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 Glacier. It was long a dormant volcano until it entered a new phase of activity by erupting on September 17 2006.[1] It is located in southwestern Alaska, approximately 200 miles (300 km) southwest of Anchorage, Alaska and 80 miles (130 km) northwest of Kodiak Island. It lies within the Katmai National Park and Preserve on the Alaska Peninsula.
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History
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 7994 BC.[2]
Pilots and other civilians reported two distinct and very large steam plumes coming from Fourpeaked volcano. They were seen as far away as Homer, Alaska located northeast of Fourpeaked across Cook Inlet. 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 eruption. [3]
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 released the following information as part of a special information release:
"...Based on all currently available evidence, AVO believes that an eruption from Fourpeaked in the next days to weeks is possible. Given below are some possible future scenarios for the current unrest at Fourpeaked, listed in order, with the most likely scenario listed first:
(1) A small to moderate eruption will occur, which may produce ash plumes exceeding 10 km (33,000 ft) above sea level. Lava flows may also occur. (2) No eruption occurs. Unrest gradually subsides to background levels. (3) A large eruption will occur, which would produce ash plumes exceeding 10 km (33,000 ft) above sea level, and possible widespread ash fall."
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 gasses at the same rate as revealed in earlier air sampling.
February 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). As of February 24, the rating for the mountain remains at Yellow/Advisory.
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.