ANATAHAN Mariana Islands, central Pacific Ocean 16.35°N, 145.67°E; summit elev. 788 m; All times are local (= UTC + 10 hours) Reports from 2003: | May | June | July | September | Reports from 2004: | February | March-April | May | June | July | August | October | December | Anatahan Eruption History Information from the USGS Global Volcanism Program -------------------------------------------------------------------------------- 7-13 May 2003 On 10 May around 1700 an eruption began at Anatahan, a volcanic island which has had no historically documented eruptions. Scientists on a small ship about 10 km away saw an ash plume that eventually rose to ~12 km a.s.l. The eruption occurred primarily from Anatahan's eastern crater and observers did not see lava flows. No precursory activity was recorded (the island of Anatahan is uninhabited and lacks working seismometers) and no signs of the impending eruption were seen by scientists who visited the island on 6 May. According to the Washington VAAC, an ash cloud was visible on satellite imagery beginning around 1730 on 10 May. The next day around 0655 ash was seen moving in three different directions; WNW at a height around 5.5 km a.s.l., SW around 8.5 km a.s.l., and two separate and smaller ash plumes were drifting SE at heights around 13.4 km a.s.l. Local authorities issued a special advisory on 11 May stating that "… the general public especially fisherman, tour operators and commercial pilots are advised to stay away from the island of Anatahan until further notice from the Office of Emergency Management." As of 13 May ash emissions continued and a hot spot was visible on satellite imagery. Residents of the small island of Anatahan (part of the United States Commonwealth of the Northern Mariana Islands) were evacuated in 1990 after a shallow earthquake swarm. The most recent reported seismicity occurred in 1993. Sources: The Margins Mariana Subduction Factory Imaging Project Research Team (from Washington University, St. Louis; Scripps Inst. of Oceanography; and CNMI Emergency Management Office), Hawaii Volcano Observatory, Washington VAAC, Variety News Staff, Voice of America News -------------------------------------------------------------------------------- 14-20 May 2003 The eruption at Anatahan that began on 10 May continued through 20 May with less intensity than when it began. The Washington VAAC reported that the ash cloud produced by the eruption drifted W and NW and was at a height of ~5 km a.s.l. on 14 May, and ~4 km a.s.l. on 15 May. As of the 20th, steam-and-ash emissions continued, with the resultant clouds remaining below 3 km and drifting primarily W. According to a news report, parts of the island of Anatahan have been covered by up to ~0.5 m of ash. News reports also stated that by 16 May ash had drifted over the Philippines, posing a threat to aviation in the vicinity. Sources: Washington VAAC, Inquirer News Service with Agence France-Presse, Saipan Tribune -------------------------------------------------------------------------------- 21-27 May 2003 Volcanic activity that began at Anatahan on 10 May continued during 21-27 May. On 21 May an ash plume was visible on satellite imagery at a height of about 4.9 km a.s.l. drifting W. Around 23 May, typhoon Chan-hom caused a shift in the prevailing wind direction near Anatahan and ash was transported S over the islands of Saipan, Tinian, Rota, and Guam. Due to the ash, airlines cancelled several flights to and from Saipan and Guam international airports. In Saipan and Guam an ash advisory, and a volcanic haze advisory, respectively, were issued on the 23rd stating that residents should be cautious of lower air quality due to the plume of ash, SO2, and other gases over the islands that morning. By 24 May the plume had drifted away from the islands. According to the Washington VAAC, satellite imagery on 24 May at 1413 showed the ash plume at a height around 5.2 km a.s.l. caught up in the cyclonic circulation of the typhoon moving S, then SE. By 27 May the ash cloud was around 3 km a.s.l. and drifting E. Sources: Washington VAAC, Pacific Daily News, Saipan Tribune 5/24, Saipan Tribune 5/26 -------------------------------------------------------------------------------- 28 May-3 June 2003 Emissions of ash and gas at Anatahan, which began on 10 May, continued during 28 May to 3 June. During most of the report week, eruption clouds rose to heights around 3 km a.s.l. Based on a report from an aircraft, the Washington VAAC stated that ash from a fairly vigorous eruption on 31 May around 1025 rose to ~7.6 km a.s.l. By 2202 there were reports of ash to ~ 6 km a.s.l. The TOMS Volcanic Emissions Group reported detecting significant SO2 emissions from Anatahan during 10-30 May, although data gaps prevented measurements on some days. Sources: Washington VAAC, Total Ozone Mapping Spectrometer (TOMS) Volcanic Emissions Group -------------------------------------------------------------------------------- 4-10 June 2003 Emissions of ash and gas at Anatahan, which began on 10 May, continued during 4-10 June. The highest reported ash plume rose to ~7.6 km a.s.l. on 3 June at 2013 according to observations from an aircraft. US Geological Survey and Commonwealth of the Northern Mariana Islands Emergency Management Office (EMO) personnel visited Anatahan on 6 June and repaired the seismic station in the east crater. EMO recommended that the state of emergency for Anatahan be extended due to continued volcanism, and that Anatahan residents be permanently relocated. Sources: Washington VAAC, US Geological Survey Hawaiian Volcano Observatory, Australian Broadcasting Corporation -------------------------------------------------------------------------------- 11-17 June 2003 As of 17 June, continuous ash-and-gas emissions persisted at Anatahan. US Geological Survey and CNMI Emergency Management Office personnel observed the volcano on 12 June. They noted that a lava dome or flow was visible on the crater floor and ash was emitted from several areas. No sound emanated from the crater, spines were visible on the crater floor, and one source for the convecting ash cloud was located on the E side of the east crater. In addition, the east crater seemed deeper than during the previous visit on 6 June. During 5-12 June, the seismic record only contained banded-volcanic tremor, but on the evening of 12 June long-period (M ~2) earthquakes began to be recorded. An explosion earthquake occurred on 14 June at 0010. Scientists believe the earthquake was associated with an explosion that removed much of the small lava dome, because the dome was no longer seen during an overflight on the 14th. After the explosion, a series of long-period earthquakes occurred at regular 1- to 2-minute intervals until ~1400. During the report period, ash was visible on satellite imagery rising to a maximum height of ~3 km a.s.l. Sources: US Geological Survey Hawaiian Volcano Observatory, Washington VAAC -------------------------------------------------------------------------------- 18-24 June 2003 The eruption that began at Anatahan on 10 May continued through 24 June, with the emission of low-level steam-and-ash plumes. On 16 June at 1613 US Geological Survey and Commonwealth Scientific and Industrial Research Organization (CSIRO) personnel saw emissions intensify from mainly low-level steam to a more ash-laden plume that rose to a height of ~2.5 km a.s.l. At this time the seismic amplitude increased from small to large. After 16 June only low-amplitude tremor was recorded by the seismic station on the island. According to the Washington VAAC, ash plumes were occasionally visible on satellite imagery at heights around 2.5 km a.s.l. Sources: US Geological Survey Hawaiian Volcano Observatory, Washington VAAC -------------------------------------------------------------------------------- 25 June-1 July 2003 The eruption that began at Anatahan on 10 May continued through 26 June, with fine ash emitted from the volcano's East Crater drifting W and SW. During 24-26 June, steam was primarily seen rising to low levels above the volcano, but there were periods when a more ash-laden plume rose to a maximum height of ~2 km above the volcano. The bottom of East Crater was obscured, so scientists could not determine if a lava dome was present. Several earthquakes near Anatahan were recorded during 24-26 June at both the Anatahan and Saipan stations. The largest earthquake occurred on 24 June with a magnitude of 4.9. During the report period, ash was sometimes visible on satellite imagery. Sources: US Geological Survey Hawaiian Volcano Observatory, Washington VAAC -------------------------------------------------------------------------------- 2-8 July 2003 Scientists visiting Anatahan on 2 July found relatively low-level eruptive activity continuing at East Crater. The emitted plumes were ~1 km a.s.l., thin, and contained little ash. Several small vents on the crater floor emitted fine-grained ash and fumaroles were visible on the lower crater walls. Volcanic tremor persisted during 2-3 July at relatively low levels. Sources: US Geological Survey Hawaiian Volcano Observatory, Washington VAAC -------------------------------------------------------------------------------- 9-15 July 2003 As of 11 July, the eruption that began at Anatahan on 10 May continued to wane as shown by decreasing volcanic-tremor amplitudes and observations. On 9 July observations revealed that only white steam was being emitted from East Crater along with a small amount of light-brown fume. During 9-15 July, only faint ash plumes were visible on satellite imagery. Sources: US Geological Survey Hawaiian Volcano Observatory, Washington VAAC -------------------------------------------------------------------------------- 10-16 September 2003 During a flight over Anatahan during the week of 7 September, USGS and Emergency Management Office (EMO) personnel did not see any ash emissions, only low-level steam-and-gas emissions. The floor of Anatahan's crater was covered by sediment-laden water. In East Crater there was an active geothermal system, consisting of mud pots, mini-geysers, and steam jetting from the crater walls. Seismicity at Anatahan was at low levels through 16 September. Source: US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 4-10 February 2004 After more than 5 months of very low-level seismic activity, long-period earthquakes began at Anatahan on 1 February with a maximum magnitude of 2. On 7 February just before 0600 seismicity peaked, with up to 15 events occurring per hour. It then decreased dramatically, but remained well above the levels during the previous few months. By 8 February the size of the volcanic earthquakes had diminished greatly, but their frequency had increased to as many as one every minute. The amplitude of the low-frequency tremor increased. During 9 and 10 February the volcanic earthquakes had become so small that they were essentially not recorded by the seismic network. The amplitude of the low-frequency tremor remained high, but decreased from its peak level during 5-7 February. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 11-17 February 2004 During 13-17 February, volcanic seismicity at Anatahan was at low background levels. There were no apparent eruption signals or precursory events. In addition, tremor and seismic-energy release were at very low levels. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 31 March- 6 April 2004 A seismic swarm began beneath Anatahan on 31 March. During 31 March to at least 4 April, volcanic seismicity was at its highest level since the eruption of May-June 2003, with events as large as M 2.5. The earthquakes were usually followed by tremor-like signals that scientists believed indicated steam and/or ash emissions to altitudes well below 1 km. As of 6 April, the seismic swarm continued to intensify slowly. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 7-13 April 2004 On 12 April the presence of a new lava dome at Anatahan within a crescent-shaped crater lake was confirmed by scientists. Fresh ejecta were visible within the lowest reaches of the crater. High levels of volcanic seismicity that began on 31 March continued through 12 April, although it was not quite as high as during its 6-7 April peak. Scientists believed that small steam and/or ash emissions occasionally rose to levels below 1 km, but could increase in height relatively abruptly without much warning. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 14-20 April 2004 Seismicity remained at high levels and dome growth continued at Anatahan during the reporting week. Small ash emissions rising to ~1 km a.s.l. were likely occurring and the threat of larger eruptions remained. Sources: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory, Washington VAAC -------------------------------------------------------------------------------- 21-27 April 2004 Seismicity at Anatahan increased abruptly on 24 April at 1052 to a level that had not been reached since the summer of 2003. Around 0600 on 26 April, seismicity leveled off. Later that day, during two 30-minute observation periods, scientists saw regular puffs of yellow/brown steam and ash emitted at 1- to 2-minute intervals. The rate of emissions virtually matched the rate of seismic events during that time. During 24-26 April, steam-and-ash plumes reached a maximum height of about 600 m above the volcano. According to the Washington VAAC, on 24 April a thin plume from Anatahan was visible on satellite imagery ~1 km above the volcano and extending NW from the volcano. Aircraft were warned to proceed with caution near the volcano. Sources: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory, Washington VAAC, Agence France-Presse -------------------------------------------------------------------------------- 28 April- 4 May 2004 Early on 28 April, the level of seismicity at Anatahan increased to its highest level since renewed seismic activity began on 24 April. At this time the lava dome probably increased in size. Seismicity decreased somewhat during the following ~5 days, but M 2-2.5 earthquakes and small explosions still occurred about every minute, and steam-and-ash emissions still rose several hundred meters above the volcano. Local authorities placed Anatahan Island off-limits until further notice. They also concluded that although the volcano was not currently dangerous to most aircraft within the Mariana Islands airspace, conditions could change rapidly and aircraft should pass upwind of Anatahan or more than 30 km downwind from the island and exercise due caution within 30-50 km of the volcano. Sources: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory, Associated Press -------------------------------------------------------------------------------- 5-11 May 2004 The moderate eruption that began at Anatahan on 24 April continued through 12 May. Seismicity remained at high levels and consisted of discrete explosion signals. Beginning around 5 May explosion signals became less frequent (averaging one event every 2 minutes), but stronger (commonly reaching about M 3). Steam-and-ash emissions continued to rise several hundred meters above the volcano. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 12-18 May 2004 During 13-17 May, volcanic activity continued at Anatahan. Explosions occasionally threw volcanic material hundreds of meters out of the crater, and steam-and-ash emissions probably rose several hundred meters above the volcano. On 17 May the seismic energy release nearly doubled in comparison to the previous several days, but remained well below the peak level reached on 24 April. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 19-25 May 2004 During 20-25 May, volcanic activity continued at Anatahan. Explosions every few minutes threw volcanic material hundreds of meters out of the crater, and steam-and-ash emissions probably rose several hundred meters above the volcano. On 25 May satellite imagery showed an ash plume extending at least 5 km NW of the volcano. