Intense fumarolic activity was occurring on the outer N slope [of Pallas Peak during the 20 September 1981 overflight]. There were sulfur deposits near the fumaroles. However, no apparent fumarolic or solfataric activity was observed at Zavaritski Caldera (46.925°N, 151.95°E) or Prevo Peak (47.02°N, 152.12°E). Both are on Simushir, the island immediately SW of Ketoi.

Geological Summary. The circular 10-km-wide Ketoi island, which rises across the 19-km-wide Diana Strait from Simushir 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 freshwater lake fills an explosion crater in the center of the island. Pallas Peak, a large andesitic 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. The first historical eruption of Pallas Peak, during 1843-46, was its largest.

Information Contacts: G. Steinberg, Sakhalin Complex Institute.