Type of Volcano: Stratovolcano

Location: 175km Southwest of Anchorage

Magma Composition: Calc-alkaline andesite to dacite

Volcano Structure: Redoubt consists of a stratovolcano that is about 10km in diameter and has a volume of around 30 to 35km2 (Miller et al, 1998). As it can be seen from the picture the volcano has relatively steep sides which are made up of layers of both pyroclastic material and lava flows and also has a crater which is filled with ice. This ice overspills and forms a glacier on its northern face (Miller et al, 1998).

Historic Activity: Redoubt has erupted a few times during history with the main ones occurring in 1902 then again from 1966 to 1968 and the latest from 1989 to 1990 (Wallace et al, 2000).

Redoubt's eruptions are generally explosive and produce lava flows as well as pyroclastic flows ( an outcrop of the 1990 pyroclastic flow deposits can be seen in picture 4). The 1989 to 1990 eruption caused large mud flows or lahars that threatened local oil storage facilities see picture 2 (Decker & Decker, 1991). Also during the 1989 eruption a large tephra plume that reached altitudes of 7 to 12km posed a threat to both passenger and military jets flying in the area.

On 15 December 1989 a large passenger plane encountered the tephra cloud 150 miles to the northeast of the volcano. The ash was sucked into the engines and stopped them all and caused the plane to drop by some 3000 feet. It was only after dropping by another 4000 feet that the pilot was able to restart the engines and fly to safety (Coch, 1995). Picture 3 shows an example of what the tephra looks like.


Picture of Mount Redoubt erupting

Picture 1 (U.S. Geological Survey W. White) showing low level eruption taken on 18 December 1989.

Mud flows threatening oil storage

Picture 2 (U.S Geological Survey T. Miller) Showing the mud flows threatening the oil storage depot (the white rectangle in the bottom centre of the picture) taken in 1990











Tephra deposit size range picture

Picture 3 (U.S. Geological Survey) Showing an example of some tephra deposits

Tephra is the term used for all lava and volcanic rock fragments that are expelled into the air during an eruption.

Pyroclastic flow deposits in outcrop

Picture 4 (U.S. Geological Survey C. Neal) Shows a section through pyroclastic flow deposits from the 1990 eruptions.

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