Umnak o͞om´năk [key], island, c.83 mi (134 km) long, off SW Alaska, one of the largest of the Aleutian Islands. Its two lobes, connected by an isthmus, are marked by volcanic features. The volcanic peaks, Mt. Vsevidof, 7,236 ft (2,206 m) high, and Mt. Recheshnoi, 6,509 ft (1,984 m) high, with geysers on its NE flank, are in the south, and Okmok, a volcanic caldera, is in the north.
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