COMPARATIVE ANALYSIS OF ASH DEPOSITS IN NEW ZEALAND AND MOUNT ST. HELENS

Volcanic ash deposits begin to weather upon deposition; the volcanic glass begins to devitrify and clay materials are deposited and formed within the pore spaces. Previous work by Almquist (2011) established a classification scheme of weathering on tephra deposits from the Waipaoa catchment in New Zealand using an SEM. This scheme showed the variation in weathering based on terrestrial vs. marine deposits from ash ranging in age from 636 ± 12 years to 17,625 ± 425 years old (ages from Lowe et al., 2008). We are examining volcanic ash collected from Mount St. Helens on the day of the 1980 eruption in order to broaden the classification scheme to more virgin material. Ash material was separated and prepared for the SEM, and analyzed using secondary electrons. In addition, FTIR analysis of the material was also collected in order to get a better understanding of the geochemistry of the weathering products. By broadening the weathering classification scheme, we hope to begin to establish a useful tool for researchers to apply a terminology to the level of weathering of ash materials.