Geologic Background:
The circular, 10-km-wide Ketoi island hosts of
one of the most complex volcanic structures of the Kuril
Islands. The rim of a 5-km-wide Pleistocene caldera is
exposed only on the NE side. A younger stratovolcano
forming the NW part of the island is cut by a
horst-and-graben structure containing two solfatara
fields. A 1.5-km-wide fresh-water lake fills an explosion
crater in the center of the island. Pallas Peak, a large
cone in the NE part of the caldera, is truncated by a
550-m-wide crater containing a brilliantly colored
turquoise crater lake. Lava flows from Pallas Peak
overtop the caldera rim and descend nearly 5 km to the SE
coast.
Historic Activity:
- Eruptions in 1843, 1925, and 1960.
- The first historical eruption of Pallas Peak, during
1843-46, was its largest.
Recent Activity:
- Last reported eruption was in 1960. Active fumaroles
in 1989.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 6, No. 12 to V. 14,
No. 3).
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