CHARACTERIZATION OF THE VOLCANIC SUBSTRATE AND SOIL FOLLOWING THE 2008 ERUPTION OF KASATOCHI ISLAND VOLCANO, ALASKA

On August 7, 2008, Kasatochi Volcano, an island volcano in the Aleutian Island chain of Alaska, erupted catastrophically blanketing the island in coarse pyroclastic, fine ash, and pyroclastic surge deposits. Kasatochi Island is part of the ecological monitoring network of the US Fish and Wildlife Service’s Alaska Maritime National Wildlife Refuge and, in 2009, the US Geological Survey, the US Fish and Wildlife Service, and the University of Alaska initiated an interdisciplinary reconnaissance study of Kasatochi Island to document the acute impacts of the eruption, and to initiate a long-term integrated monitoring and research program to document the ecological response of the terrestrial and marine ecosystems. We report here on the initial soil/substrate characterization study of this broader ecosystem effort.

Deionized water leach tests on fresh ash samples collected in 2008 from a ship deck and neighboring islands shortly after the eruption yielded leachates with circum-neutral pH (6 to 8.2) and highly leachable concentrations of SO₄, Cl, Ca, and Na (3480–11300, 1200–4310, 1570–4820, and 650–>1550 mg leached/kg ash, respectively). The possible effects of these soluble ash components on natural re-vegetation are being studied. Visits in 2009 found that, while most of the island is covered up to tens of meters of coarse pyroclastic deposits and fine ash, the crest of the former south bluff was only thinly covered by fine ash. Erosion of the ash exposed the previous soil surface along much of this bluff. No evidence of charring of the former soil was found and many fine and medium roots were visible in the pre 2008-soil A-horizon, which was covered by 11 cm of fine ash. Sporadic seedlings and shoots of rye grass emerging from the ash mantle were observed in several places along the bluff top. Other isolated occurrences of emerging vegetation were observed in the high rocky cliffs west of the bluff. Such areas may prove to be important refugia from which re-vegetation occurs. A second A horizon was noted at about 60 cm below the current surface. Analysis of this second buried A-horizon will potentially provide a time constraint on the pre 2008-eruption soil development.