Italy's Mount Etna on the island of Sicily has had historically recorded eruptions for the past 3,500 years and has been erupting continuously since September 2013 through at least March 2019. Lava flows, explosive eruptions with ash plumes, and Strombolian lava fountains commonly occur from its summit areas that include the Northeast Crater (NEC), the Voragine-Bocca Nuova (or Central) complex (VOR-BN), the Southeast Crater (SEC, formed in 1978), and the New Southeast Crater (NSEC, formed in 2011). A new crater, referred to as the "cono della sella" (saddle cone), emerged during early 2017 in the area between SEC and NSEC and has become the highest part of the SEC-NSEC complex. After several months of low-level activity in early 2018, increases in Strombolian activity at several vents began in mid-July (BGVN 43:08). This was followed by new lava flows emerging from the saddle cone and the E vent of the NSEC complex in late August and discontinuous Strombolian activity and intermittent ash emissions through November 2018 (BGVN 43:12). An eruption from a new fissure produced a lava flow into the Valle del Bove in late December 2018 and is covered in this report along with activity through March 2019 that included frequent ash emissions. Information is provided primarily by the Osservatorio Etneo (OE), part of the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV).

For the first three weeks of December 2018, Strombolian activity and ash emissions continued from the summit vents. A series of small flows from multiple vents near the scoria cone inside NSEC formed a small flow field on the E flank mid-month. A lateral eruption from a fissure on the SE flank of NSEC opened on 24 December and produced a series of flows that traveled E into the Valle del Bove for three days. Sporadic ash emissions, some with dense plumes and significant SO₂ emissions, were typical throughout January and February 2019. Activity declined significantly during March 2019 to minor ash emissions and ongoing outgassing from the summit vents. The MIROVA plot of thermal energy recorded the increased heat from the lava flows during December 2018, along with minor pulses from the ash emissions and Strombolian activity in January and February (figure 240).

Figure 240. The Etna MIROVA thermal anomaly data for 5 July 2018 through March 2019 showed a spike in thermal activity from lava flows and increased Strombolian activity in late August and during December 2018. Courtesy of MIROVA.

Activity during December 2018. Strombolian activity, with modest ash emissions, continued from the Bocca Nuova, NSEC, and NEC during the first three weeks of December. Lava flowed from the scoria cone located within the E vent of NSEC and was associated with incandescent blocks rolling down the E flank of NSEC. Variable Strombolian activity at the scoria cone beginning on 4 December produced continuous overlapping small flows from several vents near the scoria cone for two weeks (figure 241). Intermittent explosions lasted 5-10 minutes with similar length pauses; activity increased on 16 December with near-continuous lava effusion. Several small flows traveled NE, E, and SE down the E flank of NSEC during the second and third weeks of the month (figure 242). A few flows reached the base of the cone at 2,900 m elevation and were almost a kilometer in length. Small collapses of portions of the lava field also produced minor plumes of ash.

Figure 241. Map of the summit crater area at Etna (DEM 2014). Black hatch lines outline the edge of the summit craters: BN = Bocca Nuova, with the north-western depression (BN-1) and the south-eastern depression (BN-2); VOR = Voragine; NEC = Northeast Crater; SEC = Southeast Crater; NSEC = New Southeast Crater. Yellow circles are degassing vents, and red circles are vents with Strombolian activity and/or ash emissions. The cooling lava field from the E vent scoria cone at NSEC is shown in yellow; the red flows were active on 17 December 2018. Courtesy of INGV (Report 51/2018, ETNA, Bollettino Settimanale, 10/12/2018 - 16/12/2018, data emissione 18/12/2018).

Figure 242. The scoria cone inside the E vent of NSEC at Etna produced multiple small lava flows and Strombolian explosions for most of the first half of December 2018. (a) Strombolian activity at the scoria cone inside the E vent of the New Southeast Crater, seen from Milo (on Etna's eastern slope) on 11 December 2018. (b) Summit area of Etna seen from the south on 11 December 2018. (c) Eastern flank of the New South-East Crater seen from Fornazzo (eastern slope of Etna), with Strombolian activity and lava flows on 16 December 2018. (d) Active lava flows seen from Zafferana (eastern slope of Etna) on 16 December 2018. Courtesy of INGV (Report 51/2018, ETNA, Bollettino Settimanale, 10/12/2018 - 16/12/2018, data emissione 18/12/2018).

A lateral eruption and intense seismic swarm began on 24 December 2018 from a nearly 2-km-long fissure trending NNW-SSE on the SE flank of NSEC; it produced a flow into the Valle del Bove and covered about 1 km² (figures 243). The other summit craters produced intense Strombolian activity and abundant ash emissions during 24-27 December. Beginning around 0800 local time on 24 December, degassing intensity from the summit craters increased significantly. In the following hours, intermittent reddish-gray ash emissions rose from Bocca Nuova and NEC becoming continuous by late morning. Shortly after noon, an eruptive fissure opened up at the southeastern base of NSEC, releasing intense Strombolian activity which rapidly formed a dense plume of dark ash. A second smaller fissure located between NSEC and NEC also opened at the same time and produced weaker Strombolian activity that lasted a few tens of minutes. Over the following two hours, the main fissure spread SE, crossing over the western edge of the Valle del Bove and reaching down to 2,400 m elevation. Continuous Strombolian activity of variable intensity occurred at NEC and Bocca Nuova. The ash cloud created by the multiple eruptive vents generated a dense plume that drifted SE, producing ashfall mainly in the area around Zafferana Etnea and Santa Venerina (figure 244).

Figure 243. Preliminary map of the lava flows and scoria cones at Etna active during the eruption of 24-27 December 2018. The topographic base used was provided by TECNOLAB of the INGV Catania Section Observatory Etneo, Laboratory for Technological Advances in Volcano Geophysics. The abbreviations at the top left identify the various summit craters (NEC = North-East Crater, VOR = Voragine, BN = Bocca Nuova, SEC = South-East Crater, NSEC = New South-East Crater). Courtesy of INGV (Report 01/2019, ETNA, Bollettino Settimanale, 24/12/2018 - 30/12/2018, data emissione 01/01/2019).

Figure 244. Eruptive activity from the fissure at Etna that opened on 24 December 2018 included multiple flows, Strombolian explosions, and a significant ash plume that caused ashfall in nearby communities. Top left: The eruptive fissure opened near the edge of the western wall of the Valle del Bove. Top right: An ash and steam plume produced by the opening of the fissure, taken from the south. Bottom left: Ash fall on a sidewalk in Zafferana Etnea. Bottom right: Multiple lava flows were fed by an eruptive fissure that opened along the western wall of the Valle del Bove. Images taken on 24 December by B. Behncke. Courtesy of INGV (25 dicembre 2018, Redazione INGV Vulcani, L'eruzione laterale etnea iniziata il 24 dicembre 2018).

As the fissure opened it fed several flows that descended the W face of the Valle del Bove (figure 245), past Serra Giannicola Grande, merged into a single flow at the base of the wall, and continued E across the valley floor. Ash emissions decreased significantly from Bocca Nuova and NEC after 1430 on 24 December. By 1800 the fissure was active mainly at the lower end where it continued to feed the flow in the Valle del Bove with strong Strombolian activity and abundant ash emissions. Around 1830 intense Strombolian activity resumed at Bocca Nuova along with abundant ash emissions which gradually decreased overnight. Effusive activity from the fissure continued through 26 December when it decreased significantly; new lava feeding the flow ended on 27 December, but the flow front continued to move slowly (figure 246). Degassing continued at Bocca Nuova, forming a dilute ash plume that drifted hundreds of km S before dissipating. A persistent SO₂ plume was measured with satellite instruments drifting SSE during 25-30 December while the eruptive fissure was active (figure 247).

Figure 245. Visual and thermal images of the 24-27 December 2018 fissure vent at Etna taken on 26 December 2018. (a) The eruptive fissure (yellow arrows) opened on 24 December 2018 along the W wall of the Valle del Bove and sent fresh lava down the wall (black areas), the yellow dashed rectangles indicate the areas shown with thermal images in c and d. (b) The crew that carried out the overflight on 26 December, using the helicopter of the 2nd Coast Guard Air Force in Catania. (c) and (d) are thermal camera images of the eruptive fissure that highlight the flows moving down the W wall of Valle del Bove. Visible image photo by Marco Neri. Thermal images by Stefano Branca. Courtesy of INGV (Report 01/2019, ETNA, Bollettino Settimanale, 24/12/2018 - 30/12/2018, data emissione 01/01/2019).

Figure 246. The flow from the fissure eruption at Etna traveled past Serra Giannicola Grande and E into the Valle del Bove during 24-27 December 2018. By the time of this image at 1600 on 27 December, the lava flows were no longer being fed with new material and were almost stationary within the Valle del Bove. Photo by Marco Neri, courtesy of INGV (Report 01/2019, ETNA, Bollettino Settimanale, 24/12/2018 - 30/12/2018, data emissione 01/01/2019).

Figure 247. The OMPS instrument on the Suomi NPP satellite measured significant SO2 plumes from Etna during the December eruptive episode, shown here by data on (clockwise from top left) 25, 27, 29, and 30 December 2018. The SO2 plumes on these days all drifted SSE from Etna. Courtesy of NASA Goddard Space Flight Center.

A significant increase in the release of seismic strain and frequency of earthquakes began around 0830 on 24 December 2018. Around 300 events occurred during the first three hours of increased seismicity which continued throughout the week, with over 2,000 events recorded in different areas around Etna. The initial swarm was located in the summit area near the fissure with events located 0-3 km below sea level; subsequent seismicity was located in the Valle del Bove and included multiple earthquakes with magnitudes greater than M 4.0. The E and SW slopes of the volcano were also affected by seismic events. The largest earthquake (M 4.8) was recorded on 26 December at 0319 local time, located about 1 km below sea level between the towns of Fleri and Pennisi on the Faglia Fiandaca fault. It was widely felt in many urban centers and caused damage in some areas. INGV noted that it was likely not generated by movement of magmatic material in the epicentral area.

Activity during January 2019. No lava flow activity was reported in January, but sporadic ash emissions and weak Strombolian activity persisted at NEC and Bocca Nuova (figure 248); occasional nighttime incandescent bursts were seen from Voragine. During one of these ash-emission episodes, on the evening of 18 January, fine ashfall was reported on the SE flank in the towns of Zafferana Etnea and Santa Venerina. Slight increases in volcanic tremor amplitude accompanied incandescent flashes from Voragine crater on the evenings of 16 and 18 January and in the early morning of 21 January (figure 249). On 19 January gas emissions and explosions were reported from a new vent near the NE edge of VOR, about 40 m NW from the 7 August 2016 vent (figure 250).

Figure 248. Strong degassing from the summit craters at Etna was accompanied by ash emissions from NEC on 16 (a) and 19 January 2019 (b). The images were taken with the high-resolution webcam at Monte Cagliato (located E of Etna). Courtesy of INGV (Report 04/2019, ETNA, Bollettino Settimanale, 14/01/2019 - 20/01/2019, data emissione 22/01/2019).

Figure 249. Episodes of strong incandescence appeared at Etna's Voragine crater at 1710 UTC on 16 January (a), at 1143 UTC on 18 January (b), and at 0307 on 21 January (c). Photo (a) was taken from Tremestieri Etneo (south side of Etna), (b) and (c) were recorded by the high resolution camera in Monte Cagliato (eastern slope of Etna). Courtesy of INGV (Report 04/2019, ETNA, Bollettino Settimanale, 14/01/2019 - 20/01/2019, data emissione 22/01/2019).

Figure 250. A newly opened vent under the NE rim of the Voragine crater at Etna was observed on 19 January 2019. Behind it on the right, about 40 m SE, is the 7 August 2016 vent. Video taken by Prof. Carmelo Ferlito, Department of Biological, Geological and Environmental Sciences of the University of Catania. Courtesy of INGV (Report 04/2019, ETNA, Bollettino Settimanale, 14/01/2019 - 20/01/2019, data emissione 22/01/2019).

Newly available higher resolution SO₂ data from the TROPOMI Tropospheric Monitoring Instrument on board the Copernicus Sentinel-5 Precursor (S5P) satellite showed persistent SO₂ plumes from Etna that drifted significant distances in multiple directions before dissipating for much of the month. The strongest plumes were recorded during 16-22 January 2019 (figure 251).

Figure 251. Sulfur dioxide plumes were recorded from Etna during most days in January 2019 from the TROPOMI Tropospheric Monitoring Instrument on the Copernicus S5P satellite. The densest plumes were recorded during 16-22 January; plumes from 18, 19, 20 and 21 January 2019 are shown here. Courtesy of NASA Goddard Space Flight Center.

Ash emissions intensified during the last week of January. During the morning of 23 January 2019 a dense ash plume drifted ENE from NEC, producing ashfall on the E flank of the volcano as far as the coast, including in Giarre (figure 252). Discontinuous ash emissions were reported from Bocca Nuova on 25 January; the following morning ash emissions intensified again from NEC and drifted S, producing ashfall in the S flank as far as Catania (figure 253). Emissions persisted until sometime during the night of 26-27 January. The ashfall from 22-23 and 26 January were analyzed by INGV personnel; the components were 95-97% lithic fragments and crystals with only 3-5% juvenile material. An ash plume from Bocca Nuova on 28 January drifted E and produced ashfall in the Valle del Bove. Ash emission decreased from Bocca Nuova on 29-30 January; only dilute ash was observed from NEC during the last few days of the month.

Figure 252. Dense ash emissions during the morning of 23 January 2019 at Etna were observed (a) from the Catania camera CUAD (ECV), (b) from the Catania CUAD high resolution camera (ECVH), (c) from the area stop at Linera on the A18 Messina-Catania motorway (photo B. Behncke), and (d) from the hamlet of Pisano, near Zafferana Etnea, on the SE slope of the volcano (photo B. Behncke). Courtesy of INGV (Report 05/2019; ETNA, Bollettino Settimanale, 21/01/2019 - 27/01/2019, data emissione 29/01/2019).

Figure 253. Ash emissions covered the snow on the S flank of Etna on 26 January 2019. Photo was taken from the SS 121 at the Adrano junction, on the SW flank of the volcano. Photo by R. Corsaro, courtesy of INGV (Report 05/2019; ETNA, Bollettino Settimanale, 21/01/2019 - 27/01/2019 ,data emissione 29/01/2019).

Activity during February 2019. Typical degassing and discontinuous explosive activity from the summit characterized Etna during February. An explosion was observed at NEC at 0230 UTC on 2 February which initially produced a dense ash plume that drifted NE, producing ashfall in the summit area and the Piano Provenzana. Ash emission decreased throughout the day. Repeated ash emissions were visible beginning in the afternoon of 6 February from NEC after several days of cloudy weather. Continuous ash emissions were observed overnight on 7-8 February, producing a dilute plume that drifted S then SE. A similar dilute ash emission was observed on 9 February; the plume drifted SW. Analysis of the ash by INGV indicated a similar composition to the samples measured two weeks prior. Webcams captured numerous pulsating ash emissions from NEC in mid-February, many of which produced substantial SO₂ plumes (figure 254). Emissions increased in intensity and frequency and were nearly continuous during most of the third week, with plumes drifting W, S, and SE resulting in ashfall in those directions, and also led to temporary air space closures in Catania and Comiso (figures 255 and 256). Also during the third week, Strombolian activity took place at BN-1, while pulsating degassing was observed at BN-2. Incandescent degassing continued at the vent located on the N edge of Voragine. Irregular ash emissions that rapidly dispersed near the summit were produced by BN on 26 and 27 February.

