The Mount Bromo pyroclastic cone within the Tengger Caldera erupts frequently, typically producing gas-and-steam plumes, ash plumes, and explosions (BGVN 44:05). Information compiled for the reporting period of May-July 2019 is from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

The eruptive activity at Tengger Caldera that began in mid-February continued through late July 2019, including white-and-brown ash plumes, ash emissions, and tremors. During the months of May through June 2019, white plumes rose between 50 to 600 m above the summit. Satellite imagery captured a small gas-and-steam plume from Bromo on 5 June (figure 18). Low-frequency tremors were recorded by a seismograph from May through July 2019.

Figure 18. Sentinel-2 satellite image showing a small gas-and-steam plume rising from the Bromo cone (center) in the Tengger Caldera on 5 June 2019. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

According to PVMBG and a Volcano Observatory Notice for Aviation (VONA), an ash eruption occurred on 19 July 2019; however, no ash column was observed due to weather conditions. A seismograph recorded five earthquakes and three shallow volcanic tremors the same day. In addition, rainfall triggered a lahar on the SW flank of Bromo.

On 28 July the Darwin VAAC reported that ash plumes originating from Bromo rose to a maximum altitude of about 3.9 km and drifted NW from the summit, based on webcam images and pilot reports. PVMBG reported that lower altitude ash plumes (2.4 km) on the same day were also recorded by webcam images, satellite imagery (Himawari-8), and weather models.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

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/).

Large areas of floating pumice, termed rafts, were encountered by sailors in the northern Tonga region approximately 80 km NW of Vava'u starting around 9 August 2019; the pumice reached the western islands of Fiji by 9 October (figure 7). Pumice rafts are floating masses of individual clasts ranging from millimeters to meters in diameter. The pumice clasts form when silicic magma is degassing, forming bubbles as it rises to the surface, which then rapidly cools to form solid rock. The isolated vesicles formed by the bubbles provide buoyancy to the rock and in turn, the entire pumice raft. These rafts are spread and carried by currents across the ocean; rafts originating in the Tonga area can eventually reach Australia. This report summarizes the pumice raft eruption from early August 2019 using witness accounts and satellite images (acquisition dates are given in UTC). Pending further research, the presumed source is the unnamed Tongan seamount (volcano number 243091) about 45 km NW of Vava'u, the origin of an earlier pumice raft produced during an eruption in 2001.

Figure 7. The path of the pumice from the unnamed Tongan seamount from 9 August to 9 October 2019 based on eye-witness accounts and satellite data discussed below, as well as additional Aqua/MODIS satellite images from NASA Worldview. Blue Marble MODIS/NASA Earth Observatory base map courtesy of NASA Worldview.

The first sighting of pumice was around 1430 on 9 August NW of Vava'u in Tonga (18° 22.068' S, 174° 50.800' W), when Shannon Lenz and Tom Whitehead on board SV Finely Finished initially encountered isolated rocks and smaller streaks of pumice clasts. The area covered by rock increasing to a raft with an estimated thickness of at least 15 cm that extended to the horizon in different directions, and which took 6-8 hours to cross (figure 8). There was no sulfur smell and the sound was described as a "cement mixer, especially below deck." There was also no plume or incandescence observed. Their video, posted to YouTube on 17 August, showed a thin surface layer of cohesive interconnected irregular streaks of pumice with the ocean surface still visible between them. Later footage showed a continuous, undulating mass of pumice entirely covering the ocean surface. Larger clasts are visible scattered throughout the raft. The pumice raft was visible in satellite imagery on this day NW of Late Island (figure 9). By 11 August the raft had evolved into a largely linear feature with smaller rafts to the SW (figure 10). Approximately four hours later, about 15 km to the WSW, Rachel Mackie encountered the pumice. Initially the pumice was "ribbons several hundred meters long and up to 20m wide. It was quite fine and like a slick across the surface of the water." By 2130 they were surrounded by the pumice, and around 25 km away the smell of sulfur was noted.

Figure 8. The pumice raft from the unnamed Tongan seamount on 9 August 2019 taken by Shannon Lenz and Tom Whitehead on board SV Finely Finished. The photos show the pumice raft extending to the horizon in different directions. Scattered larger clasts protrude from the relatively smooth surface that entirely obscures the ocean surface. Courtesy of Shannon Lenz and Tom Whitehead via noonsite.

Figure 9. The pumice raft from the unnamed Tongan seamount on 9 August 2019 (UTC) can be seen NW of Late Island of Tonga in this Aqua/MODIS satellite image. The dashed white line encompasses the visible pumice. The location of the pumice in this image is shown in figure 7. Courtesy of NASA WorldView.

Figure 10. The Sentinel-2 satellite first imaged the pumice from the unnamed Tongan seamount on 11 August 2019 (UTC). This image indicates the pumice distribution with the main raft towards the W and the easternmost area of pumice approximately 45 km away. The eastern tip of the pumice area is located approximately 30 km WNW of Lake islands in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Michael and Larissa Hoult aboard the catamaran ROAM encountered the raft on 15 August (figure 11). They initially saw isolated clasts ranging from marble to tennis ball size (15-70 mm) at 18° 46′S, 174° 55'W. At around 0700 UTC (1900 local time) they noted the smell of sulfur at 18° 55′S, 175° 21′W, and by 0800 UTC they were immersed in the raft with visible clasts ranging from marble to basketball (25 cm) sizes. At this point the raft was entirely obscuring the ocean surface. On 16 and 21 August the pumice continued to disperse and drift NW (figures 12 and 13). On 20 August Scott Bryan calculated an average drift rate of around 13 km/day, with the pumice on this date about 164 km W of the unnamed seamount.

Figure 11. Images of pumice from the unnamed Tongan seamount encountered by Michael and Larissa Hoult aboard the catamaran Roam on 15 August. Left: Larissa takes photographs with scale of pumice clasts; top right: a closeup of a pumice clast showing the vesicle network preserving the degassing structures of the magma; bottom left: Michael holding several larger pumice clasts. The location of their encounter with the pumice is shown in figure 7. Courtesy of SailSurfROAM.

Figure 12. The pumice from the unnamed Tongan seamount (volcano number 243091) on 16 August 2019 UTC. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Figure 13. On 21 August 2019 (UTC) the pumice from the unnamed Tongan seamount (volcano number 243091) had drifted at least 120 km WNW of Late Island in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

An online article published by Brad Scott at GeoNet on 9 September reported the preliminary size of the raft to be 60 km2, significantly smaller than the 2012 Havre seamount pumice raft that was 400 km2. Satellite identification of pumice-covered areas by GNS scientists showed the material moving SSW through 14 August (figure 14).

Figure 14. A compilation of mapped pumice raft extents from 9 August (red line) through to 14 August (dark blue) from Suomi NPP, Terra, Aqua, and Sentinel-2 satellite images. The progression of the pumice raft is towards the SW. Courtesy of Salman Ashraf, GNS Science.

On 5 September the Maritime Safety Authority of Fiji (MSAF) issued a notice to mariners stating that the pumice was sighted in the vicinity of Lakeba, Oneata, and Aiwa Islands and was moving to the W. On 6 September a Planet Labs satellite image shows pumice encompassing the Fijian island of Lakeba over 450 km W of the Tongan islands (figure 15). The pumice entered the lagoon within the barrier reef and drifted around the island to continue towards the W. The pumice was imaged by the Landsat 8 satellite on 26 September as it moved through the Fijian islands, approximately 760 km away from its source (figure 16). The pumice is segmented into numerous smaller rafts of varying sizes that stretch over at least 140 km. On 12 September the Fiji Sun reported that the pumice had reached some of the Lau islands and was thick enough near the shore for people to stand on it.

Figure 15. Planet Labs satellite images show Lakeba Island to the E of the larger Viti Levu Island in the Fiji archipelago. The top image shows the island on 7 July 2019 prior to the pumice raft from the unnamed Tongan seamount. The bottom image shows pumice on the sea surface almost entirely encompassing the island on 6 September. The location of the pumice in this image is shown in figure 7. Courtesy of Planet Labs.

Figure 16. Landsat 8 satellite images show the visible extent of the unnamed seamount pumice on 26 September 2019 (UTC), up to approximately 760 km from the Tongan islands. The pumice seen here extends over a distance of 140 km. The top image shows the locations of the other three images in the white boxes, with a, b, and c indicating the locations. White arrows point to examples of the light brown pumice rafts in these images, seen through light cloud cover. The island in the lower right is Koro Island, the island to the lower left is Viti Levu, and the island to the top right is Vanua Levu. The location of the pumice in this image is shown in figure 7. Landsat 8 true color-pansharpened satellite images courtesy of Sentinel Hub.

Pumice had reached the Yasawa islands in western Fiji by 29 September and was beginning to fill the eastern bays (figure 17). By 9 October bays had been filled out to 500-600 m from the shore, and pumice had also passed through the islands to continue towards the W (figure 18). At this point the pumice beyond the islands had broken up into linear segments that continued towards the NW.

Figure 17. These Sentinel-2 satellite images show the pumice from the unnamed Tongan seamount drifting towards the Yasawa islands of Fiji. The 24 September 2019 (UTC) image shows the beaches without the pumice, the 29 September image shows pumice drifting westward towards the islands, and the 9 October image shows the bays partly filled with pumice out to a maximum of 500-600 m from the shore. These islands are approximately 850 km from the Tongan islands. The Yasawa islands coastline impacted by the pumice shown in these images stretches approximately 48 km. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Figure 18. This Sentinel-2 satellite image acquired on 9 October 2019 (UTC) shows expanses of pumice from the unnamed Tongan seamount that passed through the Yasawa islands of Fiji and was continuing NWW, seen in the center of the image. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Salman Ashraf, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Scott Bryan, School of Earth, Environmental & Biological Sciences, Science and Engineering Faculty, Queensland University of Technology, R Block Level 2, 204, Gardens Point (URL: https://staff.qut.edu.au/staff/scott.bryan); Shannon Lenz and Tom Whitehead, SV Finely Finished (URL: https://www.noonsite.com/news/south-pacific-tonga-to-fiji-navigation-alert-dangerous-slick-of-volcanic-rubble/, YouTube: https://www.youtube.com/watch?v=PEsHLSFFQhQ); Michael and Larissa Hoult, Sail Surf ROAM (URL: https://www.facebook.com/sailsurfroam/); Rachel Mackie, OLIVE (URL: http://www.oliveocean.com/, https://www.facebook.com/rachel.mackie.718); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Fiji Sun (URL: https://fijisun.com.fj/2019/09/12/pumice-menace-hits-parts-of-lau-group/).

The current eruptive period of Popocatépetl began on 9 January 2005 and it has since been producing frequent explosions accompanied by ash plumes, gas emissions, and ballistic ejecta that can impact several kilometers away from the crater, as well as dome growth and destruction. This activity continued through March-August 2019 with an increase in volcano alert level during 28 March-6 May. This report summarizes activity during this period and is based on information from Centro Nacional de Prevención de Desastres (CENAPRED), Universidad Nacional Autónoma de México (UNAM), and various webcam and remote sensing data.

An overflight on 28 February confirmed that dome 82, which was first observed on 14 February, was still present and was 200 m in diameter. During March there were 3,291 observed low-intensity emissions, and 33 larger explosions that produced ash plumes to a maximum height of 5 km, accompanied by near-continuous emission of water vapor and volcanic gases. Explosions ejected blocks that fell on the flanks out to 1.2-2 km on 1, 10, 13, 17, 26, 27, and 29 March. The events on the 17th and 27th resulted in vegetation fires. Frequent sulfur dioxide (SO₂) plumes were detected by TropOMI (figure 130). An overflight on 7 March showed intense degassing and an ash plume at 1142, preventing visibility into the crater (figure 131). On 13 March Strombolian activity was observed for approximately 15 minutes at 0500, accompanied by incandescent ejecta that deposited mainly on the ESE flank.

An overflight on 15 March was taken by CENAPRED and UNAM personnel to observe changes to the crater after explosions on the 13th and 14th. They reported that dome 82 had been destroyed and the crater maintained its previous dimensions of 300 m in diameter and 130 m deep. An explosion on the 27th ejected incandescent rocks out to 2 km from the crater and produced a 3-km-high ash plume that dispersed to the NE. Ashfall was reported in Santa Cruz, Atlixco, San Pedro, San Andrés, Santa Isabel Cholula, San Pedro Benito Juárez, and in the municipalities of Puebla, Hueyapan, Tetela del Volcán, and Morelos.

On 28 March an explosion at 0650 generated a 2.5-km-high ash plume and ejecta out to 1 km from the crater, and a 130-minute-long event produced gas and ah plumes (figure 132). On this day the volcano alert level was increased from Yellow Phase 2 to Yellow Phase 3. On the 29th an ash plume rose to 3 km and was accompanied by ejecta that reached 2 km away from the crater. Later that day a 20-minute-long event produced ash and gas. During a surveillance flight on 30 March a view into the crater showed no dome present, and the crater size had increased to 350 m in width and 250-300 m in depth after recent explosions (figure 131). On this day Strombolian activity was also observed lasting for 14 minutes, producing an ash plume to 800 m and ejecta out to 300 m from the crater. Incandescence at the crater was often seen during nighttime throughout the month.

Figure 130. Significant SO2 plumes at Popocatépetl detected by the TROPOMI instrument on the Sentinel-5P satellite during 3-11 March 2019. SO2 plumes are frequently observed and these images show examples of plume drift directions on 3 March 2019 (top left), 6 March 2019 (top right), 7 March 2019 (bottom left), and 11 March 2019 (bottom right). Date, time, and measurements are provided at the top of each image. Courtesy of NASA Goddard Flight Center.

Figure 131. Activity at Popocatépetl and views of the crater during surveillance flights in March 2019. The top images show an ash plume (left) and a gas-and-steam plume (right) on 7 March. On 30 March (bottom left and right) no lava dome was observed in the crater, which was measured to be 350 m in diameter and 250-300 m deep. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Figure 132. Explosive activity at Popocatépetl on 28 March 2019 producing ash plumes (top and bottom left) and ejecting incandescent ejecta out to 2 km from the crater at 1948. Courtesy of Carlos Sanchez/AFP (top), CENAPRED (bottom left and right), and Webcams de Mexico (bottom left).

There was a decrease in events during the next two months with 1,119 recorded low-intensity emissions and no larger ash explosions throughout April, followed by 1,210 low-intensity emissions and seven larger ash explosions through May (figure 133). Water vapor and volcanic gas emissions were frequently observed through this time and incandescence was observed some nights. A surveillance overflight on 26 April noted no new dome within the crater. On 6 May the alert level was lowered back to Yellow Phase 2. Another overflight on 9 May showed no change in the crater. An explosion at 1910 on 22 May produced an ash plume to 3.5 km above the crater with ashfall reported in Ozumba, Temamatla, Atlautla, Cocotitlán, Ayapango, Ecatzingo, Tenango del Aire and Tepetlixpa.

Figure 133. Graph showing the number of daily ash explosions and low-intensity emissions at Popocatépetl during March-August 2019. There was a decrease in the number of events during April and March, with an increase from March onwards. Data courtesy of CENAPRED.

Through the month of June there were 2,820 low-intensity emissions and 21 larger ash explosions recorded. Gas emissions were observed throughout the month. Two explosions on 3 June produced ash plumes up to 3.5 and 2.8 km, with ejecta out to 2 km S during the first explosion. On 11 June an explosion produced an ash plume to 1 km above the crater and ballistic ejecta out to 1 km E. Observers on a surveillance overflight on the 12th reported no changes within the crater

Explosions with estimated plume heights of 5 km occurred on the 14th and 15th, with the latter producing ashfall in the municipalities of San Pablo del Monte, Tenancingo, Papantla, San Cosme Mazatencocho, San Luis Teolocholco, Acuamanala, Nativitas, Tepetitla, Santa Apolonia Teacalco, Santa Isabel Tetlatlahuaca, and Huamantla, in the state of Tlaxcala, as well as in Nealtican, San Nicolás de los Ranchos, Calpan, San Pedro Cholula, Juan C. Bonilla, Coronango, Atoyatempan, and Coatzingo, in the state of Puebla.