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 26 May- 1 June 2004 During 26 May to 1 June, elevated seismicity at Anatahan consisted of discrete explosion signals. Every few minutes explosions threw volcanic material hundreds of meters out of the crater, and steam and ash likely rose a few hundred meters. Source: Emergency Management Office of the Commonwealth of the Northern Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 2-8 June 2004 During 2-8 June, elevated seismicity at Anatahan consisted of discrete explosion signals. Every few minutes explosions threw volcanic material hundreds of meters out of the crater, and steam and ash likely rose a few hundred meters. Sources: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 9-15 June 2004 Low-level volcanic and seismic activity continued at Anatahan during 9-15 June. During a visit to the volcano on 10 June, Strombolian explosions at an active spatter cone threw volcanic material as high as ~100 m every 10-60 seconds. Around 15 June, the amplitude and number of discrete seismic events appeared to slightly decrease. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 23-29 June 2004 During 14-16 June, the level of seismicity was significantly lower at Anatahan than during the previous week. After the 16th, seismicity returned to the higher levels seen before the 14th and remained there through 28 June. On the 28th a tropical storm knocked out the last seismic station on Anatahan, prohibiting further monitoring until it is repaired. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 30 June- 6 July 2004 On 2 July, the seismicity level at Anatahan rose nearly as high as it was in late April 2004. After the 2nd, seismicity declined slightly. The nature of the seismic signals suggested that Strombolian explosions occurred at intervals of tens of seconds to minutes. The Washington VAAC reported that during clear weather on 3 July, a ~30-km-long ash plume was visible below ~3 km a.s.l. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 7-13 July 2004 Seismicity continued at a high level at Anatahan following a slight decline from near-peak levels on 2 July. Observers correlated the seismic activity on July 9 and 12 with Strombolian explosions that ejected tephra about 100 m above the vent at intervals ranging from a few tens of seconds to minutes. An ash plume extending generally westward a few tens of kilometers downwind from Anatahan below ~3 km a.s.l. was observed by scientists visiting the volcano for much of the week. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 14-20 July 2004 During 14-20 July, Strombolian explosions at Anatahan were frequently accompanied by steam-and-ash explosions. The explosions threw mostly coarse volcanic material up to ~100 m at intervals lasting tens of seconds. A plume of fine ash and steam extended tens of kilometers predominately towards the W, reaching heights below ~1.8 km a.s.l. According to the Washington VAAC, low-level ash plumes were occasionally visible on satellite imagery. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 21-27 July 2004 Seismicity at Anatahan approached the highest levels of the year on 23 July. That day, Strombolian explosions frequently threw mostly coarse material up to hundreds of meters at intervals of tens of seconds to minutes. On 26 July, there were nearly continuous ash-and-gas emissions. By 27 July, seismicity had decreased to very low levels in comparison to the previous 2 months, and seismic signals indicated that the frequent individual explosions that occurred during the previous week decreased greatly in size and number. Sources: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory , Hello Pacific News -------------------------------------------------------------------------------- 28 July- 3 August 2004 During 26 July to 3 August, seismicity at Anatahan remained at very low levels. Interpretations of seismic data suggested that the frequent explosions during the previous week had decreased. Ash plumes probably did not rise higher than 6 km above the volcano. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 20-26 October 2004 On 27 September, the first long-period seismic events since July 2004 were recorded at Anatahan. Only a few, small events were recorded. Beginning on 12 October, several periods of small, rather regularly spaced long-period events were recorded at intervals of 4 to 15 seconds. This seismicity began several hours after the onset of a series of intense tropical depressions and storms. On 18 October, people in Saipan smelled H2S during very hazy visibility, but no plume was detected on satellite imagery by the Washington VAAC. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory -------------------------------------------------------------------------------- 1-7 December 2004 Based on a pilot report to the Guam Forecast Office, the Washington VAAC reported that ash from Anatahan was at a height of ~3 km a.s.l. on 2 December. Ash was not visible on satellite imagery, but a hotspot was briefly evident on infrared satellite imagery. Source: Washington VAAC