Report on Anatahan (United States) — 6 February-12 February 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 February-12 February 2008
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2008. Report on Anatahan (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 6 February-12 February 2008. Smithsonian Institution and US Geological Survey.
16.35°N, 145.67°E; summit elev. 790 m
All times are local (unless otherwise noted)
The USGS reported that seismic tremor levels at Anatahan were relatively low during 8-13 February, except for short-lived increases during 8-9 and 12-13 February. On 9 February, a diffuse steam plume that possibly contained ash was observed on satellite imagery and drifted W. The Washington VAAC reported that more steam plumes possibly containing some ash were visible on satellite imagery on 11, 12, and 13 February and drifted NW and SE. On 13 February, vog (volcanic fog) was also observed N and W of Saipan. Emissions of sulfur dioxide were detected by the satellite-based Ozone Monitoring Instrument (OMI). The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange.
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.