On 17 June an explosion produced an ash plume that reached 8 km above the crater and dispersed towards the SW. An ash plume rising 2.5 km high was accompanied by incandescent ejecta impacting a short distance from the crater on the 21st, and another ash plume reached 2.5 km on the 22nd. Explosions on 26, 29, and 30 June resulted in ash plumes reaching 1.5 km above the crater and ballistic ejecta impacting on the flanks out to 1 km.

For the month of July there was an increased total of 5,637 recorded low-intensity emissions, and 173 larger ash explosions (figure 134). On 8 July an explosion produced ballistic ejecta out to 1.5 km and an ash plume up to 1 km above the crater. An ash plume up to 2.6 km was produced on the 12th. On 19 July a surveillance overflight observed a new dome (dome 83) with a diameter of 70 m and a thickness of 15 m (figure 135). Explosions on 20 July produced ashfall, and minor explosions that ejected incandescent ballistics onto the slopes. An event on the 24th produced an ash plume that reached 1.2 km, and ash plumes the following day reached 1 km. An overflight on 27 July confirmed that these explosions destroyed dome 83, and the crater dimensions remained the same (figure 136). The following day, ash plumes reached up to 1.6 km above the crater, and up to 2 km on the 29th. Minor ashfall was reported in the municipality of Ozumba on 30 June.

Figure 134. Examples of ash plumes at Popocatépetl on 1 July (top left), 18 July (top right and bottom left), and 30 July (bottom right) 2019. In the night time image taken on 18 July hot rocks are visible on the flank. Webcam images courtesy of CENAPRED and Webcams de Mexico.

Figure 135. A surveillance overflight at Popocatépetl on 19 July 2019 confirmed a new dome, dome number 83, with a width of 70 m and a thickness of 15 m. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Figure 136. Photos of the summit crater of Popocatépetl taken during a surveillance flight on 27 July 2019 confirmed that the 83rd lava dome was destroyed by recent explosions and the crater maintained the same dimensions as previously measured. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Throughout August the number of recorded events was higher than previous months, with 5,091 low-intensity emissions and 204 larger ash explosions (figure 137). Two explosions generated ash plumes and incandescent ejecta on 2 August, the first with a plume up to 1.5 km with ejecta impacting the slopes, and the second with an 800 m plume and ejecta landing back in the crater. Ashfall from the events was reported in in the municipalities of Tenango del Aire, Ayapango and Amecameca. On the 14th ashfall was reported in Juchitepec, Ayapango, and Ozumba. Explosions on 16 August produced ash plumes up to 2 km that dispersed to the WSW. Over the following two days ash plumes reached 1.2 km and resulted in ashfall in Cuernavaca, Tepoztlán, Tlalnepantla, Morelos, Ozumba, and Ecatzingo. Over 30-31 August ash plumes reached between 1-2 km above the crater and ashfall was reported in Amecameca, Atlautla, Ozumba, and Tlalmanalco. Incandescence was sometimes observed at the crater through the month.

Figure 137. Ash plumes at Popocatépetl on 7 August (top) and 26 August 2019 (bottom). Courtesy of CENAPRED and Webcams de Mexico.

The MODVOLC algorithm for MODIS thermal anomalies registered thermal alerts through this period, with 22 in March, three in May, five in July, and one in August. The MIROVA system showed that the frequency of thermal anomalies at Popocatépetl was higher in March, sporadic in April and May, low in June, and had increased again in July and August (figure 138). Elevated temperatures were frequently visible in Sentinel-2 thermal satellite data when clouds and plumes were not covering the crater (figure 139).

Figure 138. Thermal activity at Popocatépetl detected by the MIROVA system showed frequent anomalies in March, intermittent anomalies through April-May, low activity in June, and an increase in July-August 2019. Courtesy of MIROVA.

Figure 139. Sentinel-2 thermal satellite images frequently showed elevated temperatures in the crater of Popocatépetl during March-August 2019, as seen in this representative image from 7 May 2019. Sentinel2- atmospheric penetration (bands 12, 11, 8A) scene courtesy of Sentinel Hub Playground.

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

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/); Universidad Nacional Autónoma de México (UNAM), University City, 04510 Mexico City, Mexico (URL: https://www.unam.mx/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Webcams de Mexico (URL: http://www.webcamsdemexico.com/); Agence France-Presse (URL: http://www.afp.com/).

The ongoing eruption at Semeru weakened in intensity during 2018, with occasional ash plumes and thermal anomalies (BGVN 44:04); this reduced but ongoing level of activity continued through August 2019. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC). The current report summarizes activity from 1 March to 31 August 2019. The Alert Level remained at 2 (on a scale from 1-4); the public was warned to stay 1 km away from the active crater and 4 km away on the SSE flank.

Based on analysis of satellite images, the Darwin VAAC reported that ash plumes rose to an altitude of 4-4.3 km on 19 April, 20 June, 10 July, and 13 July, drifting in various directions. In addition, PVMBG reported that at 0830 on 26 June an explosion produced an ash plume that rose around 600 m above the summit and drifted SW. A news article (Tempo.com) dated 12 August cited PVMBG as stating that the volcano had erupted 17 times since 8 August.

During March-August 2019 thermal anomalies were detected with the MODIS satellite instruments analyzed using the MODVOLC algorithm only on 5 July and 22 August. No explosions were recorded on those two days. Scattered thermal anomalies within 5 km of the volcano were detected by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system, also based on analysis of MODIS data: one at the end of March and 3-6 hotspots over the following months, almost all of low radiative power. Satellite imagery intermittently showed thermal activity in the Jonggring-Seloko crater (figure 37), sometimes with material moving down the SE-flank ravine.

Figure 37. Sentinel-2 satellite images showing the persistent elevated thermal anomaly in the Jonggring-Seloko crater of Semeru were common through August 2019, as seen in this view on 20 July. Hot material could sometimes be identified in the SE-flank ravine. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

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

Information Contacts: 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/); 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); Tempo.com (URL: https://www.tempo.com/).

Historical observations of eruptive activity from the glacier-covered Mount Michael stratovolcano on Saunders Island in the South Sandwich Islands were not recorded until the early 19th century at this remote site in the southernmost Atlantic Ocean, and remain extremely rare. With the advent of satellite observation technology, indications of more frequent eruptive activity have become apparent. Vapor emission is frequently reported from the summit crater, and AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater (Lachlan-Cope and others, 2001). Limited thermal anomaly data and satellite imagery indicated at least intermittent activity during May 2000-November 2013, and from November 2014 through April 2018 (Gray and others, 2019). Ongoing observations, including photographs from two site visits in February and May 2019 suggest continued activity at the summit during most months through May 2019, the period covered in this report. Information, in addition to on-site photographs, comes from MIROVA thermal anomaly data, NASA SO₂ instruments, and Sentinel-2 and Landsat satellite imagery.

Near-constant cloud coverage for much of the year makes satellite data intermittent and creates difficulty in interpreting the ongoing nature of the activity. Gray and others (2019) concluded recently after a detailed study of shortwave and infrared satellite images that there was continued evidence for the previously identified lava lake on Mount Michael since January 1989. MIROVA thermal anomaly data suggest intermittent pulses of thermal energy in September, November, and December 2018, and April 2019 (figure 17). Satellite imagery confirmed some type of activity, either a dense steam plume, evidence of ash, or a thermal anomaly, each month during December 2018-March 2019. Sulfur dioxide anomalies were recorded in January, February, and March 2019. Photographic evidence of fresh ash was captured in February 2019, and images from May 2019 showed dense steam rising from the summit crater.

Figure 17. MIROVA thermal anomaly data from 19 September 2018 through June 2019 showed sporadic, low-level pulses of thermal energy in late September, November, and December 2018, and April 2019. Courtesy of MIROVA.

After satellite imagery and thermal anomaly data in late September 2018 showed evidence for eruptive activity (BGVN 43:10, figure 16), a single thermal anomaly in MIROVA data was recorded in mid-November 2018 (figure 17). A rare, clear Sentinel-2 image on 2 December revealed a dense steam plume over the active summit crater; the steam obscured the presence of any possible thermal anomalies beneath (figure 18).

Figure 18. Sentinel-2 images of Mount Michael on Saunders Island on 2 December 2018 revealed a dense steam plume over the summit crater that was difficult to distinguish from the surrounding snow in Natural Color rendering (bands 4,3,2) (left), but was clearly visible in Atmospheric Penetration rendering (bands 12,11, 8a) (right). Courtesy of Sentinel Hub Playground.

Clear evidence of recent activity appeared on 1 January 2019 with both a thermal anomaly at the summit crater and a streak of ash on the snow (figure 19). Steam was also present within the summit crater. A distinct SO₂ anomaly appeared in data from the TROPOMI instrument on 14 January (figure 20).

Figure 19. A thermal anomaly and dense steam were recorded at the summit of Mount Michael on Saunders Island on 1 January 2019 in Sentinel-2 Satellite imagery with Atmospheric Penetration rendering (bands 12, 11, 8a) (left). The same image shown with Natural Color rendering (bands 4,3,2) (right) shows a recent streak of brown particulates drifting SE from the summit crater. Courtesy of Sentinel Hub Playground.

Figure 20. A distinct SO2 plume was recorded drifting NW from Saunders Island by the TROPOMI instrument on the Sentinel 5-P satellite on 14 January 2019. Courtesy of NASA Goddard Space Flight Center.

Multiple sources of satellite data and sea-based visual observation confirmed activity during February 2019. SO₂ emissions were recorded with the TROPOMI instrument on 10, 11, 15, and 16 February (figure 21). A Landsat image from 10 February showed a dense steam plume drifting NW from the summit crater, with the dark rim of the summit crater well exposed (figure 22). Sentinel-2 images in natural color and atmospheric penetration renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February (figure 23). An expedition to the South Sandwich Islands between 15 February and 8 March 2019 sponsored by the UK government sailed by Saunders in late February and observed a stream of ash on the NNE flank beneath the cloud cover (figure 24).

Figure 21. Faint but distinct SO2 plumes were recorded drifting away from Saunders Island in various directions on 10, 11, 15, and 16 February 2019. Courtesy of NASA Goddard Space Flight Center.

Figure 22. The dark summit crater of Mount Michael on Saunders Island was visible in Landsat imagery on 10 February 2019. A dense steam plume drifted NW and cast a dark shadow on the underlying cloud cover. Courtesy of Sentinel Hub Playground.

Figure 23. At the summit of Mount Michael on Saunders Island, Sentinel-2 images in Natural Color (bands 4,3,2) (left) and Atmospheric Penetration (bands 12, 11, 8a) (right) renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February 2019. Courtesy of Sentinel Hub Playground.

Figure 24. Recent ash covered the NNE flank of Mount Michael on Saunders Island in late February 2019 when observed by an expedition to the South Sandwich Islands sponsored by the UK government. Courtesy of Chris Darby.

Faint SO₂ emissions were recorded twice during March 2019 (figure 25), and a dense steam plume near the summit crater was visible in Landsat imagery on 23 March (figure 26). Two thermal anomalies were captured in the MIROVA data during April 2019 (figure 17).

Figure 25. Faint SO2 plumes were recorded on 1 and 11 March 2019 emerging from Saunders Island. Courtesy of NASA Goddard Space Flight Center.

Figure 26. A dense steam plume drifted E from the summit crater of Mount Michael at Saunders Island on 25 March 2019. Landsat-8 image courtesy of Sentinel Hub Playground.

A volcano-related research project "SSIVOLC" explored the South Sandwich Islands volcanoes during 15 April-31 May 2019. A major aim of SSIVOLC was to collect photogrammetric data of the glacier-covered Mount Michael (Derrien and others, 2019). A number of still images were acquired on 17 and 22 May 2019 showing various features of the island (figures 27-30). The researchers visually observed brief, recurrent, and very weak glow at the summit of Mount Michael after dark on 17 May, which they interpreted as reflecting light from an active lava lake within the summit crater.

Figure 27. The steep slopes of an older eroded crater on the E end of Saunders island in the 'Ashen Hills' shows layers of volcanic deposits dipping away from the open half crater. In the background, steam and gas flow out of the summit crater of Mount Michael and drift down the far slope. Drone image PA-IS-03 taken during 17-22 May 2019, courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

Figure 28. A dense steam plume drifts away from the summit of Mount Michael on Saunders Island in this drone image taken during 17-22 May 2019. The older summit crater is to the left of the dark patch in the middle of the summit. North is to the right. Image SU-3 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

Figure 29. This close-up image of the summit of Mount Michael on Saunders Island shows steam plumes billowing from the summit crater, and large crevasses in the glacier covered flank, taken during 17-22 May 2019. The old crater is to the left. Image TL-SU-1 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

Figure 30. A dense plume of steam rises from the summit crater of Mount Michael on Saunders Island and drifts over mounds of frozen material during 17-22 May 2019. The older crater is to the left, and part of the Ashen Hills is in the foreground. Image TL-SU-2 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

References: Lachlan-Cope T, Smellie J L, Ladkin R, 2001. Discovery of a recurrent lava lake on Saunders Island (South Sandwich Islands) using AVHRR imagery. J. Volcanol. Geotherm. Res., 112: 105-116.

Gray D M, Burton-Johnson A, Fretwell P T, 2019. Evidence for a lava lake on Mt. Michael volcano, Saunders Island (South Sandwich Islands) from Landsat, Sentinel-2 and ASTER satellite imagery. J. Volcanol. Geotherm. Res., 379:60-71. https://doi.org/10.1016/j.volgeores.2019.05.002.

Derrien A, Richter N, Meschede M, Walter T, 2019. Optical DSLR camera- and UAV footage of the remote Mount Michael Volcano, Saunders Island (South Sandwich Islands), acquired in May 2019. GFZ Data Services. http://doi.org/10.5880/GFZ.2.1..2019.003

Geologic Background. Saunders Island is a volcanic structure consisting of a large central edifice intersected by two seamount chains, as shown by bathymetric mapping (Leat et al., 2013). The young constructional Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Analysis of satellite imagery available since 1989 (Gray et al., 2019; MODVOLC) suggests frequent eruptive activity (when weatehr conditions allow), volcanic clouds, steam plumes, and thermal anomalies indicative of a persistent, or at least frequently active, lava lake in the summit crater. Due to this observational bias, there has been a presumption when defining eruptive periods that activity has been ongoing unless there is no evidence for at least 10 months.

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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); Chris Darby (URL: https://twitter.com/ChrisDDarby, image at https://twitter.com/ChrisDDarby/status/1100686838568812544).

Pacaya is one of the most active volcanoes in Guatemala, with activity largely consisting of frequent lava flows and Strombolian activity at the Mackenney crater. This report summarizes continued activity during February through July 2019 based on reports by Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) and Sistema de la Coordinadora Nacional para la Reducción de Desastres (CONRED), visiting scientists, and satellite data.

At the beginning of February activity included Strombolian explosions ejecting material up to 5 to 30 m above the Mackenney crater and a degassing plume up to 300 m. Multiple lava flows were observed throughout the month on the N, NW, and W flanks, reaching 350 m from the crater and resulting in avalanches from the flow fronts. Strombolian activity continued with sporadic to continuous explosions ejecting material 5-75 m above the Mackenney crater. Degassing produced plumes up to 300 m above the crater, and incandescence from the crater and lava flows were seen at night. Daniel Sturgess of Bristol University observed activity on the 24th, noting a 70-m-long lava flow with individual blocks from the front of the flow rolling down the flanks (figure 108). He reported that mild Strombolian explosions occurred every 10-20 minutes and ejected blocks, up to approximately 4 m in diameter, as high as 5-30 m above the crater and towards the northern flank.

Figure 108. An active lava flow on the NW flank of Pacaya on 24 February 2019 with incandescence visible in lower light conditions. Courtesy of Daniel Sturgess, University of Bristol.

Similar activity continued through March with multiple lava flows reaching a maximum of 200 m N and NW, and avalanches descending from the flow fronts. Ongoing Strombolian explosions expelled material up to 75 m above the Mackenney crater. Degassing produced a white-blue plume to a maximum of 900 m above the crater (figure 109) and incandescence was noted some nights.

