Shishaldin, Unimak Island, Alaska

This information was summarized from a report on Global Volcanism Program.

Since June of 1999, small low-frequency seismic events have been present at Shishaldin Volcano. These events have increased in amplitude over the last week. Seismic data shows the presence of small phreatic explosions. Last week, steam plumes with heights reaching as high as ~3,000 feet above the summit were visible. The Level of Concern Color Code has now been raised to YELLOW.

This information was summarized from a report on Global Volcanism Program.

Glowing rocks were seen erupting 200 m above the summit of Shishaldin on April 17. Lava was seen on the summit on April 18, and snowmelt was running down the northwest flank. An explosive eruption then occurred at Shishaldin on April 19, sending an ash plume 45,000 ft into the air. This event lasted about seven hours. Additional eruptions could occur with little or no warning, so the concern code has been raised to Red. Two flights were cancelled and several others were rerouted when pilots spotted the ash plume. One official stated that it was one of the most energetic eruptions of Shishaldin this century.

This information was summarized from a report sent to us by the AVO.

June 3, 1997

The National Weather Service in Cold Bay reported a small steam and ash plume rising 1,000-1,500 feet (300-450 m) above the summit of Shishaldin. The plume has drifted about 5 miles (8 km) to the north. The Alaska Volcano Observatory noted that Shishaldin is not seismically monitored but has frequent small eruptions. This update is based on information posted by the U.S. Geological Survey's Alaska Volcano Observatory on Volcan ListServ on June 3, 1997.

History

Shishaldin Volcano on Unimak Island in the eastern Aleutian Islands erupted early Saturday morning, December 23, 1995.

Pilots reported an ash plume as high as 35,000 feet (10,700 m) above sea level.Analysis of a satellite image by volcanologists at the Alaska Volcano Observatory showed a possible small ash plume extending approximately 50 km northwest of Shishaldin. The observatory also received a report of a possible very light ashfall at Cold Bay, 56 miles (90 km) northeast of Shishaldin.

Shishaldin Volcano is located near the center of Unimak Island in the eastern Aleutian Islands. It is a spectacular symmetric cone with a summit elevation of 9,373 ft (2,857 m) above sea level. A small summit crater produces a steady, vigorous cloud of steam with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, erupting at least 27 times since 1775. The most recent eruptive period occurred i n 1986-1987; activity consisted of minor steam and ash emission that continued for several months. The nearest village is False Pass, 20 miles (32 km) east-northeast of the volcano.

Based on the record of historic activity at Shishaldin, additional eruptions of ash may continue intermittently for days or weeks. The Alaska Volcano Observatory will continue to monitor the situation through pilot reports and analysis of satellite images.

This summary is based a report prepared by the U.S. Geological Survey's Alaska Volcano Observatory.Additional information and satellite images are posted on the Alaska Volcano Observatory homepage.

On Friday, January 12, 1996, the Alaska Volcano Observatory reported detection of a intermittent "hot spot" near the summit of Shishaldin. The "hot spot" was first noticed on AVHRR satellite images of the volcano on January 5, 1996. Volcanologists at the Alaska Volcano Observatory think the extra heat is caused by high temperatures in the vicinity of the continuously active fumaroles in the summit crater.

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