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Anatahan volcano roars anew

Article appeared on Signs of the Times

Tuesday, June 21, 2005

Anatahan's volcano roared in a series of eruptions Sunday afternoon, kicking up a cloud of ash to 50,000 feet and matching the intensity of the volcano's strongest historical eruption on April 6.

Seismicity on Anatahan had been increasing in the past days before Sunday's 2.6-minute eruptive pulse that started at about 3:25pm. The volcano had the highest tremor levels Saturday since early May.

The U.S. Geological Survey and the Emergency Management Office said yesterday that ash and steam reached an altitude of 50,000 feet by 4pm based on infrared imagery. But the agencies said the situation lasted briefly and dissipated as the plume moved easterly. At about 5:42pm, a commercial pilot reported steam and ash at 37,000 feet.

The ash emissions prompted Gov. Juan N. Babauta to issue a public advisory, which reached the Saipan Tribune office past midnight yesterday.

"Eruption materials are being carried away to the east of Anatahan at atmospheric levels before 20,000 feet. As dust and small particulates are settling to lower levels of the atmosphere, trade winds will carry a small amount of the dust and particulates back in the general direction of Saipan and Tinian," the agencies said.

The advisory stated that the leading edge of the dust and particulates cloud could reach the vicinity of Saipan and Tinian at dawn yesterday but disperse in the afternoon.

EMO director Rudolfo Pua said, though, that Saipan and Tinian did not experience any hazy condition yesterday. He said the governor canceled the advisory yesterday afternoon, adding that Saipan and Tinian did not experience any ashfall.

After the strong eruption Sunday, the volcano continued emitting dense ash clouds rising to 8,000 feet and moving westerly. Yesterday morning, the EMO and the USGS said that dense ash and steam reached about 178 nautical miles to the west, with volcanic smog extending to 1,017 nautical miles west-northwest and 772 nautical miles northwest of the island.

The agencies maintained that aircraft should take extra precaution within 10 nautical miles of Anatahan, advising them to pass upwind of the island or beyond 10 nautical miles downwind. They pointed out that conditions could change rapidly, and volcanic activity could suddenly escalate.

During a strong eruption on April 6, the volcano expelled about 50 million cubic meters of ash that reached 50,000 feet. The agencies have yet to estimate the volume of ash emitted in Sunday's strong explosion. But the volcano has been continuously emitting huge amounts of ash in the last several weeks.
Last Saturday, the agencies also reported of a small swarm of 10 volcano-tectonic events with magnitudes between 0.5 and 1.75 that occurred beneath or within a few kilometers of Sarigan Island.

Sarigan, which is located about 95 nautical miles north of Saipan and is the next island north of Anatahan, is actually a volcano with no known historic eruption.

Volcano-tectonic events occur when stress changes happen to solid rock due to the injection or withdrawal of magma. Volcano-tectonic earthquakes can cause land to subside and can produce large ground cracks. These earthquakes can occur as rock is moving to fill in spaces where magma is no longer present. Volcano-tectonic earthquakes may indicate that volcanic eruption can occur at anytime.