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 flank eruption at Etna occurred in 1993, but eruptive activity has been nearly continuous in the summit area since late July 1995. Unusually vigorous eruptions in early June 2001 (BGVN 26:08) were followed by still more energetic behavior. An earthquake swarm took place in mid-July, and large SSE-flank eruptions vented lavas in late July and early August on a scale not seen since 1983 (BGVN 26:09). Though this activity has been reported in previous Bulletin reports, what follows is a more detailed description of the summer 2001 activity.

Precursory phases. During the first half of 2001 most activity occurred at the Southeast Crater (SEC), starting with very slow lava extrusion from a vent on the NNE flank of its cone in late January. During the next three months the lava emission rate progressively increased and, in late April, weak ejections of lava fragments began to build small spatter cones (also known as hornitos) in the vent area. Strombolian activity resumed at the SEC's summit vent on 7 May, followed by an episode of vigorous Strombolian activity and lava fountaining two days later.

The activity then returned to lower levels, but for the next two months the SEC was the site of very picturesque continuous and persistent activity, with mild, discontinuous Strombolian explosions from the summit vent and vigorous lava emission (at times accompanied by lava spattering) from vent(s) on the NNE flank. At this spot, a large, steep-sided cone consisting of overlapping lava flows and spatter began to grow, and it was informally named "Levantino." From Levantino (figure 93, upper part), lava flowed NE (toward the Valle del Leone), E, and SE (toward the Valle del Bove), forming a composite lava field with numerous overlapping flow lobes. The longest flows extended up to 2 km from the vent(s). From late May to early June the continuous and relatively harmless activity attracted many visitors.

Figure 93. Inset map (upper left) and sketch map showing Etna's July-August 2001 lava flows, fissures, and related features. The 1983 lava flow-field on the S flank (lighter shading) is shown for comparison. The legend is also linked to numbers near the vents and fissures, as a way to indicate the sequence of activity. The pattern of activity lacked a simple spatial progression. For the time citations, note that the eruption occurred during daylight saving time (UTC + 2 hours). The sketch map is preliminary; it is a composite based on both fieldwork by Behnke and others, and already available maps appearing on the web, including those on the site of INGV-Sezione di Catania. Courtesy of Boris Behnke and Marco Neri, INGV.

The prelude to the main eruption began in early June, with the first strong phase on 7 June, which was mostly confined to lava fountaining at the Levantino, whereas only mild Strombolian activity occurred at the SEC summit vent. During the following six weeks the vigor of the eruptive episodes gradually increased and at times culminated in true lava fountaining from the summit vent. Fourteen such episodes occurred between 7 June and 13 July (7, 9, 11, 13, 15, 17, 19, 22, 24, 27-28 and 30 June; 4, 7 and 13 July), ending with the most violent outburst of the series. Immediately after its cessation, vigorous seismicity began, including shocks that were felt as far as the cities of Acireale and Catania (figure 93 index map).

Between the early mornings of 13 and 17 July, about 2,600 tremors, mostly unfelt, were recorded instrumentally. During this same time interval, severe ground cracking and faulting occurred in various places on the W rim of the Valle del Bove and near the "Cisternazza" pit crater on the Piano del Lago ("PDL," figure 3), a flat area at ~2,500 m elevation to the N of the Montagnola. Press sources cited local volcanologists saying that magma was rising through a dike and stagnating about 1 km below the surface. Steaming was observed at some of the new fractures, but as of the late evening of 16 July no magma had reached the surface. Seismicity continued at a slightly decreased rate.

Shortly after midnight on 17 July, yet another paroxysmal episode occurred at the SEC. This was similar to its 13 July predecessor, with vigorous lava fountaining from the summit vent and the Levantino. It was the last event that could be considered part of the prelude to the main eruption. Figure 93 shows a sketch map of the lava flows that ultimately resulted from the July-August 2001 eruption. The inset at upper left shows the 2001 lavas and locations of various towns on Etna's S, SE, and E flanks.

Eruption of 17 July-9 August 2001. As defined here, the main eruption lasted nearly 24 days, from early 17 July to late 9 August 2001. It began a few hours after the last paroxysmal eruptive episode at the SEC.

An eruptive fissure opened at about 0700 on 17 July at the SSE base of the SEC at ~ 2,950 m elevation (point 1 on figure 93). Vigorous lava spattering occurred at a number of vents, while lava flows advanced toward SE, in the direction of the Valle del Bove rim. Several hours later, at 2200, another fissure opened at an elevation of ~ 2,700 m (point 2 on figure 93), a bit to the W of a panoramic point on the W rim of the Valle del Bove known as "Belvedere," and lava began to extend S from there, across the Piano del Lago, and in the direction of the cable car and ski lifts (shown by the vertical dotted line just beneath PDL on figure 93).

At 0120 on 18 July, a third eruptive fissure became active on the S flank of the Montagnola at ~ 2,100 m elevation, slightly uphill of the Monti Calcarazzi (point 3 on figure 93). Activity at this fissure was initially weak, and a sluggish lava flow began to move from the lower end of the fissure toward the Monte Silvestri superiore, a large complex cinder cone formed in 1892. During the day, the activity gradually increased; lava flowed around the W side of the Monte Silvestri, crossed the road (which connected the Rifugio Sapienza-cable car area with the town of Zafferana) and passed close to buildings. By late evening on 18 July the flow front was at 1,800 m elevation. On 19 July, the lava flow fed by the vents at 2,100 m elevation continued to pass between numerous older cinder cones along the E margin of the 1983 lava flow-field. At the same time eruptive activity continued unabated at all eruptive fissures.

On the evening of 19 July at about 1900, a new vent opened on the Piano del Lago at ~2,570 m elevation, ~ 500 m N of the Montagnola (point 4 on figure 93; "Montagnola 2", "Monte del Lago" or "Cono del Laghetto", unfortunately, all three names are in common usage). The activity was characterized by violent phreatomagmatic explosions that produced a black, ash-laden column and ejected large blocks of older volcanic rocks. This phreatomagmatic activity might have been the result of magma-water interactions with shallow ground water. (The name, Piano del Lago, the "plain of the lake," derives from the fact that frequently during the spring snow-melt a small meltwater lake had formed in that area.) To observers familiar with footage of the 1963 Surtsey (Iceland) eruption, the steam-and-ash columns rising from the new vent appeared strikingly similar. After nightfall spectacular lightning flashed through the plume and ash fell over inhabited areas including the NE, E, SE, and S flanks. Close observation of the vent at 2,570 m elevation revealed a simple, though constantly eroding, pit. Rumors spread that the pit would eventually "make the Montagnola cave in;" however, it remained intact.

The front of the lava flow emitted at 2,100 m elevation (point 3 on figure 93) was at 1,350 m late on the evening of 19 July. It still advanced vigorously, though at reduced speed (~45 m/hour). Soon after, authorities declared a state of emergency.

By the evening of 20 July the front of the lava flow had reached 1,220 m elevation, but it had slowed in a gently sloping area. Nonetheless, the threat to Nicolosi had become international news. The main risk now came from forest and bush fires. Helicopters began to drop large quantities of water onto the burning forest (not onto the lava flow, as was widely reported). Fortunately, no fires broke out. By late 21 July the lava flow's front had reached 1,050 m elevation.

During the night of 19-20 July, the SEC reactivated, and lava began to issue from the NNE side of the Levantino, forming a small flow that advanced in the direction of the Valle del Bove.

At about 1100 on 21 July, yet another eruptive fissure formed (point 5 on figure 93). It emerged on the NE flank, far away from the earlier fissures (below the Pizzi Deneri on the floor of the Valle del Leone). Figure 93 portrays the impressive arcuate fracture system that developed. The lava first issued from the fissure's uppermost portion at ~ 2,700 m elevation, then from its eastern extension ~50 m further downslope. A fracture system formed between this northeasternmost fissure and the E side of the summit crater area, and fissures up to 1 m wide opened on the slope between the Bocca Nuova and the SEC, and began emitting dense vapor plumes.

The large pit crater on the Piano del Lago at 2,570 m elevation continued to produce dense, ash-laden plumes. In late July ash fell over the area between Zafferana and Acireale (inset, figure 93).

On 21 July, the eruption continued with unabated vigor at all eruptive fissures. Late that day, the lava from the vents at 2,700 m had not further advanced on the steep slope above the tourist complex of the Rifugio Sapienza area (shown as Rif. Sapienza, figure 93).

The next day, 22 July, a shift in the wind direction drove the dense ash plume produced by the phreatomagmatic vent at 2,570 m elevation directly over the Catania area, paralyzing the city's Fontanarossa International Airport, and dropping large amounts of fine, black, sand-sized tephra over streets and buildings. Eruptive activity continued without significant variations at all fissures, although the main lava flow directed toward Nicolosi had slowed significantly and advanced only a few meters per hour, still 4 km from the outskirts of the town. That evening, minor, though fast-moving lava tongues fed by the vents at 2,700 m elevation spilled down the steep slope above the tourist complex, destroying part of the ski lifts and threatening to overwhelm some of the poles of the cable car. However, none of these flows made it further than about halfway down that slope. Vigorous Strombolian activity continued at the fissure at 2,100 m elevation, and a cone about 20-30 m high had formed around the largest of its vents, while minor lava spattering from four vents in the lower part of the fissure was building a low-spatter rampart. The lava flow from this fissure moved as a single, broad unit (point 6 on figure 93). Throughout 23 July the activity showed little variation.

On 24 July it became clear that something was changing at the Piano del Lago crater, which until then had displayed only phreatomagmatic activity. Loud detonations came from the Piano del Lago vent on the morning of 25 July, as the activity there had now become purely magmatic.

A new cone was growing on the former Piano del Lago on 26 July produced near-continuous explosions accompanied by loud detonations that could be heard ten's of kilometers away. The cone received bombs ejected from at least three vents within it. Lava began flowing from vents on its S and N sides, spilling around the N and NW sides of the Montagnola and down the steep slope on the W side of that cone toward the Rifugio Sapienza. The new lava flow passed E of the lower cable car station, covered another portion of the road and advanced a few hundred meters further. Vigorous eruptive activity continued on 26 July at the eruptive fissure at 2,950 m elevation, while the fissure at 2,700 m elevation continued to emit lava but pyroclastic activity there had ended. Weak activity continued at the Valle del Leone fissure, with lava flowing toward Monte Simone (in the N part of the Valle del Bove), and the fissure at 2,100 m elevation showed no significant changes in its activity with respect to the previous days.

During 27-30 July the eruption produced some outstanding displays (figures 94 and 95) and caused the greatest impact on human structures. While the fissure in the Valle del Leone showed ever-lower levels of activity and the fissures at 2,900, 2,700, and 2,100 m elevation continued to erupt in a manner almost identical to the previous days, the Montagnola 2 cone and several nearby vents not only provided a show, but vents on its N and S flanks delivered vigorous lava flows that spilled down the steep slope to the W of the Montagnola in surges, presenting a continuous threat to the Rifugio Sapienza area.

