Fourpeaked Volcano is an active
stratovolcano
A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...
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 ...
,
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., ...
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 sou ...
. 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
In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such ...
.
September 20, 2006
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 ...
upgraded Fourpeaked volcano from the classification "not assigned" to
Level of Concern Color Code In October 2006, the United States Geological Survey (USGS) adopted a nationwide alert system for characterizing the level of unrest and eruptive activity at volcanoes. The system is now used by the Alaska Volcano Observatory, the California Volcano ...
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
A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinc ...
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.
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
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
(SO
2).
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
*
List of volcanoes in the United States
A list of volcanoes in the United States and its territories.
Alaska
American Samoa
Arizona
California
Colorado
Hawaii
/[./[Https://www.sci.news/geology/puhahonu-shield-volcano-08435.html Puhahonu ...
References
* {{cite gvp, vn=312260, name=Fourpeaked
External links
United States Geological SurveyUAF Geophysical InstituteAlaska Division of Geological and Geophysical SurveysNational 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