As of 30 January Anatahan continued to erupt, with Strombolian explosions occurring about every minute, similar to activity of the previous few weeks. Seismicity during the current eruption reached a high on 26 January, at a level about 20% above previous high levels for the year. After midday on the 27th the explosions became larger but less frequent than before. At about that time, a commercial pilot reported ash to ~3 km a.s.l. and satellite imagery also showed a plume of ash and vog (fog composed of volcanic gases) trailing 65-90 km downwind. On 30 January seismicity levels were about 15% below the peak values of January 26.

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.

Source: Emergency Management Office of the Commonwealth of the Mariana Islands and United States Geological Survey Volcano Hazards Program