Figure 94. At Etna, a night view taken from high on the S flanks near Torre del Filosofo documenting the erupting vents at 2,700 m elevation (left) and a lava fountain at the Piano del Lago cone (right), probably taken on 30 July 2001. The camera was aimed SE. Lights of towns between Acireale and Giarre are visible in the background. Photo was published in the 1 August 2001 issue of the "La Sicilia" newspaper.

Figure 95. Spectacular aerial view of the largest cone formed in Etna's eruption during July-August 2001, built on what used to be the "Piano del Lago" at ~ 2,500 m elevation on the S flank. View is to the SW. Most of the cone grew in a few days in late July; this photo shows the waning phase around 2 August when only ash was emitted. After the end of the activity the summit of the cone stood nearly 100 m higher than its base, but then partially collapsed leaving the cone ~ 80 m higher. To the left of the cone is the 1763 Montagnola crater. Between the two lies a fuming vent; it emitted one of the latest lava flows in the area (black ribbon extending to the left margin of the photo). Other lava flows that were emitted from vents at ~ 2,700 m elevation (out of the photo to the right) can be seen in the right foreground. Yet another lava lobe extends toward the lower left corner of the photo; it emerged at the E base of the Piano del Lago cone. Photograph by volcanologists of the INGV (National Institute of Geophysics and Volcanology); published on 6 August 2001 in the "La Sicilia" newspaper.

A lava flow from the southern base of the Piana del Lago cone on 27 July remained active for about 2 days (point 7 of figure 93). This cone produced three distinct lava flow units from three different vents on its SW, S, and NW sides; those from the SW vent were the most damaging. On the evening of 30 July, the eruption claimed the upper cable car station, which burst into flames as a tongue of lava invaded its interior. Behind it, the rapidly growing cone of the Piano del Lago sent its lava fountains hundreds of meters into the sky, producing ground-shaking detonations.

During late July, the rate of lava emission in the direction of the Rifugio Sapienza area diminished as a new vent opened on the S side of the Piano del Lago cone, from which a lava flow spilled over the crest of the Valle del Bove and flowed to the bottom of the Valle, covering a portion of lava erupted in 1991-1993. The Valle del Leone fissure ceased emitting lava. The Montagnola 2 had become a large cone. It again shifted from magmatic to phreatomagmatic activity. Although the level of activity at this cone was decreasing, ash columns developed, and the wind carried the ash again in the direction of Catania, again closing the Fontanarossa airport. Vigorous eruptive activity continued during the first days of August at the fissure at 2,100 m elevation, but the lava effusion rate had dropped, and only the central portion of the original flow remained active, feeding a flow that advanced on top of the larger earlier flow from the same fissure. Strong phreatomagmatic explosions occurred from time to time at the upper vents on this fissure. Lava also continued to pour from the fissure at 2,700 m elevation, and numerous active flow lobes extended SE toward Monte Nero.

Beginning on 3 August the activity at the fissure at 2,100 m elevation showed a marked decrease. During the last week of the eruption (4-10 August) lava continued to flow from that fissure at a rapidly diminishing rate, explosive activity ended, and the fissures at 2,950 and 2,700 m elevation ceased erupting. Ash emission from the Piano del Lago cone ended around 6 August. Lava was last seen flowing from the fissure at 2,100 m elevation on late 9 or early 10 August. The eruption ended after almost 24 days, much earlier than its vigorous onset had suggested.

Products of the eruption and morphological changes. The July-August 2001 eruption emitted at least eight distinct lava flows which mostly affected the S and SSW flanks of Etna. The most damaging flows came from vents near the Piano del Lago cone at 2,570 m elevation. This cone produced most of the pyroclastic material, of which the most fine-grained portion (ash) caused widespread distress.

Petrographically, the lavas fall into two main groups, one of which is essentially similar to the historical products of Etna (porphyric hawaiites with phenocrysts of plagioclase, clinopyroxene and olivine), while the other shows characteristics not seen in any Etnean lavas during the past millennia (alkalic basalts).

Several major pyroclastic edifices grew during the eruption. The largest, the Piano del Lago cone at ~2,570 m elevation, is a nearly symmetrical cone, ~80 m high, which grew mostly between 25 and 31 July. It is crowned by a large crater ~150 m across and 50-60 m deep with near-vertical walls. During a visit on 30 August a few fumaroles located on the SEC walls emitted vapor and gas without forming a visible plume. A spectacular dike was exposed at the base of the E crater wall, and a less conspicuous dike was visible at the base of the WNW crater wall. Several faults or groups of faults were visible in the E and NE crater walls; a narrow graben developed on top of the E crater wall dike. The second-largest pyroclastic edifice lies in the upper part of the fissure at 2,100 m elevation.

Extensive (non-eruptive) fracture systems formed between the various eruptive fissures. Some of them began to form before the eruption, others developed during its first week. Many of these fractures are arranged in an en echelon pattern, which is especially notable in the Valle del Leone, between the northeastern (2,600 m) vents and the SEC. Other spectacular fractures opened between the Piano del Lago cone and the eruptive fissure at 2,100 m elevation. However, the most impressive fractures developed on the E side of the former Central Crater (now occupied by the Voragine and the Bocca Nuova), where they attained widths of more than 1 m. These fractures were vigorously steaming when visited in late-August and mid-September 2001. Fracturing also affected the southern face of the SEC cone.

About 5.5 km² of Etna's upper and middle slopes were covered with new lava (compared to 7.6 km² in the 1991-1993 flank eruption). The total volume of lavas and pyroclastics emitted during the eruption is ~ 30-35 x 10⁶ m³ (25 x 10⁶ m³ of lava and 5-10 x 10⁶ m³ of pyroclastics, all calculated as dense rock equivalent), which makes this eruption a relatively modest-sized one for Etna (the 1991-1993 eruption had produced ~ 235 x 10⁶ m³ of lava). Yet the fairly high proportion of pyroclastic material distinguishes this eruption from most other recent Etnean flank eruptions.

The most productive vents were those at 2,100 m elevation, which produced the longest (~ 7 km) and most voluminous (slightly less than 14 x 10⁶ m³) single lava flow. The average combined effusion rate at all eruptive fissures throughout the eruption was ~11 m³/s, with peak rates of 14-16 m³/s. It is assumed that much of the magma that accumulated in one or more reservoirs below the base of the volcano in the years preceding the eruption was not erupted and remains available for future eruptions.

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: Boris Behncke, Dipartimento di Scienze Geologiche (Sezione di Geologia e Geofisica), Palazzo delle Scienze, Corso Italia 55, 95129 Catania, Italy.

At least two commercial aircraft flew through airborne ash near the Guatemala City airport on 21 May 1999. An eruption from Fuego that day was the first at that volcano since 1987 (BGVN 24:04). Although the aviator's reports attributed the ash from this encounter to Fuego, their aircraft intersected multiple ash plumes in widely different locations, and thus they may also have crossed plumes from Pacaya. The most likely plume near the southern approach to the airport (La Aurora, ~23 km N of Pacaya; ~40 km NE of Fuego) is from the almost constantly active Pacaya. In contrast, Fuego lies 32 km W of Pacaya and was the likely source of a plume intersected later during the flight, at higher altitude, and for much longer duration.

During the encounters the ~100 or more people on board the two aircraft, and many more on the ground, were at risk. Both encounters seriously damaged the aircraft but ended in safe landings without reported injuries. Volcanic ash can cause jet-engine failure, which creates a hazard not only to passengers, but to people on the ground as well. The risk in this situation was amplified by the airport's proximity to urban Guatemala City (population, >1.1 million).

This example leads to two conclusions discussed further below. First, ash avoidance methodology needs further refinement. Second, there exists an apparent bias towards under-reporting of aircraft-ash encounters, which could short-change their cost to air carriers, their perceived risk, and their funding allocation.

The original report of an aircraft-ash encounter was brought to our attention by Captain Edward Miller of the Air Line Pilots Association and provided on the condition that the air carrier remain anonymous. Bulletin editors also wish to acknowledge conversations with several additional anonymous contacts (commercial pilots). This case occurred in Guatemala; however, analogous situations exist at many airports adjacent to volcanoes. Modest eruptions from nearby volcanoes may be uncertain or difficult to see; they may be hard to detect or characterize; yet they still may yield mobile ash plumes carried by complex local winds to confront air traffic (Salinas, 2001; Hefter, 1998; Casadevall, 1994).

Although in most Bulletin reports we favor the use of local time to emphasize the reference frame of people on the scene, most of the source material (satellite and aviation) for this report refer to UTC (Coordinated Universal Time). UTC is the time on the Greenwich meridian (longitude zero), formerly GMT, a term which has fallen out of use. Accordingly, there are cases in this report that lack conversion to local time. Local time in Guatemala is 6 hours behind UTC.

Activity at Fuego and Pacaya. Fuego erupted on 21 May 1999 sending ash to the S, SE, and SW and ultimately dropping up to 40 cm of ash on local settlements (BGVN 24:04). The eruption occurred at 1800 local time (in terms of UTC, at 0000 the next day). Three hours later the eruption decreased and the Aeronautica Civil recommended that planes go no closer to Fuego than 40 km. One hour after that (at 2200 local, 0400 UTC), the atmospheric ash had settled, and Aeronautica Civil recommended flying no closer to Fuego than 15 km.

Bulletin reports for Pacaya in mid-1999 suggested relative calm, in harmony with the observation that it had chiefly been fuming. However, Pacaya is well-known for Strombolian outbursts. It lies directly in-line and only 23 km S of the N10°E-oriented airstrip. As is common for commercial aircraft there, the approaches described below passed very close to Pacaya. Pacaya typically has lower and smaller eruptions than Fuego, but because it lies so close to the southern approach to the airport, Pacaya's ash plumes easily enter the path of landing aircraft. The situation was particularly complex during this eruption because Fuego's ash was reported on cities that lie below the flight path as well as on the Pacaya's flanks.

Pilot's report of aircraft-ash encounter. What follows was taken from one flight crew's description of events and from later reports and dialog on the topic. In order to preserve the confidentiality of the airlines, the precise times of events on 21 May 1999 have been omitted. Pilots reported clear visibility and light wind, with both the capital and the airport in sight. They maneuvered the aircraft for a final approach from the S. Pilots were advised by air traffic control about erupted particulate ("volcanic sand") about 24 km (15 miles) SE of the airport, well away from their projected path to Runway 01. In addition, based on winds they detected as they neared the airport, the pilots concluded that the erupted particulate to the SE was downwind from their projected flight path to the airport. (In retrospect, this conclusion appears tenuous considering the possibility of either a fresh injection of ash from Fuego, or lingering ash in the trailing portion of the plume that lay to the SE.)

At ~32 km (20 miles) distance from the runway, the pilots maneuvered the plane through ~3,000 m (9,700 feet) altitude on a final approach to the airport with the plane's flaps partially extended (at ~15°, which slowed their aircraft to ~260 km/hour (160 mph), its auxiliary power unit (a small jet engine) on, and its landing gear down. Around this point in their descent, pilots saw bright yellow sparks through the windshield lasting a few seconds, a display unlike static electricity, but rather like that from a grinding wheel. This occurred again at 2,500 m (8,200 feet) altitude, but was more intense yet intermittent.