Figure 254. Substantial SO2 plumes accompanied ash emissions from Etna during many days in February 2019. The largest plumes were captured with the TROPOMI instrument on the Sentinel-5P satellite on 19, 20, 21, and 22 February. Courtesy of NASA Goddard Space Flight Center.

Figure 255. Ash emission from Etna's North-East Crater (NEC) on the morning of 18 February 2019 was captured by the INGV-OE webcam in Milo. The different colored lines roughly indicate the topographic profiles observable from that position of the various summit craters of Etna: NSEC = New South-East Crater; BN = Bocca Nuova; VOR = Voragine. Courtesy of INGV (Report 09/2019, ETNA, Bollettino Settimanale, 18/02/2019 - 24/02/2019, data emissione 26/02/2019).

Figure 256. An ash emission drifted W from Etna's NEC on 19 February 2019 as viewed from Tremestieri Etneo, located 20 km S of the volcano. Photo by Boris Behncke, courtesy of INGV-OE (Report 09/2019, ETNA, Bollettino Settimanale, 18/02/2019 - 24/02/2019, data emissione 26/02/2019).

Activity during March 2019. Discontinuous and moderate outgassing characterized activity at all the summit vents of Etna throughout March 2018 after an ash plume from Bocca Nuova on 2 March reached 4 km above the crater. The ash plume was accompanied by seismic activity that INGV concluded was likely related to an intra-crater collapse. The discontinuous degassing was interrupted on 16 March by a single small emission of brown ash from Bocca Nuova which rapidly dissipated (figure 257). During a site visit on 30 March, INGV personnel noted pulsating degassing with apparent temperatures above 250°C from the new vent formed in mid-January at the E rim of Voragine (figure 258). At NEC, low-temperature pulsating degassing was occurring at the vent at the bottom of the crater and from fumaroles along the inner walls (figure 259).

Figure 257. A small ash emission from the BN crater on 16 March 2019 was recorded by the high-resolution webcams in Monte Cagliato, on the eastern slope of Etna (a) and in Bronte, on the west side (b). Courtesy of INGV (Report 12/2019, ETNA, Bollettino Settimanale, 11/03/2019 - 17/03/2019, data emissione 19/03/2019).

Figure 258. Degassing continued at the vents along the E edge of Voragine crater at Etna on 30 March 2019, producing temperatures in excess of 250°C. In the background is the NE Crater (NEC) whose southern edge was affected by modest collapses in March 2019. Courtesy of INGV (Report 14/2019, ETNA, Bollettino Settimanale, 25/03/2019 - 31/03/2019, data emissione 02/04/2019).

Figure 259. Degassing continued from the vents located on the bottom of the NE Crater at Etna on 30 March 2019 as seen from the eastern edge with visual and thermal images. Courtesy of INGV (Report 14/2019, ETNA, Bollettino Settimanale, 25/03/2019 - 31/03/2019, (data emissione 02/04/2019).

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

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/ ); Blog INGVvulcani, Istituto Nazionale di Geofisica e Vulcanologia (INGV); (URL: http://ingvvulcani.wordpress.com); 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/).

Manam is a basaltic-andesitic stratovolcano that lies 13 km off the northern coast of mainland Papua New Guinea; it has a 400-year history of recorded evidence for recurring low-level ash plumes, occasional Strombolian activity, lava flows, pyroclastic avalanches, and large ash plumes. Activity during 2017 included a strong surge in thermal anomalies beginning in mid-February that lasted through mid-June; low levels of intermittent thermal activity continued for the rest of the year (BGVN 43:03). Activity during 2018, discussed below, included two ash explosions that rose higher than 15 km altitude, in August and December, resulting in significant ashfall and evacuations of several villages. Information about Manam is primarily provided by Papua New Guinea's Rabaul Volcano Observatory (RVO), part of the Department of Mineral Policy and Geohazards Management (DMPGM). This information is supplemented with aviation alerts from the Darwin Volcanic Ash Advisory Center (VAAC). MODIS thermal anomaly satellite data is recorded by the University of Hawai'i's MODVOLC thermal alert recording system, and the Italian MIROVA project; sulfur dioxide monitoring is done by instruments on satellites managed by NASA's Goddard Space Flight Center. Satellite imagery provided by the Sentinel Hub Playground is also a valuable resource for information about this remote location.

Satellite imagery confirmed thermal activity in December 2017, February-April 2018, and June-December 2018. Explosive activity with ash plumes was reported in June, August-October, and December 2018. Ash plumes from explosions in late August and early December rose to over 15 km altitude and caused heavy ashfall on the island. Lava flows were reported in late August, late September to early October, and December; a pyroclastic flow on the NE flank occurred during the late August explosive episode. MODVOLC thermal alerts were issued during the same periods when lava flows were reported on the NE flank. The MIROVA Log Radiative Power graph for 2018 showed intermittent pulses of thermal activity throughout the year; levels of increased activity were apparent in late December 2017-early January 2018, mid-May, August, late September-early October, and early December 2018 (figure 42). Many of these thermal events could be confirmed with either satellite or ground-based information.

Figure 42. The MIROVA Log Radiative Power graph for Manam during 2018 showed intermittent pulses of thermal activity throughout the year, many of which could be confirmed with satellite imagery or ground observations. Levels of increased activity were apparent in late December 2017-early January 2018, mid-May, August, late September to early October, and the first half of December 2018. Courtesy of MIROVA.

Activity during December 2017-July 2018. Both Sentinel-2 satellite imagery, and MIROVA data thermal evidence, indicated continued thermal activity at both of Manam's summit craters (Main and Southern) during December 2017-April 2018. Satellite imagery on 11, 26, and 31 December showed two thermal hotspots on each date, with a gas plume drifting E on 26 December 2017. One strong thermal anomaly was visible in satellite imagery on 19 February 2018 along with a SE-drifting gas plume (figure 43). A single anomaly was visible through atmospheric clouds on 1 March 2017 with a thin gas plume drifting NNE. On 10 April two hotspots were clearly visible, the one at Southern Crater was larger than the one at Main Crater, both with ESE drifting gas plumes. Though there was diffuse atmospheric cloud cover on 15 April, both anomalies were visible with SW-drifting gas plumes. On 25 April clouds covered the likely thermal anomalies, but a dense gas plume drifted N from the summit (figure 44).

Figure 43. Sentinel-2 images (bands 12, 14, 2) of Manam on 11, 26, and 31 December 2017 and 19 February 2018 all showed evidence of either one or two thermal anomalies at the summit craters and gas plumes drifting in multiple directions. Courtesy of Sentinel Hub Playground.

Figure 44. Thermal anomalies and/or gas plumes were visible at Manam's Main and Southern Craters on 1 March and 10, 15, and 25 April 2018 in Sentinel-2 imagery (bands 12, 14, 2), confirming continued activity at the volcano. Courtesy of Sentinel Hub Playground.

Although no satellite images confirmed thermal activity in May 2018, several anomalies were recorded by the MIROVA project (figure 42). Sentinel-2 imagery on 9 June confirmed two hotspots at the summit with Southern Crater's signal larger than the weak Main Crater signal; the first VAAC report of 2018 was issued on 10 June based on a pilot report of ash at 1.8 km altitude, but it did not appear in satellite imagery. Two thermal anomalies were both more clearly visible on 29 July, with NNE drifting gas plumes (figure 45).

Figure 45. Two thermal anomalies with steam and gas plumes were visible in Sentinel-2 imagery (bands 12,4, 2) at the summit of Manam on 9 June and 29 July 2018. Courtesy of Sentinel Hub Playground.

Activity during August 2018.Thermal activity began increasing in early August 2018, as seen in the MIROVA data, but satellite imagery also indicated a growing hotspot at Main Crater on 13 August. The thermal source appeared to be some type of incandescent flow on the upper NE flank that was visible in 23 August imagery along with the second anomaly at Southern Crater (figure 46).

Figure 46. Growing hotspots were visible at the summit of Manam in Sentinel-2 imagery (bands 12,4, 2) on 13 August 2018 compared with the June and July imagery (figure 45). By 23 August a much larger thermal anomaly was visible beneath cloud cover originating from Main Crater. Courtesy of Sentinel Hub Playground.

The Rabaul Volcano Observatory (RVO) issued an information bulletin early on 25 August indicating a new eruption from Main Crater (figure 47). Residents on the island reported increased activity around 0500 local time. The Darwin VAAC also issued a report a few hours later (24 August 2019 UTC) where they increased the Aviation Color code to Red, and indicated a high-impact eruption with an ash plume visible in satellite imagery that rose to 15.2 km altitude and drifted WSW after initially moving N (figure 48). Reports received at RVO indicated that ash, scoria, and mud fell in areas between the communities of Dangale on the NNE and Jogari on the SW part of the island. They also indicated that the most affected areas were Baliau and Kuluguma where wet, heavy, ashfall broke tree branches and reduced visibility (figure 49). A lava flow was observed in the NE valley slowly moving downhill, and there was evidence of a pyroclastic flow that reached the ocean in the same valley (figure 50).

Figure 47. A large explosion at Manam on 25 August 2018 (local time) produced an ash plume that rose to over 15 km altitude. Islanders reported that ash and other debris from the eruption was so thick that sunlight was totally blocked for hours. Photo taken from the New Guinea mainland by members of the Police force. Courtesy of Scott Waide.

Figure 48. A substantial ash plume from an explosion at Manam on 25 August 2018 (local time) rose to 15.2 km altitude and drifted WSW for about five hours. Photo by Sean Richards, courtesy of Scott Waide.

Figure 49. Vegetation on Manam was covered and damaged by heavy, wet, ash after an explosion on 25 August 2018. Photo by Anisah Isimel, courtesy of Scott Waide.

Figure 50. A fresh lava flow was visible in the major drainage on the NE flank at Manam a few days after a large explosion on 25 August 2018. Pyroclastic flows scorched trees and left behind debris. Posted online on 28 August 2018 by journalist Scott Waide from an article by journalist Martha Louis, EMTV.

The eruption ceased around 1030 local time and was followed by dense steam plumes rising from the summit. RVO reported the following day that six houses in Boakure village on the NE side of the island were buried by debris from the pyroclastic flow. The occupants of the houses had escaped earlier to nearby Abaria village and no casualties were reported. The OMI instrument on NASA's Aura satellite captured a significant SO₂ plume drifting WSW a few hours after reports of the 25 August eruption (figure 51). The Darwin VAAC reported a possible ash eruption on 28 August that was drifting WNW at 3.4 km altitude for a brief period before dissipating. According to RVO, several mudflows were reported in areas between the NW and SW parts of the island after the 25 August 2018 eruption, triggered by the heavy rainfall that followed.

Figure 51. The OMI instrument on NASA's Aura satellite captured a significant SO2 plume drifting WSW from Manam a few hours after reports of the 25 August 2018 eruption. Courtesy of NASA Goddard Space Flight Center.

Activity during September-November 2018. Satellite evidence during September 2018 confirmed the ongoing activity at the summit where a thermal anomaly was visible at Southern Crater on 7 September. On 12 September a gas plume drifted NW from the thermal anomaly at Southern crater while an incandescent lava flow was visible on the NE flank below Main Crater. (figure 52). RVO reported increased activity at Southern Crater during 20-24 September that included variable amounts of steam and gray to brown ash plumes. The Darwin VAAC reported a short-lived ash plume visible in satellite imagery on 23 September that rose to 8.5 km altitude and drifted NW. A small ash emission seen in visible imagery on 25 September rose to 2.4 km altitude and extended SE briefly before dissipating. Although partially obscured by clouds, the lava flow was still visible on the upper NE flank on 27 September (figure 52).

Figure 52. Satellite evidence (Sentinel-2, bands 12, 4, 2) during September 2018 at Manam confirmed the ongoing activity at the summit where a thermal anomaly was visible at Southern Crater on 7 September. On 12 September a gas plume drifted NW from Southern Crater while an incandescent flow traveled down the NE flank from Main Crater. Although partially obscured by clouds, the flow was still visible on the upper NE flank on 27 September. A nearly clear satellite image on 2 October showed incandescent lava reaching almost to the ocean in two lobes on the NE flank of the island. Courtesy of Sentinel Hub playground.

Continuous ash emissions from a new explosion were first reported based on satellite imagery by the Darwin VAAC on 30 September (UTC) at 4.3 km altitude extending SW, and also at 3.0 km altitude drifting W. The emissions at 4.3 km altitude dissipated the following day, but lower level emissions continued at 2.1 km altitude drifting NW through 3 October. On 1 October residents reported hearing continuous loud roaring, rumbling, and banging noises, and reports from Tabele on the SW side of the island indicated very bright incandescence at the summit area. The incandescence was also visible from the Bogia Government Station on the mainland. Small amounts of fine ash and scoria were reported at Jogari and surrounding villages to the N on 1 October. Field observations on 1 October confirmed the presence of a two-lobed lava flow into the NE valley. The smaller lobe traveled towards Kolang village on the N side of the valley and the larger lobe went to the S towards Boakure village. Both flows stopped before reaching inhabited areas. A nearly clear satellite image on 2 October showed the incandescent lava reaching almost to the ocean in the two lobes on the NE flank of the island (figure 52). An SO₂ plume drifting SW from Manam was captured by the OMI instrument on the Aura satellite on 1 October 2018 (figure 53).

Figure 53. The OMI instrument on NASA's Aura satellite captured an SO2 plume drifting SW from Manam on 1 October 2018. Courtesy of NASA Goddard Space Flight Center.

RVO reported that during 2-12 October Southern Crater produced variable amounts of brown, gray-brown and dark gray ash clouds that rose between a few hundred meters and a kilometer above the summit craters before drifting NW. The Darwin VAAC reported an ash emission to 10.4 km altitude on 5 October that extended 25 km W before dissipating within a few hours. Continuous emissions to 2.4 km altitude extending WNW began a few hours later and were intermittently visible in satellite imagery through 12 October. Incandescent lava was visible in satellite imagery on the NE flank on 12 October (figure 54). Activity decreased significantly during the rest of October and most of November 2018, with no ground reports, VAAC reports, or satellite imagery indicating thermal activity; only the MIROVA data showed low-level thermal anomalies (figure 42). A satellite image on 26 November 2018 indicated that thermal activity continued at one of the summit craters (figure 54).

Figure 54. Incandescent lava was visible on the NE flank of Manam on 12 October 2018 in this Sentinel-2 satellite image (bands 12, 4, 2). A single hotspot appeared through meteoric clouds on 26 November. Courtesy of Sentinel Hub Playground.

Activity during December 2018. The Darwin VAAC reported a minor ash emission on 6 December 2018 that rose to 5.2 km altitude and drifted SE for a few hours before dissipating. A much larger ash emission on 8 December was clearly observed in satellite imagery and reported by a pilot, as well as by ground and ocean-based observers. It was initially reported at 12.2 km altitude but rose to 15.2 km a few hours later, drifting E for about 10 hours before dissipating (figure 55). This was followed later in the day by an ongoing ash emission at 8.2 km altitude that drifted E before dissipating on 9 December. According to the UNHCR news organization Relief Web, the eruption started around 1300 local time on 8 December and lasted until about 1000 on 9 December. Based on reports from the ground, the eruption affected the NE part of the island. In particular, a lava flow affected Bokure (Bokuri) and Kolang (NE Manam). Communities in both localities were evacuated. The Loop PNG reported that RVO noted that the flow stopped before reaching Bokure. Ash and scoria fall was described as being moderate in downwind areas, including Warisi village on the SE side of the island. An SO₂ plume was also identified by satellite instruments. Hotspots were visible from both craters on 11 December and from one of the craters on 16 December (figure 56).

Figure 55. This image of an eruption at Manam on 8 December 2018 (local time) was likely taken from a Papua New Guinea government ship, and made available via Jhay Mawengu of the Royal Papua New Guinea Constabulary.

