Saint Paul Island (Alaska) - Geography and Geology

Geography and Geology

Saint Paul is the largest of the Pribilof Islands and lies the furthest north. With a width of 7.66 mi (12.33 km) at its widest point and a length of 13.5 mi (21.7 km) on its longest axis (which runs from northeast to southwest), it has a total area of 43 sq mi (110 km2). Volcanic in origin, Saint Paul features a number of cinder cones and volcanic craters in its interior. The highest of these, Rush Hill, rises to 665 ft (203 m) on the island's western shore, though most of the upland areas average less than 150 ft (46 m) in elevation. Most of the island is a low-lying mix of rocky plateaus and valleys, with some of the valleys holding freshwater ponds. Much of its 45.5 mi (73.2 km) of shoreline is rugged and rocky, rising to sheer cliffs at several headlands, though long sandy beaches backed by shifting sand dunes flank a number of shallow bays.

Like the other Pribilof Islands, Saint Paul rises from a basaltic base. Its hills are primarily brown or red tufa and cinder heaps, though some (like Polavina) are composed of red scoria and breccia. The island sits on the southern edge of the Bering-Chukchi platform, and may have been part of the Bering Land Bridge's southern coastline when the last ice age's glaciers reached their maximum expansion. Sediment core samples taken on Saint Paul show that tundra vegetation similar to that found on the island today has been present for at least 9,000 years. The thick rough turf is dominated by umbellifers (particularly Angelica) and Artemisia, though grasses and sedges are also abundant.