2009 Preliminary Findings
Geology and Geomorphology
The 2008 volcanic deposits contained a large proportion of lithic blocks (pieces of the pre-existing volcano) indicating that the upper part of the cone was blown away during the eruption.
|The shores of Kasatochi on August 31, 2009 - photo by Chris Waythomas, AVO, USGS
- There was larger-than-expected variation in thicknesses of the pyroclastic deposits and the extent to which the pre-eruption surfaces were impacted. 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 showing off pre-existing surfaces.
- The rapidity by which the 2008 deposits are being modified and eroded 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 a full year after the eruption, most likely from diffuse sources.
- Some of the pre-existing vegetation appears 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 species-poor remnant of a previously widespread community type were observed. Most of the plants likely originated from rhizomes, root stock 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 blow fly) were also found and these species were already 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 layed 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.
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 will likely have long term effects to the nearshore marine ecosystem.