The Geomorphology of an Aleutian Volcano following a Major Eruption: the 7–8 August 2008 Eruption of Kasatochi Volcano, Alaska, and Its Aftermath

Abstract

Analysis of satellite images of Kasatochi volcano and field studies in 2008 and 2009 have shown that within about one year of the 7–8 August 2008 eruption, significant geomorphic changes associated with surface and coastal erosion have occurred. Gully erosion has removed 300,000 to 600,000 m³ of mostly fine-grained volcanic sediment from the flanks of the volcano and much of this has reached the ocean. Sediment yield estimates from two representative drainage basins on the south and west flanks of the volcano, with drainage areas of 0.7 and 0.5 km², are about 10⁴ m³ km⁻² yr⁻¹ and are comparable to sediment yields documented at other volcanoes affected by recent eruptive activity. Estimates of the retreat of coastal cliffs also made from analysis of satellite images indicate average annual erosion rates of 80 to 140 m yr⁻¹. If such rates persist it could take 3–5 years for wave erosion to reach the pre-eruption coastline, which was extended seaward about 400 m by the accumulation of erupted volcanic material. As of 13 September 2009, the date of the most recent satellite image of the island, the total volume of material eroded by wave action was about 10⁶ m³. We did not investigate the distribution of volcanic sediment in the near shore ocean around Kasatochi Island, but it appears that erosion and sediment dispersal in the nearshore environment will be greatest during large storms when the combination of high waves and rainfall runoff are most likely to coincide.

Acknowledgments

Funding for this work was provided by a grant from the North Pacific Research Board, Project #923, and the U.S. Geological Survey Volcano Hazards Program. The authors thank the crew and staff of the U.S. Fish and Wildlife Service R/V Tiglax for logistical support of our work on Kasatochi Island. Review comments by two anonymous reviewers and the associate editor are appreciated and helped improve the clarity of the manuscript This is contribution 253 of the North Pacific Research Board.