Fourpeaked Mountain
Encyclopedia
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 and believed by many geologists to be extinct; having not erupted in over 10,000 years. However, this view changed when it entered a new phase of activity by erupting on September 17, 2006.http://www.avo.alaska.edu/volcanoes/volcact.php?volcname=Fourpeaked&eruptionid=555&page=basics
, 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 explosive eruption.
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 helicopter
s to monitor the volcano.
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.
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).
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
in Alaska. The Alaska Volcano Observatory
Alaska Volcano Observatory
The Alaska Volcano Observatory 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...
currently rates Fourpeaked as Aviation Alert Level
Volcano warning schemes
- USGS Volcano Warning Scheme for the United States :The United States Geological Survey has adopted a common system nationwide for characterizing the level of unrest and eruptive activity at volcanoes...
Green and Volcanic-alert Level
Volcano warning schemes
- USGS Volcano Warning Scheme for the United States :The United States Geological Survey has adopted a common system nationwide for characterizing the level of unrest and eruptive activity at volcanoes...
Normal. It is nearly completely covered by Fourpeaked Glacier
Fourpeaked Glacier
Fourpeaked Glacier is a calving glacier covering much of Fourpeaked Mountain, also known as Fourpeaked Volcano....
. It was long a dormant volcano and believed by many geologists to be extinct; having not erupted in over 10,000 years. However, this view changed when it entered a new phase of activity by erupting on September 17, 2006.http://www.avo.alaska.edu/volcanoes/volcact.php?volcname=Fourpeaked&eruptionid=555&page=basics
Current activity
In March, 2008, Fourpeaked saw continued, mild steaming from its summit. Since the summer of 2008 activity has significantly diminished and there has been little to no seismic activity and no eruption since the September, 2006 event.History
Before the phase that began September 17, 2006, Fourpeaked had been dormant for over 10,000 years, meaning that its last known eruption was before 8000 BC.http://www.avo.alaska.edu/activity/Fourpeaked.phpSeptember 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 HomerHomer, Alaska
Homer is a city located in Kenai Peninsula Borough in the U.S. state of Alaska. According to 2005 Census Bureau estimates, the population was 5,364. One of Homer's nicknames is "the cosmic hamlet by the sea"; another is "the end of the road"...
, Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
located northeast of Fourpeaked across Cook Inlet
Cook Inlet
Cook Inlet 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....
. 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 ObservatoryAlaska Volcano Observatory
The Alaska Volcano Observatory 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...
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
Volcano warning schemes
- USGS Volcano Warning Scheme for the United States :The United States Geological Survey has adopted a common system nationwide for characterizing the level of unrest and eruptive activity at volcanoes...
, but with the same color coding system. At that time they began installing seismic monitoring equipment on the mountain and using fixed-wing aircraft
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
as well as helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
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 swarmEarthquake swarm
Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to define the swarm itself varies, but the United States Geological Survey points out that an event may be on the order of days, weeks, or...
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
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
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
(SO2).