Volcano Type: Stratovolcano?
Volcano Status: Historical
Last Known Eruption: 1992
Summit Elevation: 1654 m 5,426 feet
Latitude: 54.518°N 54°31’6″N
Longitude: 164.65°W 164°39’0″W
Westdahl is a broad, 1654-m-high glacier-covered volcano occupying the SW end of Unimak Island. Two peaks protrude from the summit plateau, and a new crater formed in 1978 cuts the summit icecap. The broad volcano has a somewhat of a shield-like morphology and forms one of the largest volcanoes of the Aleutian Islands. The sharp-topped, conical Pogromni stratovolcano lies 5 km north of Westdahl. Pogromni rises to 2002 m, several hundred meters higher than Westdahl, but is moderately glacially dissected and presumably older. Many satellitic cones of postglacial age are located along a NW-SE line cutting across the summit of Westdahl. Some of the historical eruptions attributed to the eroded Pogromni volcano may have originated instead from Westdahl (Miller et al. 1998). The first historical eruption of Westdahl occurred in 1795. An 8-km-long fissure extending east from the summit of Westdahl produced explosive eruptions and lava flows in 1991.
Westdahl Volcano Aerial View
Westdahl Peak, including nearby Faris Peak and Pogromni volcano, is located on a gently sloping plateau (mean elevation 1220 m) that may represent the surface of a truncated ancestral cone. Westdahl Peak is about 18 km in diameter at the base. The size of the postulated ancestral cone is about 19 x 30 km at sea level, making it one of the largest volcanoes in the Aleutian Islands be it a stratovolcano or a shield. The entire ancestral cone has been extensively dissected by erosion, with the northeast-facing slopes steeper and of greater relief than the other slopes.
Westdahl Volcano Aerial View
Based on the degree of erosional dissection, most of the postulated stratovolcano must have formed before early post-glacial time. Pogromni Volcano is moderately dissected and has broad valleys that have probably been glacially eroded. Such glacial erosion could have occurred during neoglaciation beginning about 3000 years ago, although one or two thousand years seem inadequate to account for the degree of dissection. Pogromni volcano was probably active by latest Pleistocene time, which implies that truncation of the ancestral stratovolcano must have occurred earlier.
Originally posted 2010-08-21 05:01:34.