Figure 56. Sentinel-2 satellite images indicated thermal activity continuing as hotspots at the summit of Manam on 11 and 16 December 2018. Courtesy of Sentinel Hub Playground.

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: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://SO2.gsfc.nasa.gov/); Scott Waide (URL: https://mylandmycountry.wordpress.com/2018/08/, Twitter: @Scott_Waide); Jhay Mawengu, Royal Papua New Guinea Constabulary (URL: https://www.facebook.com/mawengu.jeremy.7); Relief Web, United Nations Office for the Coordination of Humanitarian Affairs, Resident Coordinator's Office, 380 Madison Avenue, 7th floor, New York, NY 10017-2528, USA (URL: https://reliefweb.int/); LOOP Pacific (URL: http://www.looppng.com/).

Merapi volcano in central Java, Indonesia (figure 69), has a lengthy history of major eruptive episodes. Activity has included lava flows, pyroclastic flows, lahars, Plinian explosions with heavy ashfall, incandescent block avalanches, and dome growth and destruction. Fatalities from these events were reported in 1994, 2006, and during a major event in 2010 (BGVN 36:01) where hundreds were killed and hundreds of thousands of people were evacuated. Renewed phreatic explosions in May 2018 cancelled airline fights and generated significant SO₂ plumes in the atmosphere. The volcano then remained quiet until an explosion on 11 August 2018 marked the beginning of the growth of a new lava dome. The period June 2018 through March 2019 is covered in this report with information provided primarily by Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), the Center for Research and Development of Geological Disaster Technology, a branch of PVMBG, which monitors activity specifically at Merapi.

Figure 69. A drone aerial photo of Merapi taken on 11 November 2018 shows the Gendol river drainage in the foreground and the upper part that is often referred to as Bebeng. Pyroclastic flows descended through this drainage in both 2006 and 2010. Courtesy of Øystein Lund Andersen.

The first sign of renewed activity at Merapi came with an explosion and the appearance of a lava dome at the summit on 12 August 2018. The growth rate of the dome fluctuated between August 2018 and January 2019, with a low rate of 1,000 m³/day in late September to a high of 6,200 m³/day in mid-October. By mid-December the dome was large enough to send block avalanches down the Kali Gendol ravine on the SSE flank. The rate of dome growth declined rapidly during January 2019, when most of the new lava moved down the ravine in numerous block avalanches. By late March 2019 the dome had reached 472,000 m³ in volume and block avalanches were occurring every few days.

After the eruptive events between 11 May and 1 June 2018, seismicity fluctuated at levels slightly above normal during June and July, with the highest levels recorded on 18 and 29 July. A VONA on 3 June reported a plume of steam that rose 800 m above the summit; for the rest of June the plume heights gradually decreased to a maximum of 400 m by the third week. During July steam plume heights varied from 30 to 350 m above the summit.

On 1 August 2018 an explosion was heard at the Babadan Post. An explosion on 11 August was heard by residents of Deles on the SE flank. Photos taken in a survey by drone the following day indicated the presence of new material in the middle of the 2010 dome fracture (figure 70). The presence of a new lava dome was confirmed with a site visit on 18 August 2018. The dome was 55 m long and 25 m wide, and about 5 m below the 2010 dome surface (figure 71). As of 23 August, the volume of the dome was 23,000 m³, growing at an average rate of 2,700 m³/day. By the end of the month the volume was estimated to be 54,000 m³ with a growth rate of 4,000 m³/day (figure 72). Throughout the month, persistent steam plumes rose 50-200 m above the summit.

Figure 70. The first sign of new dome growth at Merapi appeared in this drone photo taken on 12 August 2018. Courtesy of BPPTKG (Siaran Pers 18 Agustus 2018 Pukul 17:00 WIB, Press Release 18 August 2018, 1700 local time).

Figure 71. The new dome at the summit of Merapi on 18 August 2018. Courtesy of BPPTKG (Siaran Pers 18 Agustus 2018 Pukul 17:00 WIB, Press Release 18 August 2018, 1700 local time).

Figure 72. A comparison of the dome on 18 (top) and 28 (bottom) August 2018 at Merapi taken from the Puncak webcam on the N flank. By the end of August 2018, the dome size was about 54,000 m3. Courtesy of BPPTKG (posted via Twitter on 27 August 2018).

During September-November 2018 the summit dome grew at varying rates from 1,000 to 6,200 m³/day (table 22). At the beginning of September its volume was 54,000 m³; it had reached 329,000 m³ by the end of November (figure 73). Steam plumes in September rose from 100 to 450 m above the summit. They were lower in October, rising only 50-100 m high. During November they rose 100 to400 m above the summit. Intermittent seismic activity remained above background levels. By mid-November, the growth of the dome was clearly visible from the ground 4.5 km S of the summit (figure 74).

Table 22. The volume and growth rate of the lava dome at Merapi was measured weekly from late August 2018 through January 2019. Data courtesy of BPPTKG Merapi weekly reports.

Figure 73. Images from September-November 2018 show the growth of the lava dome at the summit of Merapi. In each pair the left image is from the Deles webcam, and the right image is from the Puncak webcam on the same date. Top: 26 September 2018, left growth lines show change from 8 to 27 September, from 18 to 26 September on right; Middle: 22 October 2018, both sets of growth lines are from 13 September to 22 October; Bottom: 22 November 2018, left growth lines are from mid-September to 21 November and right growth lines are 15 and 22 November. In each Puncak image the red outline at the center is the dome outline on 18 August 2018. Courtesy of BPPTKG, from weekly reports of Merapi activity, 21-27 September, 19-25 October, and 16-22 November 2018.

Figure 74. A comparison of the crater area of Merapi on 2 June 2018 (left) and 11 November 2018 (right). The new dome is clearly visible in the later photo. The images were taken about 4.5 km S of the summit. Persistent gas emissions rose from both the new dome and around the summit crater. Courtesy of Øystein Lund Andersen.

The lava dome continued to grow during December 2018, producing steam plumes that rose 50-200 m. As the height of the dome increased, block avalanches began descending into the upper reaches of Kali Gendol ravine on the SSE flank. Avalanches on 16 and 19 December reached 300 m down the drainage; on 21 December a larger avalanche lasted for 129 seconds and traveled 1 km based on the duration of the seismic data (figure 75). By the end of December BPPTKG measured the volume of the dome as 389,000 m³.

Figure 75. Steam and gas from a recent block avalanche rose from the edge of the new dome at Merapi on 21 December 2018 (top). By the end of December BPPTKG measured the volume of the dome as 389,000 m3. Top image from BPPTKG press release of 21 December 2018; bottom images from the weekly Merapi Mountain activities report of 21-27 December. Courtesy of BPPTKG.

The rate of dome growth declined steadily during January 2019, and by the third week most of the lava extrusion was collapsing as block avalanches into the upper part of Kali Gendol, and dome growth had slowed. Steam plumes rose 50-450 m during the month. In spite of slowing growth, a comparison of the dome size between 11 November 2018 and 13 January 2019 indicated an increase in volume of over 150,000 m³ of material (figure 76). Incandescence at the dome and in the block avalanches was visible at night when the summit was clear (figures 77 and 78). Three block avalanches occurred during the evening of 29 January; the first traveled 1.4 km, the second 1.35 km, and the third 1.1 km down the ravine; each one lasted for about two minutes. By the end of January the size of the dome was reported by BPPTKG to be about 461,000 m³.

Figure 76. A comparison of the dome growth at Merapi from 11 November 2018 to 13 January 2019 showed an increase in volume of over 150,000 m3 according to Indonesian authorities (BPPTKG), as well as the accumulation of debris as material fell down the ravine. Courtesy of Øystein Lund Andersen.

Figure 77. Incandescence appeared at the growing dome at the summit of Merapi late on 13 January 2019. Courtesy of Øystein Lund Andersen.

Figure 78. Incandescent blocks from the growing dome at Merapi traveled several hundred meters down Kali Gendol on 14 January 2019. Courtesy of Øystein Lund Andersen.

Numerous block avalanches were observed during February 2019 as almost all of the lava extrusion was moving down the slope. Multiple avalanches were reported on 7, 11, 18, 25, and 27 February, with traveling distances ranging from 200 to 2,000 m. Steam plumes did not rise more than 375 m during the month. By the end of February, the dome had only grown slightly to 466,000 m³. Seventeen block avalanches were reported during March 2019; they traveled distances ranging from 500 to 1,900 m down the Kali Gendol ravine. A drone measurement on 5 March determined the volume of the dome to be 470,000 m³; it was only 2,000 m³ larger when measured again on 21 March.

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: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Center for Research and Development of Geological Disaster Technology (URL: http://merapi.bgl.esdm.go.id/, Twitter: @BPPTKG); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com/).

The relatively remote Bagana volcano, located on Bougainville Island, Papua New Guinea, is poorly monitored and most of the available data is obtained by satellites (figure 30). The most recent eruptive phase began on or before early 2000 with intermittent ash plumes and detected thermal anomalies (BGVN 41:04, 41:07, 42:08, 43:05). The Darwin Volcanic Ash Advisory Centre (VAAC) monitors satellite imagery for ash plumes that could impact aviation.

Figure 30. Sentinel-2 satellite image (natural color, bands 4, 3, 2) of Bagana on 28 May 2018. Courtesy of Sentinel Hub Playground.

Cloud cover obscured the volcano during much of the reporting period, but significant ash plumes were identified five times by the Darwin Volcanic Ash Advisory Centre (VAAC), in May, July, and December 2018 (table 6). Infrared satellite imagery from Sentinel-2 frequently showed thermal anomalies, both at the summit and caused by hot material moving down the flanks (figure 31).

Table 6. Summary of ash plumes from Bagana reported during May 2018 through January 2019. Courtesy of the Darwin Volcanic Ash Advisory Centre (VAAC).

Figure 31. Infrared satellite images from Sentinel-2 (atmospheric penetration, bands 12, 11, 8A) showing hot areas at the summit and on the flanks on 7 July (top left), 31 August (top right), 14 November (bottom left) and 14 December (bottom right) 2018. Courtesy of Sentinel Hub Playground.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, recorded a large number of thermal alerts within 5 km of the summit throughout this reporting period (figure 32). Thermal alerts increased in number and intensity beginning mid-July 2018. This pattern is also consistent with the MODVOLC data (also based on MODIS satellite data). A total of 76 thermal anomaly pixels were recorded during the reporting period; of these, greater than 40 pixels were observed during July 2018 alone with 13 pixels reported in December 2018 (figure 33).

Figure 32. Thermal anomalies identified at Bagana by the MIROVA system (log radiative power) for the year ending 8 February 2019. Courtesy of MIROVA.

Small sulfur dioxide (SO₂) anomalies were detected by the AuraOMI instrument during this period, the highest being in the range of 1.5-1.8 Dobson Units (DU). Emissions in this range occurred during July 7, 21, and 28 July, and 3-5 and 19 December 2018.

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

Information Contacts: 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, 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/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Fuego is one of Guatemala's most active volcanoes, regularly producing ash plumes and incandescent ballistic ejecta, along with lava flows, avalanches, pyroclastic flows, and lahars down the ravines (barrancas) and rivers (figure 104). Frequent ash plumes have been recorded in recent years (figure 105). A major eruptive event occurred on 3-5 June that resulted in fatalities. Thermal data show an increase in activity from November 2018, that continued through the reporting period (figure 106). This report summarizes activity from July 2018 through March 2019 based on reports by Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH) and the National Office of Disaster Management (CONRED), Washington Volcanic Ash Advisory Center (VAAC), satellite data.

Figure 104. Map of Fuego showing the ravines, rivers, and communities. Map created in 2005 (see BGVN 30:08).

Figure 105. Ash plume altitudes from 1999 through 2019 for Fuego as reported by the Washington VAAC. The gray vertical lines represent paroxysmal eruptions. Courtesy of Rudiger Escobar Wolf, Michigan Technological University.

Figure 106. Log radiative power MIROVA plot of MODIS infrared data at Fuego for the year ending April 2019 showing increased activity since November 2018. Courtesy of MIROVA.

Gas emissions and avalanches characterized activity in early July 2018; an increase was reported on the 4th. Avalanches descended through the Cenizas, Las Lajas, and Santa Teresa ravines on the 6th. One explosion every two hours on 8 July produced ash plumes up to 4.3 km altitude (500 m above the crater) that dispersed towards the SW. Avalanches down the flanks accompanied this activity. On 10 July ash plumes rose to 4.2 and 5 km altitude dispersing to the SW, and ashfall was reported in Morelia and Panimache (figure 107). Avalanches continued on the 19-20 and 23-24 July and weak explosions on the 23-24 produced low ash plumes that dispersed to the N. Hot lahars containing blocks 2-3 m in diameter and tree trunks and branches were generated in the Taniluyá, Ceniza, El Jute, and Las Lajas ravines on 30 and 31 July, and 2 and 9 August.

Figure 107. A moderate explosion produced an ash plume at Fuego on 10 July 2018. Photo courtesy of CONRED.

During August and September, weak to moderate explosions produced ash plumes that rose to 4.7 km altitude and incandescent material was ejected to 150 m above the crater, producing avalanches down the ravines. Additional hot lahars carrying boulders and tree branches occurred on 29 August-2 September and 21-27 September down the Honda (E), El Jute (SE), Las Lajas (SE), Cenizas (SSW), Taniluyá (SW), Seca (W), Santa Teresa (W), Niagara (W), Mineral, and Pantaleón (W) drainages.

An increase in activity occurred on 29 September with degassing pulses lasting 3-4 hours recorded and heard. Avalanches occurred on the flanks and weak-moderate explosions occurred at a rate of 10-15 per hour with ash plumes rising up to 4.7 km. Hot lahars traveled down the Seca, Santa Teresa, and Mineral ravines, transporting blocks up to 3 m in diameter along with tree trunks and branches. Similar lahars were generated in the Las Lajas ravine on 5, 8, and 9 October (figure 108). The lahars were hot and smelled of sulfur, and they carried blocks 1-3 m in diameter.

On 12 October activity increased and produced incandescent ejecta up to 100-200 m above the crater and out to 300 m away from the crater, avalanches in the ravines, and a lava flow with a length of 800-1,000 m, that had reached 1,500 m by the 13th. Ash plumes reached 4.8 km altitude and dispersed up to 12 km towards the S and SE. Explosions occurred at a rate of 8-10 per hour with shockwaves that were reported near the volcano. At 1640 a pyroclastic flow was generated down the Seca ravine (figure 109). Similar activity continued through the 13th, with ash plumes reaching 5 km and ashfall reported in communities including Panimache I, Morelia, Santa Sofia, Sangre de Cristo, El Porvenir, and Palo Verde Estate. This episode of increased activity continued for 32 hours. Lahars traveled down the Ceniza and Seca ravines, the Achiguate River, and the Mineral and Taniluyá ravines (both tributaries of the Pantaleón river). A 30-m-wide lahar with a depth of 2 m was reported on 16 October that carried blocks up to 2 m in diameter, tree trunks, and branches. More lahars descended the Las Lajas ravine on the 17-18, and 20 October. Explosions continued through to the end of October, with increased activity on 31 October.

Figure 108. Seismograms and RSAM (Real-time Seismic Amplitude Measurement) graphs of activity at Fuego showing a change in signal indicative of lahars in the Las Lajas ravine on 8 and 9 October 2018 (red boxes and arrows). The change in seismic signal correlates with an increase in RSAM values. Courtesy of INSIVUMEH.

Figure 109. A pyroclastic flow at Fuego traveling down the Seca ravine on 12 October 2018. Courtesy of CONRED.

