View of part of the interior of Fisher caldera on Unimak Island in the eastern Aleutian Islands. Fisher is an 11x18 km (7x11 mi) caldera that formed about 9,100 years ago producing compositionally zoned ash flows that overtopped topographic barriers more than 500 m (1,640 ft) in elevation. There was one poorly documented historical eruption from Fisher caldera in 1826. Photograph by T. Miller, U.S. Geological Survey, August, 1974.
Credit: Image courtesy of AVO / U.S. Geological Survey.