Formation of two maars behind the Aleutian volcanic arc, Alaska peninsula, April 1977 : preliminary results : field reconnaissance, geochemistry and seismicity

Kienle, Juergen; Motyka, Roman J.; Lalla, Douglas J.; Estes, Steven A.; Huot, Jean-Paul

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UAG-R 257.pdf

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UAG R-257; Alaska Earthquake Analysis Center Seismological Report No. 4. Introduction excerpt: Maars form when the earth’s crust is initially perforated by phreato-magmatic explosions that result when magma contacts ground water at shallow depth. A rare geologic phenomenon, maars have been seen to form only twice in historic times, once in Chile in 1955 (Illies, 1959), and the second time at Iwo Jima, Japan, in 1957 (Corwin and Foster, 1959). From March 30 to April 9, 1977, two maars formed on top of a 100 m high hill in generally low-lying glacial terrane at the southern shore of Becharof Lake on the Alaska Peninsula, 3 km south of Gas Rocks. The eruption site lies behind the Aleutian volcanic arc, 13 km northwest of Peulik Volcano, a 1525 m high stratovolcano which erupted last in 1852 (Figure 1). The rims of the two maars are separated by about 400 m. The larger eastern maar is circular, about 300 m in diameter and 70 m deep, and contains a lava dome. The western maar, which actually formed first, is elliptical, with dimensions of about 170 by 105 m and a depth of about 35 m. A shallow lake was present for a few months after formation but drained subsequently, probably through underground waterways, into the deeper eastern maar which was originally dry and is not filling up with water.

Date

1978-04

Publisher

Geophysical Institute at the University of Alaska Fairbanks

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Report

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GI Reports