Frequent activity continued into November with elevated activity reported on the 2 and 4-6 November. On 6 November ash plumes rose to 4.8 km altitude and traveled 20 km W and SW resulted in ashfall on communities including Panimache, El Porvenir, Morelia, Santa Sofia, Sangre de Cristo, Palo Verde Estate, and San Pedro Yepocapa. Constant explosions ejected incandescent material to 300 m above the crater. A lava flow 1-1.2 km long observed in the Ceniza ravine generated avalanches from the front of the flow, which continued through the 9th.

Activity increased again on 17 November, initiating the fifth eruptive phase of 2018. There were 10-15 explosions recorded per hour along with ash plumes up to 4.7 km that dispersed 10-15 km to the W and SW. Incandescent material was ejected up to 200-300 m above the crater, and avalanches were generated. A new lava flow reached 800 m down the Ceniza ravine. Ashfall was reported in Panimaché I, Morelia, Santa Sofia, El Porvenir, Sangre de Cristo, Palo Verde Estate, Yepocapa, and other communities.

The elevated activity continued through 18 November with 12-17 explosions per hour and a constant ash plume to 5 km altitude, dispersing to the W and SW for 20-25 km. Moderate avalanches traveled down the Ceniza, Taniluyá, and Seca ravines out to the vegetation line. Incandescent blocks were ejected up to 400 m above the crater. Ashfall was reported in communities including Panimaché I, Morelia, Santa Sofia, Sangre de Cristo, and Palo Verde Estate. Avalanches from the front of the lava flow traveled down the Taniluyá and Seca ravines.

Ash plumes rose to 7 km altitude on the 19th and dispersed 50-60 km towards the W, SW, and NE (figure 110). Incandescent ballistic ejecta reached 1 km above the crater and scattered to over 1 km from the crater (figure 111), with the explosions shaking houses over 15 km away to the W and SW, and avalanches moved down the Seca, Ceniza, Taniluyá, Las Lajas, and Honda ravines reaching the vegetation. Two new lava flows formed, extending to 300 m down the Seca and Santa Teresa ravines. Pyroclastic flows traveled down the Seca, Las Lajas, and Honda ravines. Ashfall due to the generation of pyroclastic flows was reported in Panimaché I and II, Santa Sofía, Sangre de Cristo, Palo Verde Estate, and in Alotenango and Antigua, Guatemala, to the NE. CONRED reported the evacuation of 3,925 people. INSIVUMEH reported that the eruption phase was over at 1800 on 19 November after 32 hours of increased activity.

Figure 110. Eruption at Fuego on 19 November 2018 producing ash plumes and incandescent ejecta. Courtesy of European Pressphoto Agency via BBC News.

Figure 111. Explosions at Fuego on 19 November 2018 generated ash plumes to 5.2 km altitude, incandescent blocks up to 1 km above the crater, and avalanches. Courtesy of CONRED.

Explosions continued through 20 November at a rate of 8-13 per hour, ejecting incandescent material up to 200 m above the crater and ash plumes to at least 4.6 km that drifted 20-25 km NW, W, and SW. Avalanches continued with some reaching the vegetation. Ashfall was reported in communities including Panimaché, El Porvenir, Morelia, Santa Sofia, Sangre de Cristo, Palo Verde Estate, and San Pedro Yepocapa.

Similar activity continued through to the end of November with explosions producing shockwaves felt out to 25 km; some explosions were heard in Guatemala City, 40 km ENE. Ash plumes rose to 5 km (figures 112 and 113) and dispersed 20 km W, S, and SW, and ash fell in communities including Panimaché, El Porvenir, Morelia, Santa Sofia, Sangre de Cristo, Palo Verde Estate, San Pedro Yepocapa, Alotenango, and San Miguel Dueñas. Explosions were recorded 10 to 18 per hour. Incandescent ejecta rose to 200 m above the crater and resulted in avalanches in the Las Lajas, Ceniza, El jute, Honda, Taniluyá, Trinidad, and Seca ravines with some reaching the vegetation line. Some avalanches entrained large blocks up to 3 m in diameter that produced ash plumes as they traveled down the ravines. Hot lahars were generated in the Seca, Santa Maria, and Mineral ravines, carrying blocks up to 3 m in diameter (figure 114).

Figure 112. Explosions at Fuego generated ash plumes and caused avalanches in the Las Lajas, Trinidad, and Ceniza ravines on 22 November 2018. Courtesy of CONRED.

Figure 113. Ash plume up to 5.5 km altitude at Fuego on 28 November 2018. Courtesy of CONRED.

Figure 114. A lahar from Fuego traveling down the Mineral River in November 2018. Courtesy of CONRED.

During December white to light gray fumarolic plumes rose to a maximum height of 4.5 km. Ash plumes reached up to 5.2 km and dispersed to a maximum of 25 km S, SW, and W. There were 3-15 explosions recorded per hour with shockwaves, incandescent ejecta reaching 300 m above the crater, and avalanches down the Seca, Taniluyá, Ceniza, Trinidad, Las Lajas, and Honda ravines. Ashfall was reported in communities including Panimaché I and II, Morelia, Santa Sofia, El Porvenir, Palo Verde Estate, Sangre de Cristo, Yepocapa, La Rochela, San Andrés Osuna, Ceylon, Alotenango, and San Pedro.

Similar activity continued through January 2019 with fumarolic plumes rising to a maximum of 4.4 km altitude, ash plumes reaching 4.8 km and dispersing over 15 km to the NE, WSW, and NW; 3-25 explosions per hour sent shockwaves and avalanches in multiple directions. Ashfall was reported in Panimaché, Morelia, Santa Sofia, Sangre de Cristo, Palo Verde Estate, and San Pedro Yepocapa. Also in Alotenango, La Reunion, and El Porvenir, Alotenango.

An increase in activity began on 21 January with moderate to strong explosions producing ash plumes up to 5 km altitude that dispersed 12 km W and SW. The explosions were heard over 15 km away and shook windows and roofs out to 12 km away. Avalanches were triggered in multiple ravines. On 22 January there were 15-25 recorded explosions per hour, each lasting 2-3 minutes and producing ash plumes to 4.8 km and incandescent ejecta up to 300 m above the crater (figure 115).

Figure 115. An ash plume rising during an explosive event at Fuego on 22 January 2019. Courtesy of CONRED.

Frequent explosions continued during February through to late-March, with a range of 8-18 per hour, producing ash plumes rising to 4.8 km (figure 116), and dispersing out to 15 km in multiple directions. Incandescent ejecta rose to 350 m above the crater and resulted in avalanches down multiple ravines. Ashfall was reported in communities including El Rodeo, El Zapote, Ceylon, La Roche-la, Panimache, Morelia, Santa Sofia, Sangre de Cristo, San Miguel Dueñas, Ciudad Vieja, and Alotenango, Verde Estate, San Pedro Yepocapa, La Rochelle, and San Andrés Osuna.

On 22 March there was an increase in the number and energy of explosions with 15-20 per hour. Accompanying ash plumes rose to 5 km altitude and dispersed 25-30 km S, W, SW, E, and SE, depositing ash in La Rochela, Ceylon, Osuna, Las Palmas, Siquinalá, and Santa Lucia Cotzumalguapa. Explosions were heard over 20 km from the volcano. Incandescent ejecta rose to 300 m above the crater and moderate to strong avalanches flowed down the Seca, Taniluyá, Ceniza, Trinidad, Las Lajas and Honda ravines. Explosions increased to 14-32 events per hour by 31 March, continuing to produce ash plumes up to 5 km and depositing ash on nearby communities and causing avalanches down the flanks. A new lava flow reached 800 m down the Seca ravine.

Figure 116. Examples of small ash plumes at Fuego on 21 February and 12 March 2019. Courtesy of William Chigna, CONRED (top) and CONRED (bottom).

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); 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); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Rudiger Escobar Wolf, Michigan Technologicla University, 630 Dow Environmental Sciences, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: https://www.mtu.edu/geo/department/staff/wolf.html); William Chigna, CONRED (URL: https://twitter.com/william_chigna); BBC News (URL: https://www.bbc.com; https://www.bbc.com/news/world-latin-america-46261168?intlink_from_url=https://www.bbc.com/news/topics/c4n0j0d82l0t/guatemala-volcano&link_location=live-reporting-story); European Pressphoto Agency (URL: http://www.epa.eu/); Agence France-Presse (URL: http://www.afp.com/).

Nearly constant fountains of lava at Stromboli have served as a natural beacon in the Tyrrhenian Sea for at least 2,000 years. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N Area) and a southern crater group (CS Area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the island. Thermal and visual cameras that monitor activity at the vents are located on the nearby Pizzo Sopra La Fossa, above the Terrazza Craterica, and at a location closer to the summit craters.

Eruptive activity from November 2018 to February 2019 was consistent in terms of explosion intensities and rates from both crater areas at the summit, and similar to activity of the past few years (table 5). In the North Crater area, both vents N1 and N2 emitted a mixture of coarse (lapilli and bombs) and fine (ash) ejecta; most explosions rose less than 80 m above the vents, some reached 150 m. Average explosion rates ranged from 4 to 21 per hour. In the CS crater area continuous degassing and occasional intense spattering were typical at vent C, vent S1 was a low-intensity incandescent jet throughout the period. Explosions from vent S2 produced 80-150 m high ejecta of ash, lapilli and bombs at average rates of 3-16 per hour. Thermal activity at Stromboli was actually higher during November 2018-February 2019 than it had been in previous months as recorded in the MIROVA Log Radiative Power data from MODIS infrared satellite information (figure 139).

Table 5. Summary of activity levels at Stromboli, November 2018-February 2019. Low intensity activity indicates ejecta rising less than 80 m and medium intensity is ejecta rising less than 150 m. Data courtesy of INGV.

Figure 139.Thermal activity at Stromboli increased during November 2018-February 2019 compared with the preceding several months as recorded in the MIROVA project log radiative power data taken from MODIS thermal satellite information. Courtesy of MIROVA.

Activity at the N area was very consistent during November 2018 (figure 140). Explosions of low-intensity (less than 80 m high) to medium-intensity (less than 150 m high) occurred at both the N1 and N2 vents and produced coarse material (lapilli and bombs) mixed with ash, at rates averaging 6-16 explosions per hour. In the SC area continuous degassing was reported from vent C with a brief period of intense spattering on 26 November. At vent S1 low- to medium-intensity incandescent jetting was reported. At vent S2, low- and medium-intensity explosive activity produced a mixture of coarse and fine (ash) material at a frequency of 3-18 events per hour.

Figure 140. The Terrazza Craterica at Stromboli on 12 November 2018 as viewed by the thermal camera placed on the Pizzo sopra la Fossa, showing the two main crater areas and the active vents within each area that are discussed in the text. Heights above the crater terrace, as indicators of intensity of the explosions, are shown divided into three intervals of low (basso), medium (media), and high (alta). Courtesy of INGV (Report 46/2018, Stromboli, Bollettino Settimanale 05/11/2018 - 11/11/2018, data emissione 13/11/2018).

Similar activity continued during December at both crater areas, although there were brief periods of more intense activity. Low- to medium-intensity explosions at both N area vents produced a mixture of coarse and fine-grained material at rates averaging 4-21 per hour. During 6-7 December ejecta from the N vents fell onto the upper part of the Sciara del Fuoco and rolled down the gullies to the coast, producing tongues of debris (figure 141). An explosion at N1 on 12 December produced a change in the structure of the crater area. During 10-16 December the ejecta from the N area landed outside the crater on the Sciara del Fuoco. Intense spattering was observed from N2 on 18, 22, and 31 December. In the CS area, continuous degassing took place at vent C, along with a brief period of intense spattering on 1-2 December. Low to medium intensity incandescent jets persisted at S1 along with low-and medium-intensity explosions of coarse and fine-grained material at vent S2. Rates of explosion at the CS area were higher at the beginning of December (10-18 per hour) and lower during the last week of the month (3-4 per hour).

Figure 141. Images from the Q 400 thermal camera at Stromboli taken on 6 December 2018 showed the accumulation of pyroclastic material in several gullies on the upper part of the Sciara del Fuoco following an explosion at vent N2 at 1520 UTC. The images illustrate the rapid cooling of the pyroclastic material in the subsequent two hours. Courtesy of INGV (Report 50/2018, Stromboli, Bollettino Settimanale, 03/12/2018 - 09/12/2018, data emissione 11/12/2018).

Explosive intensity was low (ejecta less than 80 m high) at vent N1 at the beginning of January 2019 and increased to medium (ejecta less than 150 m high) during the second half of the month, producing coarse ejecta of lapilli and bombs. Intensity at vent N2 was low to medium throughout the month with both coarse- and fine-grained material ejected. Explosions from N2 sent large blocks onto the Sciara del Fuoco several times throughout the month and usually was accompanied by intense spattering. Explosion rates varied, with averages of 9 to 16 per hour, throughout the month in the N area. In the CS area continuous degassing occurred at vent C, and low-intensity explosions of coarse-grained material were reported during the second half of the month. Low-intensity incandescent jets at S1 along with low- and medium-intensity explosions of coarse and fine-grained material at S2 persisted throughout the month.

A helicopter overflight of Stromboli on 8 January 2019 allowed for detailed visual and thermal observations of activity and of the morphology of the vents at the summit (figure 142). Vent C had two small hornitos, and a small scoria cone was present in vent S1, while a larger crater was apparent at S2. In the N crater area vent N2 had a large scoria cone that faced the Sciara del Fuoco to the north; three narrow gullies were visible at the base of the cone (figure 143). Vent S1 was a large crater containing three small vents aligned in a NW-SE trend; INGV scientists concluded the vents formed as a result of the 12 December 2018 explosion. Thermal images showed relatively low temperatures at all fumaroles compared with earlier visits.

Figure 142. Thermal images from Stromboli taken during the overflight of 8 January 2019 showed the morphological structure of the individual vents of the N and CS crater areas. Courtesy of INGV (Report 03/2019, Stromboli, Bollettino Settimanale, 07/01/2019 - 13/01/2019, (data emissione 15/01/2019).

Figure 143. An image taken at Stromboli during the overflight of 8 January 2019 shows the morphological structure of the summit Terrazza Craterica with three gullies at the base of the scoria cone of vent N2. The top thermal image (inset a) shows that the fumaroles in the upper part of the Sciara del Fuoco have low temperatures. Courtesy of INGV (Report 03/2019, Stromboli, Bollettino Settimanale, 07/01/2019 - 13/01/2019, data emissione 15/01/2019).

Activity during February 2019 declined slightly from the previous few months. Explosions at vent N1 were of medium-intensity and produced coarse material (lapilli and bombs). At N2, low-intensity explosions produced fine ash. Average explosion rates in the N area ranged from 4-11 per hour. At the CS area, continuous degassing and low-intensity explosions produced coarse and fine-grained material from vents C and S2 while low-intensity incandescent jets were active at S1. The explosion rates at the CS area averaged 2-13 per hour.

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Krakatau volcano, between Java in Sumatra in the Sunda Straight of Indonesia, is known for its catastrophic collapse in 1883 that produce far-reaching pyroclastic flows, ashfall, and tsunami. The pre-1883 edifice had grown within an even older collapse caldera that formed around 535 CE, resulting in a 7-km-wide caldera and the three surrounding islands of Verlaten, Lang, and Rakata (figure 55). Eruptions that began in late December 1927 (figures 56 and 57) built the Anak Krakatau cone above sea level (Sudradjat, 1982; Simkin and Fiske, 1983). Frequent smaller eruptions since that time, over 40 short episodes consisting of ash plumes, incandescent blocks and bombs, and lava flows, constructed an island reaching 338 m elevation.

