Supporting Sound Management of Our Coasts and Seas Kasatochi Volcano

Alaska is noteworthy as a region of frequent seismic and 

 volcanic activity. The region contains 52 historically active 

volcanoes, 14 of which have had at least one major eruptive event 

since 1990. Despite the high frequency of volcanic activity in Alaska, 

comprehensive studies of how ecosystems respond to volcanic eruptions 

are non-existent. On August 7, 2008, Kasatochi Volcano, in the central Aleutian 

Islands, erupted catastrophically, covering the island with ash and hot pyroclastic flow 

material. Kasatochi Island was an annual monitoring site of the U.S. Fish and Wildlife Service, Alaska 

Maritime National Wildlife Refuge (AMNWR); therefore, features of the terrestrial and nearshore 

ecosystems of the island were well known. In 2009, the U.S. Geological Survey (USGS), AMNWR, and 

University of Alaska Fairbanks began long-term studies to better understand the effects of the eruption and 

the role of volcanism in structuring ecosystems in the Aleutian Islands, a volcano-dominated region with 

high natural resource values.

U.S. Geological Survey (USGS)

Western Region: Kasatochi Volcano

Coastal and Ocean Science

Fact Sheet 2010–3028

May 2010 Printed on recycled paper

Kasatochi

U.S. Department of the Interior

U.S. Geological Survey

Pre-eruptive Kasatochi

Kasatochi is a small stratovolcano in the central Aleutian Islands. Prior to the eruption, the volcano was about 

3 km in diameter, 300 m high, with a steep-walled caldera with a small lake in the center. Because of the nature of 

its water-filled caldera and steep, verdant slopes, Kasatochi was one of the most picturesque of the Aleutian Islands. 

Before the 2008 eruption, the island was steep and rugged with dense, low-growing vegetation dominated by many 

species of grasses and forbs making it similar to other Aleutian Islands. Kasatochi Island was set apart by the diversity 

and abundance of seabirds that nested there each summer. Most notably, Kasatochi supported a colony of about 250,000 

least and crested auklets, one of only seven such colonies in the Aleutian chain. The large numbers of seabirds attracted a 

variety of avian predators such as bald eagles and peregrine falcons. Kasatochi was also notable for supporting a rookery of 

the endangered Steller sea lion.

As the photographs of Kasatochi taken in 2008 suggest, life on the island appears to have been destroyed by the 

August 7 eruption. During summer 2009, we began a study to understand how Kasatochi had changed over the winter and to 

determine the initial fate of the terrestrial and marine plants and animals on the island.

Kasatochi Volcano in July 2008 (left) and in October 2008 (right). The volcano erupted August 7, 2008. Photographs taken by 

Jerry Morris, Security Aviation.
For more information:

Director, Alaska Science Center

U.S. Geological Survey

4210 University Drive, Anchorage, AK 99508

907-786-7000

Research Objectives

Our long-term goal is to examine how terrestrial, nearshore, and marine ecosystems at and around Kasatochi Island respond to 

the cataclysmic eruption of August 7, 2008. This is a unique opportunity to examine how volcanism and geomorphologic processes 

influence ecosystem succession on a remote maritime island through the integration of various scientific disciplines. Kasatochi 

provides a real-world laboratory where island biogeographic theory and the factors that influence dispersal and re-settlement of plant, 

invertebrate, and vertebrate species can be examined.

Post-eruption Research in 2009

During summer 2009, teams of geologists, botanists, ornithologists, and marine ecologists visited Kasatochi and nearby islands 

four times to document the effects of the eruption and establish baseline conditions from which long-term comparisons will be made. 

The teams were supported in the field by the U.S. Fish and Wildlife Service’s vessel, the M/V Tiglax. The teams set up equipment 

such as seismometers, time-lapse cameras, and bird song meters. They also established permanent transects and plots for sampling and 

for making detailed measurements.

Preliminary Findings From Summer 2009 Investigations

Geology and Geomorphology

• The 2008 volcanic deposits contained a large proportion of lithic blocks (pieces of the preexisting volcano) indicating that the upper part of the cone was blown away during the eruption.

• Larger-than-expected variation was noted in thicknesses of the pyroclastic deposits and the 

extent to which the pre-eruption surfaces were affected. In some areas, the deposits were 

tens of meters thick and the existing ground cover was stripped off. In other areas, the 

deposits were thin, already eroded, and showing pre-eruption surfaces.

• The rapidity of the modification and erosion of the 2008 deposits is remarkable. Large 

gully systems have developed and the upper 1–2 meters of deposits in steep areas have 

sloughed off and generated debris flows resulting in considerable sediment deposition in 

nearshore marine waters.

• Kasatochi continued to degas (sulfur gasses and perhaps carbon dioxide) more than 

1 year after the eruption, likely from diffuse sources.

Example of extreme rapid erosion of pyroclastic 

material from Kasatochi. Photograph by Chris 

Waythomas, U.S. Geological Survey. 

Terrestrial Ecology

• Some pre-existing vegetation seems to have survived the eruption, particularly in areas that were 

protected from the hot pyroclastic flows or where the flows eroded off quickly. 

• Scattered individuals of several plant species and one small remnant plant community were observed. 

Most of the plants likely originated from rhizomes, rootstock, or seed banks that survived the eruption.

• A few terrestrial arthropods may have survived as well. Wingless carrion beetles as well as a 

centipede and a spider were found. Several fly species (kelp flies and a blowfly) also were found and 

these species already were exploiting bird carcasses and kelp that had washed up on the island.

• Many birds returned to the island although none nested successfully. The auklet colony was buried 

under volcanic debris and ash, but hundreds of thousands of auklets still attended the former colony 

site. The auklets were unable to locate suitable nesting crevices and laid eggs on the ground or in the 

water. Nearly all birds were gone by August.

• Steller sea lions were the only wildlife species to breed successfully.

Summary

Kasatochi has changed rapidly since the August 2008 eruption. Our multidisciplinary

team of researchers will continue to document these changes in 2010 and beyond.

Financial support from the North Pacific Research Board, the USGS Office of 

the Alaska Regional Executive, the U.S. Fish and Wildlife Service, the USGS Alaska 

Science Center, and the Alaska Volcano Observatory is gratefully acknowledged.

Marine Ecology

• The nearshore, subtidal zone was largely devoid of life. Most of the kelp forests around the island had been covered with volcanic 

debris and most of the seafloor was comprised of unstable sediments. Little recovery was observed. Continued deposition of sediments 

into the nearshore due to erosion of deposits on Kasatochi likely will have long-term effects on the nearshore marine ecosystem.