Figure 109. A degassing plume at Pacaya reaching 350 m above the crater and dispersing to the S on 19 March 2019. Courtesy of CONRED.

During April lava flows continued on the N and NW flanks, reaching a maximum length of 300 m, with avalanches forming from the flow fronts. Degassing formed plumes up to 600 m above the crater that dispersed with various wind directions. Strombolian activity continued with explosions ejecting material up to 40 m above the crater. On the 2nd and 3rd weak rumbles were heard at distances of 4-5 km. Similar activity continued through May with lava flows reaching 300 m to the N, degassing producing plumes up to 600 m above the crater, and Strombolian explosions ejecting material up to 15 m above the crater.

Lava flows continued out to 300 m in length to the N and NW during June (figures 110 and 111). Strombolian activity ejected material up to 30 m above the crater and degassing resulted in plumes that reached 300 m. During July there were multiple active lava flows that reached a maximum of 300 m in length on the N and NW flanks (figure 112). Avalanches generated by the collapse of material at the front of the lava flows were accompanied by explosions ejecting material up to 30 m above the crater.

Figure 110. An active lava flow on Pacaya on 9 June 2019 with incandescent blocks rolling down the flank from the flow front. Courtesy of Paul Wallace, University of Liverpool.

Figure 111. Activity at Pacaya on 22 June 2019 with a degassing plume dispersed to the W and a 300-m-long lava flow. Photos by Miguel Morales, courtesy of CONRED.

Figure 112. Two lava flows were active to the N and NW at Pacaya on 20 July 2019. Photos courtesy of CONRED.

During February through July multiple lava flows and crater activity were detected in Sentinel-2 satellite thermal images (figures 113 and 114) and relatively constant thermal energy was detected by the MIROVA system with a slight decrease in the energy and frequency of anomalies during June (figure 115). The thermal anomalies detected by the MODVOLC system for each month from February through July spanned 6-30, with six during June and 30 during April.

Figure 113. Sentinel-2 thermal satellite images of Pacaya show lava flows to the N and NW during February through April 2019. There was a reduction in visible activity in early March. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 114. Sentinel-2 thermal satellite images of Pacaya showing lava flow and hot avalanche activity during June and July 2019. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 115. MIROVA log radiative power plot of MODIS thermal infrared at Pacaya during October 2018 through July 2019. Detected thermal energy is relatively stable with a decrease through June and subsequent increase during July. Courtesy of MIROVA.

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: 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/); 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); 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/); Daniel Sturgess, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom (URL: http://www.bristol.ac.uk/earthsciences/); Paul Wallace, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, 4 Brownlow Street, Liverpool L69 3GP, United Kingdom (URL: https://www.liverpool.ac.uk/environmental-sciences/staff/paul-wallace/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Frequent historical eruptions at Volcán de Colima date back to the 16th century and include explosive activity, lava flows, and large debris avalanches. The most recent eruptive episode began in January 2013 and continued through March 2017. Previous reports have covered activity involving ash plumes with extensive ashfall, lava flows, lahars, and pyroclastic flows (BGVN 41:01 and 42:08). In late April 2019, increased seismicity related to volcanic activity began again. This report covers activity through July 2019. The primary source of information was the Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC).

On 11 May 2019, CUEIV-UdC reported an explosion that was recorded by several monitoring stations. A thermal camera located south of Colima captured thermal anomalies associated with the explosion as well as intermittent degassing, which mainly consisted of water vapor (figure 131). A report from the Unidad Estatal de Protección Civil de Colima (UEPCC), and seismic and infrasound network data from CUEIV-UdC, recorded about 60 high-frequency events, 16 landslides, and 14 low-magnitude explosions occurring on the NE side of the crater during 11-24 May. Drone imagery showed fumarolic activity occurring on the inner wall of this crater on 22 May (figure 132).

Figure 131. Gas emissions from Colima during the 11 May 2019 eruption as seen from the Naranjal station. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 17 mayo 2019 no 121).

Figure 132. A drone photo showing fumarolic activity occurring within the NE wall of the crater at Colima on 22 May 2019. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 24 mayo 2019 no 122).

Small explosions and gas-and-steam emissions continued intermittently through mid-July 2019 concentrated on the NE side of the crater. An overflight on 9 July 2019 revealed that subsidence from the consistent activity slightly increased the diameter of the vent; other areas within the crater also showed evidence of subsidence and some collapsed material on the outer W wall (figure 133). During the weeks of 19 and 26 July 2019, monitoring cameras and seismic data recorded eight lahars.

Figure 133. A drone photo of the crater at Colima on 8 July 2019 shows continuing fumarolic activity and evidence of a collapsed wall on the W exterior side. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 12 julio 2019 no 129).

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC), Colima, Col. 28045, Mexico; Centro Universitario de Estudios Vulcanologicos y Facultad de Ciencias de la Universidad de Colima, Avenida Universidad 333, Colima, Col. 28045, Mexico (URL: http://portal.ucol.mx/cueiv/); Unidad Estatal de Protección Civil, Colima, Roberto Esperón No. 1170 Col. de los Trabajadores, C.P. 28020, Mexico (URL: http://www.proteccioncivil.col.gob.mx/).

Masaya, in Nicaragua, contains a lava lake found in the Santiago Crater which has remained active since its return in December 2015 (BGVN 41:08). In addition to this lava lake, previous volcanism included explosive eruptions, lava flows, and gas emissions. Activity generally decreased during March-July 2019, including the number and frequency of thermal anomalies, lava lake levels, and gas emissions. The primary source of information for this report comes from the Instituto Nicareguense de Estudios Territoriales (INETER).

On 21 July 2019 a small explosion in the Santiago Crater resulted in some gas emissions and an ash cloud drifting WNW. In addition to the active lava lake (figure 77), monthly reports from INETER noted that thermal activity and gas emissions (figure 78) were decreasing.

Figure 77. Active lava lake visible in the Santiago Crater at Masaya on 27 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

Figure 78. Gas emissions coming from the Santiago Crater at Masaya on 29 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

On 15 May and 22 July 2019, INETER scientists used a FLIR SC620 thermal infrared camera to measure temperatures of fumaroles on the Santiago Crater. In May 2019 the temperature of fumaroles had decreased by 48°C since the previous month. Between May and July 2019 fumarole temperatures continued to decline; temperatures ranged from 90° to 136°C (figure 79). Compared to May 2019 these temperatures are 3°C lower. INETER reports that the level of the lava lake has been slowly dropping during this reporting period.

Figure 79. FLIR (forward-looking infrared) and visible images of the Santiago Crater at Masaya showing fumarole temperatures ranging from 90° to 136°C. The scale in the center shows the range of temperatures in the FLIR image. Courtesy of INETER (March 2019 report).

According to MIROVA (Middle InfraRed Observation of Volcanic Activity) data from MODIS satellite instruments, frequent thermal anomalies were recorded from mid-March through early May 2019, with little to no activity from mid-May to July 2019 (figure 80). Sentinel-2 thermal images show high temperatures in the active lava lake on 10 March 2019 (figure 81). Thermal energy detected by the MODVOLC algorithm showed 14 hotspot pixels with the most number of hotspots (7) occurring in March 2019.

Figure 80. Thermal anomalies were relatively constant at Masaya from early September 2018 through early May 2019 and then abruptly decreased until mid-June 2019 as recorded by MIROVA. Courtesy of MIROVA.

Figure 81. Sentinel-2 thermal satellite image showing a detected heat signature from the active lava lake at Masaya on 10 March 2019. The lava lake is visible (bright yellow-orange). Approximate diameter of the crater containing the lava lake is 500 m. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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); Sheila DeForest (URL: https://www.facebook.com/sheila.deforest).

The acid lake of Rincón de la Vieja's active crater has generated intermittent weak phreatic explosions regularly since 2011, continuing during the past year through at least August 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 4 March and 2 September 2019. Clouds often prevented webcam and satellite views. The current report describes activity from March through July 2019.

OVSICORI-UNA reported that weak events occurred on 19 March at 1851 and on 29 March 2019 at 2043. A two-minute-long phreatic explosion on 1 April at 0802 produced a plume that rose 600 m above the crater rim. Continuous emissions were visible during 3-4 April, rising 200 m above the crater rim. On 3 April, at 1437, a small explosion was detected. An explosion on 10 April at 0617 produced a gas-and-steam plume that rose 1 km above the crater rim and drifted SE. On 12 April at 0643, a plume rose 500 m. Another event took place at 0700 on 13 April, although poor weather conditions prevented visual observations. On 14 April, OVSICORI-UNA noted that aerial photographs showed a milky-gray acid lake at a relatively low water level with convection cells of several tens meters of diameter in the center and eastern parts of the lake.

According to an OVSICORI-UNA bulletin, a small phreatic explosion occurred on 1 May. Another explosion on 11 May at 0720 produced a white gas-and-steam plume that rose 600 m above the crater rim. Phreatic explosions were recorded on 14 May at 1703 and on 17 May at 0357, though dense fog prevented visual confirmation of both events with webcams. On 15 May a local observer noted a diffuse plume of steam and gas, material rising from the crater, and photographed milky-gray deposits on the N part of the crater rim ejected from the event the day before. A major explosion occurred on 24 May.

OVSICORI-UNA recorded a significant phreatic 10-minute-long explosion that began on 11 June at 0343, but plumes were not visible due to weather conditions. No further phreatic events were reported in July.

Seismic activity was very low during the reporting period, and there was no significant deformation. Short tremors were frequent toward the end of April, but were only periodic in May and June; tremor almost disappeared in July. A few long-period earthquakes were recorded, and volcano-tectonic earthquakes were even less frequent.

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

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/, https://www.facebook.com/OVSICORI/).

Sakurajima rises from Kagoshima Bay, which fills the Aira Caldera near the southern tip of Japan's Kyushu Island. Frequent explosive and occasional effusive activity has been ongoing for centuries. The Minamidake summit cone has been the location of persistent activity since 1955; the Showa crater on its E flank has also been intermittently active since 2006. Numerous explosions and ash-bearing emissions have been occurring each month at either Minamidake or Showa crater since the latest eruptive episode began in late March 2017. This report covers ongoing activity from January through June 2019; the Japan Meteorological Agency (JMA) provides regular reports on activity, and the Tokyo VAAC (Volcanic Ash Advisory Center) issues tens of reports each month about the frequent ash plumes.

From January to June 2019, ash plumes and explosions were usually reported multiple times each week. The quietest month was June with only five eruptive events; the most active was March with 29 (table 21). Ash plumes rose from a few hundred meters to 3,500 m above the summit during the period. Large blocks of incandescent ejecta traveled as far as 1,700 m from the Minamidake crater during explosions in February and April. All the activity originated in the Minamidake crater; the adjacent Showa crater only had a mild thermal anomaly and fumarole throughout the period. Satellite imagery identified thermal anomalies inside the Minamidake crater several times each month.

Table 21. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater in Aira caldera, January-June 2019. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Data courtesy of JMA (January to June 2019 monthly reports).

There were eight eruptive events reported by JMA during January 2019 at the Minamidake summit crater of Sakurajima. They occurred on 3, 6, 7, 9, 17, and 19 January (figure 76). Ash plume heights ranged from 600 to 2,100 m above the summit. The largest explosion, on 9 January, generated an ash plume that rose 2,100 m above the summit crater and drifted E. In addition, incandescent ejecta was sent 800-1,100 m from the summit. Incandescence was visible at the summit on most clear nights. During an overflight on 18 January no significant changes were noted at the crater (figure 77). Infrared thermal imaging done on 29 January indicated a weak thermal anomaly in the vicinity of the Showa crater on the SE side of Minamidake crater. The Kagoshima Regional Meteorological Observatory (KRMO) (11 km WSW) recorded ashfall there during four days of the month. Satellite imagery indicated thermal anomalies inside Minamidake on 7 and 27 January (figure 77).

Figure 76. Incandescent ejecta and ash emissions characterized activity from Sakurajima volcano at Aira during January 2019. Left: A webcam image showed incandescent ejecta on the flanks on 9 January 2019, courtesy of JMA (Explanation of volcanic activity in Sakurajima, January 2019). Right: An ash plume rose hundreds of meters above the summit, likely also on 9 January, posted on 10 January 2019, courtesy of Mike Day.

Figure 77. The summit of Sakurajima consists of the larger Minamidake crater and the smaller Showa crater on the E flank. Left: The Minamidake crater at the summit of Sakurajima volcano at Aira on 18 January 2019 seen in an overflight courtesy of JMA (Explanation of volcanic activity in Sakurajima, March 2019). Right: Two areas of thermal anomaly were visible in Sentinel-2 satellite imagery on 27 January 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

Activity increased during February 2019, with 15 eruptive events reported on days 1, 3, 7, 8, 10, 13, 14, 17, 22, 24, and 27. Ash plume heights ranged from 600-2,300 m above the summit, and ejecta was reported 300 to 1,700 m from the crater in various events (figure 78). KRMO reported two days of ashfall during February. Satellite imagery identified thermal anomalies at the crater on 6 and 26 February, and ash plumes on 21 and 26 February (figure 79).

Figure 78. An explosion from Sakurajima at Aira on 7 February 2019 sent ejecta up to 1,700 m from the Minamidake summit crater. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, February 2019).

Figure 79. Thermal anomalies and ash emissions were captured in Sentinel-2 satellite imagery on 6, 21, and 26 February 2019 originating from Sakurajima volcano at Aira. Top: Thermal anomalies within the summit crater were visible underneath steam and ash plumes on 6 and 26 February (closeup of bottom right photo). Bottom: Ash emissions on 21 and 26 February drifted SE from the volcano. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

The number of eruptive events continued to increase during March 2019; there were 29 events reported on numerous days (figures 80 and 81). An explosion on 14 March produced an ash plume that rose 3,500 m above the summit and drifted E. It also produced ejecta that landed 800-1,100 m from the crater. During an overflight on 26 March a fumarole was the only activity in Showa crater. KRMO reported 14 days of ashfall during the month. Satellite imagery identified an ash plume on 13 March and a thermal anomaly on 18 March (figure 82).

Figure 80. A large ash emission from Sakurajima volcano at Aira was photographed by a tourist on the W flank and posted on 1 March 2019. Courtesy of Kratü.

Figure 81. An ash plume from Sakurajima volcano at Aira on 18 March 2019 produced enough ashfall to disrupt the trains in the nearby city of Kagoshima according to the photographer. Image taken from about 20 km away. Courtesy of Tim Board.

Figure 82. An ash plume drifted SE from the summit of Sakurajima volcano at Aira on 13 March (left) and a thermal anomaly was visible inside the Minamidake crater on 18 March 2019 (right). "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

A decline in activity to only ten eruptive events on days 7, 13, 17, 22, and 25 was reported by JMA for April 2019. An explosion on 7 April sent ejecta up to 1,700 m from the crater. Another explosion on 13 April produced an ash plume that rose 2,200 m above the summit. Most of the eruptive events at Sakurajima last for less than 30 minutes; on 22 April two events lasted for almost an hour each producing ash plumes that rose 1,400 m above the summit. Ashfall at KRMO was reported during seven days in April. Two distinct thermal anomalies were visible inside the Minamidake crater on both 12 and 27 April (figure 83).

Figure 83. Two thermal anomalies were present inside Minamidake crater at the summit of Sakurajima volcano at Aira on 12 (left) and 27 (right) April 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

There were 15 eruptive events during May 2019. An event that lasted for two hours on 12 May produced an ash plume that rose 2,900 m from the summit and drifted NE (figure 84). The Meteorological Observatory reported 14 days with ashfall during the month. Two thermal anomalies were present in satellite imagery in the Minamidake crater on both 17 and 22 May.

Figure 84. An ash plume rose 2,900 m above the summit of Sakurajima at Aira on 12 May 2019 (left); incandescent ejecta went 1,300 m from the summit crater on 13 May. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, May 2019).

