On 10 December AVO reported the following. "On 4 December, following a M 5.1 earthquake at 1836 beneath the . . . island of Atka, residents of Atka village reported "rumbling" from the cluster of volcanoes that forms the N part of the island. At the same time, residents observed increased steaming from a fumarolic area on the flank of Kliuchef volcano and noted a distinct sulphur smell. A check of satellite imagery did not confirm any change in the surface state of the volcanoes. Late this week, the weather had deteriorated and no visual observations of the volcanoes were possible. . . ."

Geological Summary. The Atka Volcanic Complex consists of a central shield and Pleistocene caldera with several post-caldera volcanoes. A major dacitic explosive eruption accompanied formation of the caldera about 500,000 to 300,000 years ago. The most prominent of the post-caldera stratovolcanoes are Kliuchef and Sarichef, both of which may have been active in historical time. Sarichef has a symmetrical profile, but the less eroded Kliuchef is the source of most if not all historical eruptions. Kliuchef may have been active on occasion simultaneously with Korovin volcano to the north. Hot springs and fumaroles are located on the flanks of Mount Kliuchef and in a glacial valley SW of Kliuchef. Korovin, at the NE tip of Atka Island, is the most frequently active volcano of the complex, and contains a double summit with two craters. The NW summit has a small crater, but the 1-km-wide crater of the SE cone has an open cylindrical vent of widely variable depth that sometimes contains a crater lake or a high magma column. A fresh-looking cinder cone lies on the flank of the partially dissected Konia volcano, located on the SE flank of the dominantly basaltic Korovin. Some late-stage dacitic lava flows are present on both Korovin and Konia.

Information Contacts: AVO.