Type of Volcano: Stratovolcano with central caldera

Location: 434km Southwest of Anchorage

Magma Composition: Low silica and low potassium andesite to dacite

Volcano Structure: The Volcano is approximately 10km in diameter and its caldera is filled by a lake (seen in picture 1) and the total height of the volcano exceeds 2km (Miller et al, 1998). Katmai is one of five stratovolcanoes in the vicinity and has been erupting since 1912, producing large pyroclastic flows together with lava flows.

Caldera Lake of Mount Katmai

Picture 1 Showing the caldera lake of Katmai (National Oceanic and Atmospheric Administration)

Historic Activity: There is not a lot of information available on the history of Katmai, however one major eruption occurred in 1912 (Wallace et al, 2000) when an eruption spanning 60 hours on 6 June produced 30 cubic km of rhyolitic to andesitic rock fragments (Decker & Decker, 1991) making it the largest eruption to occur in the world during the twentieth century (Miller et al, 1998).

The eruption converted 9 cubic km of magma into 20 cubic km of ash which made up two thirds of the total volume while the final third was made up of thick pyroclastic flows (Decker & Decker, 1991). These pyroclastic and ash flows were rapidly emplaced into the surrounding valleys with deposits reaching a thickness of up to 200m. This area then became known as the Valley of Ten Thousand Smokes and can be seen in picture 3 below.

Ash outcrop Valley Ten Thousand Smokes

Picture 2 (U.S. Geological Survey S. McNutt) Picture of an ash outcrop in the Valley of the Ten Thousand Smokes

Valley of Ten Thousand Smokes

Picture 3 (U.S. Geological Survey R. McGimsey) Picture showing ash deposits in the Valley of the Ten Thousand Smokes