Anatahan still spewing ash

Anatahan’s volcano continued to emit a plume of steam and ash that has traveled about 300 nautical miles from the island, a week after its strongest historical eruption.

The U.S. Geological Survey and the Emergency Management Office said, though, that seismicity on Anatahan has remained low after the strong eruption on Wednesday last week.

The plume now extends about 300 nautical miles west-southwest of Anatahan at an altitude of about 10,000 feet.

The agencies maintained that the plume of volcanic smog has reached the Philippines Sea, over 1,200 miles west of Anatahan.

Last week’s strong explosion was the strongest historical eruption of the volcano, which spewed 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 on Saipan, and a light dusting of ashfall that blanketed the island.

The EMO is warning aircraft to avoid passing near Anatahan, saying that, although the volcano is not currently dangerous to most aircraft within the CNMI airspace, 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.

The first historical eruption of Anatahan began on May 10, 2003, after hundreds of years of dormancy. A phreatomagmatic eruption characterized by steamy strombolian explosions sent ash to over 30,000 feet and deposited about 10 million cubic meters of material over the island and sea, according to the USGS and the EMO.

The Washington Volcanic Ash Advisory Center reported then that ash plume covered over 1-million-square miles of airspace above the Pacific Ocean, posing danger to vast airspace. Ash plume reached the Philippines’ Isabela province.

The second historical eruption began on about April 9, 2004 after about a week of increasing seismicity. That eruption primarily comprised phreatomagmatic explosions every minute and occasionally sent ash up to several thousand feet. That eruption ended on 26 July 2004.

The third historical eruption of Anatahan began on Jan. 6, 2005 after three days of precursory seismicity. Frequent phreatomagmatic explosions began to occur, occasionally throwing pyroclastic rocks with diameters of a meter and over. That eruption peaked on February 2, sending ash to 20,000 feet into the air.

The USGS and the EMO said that the eruption apparently died out on Feb. 14, by which time the 2003 crater floor had essentially been entirely covered by fresh lava to a diameter of about one kilometer. The eruption restarted on 14 March for three days, and again for five days beginning March 21.