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Fourpeaked Mountain also known as Fourpeaked Volcano is an active stratovolcano in Alaska. The Alaska Volcano Observatory currently rates Fourpeaked as Aviation Alert Level Green and Volcanic-alert Level Normal. It is nearly completely covered by Fourpeaked Glaciermarker. It was long a dormant volcano and believed by many geologists to be extinct having not erupted in over 10,000 years until it entered a new phase of activity by erupting on September 17 2006.[356651]

Fourpeaked Mountain during eruption, September 17, 2006

AVO map shows the location of Fourpeaked volcano

Current activity

Since March, 2008, Fourpeaked has seen continued, mild steaming from its summit. While it remains active, there has been little to no seismic activity and no eruption since the September, 2006 event.


Prior to the phase that began September 17 2006, Fourpeaked had been dormant for over 10,000 years, meaning its last known eruption was prior to 8000 BC.[356652]

September 17 2006

Pilots and other civilians reported two distinct and very large steam plumes coming from Fourpeaked volcano. They were seen as far away as Homermarker, Alaskamarker located northeast of Fourpeaked across Cook Inletmarker. Scientists on subsequent flights by USGS/AVO discovered that volcanic gases were being vented "vigorously" near the summit. Air sampling confirmed these findings. The Alaska Volcano Observatory officially classified this event as an explosive eruption.

September 20, 2006

The Alaska Volcano Observatory upgraded Fourpeaked from the classification "not assigned" to Level of Concern Color Code Yellow on September 20 2006. This color coded system was later renamed the Aviation Alert Level, but with the same color coding system. At that time they began installing seismic monitoring equipment on the mountain and using fixed-wing aircraft as well as helicopters to monitor the volcano.

September 25 2006 AVO eruption warning

On September 25 2006, the AVO warned that Fourpeaked would likely erupt again, and released the following information as part of a special information release:

October 3 2006

The Alaska Volcano Observatory completed installation of another seismometer near Fourpeaked. Almost immediately they detected an earthquake swarm of lower magnitude quakes. This behavior continued intermittently through the spring of 2007. Fourpeaked also continued to vent volcanic gases at the same rate as revealed in earlier air sampling.

February 2007

Fourpeaked Mountain with active fumaroles and sulfur deposits on February 22, 2007
In February, 2007 Fourpeaked began showing a relatively small but noticeable increase in activity. The Alaska Volcano Observatory reported February 8-9 that: "Three small explosive events were recorded by seismic and acoustic instruments Thursday and Friday (February 08-09) beginning at 10:36 AM AKST (1936 UTC) February 08. A possible large steam plume was observed in several partly cloudy satellite views Thursday afternoon." On February 18, the AVO reported a swarm of 13 small earthquakes under Fourpeaked,with the largest measuring 1.8 on the Richter Scale. On February 23, the AVO conducted a gas flight and detected the continued emission of sulfur dioxide (SO2).

March 2007

The Alaska Volcano Observatory began reporting in its Daily Update on Fourpeaked volcano that "several small explosion signals" were detected overnight, apparently continuing the series of small explosions which began on February 8. These "small explosions" continued until June, when Fourpeaked's classification was lowered to Green.

See also


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