The Circular Cadera of Mount Okmok, Alaska, USA53.4N 168.1W
Mount Okmok is the highest point on the rim of Okmok Caldera on the northeastern part of Umnak Island, in the eastern Aleutian Islands of Alaska, USA. Two other volcanoes, Mount Recheshnoi and Mount Vsevido, are visible on the southwestern part of the island in this orthorectified image.
Mount Okmok’s 5.8 mile (9.3 km) wide circular caldera truncates the top of a large shield volcano. A crater lake once filled much of the caldera to a depth of over 500 ft, but the lake ultimately drained through a notch eroded in the northeast rim. Only a small remnant lake about 1000 ft across exists in a depression in the western area of the largely flat caldera floor.
The last major eruptions of Okmok—with an estimated VEI strength of 6—occurred 8,300 and 2,400 years Before Present. The volcano is currently rated by the Alaska Volcano Observatory as Aviation Alert Level Yellow and Volcanic-alert Level Advisory.