GEOMORPHIC CONSEQUENCES OF VOLCANIC ERUPTIONS IN ALASKA

Eruptions of Alaskan volcanoes have significant and sometimes profound geomorphic consequences on surrounding landscapes and ecosystems. The effects of eruptions on the landscape can range from complete destruction of ecosystems to subtle perturbations of geomorphic and ecological systems. In some cases, an eruption will allow for new landscapes to evolve from freshly deposited volcaniclastic material, and in other cases, the geomorphic response to a major eruptive event may set in motion a series of landscape changes that could take centuries to millennia to be realized. Most volcanoes in Alaska support an extensive cover of glacier ice, and eruptions almost always lead to extensive meltwater production. Thus, a variety of water-sediment flows typically occur in response to eruptive activity, and occasionally, these flows can be very large (10⁷–10⁹ m³). During the 2009 eruption of Redoubt Volcano, pyroclastic flows generated by explosive destruction of lava domes swept across glacier ice and generated several very large lahars that completely inundated the Drift River valley and threatened an oil storage facility 40 km downstream from the volcano. The largest lahars were as much as 30 times larger than the largest meteorological floods in the 570 km² drainage basin. An eruption at Kasatochi volcano in the eastern Aleutian Islands on August 7–8 2008 covered the island with tens of meters of pyroclastic debris and ash, extending the coastline of the island about 400 m into the Bering sea. Kasatochi is one of a few places in the Aleutian Islands that provides suitable nesting habitat for seabirds (primarily Crested and Least Auklets), and roughly 500,000 of these birds nest here annually. The 2008 eruption destroyed all of the nesting habitat but because of the dynamic environment of Kasatochi Island and the high rates of surface erosion that occurred subsequent to the eruption, within 4 years new habitat was generated and previously existing habitat was exhumed by surface erosion allowing the birds to continue nesting on the island.

Throughout my career in Alaska, I have had numerous opportunities to consider volcanic landscapes from the perspective of process geomorphology. This approach was initially fostered by Dusty Ritter to whom I owe much appreciation and gratitude for his role in shaping and inspiring my work.