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/).

The last reported activity at Bezymianny included a 4-km plume and thermal anomalies visible on satellite imagery during December 2001 and January 2002 (BGVN 26:12). No further reports were issued until mid-November 2002.

On 18 November KVERT raised the Concern Color Code at Bezymianny from Green to Yellow after a 1-pixel thermal anomaly was observed on various satellite images on 16 and 17 November. The closest telemetered seismic stations, situated on Kliuchevskoi, 13.5 km from Bezymianny's lava dome, only recorded several shallow seismic events at Bezymianny: 13 in August and September, and 3 in October. High seismic activity at Kliuchevskoi made it difficult to separate Bezymianny's seismic events from Kliuchevskoi's. According to AVHRR satellite images the thermal anomaly had a temperature of 18°C in a background of -30°C.

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: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.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.

At 2225 on 26 October 2002 a swarm of earthquakes was recorded by the seismic network of the National Institute of Geophysics and Volcanology (INGV) in the Catania sector. Three hours after the swarm began, Etna started a new flank eruption. Until 1 November, ~500 shocks registered. The seismic swarm preceded and accompanied explosive activity in the summit area.

A survey at 0400 on 27 October found that two eruptive fissures had opened on Etna's N and S flanks; they were still propagating up- and down-slope when observed. Fire fountains escaped at both fissures.

At that time, lava flows started to pour from the lower part of the N-flank fissure, causing concern on Etna's N flank around Piano Provenzana. At the lower end of this fissure, two major flows spread NE and E. The NE flow stopped on 31 October after having traveled 2 km, behavior congruent with an observed decline in the effusion rate.

The E flow slowed down until 1 November, but it continued moving and crusting over in the middle portion of the flow field until 3 November. Scientists from INGV-CT conducted a helicopter-based aerial survey, using helicopters from the Civil Protection, and deploying a FLIR TM 695 thermal camera. Survey results showed a few sectors of solid crust and suggested the initial formation of a lava tube on this lava flow, which completely stopped on 5 November. The ski station and tourist shops on Piano Provenzana were first destroyed by the earthquakes, and then surrounded by lava flows. The flows also caused fire that engulfed parts of the pine forest. Flow mapping (shown on the INGV website) was limited by both the presence of fire around the flow fronts and ash clouds masking most of the flow field, and only the use of the FLIR TM 695 thermal camera allowed views of the active lava flows.

The N fissure opened between 2,500 and 2,350 m elevation, an area close to the fissure developed in the year 1809. The current N-flank fissure is a few kilometers long and expanded NE following the NE Rift Zone.

A lava flow from the S-flank fissure started ~12 hours after the N one. It spread SW and split in two branches around Monte Nero, following the same path as one of the 2001 lava branches. The S flows stopped on 31 October, having reached a total length of about 2 km. Fire fountains and phreatomagmatic activity decreased in intensity with time and disappeared at the N fissure, but were still continuing on the S fissure.

The S fissure, which opened at 2700 m elevation, traveled N20°W, and occurred a few hundred meters W of the 2001 S-fissure field, between Monte Frumento Supino and Cisternazza (a map appears at the INGV website, see below). Spatter falling around the S-fissure's vents formed two cinder cones at about 2,030 m elevation. Fire fountains from these vents were initially 100-300 m high, producing an ash plume and abundant ashfall on Etna's S flank. In 3 days the city of Catania received ~2.5 kg/m² of ash due to strong winds from the N. This disrupted the local airport and caused problems with travel.

The high amount of gas released by the summit vents and at the 2,750-m cone (up to 25,000 tons/day), and the continuing explosive activity at the S vent, suggest a long duration for this eruptive event (figure 96).

Figure 96. SO2 released from Etna during January 2001-1 December 2002. Courtesy INGV.

Editor's note: Summaries of Etna activity from recent issues of the Bulletin have been prepared by our staff without the benefit of crafted summaries in English. As such, the contributors found them deficient in clarity of translation. For greater clarity and more technical details consult journal publications and the INGV website.

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: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania, Piazza Roma 2, 95123 Catania (URL: http://www.ct.ingv.it/).

Following ship-based reports of activity at Tori-shima on 11 August 2002, scientists from the Japanese Meterological Agency overflew the area the next day when they observed and photographed ash plumes being erupted from the crater (BGVN 27:07). According to the Japan Coast Guard (via JMA), the activity continued as of 1200 on 14 August; the plume reached ~1.2-1.5 km above sea level on 13 August (figure 3), and ~900 m on 14 August. Emissions were observed from three active areas along the western inner-wall of the summit crater. The crater appeared to have widened. By 21 August, the Japan Coast Guard reported that Izu-Tori-shima no longer "smoked" and only weak steaming was seen in the southern portion of the crater. Faintly discolored sea surface was observed around the island.

Figure 3. Izu-Tori-Shima plume on 13 August 2002. Courtesy Air Force Weather Agency.

Geologic Background. The circular, 2.7-km-wide island of Izu-Torishima in the southern Izu Islands is capped by an unvegetated summit cone formed during an eruption in 1939. Fresh lava flows from this eruption form part of the northern coastline of the basaltic-to-dacitic edifice. The volcano is referred to as Izu-Torishima to distinguish it from the several other Japanese island volcanoes called Torishima ("Bird Island"). The main cone is truncated by a 1.5-km-wide caldera that contains two central cones, of which 394-m-high Ioyama is the highest. Historical eruptions have also occurred from flank vents near the north coast and offshore submarine vents. A 6-8 km wide submarine caldera lies immediately to the north.

Information Contacts: Tomonori Kannno and Hitoshi Yamasato, Japanese Meteorological Agency (JMA), Volcanological Division, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Volcano Research Center (VRC), Earthquake Research Institute (ERI), University of Tokyo (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); U.S. Air Force Weather Agency, Offutt AFB, NE 68113-4039, USA.

In 2001-2002 the crater at Ol Doinyo Lengai has become filled with lava. The thin lava flows (nearly devoid of silica and extremely low viscosity) have begun to regularly spill over three points on the crater rim, descending hundreds of meters downslope. The crater, whose high ground was once considered suitable for camping, is no longer free from sudden inundation by lava. Activity through December 2000 was reported in BGVN 25:12.

