Report on Makushin (United States) — 30 May-5 June 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
30 May-5 June 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Makushin (United States). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 30 May-5 June 2001. Smithsonian Institution and US Geological Survey.
53.891°N, 166.923°W; summit elev. 1800 m
All times are local (unless otherwise noted)
Since July 2000 AVO has detected a slight increase in the number of small earthquakes beneath Makushin. The earthquakes generally ranged in depth between 0 and 8 km and were too small to be felt by humans (M0-1.5). The seismic activity was not considered to be an immediate precursor to eruptive activity. Similar fluctuations in earthquake activity have been observed at a number of Aleutian volcanoes that did not result in an eruption. The Concern Color Code remained at Green.
Geological Summary. The ice-covered Makushin volcano on northern Unalaska Island west of the City of Unalaska is capped by a 2.5-km-wide 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. 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.