Report on Anatahan (United States) — 18 June-24 June 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 June-24 June 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Anatahan (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 18 June-24 June 2003. Smithsonian Institution and US Geological Survey.
16.35°N, 145.67°E; summit elev. 790 m
All times are local (unless otherwise noted)
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.
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.