Guatemala's Volcán de Fuego was continuously active through September 2019; it has been erupting vigorously since 2002 with historical observations of eruptions dating back to 1531. These eruptions have resulted in major ashfalls, pyroclastic flows, lava flows, and damaging lahars. Large explosions with hundreds of fatalities occurred during 3-5 June 2018; after a brief pause, significant activity resumed and continued during April-September 2019, the period covered in this report. Reports are provided by the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH) and the National Office of Disaster Management (CONRED); aviation alerts of ash plumes are issued by the Washington Volcanic Ash Advisory Center (VAAC). Satellite data from NASA and other sources provide valuable information about heat flow and gas emissions.

Daily activity continued at a high level throughout April-September 2019 (table 19) with multiple ash explosions every hour, incandescent ejecta reaching hundreds of meters above the summit sending block avalanches down multiple ravines, and ash falling on communities on the SW flank and beyond. During April and part of May a lava flow was also active in the Seca ravine. Although explosive activity remained at a high level throughout the period, thermal activity began a decline in May that continued through September, noticeable in both the MIROVA radiative power data (figure 117), and monthly images of MODVOLC thermal alerts (figure 118).

Table 19. Activity summary by month for Fuego with information compiled from INSIVUMEH daily reports.

Figure 117. Thermal activity at Fuego increased steadily from January through April 2019, and then began a gradual decline through September as seen in this MIROVA graph of Radiative Power. The active lava flow in the Seca Ravine in April and early May likely contributed to the higher heat values during that time. Courtesy of MIROVA.

Figure 118. A steady decline in thermal activity at Fuego is apparent in the MODVOLC thermal alert images for April-September 2019. During April and early May a lava flow was active in the Seca ravine that extended as far as 1,000 m from the summit. Courtesy of MODVOLC.

Activity increased at the very end of March 2019. The rate of explosions increased to 14-32 events per hour by 31 March; ash plumes rose to 5 km altitude and resulted in ashfall in numerous nearby communities. An early morning lava flow that day reached 800 m down the Seca ravine. Continuous white and gray fumarolic plumes reached 4.1 to 4.4 km altitude during April 2019 and drifted generally W and SW. There were about 15-20 ash-bearing explosions per hour; the highest rate of 25 per hour occurred on 10 April. Plume altitudes were below 4.8 km for most of the month; on 28 and 29 April they rose to 5.0 and 4.9 km. For most of the month they drifted W and SW; the wind direction changed to the E during 10-16 April. Most days of the month ashfall was reported in the communities of Panimaché I y II, Morelia, Santa Sofía, Finca Palo Verde, San Pedro Yepocapa, Sangre de Cristo and El Porvenir on the W and SW flank. During 10-13 April when the wind direction changed to easterly, communities to the NE, E and SE of Alotenango, Ciudad Vieja, La Reunión, La Rochela, El Rodeo, Osuna, Ceilán and others on the N and E flanks were affected by ashfall. The Washington VAAC issued multiple daily advisories on 18 days in April, identifying short-lived ash plumes drifting with the prevailing winds.

Incandescent ejecta rose 200-300 m above the summit on most days (figure 119). During 23-25 April, ejecta rose 300-450 m above the summit. Six ravines were affected by the incandescent avalanche blocks nearly every day: the Seca, Taniluyá, Ceniza, Trinidad, Las Lajas, and Honda. The explosions caused rumbles, shock waves that rattled roofs, and sounds similar to a train locomotive at intervals of 5-20 minutes in nearby communities throughout the month. A lava flow was present in the Seca (Santa Teresa) ravine for most of the month; its length varied from 200 to 800 m. Special reports of lahars were issued seven times during April. On 4 April a moderate lahar descended the Seca ravine carrying centimeter- to meter-sized blocks, tree trunks and branches. During 9-11 April nine lahars were recorded in the Las Lajas, El Jute, Seca, Rio Mineral, Taniluya, and Ceniza ravines. The largest flows were 20 m wide and 3 m deep carrying blocks and debris up to 3 m in diameter; they were warm and thick with a strong sulfurous odor. Two more lahars were reported on 18 April in the Taniluya and Ceniza ravines carrying 1-2 m sized blocks in a warm, sulfurous flow.

Figure 119. Incandescent ejecta rose several hundred meters above the summit of Fuego on 30 April 2019 and sent large blocks down multiple ravines, typical activity for the entire month. Courtesy of CONRED (Boletín Informativo No. 1242019, martes, 30 de abril 2019, VOLCÁN DE FUEGO BAJO CONSTANTE MONITOREO).

During May 2019, primarily white fumaroles rose to 4.2-4.5 km altitude and drifted W, SW, and S; gray fumaroles were reported only during the first few days of the month. Generally, 15-20 ash explosions per hour occurred; the maximum was 26 on 17 May. Ash plume heights ranged from 4.5-4.8 km altitude nearly every day, drifting 10-25 km primarily W, SW, and S throughout the month, except for 6-8 May when plumes drifted NW and 18-19 May when wind directions changed and sent ash S and SE. Plumes drifted 25-30 km SE, S, and SW on 19 May. Ashfall was reported daily from communities on the W flank including Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Los Yucales, Finca Palo Verde, Sangre de Cristo, and San Pedro Yepocapa, among others, and also from the E side including Ceilán and La Rochela when the wind direction changed. The Washington VAAC issued multiple daily ash advisories on 19 days during May.

Incandescent Strombolian activity continued sending ejecta 200-300 m above the summit during the first half of the month and 300-450 m high during the latter half (figure 120). Seven major ravines, the Seca, Taniluyá, Ceniza, Trinidad, El Jute, Las Lajas, and Honda were affected by block avalanches throughout the month. Intermittent explosions caused rumbles, shock waves that rattled roofs, and sounds similar to a train locomotive at frequent intervals on most days. The lava flow in the Seca ravine advanced from 300 m length on 2 May to 1,000 m long on 9 May. It was reported as being 500 m long on 18 May but was not active after that date. Numerous lahars descended multiple ravines in May. INSIVUMEH issued nine special reports of lahar activity on 3, 14, 16, 20, 23, and 27-29 May. They affected the Las Lajas, Ceniza, El Jute, El Mineral, and Seca ravines. The thick, pasty flows contained blocks of various sizes up to 3 m in diameter along with tree trunks and branches. Several were warm with a sulfurous smell (figure 121). SO₂ emissions remained low throughout April-September with only minor emissions recorded in satellite data on 1 April and 9 May 2019 (figure 122).

Figure 120. Incandescent ejecta at Fuego was captured on 27 May 2019 under a starry night sky by photographer Diego Rizzo in a 25-second exposure. Block avalanches are seen descending several ravines. NASA used the photo as an Astronomy Photo of the day and noted that the central plane of the Milky Way galaxy runs diagonally from the upper left, with a fleeting meteor just below, and the trail of a satellite to the upper right. The planet Jupiter also appears toward the upper left, with the bright star Antares just to its right. Much of the land and the sky were captured together in a single 25-second exposure taken in mid-April from the side of Acatenango volcano; the meteor was captured in a similar frame taken about 30 minutes earlier and added to this image digitally. Courtesy of NASA Astronomy Picture of the Day, copyright by Diego Rizzo.

Figure 121. Lahars were reported at Fuego nine separate times during May 2019. A steaming lahar descends a ravine at Fuego on 11 May 2019 (top). The Santa Teresa Canyon was clogged with debris from numerous past lahars on 22 May 2019. INSIVUMEH monitors the ravines continuously during the rainy season. Courtesy of CONRED (Boletín Informativo No. 1382019, sábado, 11 de mayo 2019, LLUVIAS GENERAN DESCENSO DE LAHARES EN EL VOLCÁN DE FUEGO and Boletín Informativo No. 1562019, miércoles, 22 de mayo 2019, SE REGISTRA DESCENSO DE LAHARES MODERADOS EN EL VOLCÁN DE FUEGO).

Figure 122. Weak SO2 emissions were recorded from Fuego on 1 April and 9 May 2019 by the TROPOMI instrument on the Sentinel 5P satellite. Courtesy of NASA Goddard Space Flight Center.

The fumarolic plumes were only white during June 2019, rising to 4.1-4.5 km altitude daily, drifting W or SW except during the first days of the month when variable winds sent the steam N, E, and SE. Explosions with ash took place 15-20 times per hour on most days with plumes rising to 4.5-4.8 km altitude and drifting primarily W or SW except for the first days of the month (figure 123). On most days, ash plumes drifted 15-20 km W and SW, except during 2-7 June when winds sent ash E, SE, N, and NW. Ashfall was reported virtually every day in Sangre de Cristo, Yepocapa, Morelia, Santa Sofía, and Panimache I and II. In addition, the communities of El Porvenir, Los Yucales, and Finca Palo Verde reported ashfall several days each week. During 2, 4, and 7 June, the N and SE winds caused ash to fall in Alotenango and San Miguel Dueñas. The Washington VAAC issued ash advisories on 15 days during June.

Figure 123. Emissions of both steam and ash rose from Fuego on 11 June 2019. Courtesy of Paul A. Wallace, University of Liverpool.

The height of the Strombolian ejecta varied from 200-300 m above the summit on many days in June , but also was sometimes stronger, rising 300-450 m. While block avalanches were reported in all seven barrancas (ravines) more than once (Seca, Taniluyá, Ceniza, Trinidad, El Jute, Las Lajas and Honda), on all days they were reported in the Seca, Taniluya, Ceniza, and Trinidad. Weak to moderate rumbles and shock waves rattled roofs every day, and train engine noises were heard every 5-10 minutes. Seven special reports of lahars were issued on days 2, 11, 21-23, and 30. They affected the Las Lajas, El Jute, Seca, El Mineral, and Ceniza ravines with thick, pasty flows containing blocks 1-3 m in size, shaking the ground as they flowed downstream.

During July 2019, white steam plumes rose daily from the summit of Fuego to an altitude of 4.1-4.3 km and drifted W and SW; higher plumes on 30 and 31 July rose to 4.5 km altitude. Fifteen to twenty ash explosions per hour were typical throughout the month and produced ash plumes that rose to 4.3-4.8 km altitude and drifted SW and W for 10-25 km before dissipating (figure 124). Near-daily ashfall was reported in Morelia, Santa Sofía, El Porvenir, Finca Palo Verde, San Pedro Yepocapa, Panimaché I y II, and Sangre de Cristo; La Rochela and Ceilán also reported ash on 4 and 6 July. Incandescent ejecta height varied from 150-450 m above the summit from day to day, sending block avalanches down all seven ravines on many days. Weak to moderate rumbles and shock waves rattled roofs every day, and train engine noises were heard every 5-15 minutes. On 19 July noises and vibrations were heard and felt 25 km away. Only one lahar was reported on 12 July in the Las Lajas ravine. It was warm, with a sulfurous odor, and carried volcanic ash, sand, and blocks 1-3 m in diameter that shook the ground as they flowed downstream. The Washington VAAC issued ash advisories on 13 days during July.

Figure 124. Steam-and-ash plumes rose from Fuego on 12 July 2019 in this image taken at dawn from Villa Flores San Miguel Petapa. Courtesy of Alex Cruz (cropped and color adjusted from original).

White steam plumes continued during August 2019, rising to an altitude of 4.1-4.5 km and drifting W and SW daily. Ash-bearing explosions continued also at a rate of about 15-20 per hour throughout the month, rising most days to between 4.5 and 4.7 km altitude. They drifted 15-20 km W or SW nearly every day before dissipating. Every day during the month, ashfall was reported in Morelia, Santa Sofía, El Porvenir, Finca Palo Verde, San Pedro Yepocapa, Panimaché I y II, Sangre de Cristo, and other communities on the SW flank. The Washington VAAC reported ash plumes at Fuego on 15 days during August (figure 125).

Figure 125. An ash emission at Fuego was recorded on 22 August 2019. Courtesy of William Chigna.

Incandescent ejecta also rose every day during August 2019 to 200-300 m above the summit, a few days were reported to 350-400 m. Every day, block avalanches descended the Seca, Taniluyá, Ceniza, and Trinidad ravines; most days blocks also traveled down the Las Lajas and Honda ravines, and many days they were also reported in the El Jute ravine (figure 126). Every 5-10 minutes, every day, weak and moderate rumbles sounding like a train engine shook buildings and rattled roofs in the nearby villages. On 13 August a small lava flow, 75-100 m long, was reported in the Seca ravine. Six lahars were reported on 3 August. They occurred in the Santa Teresa, Mineral, Ceniza, El Jute, and Las Lajas ravines. The thick pasty flows carried blocks 1-2 m in diameter, tree trunks and branches, and disrupted the roads between Siquinala and San Andres Osuna and El rodeo and El Zapote. The next day two more occurred in the Seca and Mineral drainages. From 17-20 August, six more lahars occurred, most in the Las Lajas drainage, but also in the Seca, Mineral and Ceniza ravines.

Figure 126. Incandescent blocks traveled down several ravines at Fuego on 2 August 2019. Courtesy of Publinews Guatamala.

There were no changes in the steam fumaroles during September 2019; plumes seldom rose over 4.3 km altitude and continued drifting W and SW. The ash explosion rate decreased somewhat and rates of 5-10 per hour were typical on many days. Ash plume heights remained constant around 4.5-4.7 km altitude most days, also drifting W and SW 15-20 km before dissipating (figure 127). While ashfall was reported daily in Panimaché I, Morelia, Santa Sofía, Porvenir, Palo Verde, Yepocapa and other communities on the SW flank for the first half of the month, it grew more intermittent during the second half of September. South-directed winds deposited ash on La Rochela villages and Ceylon on 25 September. The Washington VAAC issued aviation ash advisories on 11 days during the month. Strombolian ejecta mostly rose 200-300 m above the summit; occasionally it reached 300-400 m. On most days, block avalanches descended the Seca, Taniluyá, Ceniza, Trinidad, and Las Lajas ravines; occasionally they were reported in the El Jute and Honda ravines as well. Every day, rumbles and shock waves shook roofs in nearby villages every 5-10 minutes. Lahars were reported twice, on 2 ad 9 September, in the Seca and Rio Mineral drainages both days, dragging branches, tree trunks and blocks up to 2 m in diameter.

Figure 127. An ash plume drifts from the summit of Fuego on 16 September 2019, seen from the La Reunion webcam. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán de Fuego (1402-09), Semana del 14 al 20 de septiembre de 2,019).

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/ ); 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/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); NASA Astronomy Picture of the day (URL: https://apod.nasa.gov/apod/ap190527.html); 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/); Paul A. Wallace, Lecturer in Geology, University of Liverpool, Liverpool England (URL: https://www.liverpool.ac.uk/environmental-sciences/staff/paul-wallace/, Twitter: @Paul_A_Wallace, URL: https://twitter.com/Paul_A_Wallace/status/1138527752963993600); Alex Cruz, Photojournalist, Guatemala (Twitter: @ACruz_elP, URL: https://twitter.com/ACruz_elP/status/1149690904023691264/photo/1); William Chigna, Guatemala (Twitter: @William_Chigna, URL: https://twitter.com/William_Chigna/status/1164575009966370816); Publinews Guatemala, (Twitter: @PublinewsGT, URL: https://twitter.com/PublinewsGT/status/1157288917365903360).

Erta Ale, located in Ethiopia, contains multiple active pit craters both within the summit and the southeast calderas. On 17 January 2017 the active lava lake displayed intense spattering, fountaining, and rim overflows with lava flows that traveled as far as 1 km, forming a lava flow field. During April 2018 through March 2019 minor activity continued in both the summit and southeast calderas, and along the active lava flow to the E (BGVN 44:04). This report updates volcanism from April through October 2019. Information primarily comes from infrared satellite images and MODIS data.

Continued lava flow breakouts occurred from April through October 2019. On 4 May 2019 a lava flow outbreak was observed in satellite imagery NE of the summit caldera (figure 92). This outbreak continued to appear in clear-weather thermal satellite images through 13 June when it was seen south of its original location (figure 93). Faint incandescence is observed at the summit caldera between June and October 2019, though it is more pronounced in the months of August through October. On 28 June a second smaller lava flow outbreak occurred within 3.8 km of the summit location. The two lava flow outbreaks remained active at least through 18 June. The distal NE lava flow does not appear in very similar images from 17 August or 16 September 2019, but three proximal thermal anomalies are seen in the southeastern caldera within 4 km of the summit. The thermal anomalies remained within 5 km through October 2019.

Figure 92. Sentinel-2 thermal satellite imagery of Erta Ale volcanism on 4 May 2019 with thermal anomalies observed to the northeast of the summit caldera (bright orange). White plumes are seen rising from the summit with faint incandescence. Sentinel-2 satellite images with "False Color (Urban)" (bands 12, 11, 4) rendering; courtesy of Sentinel Hub Playground.

Figure 93. Sentinel-2 thermal satellite imagery of Erta Ale volcanism between 8 June and 21 October 2019. Lava flow outbreaks initially occur in the distal NE part of the lava flow, which then migrates slightly south. A second lava flow outbreak is seen less than 5 km of the summit caldera. Faint incandescence is seen at the summit caldera in each of these images. Sentinel-2 satellite images with "False Color (Urban)" (bands 12, 11, 4) rendering; courtesy of Sentinel Hub Playground.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed consistently high-power thermal anomalies during this reporting period (figure 94). Through July 2019 these thermal anomalies were detected at distances greater than 5 km from the summit. In early August 2019 there was an abrupt decrease in the distance that continued through late October 2019 (figure 94); this likely indicates when the distal NE outbreak ended and lava emissions from the closer SE locations increased (see satellite images in figure 93). The distance changes of MODIS thermal anomalies from the summit seen in MIROVA are corroborated by MODVOLC data, which show no distal NE thermal alert pixels after July 2019 (figure 95).

Figure 94. Two time-series plots of thermal anomalies from Erta Ale for the year ending on 24 October 2019 as recorded by the MIROVA system. The top plot (A) shows that the thermal anomalies were consistently strong (measured in log radiative power) and occurred frequently. The lower plot (B) shows these anomalies as function of distance from the summit, including a sudden decrease in the distance (measured in kilometers) in early August 2019 that reflects a change in lava flow outbreak location. Courtesy of MIROVA.

Figure 95. Locations of the thermal alerts at Erta Ale during November 2018-July 2019 (top) and August-October 2019 (bottom) identified by the MODVOLC system. A majority of the proximal (less than 5 km from the summit) thermal anomalies are found within the southeastern calderas while the distal (beyond 5 km) anomalies are northeast of the summit. Note that the distal NE anomalies are not present after July 2019. Two thermal alerts mark the location of the summit caldera (bottom map). Data courtesy of HIGP-MODVOLC Thermal Alerts System.

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

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

Eruptive activity at Karymsky has been frequent since 1996, with moderate ash explosions, gas-and-steam emissions, and thermal anomalies. The latest eruptive period began in mid-February 2019 (BGVN 44:05) when explosions resumed after more than four months of quiet, producing an ash plume that extended 55 km downwind. Intermittent explosive activity continued until 24 September 2019. The volcano is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT).

Ash plumes were reported during the second half of February and the first half of March 2019 (BGVN 44:05). During May-September 2019 similar activity continued, with ash plumes being generated at least every few days (table 12). Though not included in the weekly KVERT report as notable events, obvious ash plumes were also seen in Sentinel-2 imagery on 22 July and photographed from an aircraft on 23 July. Volcanologists doing fieldwork on 14 August observed an ash plume rising to 5 km altitude (figure 44). A week later, during 20-22 August, explosions generated ash plumes as high as 6 km altitude that were visible in satellite imagery (figure 45). Although not noted in KVERT reports, a photo from 9 September showed a plume blowing downwind directly from the summit crater (figure 46). No significant ash plumes were reported by KVERT after 24 August, but the last ash explosion was recorded on 24 September.

Table 12. Notable ash plumes reported from Karymsky during May-October 2019. All dates are in UTC. Courtesy of KVERT.

