On 19 June at 1525 a brief eruption at Anatahan produced a steam-and-ash cloud that reached a height of ~15.2 km (49,900 ft) a.s.l. Guam Meteorological Weather Office radar showed that the cloud drifted E. No particular seismic signal was associated with the eruption. Two days before the eruption, the amplitude of continuous tremor was relatively high. During the days before and after the eruption, ash reached 3-4.6 km (9,800-15,100 ft) a.s.l. and drifted W.

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