Figure 55. The three islands of Verlaten, Lang, and Rakata formed during a collapse event around 535 CE. Another collapse event occurred in 1883, producing widespread ashfall, pyroclastic flows, and triggering a tsunami. Through many smaller eruptions since then, Anak Krakatau has since grown in the center of the caldera. Sentinel-2 natural color (bands 4, 3, 2) satellite image acquired on 16 November 2018, courtesy of Sentinel Hub Playground.

Figure 56. Photo sequence (made from a film) at 6-second intervals from the early phase of activity on 24 January 1928 that built the active Anak Krakatau cone above the ocean surface. Plume height reached about 1 km. View is from about 4.5 km away at a beach on Verlaten Island looking SE towards Rakata Island in the right background. Photos by Charles E. Stehn (Netherlands Indies Volcanological Survey) from the E.G. Zies Collection, Smithsonian Institution.

Figure 57. Submarine explosions in January 1928 built the active Anak Krakatau cone above the ocean surface. View is from about 600 m away looking E towards Lang Island in the background. Photos by Charles E. Stehn (Netherlands Indies Volcanological Survey) from the E.G. Zies Collection, Smithsonian Institution.

Historically there has been a lot of confusion about the name and preferred spelling of this volcano. Some have incorrectly made a distinction between the pre-1883 edifice being called "Krakatoa" and then using "Krakatau" for the current volcano. Anak Krakatau is the name of the active cone, but the overall volcano name is simply Krakatau. Simkin and Fiske (1983) explained as follows: "Krakatau was the accepted spelling for the volcano in 1883 and remains the accepted spelling in modern Indonesia. In the original manuscript copy submitted to the printers of the 1888 Royal Society Report, now in the archives of the Royal Society, this spelling has been systematically changed by a neat red line through the final 'au' and the replacement 'oa' entered above; a late policy change that, from some of the archived correspondence, saddened several contributors to the volume."

After 15 months of quiescence Krakatau began a new eruption phase on 21 June 2018, characterized by ash plumes, ballistic ejecta, Strombolian activity, and lava flows. Ash plumes reached 4.9 km and a lava flow traveled down the SE flank and entered the ocean. This report summarizes the activity from October 2018 to January 2019 based on reports by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), MAGMA Indonesia, the National Board for Disaster Management - Badan Nasional Penanggulangan Bencana (BNPB), the Darwin Volcanic Ash Advisory Center (VAAC), satellite data, and eye witness accounts.

Activity during October-21 December 2018. The eruption continued to eject incandescent ballistic ejecta, ash plumes, and lava flows in October through December 2018. On 22 December a partial collapse of Anak Krakatau began, dramatically changing the morphology of the island and triggering a deadly tsunami that impacted coastlines around the Sunda Straight. Following the collapse the vent was located below sea level and Surtseyan activity produced steam plumes, ash plumes, and volcanic lightning.

Sentinel-2 satellite images acquired through October show incandescence in the crater, lava flows on the SW flank, and incandescent material to the S to SE of the crater (figure 58). This correlates with eyewitness accounts of explosions ejecting incandescent ballistic ejecta, and Volcano Observatory Notice for Aviation (VONA) ash plume reports. The Darwin VAAC reported ash plumes to 1.5-2.4 km altitude that drifted in multiple directions during 17-19 October, but throughout most of October visual observations were limited due to fog. A video shared by Sutopo on 24 October shows ash emission and lava fountaining producing a lava flow that entered the ocean, resulting in a white plume. Video by Richard Roscoe of Photovolcanica shows explosions ejecting incandescent blocks onto the flanks and ash plumes accompanied by volcanic lightning on 25 October.

Figure 58. Sentinel-2 thermal satellite images showing lava flows, incandescent avalanche deposits, and incandescence in the crater of Anak Krakatau during October 2018. Courtesy of Sentinel-2 hub playground.

Throughout November frequent ash plumes rose to 0.3-1.3 km altitude, with explosion durations spanning 29-212 seconds (figure 59). Observations by Øystein Lund Andersen describe explosions ejecting incandescent material with ash plumes and some associated lightning on 17 November (figure 60).

Figure 59. Sentinel-2 satellite images showing ash plumes at Krakatau during 6-16 November 2018. Natural color (Bands 4, 3, 2) Sentinel-2 images courtesy of Sentinel Hub Playground.

Figure 60. Krakatau erupting an ash plume and incandescent material on 17 November 2018. Courtesy of Øystein Lund Andersen.

During 1-21 December intermittent explosions lasting 46-776 seconds produced ash plumes that rose up to 1 km altitude. Thermal signatures were sporadically detected by various satellite thermal infrared sensors during this time. On 22 December ash plumes reached 0.3-1.5 km through the day and continuous tremor was recorded.

Activity and events during 22-28 December 2018. The following events during the evening of the 22nd were recorded by Øystein Lund Andersen, who was photographing the eruption from the Anyer-Carita area in Java, approximately 47 km from Anak Krakatau. Starting at 1429 local time, incandescence and ash plumes were observed and the eruption could be heard as intermittent 'cannon-fire' sounds, sometimes shaking walls and windows. An increase in intensity was noted at around 1700, when the ash column increased in height and was accompanied by volcanic lightning, and eruption sounds became more frequent (figure 61). A white steam plume began to rise from the shore of the southern flank. After sunset incandescent ballistic blocks were observed impacting the flanks, with activity intensity peaking around 1830 with louder eruption sounds and a higher steam plume from the ocean (figure 62).

Figure 61. Ash plumes at Krakatau from 1429 to 1739 on 22 December 2018. Courtesy of Øystein Lund Andersen.

Figure 62. Krakatau ejecting incandescent blocks and ash during 1823-1859 on 22 December 2018. The top and middle images show the steam plume at the shore of the southern flank. Courtesy of Øystein Lund Andersen.

PVMBG recorded an eruption at 2103. When viewed at 2105 by Øystein Lund Andersen, a dark plume across the area blocked observations of Anak Krakatau and any incandescence (figure 63). At 2127-2128 the first tsunami wave hit the shore and traveled approximately 15 m inland (matching the BNPB determined time of 2127). At approximately 2131 the sound of the ocean ceased and was soon replaced by a rumbling sound and the second, larger tsunami wave impacted the area and traveled further inland, where it reached significant depths and caused extensive damage (figures 64 and 65). After the tsunami, eruption activity remained high and the eruption was heard again during intervals from 0300 through to early afternoon.

Figure 63. Krakatau is no longer visible at 2116 on 22 December 2018, minutes before the first tsunami wave arrived at west Java. A dark ash plume takes up much of the view. Courtesy of Øystein Lund Andersen.

Figure 64. The second tsunami wave arriving at Anyer-Carita area of Java after the Krakatau collapse. This photo was taken at 2133 on 22 December 2018, courtesy of Øystein Lund Andersen.

Figure 65. Photographs showing damage caused in the Anyer-Carita area of Java by the tsunami that was triggered by the partial collapse of Krakatau. From top to bottom, these images were taken approximately 40 m, 20 m, and 20 m from the shore on 23 December 2018. Courtesy of Øystein Lund Andersen.

Observations on 23 December reveal steam-rich ash plumes and base surge traveling along the water, indicative of the shallow-water Surtseyan eruption (figure 66). Ashfall was reported on the 26th in several regions including Cilegon, Anyer, and Serang. The first radar observations of Krakatau were on 24 December and showed a significant removal of material from the island (figure 67). At 0600 on the 27th the volcanic alert level was increased from II to III (on a scale of I-IV) and a VONA with Aviation Color Code Red reported an ash plume to approximately 7 km altitude that dispersed to the NE. When Anak Krakatau was visible, Surtseyan activity and plumes were observed through the end of December. On 28 December, plumes reached 200-3000 m. At 0418 the eruption paused and the first observation of the post-collapse edifice was made. The estimated removed volume (above sea level) was 150-180 million m³, leaving a remaining volume of 40-70 million m³. The summit of the pre-collapse cone was 338 m, while the highest point post-collapse was reduced to 110 m. Hundreds of thousands of lightning strokes were detected during 22-28 December with varying intensity (figure 68).

Figure 66. Steam-rich plumes and underlying dark ash plumes from Surtseyan activity at Krakatau on 23 December 2018. Photos by Instagram user @didikh017 at Grand Cava Susi Air, via Sutopo.

Figure 67. ALOS-2 satellite radar images showing Krakatau on 20 August 2018 and 24 December 2018. The later image shows that a large part of the cone of Anak Krakatau had collapsed. Courtesy of Geospatial Information Authority of Japan (GSI) via Sutopo.

Figure 68. Lightning strokes during the eruption of Krakatau within a 20 km radius of the volcano for 30 minute intervals on 23, 25, 26, and 28 December 2018. Courtesy of Chris Vagasky.

Damage resulting from the 22 December tsunami. On the 29 December the damage reported by BNPB was 1,527 heavily damaged housing units, 70 with moderate damage, 181 with light damage, 78 damaged lodging and warung units, 434 damaged boats and ships and some damage to public facilities. Damage was recorded in the five regencies of Pandenglang, Serang, South Lampung, Pesawaran and Tanggamus. A BNPB report on 14 January gave the following figures: 437 fatalities, 10 people missing, 31,943 people injured, and 16,198 people evacuated (figure 69). The eruption and tsunami resulted in damage to the surrounding islands, with scouring on the Anak-Krakatau-facing slope of Rakata and damage to vegetation on Kecil island (figure 70 and 71).

Figure 69. The impacts of the tsunami that was triggered by a partial collapse of Anak Krakatau from an update given on 14 January 2019. Translations are as follows. Korban Meninggal: victims; Korban hilang: missing; Korban luka-luka: injured; Mengungsi: evacuated. The color scale from green to red along the coastline indicates the breakdown of the human impacts by area. Courtesy of BNPB.

Figure 70. Damage on Rakata Island from the Krakatau tsunami. This part of the island is facing Anak Krakatau and the scoured area was estimated to be 25 m high. Photographs taken on 10 January 2019 by James Reynolds.

Figure 71. Damage to vegetation on Kecil island to the East of Krakatau, from the Krakatau December 2018 eruption. Photographs taken on 10 January 2019 by James Reynolds.

Activity during January 2019. Surtseyan activity continued into January 2019. Øystein Lund Andersen observed the eruption on 4-5 January. Activity on 4 January was near-continuous. The photographs show black cock's-tail jets that rose a few hundred meters before collapsing (figure 72), accompanied by white lateral base surge that spread from the vent across the ocean (figure 73), and white steam plumes that were visible from Anyer-Carita, West Java. In the evening the ash-and-steam plume was much higher (figure 74). It was also noted that older pumice had washed ashore at this location and a coating of sulfur was present along the beach and some of the water surface. Activity decreased again on the 5th (figure 75) with a VONA reporting an ash plume to 1.5 km towards the WSW. SO₂ plumes were dispersed to the NE, E, and S during this time (figure 76).

Figure 72. Black ash plumes and white steam plumes from the Surtseyan eruption at Krakatau on 4 January 2019. Courtesy of Øystein Lund Andersen.

Figure 73. An expanding base surge at Krakatau on 4 January 2019 at 0911. Courtesy of Øystein Lund Andersen.

Figure 74. Ash-and-steam plumes at Krakatau at 1702-2250 on 4 January 2018. Lightning is illuminating the plume in the bottom image. Courtesy of Øystein Lund Andersen.

Figure 75. Ash plumes at Krakatau on 5 January 2019 at 0935. Courtesy of Øystein Lund Andersen.

Figure 76. Sulfur dioxide (SO2) emissions produced by Krakatau and drifting to the NE, E, and SE on 3-6 January 2018. Dates and times of the periods represented are listed at the top of each image. Courtesy of the NASA Space Goddard Flight Center.

During 5-9 January intermittent explosions lasting 20 seconds to 13 minutes produced ash plumes rising up to 1.2 km and dispersing E. From 11 to 19 January white plumes were observed up to 500 m. Observations were prevented due to fog during 20-31 January. MIROVA thermal data show elevated thermal anomalies from July through January, with a decrease in energy in November through January (figure 77). The radiative power detected in December-January was the lowest since June 2018.

Figure 77. Log radiative power MIROVA plot of MODIS thermal infrared data for June 2018-January 2019. The peaks in energy correlate with observed lava flows. Courtesy of MIROVA.

Morphological changes to Anak Krakatau. Images taken before and after the collapse event show changes in the shoreline, destruction of vegetation, and removal of the cone (figure 78). A TerraSAR-X image acquired on 29 January shows that in the location where the cone and active vent was, a bay had formed, opening to the W (figure 79). These changes are also visible in Sentinel-2 satellite images, with the open bay visible through light cloud cover on 29 December (figure 80).

By 9 January a rim had formed, closing off the bay to the ocean and forming a circular crater lake. Photos by James Reynolds on 11 January show a new crater rim to the W of the vent, which was filled with water (figure 81). Steam and/or gas emissions were emanating from the surface in that area. The southern lava delta surface was covered with tephra, and part of the lava delta had been removed, leaving a smooth coastline. By the time these images were taken there was already extensive erosion of the fresh deposits around the island. Fresh material extended the coast in places and filled in bays to produce a more even shoreline.

Figure 78. Krakatau on 5 August 2018 (top) and on 11 January 2019 showing the edifice after the collapse event. The two drone photographs show approximately the same area. Courtesy of Øystein Lund Andersen (top) and James Reynolds (bottom).

Figure 79. TerraSAR-X radar images showing the morphological changes to Krakatau with the changes outlined in the bottom right image as follows. Red: 30 August 2018 (upper left image); blue: 29 December 2018 (upper right image); yellow: 9 January 2019 (lower left image). Part of the southern lava delta was removed and material was added to the SE and NE to N shoreline. In the 29 December image the cone has collapsed and in its place is an open bay, which had been closed by a new rim by the 9 January. Courtesy of BNPB, JAXA Japan Aerospace Exploration Agency, and Badan Informasi Geospasial (BIG).

Figure 80. Sentinel-2 satellite images showing the changing morphology of Krakatau. The SW section is where the cone previously sat and collapsed in December 2018. In the upper right image the cone and southern lava delta are gone and there are changes to the coastline of the entire island. Natural color (bands 4, 3, 2) Sentinel-2 satellite images courtesy of Sentinel Hub Playground.

Figure 81. Drone footage of the Krakatau crater and new crater rim taken on 11 January 2019. The island is coated in fresh tephra from the eruption and the orange is discolored water due to the eruption. The land between the crater lake and the ocean built up since the collapse and the hot deposits are still producing steam/gas. Courtesy of James Reynolds.

Figure 82. An aerial view of Krakatau with the new crater on 13 January 2019. Courtesy of BNPB.

References. Simkin, T., and Fiske, R.S., 1983, Krakatau 1883: the volcanic eruption and its effects: Smithsonian Institution Press, Washington DC, 464 p. ISBN 0-87474-841-0.

Sudradjat (Sumartadipura), A., 1982. The morphological development of Anak Krakatau Volcano, Sunda Straight. Geologi Indonesia, 9(1):1-11.

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: Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN ); Geospatial Information Authority of Japan (GSI), 1 Kitasato, Tsukuba, Ibaraki 305-0811, Japan. (URL: http://www.gsi.go.jp/ENGLISH/index.html); Badan Informasi Geospasial (BIG), Jl. Raya Jakarta - Bogor KM. 46 Cibinong 16911, Indonesia. (URL: http://www.big.go.id/atlas-administrasi/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); JAXA | Japan Aerospace Exploration Agency, 7-44-1 Jindaiji Higashi-machi, Chofu-shi, Tokyo 182-8522 (URL: https://global.jaxa.jp/); 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); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com/krakatau-volcano-witnessing-the-eruption-tsunami-22december2018/); James Reynolds, Earth Uncut TV (Twitter: @EarthUncutTV, URL: https://www.earthuncut.tv/, YouTube: https://www.youtube.com/channel/UCLKYsEXfI0PGXeKYL1KV7qA); Chris Vagasky, Vaisala Inc., Louisville, Colorado (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman).