Figure 44. Aerial photo showing an ash plume rising to 5 km altitude from Karymsky 14 August 2019. Photo by D. Melnikov; courtesy of IVS FEB RAS, KVERT.

Figure 45. Satellite image from Sentinel-2 (natural color) of an ash plume at Karymsky on 21 August 2019. Courtesy of Sentinel Hub Playground.

Figure 46. Photo showing explosive activity at Karymsky at 1920 UTC on 9 September 2019. Photo by A. Manevich; courtesy of IVS FEB RAS, KVERT.

During May-October 2019, thermal anomalies were detected with the MODIS satellite instruments analyzed using the MODVOLC algorithm only on 25 July (2 pixels) and 21 August (10 pixels). Consistent with both observations, KVERT noted ash explosions on those dates. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected numerous hotspots in May, none in June, 3 in July, 5 in August, and none in September or October. KVERT reported that a thermal anomaly was visible in satellite images on most, if not all, days when not obscured by clouds.

The Aviation Color Code remained at Orange (the second highest level on a four-color scale) until 3 October, when KVERT reduced it to Yellow, after which moderate gas-and-steam activity continued.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Recent activity at Shishaldin, located on Unimak Island within the Aleutian Islands, has included a lava eruption in the summit crater, thermal anomalies, elevated seismicity, and gas-and-steam and ash plumes (BGVN 41:11). This report describes minor gas-and-steam emissions, increased seismicity, thermal anomalies, lava fountaining accompanied by minor explosive activity, and a spatter cone. The primary source of information is the Alaska Volcano Observatory (AVO). This report updates activity through September 2019.

Volcanism was relatively low between March 2016 and early July 2019; increased seismicity and steam emissions were detected in December 2017, but the activity declined in February 2018. Elevated seismicity and some thermal anomalies accompanied by incandescence observed in satellite imagery (when not obscured by clouds) returned in mid-July 2019 (figure 12).

Figure 12. Summary graphic of MODVOLC thermal alerts measured over Shishaldin during July-September 2019. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Elevated surface temperatures and low-level seismic tremors remained elevated through September 2019 (figure 13). Field crews reported an active lava lake and minor spattering within the summit crater on 23 July 2019 (figures 14 and 15). Satellite imagery showed the presence of a small spatter cone and some lava flows within the summit crater on 28 July. A small steam plume was observed in satellite imagery and webcam images on 29 July, 20 August, and 30 September.

Figure 13. Sentinel-2 satellite imagery of Shishaldin showing detected thermal anomalies between the months of July and September 2019. Top left: Satellite image on 19 July showing a gas-and-steam plume. Top center: On 29 July a thermal anomaly is detected in the summit crater. Top right: On 28 August, the thermal anomaly is still present. Bottom left: On 7 September, the thermal anomaly continues. Bottom right: On 24 September, the power of the thermal anomaly significantly decreases. Atmospheric penetration satellite image (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

Figure 14. Photo of surface lava within the summit crater at Shishaldin taken on 23 July 2019. Photo by David Fee (color corrected); courtesy of Alaska Volcano Observatory (AVO).

Figure 15. Photo of lava and a slightly growing spatter cone within the summit crater at Shishaldin taken on 23 July 2019. Photo by Dane Ketner (color corrected); courtesy of Alaska Volcano Observatory (AVO).

On 17 August 2019, a video taken by NOAA during an overflight showed repetitive minor explosive activity and low-level lava fountaining within the summit crater. This activity may have continued through 24 September, according to AVO. The spatter cone grew slightly in August and September, partially filling the summit crater. Accompanying lava flows also grew slightly during this time.

Satellite data from 3 September showed SO2 emissions and elevated surface temperatures. Satellite imagery and tiltmeter data recorded a collapse and slumping of the summit crater floor, which may have occurred on 19 September. In the last few weeks of September, seismicity and surface temperatures decreased to slightly above background levels.

According to MIROVA (Middle InfraRed Observation of Volcanic Activity) data from MODIS satellite instruments, more frequent thermal anomalies were detected in mid-July 2019 and remained elevated through early September (figure 16).

Figure 16. Thermal anomalies increased at Shishaldin from mid-July 2019 through early September and then abruptly stopped as recorded by MIROVA (log radiative power). Courtesy of MIROVA.

Geologic Background. The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, 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 steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 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/); 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).

During September 2018 through June 2019, activity at Klyuchevskoy was characterized by weak thermal anomalies and moderate Strombolian-type explosions. Ash emissions were only reported on 1-2 July and 1 August during the period of July-September 2019. The volcano is monitored by the Kamchatkan Volcanic Eruption Response Team (KVERT) and is the primary source of information.

According to KVERT, moderate activity continued from July through at least the middle of September, with gas-and-steam emissions. At the beginning of July, KVERT reported incandescence in the crater. During 1-2 July, ash plumes drifted as far as 85 km E and SE. Ash plumes were visible blowing E in Sentinel-2 images on 17 and 19 July (figure 32); steam plumes were evident on some other days. KVERT reported that an ash emission was seen in webcam images on 1 August.

Figure 32. An ash plume can be seen blowing E from the summit crater of Klyuchevskoy in this Sentinel-2 natural color (bands 4, 3, 2) satellite image from 17 July 2019. Courtesy of Sentinel Hub Playground.

No thermal anomalies were detected with the MODIS satellite instruments analyzed using the MODVOLC algorithm. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected no thermal anomalies in June, four scattered ones in July, and only one in August, all low power. According to KVERT, a weak thermal anomaly was detected throughout the reporting period, at least through mid-September, except for the numerous days when the volcano was obscured by clouds; the temperature of the anomalies had steadily decreased with time.

Instruments aboard NASA satellites detected high levels of sulfur dioxide near or directly above the volcano every day during the first week of July and on 12 July, but not on other days during the reporting period. However, the origin for the high levels may, at least in part, have been due to other active volcanoes in the area.

At the beginning of July, the Aviation Color Code (ACC) remained at Orange (the second highest level on a four-color scale). Because of decreased activity, KVERT lowered the ACC to Yellow on 30 August and to Green (the lowest on the scale) on 24 September.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Heard Island, in the Southern Indian Ocean, is about 4,000 km from its closest point to Australia and about 1,500 km from the closest point in Antarctica. Because of the island's remoteness, monitoring is primarily accomplished by satellites. The Big Ben volcano has been active intermittently since 1910, if not before (BGVN 42:10), and thermal anomalies have been observed every month since June 2018 (BGVN 43:10, 44:04). The current reporting period is from April to September 2019.

During April-September 2019, only one thermal anomaly was detected with the MODIS satellite instruments analyzed using the MODVOLC algorithm, and that was on 10 June (2 pixels). The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected a few scattered thermal alerts in late May-early June and three in September; most were between 1-2 km of the summit and of low to moderate power.

The island is usually covered by heavy clouds, obscuring satellite views. However, Sentinel-2 satellite imagery detected cloud-obscured thermal anomalies during the reporting period, most likely due to a persistent lava lake and possibly lava flows (BGVN 41:08).

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: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

The eruption at Dukono, ongoing since 1933, is typified by frequent ash explosions and ash plumes (BGVN 43:04). This activity continued through at least September 2019. The data below were primarily provided by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM), and the Darwin Volcanic Ash Advisory Centre (VAAC).

According to PVMBG, during April-September 2019 the volcano continued to generate ash plumes almost every day that rose to altitudes of 1.5-3 km (table 20, figure 12). Ashfall was reported on 8 August at the Galela Airport, Maluku Utara, 17 km NW. The Alert Level remained at 2 (on a scale of 1-4), and the 2-km exclusion zone remained in effect.

Table 20. Monthly summary of reported ash plumes from Dukono for April-September 2019. The direction of drift for the ash plume through each month was highly variable, but did not extend for any notable distances during this reporting period. Data courtesy of the Darwin VAAC and PVMBG.

Figure 12. Satellite image from Sentinel-2 (natural color) of an ash plume at Dukono on 4 August 2019, with the plume blowing almost straight up. Courtesy of Sentinel Hub Playground.

Instruments aboard NASA satellites detected high levels of sulfur dioxide near or directly above the volcano on 11, 20-22 April; 17, 22, and 27 May; 15-18 August; and 23-24 and 29 September. However, the cause of the high levels may, at least in part, have been due to other active volcanoes in the area.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

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

Activity at Poás is characterized by weak phreatic explosions and gas-and-ash-emissions, with a hot acid lake that occasionally disappears (BGVN 44:05). During the current reporting period of May-September 2019, this weak activity continued. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and most of the material below comes from their weekly bulletins (Boletin Semanal Vulcanologia).

According to OVSICORI-UNA, a period of continuous emissions occurred during 30 April-1 May with plumes rising 300 m above the crater rim and drifting SW. Ash emissions were visible for a few hours on 30 April, and incandescence was visible at night. OVSICORI-UNA did not report any additional phreatic explosions in May until daily phreatic, geyser-type explosions were observed between 29 May and 1 June, which reached approximately 100 m above the vent. A phreatic explosion on 10 June reached approximately 20-30 m in height, and frequent small phreatic explosions (heights below 20 m) were reported through 16 June.

OVSICORI-UNA reported that on 12 June small geyser-like explosions ejected material less than 50 m high at a rate of about once per hour. At 0604 on 18 June an explosion that lasted about six minutes produced a plume of unknown height. Residents reportedly heard several loud noises during 0610-0615 and observed a plume rising from the crater. Ash fell in Cajón (12 km SW), San Luis de Grecia (11 km SW), Los Ángeles, San Miguel de Grecia (11 km SW), San Isidro (28 km SE), and San Roque (23 km SSE). Whitish ash deposits surrounding the crater, especially on the W and S sectors, were visible in webcam images. On 21 June frequent small phreatic explosions from vent A (Boca Roja) were visible during good viewing conditions ejecting material less than 10 m high.

No additional phreatic activity was reported by OVSICORI-UNA during rest of June or July. The small crater lake was still present on 5 July when visible in satellite imagery and as seen by visitors (figure 130), During the first part of August geyser-like explosions occurred on several days, and reached a maximum height of 50 m. This activity culminated on 17 August with about 30 explosions/day from the vent (Boca Roja). At least one event at 0650 on that day generated a 1-km-high plume of steam, gas, and fine particles. By 26 August, the geyser-type activity had ceased. Geyser-type phreatic explosions resumed on 12 September, reaching a maximum height of 30 m. The number of explosions increased up to 10-15 events/hour and then became continuous for a short time. A phreatic explosion occurred on 22 September at 2059 that generated a plume that rose 3 km above the crater rim and drifted NE. During 22-23 September explosions generated plumes that rose 1 km.

Figure 130. View of the Poás crater on 5 July 2019. The volcano is surrounded by cloud-cover, and there is some steam rising from the crater lake. Photo by Sheila DeForest (Creative Commons BY-SA license).

According to OVSICORI-UNA, during 16-26 September sulfur dioxide emissions drifted W and NE, causing a sulfur odor in Alajuela, Heredia, San José, and Cartago. Acidic rain was recorded at an official's house in the Poás Volcano National Park (PNVP) on 23 September and at the Universidad Nacional Costa Rica (UNA) in Heredia (23 km SE) on 26 September. On 30 September, at 0540, a 5-minute long phreatic explosion ejected sediment, and produced a plume that rose 2 km above the crater rim and drifted SW. Ashfall and a sulfur odor was reported in Trojas de Sarchi (10 km SW) and Grecia (16 km SSW). Officials closed the PNVP because of the eruption and ongoing elevated seismicity; the park remained closed the next day.

During the first week of August, strong evaporation had reduced the intracrater lake significantly, and by mid-September, the lake had disappeared. At the end of September, however, some water had begun to accumulate again.

General monitoring data. During April and May, OVSICORI-UNA took few gas measurements due to an unfavorable wind direction. An SO2 measurement during the first part of June was between 100 and 200 t/d. Flux remained low through July, with low SO2/CO2 ratios, and high H2S/SO2 ratios, which OVSICORI-UNA stated were consistent with water infiltration. At the end of July, SO2 concentrations significantly increased to 300-800 t/d, with H2S disappearing and the CO2/SO2 ratio declining, with some fluctuations. Levels remained high through most of August, but had decreased to about 300 t/d by the end of the month. They rose again in September, with fluctuations, and on 29 September were measured at about 1,000 t/d before falling to between 300-400 t/d.

According to OVSICORI-UNA weekly reports, seismicity was relatively low during the reporting period, with a few VTs and LPs and normal background tremor. No significant deformation occurred, except for some deflation in June and July.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Sheila DeForest (URL: https://www.facebook.com/sheila.deforest).

Italy's Mount Etna on the island of Sicily has had historically recorded eruptions for the past 3,500 years and has been erupting continuously since September 2013 through at least September 2019. Lava flows, explosive eruptions with ash plumes, and Strombolian lava fountains commonly occur from its summit areas that include the Northeast Crater (NEC), the Voragine-Bocca Nuova (or Central) complex (VOR-BN), the Southeast Crater (SEC, formed in 1978), and the New Southeast Crater (NSEC, formed in 2011). The newest crater, referred to as the "cono della sella" (saddle cone), emerged during early 2017 in the area between SEC and NSEC. Varying activity that included several lava flows, Strombolian activity, and numerous ash plumes from most of the active summit vents and several flank fissures occurred during April-September 2019, the period covered in this report, with information provided primarily by the Osservatorio Etneo (OE), part of the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV).

Degassing of variable intensity was typical activity from all the vents at Etna during much of April 2019. Intermittent ash emission and Strombolian activity occurred at Bocca Nuova, especially during the last week. Minor ash emissions were reported from NEC and NSEC the last week as well. Most of the activity at the summit during May 2019 was focused around the New South East Crater (NSEC); repeated Strombolian activity was witnessed from the E vent near the summit throughout the month. Beginning on 30 May, two fissures opened on the N and SE flanks of NSEC and produced lava flows that traveled E and SE across the W wall of the Valle del Bove. The flows ceased during the first week of June; activity for the rest of that month consisted of intermittent explosions with small ash plumes from Voragine and Bocca Nuova. Discontinuous Strombolian explosions and isolated ash emissions from NEC, NSEC, and Bocca Nuova characterized activity during the first half of July 2019; the explosions intensified at NSEC later in the month. A lava flow emerged from the lower NE flank of NSEC on 18 July that lasted for several days. Explosions produced substantial ash plumes from the NSEC summit crater, causing ashfall nearby, and a new flow emerged from a fissure on the S flank of NSEC on 27 July.

Explosions with intermittent ash emissions during August 2019 were focused primarily on the North East Crater (NEC), with occasional ash emissions from Bocca Nuova. These continued into early September. Activity increased to include Strombolian explosions with the ash emissions at NEC, Bocca Nuova, and Voragine where a scoria cone formed deep within the crater from continued Strombolian activity. A lava flow emerged from the base of the scoria cone on 18 September and was active for about four days, sending branches of lava into multiple areas of the adjacent Bocca Nuova crater. Ash emissions at NEC continued during the end of the month. The multiple episodes of varying activity during the period were reflected in the MIROVA thermal energy data; spikes of thermal activity that corresponded to periods of lava effusion were apparent late May-early June, multiple times in July, and during the second half of September (figure 260).

Figure 260. The multiple episodes of varying activity at Etna from 11 December 2018 through September 2019 were reflected in the MIROVA thermal energy data; spikes of thermal activity were apparent in late April, late May-early June, multiple times in July, and during the second half of September. The largest energy spikes correlated with lava flows. Courtesy of MIROVA.

Activity during April-May 2019. During a site visit to the summit on 1 April scientists from INGV noted weak degassing from both pit craters, BN-1 and BN-2, within Bocca Nuova (BN); the Voragine (VOR) and North East Crater (NEC) were emitting abundant steam and gas emissions. The New Southeast Crater (NSEC) also had significant fumarolic activity concentrated primarily on the crater rim along with gas plumes visible from both the E vent and the 24 December 2018 flank fissure (figure 261). A brief episode of ash emission was observed from BN on the morning of 8 April. Persistent pulsating flashes of incandescence were noted at the E vent of NSEC during the second week. A new vent was observed in the inner wall of the Voragine crater during an inspection on 19 April, located immediately below the vent which formed on 12 January 2019 (figure 262). During the last week of April there were ten episodes of ash emission from BN, two from NEC, and one produced by the E vent at NSEC. Strombolian activity was observed on the morning of 28 April at BN-1, and persistent incandescence was visible from the E vent of NSEC. Early on 30 April both BN-1 and BN-2 were producing explosions every few seconds. Coarse ejecta (lapilli and bombs) rose higher than the crater rim; most fell back within the crater, but some material was observed on the rim the following day.

Figure 261. During a site visit to the summit of Etna on 1 April 2019 scientists from INGV noted weak degassing from both pit craters, BN-1 and BN-2, within Bocca Nuova (BN); Voragine (VOR) and North East Crater (NEC) were emitting abundant steam and gas emissions, and the New Southeast Crater (NSEC) also had significant fumarolic activity concentrated primarily on the crater rim along with gas plumes visible from both the E vent (bocca orientale) and the 24 December 2018 flank fissure. Courtesy of INGV, photos by Laboratorio di Cartografia FlyeEye Team (Report 15/2019, ETNA, Bollettino Settimanale, 01/04/2019 - 07/04/2019, data emissione 09/04/2019).

Figure 262. A new vent was observed at the W rim of Etna's Voragine crater on 19 April 2019. INGV scientists concluded that it likely formed during 17-18 April. It was located immediately below a pit crater that opened on 12 January 2019. Inset shows thermal image of the vents. Courtesy of INGV (Report 17/2019, ETNA, Bollettino Settimanale, 15/04/2019 - 21/04/2019, data emissione 24/04/2019).

Activity at the summit during May 2019 was focused around the New South East Crater (NSEC). Discontinuous Strombolian activity was observed at the E vent of NSEC early on 2 May accompanied by ash emissions from the summit vent that rose about 1,000 m (figure 263). Explosion frequency increased beginning on 5 May with weak and discontinuous ash emissions reported from the NSEC summit for the next several days; ash emissions were also observed from the Saddle vent and the NSEC E vent during 6-8 May. In addition to ash emissions and Strombolian activity continuing from both the summit and E vents at NSEC during the third and fourth weeks, overnight on 17-18 May several larger Strombolian explosions sent pyroclastic ejecta tens of meters above the crater rim (figure 264). The explosion intervals ranged from a few minutes to a few hours. The new vent that had formed at Voragine in mid-April coalesced with the 12 January vent during the second week of May; dilute ash was observed from the BN-1 vent on 23 May.

Figure 263. Strombolian activity at the E vent of NSEC at Etna was accompanied by ash emission on 2 May 2019. Left image is from the thermal camera at La Montagnola and the right image is from Tremestieri Etneo, taken by B. Behncke. Coutesy of INGV (Report 19/2019, ETNA, Bollettino Settimanale, 29/04/2019 - 05/05/2019, data emissione 07/05/2019).

Figure 264. Strombolian activity sent ejecta from a vent at Etna's NSEC crater on 14 May 2019 (a) and was captured by the Monte Cagliato thermal camera. Ash emission from the same vent was also visible that day (b) and on 17 May (c). Strombolian explosions from the E Vent of NSEC on 17 May (d) were captured by the EMOH (Montagnola) webcam. Courtesy of INGV (Report 21/2019, ETNA, Bollettino Settimanale, 13/05/2019 - 19/05/2019, data emissione 21/05/2019).