During June 2019 five eruptive events were reported, on 11, 13, and 24 June; the event on 11 June lasted for almost two hours, sent ash 2,200 m above the summit, and produced ejecta that landed up to 1,100 m from the crater (figure 85). Five days of ashfall were reported by KRMO.

Figure 85. A large ash plume on 11 June 2019 rose 2,200 m above the summit of Sakurajima volcano at Aira. Courtesy of Aone Wakatsuki.

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

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Mike Day, Minnesota, Twitter (URL: https://twitter.com/MikeDaySMM, photo at https://twitter.com/MikeDaySMM/status/1083489400451989505/photo/1); Kratü, Twitter (URL: https://twitter.com/TalesOfKratue, photo at https://twitter.com/TalesOfKratue/status/1101469595414589441/photo/1); Tim Board, Japan, Twitter (URL: https://twitter.com/Hawkworld_, photo at https://twitter.com/Hawkworld_/status/1107789108754038789); Aone Wakatsuke, Twitter (URL: https://twitter.com/AoneWakatsuki, photo at https://twitter.com/AoneWakatsuki/status/1138420031258210305/photo/3).

After a large, deadly explosive and effusive eruption during 1963-64, Indonesia's Mount Agung on Bali remained quiet until a new eruption began in November 2017 (BGVN 43:01). Lava emerged into the summit crater at the end of November and intermittent ash plumes rose as high as 3 km above the summit through the end of the year. Activity continued throughout 2018 with explosions that produced ash plumes rising multiple kilometers above the summit, and the slow effusion of the lava within the summit crater (BGVN 43:08, 44:02). Information about the ongoing eruptive episode comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and multiple sources of satellite data. This report covers the ongoing eruption from February through May 2019.

Intermittent but increasingly frequent and intense explosions with ash emissions and incandescent ejecta characterized activity at Agung during February through May 2019. During February, explosions were reported three times; events on seven days in March were documented with ash plumes and ashfall in surrounding villages. Five significant events occurred during April; two involved incandescent ejecta that traveled several kilometers from the summit, and ashfall tens of kilometers from the volcano. Most of the five significant events reported in May involved incandescent ejecta and ashfall in adjacent villages; air traffic was disrupted during the 24 May event. Ash plumes in May reached altitudes over 7 km multiple times. Thermal activity increased steadily during the period, according to both the MIROVA project (figure 44) and MODVOLC thermal alert data. MAGMA Indonesia reported at the end of May 2019 that the volume of lava within the summit crater remained at about 25 million m³; satellite information indicated continued thermal activity within the crater. Alert Level III (of four levels) remained in effect throughout the period with a 4 km exclusion radius around the volcano.

Figure 44. Thermal activity at Agung from 4 September 2018 through May 2019 was variable. The increasing frequency and intensity of thermal events was apparent from February-May. Courtesy of MIROVA.

Steam plumes rose 30-300 m high daily during February 2019. The Agung Volcano Observatory (AVO) and PVMBG issued a VONA on 7 February (UTC) reporting an ash plume, although it was not visible due to meteoric cloud cover. Incandescence, however, was observed at the summit from webcams in both Rendang and Karangasem City (16 km SE). The seismic event associated with the explosion lasted for 97 seconds. A similar event on 13 February was also obscured by clouds but produced a seismic event that lasted for 3 minutes and 40 seconds, and ashfall was reported in the village of Bugbug, about 20 km SE. On 22 February a gray ash plume rose 700 m from the summit during a seismic event that lasted for 6 minutes and 20 seconds (figure 45). The Darwin VAAC reported the plume visible in satellite imagery moving W at 4.3 km altitude. It dissipated after a few hours, but a hotspot remained visible about 10 hours later.

Figure 45. An ash plume rose from the summit of Agung on 22 February 2019, viewed from the Besakih temple, 7 km SW of the summit. Courtesy of PunapiBali.

Persistent steam plumes rose 50-500 m from the summit during March 2019. An explosion on 4 March was recorded for just under three minutes and produced ashfall in Besakih (7 km SW); no ash plume was observed due to fog. A short-lived ash plume rose to 3.7 km altitude and drifted SE on 8 March (UTC) 2019. The seismic event lasted for just under 4 minutes. Ash emissions were reported on 15 and 17 March to 4.3 and 3.7 km altitude, respectively, drifting W (figure 46). Ashfall from the 15 March event spread NNW and was reported in the villages of Kubu (6 km N), Tianyar (14 km NNW), Ban, Kadundung, and Sukadana. MAGMA Indonesia noted that two explosions on the morning of 17 March (local time) produced gray plumes; the first sent a plume to 500 m above the summit drifting E and lasted for about 40 seconds, while the second plume a few hours later rose 600 m above the crater and lasted for 1 minute and 16 seconds. On 18 March an ash plume rose 1 km and drifted W and NW. An event on 20 March was measured only seismically by PVMBG because fog prevented observations. An eruption on 28 March produced an ash plume 2 km high that drifted W and NW. The seismic signal for this event lasted for about two and a half minutes. The Darwin VAAC reported the ash plume at 5.5 km altitude, dissipating quickly to the NW. No ash was visible four hours later, but a thermal anomaly remained at the summit (figure 47). Ashfall was reported in nearby villages.

Figure 46. Ash plumes from Agung on 15 (left) and 17 (right) March 2019 resulted in ashfall in communities 10-20 km from the volcano. Courtesy of PVMBG and MAGMA Indonesia (Information on G. Agung Eruption, 15 March 2019 and Gunung Agung Eruption Press Release March 17, 2019).

Figure 47. A thermal anomaly was visible through thick cloud cover at the summit of Agung on 29 March 2019 less than 24 hours after a gray ash plume was reported 2,000 m above the summit. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

The first explosion of April 2019 occurred on the 3rd (UTC); PVMBG reported the dense gray ash plume 2 km above the summit drifting W. A few hours later the Darwin VAAC raised the altitude to 6.1 km based on infrared temperatures in satellite imagery. The seismic signal lasted for three and a half minutes and the explosion was heard at the PGA Post in Rendang (12 km SW). Incandescent material fell within a radius of 2-3 km, mainly on the S flank (figure 48). Ashfall was reported in the villages of Telungbuana, Badeg, Besakih, Pempatan, Teges, and Puregai on the W and S flanks (figure 49). An explosion on 11 April also produced a dense gray ash plume that rose 2 km above the summit and drifted W. A hotspot remained about six hours later after the ash dissipated.

Figure 48. Incandescent ejecta appeared on the flanks of Agung after an eruption on 4 April 2019 (local time) as viewed from the observation post in Rendang (8 km SW). Courtesy of Jamie Sincioco.

Figure 49. Ashfall in a nearby town dusted mustard plants on 4 April 2019 from an explosion at Agung the previous day. Courtesy of Pantau.com (Photo: Antara / Nyoman Hendra).

PVMBG reported an eruption visible in the webcam early on 21 April (local time) that rose to 5.5 km altitude and drifted SW. The ash spread W and S and ash fell around Besakih (7 km SW), Rendang (8 km SW), Klungkung (25 km S), Gianyar (20 km WSW), Bangli (17 km WNW), Tabanan (50 km WSW), and at the Ngurah Rai-Denpasar Airport (60 km SW). About 15 hours later a new explosion produced a dense gray ash plume that rose to 3 km above the summit and produced incandescent ejecta in all directions as far as 3 km away (figure 50). The ash spread to the S and ashfall was reported in Besakih, Rendang, Sebudi (6 km SW), and Selat (12 km SSW). Both of the explosions were heard in Rendang and Batulompeh. The incandescent ejecta from the explosions remained within the 4-km exclusion zone. A satellite image on 23 April showed multiple thermal anomalies within the summit crater (figure 51). A dense gray plume drifted E from Agung on 29 April (30 April local time) at 4.6 km altitude. It was initially reported by ground observers, but was also visible in multispectral satellite imagery for about six hours before dissipating.

Figure 50. An explosion at Agung on 21 April 2019 sent incandescent eject 3,000 m from the summit. Courtesy of MAGMA Indonesia (Gunung Agung Eruption Press Release April 21, 2019).

Figure 51. Multiple thermal anomalies were still present within the summit crater of Agung on 23 April 2019 after two substantial explosions produced ash and incandescent ejecta around the summit two days earlier. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG reported an eruption on 3 May 2019 that was recorded on a seismogram with a signal that lasted for about a minute. Satellite imagery reported by the Darwin VAAC showed a growing hotspot and possible ash near the summit at 4.3 km altitude moving NE. A few days later, on 6 May, a gray ash plume rose to 5.2 km altitude and drifted slowly W before dissipating; it was accompanied by a seismic signal that lasted for about two minutes. Explosions on 12 and 18 May produced significant amounts of incandescent ejecta (figure 52). The seismic signal for the 12 May event lasted for about two minutes; no plume was observed due to fog, but incandescent ejecta was visible on the flanks and the explosion was heard at Rendang. The Darwin VAAC reported an ash plume from the explosion on 17 May (18 May local time) at 6.1 km altitude in satellite imagery moving E. They revised the altitude a short while later to 7.6 km based on IR temperature and movement; the plume drifted N, NE, and E in light and variable winds. A few hours after that it was moving NE at 7.6 km altitude and SE at 5.5 km altitude; this lasted for about 12 hours until it dissipated. Ashfall was reported in villages downwind including Cutcut, Tongtongan, Bonyoh (20 km WNW), and Temakung.

Figure 52. Explosions on 12 (left) and 18 (right) May (local time) 2019 produced substantial ejecta on the flanks of Agung visible from a distance of 10 km or more in PVMBG webcams. The ash plume from the 18 May event resulted in ashfall in numerous communities downwind. Courtesy of PVMBG (Information Eruption G. Agung, May 13, 2019, Information Eruption G. Agung, May 18, 2019).

The initial explosion on 18 May was captured by a webcam at a nearby resort and sent incandescent ejecta hundreds of meters down the NE flank within 20 seconds (figure 53). Satellite imagery on 3, 8, 13, and 18 May indicated multiple thermal anomalies growing stronger at the summit. All of the images were captured within 24 hours of an explosive event reported by PVMBG (figure 54).

Figure 53. The 18 May 2019 explosion at Agung produced an ash plume that rose to over 7 km altitude and large bombs of incandescent material that traveled hundreds of meters down the NE flank within the first 20 seconds of the explosion. Images taken from a private webcam located 12 km NE. Courtesy of Volcanoverse, used with permission.

Figure 54. Satellite images from 3, 8, 13, and 18 May 2019 at Agung showed persistent and increasing thermal anomalies within the summit crater. All images were captured within 24 hours of explosions reported by PVMBG. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG issued a VONA on 24 May 2019 reporting a new ash emission. They indicated that incandescent fragments were ejected 2.5-3 km in all directions from the summit, and the seismic signal lasted for four and a half minutes (figure 55). A dense gray ash plume was observed from Tulamben on the NE flank rising 2 km above the summit. Satellite imagery indicated that the plume drifted SW and ashfall was reported in the villages of Besakih, Pempatan, Menanga, Sebudi, Muncan, Amerta Bhuana, Nongan, Rendang, and at the Ngurah Rai Airport in Denpassar. Additionally, ashfall was reported in the districts of Tembuku, Bangli, and Susut (20 km SW). The Darwin VAAC reported an ash plume visible in satellite imagery at 4.6 km altitude along with a thermal anomaly and incandescent lava visible in webcam imagery. The remains of the ash plume were about 170 km S of the airport in Denpasar (60 km SW) and had nearly dissipated 18 hours after the event. According to a news article several flights to and from Australia were cancelled or diverted, though the International Gusti Ngurah Rai (IGNR) airport was not closed. On 31 May another large explosion produced the largest ash plume of the report period, rising more than 2 km above the summit (figure 56). The Darwin VAAC reported its altitude as 8.2 km drifting ESE visible in satellite data. It split into two plumes, one drifted E at 8.2 km and the other ESE at 6.1 km altitude, dissipating after about 20 hours.

Figure 55. A large explosion at Agung on 24 May 2019 produced incandescent ejecta that covered all the flanks and dispersed ash to many communities to the SW. Courtesy of PVMBG (Gunung Agung Eruption Press Release 24 May 2019 20:38 WIB, Kasbani, Ir., M.Sc.).

Figure 56. An explosion at Agung on 31 May 2019 sent an ash plume to 8.2 km altitude, the highest for the report period. Courtesy of Sutopo Purwo Nugroho, BNPB.

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); The Jakarta Post, Mount Agung eruption disrupts Australian flights, (URL: https://www.thejakartapost.com/news/2019/05/25/mount-agung-eruption-disrupts-australian-flights.html); PunapiBali (URL: http://punapibali.com/, Twitter: https://twitter.com/punapibali, image at https://twitter.com/punapibali/status/1098869352588288000/photo/1); Jamie S. Sincioco, Phillipines (URL: Twitter: https://twitter.com/jaimessincioco. Image at https://twitter.com/jaimessincioco/status/1113765842557104130/photo/1); Pantau.com (URL: https://www.pantau.com/berita/erupsi-gunung-agung-sebagian-wilayah-bali-terpapar-hujan-abu?utm_source=dlvr.it&utm_medium=twitter); Volcanoverse (URL: https://www.youtube.com/channel/UCi3T_esus8Sr9I-3W5teVQQ); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN ).

Frequently active, Indonesia's Mount Kerinci on Sumatra has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838. Intermittent explosions with ash plumes, usually multiple times per month, have characterized activity since April 2018. Similar activity continued during February-May 2019, the period covered in this report with information provided primarily by the Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), MAGMA Indonesia, notices from the Darwin Volcano Ash Advisory Center (Darwin VAAC), and satellite data. PVMBG has maintained an Alert Level II (of 4) at Kerinci for several years.

On 13 February 2019 the Kerinci Volcano Observatory (KVO), part of PVMBG, noted a brownish-white ash emission that was drifting NE about 400 m above the summit. The seismicity during the event was dominated by continuous volcanic tremor. A brown ash emission was reported on 7 March 2019 that rose to 3.9 km altitude and drifted NE. Ash also drifted 1,300 m down the SE flank. Another ash plume the next morning drifted W at 4.5 km altitude, according to KVO. On 10, 11, and 13 March KVO reported brown ash plumes drifting NE from the summit at about 4.0-4.3 km altitude. The Darwin VAAC observed continuous ash emissions in satellite imagery on 15 March drifting W at 4.3 m altitude that dissipated after about 3 hours (figure 10). A gray ash emission was reported on 19 March about 600 m above the summit drifting NE; local news media noted that residents of Kayo Aro reported emissions on both 18 and 19 March (figure 11). An ash emission appeared in satellite imagery on 25 March (figure 10). On 30 March the observatory reported two ash plumes; a brown emission at 0351 UTC and a gray emission at 0746 UTC that both drifted NE at about 4.4 km altitude and dissipated within a few hours. PVMBG reported another gray ash plume the following day at a similar altitude.

Figure 10. Sentinel-2 satellite imagery of Kerinci from 15 (left) and 25 (right) March 2019 showed evidence of ash plumes rising from the summit. Kerinci's summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Figure 11. Dense ash plumes from Kerinci were reported by local news media on 18 and 19 March 2019. Courtesy of Nusana Jambi.

Activity continued during April with a brown ash emission reported on 3 April by several different agencies; the Darwin VAAC and PVMBG daily reports noted that the plume was about 500 m above the summit (4.3 km altitude) drifting NE. KVO observed two brown ash emissions on 13 April (UTC) that rose to 4.2 km altitude and drifted NE. Satellite imagery showed minor ash emissions from the summit on 14 April; steam plumes 100-500 m above the summit characterized activity for the remainder of April (figure 12).

