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.