Vent Mtn Surprise Lake Blocky cone Bolshoi Dome Half Cone New cone Pumice Dome Vulcan Dome West Dome 1931 Crater
Port Heiden 16 mi (26 km) NW Chignik 43 mi (69 km) SW Chignik Lagoon 43 mi (69 km) SW Chignik Lake 50 mi (80 km) SW Anchorage 419 mi (674 km) NE
From Miller and others (1998): "Aniakchak Crater is an ice-free, circular caldera about 10 km in diameter and a maximum of 1 km deep which was first described by Smith (1925). The pre-caldera cone was built upon a basement of Tertiary sedimentary and volcanic rocks and Jurassic-Cretaceous sedimentary rocks, which are exposed high on the east and south walls of the caldera (Detterman and others, 1981). The elevation of the caldera rim varies from 1,341 m to 610 m. Surprise Lake, a 3.2-km-long lake in the northeast part of the caldera at an elevation of about 335 m is the source of the Aniakchak River, which flows through a breach in the eastern wall of the caldera. Numerous domes, flows, and cones occupy the interior of the caldera (Neal and others, 1992); the largest cone is Vent Mountain, 2.5 km in diameter and rising 430 m above the floor of the caldera. The pre-caldera cone was built on the west side of a basement high. The cone was deeply dissected by numerous glaciers that cut U-shaped valleys into the slopes before the caldera-forming eruption.
"Ash flows from the caldera-forming eruption - 3430 +/- 10 yrs B.P. (Miller and Smith, 1987) - reached both the Bering Sea and the Pacific Ocean (Miller and Smith, 1977). They are typically non-welded and fill glacial valleys to a depth of at least 75 m adjacent to the caldera rim. The ash flows were highly mobile, over-running 260-meter-high passes in the Aleutian Range and traveling as far as 50 km from the caldera rim (Miller and Smith, 1977)."