At this time, air-traffic control announced to the pilots that the aircraft landing in front of them had encountered volcanic particulate; they instructed the pilots to abort their landing and climb to 3,350 m (11,000 feet) altitude. Discussions of options and ash avoidance ensued between pilots and air-traffic control; ash had by this time accumulated on the runway, further complicating landing, even for approaches in the opposite direction. The pilots retracted the landing gear, accelerated to ~410 km/hour (~250 mph), began to climb, and after some discussion with air-traffic control, held on a course NE of the airport. They were subsequently cleared to climb to 6,700 m (22,000 feet) altitude and advised to proceed to an alternate airfield.

During the climb, at ~5,800 m (19,000 feet) altitude en-route to the alternate airport, the aircraft encountered volcanic particulate for 10 minutes. Within that interval the plane spent 2 minutes during ascent engulfed in denser and heavier particulate. During that period, window arcing was constant and the beam of their landing lights revealed a conspicuous cloud of reflecting particles. During ash ingestion the engines's speed lacked noticeable fluctuations. The aircraft exited the plume at about 6,100 m (20,000 feet) altitude and landed without encountering additional ash.

Upon landing, the pilots noticed reduced visibility through abraded windshields. Post-flight examination of the airplane revealed heavy damage, requiring the replacement of the engines (US $2 million each) and auxiliary-power-unit engine. (Note, however, that no deterioration in engine power or performance was noticed during the flight.) Other replaced parts included windshields, a heat exchanger, and coalescer bags. Minor damage was seen on the horizontal stabilizer and wing leading-edges.

Volcanic Ash Advisory Statements. The U.S. National Oceanic and Atmospheric Administration (NOAA), Satellite Services Division website contains two archived statements issued by the Volcanic Ash Advisory Center (VAAC) at Washington, D.C. for Fuego on 21-22 May 1999. The statements, issued to the aviation cummunity to warn of volcanic hazards, are intended for an audience accustomed to special terminology (figures 2 and 3). In the interest of advancing understanding of how volcanological and atmospheric data get transmitted to aviators, we offer brief explanations for many of the terms used (figure 2).

Figure 2. The first archived Volcanic Ash Advisory Statement (VAAS) for the 21 May 1999 eruption at Fuego, Guatemala. The boxes contain added notes to explain some of the basic conventions and specific details seen here. This Statement currently appears on the NOAA Satellite Services Division website (see "Information Contacts," below). Local names are frequently anglicized, dropping all accents and other non-English characters (eg. México would be written MEXICO). Later Advisories adopted the abbreviation "Z" (pronounced 'Zulu' by aviators) for UTC, as in 1300 UTC written as 1300Z.

Figure 3. A later Volcanic Ash Advisory Statement (VAAS) for the 21 May 1999 eruption at Fuego, Guatemala. The statement, which was issued the next day, discloses that the eruption had then stopped and the hazard status was lowered. The statement appears on the NOAA Satellite Services Division website (see "Information Contacts," below).

The Washington VAAC received first notification of the Fuego eruption from a routine surface weather observation from Guatemala City at 2000 local time (0200 UTC) on 22 May. They issued the first Volcanic Ash Advisory Statement a half-hour later (figure 2). Six hours later they issued the second Advisory Statement (figure 3). The Advisories were composed by staff of the Satellite Analysis Branch, one of the two NOAA components forming the Washington VAAC (Streett, 1999; Washington VAAC).

The section "Details of ash cloud" first says that the "surface observation from Guatemala City indicate that the Fuego volcano is in eruption" and that no additional information is available and then briefly describes in words observations that came from satellite imagery. The first sentence, "No eruption . . ." is self-explanatory, but highlights a limitation of the method in use that needs to be emphasized to aviators: an eruption may have occurred but its status is not revealed on the imagery. The sentence, "No eruption could be detected due to thunderstorm cloudiness covering the area around the volcano" is self-explanatory. Less clear is the term convective debris. It does not refer to ash; rather, it refers to remnants of thunderstorms. The gist of these latter two sentences is simply that the thunderstorms that covered the area made it challenging or impossible to see the ash on satellite imagery. Central American thunderstorm clouds typically can reach altitudes of more than 12,000 m (40,000 feet), and can mask or obscure airborne ash residing below that level.

Members of the Washington VAAC commented that this eruption demonstrates key problems that can arise when cloudy conditions prevent satellite detection of ash, foiling a primary mode of analysis. In such cases, they rely on ground observers (including observatories and weather observers), pilot reports, and reports from airlines. Thus, their ability to issue useful information in cloudy conditions depends on the quality of communications with local observers, the Meteorological Watch Office, volcanologists, geophysical observatories, and the aviation community.

The Advisory Statement listed México City weather balloon data acquired 1,050 km NW of Guatemala City. In retrospect, the Washington VAAC noted that they generally avoid using such distant sounding data. If a closer sounding cannot be found, they prefer to use upper-level wind forecasts taken from a numerical weather model. In any case, the scarcity of local sounding data presents a challenge to the realistic analysis of airborne ash.

The outlook section says to "see SIGMETS." SIGMETS are the true warnings to aircraft for SIGnificant METeorological events. They are issued by regional Meteorological Watch Offices (MWOs), in this case the MWO (for Guatemala) is in Tegucigalpa, Honduras. SIGMETS were lacking for this eruption; although the Washington VAAC tried to contact the MWO without response. Another complexity confronted at the VAAC is a lack of a single scale for communicating a volcano's hazard status.

Reporting of aviation ash encounters. In personal communications with Bulletin editors, airline personnel stated that many more encounters have occurred than have yet been tallied in publically accessible literature. In accord with those assertions, the 21 May 1999 encounters are absent from reports compiled by the International Civil Aviation Organization (ICAO, 2001). In that document (Appendix I, table 3A, p. I-12) Fuego fails to appear as a source vent for any aircraft-ash encounter. Pacaya is listed for two encounters, in January 1987 and in May 1998 (BGVN 23:05).

Even though the number of encounters was probably under-represented and thus reflects a minimum, ICAO (2001) notes that the international costs to aviation since 1982 summed to well in excess of $250 million. They noted, "In addition to its potential to cause a major aircraft accident, the economic cost of volcanic ash to international civil aviation is staggering. This involves numerous complete engine changes, engine overhauls, airframe refurbishing... aircraft downtime... [and] volcanic ash clearance from airports and the damage caused to equipment and buildings on the ground."

The incidents here suggest that there has been a strong bias toward under-reporting aircraft-ash encounters. If this tentative conclusion is correct, it implies consistent understatements of the hazard's magnitude. This, in turn, may have thwarted meaningful analysis of how and whether to proceed with designing more robust hazard-reduction systems. Accordingly, resources that could have been devoted to the problem have not yet been committed (see Gimmestad and others, 2001 for a discussion of a prototype on-board ash-detection instrument).

Communication challenges. While much of the aviation community needs to learn about volcanism rapidly, dependably, and with the aid of the Internet, some observers charged with reporting volcanic-ash hazards in Central and South America lack access to basic communication devices like reliable telephones and fax machines. To reduce the risks, the aviation, meteorological, remote sensing, and volcanological communities need to improve their ability to pass critical information to each other rapidly and precisely. The operational systems related to volcanic ash and aviation must transcend numerous boundaries (eg., languages, infrastructure, funding, governments, agencies, air carriers, pilots, aircraft manufactures, etc.). The systems need to portray complex, dynamic processes such as the rapid rise of an explosive plume, or large-scale ash-cloud movement.

Although the infrastructure for ash avoidance is greater than ever, members of the Washington VAAC have told Bulletin editors that they still depend heavily on people on the scene of the eruption to notify them promptly when eruptions occur. They said that thus far in parts of Central and South America a problem has been the expense of communication (eg., by phone, fax, and Internet). They also said that for the same regions the U.S. meteorological database regularly lacks pilot reports. Though serious, these problems have at least been identified and their solutions would appear to lack great technical or economic barriers.

The pilots involved in the May 1999 encounter recommended that far more emphasis be placed on forecasting and avoiding ash plumes. Other pilots cited the need for fast and accurate communications between those who observe eruptive activity and air traffic control personnel.

Issues like these continue to be an important subject at gatherings on the topic of ash hazards in aviation (Casadevall, 1994; Streett, D., 1999; Washington VAAC, 1999). The Airline Dispatcher's Federation (ADF) will participate in a 7-9 May 2002 conference and workshop: "Operational Implications of Airborne Volcanic Ash: Detection, Avoidance, and Mitigation." The gathering will provide the pilot and dispatcher with insights into volcanic ash, including its characteristics, affects on aircraft, detection/tracking, effective warning systems, and mitigation. A "hands-on" exercise will make this the first gathering of its kind to provide lab-style instruction on interpretation of satellite and wind data, and on models of ash trajectory and dispersion. Representatives from the Boeing company, and a host of US government agencies and non-governmental organizations will attend. The workshop will include lectures, demonstrations, laboratory exercises, and a simulated-eruption exercise involving volcanologists, forecasters, controllers, dispatchers, and pilots.

A second international symposium on ash and aviation safety is being planned by the U.S. Geological Survey, organized by Marianne Guffanti. It will be held in Washington, D.C. in September 2003.

References. Casadevall, T.J. (ed.), 1994, Proceedings of the First International Symposium on Volcanic Ash and Aviation Safety: U.S. Geological Survey Bulletin 2047, 450 p.

Gimmestad, G.G., Papanicolopoulos, C.D., Richards, M.A., Sherman, D.L., and West, L.L., 2001, Feasibility study of radiometry for airborne detection of aviation hazards, NASA/CR-2001-210855; Georgia Tech Research Institute, Atlanta, Georgia, 51 p. (URL: http://techreports.larc.nasa.gov/ltrs/PDF/2001/cr/).

Hefter, J.L., 1998, Verifying a volcanic ash forecasting model, Airline Pilot, v. 67, no. 5, pp. 20-23, 54.

International Civil Aviation Organization (ICAO), 2001, Manual on volcanic ash, radioactive material, and toxic chemical clouds, doc 9691-AN/954 (first edition): 999 University St., Montreal, Quebec, Canada H3C 5H7 (purchasing information: sales_unit@icao.int).

Rose, W.I., Bluth, J.S.G., Schneider, D.L., Ernst, G.G.J., Riley, C.M., Henderson, L.J., and McGimsey, R.G., 2001, Observations of volcanic clouds in the first few days of atmospheric residence: The 1992 eruptions of Crater Peak, Mount Spurr volcano, Alaska, Jour. of Geology, v. 109, p. 677-694.

Salinas, Leonard J., 2001, Volcanic ash clouds pose a real threat to aircraft safety: United Airlines, Chicago, Illinois (URL: http://www.dispatcher.org/library/VolcanicAsh.htm).

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.

Streett, D., 1999, Satellite-based Volcanic Ash Advisories and an Ash Trajectory Model from the Washington VAAC: Eighth Conference on Aviation, Range, and Aerospace Meteorology, 10-15 January 1999, Dallas, Texas; American Meteorological Society, p. 290-294.