This report chronicles many visits to the volcano between January 2001 and September 2002. Fred Belton compiled reports of multiple field parties during July 2001 and May-September 2002. Other visitors are noted in the text. Jörg Keller and Aoife McGrath contributed some observations, photos, a reference, and lab data on whole-rock chemistry.

Observations during January 2001. Paul Hloben contributed the following report. "We visited Lengai 15-17 January 2001. The place was very wet, and most of the soda coating the crater floor and cones had washed away or was in solution within the crater floor and cones. The entire crater was sandy brown and muddy (except recent lava flows, which were brown or gray and rock-hard). Older cones were just soil-brown in color, like gigantic termite mounds. [In contrast, in dry conditions, older lavas generally look white in color.] At that time only two cones were active . . . one nearest the camp site located at the path leading down the volcano."

"The [T51] cone was too high for lava flows (to escape) or for viewing what was happening inside, but we heard continuous blows every 10-20 seconds. Further on (towards the crater's center) there resided twin partially collapsed cones [newly developed features between T49 and T48, figure 71]. They harbored two active ponds (the lava level was ~1.5 m below the collapsed crust at the adjacent point of access and overview). The ponds were interconnected, with lava and gas surges occurring approximately every 20-30 seconds independently in each pond. The smaller pond (on the N) was ~1-2 m in diameter. The larger pond was about 4-5 m in diameter, but not easy to see due to heat blows that forced us to retreat; we could observe it best during the night as it was glowing."

Figure 71. A sketch map of the crater at Ol Doinyo Lengai reflecting conditions seen up to 9 August 2002. In the rapidly changing landscape of the crater, some of the features may have been short-lived; some labeled features may not have existed at the same times. The lava ponds seen by Hloben in January 2001 are not shown, although some of their locations may coincide with later features. The inset shows lava flows active during 4-9 August 2002 (areas with a vertical striped pattern in the crater's W and central sectors). Chris Weber provided the base map; Fred Belton compiled field observations by multiple workers and made revisions on this base map.

Comparison of field maps indicates that the larger of the two adjacent ponds stood in an area later identified as T55 (figure 71). Apparently fresh flows had recently cooled and stopped. They crossed the outflow on the NW crater rim and descended hundreds of meters down the flanks.

Observations during June 2001. Bob Carson and a group of 18 from Whitman College used the guide services of Burra Ami Gadiye to access the summit on 28 June. Carson's report follows. "We climbed on 28 June 2001 and spent from about 0800 to 1245 in the active southern crater. The crater floor was covered with about twenty steep-sided spatter cones and countless pahoehoe flows (some of the longer flows are aa-like near their toes). Radial cracks on the young surface of the crater floor penetrate the older rocks of the crater rim.

"Spatter cone T40B had been active on 27 June, sending ~10-cm-thick pahoehoe flows ~10 m from the vent; access to moisture was turning the edges of the still-warm black natrocarbonatite flows white. Later a slightly explosive eruption spewed tiny glassy spheres of tephra (1-2 mm in diameter) onto the surface of the 27 June pahoehoe flows. Spatter cone T40B sounded like a steam engine for the entire time we were near the volcano's summit. From about 1130 to 1200 on 28 June this cone erupted spatter, throwing blobs of tar-looking lava about 2 m into the air; the blobs landed on the side of the spatter cone making lava stalactites and short pahoehoe flows so that the cone looked like a giant sand castle."

Observations during July 2001. A visit by Fred Belton, Roberto Carniel, Marco Fulle, Andrew Locock, and four others during 23-30 July 2001 revealed that most of the previous year's morphologic changes occurred in the NW third of the crater. For example, T51 was 12 m tall, twice the previous year's height. T51B represented a new spatter cone just SE of T51, that contained a low rim overhanging a pit crater. Another new cone (T53) stood ~40 m NW of T40, but was inactive. Comprising a ~4 m tall rounded cone, T53 contained a hooded cave feeding a solidified open lava lake and lava channels that had flowed N. T40 had grown several meters toward the W. T40C, also new, was a white-to-gray 5-m-tall cone just SW of T40. T49B was white with a rounded summit, standing ~6 m tall. T49C was a broad cone of about the same height; it was first noted by C. Weber in October 2000. The new feature T49D was slightly lower than T49B and had vertical sides ringed with shallow grooves. T49E, probably the newest vent, formed an oval, 15 x 6 m low-rimmed crater just below the N flank of T49C.

On 23 July, T49E contained a frothy lava lake that drained N through a lava channel and frequently overflowed its E rim. By 0630 on 24 July the lava lake's surface had completely crusted over. During the day T49E inflated as lava entered and pushed up its solid surface. Early on 25 July the lake's solid surface had been lifted nearly 1 m above its position of the previous evening. It made continuous cracking and popping noises, and small rocks fell from its rim as it became increasingly engorged with lava. Cracks abruptly opened in its NW side and released copious flows of fluid lava. The filling/draining cycle was repeated twice more that day and several times on 26 July. The most interesting event occurred at 1710 on 25 July when a 3 m section of T49E's side collapsed, releasing a sudden flood of fluid lava that swept large blocks up to 9 m from their original positions (figure 72).

Figure 72. On 25 July 2001 Lengai's ~ 2-m tall, spatter cone T49E underwent a flank collapse over a ~ 3-m-wide sector. This NE-looking photo captured the scene at a late stage of the failure. Lava can be seen escaping the cone through fractures in its disintegrating wall. The entire wall collapsed outward immediately after the photo was made. The volume of material involved in the collapse (both cooled rock wall and molten lava that swept away T49E's side) was on the order of 15-25 m3. Fred Belton, who took this picture, was standing on T49C. Standing on the crater floor just beyond T49E is Roby Carniel, who ran to safety as the failure took place. Courtesy of F. Belton.

During 27-28 July 2001 an eruption occurred that far exceeded the volume and duration of typical lava eruptions. Estimates of lava output were 5 m³/s during the greatest outflow and no less than 1 m³/s at anytime during the first 30 hours of the eruption. At 0630 on 27 July, pencil-wide streams of light gray, comparitively transparent lava flowed from T49E. T49E's lava output increased at 1113, and T49C erupted from its summit vent. At 1430 lava from those vents reached the NW crater rim overflow. Then, T49C ceased erupting, while T49D began to emit spatter from a small hole in its N side and T49B began to overflow from its summit vent. T49B developed a large dome fountain and T49D began ejecting a narrow fan of spatter at a 30° angle.

