Fourpeaked Volcano

Possibly due to a dormant period lasting over 10000 years and due to its heavily glaciated summit with no obvious summit crater, 2104m high Fourpeaked volcano has often been referred to simply as Fourpeak Mountain. Fourpeaked is located on the Alaskan Peninsula 330km SW of Anchorage, in an uninhabited region of Katmai National Park. Most of the summit region is under the thick ice of Fourpeaked Glacier, yet several ridges of andesitic volcanic material protrude. These consist of layers of lava flows and volcanic agglomerates. Based on the orientation of the lava flows and evidence of hydrothermal alteration of rocks in the summit region, the summit was long assumed to represent the active vent. This was finally confirmed in 2006, when Fourpeaked volcano entered into a period of eruptive activity.

Shishaldin Volcano 2007 Shishaldin Volcano 2007

Fourpeaked volcano, viewed from NE, September 2007

Fourpeaked volcano with nearby Douglas volcano at top left. View from W, Sept. 2007.

Until 2006, no regular monitoring network was in place at Fourpeaked or adjacent Douglas volcano. Hence, the onset of eruptive activity was documented by eyewitness accounts on 17. September 2006 and subsequently by analysis of Doppler Radar data from King Salmon. The eruption appears to have commenced near midday and resulted in a cloud reaching up to 6km altitude. Two distinct plumes, indicating at least two active vents, were observed from Homer. These plumes merged as they rose and appear to have consisted mainly of steam and volcanic gases with only small amounts of ash. An overflight several days later revealed a series of vents extending nearly 1km N from the summit area and emitting large amounts of steam and gases. Parts of the glacial cap had been melted around the vents and further areas had subsided. Strong fumarolic emissions continued for the next months, and the seismic instruments recorded a series of minor explosive events in February and March 2007. By June 2007, seismic and fumarolic activity was much reduced and the Volcanic Activity Alert Level was lowered to normal. The pictures in this summary were taken during a September 2007 overflight. Fumarolic activity could still be observed from a summit-proximal vent.

Isanotski Shishaldin Volcanoes Isanotski Shishaldin Volcanoes Isanotski Shishaldin Roundtop Volcanoes

Summit of Fourpeaked volcano. Fumarolic activity visible at location of top end of 2006 fissure.

E flank of Fourpeaked volcano. Fumarole top right.

Fumarole marking highest point of 2006 fissure, Sept. 2007.

Fourpeaked volcano is most easily viewed by small aircraft charter from Homer. Adjacent Douglas and nearby Augustine can easily be overflown during the same flight.

For information on further Alaskan volcanoes, see sections on Augustine, Douglas and Shishaldin.

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