dome during 27 April-4 May. After 4 May the overall structure of the dome changed very little. Low-level rockfall and pyroclastic-flow activity continued into late May.

Reference. Wadge, G., Macfarlane, D.G., Robertson, D.A., Hale, A.J., Pinkerton, H., Burrell, R.V., Norton, G.E., and James, M.R., 2005, AVTIS: a novel millimetre-wave ground based instrument for volcano remote sensing: J. Volcanology and Geothermal Research, v. 146, no. 4, p. 307-318.

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), Fleming, Montserrat, West Indies (URL: http://www.mvo.ms/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology, MODIS Thermal Alert System, School of Ocean and Earth Sciences and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI, USA (URL: http://modis.higp.hawaii.edu/).

According to Sonia Calvari of Istituto Nazionale di Geofisica e Vulcanologia (INGV-CT), a flank eruption started on Stromboli volcano on 27 February 2007 and continued to at least 15 March. Compared to the previous flank eruption during 2002-2003, lava effusion was about an order of magnitude greater. Initially, a NE fissure opened on the NE flank of the NE-crater, and lava emitted from the fissure formed three branches and rapidly reached the sea (figure 75).

Figure 75. Lava from Stromboli reaching the sea on 27 February 2007. Courtesy of the INGV-CT 2007 Stromboli eruption web site.

Late on the eruption's first day, the three initial flows stopped and a new vent opened at the E Margin of the Sciara del Fuoco at about 400 m elevation. In a few days, this vent emitted sufficient lava to build a lava bench several tens of meters wide, which significantly modified the coastline. These lava emissions stopped for a few hours on 9 March, after which another vent opened at about 550 m elevation on the N flank of the NE-crater, almost in the same position as one of the vents of the 2002-2003 eruption. The 550-m vent was active for less than 24 hours and, when it ceased emitting lava, the 400-m vent reopened, again feeding lava to the sea.

On 15 March 2007, while the effusion from the 400-m vent continued, a major explosion occurred at 2137 (2037 UTC). This event, similar to that on 5 April 2003 (BGVN 28:04), was recorded by all the INGV-CT monitoring web cams. As in 2003, the 2007 event occurred during a flank effusive eruption, when the summit craters were obstructed by debris fallen from the crater rims. Still images and videos can be downloaded from the INGV-CT webpage dedicated to the 2007 Stromboli eruption.

Satellite imagery. Satellite imagery revealed an ash plume fanning SSE from the eruption site beginning at 1215 UTC on 27 February 2007. Another eruption was observed on MET-8 split-window IR (infrared) imagery on the same day at 1830 UTC. Ash then blew SSE at 46-56 km/hour.

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

Information Contacts: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/); INGV-CT 2007 Stromboli eruption website (URL: http://www.ct.ingv.it/stromboli2007/main.htm); U.S. Air Force Weather Agency (AFWA)/XOGM, Offutt Air Force Base, NE 68113, USA.

New and revised information has emerged regarding the behavior of the Sulu Range (Johnson, 1971), a volcanic field adjacent to and immediately E of Walo hot springs along the coast in the N-central part of New Britain Island (BGVN 31:07 and 31:09; figure 3). Initial Rabaul Volcanological Observatory (RVO) reports mentioned apparent steam and ash emission during mid-July 2006, but although weak-to-moderate vapor emission occured, and a later section of this report discusses heightened hot spring activity, the reported "forceful dark emissions" have been instead linked to dust during mass wasting.

Figure 3. A sketch map of New Britain island showing a small portion of the main island of Papua New Guinea (lower left) and New Ireland (upper right). Volcanoes on or adjacent New Britain are labeled. Volcanoes active and erupting frequently in the last decade include (from the SW) Langila, Ulawun, and Rabaul. Volcanoes that have erupted or undergone anomalous unrest in the past few years include (from the SW) Ritter Island, the Garbuna group, Pago, Sulu Range, and Bamus.

In a 12 April Email message, Steve Saunders clarified the latest RVO views on Sulu's behavior. He noted that ". . . Sulu did not erupt! It was purely a series of seismic cris[es]. The 'emissions' which were reported before we got there turned out to be dust from landslides."

Unusually vigorous hot springs, declining seismicity. Following the first two weeks of unrest during mid-July at Sulu Range, an RVO report discussing 31 July to 2 August activity stated that area hot springs such as those at Walo were undergoing unusually strong activity. This included expelled mud, the emergence of geysers, and abnormal quantities of steam.