The dacitic Santiaguito lava-dome complex on the W flank of Guatemala's Santa María volcano has been growing and actively erupting since 1922. The youngest of the four vents in the complex, Caliente, has been erupting with ash explosions, pyroclastic, and lava flows for more than 40 years. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Daily explosions of steam and ash also continued during November 2018-February 2019, the period covered in this report, with information primarily from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and the Washington VAAC (Volcanic Ash Advisory Center).

Activity at Santa Maria continued with little variation from previous months during November 2018-February 2019. Plumes of steam with minor magmatic gases rose continuously from the Caliente crater 100-500 m above the summit, generally drifting SW or SE before dissipating. In addition, daily explosions with varying amounts of ash rose to altitudes of around 2.8-3.5 km and usually extended 20-30 km before dissipating. Most of the plumes drifted SW or SE; minor ashfall occurred in the adjacent hills almost daily and was reported at the fincas located within 15 km in those directions several times each month. Continued growth of the Caliente lava dome resulted in daily block avalanches descending its flanks. The MIROVA plot of thermal energy during this time shows a consistent level of heat flow with minor variations throughout the period (figure 89).

Figure 89. Persistent thermal activity was recorded at Santa Maria from 6 June 2018 through February 2019 as seen in the MIROVA plot of thermal energy derived from satellite thermal data. Daily explosions produced ash plumes and block avalanches that were responsible for the continued heat flow at the volcano. Courtesy of MIROVA.

During November 2018 steam plumes rose to altitudes of 2.8-3.2 km from Caliente summit, usually drifting SW, sometimes SE. Several ash-bearing explosions were reported daily, rising to 3-3.2 km altitude and also drifting SW or SE. The highest plume reported by INSIVUMEH rose to 3.4 km on 25 November and drifted SW. The Washington VAAC reported an ash emission on 9 November that rose to 4.3 km altitude and drifted W; it dissipated within a few hours about 35 km from the summit. On 11 November another plume rose to 4.9 km altitude and drifted NW. INSIVUMEH issued a special report on 2 November noting an increase in block avalanches on the S and SE flanks, many of which traveled from the crater dome to the base of the volcano. Nearly constant avalanche blocks descended the SE flank of the dome and occasionally traveled down the other flanks as well throughout the month. They reached the bottom of the cone again on 29 November. Ashfall was reported around the flanks more than once every week and at Finca Florida on 12 November. Finca San Jose reported ashfall on 11, 13, and 23 November, and Parcelamiento Monte Claro reported ashfall on 15, 24, 25, and 27 November.

Constant degassing from the Caliente dome during December 2018 formed white plumes of mostly steam that rose to 2.6-3.0 km altitude during the month. Weak explosions averaging 9-13 per day produced gray ash plumes that rose to 2.8-3.4 km altitude. The Washington VAAC reported an ash emission on 4 December that extended 25 km SW of the summit at 3.0 km altitude and dissipated quickly. Small ash plumes were visible in satellite imagery a few kilometers WNW on 8, 12, 30, and 31 December at 4.3 km altitude; they each dissipated within a few hours. Ashfall was reported in Finca Monte Claro on 1 and 4 December, and in San Marcos Palajunoj on 26 and 30 December along with Loma Linda. On 28 December ashfall on the E flank affected the communities of Las Marías, Calahuache, and El Nuevo Palmar. Block avalanches occurred daily, sending large blocks to the base of the volcano that often stirred up small plumes of ash in the vicinity (figure 90).

Figure 90. Activity during December 2018 at Santa Maria included constant degassing of steam plumes, weak explosions with ash plumes, and block avalanches rolling down the flanks to the base of the cone. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Diciembre 2018).

Multiple explosions daily during January 2019 produced steam-and-ash plumes (figure 91). Constant degassing rising 10-500 m emerged from the SSE part of the Caliente dome, and ashfall, mainly on the W and SW rim of the cone, was a daily feature. Seismic station STG-3 detected 10-18 explosions per day that produced ash plumes, which rose to between 2.7 and 3.5 km altitude. The Washington VAAC noted a faint ash emission in satellite imagery on 1 January that was about 25 km W of the summit at 4.3 km altitude. A new emission appeared at the same altitude on 4 January about 15 km NW of the summit. A low-density emission around midday on 5 January produced an ash plume that drifted NNE at 4.6 km altitude. Ash plumes drifted W at 4.3 km altitude on 11 and 14 January for short periods of time before dissipating.

Figure 91. Explosions during January produced numerous steam-and-ash plumes at the Santiaguito complex of Santa Maria. A moderate explosion on 31 January 2019 produced an ash plume that rose to about 3.1 km altitude (top). A thermal image and seismograph show another moderate explosion on 18 January 2019 that also rose nearly vertically from the summit of Caliente. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).

Ash drifted mainly towards the W, SW, and S, causing ashfall in the villages of San Marcos Palajunoj, Loma Linda, Monte Bello, El Patrocinio, La Florida, El Faro, Patzulín and a few others several times during the month. The main places where daily ashfall was reported were near the complex, in the hilly crop areas of the El Faro and San José Patzulín farms (figure 92). Blocks up to 3 m in diameter reached the base of the complex, stirring up ash plumes that settled on the immediate flanks. Juvenile material continued to appear at the summit of the dome during January; the dome had risen above the edge of the crater created by the explosions of 2016. Changes in the size and shape of the dome between 23 November 2018 and 13 January 2019 showed the addition of material on the E and SE side of the dome, as well as a new effusive flow that travelled 200-300 m down the E flank (figure 93).

Figure 92. Near-daily ashfall affected the coffee plants at the El Faro and San José Patzulín farms (left) at Santiaguito during January 2019. Large avalanche blocks descending the flanks, seen here on 23 January 2018, often stirred up smaller ash plumes that settled out next to the cone. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).

Figure 93. A comparison of the growth at the Caliente dome of the Santiaguito complex at Santa Maria between 23 November 2018 (top) and 13 January 2019 (bottom) shows the emergence of juvenile material and a 200-300 m long effusive flow that has moved slowly down the E flank. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).

Persistent steam rising 50-150 m above the crater was typical during February 2019 and accompanied weak and moderate explosions that averaged 12 per day throughout the month. White and gray ash plumes from the explosions rose to 2.8-3.3 km altitude; daily block avalanches usually reached the base of the dome (figure 94). Ashfall occurred around the complex, mainly on the W, SW, and NE flanks on a daily basis, but communities farther away were affected as well. The Washington VAAC reported an ash plume on 7 February in visible satellite imagery moving SW from the summit at 4.9 km altitude. The next day a new ash plume was located about 20 km W of the summit, dissipating rapidly, at 4.3 km altitude. Ashfall drifting SW affected Palajuno Monte Claro on 5, 9, 15, and 16 February. Ash drifting E and SE affected Calaguache, Las Marías and surrounding farms on 14 and 17 February, and fine-grained ash drifting SE was reported at finca San José on 21 February.

Figure 94. Activity at the Caliente dome of the Santiaguito complex at Santa Maria included daily ash-and-steam explosions and block avalanches descending the sides of the dome in February 2019. A typical explosion on 2 February 2019 produced an ash plume that rose to about 3 km altitude and drifted SW (left). A block avalanche on 14 February descended the SE flank and stirred up small plumes of ash in the vicinity (right, top); the avalanche lasted for 88 seconds and registered with seismic frequencies between 3.46 and 7.64 Hz (right bottom). Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 01 al 08 de febrero de 2019).

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/).

Nicaragua's Volcan Masaya has an intermittent lava lake that has attracted visitors since the time of the Spanish Conquistadores; tephrochronology has dated eruptions back several thousand years. The unusual basaltic caldera has had historical explosive eruptions in addition to lava flows and an actively circulating lava lake. An explosion in 2012 ejected ash to several hundred meters above the volcano, bombs as large as 60 cm fell around the crater, and ash fell to a thickness of 2 mm in some areas of the park. The reemergence of the lava lake inside Santiago crater was reported in December 2015. By late March 2016 the lava lake had grown and intensified enough to generate a significant thermal anomaly signature which has varied in strength but continued at a moderate level into early 2019. Information for this report, which covers the period from November 2018 through February 2019, is provided by the Instituto Nicareguense de Estudios Territoriales (INETER) and satellite -based imagery and thermal data.

The lava lake in Santiago Crater remained visible and active throughout November 2018 to February 2019 with little change from the previous few months (figure 70). Seismic amplitude RSAM values remained steady, oscillating between 10 and 40 RSAM units during the period.

Figure 70. A small area of the lava lake inside Santiago Crater at Masaya was visible from the rim on 25 November 2018 (left) and 17 January 2019 (right). Left image courtesy of INETER webcam; right image courtesy of Alun Ebenezer.

Every few months INETER carries out SO₂ measurements by making a transect using a mobile DOAS spectrometer that samples for gases downwind of the volcano. Transects were done on 9-10 October 2018, 21-24 January 2019, and 18-21 February 2019 (figure 71). Average values during the October transect were 1,454 tons per day, in January they were 1,007 tons per day, and in February they averaged 1,318 tons per day, all within a typical range of values for the last several months.

Figure 71. INETER carries out periodic transects to measure SO2 from Masaya with a mobile DOAS spectrometer. Transects taken along the Ticuantepe-La Concepcion highway on 9-10 October 2018 (left) and 21-24 January 2019 (right) showed modest levels of SO2 emissions downwind of the summit. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua. Octubre 2018 and Enero 2019).

During a visit by INETER technicians in early November 2018, the lens of the Mirador 1 webcam, that had water inside it and had been damaged by gases, was cleaned and repaired. During 21-24 January 2019 INETER made a site visit with scientists from the University of Johannes Gutenberg in Mainz, Germany, to measure halogen species in gas plumes, and to test different sampling techniques for volcanic gases, including through spectroscopic observations with DOAS equipment, in-situ gas sampling (MultiGAS, denuders, alkaline traps), and using a Quadcopter UAV (drone) sampling system.

Periodic measurements of CO₂ from the El Comalito crater have been taken by INETER for many years. The most recent observations on 19 February 2019 indicated an emission rate of 46 +/- 3 tons per day of CO₂, only slightly higher than the average value over 16 measurements between 2008 and 2019 (figure 72).

Figure 72. CO2 measurements taken at Masaya on 19 February 2019 were very close to the average value measured during 2008-2019. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua, Febrero 2019).

Satellite imagery (figure 73) and in-situ thermal measurements during November 2018-February 2019 indicated constant activity at the lava lake and no significant changes during the period. On 14 January 2019 temperatures were measured with the FLIR SC620 thermal camera, along with visual observations of the crater; abundant gas was noted, and no explosions from the lake were heard. The temperature at the lava lake was measured at 107°C, much cooler than the 340°C measured in September 2018 (figure 74).

Figure 73. Sentinel-2 satellite imagery (geology, bands 12, 4, and 2) clearly indicated the presence of the active lava lake inside Santiago crater at Masaya during November 2018-February 2019. North is to the top, and the Santigo crater is just under 1 km in diameter for scale. Courtesy of Sentinel Hub Playground.

Figure 74. Thermal measurements were made at Masaya on 14 January 2019 with a FLIR SC620 thermal camera that indicated temperatures over 200°C cooler than similar measurements made in September 2018.

Thermal anomaly data from satellite instruments also confirmed moderate levels of ongoing thermal activity. The MIROVA project plot indicated activity throughout the period (figure 75), and a plot of the number of MODVOLC thermal alerts by month since the lava lake first appeared in December 2015 suggests constant activity at a reduced thermal output level from the higher values in early 2017 (figure 76).

Figure 75. Thermal anomalies remained constant at Masaya during November 2018-February 2019 as recorded by the MIROVA project. Courtesy of MIROVA.

Figure 76. The number of MODVOLC thermal alerts each month at Masaya since the lava lake first reappeared in late 2015 reached its peak in early 2017 and declined to low but persistent levels by early 2018 where they have remained for a year. Data courtesy of MODVOLC.

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); Alun Ebenezer (Twitter: @AlunEbenezer, URL: https://twitter.com/AlunEbenezer).

The andesitic Volcán El Reventador lies well east of the main volcanic axis of the Cordillera Real in Ecuador and has historical eruptions with numerous lava flows and explosive events going back to the 16th century. The eruption in November 2002 generated a 17-km-high eruption cloud, pyroclastic flows that traveled 8 km, and several lava flows. Eruptive activity has been continuous since 2008. Daily explosions with ash emissions and ejecta of incandescent blocks rolling hundreds of meters down the flanks have been typical for many years. Activity continued during October 2018-January 2019, the period covered in this report, with information provided by Ecuador's Instituto Geofisico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and infrared satellite data.

Multiple daily reports were issued from the Washington VAAC throughout the entire October 2018-January 2019 period. Plumes of ash and gas usually rose to altitudes of 4.3-6.1 km and drifted about 20 km in prevailing wind directions before either dissipating or being obscured by meteoric clouds. The average number of daily explosions reported by IG-EPN for the second half of 2018 was more than 20 per day (figure 104). The many explosions during the period originated from multiple vents within a large scarp that formed on the W flank in mid-April (BGVN 43:11, figure 95) (figure 105). Incandescent blocks were observed often in the IG webcams; they traveled 400-1,000 m down the flanks.

Figure 104. The number of daily seismic events at El Reventador for 2018 indicated high activity during the first and last thirds of the year; more than 20 explosions per day were recorded many times during October-December 2018, the period covered in this report. LP seismic events are shown in orange, seismic tremor in pink, and seismic explosions with ash are shown in green. Courtesy of IG-EPN (Informe Anual del Volcán El Reventador – 2018, Quito, 29 de marzo del 2019).

Figure 105. Images from IG's REBECA thermal camera showed the thermal activity from multiple different vents at different times during the year (see BGVN 43:11, figure 95 for vent locations). Courtesy if IG (Informe Anual del Volcán El Reventador – 2018, Quito, 29 de marzo del 2019).

Activity during October 2018-January 2019. During most days of October 2018 plumes of gas, steam, and ash rose over 1,000 m above the summit of Reventador, and most commonly drifted W or NW. Incandescence was observed on all nights that were not cloudy; incandescent blocks rolled 400-800 m down the flanks during half of the nights. During episodes of increased activity, ash plumes rose over 1,200 m (8, 10-11, 18-19 October) and incandescent blocks rolled down multiple flanks (figure 106).

Figure 106. Ash emissions rose over 1,000 m above the summit of Reventador numerous times during October 2018, and large incandescent blocks traveled hundreds of meters down multiple flanks. The IG-EPN COPETE webcam that captured these images is located on the S caldera rim. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-282, 292, 295, 297).

Similar activity continued during November. IG reported 17 days of the month with steam, gas, and ash emissions rising more than 1,000 m above the summit. The other days were either cloudy or had emissions rising between 500 and 1,000 m. Incandescent blocks were usually observed on the S or SE flanks, generally travelling 400-600 m down the flanks. The Washington VAAC reported a discrete ash plume at 6.1 km altitude drifting WNW about 35 km from the summit on 15 November. The next day, intermittent puffs were noted moving W, and a bright hotspot at the summit was visible in satellite imagery. During the most intense activity of the month, incandescent blocks traveled 800 m down all the flanks (17-19 November) and ash plumes rose over 1,200 m (23 November) (figure 107).

