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Report on Anatahan (United States) — 9 July-15 July 2003

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 July-15 July 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, 9 July-15 July 2003. Smithsonian Institution and US Geological Survey.

Volcano Profile |  Weekly Report (9 July-15 July 2003)


Anatahan

United States

16.35°N, 145.67°E; summit elev. 790 m

All times are local (unless otherwise noted)


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.

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.

Sources: Emergency Management Office of the Commonwealth of the Mariana Islands and United States Geological Survey Volcano Hazards Program, Washington Volcanic Ash Advisory Center (VAAC)