A fissure opened at the base of the N flank of NSEC shortly after midnight on 30 May 2019 at an elevation of about 3,150 m (figure 265). It produced mild explosive activity and a lava flow that spread towards the W wall of the Valle del Bove. By 0800 UTC the flow had reached an elevation of 2,050 m. A second fissure opened at 0335 the same morning at the base of the SE flank of NSEC at an elevation of 3,050 m. The lava flowed along the W wall of the Valle del Bove towards Serra Giannicola Grande and had reached an elevation of 2,260 m by 0815. Strong winds dispersed ash emissions from the fissures to the NE for much of the day; ashfall occurred in Linguaglossa (figure 266). The Toulouse VAAC reported an ash plume drifting ENE at 3.9 km altitude on 30 May. Samples of the ash that were collected and analyzed were shown to be about 70% lithic clasts, 25% crystals, and about 5% juvenile material. It became clear the next day that two vents along the SE-flank fissure initially produced separate flows that coalesced into a single flow which expanded along the W wall of Valle del Bove. By 0830 on 31 May that flow had reached an elevation of 1,700 m at the base of Serra Giannicola Grande. The fissure at the base of the N flank continued to propagate along the W wall of Valle del Bove also, and had reached an elevation of 2,050 near Monte Simone by 1030 on 31 May (figure 267). When the new eruptive activity began on 29 May, inclinometers measured slight but prolonged deflation of the volcano.

Figure 265. Two fissures opened at Etna during the early morning of 30 May 2019. One started from the base of the N flank of the NSEC/SEC complex and flowed E towards the Valle del Bove, and a second fissure with two vents opened on the SE flank of NSEC and flowed SE towards Serra Giannicola Grande. Mapping of the lava flows were done with drones, using the Sentinel 2 satellite images of 30 May and thermal images from 2 June taken at the Schiena dell'Asino. Courtesy of INGV (Report 23/2019, ETNA, Bollettino Settimanale, 27/05/2019 - 02/06/2019, data emissione 04/06/2019).

Figure 266. Lava flows broke out at Etna on both the N and SE flanks of NSEC on 30 May 2019. Ash emissions were also produced from the fissures. The northern flank fissure is seen from the (a) Monte Cagliato thermal camera (EMCT) and (b) the Montagnola high definition camera (EMOH). The fissure on the SE flank was seen from the Montagnola thermal (c) and high definition (d) (EMOH) webcams. Ash emissions and lava flows were visible on the flank (e) and ashfall was recorded in Linguaglossa (f). Courtesy of INGV (Report 23/2019, ETNA, Bollettino Settimanale, 27/05/2019 - 02/06/2019, data emissione 04/06/2019).

Figure 267. Images of the active lava flows at Etna on 31 May 2019 indicated the extent of the flow activity. Lava was flowing from two vents along a fissure on the SE flank (a and b, drone images courtesy of the FlyEye Team OE). The thermal image of the flow (c) is from Schiena dell'Asi, the visible photo (d) is also taken from Schiena dell'Asi by L. Lodato. The thermal (e) and visual (f) images of the active lava fields were taken from the Monte Cagliato (EMCT) thermal webcam and the Monte Cagliato (EMCH) high definition webcam. Courtesy of INGV (Report 23/2019, ETNA, Bollettino Settimanale, 27/05/2019 - 02/06/2019, data emissione 04/06/2019).

Activity during June-July 2019. The flow from the N flank of NSEC ceased advancing on 1 June 2019, but the active spattering continued from the fissure on the SE flank for a few more days. The SE-flank flow had reached 1,700 m elevation in the Valle del Bove by the afternoon of 2 June (figure 268). The intensity and frequency of the explosions decreased over the next few days, with the active flow front receding back towards the vent until it stopped moving on 6 June. The NE rim of the summit cone at NSEC appeared lowered by several meters after the eruption ceased. The lava flows and explosions of 30 May-2 June produced persistent SO₂ emissions that drifted E and N for over 800 km (figure 269).

Figure 268. During the morning of 1 June 2019 Strombolian and effusive activity at Etna continued from the fissure on the SE flank of NSEC (a and b, photos by M. Neri). By the evening of 1 June there was only one remaining arm of the flow that was active (c) as seen in the Monte Cagliato (EMCT) thermal webcam. The following evening, 2 June, another thermal image(d, photo by S. Scollo) showed the remaining active arm. Courtesy of INGV (Report 23/2019, ETNA, Bollettino Settimanale, 27/05/2019 - 02/06/2019).

Figure 269. Active lava flows and Strombolian activity at Etna during 30 May-2 June 2019 contributed to significant SO2 plumes that drifted E and NE from the volcano during this time, extending as far as 800 km from the source. Captured by the TROPOMI instrument on the Sentinel 5P satellite, courtesy of NASA Goddard Space Flight Center.

Activity for the rest of June 2019 moved to the other craters, mainly Voragine, after the flows ceased at NSEC. On the morning of 6 June there were sporadic ash emissions from NEC that quickly dissipated. A small ash plume appeared from Bocca Nuova (BN) on 11 June. An explosive sequence that began on 13 June from the crater floor of Voragine continued intermittently through the third week of the month (figure 270) and produced several small ash plumes. A new vent opened on the crater floor and produced a small ash plume; ejecta also landed on the crater rim several times. On 22 June small, discontinuous ash emissions were produced from BN-1; they dispersed rapidly, but intermittent explosions continued during the following week. By the end of the month, only BN was exhibiting activity other than degassing; incandescence from the crater was seen during the night of 24 June and three isolated ash emissions were seen in the webcams on 26 June.

Figure 270. An ash plume at Etna rose from the Voragine crater on 15 June 2019 during a series of intermittent explosions. Image taken from the Torre del Filosofo by M. Coltelli. Courtesy of INGV (Report 25/2019, ETNA, Bollettino Settimanale, 10/06/2019 - 16/06/2019, data emissione 18/06/2019).

Discontinuous Strombolian explosions and isolated ash emissions characterized activity during the first half of July 2019. Pulsating degassing from NEC produced ash emissions on 2 and 3 July (figure 271), and incandescence on 4 and 5 July. Intense degassing was observed at NSEC during 1-5 July, this turned into isolated ash emissions and Strombolian activity on 5 and 6 July from the E vent with explosions occurring every 1-5 minutes; the ejecta landed on the upper E flank. Dilute ash emissions were observed from Bocca Nuova on 6 July. NEC produced two major ash emissions on the evening of 8 July and the late morning of 13 July. The ash plumes quickly dispersed in the summit area. Strombolian activity at the E vent of NSEC was witnessed on 14 July. Explosive activity at Bocca Nuova remained deep within the crater during mid-July. Steam produced by the 13 June 2019 vent on the floor of Voragine occasionally contained dilute ash. During 15-17 July sporadic explosions were observed at NSEC accompanied by small puffs of ash that rapidly dispersed.

Figure 271. Surveillance cameras at Etna captured images of explosions with ash emissions from NEC on 2 (top) and 3 (bottom) July 2019. The left images are from Montagnola and the right images are from Monte Cagliato. Courtesy of INGV (Report 28/2019, ETNA, Bollettino Settimanale, 01/07/2019 - 07/07/2019, data emissione 09/07/2019).

Beginning early on 18 July, Strombolian activity increased at NSEC from an explosion every 1-2 minutes to multiple explosions per minute in the following hours. Continuous activity during the evening decreased sharply around 2200. About an hour later visual and thermal surveillance cameras on Monte Cagliato recorded the opening of a vent on the lower NE flank of NSEC; lava slowly advanced from the vent towards Valle del Leone (figures 272 and 273). Explosive activity resumed at the NSEC summit a few hours later, accompanied by occasional ash emissions from NEC and Bocca Nuova. Explosions tapered off briefly by noon on 19 July, but a sudden increase in explosive activity during the afternoon of 19 July produced Strombolian activity and sporadic ash emissions from three vents inside the NSEC crater. Ashfall was reported that evening in communities on the S flank of Etna. The Toulouse VAAC reported significant ash above the summit at 3.7 km altitude. Activity declined again later that evening at NSEC, but abundant ash emission began at NEC that lasted until the morning of 20 July. A new phase of explosive activity began at NSEC around 0700 on 20 July with an ash plume and an increase in lava emission from the vent on the NE flank (figure 274). By the evening of 20 July only a small amount of material was feeding the lava flow; the farthest advanced fronts were at an elevation around 2,150 m, above Monte Simone. A few small ash emissions were observed at Bocca Nuova on 21 July.

Figure 272. Map of the summit craters of Etna showing the active vents and the lava flow of 19-21 July 2019. The base is modified from a 2014 DEM created by Laboratorio di Aerogeofisica-Sezione Roma 2. Black hatch marks indicate the crater rims: BN = Bocca Nuova, with NW BN-1 and SE BN-2; VOR = Voragine; NEC = North East Crater; SEC = South East Crater; NSEC = New South East Crater. Red circles indicate areas with ash emissions and/or Strombolian activity, yellow circles indicate steam and/or gas emissions only. Courtesy of INGV (Report 30/2019, ETNA, Bollettino Settimanale, 15/07/2019 - 21/07/2019, data emissione 23/07/2019).

Figure 273. Activity at Etna on 18 and 19 July 2019 included a new lava flow from a vent on the NE flank of NSEC and Strombolian activity at the NSEC summit vent. (a) Start of the flow from a vent on the NE flank of NSEC seen from the high-resolution camera at Monte Cagliato (EMCH) at 2307 UTC on 18 July. (b) Strombolian activity at the NSEC and glow of the new lava flow on the right seen from Tremestieri Etneo, 2347 that evening. (c) A new advancing lava flow and brown ash emission from NEC seen from the EMCH camera, 0338 on 19 July; (d) lava flow seen from the thermal camera at Monte Cagliato, 0700 on 19 July. Courtesy of INGV (Report 30/2019, ETNA, Bollettino Settimanale, 15/07/2019 - 21/07/2019, data emissione 23/07/2019).

Figure 274. Activity at Etna on 20 July 2019 included (a) ash emission from both NSEC and NEC craters at 0402 seen from Tremestieri Etneo, (b) ash from NSEC and the active flow on the SE flank at 0608 seen from the Monte Cagliato high-resolution camera, (c) ash emission from NSEC at 0700 seen by Tremesteieri Etneo, and (d) explosive activity at NSEC and the lava flow on the W wall of the Valle del Bove at 0700 seen from the Monte Cagliato thermal camera. Courtesy of INGV (Report 30/2019, ETNA, Bollettino Settimanale, 15/07/2019 - 21/07/2019, data emissione 23/07/2019).

Visible and thermal images taken on 24 July 2019 indicated only degassing at BN-1 and BN-2, and limited degassing from low-temperature fumaroles from the multiple vents at VOR (figure 275). After a few days of quiet, NSEC resumed discontinuous ash emissions on 25 July. A sudden increase in the amplitude of volcanic tremor was noted early on 27 July, which was followed a few hours later by the opening of a new eruptive fissure on the S flank of NSEC (figure 276). Explosive activity intensified and produced a dense ash-rich plume that dispersed to the E at an estimated altitude of 4.5-5 km. A thin layer of ash was reported in Giarre, Riposto, and Torre Archirafi. A lava flow emerged from the S portion of the fissure and expanded SW and S. By 1135 the most advanced front had reached and passed the N side of the base of the Barbagallo Mountians at an elevation of about 2,850 m. It continued to spread down into the area between Monte Frumento Supino and the pyroclastic cones of 2002-2003 (figure 277). A series of particularly strong explosions occurred from NSEC around midday, producing an ash plume that rose to 7.5 km altitude. By this time the most advanced lava fronts were located at an elevation of about 2,600 m, but they were rapidly advancing SSW towards Monte Nero, surrounding Monte Frumento Supino from the W. Explosive activity decreased significantly early in the morning on 28 July; flow activity also slowed around the same time. Occasional puffs of reddish-brown ash were noted from NEC during the morning as well. The explosions and the lava effusion ceased on the evening of 28 July. An isolated ash emission from Bocca Nuova in the early hours of 31 July was the last activity reported in July. A substantial SO₂ plume (6.59 DU) from the explosions on 27 July had drifted to the E coast of the Adriatic Sea by midday on 28 July and was detected in satellite instruments.

Figure 275. Degassing was the only activity occurring at the multiple vents at Etna's Voragine crater on 24 July 2019. The joined pit crater from the 12 January and 18 April 2019 vents is at the upper left; the newest vent formed 16 June 2019 is at lower left and appears cool in the thermal image inset a. Photo and annotations by S. Branca. Courtesy of INGV (Rep. N° 31/2019, ETNA, Bollettino Settimanale, 22/07/2019 - 28/07/2019, data emissione 30/07/2019).

Figure 276. A new eruptive fissure at Etna opened on the S flank of NSEC on 27 July 2019 (line of red circles). The base map is modified from a 2014 DEM created by Laboratorio di Aerogeofisica-Sezione Roma 2. Black hatch marks indicate the crater rims: BN=Bocca Nuova, with NW BN-1 and SE BN-2; VOR = Voragine; NEC = North East Crater; SEC = South East Crater; NSEC = New South East Crater. Red circles indicate areas with ash emissions and/or Strombolian activity, yellow circles indicate steam and/or gas emissions only. Courtesy of INGV (Report 31/2019, ETNA, Bollettino Settimanale, 22/07/2019 - 28/07/2019, data emissione 30/07/2019).

Figure 277. Lava flows and substantial ash emissions were reported at Etna on 27 July 2019. The lava flow at 1216 was located at about 2,600 m elevation (a). A thermal image of the S flank of NSEC showed the extent of the flow activity (b). A large ash plume formed after several explosions at NSEC at 1221 (c). Thermal images of the emissions were captured by the Montagnola (EMOT) webcam and by an INGV operator (d, e). Photos by S. Branca (a), B. Behncke (c), and E. Pecora (b, e). Courtesy of INGV (Report 31/2019, ETNA, Bollettino Settimanale, 22/07/2019 - 28/07/2019, data emissione 30/07/2019).

Activity during August-September 2019. Activity during August 2019 was focused primarily on the North East Crater (NEC), with occasional ash emissions from Bocca Nuova. The plumes were occasionally dense and dark brown from NEC. Weak emissions of dilute ash from NEC quickly dispersed on the morning of 4 August, followed by more intermittent ash emissions during 6-10 August; a few had significant concentrations of ash that drifted SE. Part of the N rim of NEC collapsed during the explosions of early August (figure 278). During a site inspection to the summit by INGV personnel on 16 August, continuous degassing at Bocca Nuova was interrupted every 10-15 minutes by explosions, but no ejecta was noted. Discontinuous emissions from NEC formed small ash plumes that rose a few hundred meters and remained in the summit area (figure 279). Thermal surveys that day indicated high temperatures of about 800°C along a 10-m-fracture zone on the northern rim of VOR. Ash emissions from NEC were persistent through 20 August when they decreased significantly; a few explosions had dilute ash emissions from Bocca Nuova that day and the next (figure 280). Sulfur dioxide emissions were notable during 19-22 August, drifting S and W hundreds of kilometers before dissipating. Isolated and dilute ash from NEC early on 28 August was interpreted by INGV as resulting from collapses along the inner crater walls. During site inspections on 27, 28, and 30 August, deep explosions from Bocca Nuova were heard, and degassing was observed at all of the summit vents.

Figure 278. Part of the N rim of the NEC crater at Etna collapsed during explosions in early August 2019. In this image from 10 August 2019 the collapsed N wall is shown by white arrows, the old crater rim is the dashed yellow line, and the new rim is the solid yellow line. Photo by Michele Mammino, courtesy of INGV (Report 33/2019, ETNA, Bollettino Settimanale, 05/08/2019 - 11/08/2019, data emissione 13/08/2019).

Figure 279. Discontinuous emissions at Etna on 16 August 2019 from the NEC crater formed small ash plumes that rose a few hundred meters and remained in the summit area (a). Smaller ash plumes remained within the crater (b and c). Courtesy of INGV (Report 34/2019, ETNA, Bollettino Settimanale, 12/08/2019 - 18/08/2019, data emissione 20/08/2019).

Figure 280. In the foreground weak degassing occurs on 21 August 2019 at Etna's BN-2 vent inside Bocca Nuova while a small ash plume in the background rises from NEC. Photo by F. Ciancitto, courtesy of INGV (Report 35/2019, ETNA, Bollettino Settimanale, 19/08/2019 - 25/08/2019, data emissione 27/08/2019).

Activity during September 2019 began with discontinuous and dilute ash emissions from NEC and Bocca Nuova, as well as episodes of Strombolian activity at both vents. This was followed by increased Strombolian activity, ash emissions, and a lava flow at Voragine. Isolated ash emissions occurred at NEC and VOR on 4 and 5 September. Sporadic deep explosions were heard from BN-1 during a site inspection on 7 September. Overnight during 7-8 September the visual webcams recorded incandescence at NEC and pyroclastic ejecta observed outside the crater rim that coincided with increased tremor activity. A more intense episode of Strombolian activity began the following evening at NEC. Activity was continuous from 1800 on 9 September to 0500 on 10 September, and produced dilute ash emissions that quickly dispersed (figure 281). Slight ashfall was reported in Piedimonte Etneo, Giarre-Riposto, and Rifugio Citelli. Continuous puffs of dilute ash were observed beginning at dawn on 11 September with sporadic ejecta again landing outside the crater rim. Significant SO₂ plumes were measured by satellite instruments on 10 and 11 September (figure 282).

Figure 281. Activity at Etna overnight during 9-10 September 2019 included Strombolian activity and dilute ash emissions from NEC that were observed from webcams on the S, W, and E flanks. Courtesy of INGV (Report 38/2019, ETNA, Bollettino Settimanale, 09/09/2019 - 15/09/2019, data emissione 17/09/2019).

Figure 282. Significant SO2 plumes from Etna were detected on 10 and 11 September 2019. Increased Strombolian activity was reported by INGV from the NEC crater during 9-11 September. Courtesy of NASA Goddard Space Center.

In addition to the Strombolian activity at NEC on 12 September, ash emissions began that morning at VOR. They increased in frequency and then transitioned to near-continuous Strombolian activity that produced ejecta which landed in the base of the adjacent Bocca Nuova crater. The explosions from the Strombolian activity were felt in Zafferana Etnea, Aci S. Antonio, Pedara, and neighboring areas. On 13 September the webcams observed multiple periods of continuous ash emissions from NEC and short, intense pulses of ash from VOR that accompanied Strombolian activity; coarse ejecta rose 20 m above and landed outside of the crater rim, producing impact craters on the W side of the summit between VOR and BN. The vent that sourced the Strombolian activity was located in the deepest part of the Voragine crater. By 15 September, continued ejecta had formed a scoria cone around the vent inside VOR (figure 283).

Figure 283. On 13 September 2019 Strombolian activity at Etna's NEC and VOR craters increased (a). INGV personnel observed an ash emission from NEC (b), a Strombolian explosion with ejecta from VOR (c), and impact craters from the ejecta around the rim (d). The continued activity at VOR produced a scoria cone inside the crater that grew noticeably between 13 (e) and 15 (f) September. Photos (a) and (e) courtesy of L. D'Agata, photo (f) by B. Behncke. Courtesy of INGV (Report 38/2019, ETNA, Bollettino Settimanale, 09/09/2019 - 15/09/2019, data emissione 17/09/2019).

Explosive activity inside VOR increased on the afternoon of 18 September 2019. Pyroclastic ejecta and ash erupted from several vents and reached heights of several tens of meters. A lava flow emerged from the W base of the scoria cone and headed S, advancing several hundred meters (figure 284). It then flowed over the saddle that divides VOR and BN, split into two branches, and entered Bocca Nuova. One stream poured into BN-1, and another stopped near the edge of the BN-2 pit crater. By 22 September the flow was cooling, but strong Strombolian activity continued inside Voragine. NEC was characterized by large-scale ash emissions during the end of September, including one in the morning of 27 September that sent a plume over the S flank of Etna before dissipating (figure 285). Strombolian activity continued within Bocca Nuova during the last week of the month.