Washington VAAC, 1999, Operations of the Washington Volcanic Ash Advisory Center, in Aeronautical meteorological offices and their functions, and meteorological observation networks: Third Caribbean/South American Regional Air Navigation Meeting (Car/sam/ran/3); Buenos Aires, Argentina, 5 - 15 October, 1999; International Civil Aviation Organization (http://www.ssd.noaa.gov/ VAAC/PAPERS/carsam.html).

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: Captain Edward Miller, Air Line Pilots Association (ALPA), Air Safety & Engineering Department, 535 Herndon Parkway, PO Box 1169, Herndon, VA 22070-1169, USA; Grace Swanson and Davida Streett, Washington VAAC, Satellite Analysis Branch (NOAA/NESDIS), 4700 Silver Hill Road, Stop 9910, Washington, DC 20233-9910, USA (URL: http://www.ssd.noaa.gov/); Bill Rose, Geological Engineering and Sciences, Michigan Technological University, Houghton, MI 49931, USA.

Episodes of increased seismicity occurred during December 2000 through September 2001 (BGVN 26:08). Since then seismic activity at Karymsky has remained mostly above background levels. The Concern Color Code remained at Yellow ("volcano is restless") through at least late March 2002. Apparent steam plumes were seen in satellite imagery during January-March 2002.

On 4 January 2002, the Kamchatkan Volcanic Eruption Response Team (KVERT) reported above-background seismicity during the previous week, with 40 to 80 weak local earthquakes occurring per day. Several shallow seismic events suggested gas-ash explosions. Beginning at 1200 on 10 January the number of local earthquakes increased noticeably. During 11-14 January about 200 weak local shallow seismic events occurred per day.

During late January through at least March 2002, the seismic station typically recorded approximately 10 local shallow earthquakes per hour. Around 24 January, the earthquakes became slightly stronger. The character of the seismicity during mid-March suggested weak ash-gas explosions and avalanches.

The Tokyo VAAC reported that on 1 February at 1810 an eruption produced an ash cloud that reached ~7.5 km above the summit and drifted to the E; however, the cloud was not visible on satellite imagery. On 13 February at 0945 a pilot reported an ash cloud to ~3.5 km above the volcano extending to the W. Again, this cloud was not visible on satellite imagery; it may have been a single burst that dissipated rapidly.

No ash was detected in satellite images during the report period; only steam and possible airborne volcanic aerosols were visible during late February. Thermal anomalies and plumes were visible on AVHRR satellite imagery throughout the report period (table 1).

Table 1. Thermal anomalies and plumes visible on AVHRR satellite imagery at Karymsky during January through March 2002. Courtesy KVERT.

General Reference. Khrenov, A.P., and others, 1982, Eruptive activity of Karymsky Volcano over the period of 10 Years (1970-1980): Volcanology and Seismology, no. 4, p. 29-48.

Tokarev, P.I., 1990, Eruptions and seismicity at Karymskii volcano in 1965-1986: Volcanology and Seismology, v. 11, p. 117-134 (in English).

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: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tokyo Volcanic Ash Advisory Center (VAAC),Tokyo, Japan (URL: https://ds.data.jma.go.jp/svd/vaac/data/).

This report discusses activity at Kilauea during mid-January through mid-April 2002. The flow of lava into the ocean in September (BGVN 26:12) at the Kamoamoa entry and, to a lesser extent, at the E Kupapa'u entry, terminated by the end of January. During February through mid-March lava flowed on the surface at elevations above or on the Pulama Pali slope and along the Kamoamoa lava tube system. Volcanic tremor occurred at moderate levels, and long-period (LP) earthquakes were registered below the caldera. In mid-March incandescence was visible from Pu`u `O`o crater. Incoming lava flooded the floor of Pu`u `O`o crater and excess lava flowed through lava tubes down the Pulama Pali slope to the coastal plain. Heightened activity continued and in early April a series of deflation and inflation events occurred. LP earthquakes increased and on 6 April observations of the crater lake in Pu`u `O`o crater revealed that the lava had risen to 17 m below the E rim.

Geophysical activity. Tiltmeters across the volcano showed no significant deformation until mid-March, although an M 4.1 earthquake had occurred at 0118 on 18 January. The earthquake was located 4 km SSE of the Pu`u `O`o crater at a depth of 9.1 km. During the following several days volcanic tremor remained moderate to strong at Pu`u `O`o. The swarm of long-period (LP) earthquakes at the summit continued through March. Just after 0300 on 27 March a small earthquake beneath the caldera triggered more than 30 minutes of increased tremor and small earthquakes.

Sharp deflation at Pu`u `O`o on 28 March accompanied a change in eruptive activity at the cone. On 31 March volcanic tremor was low-to-moderate at Pu`u `O`o and the continuing weak tremor below the caldera was broken occasionally by small LP earthquakes. Associated tilt across the volcano was flat or only changed slightly.

During 4-6 April, a series of deflation and inflation events occurred. In terms of tilt, at ~2100 on 4 April, Kilauea's summit deflated (~1.7 µrad); 30 minutes later Pu`u `O`o followed (~9 µrad). This was reversed at 1600 on 5 April when rapid inflation began at the summit and ~12 minutes later at Pu`u `O`o. At 1700 inflation ended at the summit, and it abruptly deflated, as did Pu`u `O`o at 1800. Subsequently, tilt at Pu`u `O`o oscillated three times between rapid deflation and slower inflation. The tilt temporarily decreased, but at 0508 on 6 April another interval of 4.5 oscillations occurred followed by resumed tilt and slow, bumpy inflation. During this turbulent period LP earthquakes increased at the summit while tremor remained steady at Pu`u `O`o. By 7 April tilt was relatively steady, volcanic tremor at Pu`u `O`o was moderate, and tremor at the summit was low to moderate.

Lava flows. During mid-January surface lava traveled along the upper portion of the flow field above the Pulama pali slope and onto the coastal flat. Surface lava also emerged along the Kamoamoa lava tube system and traveled down the Pulama pali slope. These surface flows continued to be visible through February, although the flow reaching the coastal plain had stopped at the end of January. At times during early March several rootless shields (a pile of lava flows built over a lava tube rather than over a conduit feeding magma) were active. During 12-19 March a bright glow was widely visible over Kilauea from Pu`u `O`o crater and from a rootless shield near 665 m elevation where the most intense surface activity occurred.

By 18 March lava had flooded the floor of Pu`u `O`o crater resulting in surface lava flows and lava flowing through tubes. Lava spread out on the lower fan and adjacent coastal flat, although the fronts of the flows remained ~2.3 km from the ocean. At the base of the lava fan and on the adjacent coastal flat the rootless shields remained active and small surface lava flows persisted through mid-April.

Eruptive activity changed on 28 March, as noted above, and overflight observations revealed new lava located W of the main crater. Observers also saw lava fountaining and forming a circulating pond. By 31 March a lava flow was visible on the floor of Pu`u `O`o crater and several vents were incandescent. During a brief visit to Pu`u `O`o on 6 April observers noticed that the crater lake had risen ~8 m since 29 March (the lake surface was 17 m below the E rim), several cones were active, and lava was flowing into the lava lake from two vents. By the following day activity had decreased and by 8 April incandescence was no longer visible at Pu`u `O`o.

General References. Decker, R.W., Wright, T.L., and Stauffer, P.H., 1987, (eds.), Volcanism in Hawaii: USGS Professional Paper 1350, 1667 p. (64 papers).

Ryan, M.P., 1988, The mechanics and three-dimensional internal structure of active magmatic systems: Kilauea volcano, Hawaii: JGR, v. 93, p. 4213-4248.

Dzurisin, D., Koyanagi, R.Y., and English, T.T., 1984, Magma supply and storage at Kilauea volcano, Hawaii, 1956-1983: JVGR, v. 21, no. 3/4, p. 177-207.

Heliker, C., Griggs, J.D., Takahashi, T.J., and Wright, T.L., 1986/7, Volcano monitoring at the U.S. Geological Survey's Hawaiian Volcano Observatory: Earthquakes and Volcanoes, v. 18, no. 1, p. 3-71.

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

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).

Activity at Manam remained relatively low following a 4 June 2000 eruption (BGVN 25:07). During August and September 2001, the Rabaul Volcanological Observatory (RVO) reported occasional emissions of weak-to-moderate volumes of white vapor. Weak emissions were also observed from South Crater.

On 13 January 2002 mild eruptive activity began from South Crater. Weak gray-brown ash clouds were emitted at 5-10 minute intervals. Fine, light ashfall was reported on the NE side of the island. Ashfall was reported again on 16, 20, 21, 22, 26, 29, 30, and 31 January, produced by activity ranging from gentle emissions to forceful projections of weak-to-moderate gray-brown and occasionally dark-gray ash clouds, during periods lasting a few hours. Most of the activity was accompanied by weak, deep, low roaring and rumbling noises. Explosion noises were heard on 20 January, and incandescence was observed on 17 and 20 January. The incandescence on 20 January fluctuated but occasionally intensified and projected glowing lava fragments.

Similar mild eruptive activity continued through much of February. Fine ashfall occurred on the SE part of the island. Weak-to-bright incandescence was observed on 13 February, after a loud explosion at 0225. The explosion was also followed by weak roaring and rumbling noises at one-minute intervals lasting for ~1 hour. During 20-24 February activity decreased and continuous weak volumes of white vapor were emitted. Main Crater released only weak-to-moderate volumes of white vapor.

People living in and near the four valleys (especially those in the NE and SE) were urged to be cautious and remain away from the valleys as much as possible.

More recently, a period of activity began in December 1956 that lasted through January 1966. Lava flows and a nuee ardente from the South Crater occurred in June and December 1974, and intermittent moderate explosive activity has continued, with peaks of activity in 1982 and 1984. The water-tube tiltmeter is located at Tabele Observatory, 4 km from the summit on the SW flank.

General References. de Saint Ours, P., 1982, Potential volcanic hazards at Manam Island: Geological Survey of Papua New Guinea Report 82/22, 19 p.

Scott, B.J., and McKee, C.O., 1986, Deformation, eruptive activity, and earth tidal influences at Manam volcano, Papua New Guinea, 1957-1982: Royal Society of New Zealand Bulletin 24, p. 155-171.

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

The following report covers activity at Miyake-jima after February 2001 and through April 2002, but a brief review of previous activity is included. Volcanism renewed at Miyake-jima on 27 June 2000 with a series of underwater eruptions (BGVN 25:05-25:07). Activity through October 2000 was characterized by intrusive events, collapse of the summit crater, explosive events, and degassing. SO₂ emissions were high and low levels of ash were intermittently emitted (BGVN 25:09). During October 2000 through mid-February 2001 high volumes of volcanic gas emission continued (BGVN 26:02).

After a large eruption on 18 August 2000, large amounts of volcanic gas, especially SO₂, started to discharge. SO₂ flux monitoring by COSPEC V has been conducted since 26 August 2000. Monitoring is performed almost daily by the Japanese Meteorological Agency (JMA) and Geological Survey of Japan (GSJ). Figure 14 shows the daily average of SO₂ flux during August 2000 through April 2002. The mean flux during September-December 2000 was ~40,000 metric tons per day (t/d). During 2000, the average SO₂ flux was 40,000 t/d, and it decreased to 21,000 t/d during 2001. As of March 2002 the average SO₂ flux was 10,000-20,000 t/d. During the 26 September 2001 explosion the amount of SO₂ degassing was ~15,000 t/d.

