Report on Anatahan (United States) — 11 June-17 June 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 June-17 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, 11 June-17 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)
As of 17 June, continuous ash-and-gas emissions persisted at Anatahan. US Geological Survey and CNMI Emergency Management Office personnel observed the volcano on 12 June. They noted that a lava dome or flow was visible on the crater floor and ash was emitted from several areas. No sound emanated from the crater, spines were visible on the crater floor, and one source for the convecting ash cloud was located on the E side of the east crater. In addition, the east crater seemed deeper than during the previous visit on 6 June. During 5-12 June, the seismic record only contained banded-volcanic tremor, but on the evening of 12 June long-period (M ~2) earthquakes began to be recorded. An explosion earthquake occurred on 14 June at 0010. Scientists believe the earthquake was associated with an explosion that removed much of the small lava dome, because the dome was no longer seen during an overflight on the 14th. After the explosion, a series of long-period earthquakes occurred at regular 1- to 2-minute intervals until ~1400. During the report period, ash was visible on satellite imagery rising to a maximum height of ~3 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.