Figure 284. Significant Strombolian and lava flow activity at Etna affected the Voragine crater on 18 and 19 September 2019. Visible and thermal images of the scoria cone (cono scorie) and lava flow (colata) inside Etna's large Voragine crater on 19 September 2019 (top) were taken from the southern edge of BN. Photo by F. Ciancitto. The bottom images were taken from the SW rim of BN on 18 September (left) by M. Tomasello and (right) 19 September by INGV personnel. Courtesy of INGV (Report 39/2019, ETNA, Bollettino Settimanale, 16/09/2019 - 22/09/2019, data emissione 24/09/2019).

Figure 285. An ash emission from Etna's NEC crater early on 27 September 2019 sent a plume drifting S before dissipating. It was captured by both the high-definition webcam of Bronte (EBVH, left) and the Milo (EMV) webcam. Courtesy of INGV (Report 40/2019, ETNA, Bollettino Settimanale, 23/09/2019 - 29/09/2019, data emissione 01/10/2019).

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/ ); 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/); Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue Gaspard Coriolis, F-31057 Toulouse cedex, France (URL: http://www.meteo.fr/aeroweb/info/vaac/).

Prior to renewed activity in June 2019, the most recent eruptive episode at Ubinas occurred between 13 September 2016 and 2 March 2017, with ash explosions that generated plumes that rose up to 1.5-2 km above the summit crater (BGVN 42:10). The volcano remained relatively quiet between April 2017 and May 2019. This report discusses an eruption that began in June 2019 and continued through at least August 2019. Most of the Information was provided by the Instituto Geofísico del Perú (IGP), Observatoria Vulcanologico del Sur (IGP-OVS), the Observatorio Volcanológico del INGEMMET (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET), and the Buenos Aires Volcanic Ash Advisory Center (VAAC).

Activity during June 2019. According to IGP, seismic activity increased suddenly on 18 June 2019 with signals indicating rock fracturing. During 21-24 June, signals indicating fluid movement emerged and, beginning at 0700 on 24 June, webcams recorded ash, gas, and steam plumes rising from the crater. Plumes were visible in satellite images rising to an altitude of 6.1 km and drifting N, NE, and E.

IGP and INGEMMET reported that seismic activity remained elevated during 24-30 June; volcano-tectonic (VT) events averaged 200 per day and signals indicating fluid movement averaged 38 events per day. Emissions of gas, water vapor, and ash rose from the crater and drifted N and NE, based on webcam views and corroborated with satellite data. According to a news article, a plume rose 400 m above the crater rim and drifted 10 km NE. Weather clouds often obscured views of the volcano, but an ash plume was visible in satellite imagery on 24 June 2019 (figure 49). On 27 June the Alert Level was raised to Yellow (second lowest on a 4-level scale).

Figure 49. Sentinel-2 satellite image in natural color showing an ash plume blowing north from Ubinas on 24 June 2019. Courtesy of Sentinel Hub Playground.

Activity during July 2019. IGP reported that seismic activity remained elevated during 1-15 July; VT events averaged 279 per day and long-period (LP) events (indicating fluid movement) averaged 116 events per day. Minor bluish emissions (magmatic gas) rose from the crater. Infrared imagery obtained by Sentinel-2 first showed a hotspot in the summit crater on 4 July.

According to IGP, during 17-19 July, gas-and-ash emissions occasionally rose from Ubinas's summit crater and drifted N, E, and SE. Beginning at 0227 on 19 July, as many as three explosions (two were recorded at 0227 and 0235) generated ash plumes that rose to 5.8 km above the crater rim. The Buenos Aires VAAC reported that, based on satellite images, ash plumes rose to an altitude as high as 12 km. The Alert Level was raised to Orange and the public were warned to stay beyond a 15-km radius. Ash plumes drifted as far as 250 km E and SE, reaching Bolivia. Ashfall was reported in areas downwind, including the towns of Ubinas (6.5 km SSE), Escacha, Anascapa (11 km SE), Tonohaya (7 km SSE), Sacohaya, San Miguel (10 km SE), Huarina, and Matalaque, causing some families to evacuate. The Buenos Aires VAAC reported that during 20-23 July ash plumes rose to an altitude of 7.3-9.5 km and drifted E, ESE, and SE.

IGP reported that activity remained elevated after the 19 July explosions. A total of 1,522 earthquakes, all with magnitudes under 2.2, were recorded during 20-24 July. Explosions were detected at 0718 and 2325 on 22 July, the last ones until 3 September. The Buenos Aires VAAC reported that an ash plume rising to an altitude of 9.4 km. and drifting SE was identified in satellite data at 0040 on 22 July (figure 50). Continuous steam-and-gas emissions with sporadic pulses of ash were visible in webcam views during the rest of the day. Ash emissions near the summit crater were periodically visible on 24 July though often partially hidden by weather clouds. Ash plumes were visible in satellite images rising to an altitude of 7 km. Diffuse ash emissions near the crater were visible on 25 July, and a thermal anomaly was identified in satellite images. During 26-28 July, there were 503 people evacuated from areas affected by ashfall.

Figure 50. Image of ash streaming from the summit of Ubinas on 22 July 2019 captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite. Courtesy of NASA's Earth Observatory (Joshua Stevens and Kathryn Hansen).

Activity during August 2019. IGP reported that during 13-19 August blue-colored gas plumes rose to heights of less than 1.5 km above the base of the crater. The number of seismic events was 1,716 (all under M 2.4), a decrease from the total recorded the previous week.

According to IGP, blue-colored gas plumes rose above the crater and eight thermal anomalies were recorded by the MIROVA system during 20-26 August. The number of seismic events was 1,736 (all under M 2.4), and there was an increase in the magnitude and number of hybrid and LP events. Around 1030 on 26 August an ash emission rose less than 2 km above the crater rim. Continuous ash emissions on 27 August were recorded by satellite and webcam images drifting S and SW.

IGP reported that during the week of 27 August, gas-and-water-vapor plumes rose to heights less than 1 km above the summit. The number of seismic events was 2,828 (all under M 2.3), with VT signals being the most numerous. There was a slight increase in the number of LP, hybrid, and VT events compared to the previous week. The Alert Level remained at Orange.

Thermal anomalies. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected a large concentration of anomalies between 19 July until almost the end of August 2019, all of which were of low radiative power (figure 51). Infrared satellite imagery (figure 52) also showed the strong thermal anomaly associated with the explosive activity on 19 July and then the continuing hot spot inside the crater through the end of August.

Figure 51. Log radiative power MIROVA plot of MODIS thermal anomalies at Ubinas for the year ending on 4 October 2019. Thermal activity began in the second half of July. Courtesy of MIROVA.

Figure 52. Sentinel-2 satellite images (Atmospheric penetration rendering, bands 12, 11, 8A) showing thermal anomalies during the eruption on 19 July (left) and inside the summit crater on 29 July 2019 (right). A hot spot inside the crater persisted through the end of August. Courtesy of Sentinel Hub Playground.

Geologic Background. A small, 1.4-km-wide caldera cuts the top of Ubinas, Peru's most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front of Perú. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3700 years ago extend 10 km from the volcano. Widespread plinian pumice-fall deposits include one of Holocene age about 1000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.

Information Contacts: Instituto Geofisico del Peru (IGP), Observatoria Vulcanologico del Sur (IGP-OVS), Arequipa Regional Office, Urb La Marina B-19, Cayma, Arequipa, Peru (URL: http://ovs.igp.gob.pe/); Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa (URL: http://ovi.ingemmet.gob.pe); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php?lang=es); 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); Instituto Nacional de Defensa Civil Perú (INDECI) (URL: https://www.indeci.gob.pe/); Gobierno Regional de Moquegua (URL: http://www.regionmoquegua.gob.pe/web13/); La Republica (URL: https://larepublica.pe/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

The dacitic Santiaguito lava-dome complex on the W flank of Guatemala's Santa María volcano has been growing and actively erupting since 1922. The youngest of the four vents in the complex, Caliente, has been erupting with ash explosions, pyroclastic, and lava flows for more than 40 years. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Daily explosions of steam and ash also continued during March-August 2019, the period covered in this report, with information primarily from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and the Washington VAAC (Volcanic Ash Advisory Center).

Activity at Santa Maria continued with little variation from previous months during March-August 2019, except for a short-lived increase in the frequency and intensity of explosions during early July that produced minor pyroclastic flows. Plumes of steam with minor magmatic gases rose continuously from both the S rim of the Caliente crater and from the summit of the growing dome throughout the period. They usually rose 100-700 m above the summit, generally drifting W or SW, and occasionally SE, before dissipating. In addition, daily explosions with varying amounts of ash rose to altitudes of around 2.8-3.5 km and usually extended no more than 25 km before dissipating. Most of the plumes drifted SW or SE; minor ashfall occurred in the adjacent hills almost daily and was reported at the fincas located within 10 km in those directions several times each month. Continued growth of the Caliente lava dome resulted in daily block avalanches descending its flanks to the base of the dome. The MIROVA plot of thermal energy during this time shows a consistent level of heat from early December 2018 through April 2019, very little activity during May and June, and a short-lived spike in activity from late June through early July that coincides with the increase in explosion rate and intensity. Activity decreased later in July and into August (figure 95).

Figure 95. Thermal activity at Santa Maria from 8 December 2018 through August 2019 was similar to previous months. A noticeable decrease in activity occurred during May and early June 2019 with a short-lived spike during late June and early July that corresponded to an increase in explosion rate and intensity during that brief interval. Courtesy of MIROVA.

Explosive activity increased slightly during March 2019 to 474 events from 409 events during February, averaging about 15 per day; the majority of explosions were weak to moderate in strength. The moderate explosions generated small block avalanches daily that sent debris 300 m down the flanks of Caliente dome; the explosions contained low levels of ash and large quantities of steam. Daily activity consisted mostly of degassing around the southern rim of the crater and within the central dome, with plumes rising about 100 m from the S rim, and pulsating between 100-400 m above the central dome, usually white and sometimes blue with gases; steam plumes drifted as far as 10 km. The weak ash emissions resulted in ashfall close to the volcano, primarily to the W and SW in the mountainous areas of El Faro, Patzulín, La Florida, and Monte Bello farms. During mid-March, residents of the villages of Las Marías and El Viejo Palmar, located S of the dome, reported the smell of sulfur. The seismic station STG3 registered 8-23 explosions daily that produced ash plumes which rose to altitudes between 2.7 and 3.3 km altitude. Explosions from the S rim were usually steam rich, while reddish oxidized ash was more common from the NE edge of the growing dome in the summit crater (figure 96). The constant block avalanches were generated by viscous lava slowly emerging from the growing summit dome, and also from the explosive activity. On the steep S flank of Santa Maria, blocks up to 3 m in diameter often produce small plumes of ash and debris as they fall.

Figure 96. Mostly steam rose from the S rim of the Caliente dome at Santa Maria throughout March-August 2019. On 1 March 2019, oxidized reddish ash from the growing dome was also part of the emissions (left). The dome continued to grow, essentially filling the inside of the summit crater of Caliente. Courtesy of INSIVUMEH (INFORME MENSUAL DE ACTIVIDAD VOLCÁNICA MARZO 2019, VOLCÁN SANTIAGUITO).

Late on 4 March 2019 an explosion was heard 10 km away that generated incandescence 100 m above the crater and block avalanches that descended to the base of the Caliente dome; it also resulted in ashfall around the perimeter of the volcano. Powerful block avalanches were reported in Santa María creek on 8 March. Ashfall was reported in the villages of San Marcos and Loma Linda Palajunoj on 14 March. Ash plumes on 18 March drifted W and caused ashfall in the villages of Santa María de Jesús and Calaguache. A small amount of ashfall was reported on 26 March around San Marcos Palajunoj. The Washington VAAC reported volcanic ash drifting W from the summit on 8 March at 4.6 km altitude. A small ash plume was visible in satellite imagery moving WSW on 11 March at 4.6 km altitude. On 20 March a plume was detected drifting SW at 3.9 km altitude for a short time before dissipating.

Explosion rates of 10-14 per day were typical for April 2019. Ash plumes rose to 2.7-3.2 km altitude. Block avalanches reached the base of the Caliente dome each day. Steam and gas plumes pulsated 100-400 m above the S rim of the crater (figure 97). Ashfall in the immediate vicinity of the volcano, generally on the W and SW flanks was also a daily feature. The Washington VAAC reported multiple small ash emissions on 2 April moving W and dissipating quickly at 4.9 km altitude. An ash plume from two emissions drifted WSW at 4.3 km altitude on 10 April, and on 22 April two small discrete emissions were observed in satellite images moving SE at 4.6 km altitude. Ashfall was reported on 13 and 14 April in the nearby mountains and areas around Finca San José to the SE. On 15 and 23 April, ash plumes drifted W and ashfall was reported in the area of San Marcos and Loma Lina Palajunoj.

Figure 97. Degassing from the Caliente dome at Santa Maria on 3 April (left, infrared image) and 13 April 2019 (right) produced steam-rich plumes with minor quantities of ash. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo:, Volcán Santiaguito, Semana del 30 de marzo al 05 de abril de 2019).

Constant degassing continued from the S rim of the crater during May 2019 while pulses of steam and gas rose 100-500 m from the dome at the center of the summit crater. Weak to moderate explosions continued at a rate of 8-12 per day. White and gray plumes of steam and ash rose 300-700 m above the crater daily. A moderate-size lahar on 16 May descended the Rio San Isisdro; it was 20 m wide and carried blocks 2 m in diameter. Ashfall was reported on the W flank around the area of San Marcos and Loma Lina Palajunoj on 21 and 24 May. INSIVIUMEH reported on 29 and 30 May that seismic station STG8 recorded moderate lahars descending the Rio San Isidro (a drainage to the Rio Tambor). The thick, pasty lahars transported blocks 1-3 m in diameter, branches, and tree trunks. They were 20 m wide and 1.5-2 m deep.

Weak to moderate explosions continued during June 2019 at a rate of 9-12 per day, producing plumes of ash and steam that rose 300-700 m above the Caliente crater. On 1 June explosions produced ashfall to the E over the areas of Calaguache, Las Marías and other nearby communities. Ash plumes commonly reached 3.0-3.3 km altitude and drifted W and SW, and block avalanches constantly descended the E and SE flanks from the dome at the top of Caliente. Ashfall was reported at the Santa María de Jesús community on 7 June. Ashfall to the W in San Marcos and Loma Linda Palajunoj was reported on 10, 15, 18, 20, and 22 June. Ashfall to the SE in Fincas Monte Claro and El Patrocinio was reported on 26 June. A few of the explosions on 28 June were heard up to 10 km away. On 29 June ash dispersed to the W again over the farms of San Marcos, Monte Claro, and El Patrocinio in the area of Palajunoj; the next day, ash was reported in Loma Linda and finca Monte Bello to the SW. The Washington VAAC reported ash emissions on 29 June that rose to 4.3 km and drifted W; two ash clouds were observed, one was 35 km from Santa Maria and the second drifted 55 km before dissipating.

With the onset of the rainy season, eight lahars were reported during June. The Rio Cabello de Ángel, a tributary of Río Nimá I (which flows into Rio Samalá) on the SE flank experienced lahars on 3, 5, 11, 12, 21, and 30 June (figure 98). The lahars were 15-20 m wide, 1-2 m deep, and carried branches, tree trunks and blocks 1-3 m in diameter. On 12 and 15 June, lahars descended the Río San Isidro on the SW flank. They were 1.5 m deep, 15-20 m wide and carried tree trunks and blocks up to 2 m in diameter.

Figure 98. Activity at Santa Maria on 12 June 2019 included explosions with abundant ash and lahars. This lahar is in the Rio Nimá I, and started in the Rio Cabello de Ángel. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito, Semana del 08 al 14 de junio de 2019).

An increase in the frequency and intensity of seismic events was noted beginning on 28 June that lasted through 6 July 2019. Explosions occurred at a rate of 5-6 per hour, reaching 40-45 events per day instead of the 12-15 typical of previous months. Ash plumes rose to 3.5-3.8 km altitude and drifted W, SW, and S as far as 10 km, and ashfall was reported in San Marcos Palajunoj, Loma Linda villages, Monte Bello farms, El Faro, La Mosqueta, La Florida, and Monte Claro. Activity decreased after 7 July back to similar levels of the previous months. As a result of the increased activity during the first week of July, several small pyroclastic flows (also known as pyroclastic density currents or PDC's) were generated that traveled up to 1 km down the S, SE, and E flanks during 2-5 and 13 July, in addition to the constant block avalanches from the dome extrusion and explosions (figure 99). As activity levels decreased after 6 July, the ash plume heights lowered to 3.3 km altitude, while pulsating degassing continued from the summit dome, rising 100-500 m.

Figure 99. An increase in explosive activity at Santa Maria during the first week of July 2019 resulted in several small pyroclastic flows descending the flanks, including one on 3 July 2019 (left). An ash emission on 19 July 2019 rose above the nearby summit of Santa Maria (right). Courtesy of INSIVUMEH (INFORME MENSUAL DE ACTIVIDAD VOLCÁNICA JULIO 2019, VOLCÁN SANTIAGUITO).

The Washington VAAC reported an ash plume on 2 July from a series of emissions that rose to 3.9 km altitude and drifted W. Satellite imagery on 4 July showed a puff of ash moving W from the summit at 4.3 km altitude. The next day an ash emission was observed in satellite imagery moving W at 4.9 km altitude. A plume on 11 July drifted W at 4.3 km for several hours before dissipating. Ashfall was reported on 2 July at the San Marcos farm and in the villages of Monte Claro and El Patrocinio in the Palajunoj area. On 4 and 6 July ash fell to the SW and W in San Marcos and Loma Linda Palajunoj. On 5 July there were reports of ashfall in Monte Claro and areas around San Marcos Palajunoj and some explosions were heard 5 km away. In Monte Claro to the SW ash fell on 7 July and sounds were heard 5 km away every three minutes. Incandescence was observed in the early morning on the SE and NE flanks of the dome. During 8 and 9 July, four to eight weak explosions per hour were noted and ash dispersed SW, especially over Monte Claro; pulsating degassing noises were heard every two minutes. Monte Bello and Loma Linda reported ashfall on 12, 16, 17, 19, and 20 July. On 15, 22, 26, and 29 July ash was reported in San Marcos and Loma Linda Palajunoj; 33 explosions occurred on 25 July. Two lahars were reported on 8 July. A strong one in the Rio San Isidro was more than 2 m deep, and 20-25 m wide with blocks as large as 3 m in diameter. A more moderate lahar affected Rio Cabello de Angel and was also 2 m deep. It was 15-20 m wide and had blocks 1-2 m in diameter.

Activity declined further during August 2019. Constant degassing continued from the S rim of the crater, but only occasional pulses of steam and gas rose from the central dome. Weak to moderate explosions occurred at a rate of 15-20 per day. White and gray plumes with small amounts of ash rose 300-800 m above the summit daily. Block avalanches descended to the base of the dome and sent fine ash particles down the SE and S flanks. Ashfall was common within 5 km of the summit, generally on the SW flank, near Monte Bello farm, Loma Linda village and San Marcos Palajunoj. Explosions rates decreased to 10-11 per day during the last week of the month. Degassing and ash plumes rose to 2.9-3.2 km altitude throughout the month.

On 1 August ash plumes drifted 10-15 km SW, causing ashfall in that direction. On 3 and 27 August ashfall occurred at Monte Claro and El Patrocinio in the Palajunoj area to the SW. On 7 and 31 August ashfall was reported in Monte Claro. San Marcos and Loma Linda Palajunoj reported ash on 11, 16, 19, and 23 August. On 21 August ashfall was reported to the SE around Finca San José. The Washington VAAC reported an ash plume visible in satellite imagery on 10 August 2019 drifting W at 4.3 km altitude a few kilometers from the summit which dissipated quickly. On 27 August a plume was observed 25 km W of the summit at 3.9 km altitude, dissipating rapidly. On 3 August a moderate lahar descended the Rio Cabello de Ángel that was 1 m deep, 15 m wide and carried blocks up to 1 m in diameter along with branches and tree trunks. A large lahar on 20 August descended Río Cabello de Ángel; it was 2-3 m high, 15 m wide and carried blocks 1-2 m diameter, causing erosion along the flanks of the drainage (figure 100).

