* Astronomy

Blobrana · L

RE: Anatahan Volcano

Blobrana · L

The stratovolcano Anatahan, in the central Mariana Islands, is still releasing plumes of ash and steam in March 2008.
The first historical eruption of Anatahan occurred in May 2003.

Blobrana · L

A image of Anatahan Volcano releasing a plume of steam and gas was captured by NASAs Terra satellite on December 31, 2007.
A faint plume from the volcanic island blows northwest over the Pacific Ocean.

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Credit NASA

-- Edited by Blobrana at 01:52, 2008-01-02

Blobrana · L

On March 17, 2007, the Anatahan Volcano, in the Northern Mariana Islands, released a plume of ash and/or steam. The Aqua satellite captured this image on March 18, 2007.

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Credit: NASA

Blobrana · L

The Anatahan Volcano emitted a plume of volcanic ash on March 19, 2006. The Aqua satellite captured this image the same day. In this image, the tiny volcanic island sends a plume of ash toward the southwest, over the Pacific Ocean.

Position: 16°21'30.76"N, 145°40'46.77"E

Anatahan sits near the centre of the Northern Marianas Islands. The islands result from a collision between the Pacific Plate and the Philippine Plate. As the Pacific Plate slides under the Philippine Plate, rocks heat up and break up. They eventually force their way to the surface through weak spots in the Philippine Plate and emerge as volcanoes like Anatahan.
This volcano began erupting in January 2005 and remained active for much of the year. In August 2005, the volcano quieted, but in early March 2006, the governor of the Northern Mariana Islands extended the state of emergency for the island of Anatahan, citing continued volcanic activity. Except for those conducting scientific research, the island remained off limits for human habitation and travel.

-- Edited by Blobrana at 22:55, 2006-03-20

Blobrana · L

The Anatahan Volcano north of Saipan has resumed rumbling in recent days, spewing steam and ash as high as 50,000 feet.
The latest satellite images from the Air Force Weather Agency showed a cloud of ash and steam rising 10,000 feet in the air and extending about 375 nautical miles from Anatahan island.

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Thin ash and volcanic smog, or vog, also spread 815 nautical miles northwest of the island, the satellite data indicated.
An eruption Sunday afternoon was the latest since the volcano had its largest historical eruption on April 6.
That explosion expelled an estimated 50 million cubic yards of ash, grounded several commuter flights, and exacerbated asthma conditions for residents of Saipan, about 80 miles away.
The volcano also erupted on June 11.
Vog from Anatahan's activity in recent months has reached as far as the Philippines and Palau.

Though the geologists have found evidence of ancient explosive eruptions by the volcano, the first historical eruption began in May 2003. That prompted the evacuation of the island's 20 or so residents to Saipan.
The island has been uninhabited since.
Officials of the Commonwealth of the Northern Marianas have banned all visits to the island except for scientific expeditions.
The CNMI government urged airplanes to pass upwind or at least 10 nautical miles downwind of the island. While the volcano is not now dangerous to most aircraft, conditions may change rapidly, the authorities said.
The eruption is at least the sixth in the past two years.
The Northern Mariana Islands, about 3,800 miles southwest of Hawaii, have nine active volcanoes. The island chain is home to about 70,000 people.

Blobrana · L

The volcano Anatahan still showed signs of activity when the Moderate Resolution Imaging Spectroradiometer (MODIS), flying on the Terra satellite, acquired this image on May 25, 2005. Volcanic tremors occur when magma rises inside the volcano or when the volcano erupts.
In the image, Anatahan (on the right), is clearly erupting, sending a brown plume of ash westward over the Philippine Sea.
Further west, volcanic gasses from a previous eruption have gathered in a thick white haze called "vog."
When sulphur dioxide and other volcanic pollutants mix with water and oxygen in the presence of sunlight, the result is volcanic smog, or vog, a potentially hazardous material.
This picture shows all the ingredients necessary to make vog: a volcanic ash plume, plenty of water, and sunlight. The sunlight is particularly obvious as the sunglint in the centre of the image. When the sun and the satellite are at the same angle to the ocean, sunlight bounces off the ocean surface and reflects directly into the satellite sensor.

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Image by Jesse Allen, based on data from the MODIS Rapid Response Team at NASA Goddard Space Flight Centre.

On May 18, volcanic activity at Anatahan resumed. Tremor rapidly increased by about a factor of four, diminished some, and then further intensified through May 20. Tremor then declined slowly to about 1/3 of the peak May 20 level by May 23.
Since then, tremor has increased about 50% beyond the May 20 level but has essentially levelled off at that level during the last 24 hours.
Ash Observations: Satellite imagery from the Air Force Weather Agency (AFWA) indicates dense ash and steam rising to 8,000 feet and extending about 175 nautical miles west of Anatahan. A thin plume of ash and VOG extends 1125 nautical miles west-southwest of the summit.

Background: The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of two coalescing volcanoes with a 2.3 x 5 km, E-W-trending summit depression formed by overlapping summit calderas.
The larger western caldera is 2.3 x 3 km wide and extends eastward from the island's 788 m high point.
Ponded lava flows overlain by pyroclastic deposits fill the caldera floor, whose SW side is cut by a fresh-looking smaller crater. The summit of the lower eastern cone is cut by a 2-km-wide caldera with a steep-walled inner crater whose floor is only 68 m above sea level. Sparseness of vegetation on the most recent lava flows on Anatahan indicated that they were of Holocene age, but the first historical eruption of Anatahan did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.

The first historical eruption of Anatahan began 10 May 2003 after several hours of increasing seismicity. A phreatomagmatic eruption sent ash to over 30,000 feet and deposited about 10 million cubic meters of material over the island and sea. A small craggy dome extruded in late May and was destroyed during explosions on 13-14 June after which the eruption ceased.
The second historical eruption began about 9 April 2004 after a week or so of increasing seismicity. That eruption primarily comprised phreatomagmatic (steamy strombolian) explosions every minute or so and occasionally sent ash up to several thousand feet. That eruption ended on 26 July 2004.
The third historical eruption of Anatahan began on 6 January 2005 after three days of precursory seismicity. Phreatomagmatic explosions as frequent as every 3 to 10 seconds apart occasionally threw one to two meter bombs a hundreds of meters in the air and sent ash 10,000 feet high and 60 km downwind.
Fresh ejecta and small lava flows filled the innermost crater to nearly the level of the pre-2003 East Crater floor. The eruption peaked from 26 January to 3 February, when ash rose as high as 15,000 to 20,000 feet and blew 150 km downwind, and vog nearly 600 miles downwind. The eruption died out on 14 February, resumed for three days on 14 March and resumed again for five days on 21 March and on 28 March.

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