Report on Anatahan (United States) — 5 May-11 May 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
5 May-11 May 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Anatahan (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 5 May-11 May 2004. Smithsonian Institution and US Geological Survey.
16.35°N, 145.67°E; summit elev. 790 m
All times are local (unless otherwise noted)
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.
Geological Summary. 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.