Figure 12. A dilute ash emission rose from the summit of Kerinci on 14 April 2019 (left); only steam emissions were present on a clear 29 April in Sentinel-2 imagery (right). "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Ashfall on the NE and S flanks within 7 km of the volcano was reported on 2 May 2019. According to a news article, at least five villages were affected late on 2 May, including Tanjung Bungo, Sangir, Sangir Tengah, Sungai Rumpun, and Bendung Air (figures 13 and 14). The smell of sulfur was apparent in the villages. Brown ash emissions were observed on 3 and 4 May that rose to 4.6 and 4.1 km altitude and drifted SE. The Darwin VAAC reported an emission on 5 May, based on a pilot report, that rose to 6.7 km altitude and drifted NE for about an hour before dissipating. A brown ash emission on 10 May rose 700 m above the summit and drifted SE. Satellite imagery captured ash emissions from the summit on 14 and 24 May (figure 15). For the remainder of the month, 300-700-m-high dense steam plumes were noted daily until PVMBG reported white and brown plumes on 26 and 27 May rising 500-1,000 m above the summit. Although thermal anomalies were not reported during the period, persistent weak SO₂ emissions were identified in TROPOMI instrument satellite data multiple times per month (figure 16).

Figure 13. Ashfall was reported from five villages on the flanks of Kerinci on 2 May 2019. Courtesy of Uzone.

Figure 14. An ash plume at Kerinci rose hundreds of meters on 2 May 2019; ashfall was reported in several nearby villages. Courtesy of Kerinci Time.

Figure 15. Ash emissions from Kerinci were captured in Sentinel-2 satellite imagery on 14 (left) and 24 (right) May 2019. The summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Figure 16. Weak SO2 anomalies from Kerinci emissions were captured by the TROPOMI instrument on the Sentinel-5P satellite multiple times each month from February to May 2019. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); Nuansa Jambi, Informasi Utama Jambi: (URL: https://nuansajambi.com/2019/03/20/gunung-kerinci-semburkan-asap-tebal/); Kerinci Time (URL: https://kerincitime.co.id/gunung-kerinci-semburkan-abu-vulkanik.html); Uzone.id (URL: https://news.uzone.id/gunung-kerinci-erupsi-5-desa-tertutup-abu-tebal).

Sakura-jima generated 22 eruptions in July, including 14 explosive ones. None of them caused damage. The highest plume rose to 2.2 km (at 1859 on 5 July). In July, the amount of ashfall at [KLMO] was 237 g/m³. Volcanic swarms were absent in July but 520 earthquakes were detected at a seismic station 2.3 km NW of Minami-dake crater.

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

Information Contacts: JMA.

At . . . Crater C, July marked another month of continued gas and lava emissions, and sporadic Strombolian eruptions. During July, the lava flow that began at the end of April continued to erupt and flow down an established channel. During 23 days in July, seismic station VACR (2.7 km NE of crater C) recorded an average of 18 events/day. These were interspersed with days having very low seismicity and tremor. Beginning on 23 July, Strombolian-type eruptions became common, and during 23-30 July they were seen 52 times. In some cases these eruptions were accompanied by sounds similar to a jet or steam engine. On 28 July tremor reached an amplitude of 27 mm at a frequency below 2.5 Hz.

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

Information Contacts: E. Fernández, J. Barquero, V. Barboza, R. Van der Laat, F. de Obaldia, and T. Marino, OVSICORI; G. Soto, G. Alvarado, and F. Arias, ICE; M. Mora, C. Ramirez, and G. Peraldo, Univ de Costa Rica.

Crater 1 remained restless through July, but the intensity of activity became more moderate compared to the last two months. Through July the average amplitude of continuous tremor was around 0.1 µm.

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

Information Contacts: JMA.

Beginning on 4 August, the daily number of A-type volcanic earthquakes increased to 14; two days later 125 events were registered. An eruption on 7 August from the E part of the summit, Batur Crater III, caused ashfall as far as ~6 km WSW (figure 1). Ash covered Kintamani on the caldera rim, one of Bali's famous tourist attractions. Incandescent lava fragments and black smoke were ejected to heights of 300 m. None of the larger lava fragments fell outside of the active crater. News reports indicated that the eruption generated 960 explosions through 11 August. Volcanic tremor recorded by the VSI on 13 August had a maximum amplitude of 4.5 mm, but was increasing. By 14 August, when lava reached the surface, the tremor amplitude was 23 mm.

Figure 1. Map of the Batur caldera, showing hazard zones, selected towns, and extent of ashfall from the eruption that began on 7 Aug 1994. The inner caldera is not shown, but includes most of danger zones I and II. Courtesy of VSI.

As of 18 August, no evacuations from the area around the . . . volcano had taken place. About 180,000 people live in Bangli Regency, but only ~500 live in what a spokesman called the "critical region." Batur was declared off-limits for climbers on 7 August, and local villagers were put on alert. An official at a monitoring center said tourists who evaded guards and climbed the mountain were taking large risks. According to press reports, the eruptions have not reduced the number of visitors to the popular resort island; Batur's crater attracts ~300 people every day. Many observe the volcanic activity from Kintamani, on the crater rim (figure 1).

Geologic Background. The historically active Batur is located at the center of two concentric calderas NW of Agung volcano. The outer 10 x 13.5 km wide caldera was formed during eruption of the Bali (or Ubud) Ignimbrite about 29,300 years ago and now contains a caldera lake on its SE side, opposite the satellitic Gunung Abang cone, the topographic high of the complex. The inner 6.4 x 9.4 km wide caldera was formed about 20,150 years ago during eruption of the Gunungkawi Ignimbrite. The SE wall of the inner caldera lies beneath Lake Batur; Batur cone has been constructed within the inner caldera to a height above the outer caldera rim. The Batur stratovolcano has produced vents over much of the inner caldera, but a NE-SW fissure system has localized the Batur I, II, and III craters along the summit ridge. Historical eruptions have been characterized by mild-to-moderate explosive activity sometimes accompanied by lava emission. Basaltic lava flows from both summit and flank vents have reached the caldera floor and the shores of Lake Batur in historical time.

Information Contacts: VSI; AP; Reuters; UPI; ANS; D. Shackleford, Fullerton CA, USA.

"Cumbal . . . (figure 1), has been showing signs of possible reactivation during the past year. New fumaroles have appeared and the gas column has grown noticeably larger. Cumbal was visited by volcanologists from INGEOMINAS and the Univ de Montréal on 11-15 July 1994. A portable seismometer was installed . . . at 4,185 m elev, ~580 m below the summit. Both high-frequency and long-period events were recorded, as well as some possible tremor episodes. Several fumarole fields at the summit (figure 2) exhibited maximum temperatures as follows: El Verde, 378°C; El Tábano, 191°C; La Desfondada, 132°C; La Plazuela, 99°C; La Grieta-verde, 84°C; Vecino a la verde, 80°C. El Tábano is a new fumarole field that appeared in early 1994. For comparison, in 1988 El Verde had measured temperatures of 150-326°C. The El Verde fumaroles produced audible noise. Most of the gas column at Cumbal appeared to emanate from the El Verde fumaroles."

Figure 1. Location map showing Cumbal volcano and the city of Cumbal. Modified from Mendez (1989).

Figure 2. Sketch map of the crater area of Cumbal, July 1994, showing fumarole locations. Courtesy of INGEOMINAS.

Reference. Mendez F., R.A., 1989, Catálogo de los volcanes actives de Colombia: Bol. Geol., v. 30, no. 3, 75 p.

Geologic Background. Many youthful lava flows extend from the glacier-capped Cumbal volcano, the southernmost historically active volcano of Colombia. The volcano is elongated in a NE-SW direction and is composed primarily of andesitic-dacitic lava flows. Two fumarolically active craters occupy the summit ridge: the main crater on the NE side and Mundo Nuevo crater on the SW. A young lava dome occupies the 250-m-wide summit crater, and eruptions from the upper E flank produced a 6-km-long lava field. The oldest crater lies NNE of the summit crater, suggesting SW-ward migration of activity. Explosive eruptions in 1877 and 1926 are the only known historical activity. Thermal springs are located on the SE flanks.

Information Contacts: G. Patricia Cortes and R. Torres Corredor, INGEOMINAS, Pasto; J. Stix and M. Heiligmann, Univ de Montréal.

The following describes [fieldwork] on 1-27 June and 10-18 July 1994.

"As during visits in June-July and September-October 1993, Northeast Crater was blocked and inactive, but collapse was continuing around the edge with minor rockfalls every few minutes or so. Southeast Crater was also little changed from 1993, with a quietly degassing vent under the SE rim, but no indication of gas coming out under pressure. There was strong high-temperature fumarolic activity around the crater rim, temperatures being generally highest in the cracks.

"The Chasm (La Voragine) had a single vent in its floor measuring ~ 8 x 10 m, discharging gas continuously under pressure in rhythmic puffs at a rate of ~ 30 puffs/min. On 17 June and 12 July only, distinct explosions could be heard at the rate of 1-8/min. These were the first signs of explosive activity since the end of the 1991-93 eruption, and an indication that the Strombolian degassing that has characterized the summit over the past few hundred years is resuming.

"Bocca Nuova vent was degassing almost totally silently from two vents, one to the SE and one to the W; however, on 27 June when the weather was calm, 13 very faint gas puffs/min could be heard. The SE vent seemed similar to last year, measuring ~ 10 m in diameter, but the W vent had collapsed and enlarged considerably, now measuring perhaps as much as 50 m in diameter. On the early morning of 16 June a reddish tinge to the plume above Bocca Nuova was first noticed. Upon closer inspection on 17 June, the SE vent was seen to be pouring out thick clouds of red dust, apparently a result of internal collapse within the vent, while the W vent continued to emit white fume only. Dust emission intensified in the following days, causing the downwind side (S through W) of the summit to become a striking red color. The activity was continuing in mid-July.

"The levelling traverse showed comparatively small vertical movements since September 1993. The area near Belvedere, and other areas over the dyke intruded during the 1991-93 eruption, had subsided by up to 2 cm, as had the NE rift zone near Monte Pizzillo. During the same period, a small area ~1 km SW of the summit inflated by just over 1 cm. Horizontal movements measured since October 1993 showed generally small or insignificant changes, with nearly all lines recording changes of >1 cm. Only two stations appear to have moved by more than this; a station on the E edge of Southeast Crater had shifted 3 cm E relative to nearby stations, and a station close to the NW edge of the Bocca Nuova had moved 2 cm W. These movements are consistent with expansion of the central magma column as it refills.

"Surface temperatures were measured between 1 and 27 June at four active fumarole areas with a Minolta/Land Cyclops Compac 3 hand-held radiometer (8-14 mm). Temperatures were not corrected for spectral emissivity, so all radiant temperatures are given here as brightness temperatures. On the NE rift zone, nine areas of fumaroles were observed near the N edge of the 1966-67 lavas (between 2,450 and 2,500 m altitude). Temperatures for fumaroles at the two lowest of these areas ranged between 33 and 50°C. Another area of fumaroles observed at the upper rim of the W wall of the Valle del Bove around Belvedere, above the 1991-93 dyke, had temperatures in the 57.5-84.7°C range. Temperatures measured at fumaroles and cracks in the still-cooling 1991-93 lava-flow field in the Valle del Bove were between 85 and 221°C. The locations and temperatures of fumarole areas measured in the vicinity of the summit craters are given in table 5. Temperatures of the vents within the central craters were also measured from the crater rim: 342°C for the Chasm vent, and 159 and 81.5°C, respectively, for the SE and W vents of Bocca Nuova. Active fumaroles were observed, but not measured, along the 1991-93 fissure zone and 14 December 1991 cones and flows between Southeast Crater and Belvedere, along the October 1986 fissure zone, and in the Valle del Bove below Monte Simone."

Table 5. Fumarole temperatures in the vicinity of Etna's summit craters, measured on 18 and 27 June, and 14 October 1994. Courtesy of Andrew Harris, Open University.

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

Information Contacts: J. Murray and A. Harris, Open Univ; L. Platt, Sheffield Univ; D. Renouf, UK.

Seismicity during June and July showed no significant changes. . . . Low-frequency seismicity was at very low levels during June, although a "screw-type" event did occur; this type of event was numerous before eruptions in 1992-93. Shallow "butterfly-type" activity during the first half of June was similar to May, when the number of events decreased notably. These small-amplitude, short-duration, high-frequency events, interpreted as caused by fluid movement or rock fracture at shallow depths (<2 km) near the active cone, increased in number in the second half of June and through July. During June the fracture events were located N of the volcano, near the source that was active during November-December 1993, with other fracture events to the NE or closer to the crater. Additional sources were W and S of the crater. Fracture activity within the crater consisted of very small magnitude events (M <2.3) at depths between 2.1 and 9.7 km.

The active inner cone was visited on 21 July 1994 by volcanologists from INGEOMINAS and the Univ de Montréal. The morphology of the cone was modified considerably by the eruptions of 1992-93, which seem to have progressively deepened the crater to the present level of 200-300 m (figure 71). Prior to dome emplacement during October-November 1991 the crater was ~ 150 m deep; after dome growth in 1991-92, the crater was ~80 m deep. A N-S trending fracture, named Novedad, now breaches the S crater rim. Partial collapse of the crater rim and blocks 10-20 cm in size were noted on the N side of the cone.

Figure 71. Sketch map (top) and perspective view (bottom) of the Galeras crater, July 1994. Small ovals represent fumaroles; crater depth is ~200-300 m. View is from the west. Drawn by Milton Ordonez, INGEOMINAS.

Some low-pressure fumaroles were noted in the deepest part of the crater, but gas was being emitted mainly in the shallower W and SW sectors. At Deformes fumarole, on the SW flank of the cone, temperature was measured and gas samples were collected for analysis. Maximum temperature was 138°C, significantly cooler than the ~200°C recorded in December 1992 and January 1993 (Zapata G., 1992; Goff et al., 1993). Besolima, generally the hottest measured fumarole on the cone's outer flanks, had largely disappeared. Las Chavas fumarole showed very low activity with a maximum temperature of 105°C. A new fumarole near the W rim of the cone, named Nuevas, had temperatures of 208 and 392°C. This fumarole is in the area where Florencia fumarole and remnants of the lava dome (destroyed in July 1992) had temperatures of 640°C on 26 November 1992 (Zapata G., 1992).

Stationary COSPEC measurements of SO₂ in June from five points around the volcano showed low levels of gases (18-176 t/d), similar to the measurements obtained using the mobile COSPEC (79-217 t/d). July degassing was concentrated on the W periphery of the active cone, with low concentrations of SO₂ (<220 t/d) measured by COSPEC.

Electronic tiltmeter variations in June at the Peladitos station were 2.4 µrad in the tangential component and 7.8 µrad in the radial component. The Crater tiltmeter fluctuated in June due to electronic problems; no deformation was observed in July. On 7 July the Agua Tibia springs, located in the Rio Azufral valley 5 km W of the active cone, had a temperature of 21°C and pH of 5.

References. Zapata G., J.A., 1992, Visita al crater del volcan Galeras: INGEOMINAS Internal Report, 30 November 1992, 2 p.

Goff, F., McMurtry, G.M., Adams, A.I., and Roldán-M., A., 1993, Stable isotopes and tritium of magmatic water at Galeras volcano, Colombia: EOS, Trans. Am. Geophys. Union, 74(43), p. 690.

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

Information Contacts: R. Corredor and C. Gonzalez, INGEOMINAS, Pasto; J. Stix and M. Heiligmann, Univ de Montréal.

A NOTAM that originated from the Ujung Pandang FIR on 6 May 1994 requested that all aircraft avoid the area around Gamalama volcano. VSI did not note any unusual activity on that day, and no ash cloud was detected on satellite imagery. The warning only noted that the height of "dust" was variable.

Members of the SVE visited Gamalama at 1130 on 21 July. Summit activity consisted of violent degassing from the summit crater, producing a white-gray plume above the volcano; no solid material was ejected during the observations. A small active fumarolic area on the W crater rim exhibited yellow sulfur deposits. White vapor was rising from a large crack on the E crater rim, a part of the crater that appeared to be very unstable. The bottom of the crater could not be seen from the rim.

VSI reported that activity from the main crater increased with a sudden eruption on 5 August 1994 at 2125. The eruption produced an ash cloud to a height of 3,000 m above the summit . . . and accompanying ash falls. A felt earthquake a few minutes before the eruption had an intensity of MM II-III. Volcanic tremor recorded since 10 August preceded another eruption at about 2400 on 13 August from the same location. A news report indicated that explosions on 14 August caused ashfall in Ternate (~ 4 km SE), and that 5-20 minor explosions/day had occurred in recent days.

