Seven Hills, Semisopochnoi, Alaska
Saturday, January 1, 2011 9:17:40 AM
The seven hills of the island are volcanic peaks, each with a summit crater, including Cerberus, Sugarloaf Peak, Lakeshore Cone, Anvil Peak, Pochnoi, Ragged Top, and Three-quarter Cone. The high point of the island is Anvil Peak at 1,221 m, a double-peaked cone. The three-peaked Mount Cerberus volcano (774 m high) grew up within the caldera as the volcano rose up from the sea floor. Most documented eruptions have come from Cerberus, with the most recent major eruption recorded in 1873. The most recent eruption on the island, though minor, came from Sugarloaf in 1987.
Semisopochnoi is one of the Aleutian Islands, a chain of more than 300 small volcanic islands, forming part of the Aleutian Arc in the Northern Pacific Ocean. The Aleutian arc extends about 3,000 km from the Gulf of Alaska to Kamchatka. It marks the region where the Pacific plate subducts into the mantle beneath the North American plate. This subduction is responsible for the generation of the Aleutian Islands and the deep offshore Aleutian Trench. Relative to a fixed North American plate, the Pacific plate is moving north-west at a rate that increases from 6.6 cm per year in the arc's eastern region to 8.6 cm per year near its western edge. In the east, the convergence of the plates is nearly perpendicular to the plate boundary. However, because of the boundary's curvature, as one travels westward along the arc, the subduction becomes more and more oblique to the boundary until the relative plate motion becomes almost parallel to the boundary at its western edge.
Semisopochnoi Island is uninhabited and provides an important nesting area for maritime birds, it supports more than a million seabirds, particularly auklets.