Figure 100. A substantial lahar at Santa Maria on 20 August 2019 sent debris down the Río Cabello de Ángel in the vicinity of El Viejo Palmar (left), the spectrogram of the seismic signal lasted for 2 hours and 16 minutes (top right), and the seismograph was saturated with the lahar signal in red (bottom right). Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito, Semana del 17 al 23 de agosto de 2019).

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

Near-constant fountains of lava at Stromboli have served as a natural beacon in the Tyrrhenian Sea for at least 2,000 years. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N area) and a southern crater group (CS area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano-island. Periodic lava flows emerge from the vents and flow down the scarp, sometimes reaching the sea; occasional large explosions produce ash plumes and pyroclastic flows. Thermal and visual cameras that monitor activity at the vents are located on the nearby Pizzo Sopra La Fossa, above the Terrazza Craterica, and at multiple locations on the flanks of the volcano. Detailed information for Stromboli is provided by Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) as well as other satellite sources of data; March-August 2019 is covered in this report.

Typical eruptive activity recorded at Stromboli by INGV during March-June 2019 was similar to activity of the past few years (table 6); two major explosions occurred in July and August with a fatality during the 3 July event. In the north crater area, both vents N1 and N2 emitted fine (ash) ejecta, occasionally mixed with coarser lapilli and bombs; most explosions rose less than 80 m above the vents, some reached 150 m. Average explosion rates ranged from 1 to 12 per hour. In the CS crater area continuous degassing and occasional intense spattering were typical at vent C, vent S1 was a low-intensity incandescent jet throughout the period. Explosions from vent S2 produced 80-150 m high ejecta of ash, lapilli, and bombs at average rates of 2-17 per hour.

After a high-energy explosion and lava flow on 25 June, a major explosion with an ash plume and pyroclastic flow occurred on 3 July 2019; ejecta was responsible for the death of a hiker lower down on the flank and destroyed monitoring equipment near the summit. After the explosion on 3 July, coarse ejecta and multiple lava flows and spatter cones emerged from the N area, and explosion rates increased to 4-19 per hour. At the CS area, lava flows emerged from all the vents and spatter cones formed. Explosion intensity ranged from low to very high with the finer ash ejecta rising over 250 m from the vents and causing ashfall in multiple places on the island. This was followed by about 7 weeks of heightened unrest and lava flows from multiple vents. A second major explosion with an ash plume and pyroclastic flow on 28 August reshaped the summit area yet again and scattered pyroclastic debris over the communities on the SW flank near the ocean.

Table 6. Summary of activity levels at Stromboli, March-August 2019. Low-intensity activity indicates ejecta rising less than 80 m, medium-intensity is ejecta rising less than 150 m, and high-intensity is ejecta rising over 200 m above the vent. Data courtesy of INGV.

Thermal activity was low from March through early June 2019 as recorded in the MIROVA Log Radiative Power data from MODIS infrared satellite information. A sharp increase in thermal energy coincided with a large explosion and the emergence of numerous lava flows from the summit beginning in late June (figure 144). High heat-flow continued through the end of August and dropped back down at the beginning of September 2019 after the major 28 August explosion.

Figure 144. Thermal activity at Stromboli was low and intermittent from 12 November 2018 through early June 2019, based on this MIROVA plot of thermal activity through August 2019. A spike in thermal energy in late June coincided with a major explosion on 3 July and the emergence of lava from the summit area. Heightened activity continued from 3 July through 28 August with multiple lava flows emerging from both crater areas. Courtesy of MIROVA.

Activity during March-June 2019. Activity was low during March 2019. Low- to medium-intensity explosions occurred at both vents N1 and N2 in the north area. Ejecta was mostly coarse grained (lapilli and bombs) from N1 and fine-grained ash mixed with some coarse material from N2. Intense spattering activity was reported from N2 on 29 March. Explosion rates were reported at 5-12 per hour. At the CS area, medium-intensity explosions from both south area vents produced lapilli and bombs mixed with ash at a rate of 2-9 explosions per hour.

During a visit to the Terrazza Craterica on 2 April 2019, degassing was visible from vents N1, N2, C, and S2; activity continued at similar levels to March throughout the month. Low- and medium-intensity explosions with coarse ejecta, averaging 3-12 per hour, were typical at vent N1 while low-intensity explosions with fine-grained (ash) ejecta occurred at a similar rate from N2. Continuous degassing was observed at the C vent, and low-intensity incandescent jets were present at S1 throughout the month. Multiple emission points from S2 (as many as 4) produced low- to medium-intensity explosions at rates of 4-14 explosions per hour; the ejecta was mostly fine-grained mixed with some coarse material. Frequent explosions on 19 April produced abundant pyroclastic material in the summit area.

Low to medium levels of explosive activity at all of the vents continued during May 2019. Emissions consisted mostly of ash occasionally mixed with coarser material (lapilli and bombs). Rates of explosion were 2-8 per hour in the north area, and 5-16 per hour in the CS Area. Explosions of low-intensity continued from all the vents during the first part of June at rates averaging 2-12 per hour, although brief periods of high-frequency explosions (more than 21 events per hour) were reported during the week of 10 June. Strong degassing was observed from crater C during an inspection on 12 June (figure 145); by the third week, continuous degassing was interrupted at C by sporadic short-duration spattering events.

Figure 145. The Terrazza Craterica as seen from the Pizzo sopra la Fossa (above, near the summit) at Stromboli on 12 June 2019. In red are the two craters (N1 and N2) of the N crater area, in green is the CS crater area with 2 vents (C1 and C2) in the central crater and S2, the largest and deepest crater in the CS area, also with at least two vents. S1 is hidden by the degassing of crater C. Photograph by Giuseppe Salerno, courtesy of INGV (Report 25/2019, Stromboli, Bollettino Settimanale, 10/06/2019-16/06/2019).

Late on 25 June 2019, a high-energy explosion that lasted for 28 seconds affected vent C in the CS area. The ejecta covered a large part of the Terrazza Craterica, with abundant material landing in the Valle della Luna. An ash plume rose over 250 m after the explosion and drifted S. After that, explosion frequency varied from medium-high (17/hour) on 25 June to high (25/hour) on 28 June. On 29 June researchers inspected the summit and noted changes from the explosive events. Thermal imagery indicated that the magma level at N1 was almost at the crater rim. The magma level at N2 was lower and explosive activity was less intense. At vent C, near-constant Strombolian activity with sporadic, more intense explosions produced black ash around the enlarged vent. At vent S2, a pyroclastic cone at the center of the crater produced vertical jets of gas, lapilli, and bombs that exceeded 100 m in height (figure 146).

Figure 146. A high-energy explosion at Stromboli late on 25 June 2019 affected vent C in the CS Area (top row). The ejecta covered a large part of the Terrazza Craterica. An ash plume rose over 250 m after the explosion and drifted S. On 29 June (bottom row) thermal imagery indicated that the magma level at N1 was almost at the crater rim. At vent C, near-constant Strombolian activity was interrupted with sporadic, more intense explosions. At vent S2, a pyroclastic cone at the center of the crater produced vertical jets of gas, lapilli, and bombs that exceeded 100 m in height. Photo 2f by L. Lodato, courtesy of INGV (Rep 27/2019, Stromboli, Bollettino Settimanale, 24/06/2019-30/06/2019).

Activity during July 2019. A large explosion accompanied by lava and pyroclastic flows affected the summit and western flank of Stromboli on 3 July 2019. Around 1400 local time an explosion from the CS area generated a lava flow that spilled onto the upper part of the Sciara del Fuoco. Just under an hour later several events took place: lava flows emerged from the C vent and headed E, from the N1 and N2 vents and flowed N towards Bastimento, and from vent S2 (figure 147). The emergence of the flows was followed a minute later by two lateral blasts from the CS area, and a major explosion that involved the entire Terrazza Craterica lasted for about one minute (figure 148). Within seconds, the pyroclastic debris had engulfed and destroyed the thermal camera located above the Terrazza Craterica on the Pizzo Sopra La Fossa and sent a plume of debris across the W flank of the island (figure 149). Two seismic stations were also destroyed in the event. The Toulouse VAAC reported a plume composed mostly of SO₂ at 9.1 km altitude shortly after the explosion. They noted that ash was present in the vicinity of the volcano, but no significant ashfall was expected. INGV scientists observed the ash plume at 4 km above the summit.

Figure 147. A major eruptive event at Stromboli on 3 July 2019 began with an explosion from the CS area that generated a lava flow at 1359 (left). About 45 minutes later (at 1443:40), lava flows emerged from all of the summit vents (right), followed closely by a major explosion. Courtesy of INGV (Eruzione Stromboli. Comunicato straordinario del 4 luglio 2019).

Figure 148. A major explosion at Stromboli beginning at 1445 on 3 July 2019 was preceded by lava flows from all the summit vents in the previous 60 seconds (top row). This thermal camera (SPT) and other monitoring equipment on the Pizzo Sopra La Fossa above the vents were destroyed in the explosion (bottom row). Courtesy of INGV (Il parossismo dello Stromboli del 3 luglio 2019 e l'attività nei giorni successivi: il punto della situazione al 13 luglio 2019).

Figure 149. The monitoring equipment at Stromboli on the Pizzo Sopra La Fossa above the summit was destroyed in the major explosion of 3 July 2019 (left, photo by F. Ciancitto). Most of the W half of the island was affected by pyroclastic debris after the explosion, including the town of Ginostra (right). Courtesy of INGV (Report 28/2019, Stromboli, Bollettino Settimanale, 01/07/2019 - 07/07/2019).

Two pyroclastic flows were produced as a result of the explosions; they traveled down the Sciara and across the water for about 1 km before collapsing into the sea (figure 150). A hiker from Sicily was killed in the eruption and a Brazilian friend who was with him was badly injured, according to a Sicilian news source, ANSA, and the New York Post. They were hit by flying ejecta while hiking in the Punta dei Corvi area, due W of the summit and slightly N of Ginostra, about 100 m above sea level according to INGV. Most of the ejecta from the explosion dispersed to the WSW of the summit. Fallout also ignited vegetation on the slopes which narrowly missed destroying structures in the town. Ejecta blocks and bombs tens of centimeters to meters in diameter were scattered over a large area around the Pizzo Sopra La Fossa and the Valle della Luna in the direction of Ginostra. Smaller material landed in Ginostra and was composed largely of blonde pumice, that floated in the bay (figure 151). The breccia front of the lava flows produced incandescent blocks that reached the coastline. High on the SE flank, the abundant spatter of hot pyroclastic ejecta coalesced into a flow that moved 200-300 m down the flank before cooling, crossing the path normally used by visitors to the summit (figure 152).

Figure 150. At the time of the major explosion of Stromboli on 3 July 2019 people on a German ship located about 2 km off the northern coast captured several images of the event. (a) Two pyroclastic flows traveled down the Sciara del Fuoco and spread over the sea up to about 1 km from the coast. (b) The eruption column was observed rising several kilometers above the summit as debris descended the Sciara del Fuoco. (c) Fires on the NW flank were started by incandescent pyroclastic debris. The photos were taken by Egon Karcher and used with permission of the author by INGV. Courtesy of INGV (Il parossismo dello Stromboli del 3 luglio 2019 e l'attività nei giorni successivi: il punto della situazione al 13 luglio 2019).

Figure 151. Pumice filled the harbor on 4 July 2019 (left) and was still on roofs (right) on 7 July 2019 in the small port of Ginostra on the SW flank of Stromboli after the large explosion on 3 July 2019. Photos by Gianfilippo De Astis, courtesy of INGV (Il parossismo dello Stromboli del 3 luglio 2019 e l'attività nei giorni successivi: il punto della situazione al 13 luglio 2019).

Figure 152. A small lava flow high on the SE flank of Stromboli formed during the 3 July 2019 event from abundant spatter of hot pyroclastic ejecta that coalesced into a flow and moved 200-300 m down the flank before cooling, crossing the path normally used by visitors to the summit. Photo by Boris Behncke taken on 9 July 2019, courtesy of INGV (Il parossismo dello Stromboli del 3 luglio 2019 e l'attività nei giorni successivi: il punto della situazione al 13 luglio 2019).

INGV scientists inspected the summit on 4 and 5 July 2019 and noted that the rim of the Terrazza Craterica facing the Sciara del Fuoco in both the S and N areas had been destroyed, but the crater edge near the central area was not affected. In addition, the N area appeared significantly enlarged and deepened, forming a single crater where the former N1 and N2 vents had been located; an incandescent jet was active in the CS area (figure 153). Explosive activity declined significantly after the major explosions, although moderate overflows of lava continued from multiple vents, especially the CS area where the flows traveled about halfway down the southern part of the Sciara del Fuoco; lava also flowed E towards Rina Grande (about 0.5 km E of the summit). The main lava flows active between 3 and 4 July produced a small lava field along the Sciara del Fuoco which flowed down to an elevation of 210 m in four flows along the S edge of the scarp (figure 154). Additional block avalanches rolled to the coastline.

Figure 153. The summit craters of Stromboli were significantly altered during the explosive event of 3 July 2019. The rim of the Terrazza Craterica facing the Sciara del Fuoco in both the CS and N areas was destroyed, but the crater edge near the CS area was not affected. In addition, the N area was significantly enlarged and deepened, forming a single crater where the former N1 and N2 vents had been located; an incandescent jet was active in the CS area. Courtesy of INGV (Report 28/2019, Stromboli, Bollettino Settimanale, 01/07/2019 - 07/07/2019).

Figure 154. The main lava flows active between 3 and 4 July at Stromboli after the major explosion on 3 July 2019 produced a small lava field along the Sciara del Fuoco. Left: Aerial photo taken by Stefano Branca (INGV-OE) on 5 July; the yellow arrow shows a small overflow from the N crater area, the red arrow shows the largest overflow from the CS crater area. Right: Flows from the CS area traveled down to an elevation of 210 m in four flows along the S edge of the scarp. Additional block avalanches rolled to the coastline. Right photo by Francesco Ciancitto taken on 5 July 2019. Courtesy of INGV (Il parossismo dello Stromboli del 3 luglio 2019 e l'attività nei giorni successivi: il punto della situazione al 13 luglio 2019).

During the second week of July lava flows continued; on 8 July volcanologists reported two small lava flows from the CS area flowing towards the Sciara del Fuoco. A third flow was noted the following day. The farthest flow front was at about 500 m elevation on 10 July, and the flow at the center of the Sciara del Fuoco was at about 680 m. An overflow from the N area during the evening of 12 July produced two small flows that remained high on the N side of the scarp; lava continued flowing from the CS area into the next day. A new flow from the N area late on 14 July traveled down the N part of the scarp (figure 155).

Figure 155. During the second week of July 2019 lava flows at Stromboli continued from both crater areas. Top left: Lava flows from the CS area flowed down the Sciara on 9 July while Strombolian activity continued at the summit, photo by P. Anghemo, mountain guide. Bottom left: A lava flow from the CS area at Stromboli is viewed from Punta dei Corvi during the night of 12-13 July 2019. Photo by Francesco Ciancitto. Right: The active flows on 10 July (in red) were much closer to the summit crater than they had been during 3-4 July (in yellow). Courtesy of INGV, top left and right photos published in Report 29/2019, Stromboli, Bollettino Settimanale, 08/07/2019 - 14/07/2019; bottom left photo published in 'Il parossismo dello Stromboli del 3 luglio 2019 e l'attività nei giorni successivi: il punto della situazione al 13 luglio 2019'.

A new video station with a thermal camera was installed at Punta dei Corvi, a short distance N of Ginostra on the SW coast, during 17-20 July 2019. During the third week of July lava continued to flow from the CS crater area onto the southern part of the Sciara del Fuoco, but the active flow area remained on the upper part of the scarp; block avalanches continuously rolled down to the coastline (figure 156). During visits to the summit area on 26 July and 1 August activity at the Terrazza Craterica was observed by INGV scientists. There were at least six active vents in the N area, including a scoria cone and an intensely spattering hornito; the other vents were ejecting coarse material in jets of Strombolian activity. In the CS area, a large scoria cone was clearly visible from the Pizzo, with two active vents generating medium- to high-intensity explosions rich in volcanic ash mixed with coarse ejecta (figures 157 and 158). Some of the finer-grained material in the jets reached 200 m above the vents. A second smaller cone in the CS area faced the southernmost part of the Sciara del Fuoco and produced sporadic low-intensity "bubble explosions." Effusive activity decreased during the last week of July; the active lava front was located at about 600 m elevation. Blocks continued to roll down the scarp, mostly from the explosive activity, and were visible from Punta dei Corvi.

Figure 156. Lava continued to flow from the CS area at Stromboli during the third week of July 2019, although the active flow area remained near the top of the scarp. Block avalanches continued to travel down the scarp. Image taken by di Francesco Ciancitto from Punta dei Corvi on 19 July 2019. Courtesy of INGV (Report 30/2019, Stromboli, Bollettino Settimanale, 15/07/2019 - 21/07/2019).

Figure 157. Thermal and visible images of Terrazza Craterica at the summit of Stromboli from the Pizzo Sopra La Fossa on 1 August 2019 showed significant changes since the major explosion on 3 July 2019. A large scoria cone was present in the CS area (left) and at least six vents from multiple cones were active in the N area (right). The active lava flow 'Trabocco Lavico' emerged from the southernmost part of the CS area (far left). Courtesy if INGV (Report 32/2019, Stromboli, Bollettino Settimanale, 29/07/2019 - 04/08/2019.

Figure 158. At the summit of Stromboli on 1 August 2019 two active vents inside a large cone in the CS area generated medium- to high-intensity explosions rich in volcanic ash mixed with coarse ejecta (left). There were at least six active vents in the N area (right), including a scoria cone and an intensely spattering hornito; the other vents were ejecting coarse material in jets of Strombolian activity. Courtesy of INGV (Report 32/2019, Stromboli, Bollettino Settimanale, 29/07/2019 - 04/08/2019).

Activity during August 2019. A small overflow of lava on 4 August 2019 from the N area lasted for about 20 minutes and formed a flow that went a few hundred meters down the Sciara del Fuoco. Observations made at the summit on 7 and 8 August 2019 indicated that nine vents were active in the N crater area, three of which had scoria cones built around them (figure 159). They all produced low- to medium-intensity Strombolian activity. In the CS area, a large scoria cone was visible from the summit that generated medium- to high-intensity explosions rich in volcanic ash, which sometimes rose more than 200 m above the vent. Lava overflowing from the CS area on 8 August was confined to the upper part of the Sciara del Fuoco, at an elevation between 500 and 600 m (figure 160). Occasional block avalanches from the active lava fronts traveled down the scarp. Ashfall was reported in the S. Bartolo area, Scari, and Piscità during the first week of August.

Figure 159. Nine vents were active in the N crater area of Stromboli on 7 August 2019, three of which had scoria cones built around them. They all produced low- to medium-intensity Strombolian activity (top). In the CS area (bottom), a large scoria cone was visible from the summit that generated medium- to high-intensity explosions rich in volcanic ash, which sometimes rose more than 200 m above the vent. Visible images taken by S. Consoli, thermal images taken by S. Branca. Courtesy of INGV (Report 33/2019, Stromboli, Bollettino Settimanale, 05/08/2019 - 11/08/2019).

Figure 160. Multiple Lava flows were still active on the Sciara del Fuoco at Stromboli on 7 August 2019. Top images by INGV personnel S Branca and S. Consoli, lower images by A. Di Pietro volcanological guide. Courtesy of INGV (Report 33/2019, Stromboli, Bollettino Settimanale, 05/08/2019 - 11/08/2019).

