Report on Anatahan (United States) — 26 January-1 February 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 January-1 February 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Anatahan (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 26 January-1 February 2005. Smithsonian Institution and US Geological Survey.
16.35°N, 145.67°E; summit elev. 790 m
All times are local (unless otherwise noted)
As of 30 January Anatahan continued to erupt, with Strombolian explosions occurring about every minute, similar to activity of the previous few weeks. Seismicity during the current eruption reached a high on 26 January, at a level about 20% above previous high levels for the year. After midday on the 27th the explosions became larger but less frequent than before. At about that time, a commercial pilot reported ash to ~3 km a.s.l. and satellite imagery also showed a plume of ash and vog (fog composed of volcanic gases) trailing 65-90 km downwind. On 30 January seismicity levels were about 15% below the peak values of January 26.
Geologic Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine cone, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows had indicated that they were of Holocene age, but the first historical eruption did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.