Figure 107. Ash plumes rose over 1,000 m above the summit on 17 days during November 2018 at Reventador, and incandescent blocks traveled 400-800 m down the flanks on many nights. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-306, 314, 318, 324).

Steam, gas, and ash plumes rose over 1,200 m above the summit on 1 December. The next day, there were reports of ashfall in San Rafael and Hosteria El Hotelito, where they reported an ash layer about 1 mm thick was deposited on vehicles during the night. Ash emissions exceeded 1,200 m above the summit on 5 and 6 December as well. Incandescent blocks traveled 800 m down all the flanks on 11, 22, 24, and 26 December, and reached 900 m on 21 December. Ash emissions rising 500 to over 1,000 m above the summit were a daily occurrence, and incandescent blocks descended 500 m or more down the flanks most days during the second half of the month (figure 108).

Figure 108. Ash plumes that rose 500 to over 1,000 m were a daily occurrence at Reventador during December 2018. Incandescent blocks traveled as far as 900 m down the flanks as well. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-340, 351, 353, 354, 358, 359).

During the first few days of January 2019 the ash and steam plumes did not rise over 800 m, and incandescent blocks were noted 300-500 m down the S flank. An increase in activity on 6 January sent ash-and-gas plumes over 1,000 m, drifting W, and incandescent blocks 1,000 m down many flanks. For multiple days in the middle of the month the volcano was completely obscured by clouds; only occasional observations of plumes of ash and steam were made, incandescence seen at night through the clouds confirmed ongoing activity. The Washington VAAC reported continuous ash emissions moving SE extending more than 100 km on 12 January. A significant explosion late on 20 January sent incandescent blocks 800 m down the S flank; although it was mostly cloudy for much of the second half of January, brief glimpses of ash plumes rising over 1,000 m and incandescent blocks traveling up to 800 m down numerous flanks were made almost daily (figure 109).

Figure 109. Even during the numerous cloudy days of January 2019, evidence of ash emissions and significant explosions at Reventador was captured in the Copete webcam located on the S rim of the caldera. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, number 2019-6, 21, 26, 27).

Visual evidence from the webcams supports significant thermal activity at Reventador. Atmospheric conditions are often cloudy and thus the thermal signature recorded by satellite instruments is frequently diminished. In spite of this, the MODVOLC thermal alert system recorded seven thermal alerts on three days in October, four alerts on two days in November, six alerts on two days in December and three alerts on three days in January 2019. In addition, the MIROVA system measured moderate levels of radiative power intermittently throughout the period; the most intense anomalies of 2018 were recorded on 15 October and 6 December (figure 110).

Figure 110. Persistent thermal activity at Reventador was recorded by satellite instruments for the MIROVA system from 5 April 2018 through January 2019 in spite of frequent cloud cover over the volcano. The most intense anomalies of 2018 were recorded on 15 October and 6 December. Courtesy of MIROVA.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/).

Activity at Kuchinoerabujima is exemplified by interim explosions and periods of high seismicity. A weak explosion occurred on 3 August 2014, the first since 1980, and was followed by several others during 29 May-19 June 2015 (BGVN 42:03). This report describes events through February 2019. Information is based on monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Activity during 2016-2018. According to JMA, between July 2016 and August 2018, the volcano was relatively quiet. Deflation had occurred since January 2016. On 18 April 2018 the Alert Level was lowered from 3 to 2 (on a scale of 1-5). A low-temperature thermal anomaly persisted near the W fracture in Shindake crater. During January-March 2018, both the number of volcanic earthquakes (generally numerous and typically shallow) and sulfur dioxide flux remained slightly above baselines levels in August 2014 (60-500 tons/day compared tp generally less than 100 tons/day in August 2014).

JMA reported that on 15 August 2018 a swarm of deep volcanic earthquakes was recorded, prompting an increase in the Alert Level to 4. The earthquake hypocenters were about 5 km deep, below the SW flanks of Shindake, and the maximum magnitude was 1.9. They occurred at about the same place as the swarm that occurred just before the May 2015 eruption. Sulfur dioxide emissions had increased since the beginning of August; they were 1,600, 1,000, and 1,200 tons/day on 11, 13, and 17 August, respectively. No surficial changes in gas emissions or thermal areas were observed during 16-20 August. On 29 August, JMA downgraded the Alert Level to 3, after no further SO2 flux increase had occurred in recent days and GNSS measurements had not changed.

A very weak explosion was recorded at 1831 on 21 October, with additional activity between 2110 on 21 October and 1350 on 22 October; plumes rose 200 m above the crater rim. During an overflight on 22 October, observers noted ash in the emissions, though no morphological changes to the crater nor ash deposits were seen. Based on satellite images and information from JMA, the Tokyo VAAC reported that during 24-28 October ash plumes rose to altitudes of 0.9-1.5 km and drifted in multiple directions. During a field observation on 28 October, JMA scientists did not observe any changes in the thermal anomalies at the crater.

JMA reported that during 31 October-5 November 2018, very small events released plumes that rose 500-1,200 m above the crater rim. On 6 November, crater incandescence began to be periodically visible. During 12-19 November, ash plumes rose as high as 1.2 km above the crater rim and, according to the Tokyo VAAC, drifted in multiple directions. Observers doing fieldwork on 14 and 15 November noted that thermal measurements in the crater had not changed. Intermittent explosions during 22-26 November generated plumes that rose as high as 2.1 km above the crater rim. During 28 November-3 December the plumes rose as high as 1.5 km above the rim.

JMA reported that at 1637 on 18 December an explosion produced an ash plume that rose 2 km and then disappeared into a weather cloud. The event ejected material that fell in the crater area, and generated a pyroclastic flow that traveled 1 km W and 500 m E of the crater. Another weak explosion occurred on 28 December, scattering large cinders up to 500 m from the crater.

The Tokyo VAAC did not issue any ash advisories for aviation until 21 October 2018, when it issued at least one report every day through 13 December. It also issued advisories on 18-20 and 28 December.

Activity during January-early February 2019. JMA reported that at 0919 local time on 17 January 2019 an explosion generated a pyroclastic flow that reached about 1.9 km NW and 1 km E of the crater. It was the strongest explosion since October 2018. In addition, "large cinders" fell about 1-1.8 km from the crater.

Tokyo VAAC ash advisories were issued on 1, 17, 20, and 29 January 2018. An explosion at 1713-1915 on 29 January produced an ash plume that rose 4 km above the crater rim and drifted E, along with a pyroclastic flow. Ash fell in parts of Yakushima. During 30 January-1 February and 3-5 February, white plumes rose as high as 600 m. On 2 February, an explosion at 1141-1300 generated a plume that rose 600 m. No additional activity during February was reported by JMA. The Alert Level remained at 3.

Geologic Background. A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km west of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. The youngest cone, centrally-located Shintake, formed after the NW side of Furutake was breached by an explosion. All historical eruptions have occurred from Shintake, although a lava flow from the S flank of Furutake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shintake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

Kerinci is a frequently active volcano in Sumatra, Indonesia. Recent activity has consisted of intermittent explosions, ash, and gas-and-steam plumes. The volcano alert has been at Level II since 9 September 2007. This report summarizes activity during July 2018-January 2019 based on reports by The Indonesia 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.

Throughout this period dilute gas-and-steam plumes rising about 300 m above the summit were frequently observed and seismicity continued (figure 6). During July through January ash plumes were observed by the Darwin VAAC up to 4.3 km altitude and dispersed in multiple directions (table 7 and figure 7).

Figure 6. Graph showing seismic activity at Kerinci from November 2018 through February 2019. Courtesy of MAGMA Indonesia.

Table 7. Summary of ash plumes (altitude and drift direction) for Kerinci during July 2018 through January 2019. The summit is at 3.5 km altitude. Data courtesy of the Darwin Volcanic Ash Advisory Center (VAAC) and MAGMA Indonesia.

Figure 7. Dilute ash plumes at Kerinci during July 2018-January 2019. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub Playground.

Based on satellite data, a Darwin VAAC advisory reported an ash plume to 4.3 km altitude on 22 July that drifted to the SW and S. Only one day with elevated thermal emission was noted in Sentinel-2 satellite data for the entire reporting period, on 13 September 2018 (figure 8). No thermal signatures were detected by MODVOLC. On 28-29 September there was an ash plume observed to 500-600 m above the peak that dispersed to the W. Several VAAC reports on 2 and 18-22 October detected ash plumes that rose to 4.3 km altitude and drifted in different directions. On 19 January from 0734 to 1000 an ash plume rose to 200 m above the crater and dispersed to the E and SE (figure 9).

Figure 8. Small thermal anomaly at Kerinci volcano on 13 September 2018. False color (urban) image (band 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 9. Small ash plume at Kerinci on 19 January 2018 that reached 200 m above the crater and traveled west. Courtesy of MAGMA Indonesia.

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

Plumes . . . were recorded on images from the NOAA 9 polar orbiting weather satellite in January (table 8). Most plumes extended SE of the volcano.

Table 8. Lengths of plumes from Sakura-jima detected on NOAA 9 weather satellite images, January 1986.

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: Will Gould, NOAA/NESDIS/SDSD.

Juergen Kienle reports that seismicity at Augustine began to increase last summer for the first time since 1976, when the volcano last erupted. Between 12 July and 7 August, approximately 300 shallow microearthquakes were recorded each day on Augustine's network of four seismic stations. From then until late February, recorded earthquakes averaged 12/day, with occasional short bursts of seismicity. A small swarm took place during September with 100 events/day over a 2-3-day period. An intense peak occurred on 22 February between 0700 and 0800, when 70 microearthquakes were recorded on the seismometer less than 1 km from the dome, 2 hours before USGS scientists flew over the volcano and reported active degassing (see below). Since the end of February, seismicity has intensified, with concentrated swarms (3-4 events/hour lasting 1-2 hours) occurring approximately twice a day. These microearthquakes were all shallow and indicate fracturing and degassing of the dome.

The following is a report from M.E. Yount. "On 17 February, James Riehle saw what he believed to be an explosion plume over Augustine Volcano, while on Wolverine Peak more than 300 km from Augustine. The plume rose to an estimated altitude of more than 3 km. It was dispersed by winds within ~0.5 hour, with the lower portion of the plume drifting W or NW and the upper portion drifting E or SE. Seismic recorders at the USGS office in Anchorage, which monitor some of the University of Alaska Geophysical Institute seismometers, had shown an increase in small events near Augustine, beginning 13 February. On 20 and 21 February, the USGS began receiving reports from observers in Homer (110 km NE of Augustine) and from pilots flying near the volcano that it was vigorously steaming.

"On 22 February, USGS personnel flew over the volcano and confirmed that it was actively degassing from the moat around the summit dome. The main fumarolic vent was in the moat E of the dome. During the observations (between 1000 and 1018), fumarolic activity was continuous and steady. The plume was whitish, with a few grayish wisps. The SE and W sectors of the snow-covered cone were lightly dusted with ash, believed to be comminuted portions of the 1976 dome. No sign of avalanches or falling blocks from the dome were observed. During a 28 February overflight, USGS personnel noted an increase in the amount and area of fumarolic activity compared to 22 February. Augustine may be following its traditional pattern of slowly forcing the summit dome up followed by dome destruction and pyroclastic flow activity."

On 14 March, images from the NOAA-9 polar orbiting satellite showed a plume extending ~50 km S from Augustine at 1413 and 1555. No plume had been visible on 13 March, and clouds obscured the area 15-17 March. USGS scientists also flew over the volcano on 14 March, noting that the plume rose ~1,000 m above the summit and looked similar to the plume seen during their overflight on 28 February.

Geologic Background. Augustine volcano, rising above Kamishak Bay in the southern Cook Inlet about 290 km SW of Anchorage, is the most active volcano of the eastern Aleutian arc. It consists of a complex of overlapping summit lava domes surrounded by an apron of volcaniclastic debris that descends to the sea on all sides. Few lava flows are exposed; the flanks consist mainly of debris-avalanche and pyroclastic-flow deposits formed by repeated collapse and regrowth of the volcano's summit. The latest episode of edifice collapse occurred during Augustine's largest historical eruption in 1883; subsequent dome growth has restored the volcano to a height comparable to that prior to 1883. The oldest dated volcanic rocks on Augustine are more than 40,000 years old. At least 11 large debris avalanches have reached the sea during the past 1800-2000 years, and five major pumiceous tephras have been erupted during this interval. Historical eruptions have typically consisted of explosive activity with emplacement of pumiceous pyroclastic-flow deposits followed by lava dome extrusion with associated block-and-ash flows.

Information Contacts: Juergen Kienle, Geophysical Institute, University of Alaska, Fairbanks; M.E. Yount, T. Miller, and James Riehle, USGS Anchorage; M. Matson, NOAA/NESDIS.

"A new extrusive phase from Bagana's summit crater commenced on 16 February. The extrusion was preceded by several days' increase in seismicity, including three periods of 'tremor,' 30 minutes long (on the 5th and 6th) and an increase in the number of B-type events after the 10th. An increase in the amount of vapour released from the crater was also noted from the 7th onward.

"On the 16th, the vapour cloud became thick and coloured, while the seismicity rose suddenly to 140-175 events/day. From that night until the 21st, weak night glow from the crater was observed and extrusions of lava resulted in numerous incandescent avalanches of boulders on the NW, N, and NE flanks of the cone.

"At the end of the month, seismicity was still at a high level (>100 events/day), with periods of 'tremor' (on the 20th, 26th, and 28th), although visible activity had declined.

"Similar phases of extrusive activity occurred in November 1985 and January 1986 and resulted in increased movement of the long-established blocky lava flow down the N flank of the volcano."

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

Information Contacts: P. Lowenstein, RVO.

While spending the night of 5 March at the foot of Northeast Crater, geologists observed ash emission every 5-15 minutes with ejection of glowing red bombs 6-7 times/hour. Bombs reached the base of the crater. Significant degassing occurred from both of the central craters (The Chasm and Bocca Nuova). However, there were no explosions, nor was glow visible at night.

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: F. LeGuern, CNRS; Compagnie Republicaine de Securité de Briancan.

The eruptive episode . . . ended on 7 February. Aphyric basalt lavas covered 95% of the floor of Dolomieu Crater. The volume of lava emitted is estimated to be 7 x 10⁶ m³. Deflation was observed on the summit levelling stations in mid-February. A short seismic crisis occurred on 11-12 February; events were located E of the summit at 3 km depth. Since then seismic activity has returned to a very low level. Volcanic activity in 1985 is summarized in table 3. The total amount of lava emitted [in 1985] is estimated to be 33 x 10⁶ m³.

Table 3. Summary of 1985 eruptive episodes at Piton de la Fournaise.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: H. DeLorme and J-F. DeLarue, OVPDLF; P. Bachelery, Univ de la Réunion.

The island formed 20 January . . . has been eroded away by wave action since volcanic activity ceased. The island's disappearance was reported by the JMSDF after an hour-long helicopter flight that began 8 March at 0745. The surface of the new edifice was seen under white water, and there was no sign of a volcanic plume.

On 28 January, airplane pilots observed light brown floating pumice within a roughly rectangular NW-SE-trending zone ~200 km long by 50 km wide, extending from ~100 to 300 km SE of the volcano. The pumice was in subparallel teardrop-shaped rafts roughly 4 km wide and 10 km long, elongate perpendicular to the apparent direction of drift.

Rocks collected from Fukutoku-Okanoba after previous eruptions in 1904, 1914, and 1982 were trachyandesites with high alkali contents.

Geologic Background. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: M. Matson, NOAA/NESDIS; Kyodo Radio, Tokyo; UPI.

The submarine eruption . . . described in 10:12 had been observed by residents of a nearby island in early December and was continuing in late February, but had ended by 3 March.