Figure 14. Daily averages of SO2 flux at Miyake-jima during August 2000 through April 2002. Courtesy JMA, GSJ, and KSVO.

In November 2001 the GSJ reported that the strong eruptions of July-August 2000, initially thought to be solely phreatic, had been phreatomagmatic. For instance, tephra from the 18 August 2000 eruption was ~30-40% juvenile in nature. Following the 29 August 2000 eruption, activity was much weaker. A summit pit crater or caldera, formed as a result of "drain back" as magma was intruded elsewhere, stabilized in August 2000 with a diameter of 1.4 km.

On 16 March 2001 the JMA reported that the strongest tremor since 29 August 2000 had occurred. Three days later, on 19 March, an eruption produced a black ash cloud that rose 800 m above the volcano.

In mid-May 2001, based on information from the JMA, the Volcanic Research Center reported that no ash clouds had been observed since 19 March. They also reported that steam plumes with abundant SO₂ were continuously emitted from the summit caldera to 0.5-2 km above the caldera rim. Continuous SO₂ emission released as much as 33,000 to 46,000 metric tons of SO₂ per day (figure 14). Low-level seismic activity continued; on 5 May 2001 a total of 446 small low-frequency earthquakes were registered, and on 7 May an M 2.8 earthquake occurred. Global positioning system (GPS) measurements showed steady, continuous deflation of the volcano, though the rate was lower than before September 2000. Very small collapses of the caldera rims were occasionally seen during air inspections.

About 20 small eruptions were recorded by the JMA during 2001 through the end of March 2002. Major eruptions were reported on 27 May, 26-27 September, and 16 October 2001. The eruptions produced ash plumes up to 1,500 m high.

On 25 January 2002 at 1015 Air Force Weather Agency staff detected a faint E-drifting volcanic plume emanating from Miyake-jima on MODIS imagery (figure 15).

Figure 15. MODIS imagery on 25 January 2002 at 1015 shows a plume drifting E from Miyake-jima. Courtesy AFWA and NASA.

The GSJ reported that as of 1 April 2002, eruptions were continuing and significant quantities of SO₂ (10,000-20,000 t/d) discharged from the summit pit crater (figure 14). According to a news report, a minor eruption occurred at Miyake-jima on 2 April shortly after 1000. While evacuated residents were visiting the island, ash rose to ~300 m above the volcano and fell around Miyake-jima. The island is currently uninhabited because activity that began on 26-27 June 2000 prompted officials to order an evacuation on 1 September 2000.

Geologic Background. The circular, 8-km-wide island of Miyakejima forms a low-angle stratovolcano that rises about 1100 m from the sea floor in the northern Izu Islands about 200 km SSW of Tokyo. The basaltic volcano is truncated by small summit calderas, one of which, 3.5 km wide, was formed during a major eruption about 2500 years ago. Parasitic craters and vents, including maars near the coast and radially oriented fissure vents, dot the flanks of the volcano. Frequent historical eruptions have occurred since 1085 CE at vents ranging from the summit to below sea level, causing much damage on this small populated island. After a three-century-long hiatus ending in 1469, activity has been dominated by flank fissure eruptions sometimes accompanied by minor summit eruptions. A 1.6-km-wide summit caldera was slowly formed by subsidence during an eruption in 2000; by October of that year the crater floor had dropped to only 230 m above sea level.

Information Contacts: Japan Meteorological Agency (JMA), Volcanological Division, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Setsuya Nakada and Hidefumi Watanabe, Volcano Research Center, Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Akihiko Tomiya, Geological Survey of Japan (GSJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 7, Tsukuba 305-8567, Japan (URL: http://staff.aist.go.jp/a.tomiya/miyakeE.html); Charles Holliday, Air Force Weather Agency (AFWA),106 Peacekeeper Dr., Ste 2NE; Offutt AFB, NE 68113-4039 USA; National Aeronautics and Space Administration (NASA), Washington, DC 20456-0001, USA (URL: https://www.nasa.gov/); Kusatsu-Shirane Volcano Observatory (KSVO), Tokyo Institute of Technology, Kusatsu, Agatsuma-gun, Gunma 377-17, Japan; Dow Jones News.

During 17-18 January 2002 Nyiragongo, located ~18 km N of Lake Kivu in the Democratic Republic of Congo (DRC) close to the border of Rwanda, erupted an estimated 20 x 10⁶ m³ volume of lava (BGVN 26:12). Lava flows originated from the central crater and from several locations along a huge system of fractures that rapidly developed along the entire S flank of the volcano down to the city of Goma (~400,000 people) on the N shore of Lake Kivu. Goma was then invaded by extensive lava flows, which destroyed at least 13% of the surface of the city before reaching the lake. The advancing lava flows caused the spontaneous evacuation of at least 300,000 people, mostly toward the neighboring town of Gisenyi in Rwanda, and left more than 40,000 people homeless. About 100 people died as a consequence (direct or indirect) of the eruption. This disaster required an urgent public health response to evaluate the hazards to life and health. The assessment was especially important because of the humanitarian crisis in the eastern DRC that led many of the people who had fled from the lava flows to return to the city within one or two days, despite the danger of further eruptive activity or the possible risks arising from the proximity of the cooling lava flows (Baxter, 2002).

The following report, with the exception of the Moderate Resolution Imaging Spectroradiometer (MODIS) imagery, was compiled from field visits carried out by the volcanologists representing the United Nations Office for the Coordination of Human Affairs (UN-OCHA): Dario Tedesco, Paolo Papale, Orlando Vaselli, and Jacques Durieux. The team flew over the volcano and Goma in a helicopter on 22 and 24 January, and made field observations during 23 January-4 February. One team member continued studies on Lake Kivu until 13 February. The report provides an initial reconstruction of the main events of the eruption based on reports from local witnesses, observations and reports by researchers at the Goma Volcano Observatory (GVO), a closer inspection of seismograms recorded by GVO seismic stations, and field work by the UN-OCHA team. The UN-OCHA team worked closely with a French-British team of scientists (Patrick Allard, Peter Baxter, Michel Halbwachs, and Jean-Christophe Komorowski), whose report (Allard and others, 2002) will be summarized in a future Bulletin.

Activity during December 2000-January 2002. Since December 2000 the two GVO seismic stations had recorded long-period (LP) earthquake swarms. Commonly, each LP event was shortly followed by volcanic tremor.

On 6 February 2001 Nyamuragira erupted (BGVN 26:01). Following the 2-week eruption, seismicity did not decrease. On the contrary, volcanic tremor and LP earthquakes reappeared at both stations (Bulengo, BSS, S of Nyiragongo and Katale, KSS, NE of Nyiragongo, ~40 km from Bulengo), without showing any particular pattern, from March 2001 through January 2002. During the 10 months that preceded the January 2002 eruption, it was impossible to distinguish which volcano was the source of the seismicity.

In addition to the increased seismic activity, on 5 October strong vibrations were felt and on 7 October a strong tectonic earthquake (M 3.5-4.0), unusual for this region, was felt by the population. This earthquake was followed a few hours later by high-amplitude volcanic tremor.

Field trips by GVO personnel to the summit of Nyiragongo during 29 October-1 November and 8-10 December 2001 revealed several important changes. Immediately after the October tectonic event a white plume was visible inside the 1977 eruptive fracture on top of and inside the Shaheru crater (2 km S of the summit crater) at 2,700 m elevation. A similar plume was emerging from new cracks in the inner wall of the central crater, while a dark plume was visible from the small 1995 spatter cone inside the volcano. The new fumaroles on the side of the small central crater had a temperature of 70°C; the ground temperature, which was normally at 5-9°C, was recorded as 28°C; cracks near Shaheru crater were at ~50°C.

An increase in seismicity similar to that observed during early October occurred beginning on 4 January 2002, when an M > 4 earthquake occurred. On 7 January seismic activity triggered some visible changes, including reactivation of fumarolic activity. Following the 4 January earthquake seismicity remained high until 16 January. The onset of the eruption was preceded by about 8 hours of calm consisting of very low seismicity (without tremor or LP earthquakes).

Eruption during 17-18 January 2002. Early on 17 January a huge system of fractures began to develop on the S flank and eventually extended from high elevations down to Goma and Lake Kivu. The main trend of fractures was N15°W, which is similar to the general trend of the rift valley in the Nyiragongo region. The system of fractures appears to have propagated down from the volcano, starting at 2,800-3,000 m elevation (300-400 m N of the old Shaheru crater), and covering a distance of ~10 km towards Goma in less than 8 hours. The uppermost portion of the fracture started erupting at 0835 on 17 January. A single fracture ~2 m wide was visible above and inside Shaheru. Reactivated during the January event, it corresponded to the eruptive fracture of January 1977. Below the Shaheru crater the fracture was replaced by a more complex system, with two parallel main fractures ~300 m apart, also propagating N15°W. At about 1000 the system of fractures had reached ~1,900 m elevation; they then took ~30 minutes to cross the last system of ancient cones N of Goma, at ~1,700 m. By about 1400 the fractures were in the proximity of the Munigi village on the outskirts of Goma.

As the fractures advanced, several started erupting. Beginning around 1000 and lasting for at least two hours, lava flows escaped at ~1,950-2,000 m elevation S of the ancient Kanyambuzi-Mudjoga tuff cones. Fractures on the gentle slopes N of Goma lacked venting lava along a portion a few kilometers in length, but, at several locations the tips of intruded dykes ascended within only a few ten's of centimeters to a few meters below the ground surface.

At 1610 on 17 January the southernmost system of vents opened S of Munigi village and on the outskirts of Goma at 1,570-1,580 m elevation. Lava flows from these vents affected the Goma airport and destroyed part of the city before reaching the lake. About 10-20 minutes later a new N15°W-oriented fracture began to erupt at 1,950-2,000 m elevation, located ~1.5 km W of the main fracture system. Lava flows from this fracture partially destroyed the western part of Goma without reaching the lake.

Around the same time a fracture a few hundred meters long opened on the NW flank of the cone, at ~2,700-3,000 m elevation as estimated by helicopter, producing a lava flow that did not affect inhabited areas. Unlike the southern fracture system, this fracture had an estimated N30°E to N60°E trend. The eruptive activity at several places along the fracture system on the S flank reportedly lasted through part of the night or even up to daylight on 18 January.

MODIS images on 18, 21, and 27 January showed a hot spot in the vicinity of the volcano (figure 13). The 18 January image showed a single, large hot spot (3-4 pixels wide and ~11 pixels long on the S flank of Nyiragongo. The elongate hot spot had a NNE-SSW orientation. Its proximal section was located about mid-way up the S flank of the volcano (in the vicinity of the Shaheru-Djoga cinder cones and 1977 S-flank fissure) and the distal section was directly over Goma. The hot spot decreased over the following days, and by 27 January was barely visible.

Figure 13. Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images on 18, 21, and 27 January showing a hot spot near Nyiragongo during the eruption. The 18 January image shows a single, large hot spot (3-4 pixels wide and ~ 11 pixels long) on the S flank. The hot spot decreased over the following days, and by 27 January was barely visible. Courtesy HIGP/SOEST.