At 1510 the previously solid surface of T49E abruptly released fountains 1-2 m high, and T49C began erupting clots of spatter every 10 seconds. Thus, four vents were erupting simultaneously. Highly fluid lava flowed in meter-wide channels toward the NW, E, and S. Lava crossed the NW crater rim overflow and cascaded hundreds of meters down the NW flank of Lengai. Lava did not cross the E rim of Lengai because it flowed into a fissure in the crater floor ~25 m NW of the E rim overflow, at a rate of ~1 m³/s. About 1 hour later a vent opened on the E flank of Lengai ~12 m below the rim overflow area and released torrents of lava that flowed far down the flank and started brush fires. Destruction of a seismic station (established 4 m E of the fissure by Joshua Jones, Univ. of Washington) was narrowly averted thanks to the fissure's absorption of the lava flow and Carniel and Locock moving the equipment to a more secure location on the crater rim.

After sunset, spectacular orange fountains played steadily from T49B and T49D. Jets of incandescent gas appeared as flames 1-2 m high above the vent of T49C. By 0600 on 28 July the lava fountain from T49B was diminished but T49D continued to feed a large lava channel toward the E. Width of the channel exceeded 1 m, and depth of the fluid lava within it varied in the range 0.5-1 m. During all of 28 July lava flowed hundreds of meters down a gully on Lengai's E flank after emerging from the channel and the crater-floor fissure, both of which had been enlarged by thermal erosion. During the afternoon, the vigor of T49D's activity gradually diminished and its lava became increasingly frothy. Early on 29 July the eruption ceased and there was no further activity before observers left at 0715 on 30 July. J. Jones revisited the crater on 31 July and 6 August 2001 but saw no activity or fresh lava flows.

Observations during February-September 2002. During 3-7 February 2002, several members of the Societe de Volcanologie Geneve observed lava flows and strong fountains from the T49 complex and reported a new overflow of lava on the W crater rim (Bessard, 2002).

Aoife McGrath climbed the volcano on 26 May 2002 and reported continual small-scale eruptions at T49B. A new spatter cone had formed ~30 m SW of T49B and, according to mountain guide Burra Ami Gadiye, was about 4 months old.

During 18-22 June 2002, Christoph Weber, Jurgis Klaudius, and a film team observed the crater (figures 73 and 74). Fresh lava had flowed 120 m W from T49B and several recent 20-80 m flows originated from T46. Fresh lava was also seen on T37B, and fresh lapilli covered T48, a feature that was audibly active at depth. A new vent, designated T54, was visible between T46 and the W-rim overflow. It was an open solidified lava pond with a 40 m overflow to the W, which covered flows that had passed over the W rim in February 2002. Since August 2001, the diameter of the T49 complex had greatly increased, and there were more and hotter (>125°C) fumaroles in the crater. During this visit, spatter cones T49D, T51B, and T52C were no longer visible.

Figure 73. N-looking view labeling key features in the central-western crater of Ol Doinyo Lengai, as photographed on an 18-22 June 2002 crater visit. Courtesy of Chris Weber and Jurgis Klaudius.

Figure 74. View of Ol Doinyo Lengai's entire crater as seen from the summit region (looking N) during 18-22 June 2002. Courtesy of Chris Weber and Jurgis Klaudius.

During a five-hour period on 18 June lava spattered up to 3 m above the top of T49B (figure 75) and produced a 50-m lava flow to the NE. On 19 June spattering from T49B occurred several times until 1615, after which no further activity was seen through 22 June. On 22 June the team witnessed a ~10 m³ section of the crater wall in an area below the summit collapse into the crater. On each day there were 2-3 discrete tremors of about 1-cm amplitude, accompanied by gunshot sounds. They were distinctly different events from the continuous tremors caused by subsurface lava movement.

Figure 75. A lone photographer with a tripod photographs Ol Doinyo Lengai's vent T49B as it emits spatter in June 2002. The zone of airborne spatter is not visible on the photograph. A fresh lava flows passes close to the photograher. Courtesy of Christoph Weber.

During the first half of July 2002 Jörg Keller was working near Lengai. He noted that until his departure on 14 July, a number of visitors returning from the summit reported either no activity or slight spattering from two cones.

During 4-9 August 2002, Fred Belton, Sven Dahlgren, Jeff Brown, and seven others observed four new spatter cones that had formed between 22 June and 4 August. One of these new cones was T55. Inactive when visited, T55 formed a white cone under 2 m tall containing a wide crater. T56, black and active, was ~7 m tall including a distinctive thin spire rising ~2 m above the summit. T57, ~4 m tall, was partly black but inactive. T57B stood ~7 m tall and was covered by fresh black lava. T54, documented by Weber on 21 June, had disappeared. Older cones such as T37B, T49B, and T49C had grown significantly since 2001 and towered above the N half of the crater rim.

Throughout the visit, T57B ejected clots of lava, expelled loud gas puffs, and produced thick clinkery aa flows. T56 spattered intermittently, T48 erupted pahoehoe lava from vents near its NW base, and T44 and T46 also produced spatter and a few short flows.

At around noon on 4 August a new vent, T49F, abruptly opened in rough, steaming ground near the W base of T49B. The eruption began with noisy ejection of spherical lapilli to a height of ~7 m and fluid lava to a height of 1 m. Throughout the day, the vent erupted at intervals of 1-2 hours, ejecting clouds of lapilli and forming aa lava flows that moved slowly W and NW to the crater rim area. Around 0200 on 5 August T49F eruptions dramatically increased in height and volume. Fountains played to at least 15 m and produced a flood of fluid pahoehoe that flowed W with great speed, destroying a supply camp. Similar eruptions continued for the next 28 hours, at first about two hours apart with gradually lengthening periods of repose between eruptions.

A typical T49F eruption consisted of lava first flowing or spattering from the low, open vent, then the abrupt onset of violent fountains that played for 2-4 minutes to a height of 10-15 m at a ~60° angle toward the W, and finally a decrease in fountain height and the draining of lava back into the vent. The final draining accompanied loud noises that to J. Brown sounded like "sheet metal being bent." By the afternoon of 5 August the site of the supply camp was under at least 1 m of thick pahoehoe slabs. The area just W of the vent was more than ankle deep in 2-8-mm-diameter spherical lapilli. Three vigorous fountaining episodes at T49F the night of 5 August started brush fires along the W crater rim. After dawn on 6 August, T49F's activity gradually waned, completely stopping by evening.