Following eruptions in May 1993 (18:5 & 7; and VSI, 1993a), seismicity steadily decreased to low levels by the end of June; vapor emission stopped by the end of August 1993 (VSI, 1993b). Seismicity began increasing again in December 1993 (VSI, 1993b), and explosions were reported during January-March 1994 (19:05).

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

Information Contacts: W. Tjetjep, VSI; H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland; BOM Darwin, Australia; AP; Radio Republik Indonesia.

The destructive earthquake-triggered mudflows of 6 June (19:5) were the subject of a preliminary report (Casadevall and others, 1994) following an investigation by a team from INGEOMINAS and the USGS during 30 June-9 July. What follows is a summary of that report, which includes first-hand observations on slope-failure and transport of loosened material.

The M 6.4 earthquake that struck on 6 June 1994 is now termed the Paez earthquake. Although the preliminary epicenter determination was W of the volcano's summit, a more recent estimate places it on Nevado del Huila's SSW flank, several kilometers N of the village of Irlanda (figure 1; BGVN 19:5). Prior to the earthquake, normal background seismicity prevailed; a series of aftershocks also took place beneath the volcano.

Earthquake damage was attributed to shaking, mass movement of loosened material, and flooding. The volcano's topography and volcanic deposits contributed to the disaster, but the primary area of landslides lay S of the main volcanic edifice and reached a maximum elevation of ~3,000 m. Aerial observers on 7 July saw no changes in either the vigor of fumaroles present near the summit or in the distribution and surface appearance of glaciers. Though dislodged ice was noted in news reports, none was found during fieldwork. The latest estimates on direct human impact from the earthquake are >150 fatalities, 500 people listed as missing, and 20,000 people displaced. Six bridges and >100 km of roads were destroyed.

All mass movement due to slope failure was previously called "mudflows" (19:5). The new report uses more precise terminology (Varnes, 1978), and provides an English-Spanish glossary that includes these and other terms: (a) rock, soil, and earth falls, (b) various kinds of slides including earth slides and debris slides, (c) rock avalanches, (d) debris avalanches, and (e) earth flows. According to this scheme, the bulk of the observed slides were earth slides derived from weathered residual soils that have developed on the bedrock. Lack of bedrock involvement and the limited amount of translations that involved bouncing, rolling, or falling resulted in few mass movements categorized as rock avalanches.

Nearly all of the 6 June earthquake-triggered landslides originated on slopes of >=30°. In this steep terrain they mainly began as shallow slips in residual soils. The soils had been saturated a few weeks prior to the earthquake by heavy rains. Reduced shear strength because of the saturated soils was a major factor in the observed slope failures and the velocity of the downslope movements. Typically these water-charged slides were ~ 1-2 m thick, and immediately liquified, transforming into either debris avalanches or earth flows moving rapidly downslope. In total, these processes stripped >50% of the vegetation from the steep hillsides. The slides themselves caused little direct damage since the steep slopes were generally uninhabited.

Adjacent to the volcano, in up-river villages such as Irlanda and Wila, damage took place as the mobile earth flows ran across relatively flat terrace surfaces. Earth flows in Irlanda were only 2 m thick, but they destroyed the houses and structures in their path. Some of the damage at Irlanda may have been caused by a high-velocity earth flow that began on the opposite side (the E side) of Rio Paez and crossed over.

The 1994 debris flows in the Rio Paez were cohesive (>3% of sediment with <0.004 mm size), which means that they remain intact and travel long distances. On the other hand, large previous debris flows preserved in lateral terraces along the river are of the noncohesive type that transformed into hyperconcentrated flows as they moved downstream. The noncohesive debris flows are thought to have been more closely related to past explosive volcanism and provide one means of analyzing past behavior at Huila. This point is noteworthy because the headwaters of the Rio Paez provide the drainage for almost the entire volcano. Because the bulk of debris flows must travel down the Rio Paez, study of the deposits along it should provide a thorough record of the volcano's seismically and magmatically generated deposits.

The report noted several analogous cases of "widespread stripping of saturated materials and vegetative cover from steep slopes" during seismic loading. One case involved the M 6.1 and 6.9 earthquakes of March 1987 in NE Ecuador. Those earthquakes triggered an estimated 75-110 million m³ of mass wasting, killed an estimated 1,000 people, destroyed a major oil pipeline, and caused US $1 billion in damages. These events are also of interest because Mount Rainier (Washington State, USA) contains a gravitationally unstable zone of altered rock high on its edifice. The zone could detach during seismic loading and move downslope, eventually reaching heavily populated areas.

Researchers continue to watch the volcano to see if the recent seismicity causes any changes to its normally passive hydrothermal system. Monitoring is done from an observatory in Popayan, 83 km SW.

References. Casadevall, T.J., Schuster, R.L., and Scott, K.M., 29 July 1994, Preliminary report on the effects of the June 6, 1994 Sismo de Paez (Paez earthquake), Southern Colombia: U.S. Geological Survey Response Team, 15 p.

Varnes, D.J., 1978, Classification of mass movements, in Schuster, R.L., and Krizek, R.J. (eds.), Landslides: Analysis and Control: U.S. National Academy of Sciences, Transportation Research Board Special Report 176, p. 11-33.

Geologic Background. Nevado del Huila, the highest peak in the Colombian Andes, is an elongated N-S-trending volcanic chain mantled by a glacier icecap. The andesitic-dacitic volcano was constructed within a 10-km-wide caldera. Volcanism at Nevado del Huila has produced six volcanic cones whose ages in general migrated from south to north. The high point of the complex is Pico Central. Two glacier-free lava domes lie at the southern end of the volcanic complex. The first historical activity was an explosive eruption in the mid-16th century. Long-term, persistent steam columns had risen from Pico Central prior to the next eruption in 2007, when explosive activity was accompanied by damaging mudflows.

Information Contacts: INGEOMINAS, Popayan; T. Casadevall, USGS.

At 0915 on 3 February 1994, a small phreatic eruption took place from the S part of the crater lake. Coincident with the eruption, lake level rose ~1 m. Visual and seismic activity then returned to normal through July. During 7-14 August, the number of volcanic earthquakes and tremor increased compared to earlier in August. The temperature of the light-green crater lake was 39-42°C.

Geologic Background. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor, and tourists are drawn to its waterfalls, hot springs, and volcanic scenery.

Information Contacts: VSI.

On the morning of 15 July a pilot observed steam plumes rising from multiple vents to ~600 m above the summit. FWS personnel in Adak . . . reported steam plumes during 16-22 July. A distinct hot spot . . . was seen on a satellite image from 0906 on 22 July. FWS personnel aboard the RV Tiglax observed incandescent flows on the flank of Kanaga during the night of 27-28 July; low-level steaming from the summit area was continuing. Also in late July the FWS crew saw a blocky lava flow entering the sea on the NW flank, forming a new headland and small cove. Pilots reported incandescent flows on the NW flank during the following week, and steam plumes to 1,500 m altitude. On 10 August the RV Tiglax passed within ~3 km of shore and the crew observed the two NW-flank lava flows for the first time during daylight. Steam was rising from where the flows were entering the sea, and a strong SO₂ odor was detected. Satellite imagery again recorded hot spots . . . during 2-12 August.

At 0500 on 18 August, the FAA received a pilot report of "glowing" at the summit. Pilots reported a light gray, dense steam cloud at 0800 rising to 4,500 m above the summit that had a mushroom-shaped top and was trailing to the E. A satellite infrared image taken at 0836 showed a summit hot spot twice as large as that seen in recent weeks, suggesting an increase in heating associated with production of lava flows. Also visible in the image was a plume extending 15-20 km NE; enhancements of calibrated data suggested that the plume may have contained some ash. Throughout the day, pilots and FWS personnel in Adak observed an eruption cloud consisting of a white, dominantly steam portion, which rose to ~4,500 m altitude, and a vigorously roiling, gray, ash-bearing portion that rose to an estimated 2,400-3,000 m altitude. A loud rumbling, similar to the sound of a freight train, was heard in Adak all afternoon and into the evening. Prevailing winds carried the plume NE, and a light curtain of fallout was observed. Satellite images from 1133 and about 2000 on 18 August showed a plume drifting NE.

The summit hot spot, which on 18 August appeared to have doubled in size, persisted on a satellite image from 1004 on 19 August. No plume was visible that day, although cloud cover may have obscured it. FWS observers reported continued rumbling from the direction of the volcano. Kanaga continued to erupt minor amounts of ash during 20-21 August, interfering with local air traffic and dropping a light dusting of ash on the community of Adak. As of midday on 22 August, analysis of satellite imagery indicated a possible plume, containing minor ash, drifting generally ESE from the volcano over Adak. The FAA enforced a 24-km restricted flight zone around Kanaga until 1430 to minimize the possibility of aircraft encountering an ash cloud during instrument approach and departure. Poor weather obscured the volcano through the morning of 22 August. However, no ash cloud was seen from Adak as visibility improved through the day.

Pilots and other observers continued to report and photograph avalanches of hot fragmental debris cascading down the N flank of the volcano into the ocean. Although AVO has been unable to clearly discern the source of this material, it likely represents collapse of a growing lava dome or ejection of hot blocks of lava from near or within the summit crater. Based on the last eight months of activity, continuing episodes of ash eruption accompanied by avalanching of hot debris down the volcano's flanks can be expected. Depending on wind conditions and the size of a given eruptive episode, additional ashfall on Adak is possible.

. . . .The eruption has been characterized by intermittent, low-level steam and ash emissions producing plumes rarely rising over 3,000-4,500 m altitude and drifting a few tens of kilometers downwind. Although tracking of ash fallout is limited due to the remote location of Kanaga, it appears from satellite imagery that detectable fallout has been confined to within a few tens of kilometers of the volcano. On 22 August, AVO learned that several very light dustings of fine ash on the N portions of Adak had occurred over the past few months.

Geologic Background. Symmetrical Kanaga stratovolcano is situated within the Kanaton caldera at the northern tip of Kanaga Island. The caldera rim forms a 760-m-high arcuate ridge south and east of Kanaga; a lake occupies part of the SE caldera floor. The volume of subaerial dacitic tuff is smaller than would typically be associated with caldera collapse, and deposits of a massive submarine debris avalanche associated with edifice collapse extend nearly 30 km to the NNW. Several fresh lava flows from historical or late prehistorical time descend the flanks of Kanaga, in some cases to the sea. Historical eruptions, most of which are poorly documented, have been recorded since 1763. Kanaga is also noted petrologically for ultramafic inclusions within an outcrop of alkaline basalt SW of the volcano. Fumarolic activity occurs in a circular, 200-m-wide, 60-m-deep summit crater and produces vapor plumes sometimes seen on clear days from Adak, 50 km to the east.

Information Contacts: AVO.

"The . . . eruption continued throughout July with more lava entering the ocean in the W Kamoamoa/Lae Apuki area. On the morning of 8 July, a piece of the Kamoamoa bench, ~4,000 m², fell into the ocean. Littoral explosions following the collapse deposited a small amount of spatter on the delta. A wave associated with the collapse event deposited blocks on the surface of the delta, 40 m inland of the sea cliff. One line of stations, set up to monitor movement of cracks on the active bench, disappeared into the ocean with the collapse. Following the event, the remaining lines recorded several centimeters of seaward movement. The cracks on the bench continued to widen throughout the month. Some of the larger cracks contained standing water.

"Surface activity was confined mostly to the W Kamoamoa/Lae Apuki bench; however, on 11 July, a surface flow broke out of the active tube on Pali Uli. This flow did not reach the ocean before stagnating. There were no significant changes in the Pu`u `O`o lava pond, which was 79 m below the crater rim in July.

"The ocean entries were intermittently explosive, following the 8 July collapse, due to smaller collapses along the front of the bench. Littoral explosions increased in frequency and magnitude later in the month. The most dramatic event began on the afternoon of 26 July. By the following day, large spatter bursts had built a 10-m-high littoral cone on the leading edge of the Kamoamoa/Lae Apuki bench. Explosive activity was initially episodic but was continuous by at least 1810 on 27 July. At 2025 a cascade of lava, about 5 m wide, ripped out of the tube on Pali Uli, from the same area as the 11 July flow. Within 50 minutes, the explosive activity at the ocean had subsided. The cascade on Pali Uli fed flows that eventually stagnated the following day. Activity at the ocean paused briefly, but by 1112 on 28 July, plumes were again visible off the Kamoamoa/Lae Apuki bench. Surface flows broke out on the bench, and by the end of the month extended the bench 5-10 m W."

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

Information Contacts: T. Mattox, HVO.

Ash explosions continued at a rate of 300-450/day in early August. The height of the ash columns, measured from the [Pasuaran Observatory] during clear weather, ranged from 150 to 500 m above the summit, with incandescent projections evident at night. The sporadic eruptions have deposited ash over almost the entire island. During the second week of August, explosion earthquakes averaged 460 events/day. Occasionally, explosion sounds were heard and vibrations felt at the observatory.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: VSI.

"Eruptive activity at Crater 2 continued during July, while Crater 3 activity was at a low level. Throughout the month, Crater 2's normal moderate emissions of thin white-grey vapour were disrupted by forceful ejections of thick, mushroom-shaped, grey-brown ash clouds accompanied by low explosion and rumbling sounds. These caused fine ashfall NW of the volcano. On 16 and 22 July, the ash clouds rose several thousands of meters above the crater. Steady weak night glow was reported on 26 July and there was fluctuating weak-bright glow on the 29th. Crater 3 continued to emit small volumes of mostly white vapour, sometimes with blue and grey vapour. There were no audible sounds or night glow reported during July. Seismic activity throughout the month remained at a low level with between 1 and 7 small low-frequency earthquakes/day."

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

Information Contacts: B. Talai, R. Stewart, and C. McKee, RVO.

Renewed Vulcanian activity during 20-26 July generated plumes up to ~9,000 m altitude, ~4,000 m above the summit . . . . On 20 July at 1630 a grayish column 400-500 m high was emitted from the crater. The next day at 1230 a brownish eruptive column rose 3,000-4,000 m and immediately drifted NE. Very fine ashfall was reported in Salar de Olaroz in the Argentine Puna, 120 km NE of the vent. At 1430 on 23 July another eruption plume to a height of 3,000-4,000 m was blown NNE. No ashfall was reported in the Argentine Puna following this activity.

A single short-lived Vulcanian explosion at about 1200 on 26 July generated a column and NNE-trending plume that soon detached from the volcano; prevailing high-level winds then shifted the plume toward the E. Witnesses from Toconao (35 km NW) and San Pedro de Atacama (70 km NW) reported a moderate explosion followed by a dark-colored mushroom-shaped column that slowly rose to 4,000 m height. Pilots from Aerolineas Argentinas, AeroMonterrey, and Lineas Aereas de Chile reported to the Argentina National Metereological Service that the plume, ~30 km wide and 200 km long, reached an altitude of 9,000 m. Ashfall was only reported in areas close to the volcano. No ashfall was reported in the small village of Catua along the Chilean-Argentine border, 80 km E of Lascar. Immediately after the eruption the volcano showed very diminished activity, with weak white fumarolic plumes that hardly rose above the crater rim. From 27 July to 4 August the volcano exhibited normal fumarolic activity.

Infrared images of the 26 July ash cloud were captured by Raúl Rodano and Luis Ganz from the Meteosat 3 satellite (figure 22). An image taken at 1346 on 26 July showed an ESE-directed plume 50 x 20 km in size, reaching an altitude between 3,600 and 5,400 m (figure 22, top). At 1523 another image showed a 130-km-long plume with the trailing edge located 60 km from Lascar (figure 22, middle). On the E side of the plume, a core (40 km in diameter) developed vertically and reached ~7,000 m altitude. The lower levels of the plume were oriented ESE, following the general atmospheric circulation. Because of wind-shear between 5,400 and 7,000 m, the plume was reoriented NNE by upper-level winds (200°- 70 km/hour). On the image taken at 1631, the plume is 180 km long and 100 km from the source (figure 22, bottom). Based on analysis of this imagery, the NNE-oriented E end of the plume reached an estimated maximum height of 7,500 m. Although the sky was cloudy by 1830, scattered parts of the NNE-oriented plume could be seen 80 km E of Jujuy, Argentina, drifting E at 80 km/hour at an estimated altitude of 4,500 m. With frame animation it was possible to discern the dispersed plume reaching Presidente Roque Saenz Pena city, 800 km E of Lascar, at 2009 on 26 July.

