Report on Makushin (United States) — 24 June-30 June 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
24 June-30 June 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Makushin (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 24 June-30 June 2020. Smithsonian Institution and US Geological Survey.
53.891°N, 166.923°W; summit elev. 1800 m
All times are local (unless otherwise noted)
AVO reported continuing numerous smaller earthquakes in an area about 10 km E of the Makushin’s summit at a depth of about 8 km during 24-30 June; the frequency and magnitude had been declining since 15 June but the rate became variable on 24 June. No surficial activity was visible in satellite or webcam images; only typical minor steaming from summit crater lake. Earthquakes with a M 3 and M 3.8 were recorded at 1653 and 1802 on 28 June, with the larger event strongly felt in Unalaska (14 km E). The Aviation Color Code and Volcano Alert Level remained at Yellow and Advisory, respectively.
Geological Summary. The ice-covered Makushin volcano on northern Unalaska Island is capped by a 2.5 km caldera. Its broad, dome-like structure contrasts with the steep-sided profiles of most other Aleutian stratovolcanoes. Much of the edifice was formed during the Pleistocene, but the caldera (which formed about 8,000 years ago), Sugarloaf cone on the ENE flank, and a cluster of about a dozen explosion pits and cinder cones at Point Kadin on the WNW flank, are of Holocene age. A broad band of NE-SW-trending vents cuts across the volcano. The composite Pakushin cone, with multiple summit craters, lies 8 km SW. Table Top (Pleistocene, 68 +/- 14 ka) and Wide Bay (Holocene) cinder cones are about 20 km ENE on the peninsula across the bay from the City of Unalaska. Frequent explosive eruptions have occurred during the past 4,000 years, sometimes accompanied by pyroclastic flows and surges. Geothermal areas are found in the summit caldera and on the SE and E flanks. Small-to-moderate explosive eruptions have been recorded since 1786.