Drone surveys on 13 and 14 August 2019 confirmed that sustained Strombolian activity continued both in the N area and the CS area. Lava flows continued from two vents in the CS area; they ceased briefly on 16 and 17 August but resumed on the 18th, with the lava fronts reaching 500-600 m elevation (figure 161). A fracture field located in the southern part of the Sciara del Fuoco was first identified in drone imagery on 9 July. Repeated surveys through mid-August indicated that about ten fractures were identifiable trending approximately N-S and ranged in length from 2.5 to 21 m; they did not change significantly during the period. An overflight on 23 August identified the main areas of activity at the summit. A NE-SW alignment of 13 vents within the N area was located along the crater edge that overlooks the Sciara del Fuoco. At the CS area, the large scoria cone had two active vents, there was a pit crater, and two smaller scoria cones. A 50-m-long lava tube emerged from one of the smaller lava cones and fed two small flows that emerged at the top of the Sciara del Fuoco (figure 162).

Figure 161. Detail of a vent at Stromboli on 14 August 2019 located in the SW part of the Sciara del Fuoco at an elevation of 730 m. Flow is tens of meters long. Courtesy of INGV (COMUNICATO DI DETTAGLIO STROMBOLI del 20190816 ORE 17:05 LT).

Figure 162. Thermal and visual imagery of the summit of Stromboli on 23 August 2019 revealed a NE-SW alignment of 13 vents within the N area located along the crater edge that overlooks the Sciara del Fuoco. At the CS area, the large scoria cone had two active vents (1 and 2), there was a pit crater (3), and two smaller scoria cones (4). A 50-m-long lava tube formed from one of the smaller lava cones (5) and fed two small flows that emerged at the top of the Sciara del Fuoco. Photos by L. Lodato and S. Branca, courtesy of INGV (Report 35/2019, Stromboli, Bollettino Settimanale, 19/08/2019 - 25/08/2019).

INGV reported a strong explosion from the CS area at 1217 (local time) on 28 August 2019. Ejecta covered the Terrazza Craterica and sent debris rolling down the Sciara del Fuoco to the coastline. A strong seismic signal was recorded, and a large ash plume rose more than 2 km above the summit (figure 163). The Toulouse VAAC reported the ash plume at 3.7-4.6 km altitude, moving E and rapidly dissipating, shortly after the event. Once again, a pyroclastic flow traveled down the Sciara and several hundred meters out to sea (figures 164). The entire summit was covered with debris. The complex of small scoria cones within the N area that had formed since the 3 July explosion was destroyed; part of the N area crater rim was also destroyed allowing lava to flow down the Sciara where it reached the coastline by early evening.

Figure 163. A major explosion at Stromboli on 28 August 2019 produced a high ash plume and a pyroclastic flow. The seismic trace from the STR4 station (top left) indicated a major event. The ash plume from the explosion was reported to be more than 2 km high (right). The thermal camera located at Stromboli's Punta dei Corvi on the southern edge of the Sciara del Fuoco captured both the pyroclastic flow and the ash plume produced in the explosion (bottom left). Seismogram and thermal image courtesy of INGV (INGVvulcani blog, 30 AGOSTO 2019INGVVULCANI, Nuovo parossismo a Stromboli, 28 agosto 2019). Photo by Teresa Grillo (University of Rome) Courtesy of AIV - Associazione Italiana di Vulcanologia.

Figure 164. A pyroclastic flow at Stromboli traveled across the sea off the W flank for several hundred meters on 28 August 2019 after a major explosion at the summit. Photo by Alberto Lunardi, courtesy of INGV (5 SETTEMBRE 2019INGVVULCANI, Quando un flusso piroclastico scorre sul mare: esempi a Stromboli e altri vulcani).

At 1923 UTC on 29 August a lava flow was reported emerging from the N area onto the upper part of the Sciara del Fuoco; it stopped at mid-elevation on the slope. About 90 minutes later, an explosive sequence from the CS area resulted in the fallout of pyroclastic debris around Ginostra. Shortly after midnight, a lava flow from the CS area traveled down the scarp and reached the coast by dawn, but the lava entry into the sea only lasted for a short time (figure 165).

Figure 165. Lava flows continued for a few days after the major explosion of 28 August 2019 at Stromboli. Left: A lava flow emerged from the N crater area on 29 August 2019 and traveled a short distance down the Sciara del Fuoco. Incandescent blocks from the flow front reached the ocean. Photo by A. DiPietro. Right: A lava flow that emerged from the CS crater area around midnight on 30 August 2019 made it to the ocean around dawn, as seen from the N ridge of the Sciara del Fuoco at an altitude of 400 m. Photo by Alessandro La Spina. Both courtesy of INGV. Left image from 'COMUNICATO DI ATTIVITA' VULCANICA del 2019-08-29 22:20:06(UTC) – STROMBOLI', right image from INGVvulcani blog, 30 AGOSTO 2019 INGVVULCANI, 'Nuovo parossismo a Stromboli, 28 agosto 2019'.

An overflight on 30 August 2019 revealed that after the explosions of 28-29 August the N area had collapsed and now contained an explosive vent producing Strombolian activity and two smaller vents with low-intensity explosive activity. In the CS area, Strombolian activity occurred at a single large crater (figure 166). INGV reported an explosion frequency of about 32 events per hour during 31 August-1 September. The TROPOMI instrument on the Sentinel-5P satellite captured small but distinct SO₂ plumes from Stromboli during 28 August-1 September, even though they were challenging to distinguish from the larger signal originating at Etna (figure 167).

Figure 166. A 30 August 2019 overflight of Stromboli revealed that after the explosions of 28-29 August the N area had collapsed and now contained a single explosive vent producing Strombolian activity and two smaller vents with low intensity explosive activity. In the CS area, a single large crater remained with moderate Strombolian activity. No new lava flows appeared on the Sciara del Fuoco, only cooling from the existing flows was evident. Courtesy of INGV (Report 35.6/2019, Stromboli, Daily Bulletin of 08/31/2019).

Figure 167. Small but distinct SO2 signals were recorded from Stromboli during 28 August through 1 September 2019; they were sometimes difficult to discern from the larger signal originating at nearby Etna. Courtesy of NASA Goddard Space Flight Center.

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue Gaspard Coriolis, F-31057 Toulouse cedex, France (URL: http://www.meteo.fr/aeroweb/info/vaac/); AIV, Associazione Italiana di Vulcanologia (URL: https://www.facebook.com/aivulc/photos/a.459897477519939/1267357436773935; ANSA.it, (URL: http://www.ansa.it/sicilia/notizie/2019/07/03/-stromboli-esplosioni-da-cratere-turisti-in-mare); The New York Post, (URL: https://nypost.com/2019/07/03/dozens-of-people-dive-into-sea-to-escape-stromboli-volcano-eruption-in-italy/).

Explosive volcanism continued through October but caused no damage. There were 31 eruptions . . ., including 14 explosive ones. On 5 October a NOTAM . . . described eruptions at 0136 and 0447 that rose to 3.35 km. On the other hand, JMA reported that at 1628 on 6 October the "highest ash plume of October" rose to 3.3 km, so apparently there was relatively vigorous activity on both days. Volcanic earthquake swarms were detected 130 times, reaching a maximum amplitude of 2 µm. During October, a seismic station 2.3 km NW of Minamidake crater registered 862 distinct events. October ashfall collected at the Kagoshima Meteorological Station, 10 km W, measured 136 g/m².

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: JMA; [SAB].

Continuing activity in September consisted of Strombolian eruptions and lava output from Crater C and fumarolic activity from Crater D. Two lobes of lava continued to progress toward the Tabacón valley (figure 70). ICE workers suggested that at elevations below 800 m the estimated velocities of lava flows have averaged roughly 2.5 m/day. In some of the steeper upslope reaches flows may have averaged as much as roughly 50 m/day, but velocities were more typically 10-20 m/day. These values are approximate, because field work is hampered by hazards associated with sudden collapse of lava-flow fronts.

Figure 70. Rough field sketch of Arenal, from the ash-sampling locality mentioned in the text (1.8 km W of the summit); view is toward the E. Courtesy of G. Soto, ICE.

In the summit crater, vents active for the past several months had built two small cones. The northernmost cone extruded lava during the past several months. The southerly cone appears to be mainly composed of pyroclastic materials. Toward the crater's center there was a third vent. Summit fumaroles remained vigorous and occasional explosions took place (table 6); at night a red glow still prevailed over the crater area suggesting ponded lava remains molten there. Seismicity reported by ICE appears in table 7; their mid-October sampling found that both pH values and water temperatures remained unchanged.

Table 6. Ash collected downwind at a spot 1.8 km W of Arenal's crater. "Collection Interval" refers to the time period in 1994 when the ash sample accumulated (also shown as "Days," the number of days), but the mass/area value is a computed daily average. Courtesy of G. Soto, ICE.

Table 7. Number of seismic events and tremor duration at Arenal. October values are extrapolated from 20 days of observations. Courtesy of ICE.

OVSICORI-UNA reported that September seismic events often accompanied gas- and ash-bearing eruptions. During September seismic events in the frequency range 1.2-2.5 Hz totaled 657; tremor duration totaled 55 hours.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G. Soto and F. Arias, ICE; M. Mora, Univ de Costa Rica.

After ejecting mud and blocks on 12 September, Crater 1 remained restless in October (figure 25). The water-covered crater floor ejected mud intermittently, sometimes accompanied by ash plumes. In one case on 27 October, ejected mud flew more than 100 m above the crater bottom. Tremor amplitude (at Station A, 800 m W of the crater) generally remained less than 1 µm. Some larger tremor episodes exceeded 10 µm and were felt by personnel at the Aso Weather Station.

Figure 25. Seismicity and plume heights at Aso, January-October 1994. Earthquakes and tremor were registered at a station 0.8 km W of Nakadake cone. Plume heights were estimated by personnel at AWS. Courtesy of JMA.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.

Cloudy weather prevented observations on most days during the second half of September and October, but seismicity remained at normal levels. A gas-and-steam plume rose to 100 m above the volcano on 16 September, and to 1,000 m the week of 18-24 September. Activity was at normal levels the next two weeks. When conditions permitted, observers in Kozirevsk (~45 km WNW) saw a white steam cloud reaching 500-700 m above the crater on 13 October, 200 m on the 20th and 22nd, and 50 m on the 27th.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: V. Kirianov, IVGG; AVO.

A news report on 3 November noted that gas emissions from the summit are frequent, many minor volcanic earthquakes have been felt during the last two years, and nearby hot springs were also emitting volcanic gases. The official Xinhua News Agency quoted Ruoxin Liu from the State Seismological Bureau, but we have received no direct confirmation.

Charles Dunlap, Susanne Horn, and Hans Schmincke worked on and around the summit with Chinese geologist Tang Deping during 21-25 July 1993, but saw no emissions. One hot spring area was observed by Dunlap in the N-flank valley, which begins at the lake outlet into the Erdobaihe River. These springs were next to the trail to the waterfall and on up to the lake's edge; eggs were boiled in the spring water for sale to tourists. A weak sulfur smell was detected, but it was not as pronounced as at some springs in Yellowstone or Long Valley (USA). No other emissions were noticed from these springs. Another hot spring location W of this valley was not visited, but apparently it is popular as a bath. On the E border of the crater lake (Korean side), water from a hot spring with a temperature of 700°C was being pumped to the crater rim to provide healing potions.

Baitoushan (Korean name P'aektu-san) is a large stratovolcano on the Korea-Manchurian border ~300 km SE of Changchun and 325 km WSW of Vladivostok, Russia. The 60-km-diameter volcano was constructed over the Changbaishan (Laoheidingz) shield volcano and has a 5-km-wide summit caldera. One of the world's largest known Holocene explosive eruptions took place around 1000 A.D., depositing tephra as far away as N Japan and forming in part the 850-m-deep depression filled by Tianchi Lake. The much better exposed pyroclastic deposits on the North Korean side studied by Horn and Schmincke are extremely thick and include major ignimbrites. Four historical eruptions have been recorded since the 15th century (1413, 1597, 1668, and 1702). Chinese geologists spoken to by Dunlap thought that these historical events were probably phreatic explosions, and that there have possibly been occasional gas emissions within approximately the last 50 years.

Geologic Background. Massive Changbaishan stratovolcano, also known as Baitoushan and by the Korean names of Baegdu or P'aektu-san, is a relatively poorly known, but volcanologically significant volcano straddling the China/Korea border. A 5-km-wide, 850-m-deep summit caldera is filled by scenic Lake Tianchi (Sky Lake). A large Korean-speaking population resides near the volcano on both sides of the border. The 60-km-diameter dominantly trachytic and rhyolitic volcano was constructed over the Changbaishan (Laoheidingzi) shield volcano. Satellitic cinder cones are aligned along a NNE trend. One of the world's largest known Holocene explosive eruptions took place here about 1000 CE, depositing rhyolitic and trachytic tephra as far away as northern Japan and forming in part the present caldera. Minor historical eruptions have been recorded since the 15th century.

Information Contacts: C. Dunlap, University of California - Santa Cruz; S. Horn and H. Schmincke, GEOMAR; Xinhua News Agency, China; UPI.

The following describes [fieldwork] between 23 September and 14 October 1994.

"There are continuing signs that activity is increasing. At the Chasm (La Voragine), 1-4 very low rumbles/min were heard, but on 14 October six explosions much louder than those heard in June/July (19:07) were heard in 10 minutes. The Bocca Nuova was also producing around one distinct long explosive blast per minute, as opposed to the faint gas puffs heard in the summer. However, no audible explosions were heard when the Chasm was active on 14 October. Northeast and Southeast craters were quiet as in June/July, but temperatures more than 100°C higher were measured at the fumaroles on their outer slopes. Another sign of increasing activity was that during the five days of levelling (25-30 September), 22 earth tremors were detected by the shaking of the instrument. This is > 10 times higher than 1993, and the largest total of tremors noted in this way since September 1991, before the 1991-93 eruption.

"The levelling traverse showed a slight subsidence of the summit since June 1994, the maximum value being just under 3 cm compared to the Piano Provenzana, 6.5 km NNE of the summit. The subsidence is more or less concentric around the summit, with the exception of some stations on the upper E flank and over the 1991-93 dyke, which have subsided nearly a centimetre more than those nearby.

"On 14 October the areas of active fumaroles measured during June were visited. These were measured again using a Minolta/Land 330 hand-held radiometer (8.5-14.5 mm). Temperatures were not corrected for spectral emissivity, so all radiant temperatures are given as brightness temperatures (table 5). At the N, W, and S rim of Northeast Crater, maximum fumarole and rift temperatures were 105-135°C higher than those measured in June. H₂S was also smelled in the vicinity of these high-temperature fumaroles. Higher maximum temperatures were also measured from rifts at the N rim of Southeast Crater, these being up to 170°C higher than those measured in June. It is stressed that these rises in temperature may be the result of different fumaroles being measured on the two dates, though in view of the thorough coverage in June this seems unlikely. Elsewhere, fumarole temperatures were similar to those measured in June. Fumarolic activity only was observed on the floor of Northeast Crater, which was measured from the rim at 40.1°C. The bocca on the floor of the Chasm was measured from the crater rim at 339°C. At the Bocca Nuova, a temperature of 173°C was measured for the SE bocca and of 40.7°C for the NW floor; these were measured from the crater rim. At Southeast Crater, fumaroles decreased in temperature and number around the W and E rims, such that fumaroles were few and cool on the S rim."

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: J. Murray and A. Harris, Open Univ.

During October activity at Galeras remained low. In terms of seismicity, on 20 October sporadic "screw-type" events reappeared. Screw-type events are comparatively monochromatic and with slowly decaying coda (late arriving) waves. They were so-named because their seismograph records look similar to the profile of a finely threaded screw. They are considered significant because they preceded five of the six eruptions between July 1992 and June 1993; on the other hand they have also occurred without being followed by an eruption. During October, seismic stations located 0.9-2.4 km from the active crater detected seven screw-type events. The codas of the screw-type events had durations of 31-63 seconds and a computed damping coefficient of 0.02. The seismic signals detected at all three stations had the same dominant frequency, ~ 2.5 Hz, and the spectra ranged from ~ 2.4 to 10.3 Hz.

Small earthquakes (M<2.4) took place at depths up to 5 km. These earthquakes had epicenters clustered beneath and around the active crater, most plotting within a radius of ~4 km. Butterfly-type events also took place. The SO₂ flux obtained by the mobile COSPEC method showed fairly low values: 38-832 t/d. Degassing continued to be concentrated chiefly on the active cone's W fringe with smaller fumaroles at the interior of the main crater.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: INGEOMINAS, Pasto.

An eruption late on 15 October sent a plume ~ 300 m above the summit . . ., according to news reports. No casualties or damage were reported, although some ash fell in several villages on the slopes of the volcano and the explosion shook buildings.

Geologic Background. Gamalama is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera, and is one of Indonesia's most active volcanoes. The island was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the thorough documentation of Gamalama's historical activity. Three cones, progressively younger to the north, form the summit. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano. Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.

Information Contacts: Antara News Agency; Reuters.

During October, the crater lake at Irazú remained high, covering the crater floor with yellow-colored water. In addition to active flank fumaroles on the NW, subaqueous fumaroles bubbled consistently in the N, NW, W, SW, and SE parts of the lake, near the crater wall. Rockslides were seen coming down the N, SW, and E crater wall. Seismic events in October totaled 18 earthquakes with S minus P values of 2-3 seconds; some events reached M 2 with epicenters <3 km from the crater and focal depths of 4.0-4.5 km. Geodetic and leveling surveys in September found no significant changes.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI-UNA; G. Soto and F. Arias, ICE; Mauricio Mora, Escuela Centroamericana de Geología, Univ de Costa Rica.

"A minor seismic unrest occurred on the morning of 18 October, the second one this year, after 15 years of dormancy at this caldera. The local seismograph recorded a large number of low-frequency events starting at about 0200 on 18 October. Events occurred at a rate of up to 2-4/minute. The activity waned after 0930. Although of short duration, this swarm of events was similar to the unrest recorded between 17 May and mid-June 1994, when the long-term deflation of the caldera floor was interrupted."

Geologic Background. Karkar is a 19 x 25 km wide, forest-covered island that is truncated by two nested summit calderas. The 5.5-km-wide outer caldera was formed during one or more eruptions, the last of which occurred 9000 years ago. The eccentric 3.2-km-wide inner caldera was formed sometime between 1500 and 800 years ago. Parasitic cones are present on the N and S flanks of this basaltic-to-andesitic volcano; a linear array of small cones extends from the northern rim of the outer caldera nearly to the coast. Most historical eruptions, which date back to 1643, have originated from Bagiai cone, a pyroclastic cone constructed within the steep-walled, 300-m-deep inner caldera. The floor of the caldera is covered by young, mostly unvegetated andesitic lava flows.

Information Contacts: C. McKee and P. de Saint-Ours, RVO.

"In September, lava continued to enter the ocean in the Laeapuki area . . . . The W branch of the tube on the bench stopped transporting lava, and flows entering the ocean consolidated in front of the 27 July littoral cone. Littoral explosions increased in size and frequency coincident with the consolidation of the littoral tube system. On 14 September, ~10-15 m of the active bench collapsed into the ocean. The bench built out into the ocean until 1 October, when part of the active bench collapsed again. Flows built a small, thick bench following each collapse. Near the end of September, the flux at this ocean entry appeared to diminish, possibly because of the diversion of lava to a prolific E flow. Lava continued to enter the ocean in this area until 5 October, when the eruption paused for the first time since April.

"The large surface flow that broke out on 20 August at 270 m elevation continued to cover new land on the E side of the Kamoamoa flow-field. Throughout most of September there were active breakouts on this flow from the base of Pulama pali to below Paliuli. All of these breakouts were fluid pahoehoe toes and sheet flows. Sheet flows on the E margin of the flow field frequently ignited methane explosions, which were recorded by the Wahaula seismometer. Breakouts began to close the gap between the Kamoamoa and Kupaianaha flows; <200 m separated the two flow fields. Lava from this E flow entered the ocean on the E side of the Kamoamoa flow field intermittently during 2-9 October.