RVO noted waning seismicity in late July. Seismicity had declined to relatively low levels, although small volcano-tectonic events continued to be recorded. The small earthquakes were centered around the settlements of Silanga, Sege, and Sale (figure 4; respectively, from Mt.Ruckenberg's summit, located 12.7 km to the SW; 7.2 km SW, and 5.5 km S). The 31 July to 2 August earthquakes were described as more irregular and less frequent than those in preceeding weeks.

Figure 4. Geological map showing the cluster of overlapping cones of the Sulu Range. Walo village lies just off the map near the coast within a few kilometers of the map 's W margin. The thermal area by the same name lies ~ 5 km SW of Lava Point. The prominent cone on the N edge of the Range is called Mount Ruckenberg or Mount Karai. The initial "vent location" was 2 km SW of Mount Karai between Ubia and Ululu volcanoes. Part of that area is crossed by two parallel, closely spaced faults. The narrow zone between those faults was down-thrown. A SW-directed debris flow was also mapped near this area. Three centers in the N, Ruckenberg (Karai), Kaiamu maar, and Voku, are specifically mentioned in the text as areas with recently documented Holocene activity. Modified from a map by Chris McKee, RVO.

The pattern of located earthquakes defined an irregular ellipse, with major axis 9 km E-W. Two earthquakes represented a 1-2 km extension N from the ellipse under Bangula Bay. There were also two earthquakes offshore about 4-5 km due N of Cape Reilnitz, a broad promontory the most extreme point of which lies 18 km to the W of Mt. Ruckenberg's summit. As of the end of July an area devoid of earthquakes remained; it was 2-3 km in diameter and centered on Walo village.

The RVO estimated that the top of the underlying magma body was 10-15 km deep when volcano-tectonic earthquakes began on 6 July 2006. They judged that volatiles or heat escaping from the magma were responsible for onset of the mud and water ejections at the once quiet hot springs.

Postulated intrusion. Randy White (US Geological Survey) analyzed the July seismic crisis, which in his interpretation did not follow the pattern of a tectonic earthquake with a main shock and associated aftershocks, but did follow behavior of many earthquakes accompanying the onset of volcanic unrest. He attributed the seismicity to a dike intruded to shallow depth (and confined to the subsurface). According to White, the epicenters well outboard of, but surrounding the area of intrusion, occurred in a pattern similar to those accompanying many shallow intrusions.

The elevated seismicity began after a volcano-tectonic earthquake, M ~ 6 on 19 July (BGVN 31:07). It was located on the N side of New Britain, slightly offshore, and a few ten's of kilometers from the Sulu Range. The focal depth was thought to be in the 10-20 km range. White noted that soon after the 19 July earthquake, Australia provided portable seismometers. Once those arrived and began recording data, computed moment tensors indicated that subsequent earthquakes were very shallow. Epicenters occurred slightly W of the Sulu Range.

Short level-lines installed by RVO in August 2006 showed, by November, ~ 2 cm of deflation of the Kaiamu area in relation to a datum ~ 1 km E on the Kaiamu-Sulu track. By April 2006 the measured levels had returned to approximately the August datum line.

To the W of the area at Lasibu a similar pattern existed, with over 2.5 cm of deflation locally measured by November and an approximate return to the datum-line by April 2006. The center of the area delimited by seismicity is swamp and difficult to access. Google satellite images show an interesting series of raised shorelines W of Kaiamu.

Upon prompting from White, Chuck Wicks acquired satellite radar (L-band imagery) from Japanese collaborators for the Sulu Range. The radar data were taken weeks before and weeks after the July seismicity. When processed to obtain radar interferometry, the data indicated over 80 cm of vertical surface deformation. The deformation was centered in a region W of the Sulu Range along an area along the coast ~ 5 km W of Lava Point (Lara Point on some maps). It trends ENE. The data were interpreted as a shallow dike intrusion on the order of ~ 8 m wide trending out beneath Bangula Bay.

Wick's preliminary analysis suggests the intrusion's volume may be on the order of one cubic kilometer. White's qualitative estimate of the volume, from the intensity, style, and duration of the seismicity, were consistent with that analysis. In addition, the strike-slip focal mechanisms seen in the seismic data suggested the dike-intrusion episode caused movement along a nearby strike-slip fault.

Geological investigations conducted in the past several months by Herman Patia and Chris McKee indicated that Sulu Range has been quite active 'recently.' The latest eruptive phase at Kaiamu maar was radiocarbon-dated at 1,300 BP. Since that time at least seven eruptions have taken place at other vents, notably Voko, involving phreatomagmatic eruptions. Ruckenberg (Karai) appears to be the source of the most recent activity. Within the last 200 years it produced lava flows.