Figure 22. Infrared images of the 26 July 1994 plume from Lascar (white area) taken from the Meteosat 3 satellite. At 1346 (top) the small plume (50 x 20 km) was moving ESE. By 1523 (middle) the trailing edge of the 130-km-long detached plume was located 60 km from the volcano. On the image taken at 1631 (bottom), the plume was 100 km from the source, 180 km long, and the E end was oriented NNE. Approximate location of Lascar is shown by the black triangle; Jujuy, Argentina, is indicated by the white square. Courtesy of Raúl Rodano and Luis Ganz.

These eruptions comprise the fourth period of Vulcanian activity following the large subplinian eruption of 19-20 April 1993. Eruptions were also reported in August and December 1993, and February 1994. All are thought to have been caused by blockage of the degassing magmatic system due to collapse of the dome formed in the late stages of the April 1993 eruption. The present morphology of the crater is unknown, although this renewed activity suggests further subsidence of the crater floor due to conduit degassing. Lascar, the most active volcano of the northern Chilean Andes, contains five overlapping summit craters along a NE trend. Prominent lava flows descend its NW flanks.

Reference. Gardeweg P., M.C., 1994, La Explosion del 26 de Julio, 1994, X Informe sobre el comportamiento del Volcan Lascar: Informe Inedito, Biblioteca Servicio Nacional de Geologia y Mineria, 4 p.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: M. Gardeweg, SERNAGEOMIN, Santiago; J. Viramonte, R. Becchio, I. Petrinovic, and R. Arganaraz, Instituto Geonorte Univ Nacional de Salta, Argentina; B. Coira and A. Perez, Instituto de Geologia Universidad de Jujuy, Argentina; R. Rodano and L. Ganz, Aerolineas Argentinas Weather Division, Buenos Aires, Argentina; H. Corbella, CONICET - Argentine Museum of Natural Sciences, Buenos Aires.

"During July, there was a brief increase in the level of activity from Southern Crater, while Main Crater activity continued to remain at a low level. Activity from Southern Crater was low from 1 to 4 July with gentle emissions of small volumes of white vapour. From 1430 on 5 July onwards, activity increased as weak deep-sounding explosions were heard at 5-10 minute intervals accompanying forceful emissions of grey-brown ash clouds. Incandescent lava fragments were seen being ejected from Southern Crater during the evening until the activity stopped at 2130. Ash emissions continued to occur until 7 July, and only one explosion was heard on 6 July. For the remainder of the month, activity at Southern Crater continued at the normal low level, with only white vapour emissions and blue vapour observed on 12 and 15 July.

"Throughout the month Main Crater continued to emit white vapour, weak to moderate in volume. A whitish-grey plume was seen on 31 July. No sounds were heard and no night glow was observed.

"Seismic activity remained at a low-moderate level throughout the month, with small fluctuations in the number and amplitude of low-frequency earthquakes. On average ~1,170 earthquakes/day were recorded, and there was a brief quiet period from 25 to 27 July when <500 earthquakes/day were recorded. There were no significant tilt changes in July.

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: B. Talai, R. Stewart, and C. McKee, RVO.

An eruption at 0016 on 12 August 1994 sent an ash column to ~6 km altitude, a height of 3,200 m above the summit. Another explosion at 0046 ejected ash 280 m high. From the observatory ~7 km from the crater, observers noted incandescent projections as high as 300 m above the crater rim, accompanied by explosion sounds and vibrations. Ashfall in and around the city of Bukittinggi . . . ranged from 0.5 to 1 mm thick. Shallow volcanic earthquakes were recorded after the explosions, but gradually decreased.

Eruptions during the first half of 1993 (VSI, 1993a) produced lapilli and ash that were deposited in a radius of 1.5-3 km from the active crater. A dark gray column rose as high as 1,200 m above the summit . . . , but was usually in the 400-500 m range. Explosion earthquakes from January to July 1993 fluctuated between 1 and 77 events/day. The frequency of explosions increased in July 1993, but then decreased from August through December (VSI, 1993b). These explosions during Jul-Dec 1993 deposited lapilli and ash within a 750-m-radius of the active crater. Incandescent material fell within a few tens of meters of the crater rim. Average plume height in the second half of 1993 was 400-800 m, reaching a maximum of 3,200 m above the summit. Throughout 1993, deep volcanic earthquakes (A-type) were detected at a rate of 6-41/month. Between 42 and 338 shallow (B-type) events were recorded each month.

Geologic Background. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2000 m above the Bukittinggi plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Information Contacts: VSI.

Scientists from FIU and INETER visited Masaya for about an hour on the afternoon of 26 May 1994 and noted that the two incandescent openings (5-7 m in diameter) in the cooling lava lake observed on 1 March near the N wall of Santiago crater (BGVN 19:03) had coalesced into a single opening 10-12 m long. A sulfur-rich plume was being emitted from the opening at a rate of several pulses/minute; the pulses were accompanied by jetting sounds easily heard from the S rim. Fresh, black ash covered the crater floor immediately SW of the opening. INETER scientists reported that small Strombolian explosions ejected incandescent material from the opening several times during May and June 1994.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: Peter C. La Femina, Michael Conway, and Andrew MacFarlane, FIU; Christian Lugo, INETER.

A nuée ardente erupted around 1400 on 16 July 1994, an event preceded by a clear increase in tilt several days before the eruption. Figure 9 shows tilt measurements during the interval 1-18 July. One set of measurements came from a site on Merapi's summit (Goa Jepang, ~2,900 m elevation); the other set of measurements came from a cave on Merapi's S flank (~1,000 m elevation).

Figure 9. Tilt at Merapi recorded at both the summit and in a cave on the S flank, 1-18 July 1994 Courtesy of Arnold Brodscholl.

The daily temperature variation in the cave is<1°C, suggesting little influence from temperature there (left-hand scale). The daily record of tilt varied significantly less at the cave site (typically <100 µrad) than at the summit site (typically ~150 µrad), an observation consistent with the more stable temperature in the cave.

Tilt began increasing at both sites roughly five days prior to the eruption. During this interval the tilt at both sites correlated consistently overall, and moderately at the finer-scale. Tilt ceased to track consistently near the end of the eruption, when the flank site underwent a dramatic decrease, a turn-around that began prior to the end of the eruption. Summit tilt measurements in January 1993 were similar to those presented here but then measurements at the cave site were a rarity, leaving the increased tilt without confirmation.

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

Information Contacts: A. Brodscholl, GMU; Subandryo, VSI; B. Voight, Pennsylvania State Univ.

Beginning on 11 June, scientists from FIU and INETER deployed a datalogger in the crater to continuously monitor fumarole temperatures and barometric pressure. The team entered the summit crater three times along a trail that crosses an active avalanche chute and leads around to the NE crater rim. Condensate and Giggenbach-type samples were collected from fumaroles along the SW crater wall. These fumaroles were very corrosive, as indicated by the destruction of the datalogger thermocouples, and had temperatures ranging from 238 to 655°C. A voluminous plume was rising from the crater on 13 March.

Geologic Background. Momotombo is a young stratovolcano that rises prominently above the NW shore of Lake Managua, forming one of Nicaragua's most familiar landmarks. Momotombo began growing about 4500 years ago at the SE end of the Marrabios Range and consists of a somma from an older edifice that is surmounted by a symmetrical younger cone with a 150 x 250 m wide summit crater. Young lava flows extend down the NW flank into the 4-km-wide Monte Galán caldera. The youthful cone of Momotombito forms an island offshore in Lake Managua. Momotombo has a long record of Strombolian eruptions, punctuated by occasional stronger explosive activity. The latest eruption, in 1905, produced a lava flow that traveled from the summit to the lower NE base. A small black plume was seen above the crater after a 10 April 1996 earthquake, but later observations noted no significant changes in the crater. A major geothermal field is located on the south flank.

Information Contacts: Peter C. La Femina, Michael Conway, and Andrew MacFarlane, FIU; Christian Lugo M., INETER.

High lava fountaining in early July took place from a new vent on the W flank, named Kimera. Located ~100 m S of the 1971 Rugarama cone, this vent became active at 2148 on 4 July, but remained active for only 4-5 days. The lava flows generally moved W until at least 10 July, when the flows reached their maximum extent. By 11 July, the small lake (Magera) at the E foot of a Precambrian escarpment was entirely filled and dried by the flow. High SO₂ concentrations detected by the TOMS during 5-10 July were most likely caused by this activity at Nyamuragira and not from the lava lake at Nyiragongo. Nyamuragira also emitted levels of SO₂ detectable by satellite during 17-19 July 1986 (275-375 ± 30% kt) and on 24 September 1991 (20 kt).

A press report described falls of both ash and Pele's hair during the first half of July in the Mokoto Hills, above the W escarpment of the rift ~20 km from the volcano. Several farmers reported problems caused by cattle eating ash-laden grass.

Long-term monitoring data indicated an apparent acceleration in seismo-geodetic activity in the past 10 years. Seismicity steadily increased from <200 volcanic events/month in 1960-65 to ~300-400/month in the early 1980's (figure 13). Increased seismicity after 1985 suggests an acceleration of magma supply into the volcano. The geodimeter network operating on the Nyamuragira summit has also revealed a gradual strain increase since 1980, showing that the crater is dilated.

Figure 13. Monthly number of volcanic earthquakes at Nyamuragira, 1960-92. The short-period seismic station is located 110 km from the volcano. Vertical arrows indicate flank eruptions. Courtesy of H. Hamaguchi.

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

Information Contacts: N. Zana, Centre de Recherche en Géophysique, Kinshasa; H. Hamaguchi, Tohoku Univ; J. Durieux, GEVA, Lyon, France; G. Benhamou, Libération newspaper, France; T. Casadevall, USGS; I. Sprod, GSFC.

For four days around 14 July a dense steam-and-gas plume was visible from Goma, and red glow could be seen at night. An amateur video taken on an unknown day between 19 and 24 July included a 6-second partial view of the crater that revealed a large very active lava fountain roughly in the center of the crater. A large, flat spatter cone had been built, with a least three large openings in the walls and lava flows radiating from the openings. The entire lava lake was not active. The background was hidden by gases and clouds, making it impossible to determine the elevation of the lava lake surface. Following the 1982 activity, the surface was 400 m below the crater rim. A very strong red glow was again observed above the crater during the night of 29 July. Very little red glow was reported in early August.

Another eruption within the summit lava lake began at about 1900 on 10 August. Red glow above the summit could be seen from Goma during daylight as well as at night. Press reports also stated that "ash and dust" had been emitted from the volcano. The increased activity on 10-13 August and strong red glow visible from the refugee camps caused some concern among the refugees and relief workers.

Volcanologists from Zaire, Japan, France, and the USGS were all present in Goma from 19 to 23 August. The primary purpose of the USGS scientists was to evaluate the hazards posed to the ongoing relief operations in Goma, which contained more than one million Rwandan refugees and the large Zairian population. Specific hazards addressed included the threat of active lava flows to resettlement camps and infrastructure, the threat of volcanic ash to air relief operations, and the threat of CO₂ accumulation to refugees in resettlement camps along the Goma-Sake road.

During the flight to Goma on 19 August, USGS volcanologists flew over and around the crater. Although the crater floor was clearly visible, no signs of activity were observed. However, during the pre-dawn hours on 20 August, strong red glow above the main crater could be seen. Early that morning the French Army flew USGS and French volcanologists to the summit. At that time the lava lake was very active, with fountaining of lava up to 40 m above the surface of the crater floor, estimated to be ~450 m below the crater rim. Seismograms from instruments operated by Zairan scientists clearly showed this eruptive activity. The eruption-related seismicity had ended by 22 August, and no additional red glow was noted. No activity was observed during an aerial inspection the next day, but red glow was again seen early on 24 August.

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: H. Hamaguchi, Tohoku Univ; J. Durieux, GEVA; T. Casadevall and J. Lockwood, USGS; AP.

Despite roughly 3 months of rainy weather, the colorful northernmost crater lake that evaporated this past year remained nearly dry, venting became alarmingly noisy, and in the interval from 9 July to 5 August the volcano produced a series of ash falls. These falls were carried to the SW and covered a roughly 56 km² area.

Increased vigor of fumaroles has led to vapor columns reaching >1 km above the lake floor; the columns were blown to the W and SW. Some of the columns were red to orange in color, presumably due to combustion of sulfur. In the recent past the most vigorous fumaroles were located near the former lake's center. These fumaroles diminished in size; during July the ones located SW of the former lake were of greatest importance.

On 21 July, a fumarole S of the former lake generated a white-colored column; thermocouple measurements of the fumarole revealed a 495°C temperature. The highest pressure fumarole, also located S of the former lake, emitted a red- to orange-colored plume. Continuously jetted gases contained entrained sediment. These escaping gases had a temperature of 515°C, measured with a pyrometer aimed toward the vent. Other fumaroles issued sporadic sediment and colored gases; temperature at the dome was 81°C. ICE and ECG reported jetting gases thrusting to 350 m above the crater floor and then rising convectively to 1 km. Using infrared thermometry, temperatures as high as 700°C were measured in the S-vent area.

Ash was erupted on the night of 9 July and into the morning of 10 July. Continued reports of ash fall came from San Miguel Arriba, Trojas, San Luis de Grecia, Cajon, and Porvenir de Sarchi (figure 53). These reports continued for 2 days; later, mapping and compilation led to an ash distribution map for this and later eruptions in July (figure 53). Blocks were principally limited to the crater area, fine ash covered much of the summit area, and the finest ash blew as far as about 15 km. The fumaroles ejecting lake sediment continued to grow, and ejected ash with blocks. Such events were noted seven times in late July (24, 25, 27, 28, 29, and twice on 30 July). In general, the strongest ash eruptions were accompanied by loud jet-like noises.

Figure 53. Distribution of ash from Poás during July 1994. Scale is approximate; roads indicated by dashed lines, rivers by solid lines, and settlements by dots. Courtesy of OVSICORI-UNA.

OVSICORI-UNA reported July seismicity from station POA2 (2.5 km SW of the active crater) in terms of several types of events (figure 54). In July, a total of 4,994 events took place. Starting on 26 July several high-frequency (volcano-tectonic) earthquakes took place each day.

Figure 54. Poás seismicity for July 1994. Courtesy of OVSICORI-UNA.

The amount of deformation on two distance-measurement lines has, since 1973, shown a tendency toward contraction, amounting to about 0.7 and 1.8 ppm/month, respectively. Between 24 June and 5 July both lines suddenly contracted about 19 ppm. From 22 July until the end of the month there were no further significant changes. Back in the interval between 8 March and 12 May a component of two leveling lines deflated slightly (10 µrad). During the last re-occupation of the leveling lines, which took place at the end of July, one line 2 km S of the active crater had inflated by about 17 µrad.

The increased degassing has led to a variety of health and environmental problems. Crops and soils have been damaged. Residents on the W and SW flanks continue to report irritations to the throat, skin, and eyes when gases and ash enter their communities.

On the morning of 22 August an American Airlines flight reported an eruption cloud to ~6 km. Visibility over Poás was poor due to thunder storms to the E and clouds in its vicinity; satellite imagery was unable to detect the plume. Jorge Barquero described this plume as consisting of vapor and gas. A plume on the previous day reached to about 2 km above the vent; heights of these plumes were highly dependant on local wind conditions. As of 22 August, no confirmed ash-bearing plumes had erupted since 5 August.

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

Information Contacts: E. Fernández, J. Barquero, V. Barboza, R. Van der Laat, F. de Obaldia, and T. Marino, OVSICORI; G. Soto, G. Alvarado, and F. Arias, ICE; M. Mora, C. Ramirez, and G. Peraldo, UCR.