From Saira village, roughly 25 km from Kavachi on Vangunu Island, Oliver Jino reported that the eruption sequence began on 9 December. After the previously reported observations from aircraft and ships 30 December-7 January, the next sighting was on 20 January, when Dr. G. Baines noted three ejections of water and steam, 1.5-2 minutes apart, from a Solair plane flying >45 km from the volcano. An area that looked like a coral reef but was probably volcanic debris extended downcurrent from the vent. On 24 January, Mr. B. Papukera, another Solair passenger, observed a single similar ejection. No activity was evident from a Solair plane on 5 February. On 25 February, Solair Captain Don Lemon observed renewed activity ejecting water and steam to 100 m or more asl. Two days later, Lemon again flew near the volcano, observing gas bubbles over the vent and muddy-looking water drifting away from it, but no explosions. On 3 March, personnel in a powered dinghy from the RV Thomas Washington searched the area but found no sign of activity.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island about 30 km N of the site of subduction of the Indo-Australian plate beneath the Pacific plate. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Information Contacts: D. Tuni, Ministry of Natural Resources, Honiara.

EPISODE 42

Eruptive activity . . . resumed in February . . . . After 25 days of repose, the summit began to deflate on 22 February at 1000 and 10 minutes later lava fountaining began at the Pu`u `O`o vent. Low-level fountaining and pahoehoe spillovers occurred intermittently until 1515 when continuous lava production began. High-amplitude harmonic tremor started 25 minutes later.

Fountain heights increased steadily over the next 7 hours until they reached ~300 m above the vent at 2230 and were sustained at that level for several hours. Four pulses of fountain jetting 360-450 m high, each lasting several minutes, occurred between 0233 and 0416 on the 23rd. After the fourth pulse at 0416, fountaining declined quickly and lava production stopped at 0420. Strong harmonic tremor ended at 0419, but was followed by moderate-amplitude, pulsating tremor for a day. Summit deflation, totalling 14.8 µrad, ended at 0700 on the 23rd; by the end of February, the summit had reinflated by 4.3 µrad (figure 43). Episode 42 lava flows extended ~3.5 km SE from Pu`u `O`o on a broad front. A small flow advanced ~1 km to the N.

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: C. Heliker, G. Ulrich, R. Koyanagi, and R. Hanatani, HVO; E. Nielsen, SI.

"A moderate level of activity continued in February. Crater 2 occasionally released white to greyish vapour. A number of explosion shocks (0-10 daily) were recorded, some of which were heard at the Cape Gloucester observation post . . . . Two periods of high background seismicity, consisting of sub-continuous, high-frequency 'tremor,' occurred 6-11 and 21-25 February, possibly related to periods of high rainfall. Weak, fluctuating glow was observed on the night of the 20th."

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: P. Lowenstein, RVO.

"Seismicity . . . increased further in February, with 317 recorded events. Ground deformation measurements, however, showed only minor uplift (up to 4 mm), with slight inflationary tilt and EDM changes in the Greet Harbour area."

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: P. Lowenstein, RVO.

Hydrothermal eruptions, apparently accompanied by felt earthquakes, were observed 8 and 9 February. On 8 February at 1202, ranger Lisle Irwin saw a vigorous steam column rise > 150 m above Crater Lake and heard loud roaring from his vantage point 2 km to the NE. Inside Dome Shelter, ~350 m NNW of the lake, Rob McCallum felt what he described as a slight earthquake during the eruption. Irwin noted no fresh ejecta deposits around the lake after the eruption. At 1517, he observed a second apparently smaller eruption that produced a steam column and audible water surges over the lake's outlet channel. While flying over the crater the next day at 0719, ranger Paul Dale saw a small column of muddy water rising to ~5 m before it was obscured by steam. Between 1300 and 1330, two climbers saw a "high bubbling circle in the middle of the lake and at the same time felt the ground shake."

When geologists visited the crater 11 February, lake temperature had risen to 46°C (from 29°C on 14 January) and there was evidence of surging of 1 vertical meter or more within the previous 12-24 hours. Strands of sulfur were floating on the lake and there was a strong odor of SO₂. Activity was similar on 14 February, and there appeared to have been additional but somewhat weaker surging in the preceding 24 hours. Deformation surveys 11 and 14 February suggested minor deflation since a small inflation peak was measured in mid-January. The lake temperature had dropped to 34°C by 26 February and there was no evidence of further eruptions.

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: NZGS, Rotorua.

Colombian geologists reported that microseismic activity diminished between mid-February and mid-March, with an average of 5 high-frequency and 12-15 low-frequency events daily. Seismic events of mixed frequency also diminished, to 1/day. Activity on 28 February was abnormally low, with only one low-frequency event. Epicenters were within 3-4 km of the crater, and focal depths were at 1-3 km below a datum at 4.7 km above sea level . . . .

The vapor column reached heights of 100-800 m, without significant ash emission. Rates of SO₂ emission measured by COSPEC in early March were generally of the order of 500 t/d; during the afternoon of 4 March, values of ~1,000 t/d were recorded, about the same as a month earlier. Fissures in pyroclastic material on glaciers on the NE part of the volcano showed displacements of 20-30 mm/day. Electronic tilt instruments recorded ~0.1 µrad of inflation/day on the W flank. No significant changes were detected on the E flank.

Additional seismic information comes from Jim Zollweg. "After the 13 November eruption, a 6-station telemetry network was installed around the volcano. All stations use vertical 1-Hz seismometers and radio-telemeter to the Comité de Estudios Vulcanológicos headquarters in Manizales. Sites were chosen 4-10 km from Arenas, Ruiz's active crater. The first station was operating on 17 November, four stations were functioning by 28 November, and all six by 2 December, although some locations were changed later. Recording is analog using pen-and-ink or smoked paper.

"Seismic activity was moderate in November and December, consisting chiefly of high-frequency earthquakes with magnitudes to 3.5. There were about half as many low-frequency as high-frequency earthquakes during those months. About 1,300 earthquakes were counted in December (countable events had coda lengths of at least 5 seconds on the Olleta telemetry station). In January, activity was considerably lower because of a major decrease in the rate of occurrence of high-frequency events. Only a few surface-type events (gas emission signals or avalanches) were recorded by telemetry stations in any month. Instances of harmonic tremor sustained for more than a minute were also uncommon, particularly in December. The most important tremor recorded since the stations were installed occurred 3-5 January, preceding and during a minor eruption 4-5 January. This tremor was unusual because of its wide range of frequency content; frequencies of 7 Hz or more were recorded within a few hours of its onset, and frequencies as low as 0.7 Hz occurred later in the episode.

"Very few low-frequency earthquakes have been locatable, and those with epicenters that could be computed usually occurred near Arenas Crater (within the limits of accuracy of the solutions). More than 150 high-frequency earthquakes have been located, and 81 of the better solutions are plotted in figure 6. Events were located using the program HYPOINVERSE, and an ad-hoc crustal model based on geological considerations. Events plotted within the network have epicentral 95% confidence limits of 1 km or less. Those plotted outside the network may have epicentral 95% confidence limits as poor as 3 km, depending on distance from the network. Focal depths of the high-frequency events are usually between 2 and 5 km (beneath a datum at 4.7 km asl), but depend on the crustal model used. The probable error range makes it difficult to say whether there are significant depth differences between events.

Figure 6. Earthquake epicenters at Ruiz, 28 November 1985-21 January 1986. The 5,000-m contour is outlined. Filled triangles are telemetered stations; others are shown by open triangles. Not all were operating simultaneously; PIRT and ARBO are no longer operating. Courtesy of Jim Zollweg.

"Most of the high-frequency earthquakes occurred in one of two linear zones that intersect under the center of Ruiz. The E-W-striking zone is ~6 km long and was responsible for most of the seismicity. There is an interesting temporal pattern to the epicenters. Locations between 28 November and 5 December mainly fell in the central and eastern parts of the E-W zone, whereas vigorous swarms 6-13 December were mainly confined to the W half of the zone. There was a pronounced hiatus in high-frequency activity 14-21 December, followed by a swarm of events 22-25 December along the second zone, striking NW-SE. Between 26 December and 3 January, earthquakes reverted to a small area near the intersection of the two zones. High-frequency activity was comparatively low in the weeks following the 4-5 January eruption. First motions have been mostly compressions for nearly all events under Ruiz, suggesting a normal faulting environment. The data for the high-frequency sequences suggest the intrusion of dike-like bodies of magma along pre-existing fault zones."

Deformation monitoring has been summarized by Barry Voight. "Preliminary data from EDM reflector stations suggest that much of the observed summit surface deformation is due to ice movement decoupled from underlying bedrock. The data place constraints on the volume of rock susceptible to massive gravitational failure. EDM reflector stations (Martica and Finger) were installed at ~5,100 m elevation near the center of the Río Azufrado headwall. They were first measured on 14 February. Preliminary data from repeated distance measurements to 7 March suggest that the motions of glacier ice and underlying bedrock are decoupled. The fracture pattern observed on the surface of the summit plateau E of Arenas Crater dominantly reflects the propagation of crevasse patterns through the veneer of surficial deposits. The steady outward motion of the summit area as deduced from observation of surficial fracturing and EDM monitoring mainly reflects movements in glacier ice rather than motion of underlying bedrock. At other locations, some cracks give the appearance of possibly extending into bedrock, for example at the septum separating the crater from the headwall of the Río Azufrado. Although my current impression is that all of the headwall is probably stable with respect to deep-seated rock failure, the potential for mass movement involving a portion of the crater remains to be thoroughly evaluated."

Fabian Hoyos P. reported that isotopic analyses of several hot springs and the crater fumarole were sampled on 8 July 1985 in cooperation with the Central Hidroeléctrica de Caldas (CHEC). Isotopic compositions of 8 July 1985 hot spring samples were similar to those reported in 1968 and 1980 to CHEC. Water vapor collected the same day from the summit crater fumarole had an isotopic composition corresponding to that of meteoric water precipitated at ~2,800 m asl (table 2). Other samples collected until just before the 13 November eruption are being analyzed.

Table 2. Isotope analyses by Sara Kealy, Arizona State Univ, of samples collected from fumaroles at Ruiz, 8 July 1985. Data courtesy of Fabian Hoyos P. and Sara Kealy.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: I. Mejía and E. Parra, Comité de Estudios Vulcanológicos, Manizales; A. Londoño, L. Rodriguez, and N. Rojas, Univ Nacional, Manizales; N. García, Industria Licorera de Caldas, Manizales; F. Hoyos, Univ Nacional, Medellín, Colombia; J. Zollweg, USGS, Univ of Washington; B. Voight, Penn State Univ; S. Williams, Louisiana State Univ.

Activity remained at background levels for the 8th consecutive month, the longest repose period since activity began in 1980. February's single successful SO₂ flight (on the 10th) measured 45 plus or minus 10 t/d. Maximum deformation rates were ~1 mm/day. Seismicity also remained low, with no evidence of energetic gas emission.

Geologic Background. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but few lava flows extended beyond the base of the volcano. The modern edifice was constructed during the last 2200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.

Information Contacts: D. Swanson, E. Endo, and S. Brantley, CVO; C. Jonientz-Trisler, University of Washington.

The series of shallow earthquakes near Tacaná was continuing in early March. Many of the shocks were felt near the volcano. There were no apparent changes to fumaroles on and around the volcano. To supplement permanent seismometers 30 km SW and 80 km N of the volcano (near Tapachula and Comitán), Mexican geophysicists installed portable instruments about 27 km NW of the volcano (at Motozintla), W of the volcano (at El Aguila) and about 6 km S of the summit (at Unión Juárez).

The majority of felt events were subduction zone earthquakes centered under the coast of northernmost Guatemala. Other events originated in a fault system NE of the volcano, in Guatemala. A third type consisted of events under the volcano, characterized by sharp P arrivals and very long S-wave trains, that were strong enough to be felt and heard within 10 km of the volcano. Apparent volcanic tremor episodes with amplitudes just above noise levels were recorded 2-3 times a day. The rate of seismic energy release increased substantially 18-25 February, declined significantly after 25 February, then started to increase again on 3 March. On 3 March between 0400 and 1200, a bubble tiltmeter 6 km S of the summit (at 1,800 m elevation) indicated a sharp deformation event corresponding to about 100 microradians of deflation on an azimuth of 073°. However, relevelling of a line extending 1 km N and 4 km S of the tiltmeter (including one station only a few tens of meters away) revealed no changes. On 10 March about 0200, seismic instruments detected several events that looked like explosion shocks, followed by about 2 minutes of very minor tremor. The events were felt and heard by many residents of towns around the volcano, but no eruption occurred. The government of the state of Chiapas, México has prepared a contingency plan to respond to several levels of volcanic risk, including evacuation of people within 15 km of the volcano if necessary.

Geologic Background. Tacaná is a 4064-m-high composite stratovolcano that straddles the México/Guatemala border at the NW end of the Central American volcanic belt. The volcano rises 1800 m above deeply dissected plutonic and metamorphic terrain. Three large calderas breached to the south, and the elongated summit region is dominated by a series of lava domes intruded along a NE-SW trend. Volcanism has migrated to the SW, and a small adventive lava dome is located in the crater of the youngest volcano, San Antonio, on the upper SW flank. Viscous lava flow complexes are found on the north and south flanks, and lobate lahar deposits fill many valleys. Radial drainages on the Guatemalan side are deflected by surrounding mountains into the Pacific coastal plain on the SW side of the volcano. Historical activity has been restricted to mild phreatic eruptions, but more powerful explosive activity, including the production of pyroclastic flows, has occurred as recently as about 1950 years ago.

Information Contacts: S. de la Cruz-Reyna, UNAM, México D.F.

"Activity . . . remained at a low, non-eruptive level throughout February. No significant visible or audible activity was reported, and the seismicity remained [at about] 100 events/day."

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 north coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1000 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: P. Lowenstein, RVO.

Minor magmatic eruptive activity resumed ... about 1 February from a new vent within the 1978 Crater complex. On 3 February helicopter pilot Ian Johnson observed a new active vent and associated tephra fall.

About 15 low-frequency B-type earthquakes/day occurred from December into February with unusually large (50 mm p-p) amplitudes, although a gradual decline in amplitudes was apparent. Significant periods of volcanic tremor were recorded in January (11, 19, 20-21, 25-29) and February (1-5) but no vent-forming episode could be clearly recognized.

When geologists visited the volcano 10 February, there was a new vent ~ 25 m in diameter near the base of the E crater wall, farther E than any vent of the 1976-82 eruption sequence. The vent emitted vapor at a moderate rate and a small amount of very fine ash was occasionally present in the gas plume.

A fresh layer of ash, 10-15 mm thick, was on the main crater floor to 150-200 m E of the new vent and a small ejecta apron extended 30-50 m W of the vent. Small scoria bombs were sparsely scattered on the surface within 50 m of the new vent. Bombs were rarely larger than 100 mm in diameter. One had clearly flattened on impact, indicating it was still soft when it fell. The scoria is fresh, dark brown, vesiculated glassy andesite with phenocrysts of plagioclase and pyroxene. Recently deposited tephra comprise reworked crater-fill detritus, some fresh crystals, and brown glass.

Fumarole temperatures of 350-360°C were measured on 10 February, 25° cooler than on 13 November (10:11) and 15-25° cooler than on 7 February. COSPEC measurements on 7 February showed an SO₂ emission rate of 570 t/d, a substantial increase over the 320 t/d detected on 21 November 1984 and 350 t/d recorded on 7 January 1985.

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: New Zealand Geological Survey (NZGS); P. Kyle, New Mexico Inst of Mining & Technology.

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/).