Activity following the eruption. During the night of 21 January some earthquake swarms created panic in the population. During about 0600-1800 on 22 January no earthquakes were felt. However, at about 1800 a sequence began during which ~20 earthquakes were felt in less than 3 hours. The following days were characterized by periods of intense seismicity, alternating with intervals (~10-15 hours) of lower seismic activity.

Seismic events showed quite a range of magnitude, frequency content, and S-P times, suggesting several different origins. The earthquakes that occurred in the days following the eruption were ~M > 5. During the 5 days following the eruption ~100 tectonic earthquakes (M > 3.5) occurred with epicenters in the Goma-Nyiragongo region. Several houses collapsed or were seriously damaged due to seismic loading in Gisenyi, where nine people died as a direct result of roof collapse. Seismic signals showed a typical sequence of tectonic events, followed within minutes to hours by LP events and volcanic tremor lasting continuously for more than 10 hours. Such a sequence, which is identical to the typical sequence recorded during the year preceding the eruption, suggested rock fracturing followed by the intrusion and ascent of magma.

An estimate of the location of seismic events made by comparing the arrival time differences of P- and S-waves at the three seismic stations of Bulengo, Katale, and Goma (the last one provided by the French-British team) showed that on 27 and 28 January the shocks were concentrated in the area between the Nyiragongo crater and Goma, probably 4-6 km N of Lake Kivu. During the first days of February the epicenters of earthquakes were clustered in two areas. The first was along the system of fractures, stretching a few kilometers N and S of Goma (in part, beneath Lake Kivu). The second cluster lay S of the town of Sake, 15-20 km W of Goma, close to the W border of the rift.

Observations during a helicopter flight over the volcano on 21 January revealed that the crater floor (old surface of the 1994-95 lava lake) was cut by a N-S elongated depression (like a small graben) underlain by steaming cracks. The next day witnesses from villages 6 km SW and ~10 km N of the summit crater reported that at about 2100 an earthquake was felt and immediately followed by a red glow or "flames" above the crater. Later that evening fine ash fell along the road from Goma to Sake. On the morning of 23 January ash fell in Goma and at the airport. A helicopter survey revealed a layer of ash on the volcano's upper S and E flanks and devastated vegetation on the crater's N flank.

On 24 January the inside of the crater appeared as a huge cavity with an estimated depth of 800 m and a grayish-yellow colored floor. The old terraces that represented the remnants of the lava lake at different stages of its long history were nearly totally absent. The interpretation is that either the emptying of the lava lake, the fracturing of the system, or more likely both, destabilized the inner part of the crater. Seismic records showed higher-amplitude tremor, presumably related to the crater-floor collapses, starting on 22 January at 2051 and lasting for ~4 hours. During the same flight on 24 January an explosion or a new collapse at the crater produced a small cloud of steam and ash that reached a few hundred meters above the crater rim.

Gas blasts sporadically occurred, mainly after the eruption, ~100-200 m away from the main path of the lava flow in Goma causing displacement of pavement in small buildings. In a small garage in Goma a thick (~10 cm) concrete pavement was cracked and uplifted up to 50-70 cm by the gas blasts.

Observations and research at Lake Kivu. Interesting phenomena were noted on the shore of Lake Kivu in the area of Himbi. Women who used to wash clothes close to the lake observed that the water level had decreased a few centimeters 3-5 days before the eruption. During the night and early morning of 17-18 January waiters at a restaurant observed crabs and crayfish jumping out of the lake. During 20-21 January dead fish and bubbling spots were observed in the small bay close to the restaurant. Waiters stated that the temperature of the lake in those zones had increased and a brown-black stain appeared from the bottom of the lake in an area of several square meters. At the same time an odor of spoiled eggs (suggesting presence of H₂S) was present. A similar phenomenon occurred early in the morning (at about 0230) on 30 January after an M 4.5 earthquake. The owners of the restaurant suddenly awoke due to difficulty breathing and the strong smell of rotten eggs. In both cases, the "normal" conditions were reestablished in a "short" (not well-defined) time. Soil-gas measurements indicated that CO₂ concentrations reached values up to 20%.

A geochemical survey of the main fluid manifestations in and around the S part of Nyiragongo was carried out during the days after the 17 January eruption. Sampling included water from Lake Kivu, cold and thermal springs, dry vents, and soil gases. The main conclusions of this survey were: 1) contrary to rumors following the entry of lava flows into the lake, lake water only a few meters away from the lava front was not polluted; 2) the geochemical characteristics of water from the lake and from springs on land are close to those found previously by Tietze and others (1980) and Tuttle and others (1990); and 3) the analyzed gases appear to have a clear magmatic origin as revealed by their isotopic signature. An exception to the final conclusion is that gases from the Rambo sampling point, which sits next to a brewery in Gisenyi, appear to represent mixtures between biogenic (organic) and magmatic sources.

Immediately following the eruption, fishermen reported visible changes in the water level at Lake Kivu. This was confirmed by women who visited the lake shore daily for washing or collecting water. A series of measurements was started in close cooperation with the UN field officer Dominic Garcin, who has a vast knowledge of the lake. The first measurements were obtained on 28 January along the shoreline from Gisenyi to Sake. The results confirmed a significant subsidence of the ground and rise of the water level. The subsidence was highest (37 cm) in Goma, then progressively vanished towards the E (~10 cm in Gisenyi but 0 cm ~2 km farther E) and W (0 cm ~15 km W of Goma). After these first measurements, several others were systematically taken along the N shoreline of Lake Kivu as well as around the lake up to ten's of kilometers S of Goma, and at Idjwi Island, ~30 km S of Goma. The measurements showed that ground subsidence is an ongoing phenomenon in the entire rift area near Lake Kivu. One month after the eruption, maximum measured ground subsidence was 50-60 cm at the Goma harbor and at Idjwi Island (figure 14). Scientists note that the February-March westward shifting of the ground subsidence corresponds to a similar westward shifting of epicenters.

Figure 14. Plots showing cumulative, asymmetrical land subsidence in the Goma area across the far S flanks of Nyiragongo. The subsidence was measured with respect to pre-subsidence surface of Lake Kivu, and surveyed along an E-W transect. The four survey dates (all in early 2002) each established the greatest subsidence at Goma, and lesser subsidence towards the East African rift's margins. Courtesy UN-OCHA team.

Conclusions. The characteristics of the erupted products and associated lava flows, together with the available information on the state of the volcano prior the eruption, suggest different dynamics of magma emission in the upper and lower portions of the fracture system. Two different interpretations have been offered. The "magmatic" hypothesis is that the energy for intense fracturing of the volcanic apparatus came from deep magma pushing from below inside the volcanic system. The "tectonic" hypothesis is that the energy for fracturing came from a non-volcanic source and was due to a rifting event related to regional tectonics. Further discussion of both hypotheses is offered in the report by the UN-OCHA team (Tedesco and others, 2002).

Goma is considered at a very high risk should reactivation of the volcano and rift system occur. The security of its inhabitants cannot be guaranteed even with the most sophisticated instrumental network. Thousands of lives can be saved by increased surveillance, continued scientific investigation, contingency plans, and information campaigns.

An outstanding effort by the UN and several donors allowed for the development of short and long-term aid to the Goma Volcano Observatory (GVO). This effort included support for foreign volcanologists, purchase of new equipment, establishing a new monitoring network, and help with logistics (transportation, communications, salaries, etc.). GVO is now publishing weekly reports on volcano activities.

References. Allard, P., Baxter, P., Halbwachs, M., and Komorowski, J-C, 2002, Final report of the French-British scientific team: submitted to the Ministry for Foreign Affairs, Paris, France, Foreign Office, London, United Kingdom and respective Embassies in Democratic Republic of Congo and Republic of Rwanda, 24 p.

Baxter, P.J., 2002, Eruption at Nyiragongo volcano, Democratic Republic of Congo, 17-18 January 2002: a report on a field visit to assess the initial hazards of the eruption, 15 p.

Tedesco, D., Papale, P., Vaselli, O., and Durieux, J., 2002, The January 17th, 2002 eruption of Nyiragongo, Democratic Republic of Congo: UN-OCHA report, 17 p.

Tietze, K., Geyh, M., Muller, H., Schroder, L. Stahl, W., and Wehner, H., 1980, Geol. Rund., v. 69, p. 452-472.

Tuttle, M.L., Lockwood, J.P., and Evans, W.C., 1990, Natural hazards associated with Lake Kivu in Rwanda and Zaire, central Africa: U.S. Geological Survey, Open File Report 90-691, 47 p.

General Reference. Tazieff, H., 1979, Nyiragongo, the forbidden volcano, translated by J. F. Bernard: Barron's, New York, 287 p. Originally published as Nyiragongo: Flammarion, Paris, 1975.

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: Dario Tedesco, Dipartimento Scienze Ambientali, Seconda Universita' di Napoli, Via Vivaldi 43, 81100 Caserta, Italy; Paolo Papale, Istituto Nazionale di Geofisica e Vulcanologia, via S. Maria, 53, I-56126 Pisa, Italy; Orlando Vaselli, Dipartimento Scienze della Terra, via G. La Pira, 4, 50121 Firenze, Italy; Jacques Durieux, Groupe d'Etude des Volcans Actifs, 6, Rue des Razes 69320 Feyzin, France; Dieudonné Wafula, Goma Volcano Observatory, Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DRC; Andy Harris, Eric Pilger and Luke Flynn, Hawaii Institute of Geophysics and Planetology at the School of Ocean and Earth Science Technology (HIGP/SOEST), University of Hawaii, 2525 Correa Road, Honolulu, HI 96822 USA; Peter Baxter, Department of Community Medicine, Institute of Public Health, University of Cambridge, University Forvie Site, Robinson Way, Cambridge, CB2 2SR, United Kingdom.

At least two commercial aircraft flew through airborne ash near the Guatemala City airport on 21 May 1999. An eruption from Fuego that day was the first at that volcano since 1987 (BGVN 24:04). Although the aviator's reports attributed the ash from this encounter to Fuego, their aircraft intersected multiple ash plumes in widely different locations, and thus they may also have crossed plumes from Pacaya. The most likely plume near the southern approach to the airport (La Aurora, ~23 km N of Pacaya; ~40 km NE of Fuego) is from the almost constantly active Pacaya. In contrast, Fuego lies 32 km W of Pacaya and was the likely source of a plume intersected later during the flight, at higher altitude, and for much longer duration.

During the encounters the ~100 or more people on board the two aircraft, and many more on the ground, were at risk. Both encounters seriously damaged the aircraft but ended in safe landings without reported injuries. Volcanic ash can cause jet-engine failure, which creates a hazard not only to passengers, but to people on the ground as well. The risk in this situation was amplified by the airport's proximity to urban Guatemala City (population, >1.1 million).

This example leads to two conclusions discussed further below. First, ash avoidance methodology needs further refinement. Second, there exists an apparent bias towards under-reporting of aircraft-ash encounters, which could short-change their cost to air carriers, their perceived risk, and their funding allocation.