"Two pauses in October were only the 4th and 5th to occur since E-53 began in February 1993. On 6 October, all surface activity stopped, no lava entered the ocean, and there was no lava in the tube system. By the following morning lava had reoccupied the tube all the way to the Laeapuki ocean entry and fed breakouts close to 270 m elevation. Lava also continued to ooze and dribble into the ocean on the E side of the flow field. Following this pause, a number of breakouts were observed on Pulama pali and on the E flow. Lava entering the ocean in the Laeapuki area began to build a new bench E of the littoral cone formed on 27 July. Lava from the E flow entered the ocean once again on 22 October. On 24 October, the eruption appeared to be sputtering — flows slowed and then surged, entries died and then reactivated. By 25 October, all surface activity had stagnated. The eruption restarted the following day, and this time the tube system was reoccupied to only 550 m elevation. Below this elevation, large channelized aa and pahoehoe flows swept down the flow field. By 31 October, these flows had cascaded over Paliuli and begun to make their way to the ocean.

"Pu`u `O`o pond was a little more dynamic during this interval. From 13 September to 6 October, the pond level slowly dropped from 79 to 88 m below the crater rim. At its lowest level, the entry of lava from the W side of the pond was clearly visible. In October, the pond level rose from 88 to 60 m below the crater rim and activity on the pond surface became more vigorous. There was little change around the active vents, except that the collapse pit on the W flank of Pu`u `O`o doubled in size during September."

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: T. Mattox, HVO.

Activity had decreased by 4 October, and continued to decline the following week. Continuous tremor after 3 October and into early November had a maximum amplitude of 0.23-0.53 µm, registered 11 km from the volcano. On 5 and 7-9 October the volcano was obscured by clouds, but on 6 October the fumarolic plume from the summit crater rose ~600 m above the rim and was directed NE. Observers in Kliuchi [(30 km NNE)] reported decreased activity during 8-15 October. Gas-and-steam columns rising from two apertures at the summit reached 2,500 m above the crater on 10 October and 800 m on 14 October. Once again during clear weather a gas-and-steam column was seen rising 200 m above the summit crater on 17, 22, and 23 October and to 800-1,500 m on 18-20 October. During 27-29 October the column rose 200-800 m above the summit. The volcano was obscured by clouds from 30 October to 2 November.

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: V. Kirianov, IVGG; AVO.

Eruptive activity in September and October at both craters consisted of moderate and intermittent Vulcanian explosions. Crater 3 was active during the first nine days of the month. It released a moderately thick vapor plume, with occasional dark gray ash clouds, accompanied by explosions and rumbling sounds, and resulting in light ash falls onto the NW flank and coastal villages. For the remainder of September and October, it only emitted very thin wisps of vapor, occasionally accompanied by blue vapor.

At Crater 2, background levels of moderate white and blue vapour emissions continued, and very weak night glow was seen on 7 September. However, activity picked up on the 12th and 13th with occasional dark ash-laden, convoluting Vulcanian explosions. Similar low-level eruptive activity resumed on 15-18, 24, and 28-29 September.

A good correlation could be seen between the level of seismicity and volcanic activity in September. The two local seismographs recorded 2-5 explosive events/day during 1-9 September at Crater 3, and then 2-8 events/day during each of the intermittent phases of activity at Crater 2. Seismicity remained at a low level throughout October.

Emissions from Crater 2 in October consisted of thin white vapour with occasional dark gray, ash-laden convoluting columns rising up to a few hundred meters above the crater. Fine ash fell on downwind coastal areas. Weak night glow accompanied these explosions on 3, 6, 9, 21-22, and 30 October.

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: C. McKee and P. de Saint-Ours, RVO.

"Following intermittent periods of minor eruptive activity during the previous months, activity at S Crater was low during the first week of September. Weak white-pale grey emissions returned, accompanied by occasional roaring sounds and low-level seismicity (~1,000 small long-period events/day, with a scaled amplitude of 7-10 mm). Periods of stronger activity occurred on 8-11, 14-20, 22, and 29 September.

"Starting at 1845 on 8 September, a loud explosion accompanied a period of incandescent projections to 150 m above the crater, followed by the sounds of blocks tumbling into the radial valleys. For the next three days, grey ash-laden clouds were intermittently ejected above the crater, with weak glow and incandescent projections at night. The eruptive sequence ended with one hour of loud explosions and incandescent projections to 500 m above the crater on the 11th. This was accompanied by a marked rise in seismic amplitude (up to 16 mm), but little change in the event rate (950-1,300/day).

"From 14-20 September, S Crater emitted ash-laden vapour up to 600 m above the crater, and there was light ashfall on the NW flank and on coastal villages. It was accompanied by weak-loud roaring sounds and a moderate level of seismicity (~850-1,200 events/day, with amplitudes of 12-14 mm). When this active phase ended on the 20th, the amplitude of the background seismicity rose markedly to ~15 mm. With the outbreak of the next eruptive phase, the amplitude decreased but the daily event count rose to ~1,500.

"Very thin white and blue vapour is all that was emitted by S Crater on 21 September, but from then onwards, large dark ash clouds were rising at 10-20-minute intervals, to 800-1,000 m above the crater. No sound or night glow was visible for the first few days. On the 26th, the ash column reached 2,000 m above the crater and weak incandescent projections were seen throughout the night, reaching ~200 m above the crater at intervals of 1-2 hours. This level of activity, with a background seismicity of 1,400 events/day of moderate amplitude (11-13 mm), lasted until the 28th. The dark emissions became continuous on the 29th but then died out progressively.

"South Crater was mildly active in early October. Weak to moderate emissions of white and grey vapour were released at intervals of 10-20 minutes, resulting in light ashfall downwind. A weak glow and incandescent projections were visible on the nights of 2-3 and 7 October. Throughout this time the seismicity was at a moderately low eruptive level of 1,300-1,500 events/day of 10-14 mm maximum amplitude. The water-tube tiltmeter at Tabele Observatory showed no trend.

"Starting on 14 October, seismicity increased to 15 mm maximum amplitude and Strombolian explosions occurred at intervals of 2-15 minutes, with roaring and explosion sounds. On the 16th, seismicity rose to 1,640 events of 16 mm maximum amplitude, accompanying Strombolian projections 125-320 m above the crater. Through the 17th, the moderately strong and loud Strombolian activity became sub-continuous. Ballistic blocks cascaded down the headwall of SW Valley and into the upper SE Valley. After 1500, a forceful column of ash was rising 6-10 km above the vent. At nightfall, continuous incandescent projections reached 1,100-2,000 m above the crater. The strength of the eruption seemed to increase after midnight until daybreak, with explosions rattling the walls of the . . . observatory. Seismicity peaked-up simultaneously with innumerable events of relative maximum amplitude of 130 mm. A lava flow poured out at a very high rate through a breach on the E side of S Crater and followed the N wall of the SE valley.

"Activity declined during the 18th. The ash column was still rising 4-6 km, with moderately strong roaring sounds and explosions, and the amplitude of earthquakes was still up to 30 mm. The eruption gradually waned after 1630. In the evening, explosions were 2-4 minutes apart, accompanied by weak incandescent projections. The lava flow entered the sea sometime during the night. On the 19th, S Crater had only weak-to-moderate, less forceful emission and seismicity had dropped to non-eruptive levels (~1,000 events/day of 10 mm maximum amplitude). Interestingly, there was no response of the tiltmeter to this eruption.

"Aerial and field inspections on the 18th (R. Middleton) and 19-20th (B. Talai) revealed an absence of pyroclastic-flow deposits, which is unusual for an eruption of this intensity at Manam. The lava flow was of aa-type, <50 m wide up-slope and bounded by levees. It broadened when reaching the base of the terminal cone, between 800 and 600 m elev. It reached a maximum width of ~300 m at 260 m elev where the main front stopped, and a thickness of 3-5 m. The smaller lobe that progressed to the sea following a dry creek on the N side of the valley had a flow front ~100 m wide and 4-5 m high. It extended the coast out by 10-15 m, but had stopped flowing by the 19th. The only damage was to the forest and a copra dryer.

"In the SW valley, effects were limited to a large build-up of talus at the foot of the rock face, down to ~900 m elevation. On the NW side of the island, downwind ash deposits were limited to ~3 mm of fine grey ash with scattered scoria fragments of <1 cm, in a fan area only ~1 km wide. After a 3-day period of inactivity and through the rest of October, weak white and blue vapour emission and weak glow at night recurred.

"All through September, activity at Main Crater consisted of weak, thin to moderately thick emissions of white vapour, without noise or night glow, as in the previous months. There was, somewhat surprisingly, no significant change in the trend and fluctuations of tilt measurements. Activity in Main Crater also remained undisturbed during October, as it released only occasional thin white vapour."

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 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche 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 historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical 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: C. McKee and P. de Saint-Ours, RVO.

Collapse of the active summit dome on 22 November produced pyroclastic block-and-ash flows and glowing surges that traveled SSW up to 7.5 km from the summit (figure 13). As of 28 November, 41 people had died and another 43 were at hospitals in serious condition. All of the victims lived in areas near the banks of the Boyong River. That river flows off Merapi's S flanks and, at ~28 km map distance from the summit, passes through the city of Yogyakarta (population ~50,000). The threats to areas on Merapi's S flank were noted in February 1994, when rockfalls were first observed and reported along the Boyong River. Every month since March, the possibility of SW-flank destruction had been mentioned in Berita Merapi (Merapi News) informing local governments, including Sleman Regency (where this disaster took place), of hazards posed by nuées ardentes. Rockfalls from the dome have recently traveled down the Boyong and other rivers for distances of 500-1,500 m.

Figure 13. Deposits of the Merapi eruption of 22 November 1994 shown on a 500-m-contour base map of the SW quadrant with the primary drainages and some towns labeled. Courtesy of Sukhyar, MVO.

The eruption was preceded by low-frequency earthquakes on 20 October. Multiphase seismic events and rockfalls continued to be recorded at normal levels, with occasional low-frequency events, but one tremor episode occurred on 3 November. On 4 November this change in seismic behavior was reported to the Chief of Regencies. During 21-22 November, a team from MVO climbed to the summit to observe dome development and to install an extensometer station to measure the offset along cracks.

The first nuée ardente was recorded instrumentally at 1014 on 22 November, and was observed visually from the Plawangan, Ngepos, Babadan, and Jrakah observation posts. The team at the summit saw a vertical plume that originated from a location somewhere on the S part of the dome.

The intensity of the nuées ardentes increased at 1020, prompting the observer at Plawangan to send a warning to the forestry officer at Kaliurang (figure 13), a well-known tourist resort. The officer then yelled a warning to the local people. Five minutes later (1025) MVO instructed all observation posts and radio stations of the Regional Task Force that the alert status had been raised to the highest level (Level 4), and that evacuations should begin. At 1045 the observer at Plawangan sent a message to the Chief of Pakem District, but he was already in the field, probably because he had heard the previous warning. Another evacuation warning was radioed to regional task forces at 1100. By 1215 the first victim had been discovered. The Plawangan observation post was abandoned at 1508 and the personnel temporarily moved to Kaliurang. The nuées ardentes had diminished by 1720 that evening.

A NOAA/NESDIS volcano hazards alert stated that at 1346 on 22 November a plume rose to ~10 km. At that time winds aloft were toward the W at 18 km/hour. These same points were repeated in an aviation safety alert (NOTAM).

A UNDHA report on 23 November stated that 25 of 40 employees building a water treatment facility were still missing, while 15 were found dead. Evacuees totalled 6,026 from the neighboring villages in the subdistrict of Pakem. Evacuation and emergency response measures had been undertaken by the local authorities and community members. The UNDHA reported that local volcanology officials advised authorities and local people to remain on alert for seven days.

A 23 November Tokyo Kyodo broadcast (in English) reported "Indonesia's team for disaster safety in Yogjakarta said ash rain has reached Temanggung, ~45 km NW of Merapi." A UPI news report stated that, on the morning of 23 November, an official of the natural disasters office in Sleman said that 118 people were in three hospitals suffering from serious burns. The report further stated that "hundreds of homes have collapsed and thousands of cattle were buried by ash." On 26 November UPI reported that >4,700 people remained in evacuation centers.

According to press accounts and other information collected by the U.S. Embassy and issued on 23 and 25 November, most of the casualties occurred when superheated gases swept through two small villages (Desa Purwobinangun and Desa Hargobinangun in the Sleman district). The eruption ignited ~500 hectares of rainforest near Kaliurang, which press reports said had been damaged by ashfall. Embassy reports on 25 November stated that an estimated 34-200 people were still missing (there had been no communication with some affected villages on the slopes of the volcano). Well over 500 injured persons had been treated at local hospitals. The 25 November Embassy report said that "Local authorities are now concerned about an accumulation of volcanic material [on Merapi's flanks]. It is feared that the approaching rainy season could dislodge this material (estimated in the range of 11 million m³) causing dangerous [mudflows] in the villages below. City officials in Yogyakarta . . . are reported to be constructing a third catchment dam to regulate volcanic material entering the Code river, which runs through the city."

A 23 November Reuters press report stated that "The official Antara news agency said that despite warnings, local people were reluctant to leave the area, regarding the volcano as sacred and likely to offer some supernatural signs if it were to cause a major disaster."

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: Sukhyar, MVO; SAB; UNDHA; AP; Reuters; UPI; ANS.

Heavy rains caused the nearly dry crater lake to rise 1.8 m with respect to the level in September, filling it enough so that the diameter reached about 180 m. A pan-like structure on the crater floor became covered by silt and pale-green 60°C lake water. In October, a zone of boiling water was located at a site in the NW quadrant of the crater, outside the lake. The zone produced tiny (1- to 2-m high) phreatic eruptions and modest (<100-m high) gas columns. Fumaroles on the dome appeared unchanged. During October, low-frequency seismic events at Poás totaled 3,630 (see table 6).

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza Moreira, OVSICORI-UNA; G. Soto and F. Arias, ICE; M. Mora, UCR.

During late-October, Carlos Valdéz-González and co-workers identified a sudden, prominent (roughly 1.6- to 10-fold) increase in daily earthquakes compared to previous months (figure 4). Station locations and the terms "A-", "B-", and "AB-type" were previously defined (19:1-2). Although Figure 4 shows only B-type events, the other two types remained at 0-1 events/day during September and October. Prior to mid-October, the daily count of B-type events generally remained below 10, but by 28 October they climbed to 26. The B-type events for the first half of 1994 were previously published (19:06). Carlos Valdés-González noted that this was the fastest rate of increase in the last 23 months.

Figure 4. Daily number of B-type seismic events at Popocatépetl, May-October, 1994. Courtesy of Carlos Valdés-González, UNAM.

Ignacio Galindo contributed the following report.

"A new series of ultraviolet absorption correlation spectrometry (COSPEC) measurements was made by scientists from Univ de Colima (A. González, J.C. Gavilanes and C. Navarro), UNAM (H. Hidalgo) and USGS (T. Casadevall) on 5 November from a rented Cessna 310 airplane. The measurements were requested by the Secretaría de Gobernación through the Centro Nacional para la Prevención de Desastres (CENAPRED). Between 1024 and 1148 on 5 November, the plume was traversed 12 times at an altitude between 3,539 and 4,545 m a.s.l. [above sea level] in partially cloudy conditions. The aircraft's global positioning system (GPS) computed the wind speed independently for each traverse. These measurements were each used to make individual SO₂ flux calculations, removing the need to use average wind speed (19:08). This procedure is advantageous when the wind speed varies significantly. SO₂ data were sent to a datalogger, besides the typical COSPEC strip chart. All the recorded data were transferred into a personal computer where evaluation software produced the final SO₂ results together with a statistical analysis of the time series. A manual SO₂ determination using data from strip chart records (as reported in 19:08) was also made by C. Navarro; it reproduced the average values within 2.4% on average.

"The SO₂ flux on 5 November ranged from 924 to 1,877 metric tons/day (t/d), with a standard deviation of 285 t/d and an average value of 1,261 t/d. Table 1 compares our recent measurements with those of 4 May, which were determined with the same methodology (19:04). The SO₂ flux increased substantially between 4 May and 5 November. Although our determinations show absolute values less than those reported by other authors (19:1 & 8), both data sets show increased SO₂ flux."

Table 1. Popocatépetl SO₂ flux measurements on 4 May and 5 November 1994. Courtesy of Ignacio Galindo, Univ de Colima.

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: Guillermo González-Pomposo¹, Carlos Valdés-González, and A. Arciniega-Ceballos, Departamento de Sismología y Volcanología, Instituto de Geofísica, UNAM; Ignacio Galindo, Arturo González, J.C. Gavilanes, Carlos Navarro, CUICT-Univ de Colima; Hugo Delgado, Instituto de Geofísica, UNAM; T. J. Casadevall, USGS; ¹Also at Benmérita Univ Autónoma de Puebla.

"The eruption . . . continued throughout October. However, only one of the two centres initially active, Tavurvur, on the NE part of the caldera, remained in eruption. It displayed moderate Vulcanian-type activity, accompanied by the production of a lava flow. Eruptive activity at the other intra-caldera cone, Vulcan, on the W side of the bay, ended on 2 October. Thereafter, its activity was reduced to weak fumaroles and bubbling pools of water at the bottom of its new NE crater.

"Overall, the level of activity at Tavurvur progressively decreased, in spite of variations in the strength, frequency, ash content, and height of its Vulcanian explosions. Only one crater was active on the E side of the cone; up to four were active in the first few weeks of the eruption. During the first few days of October, explosive phases occurred at intervals of 30-120 seconds. They produced billowing columns rising dynamically, with large ballistic fragments, up to 400-800 m above the crater. In between, ash emission was usually continuous though less forceful. Occasionally, the vent remained free of emissions for a few minutes. A second vent on the W side of the same crater occasionally produced a darker but weaker emission, with apparently unrelated frequency. Depending on wind strength, the emission plume levelled off between 1 and 2 km height, and spread W over the town of Rabaul, the pale yellow to brown mass remaining visible for 20 km.

"Through October, the interval between explosive phases increased, though irregularly, to 1-4 minutes. Explosions were irregular in strength but rose less and less frequently to >600 m, and the ash content of the plume decreased. The visible extension of the plume also decreased to ~15 km. Longer periods of weak activity were commonly followed by larger (and louder) explosions that ejected ballistic material as far as 1.5 km from Tavurvur's summit, onto the lower slopes of the cone or into Greet Harbour. During periods of lesser ash content in the emission, these projections caused incandescent night displays (22-27 October). At times of dense ash emission, lightning occurred under and around the plume. Sound effects of the eruption were variable. Rumbling sounds were the most common and apparently louder during periods of lesser ash content in the emission. At other times, Tavurvur could be silent for a couple of hours, or even days, without noticeable change in activity. The largest explosions (like at 0640 on 14 October or 2125 on the 16th) were heard as impressive, sharp detonations up to 20 km away and their air-waves were felt up to 10 km away.

"Backfall of material around the vent progressively built a cone ~30 m high with a radius of ~80 m. Light ashfall on the town of Rabaul and beyond it on the N coast continued throughout October. The first torrential rainfalls of the pending rainy season contributed to the major destruction within the town area. Most buildings in the S and central parts of Rabaul township collapsed under the weight of 0.3-1.2 m of ash/mud. Subsequent rainfalls also caused large flash-floods of mud that temporarily cut off access roads and flooded several buildings and villages. Earthmoving equipment was used to construct drains and barriers in an attempt to alleviate destruction in the remaining parts of town from expected mudflows at the start of the rainy season in December.