"July was relatively quiet, with 220 detected earthquakes . . . . Activity was highest in the middle of the month, with half the earthquakes occurring between 13 and 19 July, and two swarms on those days. Most of the earthquakes, including the 13 July swarm, were located on the NE portion of the ring fault on the E side of Greet Harbour at depths of 0-4 km. Most of the rest were located near the W portion of the ring fault. An exception to this was the swarm on 19 July, which was located, albeit poorly, in the center of Karavia Bay. None of the earthquakes were large enough to be felt. The largest earthquake during the month, M 2.7, occurred on 5 July. Leveling measurements on 19 July showed a very small amount of subsidence, <9 mm, at the end of Matupit Island since 27 June.

"On 13 July, signals were recorded from three earthquakes that originated outside the network, somewhere N of Rabaul. S-P times between 2 and 4 seconds were consistent with locations near Tavui caldera, an underwater caldera N of Rabaul. This caldera was only discovered in 1984 and virtually nothing is known about it. Records are currently being checked for any other seismic activity that may have come from this vicinity."

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: B. Talai, R. Stewart, and C. McKee, RVO.

When visited on 8 June, Crater Lake appeared a very pale, almost yellowish, gray. On 4 July, as was more typical for the recent past, the crater lake was a uniform battleship-gray with no evidence of convection or slicks. Temperature at Outlet, 22°C, was slightly higher than for June-July in past years. The lake is currently cooling following a minor heating event in early June that followed strong acoustic signals, minor earthquakes, and volcanic tremor 10-15 days earlier. These two recent visits revealed no evidence of eruptive activity.

On 4 July, unusually thick accumulations of snow prevented deformation surveys and emphasized the need to install tiltmeters in key locations to improve the continuity of monitoring. Snow and ice were removed from the ARGOS satellite installation, but the solar panel could not be located under deep snow and battery and transmission power steadily declined.

A working party coordinated by the Ministry of Civil Defence has considered developing a contingency plan for volcanic hazards. They also may adopt a system using "Volcanic Alert Levels" graded from 1 (low level) to 5 (highest level, hazardous eruption in progress).

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: P. Otway, B. Scott, and A. Hurst, IGNS Wairakei.

Eruptive activity on 3 February 1994 produced ashfalls, lava avalanches, and pyroclastic flows, destroying a village and killing 6 people (19:01). Total volume of the pyroclastic-flow deposits was about 6 million m³.

During 5-14 August observations, visual and seismic activity . . . were normal. The daily number of explosion earthquakes fluctuated between 40 and 100 events, and volcanic tremor was occasionally recorded with a maximum amplitude of 4 mm. Ash eruptions generated clouds up to 500 m above the summit. There were no pyroclastic flows or lava avalanches.

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

Information Contacts: VSI.

An eruption on 31 July produced a gas-and-ash column that rose ~800 m above the 1,060-m-high summit. Ashfall was reported SW of the volcano (figure 6). Phreatic activity continued until 12 August with gas emission and minor ash explosions. Seismicity has been recorded continuously since December 1993, when a permanent telemetered seismic station (TELN: short-period, vertical-component) was installed ~500 m E of the active crater rim (figure 7). Also since December 1993, the Instituto Nicaragüense de Estudios Territoriales (INETER) has collaborated with the government, local authorities, civil defense, and the media, to educate the population about the situation at the volcano. Due to the relatively low magnitude of this eruption, it was not necessary to carry out the prepared evacuation plans.

Figure 6. Ashfall from Telica, 31 July-6 August 1994. Courtesy of INETER.

Figure 7. Sketch map of the summit area at Telica, showing locations of crater fumaroles (left) and seismic stations (right). Courtesy of INETER.

A seismic event on 15 June 1994 was recorded by several stations of the Nicaraguan seismic network, up to distances of ~40 km from Telica. This event at a depth of 6 km had a maximum magnitude of 2.1. The 31 July eruption was preceded by a steady increase in seismicity during 15-25 July (figure 8), recorded by station TELN. Seismicity had increased from25 events/day at the end of May. By the end of July there were up to 150 events/day.

Figure 8. Seismicity at Telica, February-August 1994. Courtesy of INETER.

Crater and fumarole observations, March-June 1994. Beginning on 3 June, scientists from Florida International Univ (FIU) and INETER spent 15 days at Telica as part of an ongoing investigation to determine the areal extent and intensity of degassing, and the role of structural controls on degassing from the volcanic complex. A lacustrine deposit was observed in March at the S end of the crater, and a small, muddy brown lake was visible in May-June. All observations were made from the NE rim, where jetting sounds were clearly audible. Sulfur-rich steam from the crater sometimes moved down the slopes of the volcano, filling the NW valley with high concentrations of SO₂; sulfur odor could occasionally be smelled on the NE slope. Residents on the flanks of the volcano stated that the activity was not unusual for this time of the year.

Fumarole temperatures near station TELN were in the 81-86°C range, similar to temperatures in September 1993 and March 1994. A low-temperature fumarole was discovered on the lower ESE slope of the ridge occupied by the seismic station. A data-logger recorded fumarole temperatures and barometric pressure for four days. Fumaroles near TELN and in the active crater exhibited increased flux since March. At times the crater fumaroles appeared to be emitting steam and gases in discrete clouds at intervals of several minutes. The most intense fumarole was in the upper NW corner of the crater (A on figure 7). Other fumaroles were observed in the lower NW corner, on the N, E, and SE crater walls, and in avalanche deposits on the S and SE parts of the crater floor. Fumarole A had temperatures of 150-160°C in July 1994 (figure 7). In the NE corner of the crater, fumarole B increased in temperature from 55°C in April to 174°C in July. Another fumarole area on the E side of the crater (C) had a temperature of 498°C in July, a significant increase from 246°C in 1990.

Eruptive activity. A relatively small explosive eruption at about 1645 on 31 July produced a gas-and-ash column that rose ~800 m above the summit. The light-gray ash cloud was driven SW by the wind, depositing about 2 mm of ash in the towns of Chichigalpa (20 km WSW), Quezalguaque (12.5 km SSW), and Posoltega (16 km SW) (figure 6). No seismic events were felt by residents near the volcano, but the sound of the explosion was heard at distances up to 10 km.

Following the 31 July eruption, phreatic activity continued in the next hours and days with varying intensity of gas emanation and ash expulsion. One of the strongest explosions, on 5 August, produced an ash column 1,200 m high. One phase of gas emission reached heights of 200-300 m above the crater rim. Gas also filled a valley W of the volcano with high concentrations of SO₂, sometimes causing breathing problems for INETER scientists who traveled through the valley at a distance of ~2 km from the crater. Seismicity at shallow depths (~2 km) beneath the crater was recorded by TELN and four stations installed after the eruption began: telemetric stations TEL 2, 3, & 4, and local digital registration station TEL 5 (figure 7). The numerous weak events during the eruption were only recorded by the local seismic stations.

Chemical analyses of washed ash samples collected on different days indicated an increase of the SO₄^2- and Cl^- contents over time. Several very heavy rainfalls occurred during the eruptive period. Analyzed rainwater samples also showed high concentrations of SO₄^2- with respect to Cl^- and F^2-, and a corresponding low pH level. Similar measurements two weeks before the eruption showed normal low concentrations of SO₄^2- and Cl^-.

Early eruption products consisted of very fine-grained, light-colored, blocky ash. INETER volcanologists believe that the ash was non-juvenile, and was ejected during phreatic or phreatomagmatic eruptions. Major explosions generally lasted for ~10-25 minutes. Early eruption columns were mostly white in color, and ranged from several hundred meters to 1,400 m above the vent. On 9 and 10 August, the ash was black, significantly darker than before, with correspondingly darker eruption plumes. The ash remained blocky and non-vesicular.On 10 August, 40-50 high-frequency seismic events were recorded, including one that lasted 4.5 hours. High-frequency events prior to 10 August occurred at a rate of ~70-90/day and were associated with more frequent explosions (10-20/day). The number of daily explosions also decreased to 6 on 10 August, including one major explosion that lasted for 16 minutes. An explosion at 1800 on 11 August generated a plume that rose 350 m, but only 16 high-frequency events were detected that day. On the early morning of 12 August one of the strongest explosions of this eruption occurred; activity then decreased throughout the day. By that evening the explosions had stopped and gas emanation and seismicity reached very low levels.

Seismicity had increased slightly by 16 August, five microseismic events were detected during 24 hours on 17-18 August, and on 20 August tremor lasted for 6.2 hours. However, no seismic events were detected on 21-22 August, and activity remained low as of 26 August.

On 23 August, Oto Matias (INSIVUMEH, Guatemala) arrived with a COSPEC instrument to assist INETER scientists in making SO₂-flux measurements. Attempts to carry out COSPEC measurements of the SO₂ concentration in the gas plume were made on 24 August, but low levels of gas emission and cloudy skies prevented good results.

Soil sampling. During three field surveys by FIU and INETER scientists in early June, >60 stations were deployed over 50 km² to determine the concentration of radon (Rn), CO₂, Hg, and He in soils. One identified anomaly had intensified between March and May/June 1994. This anomaly, ~750 m long and 250 m wide, surrounded the TELN seismic station. Along this anomaly, Hg values ranged from several tens of ppb to >2,900 ppb, He from 5,399 to 5,415 ppb, CO₂ to 2.1 volume %, and Rn to 1,819 pico-Curies/liter.

San Jacinto Hot Springs. The village of San Jacinto, 9 km NE of the town of Telica and 2 km E of Santa Clara volcano, contains a field of boiling mudpots (BGVN 19:03). Soil samples for Hg and CO₂ measurements were collected from the hydrothermal field in March and May/June 1994. The March samples contained CO₂ concentrations up to 0.09 volume % and Hg from 6,710 to 21,512 ppb. The onset of the rainy season had resulted in an increase in both the size of the field and the steam flux since 9 March. Exploration for a new geothermal power plant was taking place approximately 250 m WNW.

Historical activity. Telica is a composite volcano located 19 km N of León at the NW end of a large volcanic complex. Known historical activity dates from a strong eruption that occurred in 1527-29. Strong activity was also noted in 1685, 1740-43, and at least 7 times in the 20th century. During several eruptions ash has damaged agricultural crops. In February 1982 several strong explosions generated ash columns of 3.5 km height and the ashfall affected nearby towns. The most recent eruption of Telica in November 1987 included Strombolian-type activity.

Eruptions in pre-historical times produced ash deposits of 50 cm thickness or more within a radius of 50 km. A volcanic hazard map (figure 9) suggests that ashfall poses the greatest threat to the local population. Lava flows have occurred, but with low frequency, most recently ~1,000 years ago. The hazard zone for pyroclastic eruptions lies within ~2 km of the crater. Lahars have occurred as a result of very strong eruptions during the rainy season.

Figure 9. Volcanic hazards map of Telica. Hazard zones are shown for ashfall and tephra, lava flows, and column collapse. Courtesy of INETER.

Geologic Background. Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Information Contacts: H. Taleno, L. Urbina, M. Navarro, O. Canales, C. Guzman, C. Buitrago, A. Izaguirre, Christian Lugo M. (Vulcanology); W. Strauch (Seismology); C. Urbina, and A. Acosta (Electronics), INETER, Managua; Peter C. La Femina, Michael Conway, and Andrew MacFarlane, Florida International Univ, USA.

"The level of activity . . . was slightly lower in July . . . . The summit crater continued to emit mainly white vapour, of variable volume. Faint blue vapour emissions were seen on 3, 5, 9, and 20 July. No sounds or night glow were reported.

"Seismic activity . . . continued the pattern of previous months, with mainly sub-continuous, low-level, low-frequency tremor, and the occasional larger low-frequency earthquake. Only two high-frequency earthquakes were recorded during the month. Amplitude measurements and RSAM monitoring were made difficult at the start of the month by storm-generated noise. However, both showed a gradual increase through the month until about 23 July when there were sharp drops; gradual increases were again seen through the end of the month."

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: B. Talai, R. Stewart, and C. McKee, RVO.

Lobe 13 . . . grew endogenously at slow rates until late-July. Its final size was ~80 m long, 70 m wide, and 30 m high; it lies hidden behind the roughly 10x longer lobe 11, which forms the prominent bulge on figures 73 and 74.

Figure 73. Sketch of the Unzen lava done showing features of the 22 July photograph (figure 74); view is roughly [from] the N. Vegetated surfaces are shown in black, undifferentiated dome, talus, pyroclastic-flow, and other deposits shown lightly shaded. Courtesy of S. Nakada.

Figure 74. Photograph of the lava dome at Unzen, 22 July 1994. Taken from a helicopter looking [from] approximately N. Courtesy of S. Nakada.

In Unzen's summit area, the endogenous dome developed three E-W trending ridges along its top. The highest (central) ridge uplifted in early-July between two other ridges. The central ridge and a N ridge moved to the N at a rate of ~2 m/day during July, leaving behind the S ridge and increasing the width of a graben between them. The central ridge also rose vertically at a rate of <1 m/day. The E part of the central ridge consisted of brown-colored massive lava that was rounded, convex upward, and relatively smooth. The ridge was composed of massive lava squeezed from the interior of the dome, an effect also seen in April. When the lava reached the top of the ridge it broke and collapsed.

The ridges stopped moving N at the end of July. Occasionally there were small, low-density rockfalls to the SW in early- to mid-August. Owing to fragmentation, the massive lava of the central ridges decreased its height by ~20 m during the first two weeks in August, and at the same time the talus slope hardly advanced in any direction. These observations imply that for this two-week period in August an extremely low eruption rate (estimated at 4m³/day) prevailed.

During mid-July to early-August a continuous rain of N-directed rockfalls occurred when the N ridge became exposed at the cliff top. These rockfalls transformed into small pyroclastic flows, generally with run-out distances under 1 km. Pyroclastic flows were detected seismically at a station 1 km WSW of the dome and real-time monitoring of the dome was accomplished by four sets of visible and thermal infrared video cameras. During July this system detected 44 pyroclastic flows.

During most of July, microearthquakes beneath the dome generally took place <80 times a day. The total number of earthquakes in July was 2,488, roughly a 20% drop from the previous two months.

EDM by the JMA and the GSJ found that during late-June through mid-July the radial distance to one reflector on Unzen's N flank shortened rapidly, by tens of centimeters/day. The lack of confirmation from other reflectors suggested that the area in motion was of limited size.

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

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

Routine monitoring visits on 23 April and 28 June 1994 found no evidence of any eruptive activity. On 23 April the floor of Princess Crater was occupied by a muddy pond that contained fresh landslide debris (see figure 21). The divide between Wade and Royce craters had been destroyed. Active fumaroles included those in TV1 Crater, and those escaping from beneath landslide debris in the Royce area.

Scientists who made brief trips on 12 and 15 May noted 5-10 m subsidence of the lake occupying the active vent area on the floor of Wade Crater; the lowered lake level persisted until at least 29 May. A triangulation survey on 28 June determined the lake to be 56 m below sea level and 92 m below the rim of the 1978/90 Crater Complex.

Deformation was surveyed in nearly ideal conditions on 28 June, achieving a good error of closure; the results showed that since 19 January 1994 a subtle but significant crater-wide uplift, typically 5-10 mm, has taken place. Stronger uplifts occurred at Donald Mound (+15 mm) and SE of Peg M (+21 mm). This kind of crater-wide inflation was last seen in the three years preceding the 1976-93 eruptions.

A magnetic survey of established sites revealed a pattern of net magnetic changes very similar to the two previous periods of measurements in 1993. A negative anomaly lay to the N of Donald Mound (-100 nT), and a positive one to the S (+60 nT). P. Rickerby noted that "these anomalies could be interpreted as resulting from shallow heating under Donald Mound (~50 m deep) and shallow cooling under TV1."

Seismicity recorded during January-June 1994 has generally showed little change; tremor in this interval has remained near background, though it has been present on 54% of the obtained records.

Geologic Background. Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project.

Information Contacts: T. Hunt, B. Scott, T. Kabayashi, and T. Tosha, IGNS, Wairakei; P. Rickerby, Victoria Univ, Wellington.

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/).