The original report of an aircraft-ash encounter was brought to our attention by Captain Edward Miller of the Air Line Pilots Association and provided on the condition that the air carrier remain anonymous. Bulletin editors also wish to acknowledge conversations with several additional anonymous contacts (commercial pilots). This case occurred in Guatemala; however, analogous situations exist at many airports adjacent to volcanoes. Modest eruptions from nearby volcanoes may be uncertain or difficult to see; they may be hard to detect or characterize; yet they still may yield mobile ash plumes carried by complex local winds to confront air traffic (Salinas, 2001; Hefter, 1998; Casadevall, 1994).

Although in most Bulletin reports we favor the use of local time to emphasize the reference frame of people on the scene, most of the source material (satellite and aviation) for this report refer to UTC (Coordinated Universal Time). UTC is the time on the Greenwich meridian (longitude zero), formerly GMT, a term which has fallen out of use. Accordingly, there are cases in this report that lack conversion to local time. Local time in Guatemala is 6 hours behind UTC.

Activity at Fuego and Pacaya. Fuego erupted on 21 May 1999 sending ash to the S, SE, and SW and ultimately dropping up to 40 cm of ash on local settlements (BGVN 24:04). The eruption occurred at 1800 local time (in terms of UTC, at 0000 the next day). Three hours later the eruption decreased and the Aeronautica Civil recommended that planes go no closer to Fuego than 40 km. One hour after that (at 2200 local, 0400 UTC), the atmospheric ash had settled, and Aeronautica Civil recommended flying no closer to Fuego than 15 km.

Bulletin reports for Pacaya in mid-1999 suggested relative calm, in harmony with the observation that it had chiefly been fuming. However, Pacaya is well-known for Strombolian outbursts. It lies directly in-line and only 23 km S of the N10°E-oriented airstrip. As is common for commercial aircraft there, the approaches described below passed very close to Pacaya. Pacaya typically has lower and smaller eruptions than Fuego, but because it lies so close to the southern approach to the airport, Pacaya's ash plumes easily enter the path of landing aircraft. The situation was particularly complex during this eruption because Fuego's ash was reported on cities that lie below the flight path as well as on the Pacaya's flanks.

Pilot's report of aircraft-ash encounter. What follows was taken from one flight crew's description of events and from later reports and dialog on the topic. In order to preserve the confidentiality of the airlines, the precise times of events on 21 May 1999 have been omitted. Pilots reported clear visibility and light wind, with both the capital and the airport in sight. They maneuvered the aircraft for a final approach from the S. Pilots were advised by air traffic control about erupted particulate ("volcanic sand") about 24 km (15 miles) SE of the airport, well away from their projected path to Runway 01. In addition, based on winds they detected as they neared the airport, the pilots concluded that the erupted particulate to the SE was downwind from their projected flight path to the airport. (In retrospect, this conclusion appears tenuous considering the possibility of either a fresh injection of ash from Fuego, or lingering ash in the trailing portion of the plume that lay to the SE.)

At ~32 km (20 miles) distance from the runway, the pilots maneuvered the plane through ~3,000 m (9,700 feet) altitude on a final approach to the airport with the plane's flaps partially extended (at ~15°, which slowed their aircraft to ~260 km/hour (160 mph), its auxiliary power unit (a small jet engine) on, and its landing gear down. Around this point in their descent, pilots saw bright yellow sparks through the windshield lasting a few seconds, a display unlike static electricity, but rather like that from a grinding wheel. This occurred again at 2,500 m (8,200 feet) altitude, but was more intense yet intermittent.

At this time, air-traffic control announced to the pilots that the aircraft landing in front of them had encountered volcanic particulate; they instructed the pilots to abort their landing and climb to 3,350 m (11,000 feet) altitude. Discussions of options and ash avoidance ensued between pilots and air-traffic control; ash had by this time accumulated on the runway, further complicating landing, even for approaches in the opposite direction. The pilots retracted the landing gear, accelerated to ~410 km/hour (~250 mph), began to climb, and after some discussion with air-traffic control, held on a course NE of the airport. They were subsequently cleared to climb to 6,700 m (22,000 feet) altitude and advised to proceed to an alternate airfield.

During the climb, at ~5,800 m (19,000 feet) altitude en-route to the alternate airport, the aircraft encountered volcanic particulate for 10 minutes. Within that interval the plane spent 2 minutes during ascent engulfed in denser and heavier particulate. During that period, window arcing was constant and the beam of their landing lights revealed a conspicuous cloud of reflecting particles. During ash ingestion the engines's speed lacked noticeable fluctuations. The aircraft exited the plume at about 6,100 m (20,000 feet) altitude and landed without encountering additional ash.

Upon landing, the pilots noticed reduced visibility through abraded windshields. Post-flight examination of the airplane revealed heavy damage, requiring the replacement of the engines (US $2 million each) and auxiliary-power-unit engine. (Note, however, that no deterioration in engine power or performance was noticed during the flight.) Other replaced parts included windshields, a heat exchanger, and coalescer bags. Minor damage was seen on the horizontal stabilizer and wing leading-edges.

Volcanic Ash Advisory Statements. The U.S. National Oceanic and Atmospheric Administration (NOAA), Satellite Services Division website contains two archived statements issued by the Volcanic Ash Advisory Center (VAAC) at Washington, D.C. for Fuego on 21-22 May 1999. The statements, issued to the aviation cummunity to warn of volcanic hazards, are intended for an audience accustomed to special terminology (figures 31 and 32). In the interest of advancing understanding of how volcanological and atmospheric data get transmitted to aviators, we offer brief explanations for many of the terms used (figure 31).

Figure 31. The first archived Volcanic Ash Advisory Statement (VAAS) for the 21 May 1999 eruption at Fuego, Guatemala. The boxes contain added notes to explain some of the basic conventions and specific details seen here. This Statement currently appears on the NOAA Satellite Services Division website (see "Information Contacts," below). Local names are frequently anglicized, dropping all accents and other non-English characters (eg. México would be written MEXICO). Later Advisories adopted the abbreviation "Z" (pronounced 'Zulu' by aviators) for UTC, as in 1300 UTC written as 1300Z.

Figure 32. A later Volcanic Ash Advisory Statement (VAAS) for the 21 May 1999 eruption at Fuego, Guatemala. The statement, which was issued the next day, discloses that the eruption had then stopped and the hazard status was lowered. The statement appears on the NOAA Satellite Services Division website (see "Information Contacts," below).

The Washington VAAC received first notification of the Fuego eruption from a routine surface weather observation from Guatemala City at 2000 local time (0200 UTC) on 22 May. They issued the first Volcanic Ash Advisory Statement a half-hour later (figure 31). Six hours later they issued the second Advisory Statement (figure 32). The Advisories were composed by staff of the Satellite Analysis Branch, one of the two NOAA components forming the Washington VAAC (Streett, 1999; Washington VAAC).

The section "Details of ash cloud" first says that the "surface observation from Guatemala City indicate that the Fuego volcano is in eruption" and that no additional information is available and then briefly describes in words observations that came from satellite imagery. The first sentence, "No eruption . . ." is self-explanatory, but highlights a limitation of the method in use that needs to be emphasized to aviators: an eruption may have occurred but its status is not revealed on the imagery. The sentence, "No eruption could be detected due to thunderstorm cloudiness covering the area around the volcano" is self-explanatory. Less clear is the term convective debris. It does not refer to ash; rather, it refers to remnants of thunderstorms. The gist of these latter two sentences is simply that the thunderstorms that covered the area made it challenging or impossible to see the ash on satellite imagery. Central American thunderstorm clouds typically can reach altitudes of more than 12,000 m (40,000 feet), and can mask or obscure airborne ash residing below that level.

Members of the Washington VAAC commented that this eruption demonstrates key problems that can arise when cloudy conditions prevent satellite detection of ash, foiling a primary mode of analysis. In such cases, they rely on ground observers (including observatories and weather observers), pilot reports, and reports from airlines. Thus, their ability to issue useful information in cloudy conditions depends on the quality of communications with local observers, the Meteorological Watch Office, volcanologists, geophysical observatories, and the aviation community.

The Advisory Statement listed México City weather balloon data acquired 1,050 km NW of Guatemala City. In retrospect, the Washington VAAC noted that they generally avoid using such distant sounding data. If a closer sounding cannot be found, they prefer to use upper-level wind forecasts taken from a numerical weather model. In any case, the scarcity of local sounding data presents a challenge to the realistic analysis of airborne ash.

The outlook section says to "see SIGMETS." SIGMETS are the true warnings to aircraft for SIGnificant METeorological events. They are issued by regional Meteorological Watch Offices (MWOs), in this case the MWO (for Guatemala) is in Tegucigalpa, Honduras. SIGMETS were lacking for this eruption; although the Washington VAAC tried to contact the MWO without response. Another complexity confronted at the VAAC is a lack of a single scale for communicating a volcano's hazard status.

Reporting of aviation ash encounters. In personal communications with Bulletin editors, airline personnel stated that many more encounters have occurred than have yet been tallied in publically accessible literature. In accord with those assertions, the 21 May 1999 encounters are absent from reports compiled by the International Civil Aviation Organization (ICAO, 2001). In that document (Appendix I, table 3A, p. I-12) Fuego fails to appear as a source vent for any aircraft-ash encounter. Pacaya is listed for two encounters, in January 1987 and in May 1998 (BGVN 23:05).

Even though the number of encounters was probably under-represented and thus reflects a minimum, ICAO (2001) notes that the international costs to aviation since 1982 summed to well in excess of $250 million. They noted, "In addition to its potential to cause a major aircraft accident, the economic cost of volcanic ash to international civil aviation is staggering. This involves numerous complete engine changes, engine overhauls, airframe refurbishing . . . aircraft downtime . . . [and] volcanic ash clearance from airports and the damage caused to equipment and buildings on the ground."

The incidents here suggest that there has been a strong bias toward under-reporting aircraft-ash encounters. If this tentative conclusion is correct, it implies consistent understatements of the hazard's magnitude. This, in turn, may have thwarted meaningful analysis of how and whether to proceed with designing more robust hazard-reduction systems. Accordingly, resources that could have been devoted to the problem have not yet been committed (see Gimmestad and others, 2001 for a discussion of a prototype on-board ash-detection instrument).

Communication challenges. While much of the aviation community needs to learn about volcanism rapidly, dependably, and with the aid of the Internet, some observers charged with reporting volcanic-ash hazards in Central and South America lack access to basic communication devices like reliable telephones and fax machines. To reduce the risks, the aviation, meteorological, remote sensing, and volcanological communities need to improve their ability to pass critical information to each other rapidly and precisely. The operational systems related to volcanic ash and aviation must transcend numerous boundaries (eg., languages, infrastructure, funding, governments, agencies, air carriers, pilots, aircraft manufactures, etc.). The systems need to portray complex, dynamic processes such as the rapid rise of an explosive plume, or large-scale ash-cloud movement.

Although the infrastructure for ash avoidance is greater than ever, members of the Washington VAAC have told Bulletin editors that they still depend heavily on people on the scene of the eruption to notify them promptly when eruptions occur. They said that thus far in parts of Central and South America a problem has been the expense of communication (eg., by phone, fax, and Internet). They also said that for the same regions the U.S. meteorological database regularly lacks pilot reports. Though serious, these problems have at least been identified and their solutions would appear to lack great technical or economic barriers.