On 7 and 8 August T49F was completely inactive, thin pahoehoe lava flowed from T48, and T57B produced meter-thick clinkery aa flows. In the central crater there was an exceptionally strong smell of sulfur that at times made breathing uncomfortable, continuous low-pitched audible vibrations, and frequent hard bumps and tremors underfoot, especially near T57B and T56.

At about 2300 on 8 August a fissure ~12 m in length opened between T52B and T56 and began erupting a curtain of fire 6-8 m high with nearly continuous violent explosions. After midnight observers began to see an elongated spatter cone containing an extremely vigorous lava lake, whose surface rose ~0.3 m/hour. The new cone (T58) gradually merged with the flanks of T52B and T56. By 0830, T58 was over 2 m tall and its lava lake measured ~5 x 9 m. Lava bubbles over 2 m in diameter burst every 1-3 seconds and the activity showed no sign of abating when observers left at 0830 on 9 August. A photo from 17 August by Jean Bahr documented that T58 had grown to ~10 m in height and had a wide circular summit vent.

On 26 September 2002, Celia Nyamweru and twenty St. Lawrence University students visited the crater during 0630-0830. Lava spattered from T55 at 10-20 second intervals. Highly fluid pahoehoe lava emerged from the lower N slope of T49 and moved across other recent flows, probably from the previous night, which had passed between T40 and T40C and partially surrounded T53. Lava had accumulated against the N wall of the crater rim (then only 5 m high) and was heard flowing into a crack in the wall. The visitors could not see where the lava was going, but the next morning (27 September) as they were leaving the area by road a grass fire (started by lava?) was visible on the cone's upper NW slope. A local Maasai woman said that she had heard a loud noise from the volcano in the night. However, no activity was visible from the lowland N of Lengai.

Nyamweru's team observed one big crack, with steam, sulfur fumes, and black and yellow staining, running NW across the NW crater floor near T53. Other cracks on the NE floor were up to 30 or 40 cm wide and ran into cracks in the crater wall that were not steaming. The cones T26, T27, and T30 were still visible at the base of the S crater wall, surrounded by younger but deeply weathered lavas. The rim of T30 was less than 3 m above the lava surface, but its circular pit was still very well defined. In the NE segment of the crater floor a big blocky flow, brown and crumbly, bordered the NE wall for a considerable distance. It may have originated from T57 or T57B. Many cones from all parts of the crater were gently emitting steam, including T51, T45, T37, T30, and T47. The SE crater floor was very heavily weathered, with no sign of any fresh lava. There were a couple of patches of ground (each a shallow depression about 50 m²) that seemed to be the sites of former standing water. The depressions were floored with very fine pale brown clay/mud, which showed some fine layers and some areas with polygonal cracks. This seemed to be 'sediment' washed off the weathered lava by rain.

The most striking features of the topography were the extent to which the central crater floor has been built up. Except for the big wall to the S that rises to the summit, the topographic expression of the outer crater wall has diminished considerably (table 3). This impression was reinforced on 27 September when at a point about 10 km E of Lengai, they could look back and see the tops of several spatter cones showing above the eastern crater wall.

Table 3. Lava escaped Ol Doinyo Lengai's summit crater at three spots on the rim descending over the NW, E, and W sides. Visitors to the summit recorded these widths at each of the crater outlets. Courtesy of C. Nyamweru and F. Belton.

Jörg Keller provided photographs showing the evolution of the crater from 1988 through the present, emphasizing the progressive upward growth of the crater floor (figure 76). The sequence shows how the volcano has reached a critical stage where extremely fluid lavas can pour down the flanks.

Figure 76. A suite of photographs showing Lengai's crater evolution, 1988-2002. The photographs were taken from the same position with respect to the summit (looking toward the N). Courtesy Jörg Keller and Jurgis Klaudius.

Whole-rock chemistry. Lengai's lavas have been analyzed by several techniques. High-precision XRF (x-ray fluorescence) analyses (table 4) were cross-checked and confirmed with ICP and ICP-MS (inductively coupled plasma and inductively coupled plasma mass spectrometer) instruments. The geochemistry of these lavas are of interest because of their unusual low-silica natrocarbonatite compositions.

Table 4. Natrocarbonatite compositions at Ol Doinyo Lengai for lavas erupted in 1988, 1995, and 2000. Analyses were by XRF. * From Keller and Krafft, 1990. Courtesy of Jürg Keller and Aoife McGrath.

Safety warnings. Deep radial cracks in the crater floor present a serious risk to visitors walking in the crater of Ol Doinyo Lengai, especially at night. Some of the cracks may be hidden by thin lava flows. Protective eyeglasses should be worn near any type of activity. In 2001 an observer without glasses was hit in one eye by spatter and escaped serious injury because his eye was closed at the moment of impact. He sustained second-degree burns on both eyelids.

Camping inside the active N crater has become much more dangerous due to increased crater floor steepness that allows lava from the central spatter cones to reach the crater rim very quickly. Around 0200 on 5 August 2002, fluid pahoehoe lava from the T49F vent destroyed a supply camp and injured Paul Mongi, a Tanzanian guide. One of Belton's websites gives credit to guides like Mongi, who have aided numerous visitors. (Mongi has recovered from second-degree burns on one foot, sustained when lava ignited his sleeping bag.) Lava invaded the camp in spite of a small ridge separating the camp from the crater floor. No location in the active crater is safe from lava flows. Sudden outbreaks of explosive lava fountains are also a serious risk. On 8 August 2002 two observers walked across the site of the T58 fissure eruption little more than an hour before the activity began. Contributors recommended that camps be set up in the inactive S crater, a 15 minute walk away.

References. Keller, J., and Krafft, M., 1990, Effusive natrocarbonatite activity of Oldoinyo Lengai, June 1988, Bulletin of Volcanology, v. 52, no. 8, p. 629-645.

Bessard, Yves, 2002, Ol Doinyo Lengai: Société de Volcanologie-Geneve (SVG), no. 22 (April 2002), p. 2-10 (URL: http://www.volcans.ch/).

Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: Fred Belton, Developmental Studies, Middle Tennessee State University, Murfreesboro, TN 37132, USA (URL: http://oldoinyolengai.pbworks.com/); Paul Hloben, P.O. Box 71860, Bryanston 2021, South Africa; Bob Carson, Department of Geology, Whitman College, Walla Walla, WA 99362, USA; Burra Ami Gadiye, c/o Sengo Safari Tours, P.O. Box 207, Arusha, Tanzania, Africa; Roberto Carniel, Dip. Georisorse e Territorio, Universita' di Udine Via Cotonificio, 114-33100 Udine, Italy (URL: http://www.swisseduc.ch/stromboli/); Sven Dahlgren, Fylkeshuset, Svend Foynsgt 9, 3126 Tonsberg, Norway; Marco Fulle, Osservatorio Astronomico, Via Tiepolo 11, I-34131 Trieste, Italy (URL: http://www.swisseduc.ch/stromboli/); Jörg Keller, Universitaet Freiburg, Albertstr. 23b, D-79104 Freiburg, Germany; Aoife McGrath, Senior Exploration Geologist, Geita Gold Mine, P.O. Box 532, Geita, Mwanza, Tanzania; Jurgis Klaudius, Institut für Mineralogie, Petrologie und Geochemie, Albertstr. 23 B, 79104 Freiburg, Germany; Andrew Locock, Dept. of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA; Celia Nyamweru, Dept. of Anthropology, St. Lawerence University, Canton, NY 13617, USA (URL: http://blogs.stlawu.edu/lengai/); Joshua Jones, Department of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; Jean M. Bahr, University of Wisconsin-Madison, Dept. of Geology & Geophysics, 411 Weeks Hall, 1215 W Dayton St. Madison, WI 53706, USA (URL: http://geoscience.wisc.edu/geoscience/people/faculty/jean-bahr/); Christoph Weber, Volcano Expeditions International, Muehlweg 11, 74199 Untergruppenbach, Germany (URL: http://www.Vulkanexpeditionen.de/).

An eruption began at Nyamuragira on 25 July 2002 (BGVN 27:07). Flights on 1 and 3 August confirmed that the eruption was continuing at a high rate, but another look on 27 September showed that the eruption had ceased. An unusually large earthquake (Mw 6.1-6.2) and its aftershock (Mw 5.5) struck the region on 24 October 2002.

During 6-8 August a team composed of scientists from the Goma Volcano Observatory (GVO) (Kaseraka Mahinda and François Lukaya) and a UN-OCHA consultant volcanologist (Jacques Durieux) made a survey trip to the active eruption site of Nyamuragira. The team landed by helicopter in the summit caldera, reached the eruption site by foot, and spent 24 hours on the scene.

The team saw the eruption at 0330 on 25 July with lava venting at 3 different fractures, or fracture systems. One fracture was open in the central caldera, and lava flows had covered a major part of the floor and partially filled the pit crater (Crater B). Another fracture was active on the S flank, with lava fountains and one lava flow traveling towards the SW. This fracture was active during the first hours of the eruption only.

N-flank fractures had opened and extended for ~2 km, reaching from the crater rim (2,959 m) down to an elevation of ~2,540 m. At the beginning of the activity, lava fountains appeared along the fractures and spatter accumulated around them. Numerous lava flows (pahoehoe and aa) were emitted from several points of the fracture system. Both the fountaining and the presence of multiple fissure vents followed Nyamuragira's usual eruptive pattern.

On 6 August only the lower part of the fracture was active; a cone (several hundreds meters long, ~70 m high) contained three very active lava fountains ejecting scoria to an altitude of ~100 m. From a breach in the lowest part of the cone (on the S), very fast moving lava flowed NE. At that time the lava extrusion rate was ~3 x 10⁶ m³ per day, a typical value at this volcano. The activity of fountaining and lava emission regained some intensity at the beginning of the night but dropped dramatically during the early morning of 7 August. At that time, only one weak lava fountain remained active in the new crater. Decreasing tremor registered across GVO's seismic network, and low tremor prevailed on the morning of 8 August.

An overflight on 27 September confirmed the end of this eruptive episode when observers failed to see any still-active lava flow and the eruptive cones displayed only fumaroles. At that time, however, weak tremor still consistently registered, with slightly less at Nyamuragira (Katale station) than at Nyiragongo (Rusayo station). Nyamuragira also was the scene of a greater number of high frequency (HF) and long-period (LP) earthquakes.

A large tectonic earthquake (Mw 6.1-6.2; m_b 5.8; Ms 6.3), one of the two largest in at least 30 years, occurred on 24 October. A second large-magnitude event (Mw 5.5) occurred about an hour later. For further details on these events, see the text and tables in the section "Regional seismicity" within the report on Nyiragongo in this Bulletin.

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

Information Contacts: Kasereka Mahinda and François Lukaya, Goma Volcano Observatory, Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Jacques Durieux, Resident Volcanologist, United Nations Office for the Coordination of Humanitarian Affairs (OCHA), United Nations, New York, NY 10017 USA (URL: https://reliefweb.int/).

An expedition visited the summit of Nyiragongo during 17-18 May 2002 to look for possible extrusive activity (BGVN 27:05). During the visit, a small lava fountain was observed on the floor of the crater.

A team ascended to the summit by foot during 16-17 July 2002. As they climbed the team first observed a gray-black plume at 2,700 m elevation, and began to clearly smell SO₂ at 3,100 m. From the crater rim (3,425 m) the inner crater was only partially visible because of dense fog and the dark plume. Sounds of molten lava (fountains and spatters) falling on rocks were heard. Despite the extremely poor visibility, it was possible, around 0600, to witness some lava fountaining. The height was estimated as 100 m above the crater floor. During the night, a continuous and strong ashfall affected the upper part of the volcano. On the morning of 17 July the ashfall had ended and only a white plume exited the crater. It was clear that the lower and central part of the crater was extremely active and the presence of a new lava lake was suspected.

On 20 July, the Goma Volcano Observatory (GVO) reported that during the previous weeks, episodes of tremor (some lasting for 23 hours per day) were recorded on several seismic stations around the volcano. Because of poor atmospheric conditions, no helicopter flights were organized. From very limited views through clouds, a white to gray plume was suspected to rise above the crater.

