…as Anatahan eruption escalates, but drops again

Anatahan’s volcanic eruption escalated over the weekend and registered the second strongest activity for the year, emitting thick ash plume into the air.

The U.S. Geological Survey and the Emergency Management Office compared Saturday’s activity to the previous peaks of eruptive activity in February and March. They said the eruption escalated in magnitude, equivalent to one-half that of the strongest historical eruption of the volcano last April 6, which spewed out about 50 million cubic meters of ash.

Citing reports from the Air Force Weather Agency, the agencies said that the volcano emitted ash and steam plume to about 10,000 feet in the air, which extended out to 100 nautical miles and thinned to volcanic smog by 150 nautical miles.

They said the vog plume extended 400 nautical miles to the west-southwest before curving back to the northeast, reaching about 325 nautical miles northeast of Anatahan.

Yesterday, though, the agencies said that the eruption significantly declined Saturday afternoon. After dropping by 65 percent, the magnitude of the activity remained steady for about 17 hours before declining by another 65 percent early yesterday.

But the USGS and the EMO said in a joint report yesterday that ash plume remained spread about 10,000 feet in the air. “The main ash and steam plume…extends 34 nautical miles to the west-southwest, then thins and extends another 105 nautical miles to the southwest.”

“The extensive vog plume reaches from 700 nautical miles west of Guam to 360 nautical miles northeast of Anatahan,” the agencies added.

Late last week, the agencies reported that ash plume rose to about 15,000 feet, but it extended north-northwest. The agencies have not quantified the amount of ash being emitted by the volcano this time. The EMO reported no ashfall on Saipan over the weekend.

The agencies said seismicity on Anatahan began to intensify last Tuesday, reaching about one quarter of the explosive eruption last April 6. They reported at least two “small” explosions occurring Wednesday, besides another one last Monday.

The EMO had issued a volcanic haze advisory for Alamagan, Pagan and Agrihan Wednesday and lifted it the following day.

Last April 6, the volcano spewed out about 50 million cubic meters of ash. The eruption sent clouds of ash to an altitude of 50,000 feet, resulting in the cancellation of international and domestic flights. Saipan also experienced ashfall. According to the EMO and the USGS, the vog plume from that eruption remains widespread over the western Philippine Sea, over 1,300 nautical miles west of Anatahan.

The EMO continued to warn aircraft to avoid passing near Anatahan. Although the EMO said that the volcano is not currently dangerous to most aircraft within the CNMI airspace, it added that conditions might change rapidly. It advised aircraft to pass upwind of Anatahan or beyond 10 nautical miles downwind from the island and exercise due caution within 10 nautical miles.