Report on Atka Volcanic Complex (United States) — 11 August-17 August 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
11 August-17 August 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Atka Volcanic Complex (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 11 August-17 August 2021. Smithsonian Institution and US Geological Survey.
Atka Volcanic Complex
52.331°N, 174.139°W; summit elev. 1518 m
All times are local (unless otherwise noted)
The number of small shallow earthquakes increased at Atka during 10-11 August, prompting AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. The earthquakes were located at a depth of 3-6 km and around 7 km SW of Korovin, though may be related to the several vents that are part of the Atka volcanic complex. Seismicity declined afterwards but remained above background levels through 16 August, and was near baseline levels by 17 August.
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.