"A viscous lava flow, aa to blocky in texture, began on 30 September from a source SW of the main active vent of Tavurvur. Its flow rate was extremely low and its progression slow. On 5 October, as this lobe was still moving within the lower W part of the crater, a new lobe formed and started to override it. On the 8th, an outbreak of apparently more fluid, darker lava started on the W side of the original lobe source. The two initial lobes merged together on 12 October as they started to spill over the lower side of the crater rim onto the W flank of Tavurvur cone. On the 14th, a new lobe started to form from an outbreak through the flow, near the initial source. This became the main feeder to the combined flow system, although it progressed slower and slower until 25-27 October when the flow-front stopped ~100 m below the rim of the cone, 2/3 of the way to the coast.

"The extensive pumice raft, formed as a result of the early Plinian phases and pyroclastic surges, kept drifting across the bay in response to wind shifts. At times of strong SE winds it occupied the N half of the bay, packing to thicknesses of up to 1.7 m (G. Halls, Hydrographic Surveys, Pty Ltd, pers. communication). A few hours of lull or a reversal in the trade wind, and it decompressed and spread over the SE part of the bay, only to drift back a few hours later.

"Ten of the 14 stations of the RVO seismic network were progressively disabled by volcanic products, lightning, interruption of power supply, or vandalism, within the first week of the eruption. By early October, however, in a prompt response to an RVO and PNG Government invitation, a team from the USGS Volcano Disaster Assistance Program was on-site deploying a network of 10 digitized stations with P-picker, Tom Murray's RSAM, and Willie Lee's data management systems on personal computers.

"Following the end of eruptive activity on the Vulcan side, seismicity was scattered under the whole caldera, including outside the usual annular seismic zone. A high concentration of events at Tavurvur corresponded to explosion earthquakes. The level of seismicity indicated by RSAM and the number of detected events showed a general decline, with some fluctuations, throughout the month (figure 20). Most detected events consisted of low-frequency and explosion earthquakes with delayed air-phases distinctive throughout the network.

Figure 20. Fluctuations in the level of seismicity recorded at Rabaul, October 1994. Courtesy of RVO.

"All real-time ground deformation monitoring (electronic tilts and tide gauges) had progressively been lost over the last few years prior to the eruption by lack of appropriate funding. From the onset of the eruption, ash density in the bay prevented EDM monitoring. For the first week thereafter the only accessible ground deformation data were from two water-tube tiltmeters on the outer caldera rim. They indicated radial deflation of the caldera, which started with the triggering earthquakes (M_L 5.1) on 18 September and amounted to 30 and 37 µrad, respectively, by the end of September. By late September a few other stations had been recovered, including a dry-tilt array near the centre of the caldera at the S end of Matupit Island. In early October two electronic tiltmeters were deployed by the USGS team. Sea shore surveying around the bay resumed on 27 September, and geodetic levelling to Matupit Island on 4 October.

"All collected data revealed a caldera-wide subsidence amounting to ~1 m near the centre and 20-30 cm near the edges. The resulting bowl-shaped subsidence is, however, perturbed by the residuals of a pre-eruption uplift on the night of 18-19 September around the two pending eruptive centres, which amounted to 5-6 m on the E shore of Vulcan and 1-2 m at Tavurvur and Matupit Island. Minor caldera subsidence continued through October, although mainly affecting the central area within 3 km of Tavurvur. The maximum measured subsidence amounted to 20 cm at the Tavurvur tide gauge, near the long-recognized apex of ground deformation, with progressively decreasing rates from ~1.5 to 0.4 cm/day. Simultaneously, the Matupit Island tiltmeter recorded a deflation of >110 µrad, radial to the same centre of deformation, at a slowly decreasing rate (figure 21)."

Figure 21. Changes recorded by the Matupit Island tiltmeter, October 1994. Although an upward trend is seen on the plot, the change reflects a steady deflation of the central part of the caldera. Courtesy of RVO.

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: C. McKee and P. de Saint-Ours, with additional contributions fromRVO Staff, RVO; T. Murray, A. Lockhart, and E. Endo, CVO; R. Johnson, AGSO; H. Davies, Univ of Papua New Guinea.

Seismic station RIN (5 km W of the active crater) received 31 events of high-frequency. The events were only detected locally, they had Richter magnitudes of less than 1, and S minus P times of less than 2 seconds. For comparison, during April, the local seismic station received only 13 low-frequency events. In contrast, there were 283 low-frequency events during the previous month, the most reported so far this year.

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

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI.

An eruption in June (19:05) sent ash plumes 2,000 m above the summit, resulting in ashfall on nearby villages. Activity of some kind was apparently continuing in late October. A NOTAM from the Bali FIR reported a volcanic ash cloud up to 900 m above the summit, with an average of one eruption per day.

On 3 November, a cold lahar from the summit area traveled down the Kokok Jenggak River. Thirty people from the village of Aikmel who were collecting water from the river were killed; one person remained missing as of 9 November. No damage to the village was reported. Local volcanologists noted that additional lahars could be triggered by heavy rainfall.

Geologic Background. Rinjani volcano on the island of Lombok rises to 3726 m, second in height among Indonesian volcanoes only to Sumatra's Kerinci volcano. Rinjani has a steep-sided conical profile when viewed from the east, but the west side of the compound volcano is truncated by the 6 x 8.5 km, oval-shaped Segara Anak (Samalas) caldera. The caldera formed during one of the largest Holocene eruptions globally in 1257 CE, which truncated Samalas stratovolcano. The western half of the caldera contains a 230-m-deep lake whose crescentic form results from growth of the post-caldera cone Barujari at the east end of the caldera. Historical eruptions dating back to 1847 have been restricted to Barujari cone and consist of moderate explosive activity and occasional lava flows that have entered Segara Anak lake.

Information Contacts: UNDHA; BOM Darwin, Australia.

Several hours of observations were made on 7 August by J. Sesiano from the N rim of Jonggring Seloko crater. Gas-and-ash plumes rose hundreds of meters above the crater. Generally mild explosions occurred at intervals of ~15-20 minutes, each resulting in a white plume that barely rose above the crater rim. The explosions originated from the same vent where very slow lava extrusion was feeding a flow moving SE that exhibited red glow and incandescent cracks at night. Based on the movement of unique morphological features of the lava flow, a velocity of tens of meters/day was estimated. Incandescent boulders were thrown from the flow front by violent explosions that occurred an average of 4-5 times/day. Collapses of the lava flow, located on a 35° slope, sent boulders down into the valley accompanied by small pyroclastic flows. Whistles and roaring noises were heard almost continuously, similar to the noises heard at a busy airport: jets taking off, landing, turning off engines, and disappearing into the distance. Thunder-like claps, rhythmic pulses (~1 Hz frequency, for ~10 minutes), and other sounds could also be heard. Seismicity recorded by VSI during 5-14 August indicated that activity was at normal levels, with 40-100 explosion events/day (19:07).

A NOTAM issued from the Bali Flight Information Region (FIR) on 24 October noted volcanic ash from Semeru, but the cloud top and drift direction were unknown.

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

Information Contacts: J. Sesiano, Univ de Genéve; BOM Darwin, Australia.

Seismicity remained at normal levels (1-4 events/day) through the second half of September and early October. A gas-and-steam plume rose ~800 m above the extrusive dome during 18-24 September. Starting on 4 October, daily seismicity rose to 9 events, followed by 21 events the next day and 14 events on 6 October. By 9 October the gas-and-steam plume was rising up to 1,000 m above the crater rim and was directed NE for ~1 km. Seismicity at or near the active dome remained above normal (5-15 events/day), and weak tremor was recorded for ~30 minutes/day during 8-26 October. A gas-and-steam plume rising 1,000-2,500 m above the crater was observed from Kliuchi (8 km S) on 8-15 October. The plume rose 400 m above the crater on the 23rd and 200 m on the 27th; the volcano was obscured by clouds the remainder of the time through 3 November. Seismic activity in late October-early November remained above normal levels, with 7-19 events/day occurring at or near the active dome, and weak volcanic tremor lasting for 24-84 minutes/day.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: V. Kirianov, IVGG; AVO.

Following the slow decrease of tremor energy during June, all seismicity increased in July (figure 36). Tremor energy reached an unusually high peak on 27 July; at the same time, a peak in the number of events was recorded. Although more events were recorded on 19 July (864), that was a period of almost continuous explosive activity. A considerable number of saturating events were recorded after 20 July. Volcano guides observed very strong external activity, with pyroclastic material often reaching the usual tourist zones. A decline in tremor energy was observed after 10 August; a slow increase then followed, reaching a new maximum at the end of the month. The number of recorded events followed a similar trend. Another major decrease in tremor energy characterized the first half of September; later fluctuations remained in a "low-energy" range. Vigorous eruptions seen on 21-22 August occurred during a period of low seismicity compared to late July and late August.

Figure 36. Seismicity recorded at Stromboli, 27 June-29 September 1994. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 Nm/s (instrument saturation level). The line shows daily tremor energy computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of R. Carniel.

Observations of crater activity were made by R. Carniel (Univ of Udine) during field work with R. Schick (Univ of Stuttgart) and collaborators at the end of September and early October. Similar observations were made by geologists from Open Univ during 1-13 October, with detailed explosion counts for 3 hours on 1 October, 4 hours on the 5th, and one hour on the 9th. Explosions sent incandescent ejecta, ash, and/or gas to heights of <=300 m, from as many as 10 active vents (figure 37). No active vents were observed in Crater 2, but a hornito (2/1) was visible, and there was minor degassing from an unknown source. Brightness temperatures of fumaroles along the zone E of the Pizzo Sopra la Fossa (39-77°C) were measured by Open Univ geologists with a Minolta/Land Cyclops Compac 3 hand-held radiometer (8-14 mm).

Figure 37. Sketch map of the active craters at Stromboli, 1-13 October 1994. Courtesy of A. Harris [and A. Maciejewski].

Within Crater 1 in late September, Carniel noted three cones ~25 m high that had been built during the very strong activity in July and August (1/5, 1/6, & 1/7; figure 37). Continuous red glow at night could be seen from the top of each. Two other Crater 1 vents were active, the first (1/4) producing short, lateral explosions with large pyroclasts ejected onto the Sciara del Fuoco, and the second closer to Pizzo producing longer and higher explosions (<=200 m). Directed explosions suggested the possibility of a third vent close to the second one. When one of the two W-most cones in Crater 1 erupted (typically with strong degassing and little pyroclastic material) the other exhibited weak degassing. When the second vent erupted, the red glow from the remaining cone strengthened, sometimes with minor degassing.

Crater 1 contained six active vents during visits by Open Univ scientists. Explosions from vents 1/1 (~2/hour), 1/2 (4-9/hour), and 1/3 (0-2/hour) sent incandescent ejecta, occasionally with ash, to heights of 30-250 m. Glow was seen above 1/1 and 1/2 on the night of 5 October. Up to 40% of the ejecta from 1/2 and 1/3 fell outside of the crater area. These explosions were often followed by a gradually fading gas-jet noise of variable length. Explosions seen by the Open Univ team from 1/4 (2/hour) sent incandescent ejecta, including bombs and spatter, 30-150 m E onto the Sciara del Fuoco. On 5 October hornito 1/5 was the source of gas-jet eruptions, and a small amount of incandescent ejecta rose ~50 m; during 10 October more ejecta were seen in 100-m-high gas jets. Hornito 1/7 constantly degassed, and its summit vent was incandescent with a continuous gas flare 1-2 m high. On 10 October this flare increased 1-2 seconds before vent 1/3 erupted. Hornito 1/6 and vents 1/8 and 1/9 vents were only degassing.

The lava pond in Crater 3 had become a small spatter cone (3/2) when observed by Carniel, with a hole through which magma could be seen; activity was limited to degassing. One vent produced high, black, mushroom-shaped columns, and the second (in front towards Pizzo) sent pyroclasts >200 m above the craters. The opening of a new vent was also observed. Explosions from Crater 3 on 28 September were stronger, although less frequent, than from Crater 1. On 5 October the same sequence was observed, with the second vent exploding first and fewer pyroclasts ejected near the end of the explosion by a very small vent to the right of the older one. Guides reported that this vent was first observed on 1 October, when similar explosions from the small vent ejected spatter.

Open Univ geologists noted that only vent 3/2 was active on 1 October, with 3 emissions/hour of brown ash and blocks. By 5 October the quantity of ash emitted had decreased, but the amount of incandescent ejecta had increased, and more frequent explosions (5/hour) were accompanied by loud detonations. Ejecta rose 80-300 m, with some material landing outside of the crater or on the inner crater wall. During night observations on 5 October vent 3/2 would start erupting ~1-3 seconds after 3/1. On 8 October, Crater 3 released gas, sometimes accompanied by minor amounts of ejecta <30 m above the crater rim, and small brown ash clouds 30-100 m high. Similar activity on 9 October was accompanied by an increasing amount of brown ash and incandescent ejecta. During 1 October small lava fountains from vents 3/3 and 3/4 were simultaneous with gas emissions from 3/3. Vent 3/4 was also continuously active with puffs of gas (~1/second). The interior of vent 3/4 was incandescent by day, and glow was observed above 3/1, 3/2, and 3/3 at night. During the night of 5 October the brightness temperature of 3/4 was measured as 873°C, using a Minolta/Land Cyclops 152 hand-held radiometer (0.7-1.1 mm), similar to October 1988 (13:11). Incandescent gas puffs were seen above 3/4 during the night of 10 October. Only minor gas emission was observed from vent 3/5.

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: R. Carniel, Univ di Udine; A. Harris and A. Maciejewski, Open Univ.

The 4th anniversary of Unzen's current eruptive episode took place on 17 November. During the first half of November, Unzen's surface activity reached the lowest level seen in the course of 3.5 years of lava dome growth; earthquakes also reached a low level. From mid-October through mid-November the eruption had a low rate of lava extrusion (<10⁴ m³/day) and a low frequency of pyroclastic flows.

During November, only the N slope moved, and the dome's slow endogenous growth produced velocities as low as a few meters in several tens of days. During mid-October to mid-November the top of the endogenous dome occupied an area 400 x 300 m that was covered with oxidized lava fragments and blocks. During this interval the dome's top became flat to partly convex downward. A small spine 20 m across sprouted near the center of the flat dome top in early October. Extrusion during October caused the spine to rise at the rate of 1 m/day, double the November rate. By mid-November the spine had reached ~50 m high.

Small rockfalls originated at the uppermost NE slopes on the endogenous dome. They typically took place episodically, with many falls confined to a few days during intervals of 2-3 weeks. Some of them developed into pyroclastic flows with travel distances <2 km. During mid-October through mid-November pyroclastic flows lacked accompanying pyroclastic surges. On 26 and 27 October, partial collapses of lava blocks from old lobes generated pyroclastic flows, which traveled ~2.5 km SE and ~2.2 km NE. No pyroclastic flows took place in early to mid-November, which probably reflects the low extrusion rate during this period; in contrast to earlier large Merapi-type pyroclastic flows that seemed to result from large collapses driven by high extrusion rates.

COSPEC analysis by the Tokyo Institute of Technology in late September showed that SO₂ flux from the dome had remained at the low value of ~40 t/d since February 1994. Based on air-photograph measurements by the Geographical Survey Institute of Japan, the total volume of magma erupted from May 1991 to September 1994 was 0.20 km³ (dense-rock-equivalent value), twice the volume of the current dome (0.10 km³). The average eruption rate from February until the beginning of September (7 months) was 6 x 10⁴ m³/day (±2 x 10⁴ m³/day).

During October, microearthquakes detected 3.6 km W of the dome (station A) totaled 993; seven pyroclastic flows were caused by dome collapse. The pyroclastic flows were detected remotely using a seismic station 1 km WSW of the dome and four sets of visible and infrared video cameras.

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: S. Nakada, Kyushu Univ; JMA.

Beginning about 0730 in the morning of 26 September residents of the Centro de Ski Villarrica-Pucón (a ski resort) saw "scrolls of black vapor" emitted about once each minute from the main crater of Villarrica volcano. Vapor rose ~500-750 m above the summit. . . . Four such small explosions took place in the morning, the last, at 1100, coincided with a strong tremor felt at the ski resort.

Figure 3 shows the ash distribution seen by aerial observers in the upper part of the ski area (Piedra Blanca). The distribution was composed of thin ash chiefly visible due to the contrast with the white snow. One part of the ash distribution was bounded by a SE-trending band of heavier deposition. This ash fall deposit extended over 8 km, visible to the east as far as the limit of contrasting background snow.

Figure 3. Ash distribution following the 26 September 1994 Villarrica eruption (mapping by Hugo Moreno on 26 September).

Later on 26 September, between 2030 and 2130, observers saw incandescence above the crater that they attributed to glowing lava in the crater reflected in the fumarolic column. The next day (27 September) was partly cloud-covered, but strong fumarolic activity formed low-lying scrolls directed toward the E. Later, during a clearing in the clouds, observers saw a 500-m-long ash fall layer extending W.

Several seismic stations were installed on 26 September. Although two seismic stations were installed farther from the summit, it was not until 1630 that the station closest to the summit was installed near the Rio Voipir (at the 500-m contour, 13.5 km E of Villarrica). The record there showed continuous harmonic tremor along with other seismic events until about 2110. After that, and until 0600 on 27 September, tremor fell abruptly; however, three long-period volcanic earthquakes occurred in this interval. At 0700 harmonic tremor returned.

Starting at both 0741 and 0800 similar seismic sequences consisted of early events followed by a later event. The same sequence repeated about every 4 hours until the last one ended at 1000 on 28 September. The 4-hour sequence was interpreted as magmatic injections leading to gas-charged explosions. Thus, the main part of the eruptive episode lasted ~3.5 hours (0730-1100 on 26 September). It produced a magmatic eruption with a VEI of 1. The seismic signature associated with frequent gas-charged explosions was not previously seen at this volcano.

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

Information Contacts: H. Moreno, G. Fuentealba, and M. Petit-Breuilh, SERNAGEOMIN, Temuco.

"Gran Cratere was visited on 7 and 11 October 1994 by Open Univ geologists and observations were made of the fumarole zone, which extends from the floor of the lower crater to the rim of the upper crater, and onto the NE outer crater flanks. On 7 October, temperatures of >500 fumaroles were measured (table 2) with a Minolta/Land Cyclops Compac 3 hand-held radiometer (8-14 mm). The only area within the fumarole zone not sampled was that extending from the rim of the lower crater to its floor. Because radiant temperatures have not been corrected for spectral emissivity, all are given as brightness temperatures.

Table 2. Summary of fumarole and fissure temperatures measured at Gran Cratere, Vulcano, 7 October 1994. The upper temperature range of the Compac 3 is given as 500°C by the manufacturer. Courtesy of A. Harris, Open Univ.

"Fumaroles along the crater rim are located in a sinuous 1-3 m wide fissure that runs along the NE crater rim for ~200 m. Within this zone, low-temperature (54-148°C) and medium-temperature (164-286°C) fumaroles dominate and sublimates are common. Maximum temperatures (305-449°C) came from fumaroles within gray rubble-filled depressions, which occurred less commonly along this fissure line. The crater rim fumaroles were bounded at the N end by a rubble-filled fissure, ~60 m long, which cuts the rim obliquely with a N-S trend and extends onto the outer and inner slopes of the crater. This fissure contains fumaroles at temperatures between 134 and 345°C (table 2). The upper slopes of the inner NE flank of the upper crater and S edge of the fumarole zone were dominated by low- to medium-temperature fumaroles, with less common high-temperature fumaroles in rubble-filled depressions and fissures. However, the lower slopes of the inner NE flank of the upper crater were dominated by an area (~70 x 15 m) of gray rubble and high-temperature fumaroles (211-507°C), with lower temperature fumaroles (60-191°C) and sublimates far less common. High temperatures were found in the middle and towards the N side of this area. During measurements there was constant discharge of gases from the fumaroles."

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: A. Harris, Open Univ.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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