Edgecumbe

The Edgecumbe volcanic field covers about 260 km2 of Kruzov Island west of Sitka in SE Alaska. The basaltic-to-dacitic field is dominated by the large composite cones of Mount Edgecumbe, Crater Ridge, and Shell Mountain. This Pleistocene-to-Holocene system is 16 km E of the Queen Charlotte-Fairweather transform fault separating the North American and Pacific plates. Mount Edgecumbe is a stratovolcano with a well-defined crater, and is the largest edifice of the field. Crater Ridge is truncated by a 1.6-km-wide, 240-m-deep caldera. These and other vents are oriented along a SW-NE line. Volcanic activity originated about 600,000 years ago along fissures cutting Kruzof Island. A series of major silicic explosive eruptions took place about 9,000-13,000 radiocarbon years ago. The latest dated eruptions were phreatomagmatic explosions during the mid-Holocene, and all postglacial activity has been pyroclastic. Reports of observed eruptions are unsubstantiated.