Reference. Johnson, RW., 1971, Bamus volcano, Lake Hargay area, and Sulu Range, New Britain: Volcanic geology and petrology: Australia Department of National Development, Bureau of Mineral Resources, Geology and Geophysics, Record 1971/55.

Geologic Background. The Sulu Range consists of a cluster of partially overlapping small stratovolcanoes and lava domes in north-central New Britain off Bangula Bay. The 610-m Mount Malopu at the southern end forms the high point of the basaltic-to-rhyolitic complex. Kaiamu maar forms a peninsula with a small lake extending about 1 km into Bangula Bay at the NW side of the Sulu Range. The Walo hydrothermal area, consisting of solfataras and mud pots, lies on the coastal plain west of the SW base of the Sulu Range. No historical eruptions are known from the Sulu Range, although some of the cones display a relatively undissected morphology. A vigorous new fumarolic vent opened in 2006, preceded by vegetation die-off, seismicity, and dust-producing landslides.

Information Contacts: Steve Saunders, Herman Patia, and Chris McKee, Rabaul Volcanological Observatory (RVO), Department of Mining, Private Mail Bag, Port Moresby Post Office, National Capitol District, Papua New Guinea; USGS Earthquakes Hazard Program (URL: http://earthquakes.usgs.gov/); Randy White and Chuck Wicks, US Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025, USA; United Nations Office for the Coordination of Humanitarian Affairs (URL: https://reliefweb.int/).

This report covers the time interval early January to 2 March 2007, based on Special Reports of the Ecuadorian Geophysical Institute (IG). This reporting interval was mainly one of relative quiet. In contrast, our previous report (BGVN 32:12), covered IG reports describing energetic eruptions of July and August 2006. Those IG reports also mentioned eruption-related fatalities and the discovery of a new growing bulge on the volcano's N flank. A map and geographic background were tabulated in BGVN 29:01.

Relative quiet prevails and some residents return. As touched on in BGVN 32:12, after August 2006, the volcanic vigor at Tungurahua was minimal and of low energy. The decrease in activity was gradual through mid-December 2006. The vigor remained low until mid-January 2007. Ash emissions did occur but were consistently minor.

IG reports noted that the relative tranquility at Tungurahua could reflect a pattern similar to that seen there in 1918. That was a case when various months of volcanic quiet occurred, only to be followed by explosive eruptions of large size. The latter generated pyroclastic flows.

During the quiet that followed the July and August 2006 eruptions, residents who had evacuated from the margins of the volcano returned to their properties. The IG noted that, unfortunately, these returning residents became more vulnerable to volcanic hazards and made emergency response more difficult.

Vigor increases. Between 20 January and 5 February 2007 internal seismic activity resumed, behavior consisting of a few earthquakes inferred as associated with fractures (volcano-tectonic earthquakes, VTs). On 13 February the volcano emitted an eruptive column with moderate ash content. After 19 February there was a reoccurrence of seismic VTs. These were of shorter duration but higher intensity than those that occurred during the previous period.

During 23-24 February 2007, volcanic tremors and seismic LP's were registered at the Volcanic Observatory of Tungurahua (VOT). At 0310 on 24 February, VOT staff and local observers reported continuous roars of moderate intensity, and discharge of incandescent material that both rose to ~ 800 m above the summit and descended ~ 1000 m down the volcano's flanks.

The emission column headed NW. Fine tephra fell, followed by a thick ashfall that was black in color. It left a deposit 3 mm thick in the towns of Pillate and San Juan. Reports received from Cotaló, Bilbao, Manzano, and Choglontús that indicate a thick, dark ashfall in those spots left a deposit 2 mm thick. Ashfall was also reported in the area of Quero.

Seismic activity decreased on 24 February as well as the intensity and frequency of the roars. As of 2 March, sporadic explosions of ash and incandescent material had been observed. Around this time some bad weather prevented clear views of the upper volcano; however, some reporters noted minor ashfall along the SW portion of the crater. Additionally, the SO₂ flux increased to ~ 2,000 metric tons a day for the first time since the beginning of the year. The IG's "Seismic Activity Index" indicated an increase of the volcano's internal activity.

Two scenarios envisioned. Given the available data, the IG concluded that the volcano had received a new influx of magma. They proposed two potential scenarios: (1) the current levels of activity will continue and constant emissions of ash, (potentially more intense) will be generated. Ash clouds will be blown by winds that at this time of the year are predominantly westerly, with occasional S and NW variations. These ash clouds could generate heavy ashfall in the towns downwind from the volcano; or (2) the volume and speed of ascent of the magmatic gases originating from the new magma will increase dramatically, in which case, new explosive eruptions of pyroclastic flows similar to those on 14 July and 16 August could occur.

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

Information Contacts: Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/).