Physical Sciences and Mathematics Commons^™

Mineralogy And Phase Chemistry Of Mount St. Helens Tephra Sets W And Y As Keys To Their Identification, Diane R. Smith, W. P. Leeman

Geosciences Faculty Research

Voluminous and widespread tephras were produced frequently during the last 36,000 yr of volcanic activity at Mount St. Helens. Numerous tephra sets have been defined by D. R. Mullineaux, J. H. Hyde, and M. Rubin (1975, U.S. Geological Survey Journal of Research, 3, 329–335) on the basis of field relations, Fe-Mg phenocryst assemblage, and ¹⁴C chronology and are valuable marker beds for regional stratigraphic studies. In this study modal abundances and mineral compositions were determined (via petrographic and electron microprobe techniques) for numerous samples of individual layers within tephra sets W and Y to evaluate the degree of …