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America's Coasts

Aleutian Arc

More than 80 volcanoes have been named in the Aleutian Arc, which extends for 2,500 km along the southern edge of the Bering Sea and the Alaskan mainland. Over 44 have erupted, sometimes repeatedly, since 1741, when written records began. Aleutian Arc volcanism is the result of the active subduction of the Pacific Plate beneath the North American Plate.

Volcanoes have influenced the Aleutian Arc in two ways. First, they have been constructive agents, creating islands as eruption after eruption has vented rock and ash. In some places, fresh lava or mud flows accompanying eruptions have buried the existing coast, extending the shore seaward. Usually, loose mudflow and ash deposits are reworked rapidly by waves, providing sediment for beach development. In addition, for years after an eruption, streams may carry rock and ash to the coast, allowing the coast to extend seaward.

The second effect has been destructive. Small islands have been largely destroyed by volcanic eruptions. Bogoslof, in the eastern Aleutians, is an example in which both rapid construction and destruction have influenced the island's shape over time.

Map of United States showing Alaska

Source: NationalAtlas.gov

Alaska Coasts

The eruptions of Mts. Katmai and Novarupta in 1912 produced ash layers 3 to 15 meters thick. The Katmai River and Soluka Creek carried vast amounts of loose ash to the sea, filling a narrow bay and burying a series of old beach ridges.