A series of Nyiragongo crater observations were made in September and October of 2002. During 29-30 September the level of the bottom of the crater was stable and occupied by accumulated debris. The crater also contained several vents, the largest of which continued to eject gases at very high pressure. The red coloration of the plume at night was attributed by the GVO to Strombolian explosions and combustion of gases. Burned plants were seen on the crater's E side. An 8 October flight found the crater to be entirely filled by visible vapor as a result of magma degassing. An 11 October flight revealed a new crack at the top of Nyiragongo (at 01°36.840' S and 029°14.505' E), trending in an E-W direction. Scientists conducted gas measurements on 12 October on the ground at Kibunga (Binza); the sampled gases lacked indications of deep origin.

Dario Tedesco indicated that during the two nights preceding a large earthquake on 24 October (see "Regional seismicity" below), incandescence was visible above Nyiragongo's crater from Goma. Witnesses also reported that around this time they saw projections of incandescent lava rising above the crater's confines (perhaps signifying a particularly intense episode of lava fountaining).

Regional seismicity. During 29 September-5 October, GVO noted a slight decrease in high-frequency (HF) and a strong increase in long-period (LP) seismicity compared to mid-August. Specifically, a total of 260 HF and 1,024 LP earthquakes occurred during the week (compared to 290 HF and 287 LP events during 18-24 August). Volcanic tremor was registered at all seismic stations (except in Lwiro), consistent with the eruption at Nyamuragira and a gas plume at Nyiragongo. The tremor was slightly less significant at Nyamuragira (Katale station) than at Nyiragongo (Rusayo station). The spatial distribution of the epicenters revealed that the LP earthquakes were mostly located in the vicinity of Nyamuragira. In contrast, HF epicenters were dispersed, occurring both in the N, at Virunga and Masisi, and in the S, at Lake Kivu. Located magmatic and HF earthquakes tended to be distributed to the E of Nyamuragira and Nyiragongo, at depths of 5-15 km. Tremor, practically constant in amplitude, duration (several hours per day), and temporal distribution, registered at Katale and Rusayo stations. The tremor was taken to indicate great activity at Nyamuragira and Nyiragongo. At each volcano, there was a negative correlation between the abundance of tremor and presence of LP swarms.

During 6-12 October, GVO noted a total of 342 HF and 996 LP earthquakes. Magmatic and HF earthquakes at Nyamuragira and Nyiragongo yielded hypocenters at 5-20 km depths. Other observations of seismicity were similar to the previous week.

A tectonic earthquake was felt in Goma and surrounding areas on 8 October 2002. The region had been the scene of an unusual number of recent earthquakes (table 4). The U.S. Geological Survey's National Earthquake Information Center (NEIC) catalog for 2002 included an anomalously large swarm of tectonic earthquakes in the area, including many events over M 4 during January 2002. Epicenters in the January swarm were commonly within 50 km, and in one case 6 km, of Nyiragongo. The 8 October earthquake mentioned above is absent from table 4, perhaps because of insufficient magnitude or depth.

Table 4. A list containing all earthquakes of M 2 or greater within 200 km of Nyiragongo during 1 January 2002-26 November 2002. Data courtesy of US Geological Survey, National Earthquake Information Center (NEIC) catalog of historical and preliminary data; Bruce Presgrave (NEIC) first noted the anomalously large number of earthquakes in January 2002. Magnitudes include mb, Ms, Mw, and Mn; all are computed magnitudes (where available). Moment magnitude (Mw) is a preferred magnitude scale for large earthquakes; it is in common use, computed from a long-period body- and mantle-wave moment tensor-inversion method. Surface-wave magnitude (Ms) is computed from the vertical component of surface waves of 20-second period; Ms does not increase beyond magnitude 8, and thus indicates smaller values than some other magnitude scales for large earthquakes (not a big factor here). Body-wave magnitude (mb) is computed using short-period P waves; for large natural earthquakes it is generally less uniform and reliable than the moment magnitude. The Mn magnitude, sometimes labeled MbLg, is computed from the vertical component of 1-second Lg seismic-waves (short-period surface waves).

A violent earthquake (Mw 6.1-6.2), one of the two largest in at least 30 years in this area, occurred at 0808 on 24 October (table 4). GVO reported that it was felt in surrounding areas, including Rutshuru, Goma, Bukavu, Butare, Kigali, and Bujumbura. GVO's seven operating seismic stations (Lwiro, Goma, Kunene, Katale, Kubumba, Rusayo, and Bulengo) recorded the earthquake but the high amplitude of the signals caused saturations, thwarting attempts to use local data to obtain rapid, meaningful solutions for seismic parameters. A second large-magnitude event (Mw 5.5) occurred about an hour later. Both earthquakes struck SW of Nyiragongo, at distances of 56 and 66 km (tables 4 and 5).

Table 5. A list containing earthquakes of M 5 or greater located within 300 km of Nyiragongo during 1 January 1973-26 November 2002. Earthquake depths were typically ~10-33 km. Data courtesy of US Geological Survey, National Earthquake Information Center (NEIC) catalog of historical and preliminary data. See the previous table caption for a discussion of the magnitude types.

Soon after the earthquakes, a GVO team measured the temperature and composition of gas released from fractures on the S flank of Nyiragongo and along the N shore of Lake Kivu. No significant changes were found with respect to the measurements taken in the previous days.

Damage was reported at Bukavu (fissures in house walls), Lwiro (some houses destroyed, roof of the seismic station collapsed, and walls of laboratories fissured), Mugeri (a church destroyed), Goma (several house walls fissured, and a truck accident killed two people), and Kigali (walls of several houses fissured, and a school wall collapsed, causing panic).

Since earthquakes commonly occur and are expected to occur again in the future in the active rift, GVO recommended an education campaign discussing seismic hazards and response related to Africa's Great Lakes region.

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

Information Contacts: Kavotha Kalendi Sadaka, Celestin Kasereka, Jean-Pierre Bajope, Mathieu Yalire, and Paolo Papale, Goma Volcano Observatory, Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Jacques Durieux, Dario Tedesco, and Jack Lockwood, Groupe d'Etude des Volcans Actifs, 6, rue des Razes, 69320 Feyzin, France; Bruce Presgrave, National Earthquake Information Center, P.O. Box 25046, MS 966, Lakewood, CO 80225, USA (URL: https://earthquake.usgs.gov/); United Nations Office for the Coordination of Humanitarian Affairs (OCHA), United Nations, New York, NY 10017, USA (URL: https://reliefweb.int/).

