Report on Anatahan (United States) — 14 May-20 May 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 May-20 May 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, 14 May-20 May 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 at Anatahan that began on 10 May continued through 20 May with less intensity than when it began. The Washington VAAC reported that the ash cloud produced by the eruption drifted W and NW and was at a height of ~5 km a.s.l. on 14 May, and ~4 km a.s.l. on 15 May. As of the 20th, steam-and-ash emissions continued, with the resultant clouds remaining below 3 km and drifting primarily W. According to a news report, parts of the island of Anatahan have been covered by up to ~0.5 m of ash. News reports also stated that by 16 May ash had drifted over the Philippines, posing a threat to aviation in the vicinity.
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.