Anatahan eruptions escalate

Volcanic eruptions on Anatahan island have escalated, with the volcano spewing pyroclastic rocks hundreds of feet into the air, while seismicity and ash emissions continued to intensify and billow during the past days, sometimes rising up to 5,000 feet.

The Emergency Management Office reported this after conducting an overflight on Anatahan— an uninhabited island located about 120 kilometers north of Saipan—last Friday.

“Everytime there were explosions, there were black rocks—sometimes red—being thrown several hundred feet into the air,” said EMO’s Juan Takai Camacho, who flew over the island Friday.

Aboard a fix-wing aircraft, the team flew at an altitude of about 4,850 feet and descended further near the crater, Camacho said. During the 45-minute overflight, Camacho said he observed no lava flowing from the volcano’s crater.

With the new batch of eruptions, ash may again bury Anatahan, which Camacho observed to be regaining its greenery after over a million of cubic yards of ash deposited on land and sea following the big eruption in 2003. Thick ash billowing out from the crater made the overflight difficult, narrated Camacho.

Camacho also said three commercial planes passing over the island Thursday—Japan Airlines, Continental Airlines and a New Zealander aircraft—had to fly at an altitude of over 35,000 feet due to the eruptions.

In a joint report released last Saturday, the EMO and the U.S. Geological Survey said that full-scale strombolian eruption is possible as seismic activity on Anatahan increases.

“During the last 48 hours, the seismic signals have changed from harmonic tremor to a somewhat broader band tremor with frequent explosion signals recorded by the microphones several times per minute. A relatively full scale strombolian eruption is now underway and has been for the last two days,” the agencies said, comparing the volcanic activity to the one last year.

The volcano’s activity intensified beginning last Jan. 4-5 last week after months of extremely low seismic activities, which followed the second batch of eruptions from April to June last year.

The volcano on Anatahan first erupted after centuries of dormancy on May 10, 2003, with ash plume rising to an altitude of over 30,000 feet that covered over 1-million-square kilometers of airspace above the Pacific Ocean and reached Philippine jurisdiction.

That eruption, which ceased by mid-June that year, deposited about 10-million cubic meters of material over Anatahan island and the sea.

“A dome is visible in the crater, and bombs were observed rising to less than 2000 ft. We believe that an ash plume likely extends to 100 km or more downwind at this time,” the EMO said.

The latest report released by the Volcanic Ash Advisory Center in Washington, D.C. said the center could not determine the extent of ash plume from the volcano’s crater by satellite imagery due to obscuring clouds. However, the VAAC’s satellite monitoring last week showed the ash plume moving westward. No ashfall has been reported on Saipan so far.

Guam tower first sighted ash plume rising to about 500 feet early Thursday morning, the agencies said. By noontime that day, the VAAC reported the plume to extend westward about 60 kilometers long and 20 kilometers wide.

According to the EMO and the USGS, the volcano had no historical eruptions before May 10, 2003. A second eruption began about April 9, 2004, after more than a week of increasing seismicity.

The second eruption consisted of passive extrusion during mid-April, which later developed to strombolian explosions every minute or two on April 24, the agencies said. The strombolian explosions continued every minute or two through mid-July, often sending a thin plume of gas and ash upward a few thousand feet and 100 km downwind.

According to the agencies, the second eruption essentially ended on July 26, although visitors to the island three months later could still see very small amounts of steam and ash rising 100-200 ft above the crater rim and could smell sulfur dioxide near the crater.

Anatahan remains off-limits to the public, except for government and approved scientific missions, pursuant to a continuing emergency declaration by Gov. Juan N. Babauta.

“Although the volcano is not currently dangerous to most aircraft within the CNMI airspace, conditions may change rapidly, and aircraft should pass upwind of Anatahan or farther than 30 km downwind from the island and exercise due caution within 30-50 km of Anatahan,” the EMO maintained.

Among the islands north of Saipan, Anatahan is the second closest next to Farallon de Mendinilla. While the U.S. military has been using FDM for bombing practices, it had requested the Marianas Public Lands Authority to use a crater on Anatahan for military training, before the volcanic eruption happened in 2003.

Anatahan runs about 9.5 km long and 4 km wide and was believed formed to be such due to prehistoric volcanic activities. It has two coalescing volcanoes and is mostly mountainous, with its peak rising to an altitude 2,585 feet.