On 3 November 2002, fishermen reported strong exhalative phenomena in the Lisca Bianca-Bottaro-Lisca Nera area, E of Panarea Island (figure 1). They described boiling seawater, dead fish, and an intense sulfur smell. On 4 November, scientists of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) carried out aerial and sea surveys between Panarea and the Lisca Bianca-Dattilo-Bottaro islets from a Civil Protection helicopter and a Coast Guard boat.

Figure 1. Bathymetric map of the Panarea Island area, showing the area of degassing in November 2002. Modified from Gabbianelli et. al. (1990); courtesy of INGV.

In three distinct areas between Lisca Bianca and Lisca Nera (figure 2), discolored water was visible, accompanied by intense gas bubbling. The first area, located W of Lisca Bianca, had three distinct degassing points in which bubbles with diameters of some meters reached the sea surface. A second area stretched SSE from W of Bottaro; on the sea surface there was only one point where vigorous outbursts of meter-sized bubbles were noted (figure 3). The third and smallest area was just SW of the second one. Water depths in all three areas are shallower than 30 m.

Figure 2. Bathymetric map and location of degassing points on 4 November 2002. Modified from Gabbianelli et. al. (1996); courtesy of INGV.

Figure 3. Aerial photo of the Lisca Bianca-Bottaro-Lisca Nera-Panarea Island area with evident water discoloration phenomena on 4 November 2002. Courtesy of INGV.

During the preliminary survey, INGV scientists recorded thermal images of the sea surface. Direct pH and temperature measurements were carried out at different depths, and seawater samples were collected. Neither temperature measurements nor thermal images identified appreciable thermal anomalies, because water temperatures (22-23°C) near the degassing points were similar to those close to the island's pier. Conversely, pH values were about 5.6-5.7, significantly lower than typical seawater values.

A field survey was also carried out in the Calcara Beach area, where fumarolic activity has been known since the Roman Age. No anomalies were detected in either the fumarolic flux or in the measured temperature (100°C). Finally, field and aerial surveys were performed in order to exclude the occurrence of ground fissuring or other related anomalous phenomena on Panarea Island.

On 5 November the aerial survey highlighted a remarkable decrease in the intensity of exhalation activity and a sharp reduction of the area affected by water discoloration. In particular, gas bubbling was restricted to the area W of Bottaro. Repeated thermal investigations did not find any significant anomaly. Vigorous bubbling and water discoloration further decreased in the following days.

Seismicity. In the early morning on 3 November the INGV seismic station PAN recorded a swarm of microseisms close to Panarea. PAN, in the E part of the island, is equipped with a 1-Hz vertical seismometer. Although isolated micro-events were recorded beginning at 0253 GMT, the most intense phase of the swarm, in terms of number of events, occurred between 0337 and 0500 GMT. During the swarm, geophysicists noted some hundreds of micro-events with average durations of 8 seconds and magnitudes generally less than 1. After the climax, isolated events continued. Overall, there were a few events with magnitudes between 1 and 1.5; it was impossible to locate their hypocenters because they were not detected at stations more distant from the island. According to S-P arrival time differences, the source could lay within a radius of 2-3 km from the island. The spectrum of the events analyzed shows a broad frequency content, with dominant peaks from 5 to 16 Hz.

Background. Panarea, the smallest island of the Aeolian volcanic arc in the Southern Tyrrhenian Sea, is located ~30 km SW of Stromboli. Panarea is a cone-shaped edifice rising from 1,700 m below sea level to 421 m at Punta del Corvo peak. The subaerial portion of the island was built by prevailing effusive activity and emplacement of domes from 149 to 124 Ka (Calanchi et al., 1999). A second stage, during which pyroclastic activity prevailed, occurred between 59 and 13 Ka (Losito, 1989). As of November 2002 the only volcanic activity consists of a broad fumarolic field in a submarine crater, whose rim is inferred by the semicircular distribution of the islets of Dattilo, Lisca Bianca, Bottaro, and Lisca Nera (Gabbianelli et al., 1990, Italiano and Nuccio, 1991). Panarea and the Aeolian Islands are monitored by the Istiuto Nazioanle di Geofisica e Vulcanologias, Sezz. Catania and Palermo.

References. Calanchi, N., Tranne, C.A., Lucchini, F., Rossi, P.L., and Villa, I.M., 1999, Explanatory notes to the geological map (1:10000) of Panarea and Basiluzzo islands (Aeolian arc. Italy): Acta Vulcanologica, v. 11, no. 2, p. 223-243.

Gabbianelli, G., Gillot, P.Y., Lanzafame, G., Romagnoli, C., and Rossi, P.L., 1990, Tectonic and volcanic evolution of Panarea (Aeolian Islands, Italy): Marine Geology, v. 92, p. 313-326.

Gabbianelli, G., Cortecci, G., Capra, A., Giacomelli, L., Pompilio, M., and Rossi, P.L., 1996, Lineamenti geo-vulcanologici ed ambientali del'area craterica sottomarina di Dattilo-Lisca Bianca (Isola di Panarea, Arcipelago Eoliano) in Caratterizzazione ambientale marina del sistema Eolie e dei bacini limitrofi di Cefalù e Gioia (EOCUMM 95) (edited by Faranda, F.M., and Povero, P.): Data Report, p. 455-462.

Italiano, F., and Nuccio, P.M., 1991, Geochemical investigation of submarine volcanic exhalations to the east of Panarea, Aeolian Islands, Italy: Journal of Volcanology and Geothermal Research, v. 46, p. 125-141.

Losito, R., 1989, Stratigrafia, caratteri deposizionali e aree sorgenti dei Tufi Bruni delle Isole Eolie: Unpublished Ph.D. thesis, Bari University, 92 p.

Geologic Background. The mostly submerged Panarea volcanic complex lies about midway between Stromboli and Lipari in the eastern part of the Aeolian Islands. Panarea, the smallest island in the Aeolian Archipelago, lies on the western side of a shallow platform whose shelf margin is at about 130 m depth. A series of small islands breach the surface to form the Central Reefs, the rim of a crater 2 km E of Panarea, whose shallow submerged floor contains Roman ruins. The submerged Secca dei Pesci lava dome lies at the SE end of the platform, and the rhyolitic Basiluzzo lava dome rises 165 m above the surface at the NE end, along a ridge trending towards Stromboli volcano. The complex was constructed in two main stages: an initial effusive activity phase that produced lava domes, and an explosive stage. The youngest subaerial airfall-tephra deposits are dated to about 20,000 years ago; a date of less then 10,000 BP on a lava flow is uncertain. Vigorous hydrothermal activity has continued at fumarolic fields at several locations on the submerged platform; submarine hydrothermal explosions have occurred in historical time.