The pilots involved in the May 1999 encounter recommended that far more emphasis be placed on forecasting and avoiding ash plumes. Other pilots cited the need for fast and accurate communications between those who observe eruptive activity and air traffic control personnel.

Issues like these continue to be an important subject at gatherings on the topic of ash hazards in aviation (Casadevall, 1994; Streett, D., 1999; Washington VAAC, 1999). The Airline Dispatcher's Federation (ADF) will participate in a 7-9 May 2002 conference and workshop: "Operational Implications of Airborne Volcanic Ash: Detection, Avoidance, and Mitigation." The gathering will provide the pilot and dispatcher with insights into volcanic ash, including its characteristics, affects on aircraft, detection/tracking, effective warning systems, and mitigation. A "hands-on" exercise will make this the first gathering of its kind to provide lab-style instruction on interpretation of satellite and wind data, and on models of ash trajectory and dispersion. Representatives from the Boeing company, and a host of US government agencies and non-governmental organizations will attend. The workshop will include lectures, demonstrations, laboratory exercises, and a simulated-eruption exercise involving volcanologists, forecasters, controllers, dispatchers, and pilots.

A second international symposium on ash and aviation safety is being planned by the U.S. Geological Survey, organized by Marianne Guffanti. It will be held in Washington, D.C. in September 2003.

References. Casadevall, T.J. (ed.), 1994, Proceedings of the First International Symposium on Volcanic Ash and Aviation Safety: U.S. Geological Survey Bulletin 2047, 450 p.

Gimmestad, G.G., Papanicolopoulos, C.D., Richards, M.A., Sherman, D.L., and West, L.L., 2001, Feasibility study of radiometry for airborne detection of aviation hazards, NASA/CR-2001-210855; Georgia Tech Research Institute, Atlanta, Georgia, 51 p. (URL: http://techreports.larc.nasa.gov/ltrs/PDF/2001/cr/).

Hefter, J.L., 1998, Verifying a volcanic ash forecasting model, Airline Pilot, v. 67, no. 5, pp. 20-23, 54.

International Civil Aviation Organization (ICAO), 2001, Manual on volcanic ash, radioactive material, and toxic chemical clouds, doc 9691-AN/954 (first edition): 999 University St., Montreal, Quebec, Canada H3C 5H7 (purchasing information: sales_unit@icao.int).

Rose, W.I., Bluth, J.S.G., Schneider, D.L., Ernst, G.G.J., Riley, C.M., Henderson, L.J., and McGimsey, R.G., 2001, Observations of volcanic clouds in the first few days of atmospheric residence: The 1992 eruptions of Crater Peak, Mount Spurr volcano, Alaska, Jour. of Geology, v. 109, p. 677-694.

Salinas, Leonard J., 2001, Volcanic ash clouds pose a real threat to aircraft safety: United Airlines, Chicago, Illinois (URL: http://www.dispatcher.org/library/VolcanicAsh.htm).

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.

Streett, D., 1999, Satellite-based Volcanic Ash Advisories and an Ash Trajectory Model from the Washington VAAC: Eighth Conference on Aviation, Range, and Aerospace Meteorology, 10-15 January 1999, Dallas, Texas; American Meteorological Society, p. 290-294.

Washington VAAC, 1999, Operations of the Washington Volcanic Ash Advisory Center, in Aeronautical meteorological offices and their functions, and meteorological observation networks: Third Caribbean/South American Regional Air Navigation Meeting (Car/sam/ran/3); Buenos Aires, Argentina, 5 - 15 October, 1999; International Civil Aviation Organization (http://www.ssd.noaa.gov/ VAAC/PAPERS/carsam.html).

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Captain Edward Miller, Air Line Pilots Association (ALPA), Air Safety & Engineering Department, 535 Herndon Parkway, PO Box 1169, Herndon, VA 22070-1169, USA; Grace Swanson and Davida Streett, Washington VAAC, Satellite Analysis Branch (NOAA/NESDIS), 4700 Silver Hill Road, Stop 9910, Washington, DC 20233-9910, USA (URL: http://www.ssd.noaa.gov/); Bill Rose, Geological Engineering and Sciences, Michigan Technological University, Houghton, MI 49931, USA.

After explosions at Tavurvur during June and August 2001, activity decreased through October. During February-March 2002, the Rabaul Volcanological Observatory (RVO) reported that volcanic and seismic activity remained low, with some low-frequency earthquakes recorded. The active vent emitted weak-to-moderate amounts of white vapor. Ground deformation measurements showed no significant changes.

During mid-February, moderate-to-strong gas emissions drifted to the SE and E and damaged vegetation on the adjacent cone South Daughter, suggesting the presence of volcanic gases like sulphur dioxide within the emissions. The last ash-producing activity from Tavurvur occurred in early September 2001. RVO reported that the chance of mild ash activity occurring in the near future is very remote.

A few tectonic earthquakes were felt during mid-February. They were located 35-80 km NW and SW from the Rabaul-Kokopo area. An M 5.6 tectonic earthquake was felt at 0650 on 17 March. The earthquake was located offshore in the Pomio area. On 21 March, some high-frequency earthquakes occurred NE of Rabaul. Since 1995, these high-frequency earthquakes have been associated with eruptive activity at Tavurvur. During mid-March, some earthquakes were felt, unrelated to volcanic activity, that had magnitudes of 5.3-5.6.

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

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

During late January to early April 2002, seismic activity at Shiveluch remained above background levels and the lava dome in the active crater continued to grow. Explosions, avalanches, pyroclastic flows, and plumes from combinations of steam, gas, and ash, all occurred without warning and rose as high as 7-10 km altitude. Many shallow earthquakes (ML less than or equal to 2.5) occurred within the volcano's edifice along with other shallow seismic events. The Alert Level was raised from Yellow to Orange during a period of increased activity, 12 February-mid-March. Then the Level was returned to Yellow.

Typical activities from the end of January through the first half of February 2002 included weak seismic events and short-lived explosions, which sent ash-gas plumes to heights of 0.8-1.0 km above the ~2.5 km-high dome (reaching 3.3-3.5 km altitude). Occasional explosions sent plumes to higher altitudes; on 25 January a plume rose to ~4.5 km altitude, while an explosive eruption on 1 February sent ash-gas plumes to heights over 5.0 km.

For the latter eruption, Advanced Very High Resolution Radiometer (AVHRR) satellite images show thermal anomalies up to 10 pixels. Many of these "hot" pixels were at the detector saturation level of 48°C, and appeared against typical background temperatures as low as -25°C. A satellite image on 2 February revealed a 40-pixel thermal anomaly; however, only 5-7 of the pixels had temperatures above 40°C, indicating that only those pixels were influenced by hot material on the ground. The other pixels with elevated temperatures were associated with a cloud caused by hot avalanches.

On the evening of 12 February, the character of the seismicity changed suggesting the occurrence of more intense gas-ash explosions. During the next 30 days, explosions occurred frequently, producing ash-and-gas plumes that rose over 1 km above the dome and occasionally over 3 km above it. On 22 February, a series of shallow seismic events registered for ~1 hour, possibly related to ash-gas explosions or a hot rock avalanche. A similar series was recorded on the night of 27 February, and the next morning observers from Klyuchi town (46 km S) reported a 2-km-long pyroclastic flow to the SE of the dome.

AVHRR images of the resulting plumes showed that some extended to distances of 100 km in various directions, depending upon local wind conditions. A satellite image on 21 February showed a circular ash cloud, 20 km in diameter, at an altitude of ~7.1 km. By 15 March seismic activity declined but remained above background levels. Short-lived explosions continued to send plumes as high as 7.5 km altitude during the last week of March.

Thermal anomalies and pixel size on AVHRR imagery. Dave Schneider (USGS, AVO) provided an explanation of relevant aspects of pixel size and thermal anomalies. The size of a "raw" AVHRR pixel varies across and along the scan of the sensor. The instrument scans from side to side as the satellite moves in orbit. Along the nadir (the line directly beneath the satellite sensor), the pixel size is ~1.1 km on a side. At the far extreme of the scan (55° from nadir) the pixel size increases to 2.4 x 6.5 km. The raw image looks very distorted due to this change in pixel size, so the raw data are resampled to a resolution of 1 x 1 km when processing the data for display. This resampling can generate artifacts, including duplicate "hot" pixels. Analysts usually recognize and account for this problem, and then accurately report the appropriate number of hot pixels.

Another complication is the cause and significance of hot pixels. An AVHRR pixel will begin to appear anomalously warm, compared to its neighbors, when very hot material (hundred's of degrees) occupy a very small percentage of the total pixel area (much less that 1%). So, when a report mentions four hot pixels, and the pixel is 1 km square, one might be tempted to interpret this as 4 km2 of hot material. However, this is not correct. Typically, only a very small portion of a pixel area is hot, but sufficiently hot to reach the pixel's saturation value of ~50°C. The numbers of hot pixels are not all that relevant in an absolute sense. In a relative sense, however, the number of hot pixels can be important, for example, during episodes where we have seen anomalies grow from 1-4 hot pixels and then reach 10-20 hot pixels after an eruption.

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

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller and Dave Schneider, 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, USA.

An eruption occurred at Ulawun during 25-30 April 2001 (BGVN 26:06). Limited evacuations occurred on 3 May due to the occurrence of relatively high seismic activity and the possibility of further volcanic activity. On 14 June the Rabaul Volcanological Observatory (RVO) recommended that the Alert Level be reduced from 2 to 1. At this stage of alert, people could move back to their homes with the approval of the local disaster committee.

Volcanic tremor began at 2200 on 24 September. It peaked at about 1000 on 27 September and generally declined afterward. By 30 September seismic activity was at moderate levels. During 27-30 September a very slow deflationary trend was detected. Volcanic tremor continued to occur at moderate-to-high levels until it dropped dramatically on 11 October. After 11 October seismicity only consisted of discrete low-frequency earthquakes. On 8 and 9 October loud roaring noises emanated from the volcano.

During October through March 2002 activity was generally low. The main crater produced weak-to-moderate volumes of white and white-gray vapor. The N valley vent occasionally released weak volumes of thin white vapor. RSAM data revealed conspicuous seismicity on 26 October; incandescence was observed that night. A rapid trend of deflation beneath the summit area during the previous two weeks stopped on 24 December.

During mid-February tremor increased to moderate levels for the first time since December 2001. On 21 February weak roaring noises were heard and weak incandescence was visible for a short time. After 22 February tremor returned to background levels. Seismic activity returned to background levels after volcanic tremor ceased on 18 March. Discrete low-frequency earthquakes continued to occur in small numbers. The electronic tiltmeter continued to show long-term deflation of the summit area. Based on recent observations, activity at Ulawun is expected to remain low.

General References. Johnson, R.W., Davies, R.A., and White, A.J.R., 1972, Ulawun volcano, New Britain: Australia Bureau of Mineral Resources, Geology and Geophysics, Bulletin 142, 42 p.

McKee, C.O., 1983, Volcanic hazards at Ulawun volcano: Geological Survey of Papua New Guinea Report 83/13, 21 p.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

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/).