Report on Makushin (United States) — 2 September-8 September 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 2 September-8 September 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, 2 September-8 September 2020. Smithsonian Institution and US Geological Survey.
53.891°N, 166.923°W; summit elev. 1800 m
All times are local (unless otherwise noted)
Seismicity at Makushin returned to background levels after steadily declining for almost three months following a sequence of earthquakes about 10 km E of the summit at a depth of 8 km that had started on 15 June. AVO lowered the Aviation Color Code and Volcano Alert Level remained at Green and Normal, respectively, on 8 September.
Geologic Background. The ice-covered, 1800-m-high Makushin volcano on northern Unalaska Island west of the town of Dutch Harbor is capped by a 2.5-km-wide caldera. The broad, domical structure of Makushin contrasts with the steep-sided profiles of most other Aleutian stratovolcanoes. Much of the volcano was formed during the Pleistocene, but the caldera (which formed about 8000 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 satellitic vents cuts across the volcano. The composite Pakushin cone, with multiple summit craters, lies 8 km to the SW of Makushin. Frequent explosive eruptions have occurred during the past 4000 years, sometimes accompanied by pyroclastic flows and surges. Geothermal areas are found in the summit caldera of Makushin and on the SE and eastern flanks of the volcano. They represent the largest and most investigated high-temperature geothermal resources in Alaska. Small-to-moderate explosive eruptions have been recorded at Makushin since 1786.