Information Contacts: Susanna Falsaperla, Luigi Lodato, and Massimo Pompilio, Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Catania (INGV), Piazza Roma, 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/en/).

During July-October 2002, volcanic activity at Popocatépetl consisted of small-to-moderate, but at times explosive, eruptions of steam, gas, and generally minor amounts of ash. Explosions on 1 and 2 July produced ash plumes that reached 2 km and 700 m above the crater, respectively. Volcano-tectonic (VT) earthquakes (M 1.8-2.9) occurred almost daily. The earthquakes were located mostly to the S and E at depths up to 8 km beneath the crater. Isolated episodes of low-amplitude harmonic tremor were registered, typically for a few hours daily.

The Centro Nacional de Prevencion de Desastres (CENAPRED) reported that during most of July through mid-August, up to 25 small-to-moderate emissions per day were accompanied by steam, gas, and sometimes small amounts of ash. The number of exhalations per day increased during 22-24 July (43, 80, and 55) and 15-17 August (68, 58, and 70). Around 25-45 exhalations occurred per day through the end of August. During September and October, no more than 26 exhalations were registered per day.

Activity reported by CENAPRED in July was probably related to changes in morphology of the intracrater dome (BGVN 27:02 and 27:06). Compared to an aerial photo taken on 29 April (figure 46), an image on 22 May 2002 (figure 47) showed that the dome had diminished in size.

Figure 46. Vertical aerial photo of Popocatépetl taken on 29 April 2002. The top of the image is generally towards the N. Courtesy CENAPRED.

Figure 47. Vertical aerial photo of Popocatépetl taken on 22 May 2002. The photo provided evidence that the dome was diminished in size compared to 29 April 2002 (figure 46). The top of the image is generally towards the NNW. Courtesy CENAPRED.

CENAPRED stated that future activity could consist of isolated minor explosions with emission of incandescent fragments out to short distances from the crater or emissions of variable quantities of ash. The Alert Level remained at 2, and CENAPRED recommended that people avoid the zone extending out to 12 km from the crater, although the road between Santiago Xalitzintla (Puebla) and San Pedro Nexapa (Mexico State), including Paso de Cortés, remained open for controlled traffic.

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

Information Contacts: Centro Nacional de Prevencion de Desastres (CENAPRED), Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacan, 04360, Mexico D.F. (URL: https://www.gob.mx/cenapred/).

The last reported activity at Ruang occurred when Qantas Airlines pilots observed an eruption around 1600 on 27 June 1996 (BGVN 21:08). A resulting plume moved W and reached an altitude of ~6 km. However, the eruption was not visible in GMS satellite imagery. The last known confirmed eruption at Ruang occurred in 1949.

A drastic increase of seismic events - from 3 to 24 events/day - was observed on 24 September by the Volcanological Survey of Indonesia (VSI). The next day, people near the volcano reported hearing a noise, and ash eruptions began by 0100. By 0300 ash emissions were continuous, and ash began falling around Ruang island and the nearby island of Tagulandang. Observers reported that the sounds accompanying the eruption were weak. By 0400 more than 1,000 people living near the volcano were evacuated to a nearby island. Around 0800, the Alert Level advanced to the highest status (level 4).

The first strong eruption commenced at 1140 on 25 September, producing thick black clouds that rose 3 km. Ten minutes later, a second eruption sent ash clouds rising 5 km. At 1210 the activity subsided enough to observe glowing material on E flank. The specific eruption site has not been firmly established. It has been presumed by VSI that it originated from "Crater II" or "where the 1949 lava originated (E side of summit)." The eruption column was reported from ground-based observations as rising to at least 5 km, and by Darwin VAAC advisories as rising to about 17 km. According to the Darwin VAAC, satellite imagery revealed that the ash cloud drifted westward to Borneo and Sumatra. Satellite images from NOAA showed the plume drifting SW with other components drifting W (figure 1). By 30 September the volcano was quiet with only a thin white plume rising about 100 m. The Alert Level was reduced from 4 to 3 on 30 September 2002.

Figure 1. Satellite imagery on 25 September 2002 showed a large eruption plume from Ruang. The volcano's location is shown by the arrow. The plume appears to branch into SW- and W-drifting components. Courtesy NOAA.

Geologic Background. Ruang volcano, not to be confused with the better known Raung volcano on Java, is the southernmost volcano in the Sangihe Island arc, north of Sulawesi Island. The 4 x 5 km island volcano rises to 725 m across a narrow strait SW of the larger Tagulandang Island. The summit contains a crater partially filled by a lava dome initially emplaced in 1904. Explosive eruptions recorded since 1808 have often been accompanied by lava dome formation and pyroclastic flows that have damaged inhabited areas.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Center (VAAC), Bureau of Meteorology, Northern Territory Regional Office, P.O. Box 735, Darwin, NT 0801 Australia; NOAA/NESDIS Satellite Analysis Branch, Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA.

On 10 September 2002 the Alaska Volcano Observatory (AVO) detected 1-minute-long pulses of low-frequency tremor arriving every 2-5 minutes on several seismic stations at Veniaminof. This type of seismicity is indicative of volcanic unrest. Retrospective analysis of seismic data suggested that tremor began as early as 8 September. The overall level of seismicity decreased through late September, but remained above the background level established during the summer of 2002.

On 24 September, residents of Perryville, 35 km S of the volcano, reported and photographed small bursts of steam, possibly containing minor amounts of ash, rising just above the historically active intracaldera cinder cone. Without additional observations, AVO could not determine if this indicated very low-level eruptive activity or vigorous steaming from the cone. On several occasions of relatively clear weather conditions, AVO observed no signs of elevated temperature or ash emission on satellite imagery.

A satellite image recorded on 2 October suggested an apparent gray, diffuse deposit extending across the caldera from the historically active intracaldera cinder cone. This could reflect a small explosion, vigorous steam emission, or redistribution of material on the cone by strong winds. No thermal anomalies were observed on satellite imagery. AVO considered the activity at Veniaminof to be minor, but the exact nature of the unrest remained unknown. Due to the continuing seismicity and reports of unusual steaming, the Concern Color Code remained at Yellow.

Geologic Background. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, 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.

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/).