Fourpeaked Volcano is an active stratovolcano in the U.S. state of

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S. ...

. The

Alaska Volcano Observatory The Alaska Volcano Observatory (AVO) is a joint program of the United States Geological Survey, the Geophysical Institute of the University of Alaska Fairbanks, and the State of Alaska Division of Geological and Geophysical Surveys (ADGGS). AVO ...

rates Fourpeaked Volcano as Aviation Alert Level Green and Volcanic-alert Level Normal. It is nearly completely covered by Fourpeaked Glacier.

History

Before the eruption began on September 17, 2006, Fourpeaked volcano had been dormant for over 10,000 years.

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

Homer Homer (; grc, Ὅμηρος , ''Hómēros'') (born ) was a Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Homer is considered one of the ...

located northeast of Fourpeaked across

Cook Inlet Cook Inlet ( tfn, Tikahtnu; Sugpiaq: ''Cungaaciq'') stretches from the Gulf of Alaska to Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding Anchorage. On its so ...

. 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

upgraded Fourpeaked volcano 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

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

s 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 In seismology, an earthquake swarm is a sequence of seismic events occurring in a local area within a relatively short period. The time span used to define a swarm varies, but may be days, months, or years. Such an energy release is different f ...

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. Fourpeaked - Fumarole on NW side (2007-02-22)

Fourpeaked - Fumarole on NW side (2007-02-22)

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 magnitude scale The Richter scale —also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale—is a measure of the strength of earthquakes, developed by Charles Francis Richter and presented in his landmark 1935 ...

. 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.

References

* {{cite gvp, vn=312260, name=Fourpeaked

External links

United States Geological Survey

UAF Geophysical Institute

Alaska Division of Geological and Geophysical Surveys

National Public Radio report
21st-century volcanic events 2006 in Alaska Volcanoes of Alaska Mountains of Alaska Stratovolcanoes of the United States Active volcanoes Volcanoes of Kenai Peninsula Borough, Alaska Mountains of Kenai Peninsula Borough, Alaska Katmai National Park and Preserve Aleutian Range Pleistocene stratovolcanoes Holocene stratovolcanoes