Examination of Volcanic Glass From the Pacific Northwest, USA, Using Light Microscopy, SEM- XRF and Cathodoluminescence.

Volcanic glass is an extrusive fragmented volcanic rock commonly of rhyolitic composition that is derived from erupting volcanoes.  Volcanic glass content in soil from the Pacific Northwest can be quite substantial. Research conducted on the Columbia Plateau suggests that volcanic glass in soil ranges from 1.3% to as high as 51.6% and that glass content increases from the southwest to the northeast across the plateau.  Current research conducted on a subset of 10 samples from a 100 meter grid location in Stevens County, Washington revealed glass volume percent estimates ranging from 17.3 % to 29 %. 

Examination of individual pumice grains derived from volcanic ash samples (Mt. Mazama, Meadow Creek, Mt. St. Helens collected in 1980 at several locations, and Lava Creek) was conducted in an attempt to characterize and differentiate eruptive events.  Pumice grains were characterized using polarized light microscopy with dispersion staining, scanning electron microscopy-x-ray fluorescence spectroscopy (SEM-XRF) and cathodoluminescence (CL).  The characterization and comparison of pumice can be used as a discriminating tool in soil examination casework.  Volcanic glass weight percent estimates coupled with optical and chemical data will be presented as part of an analytical scheme in the examination of soils in a volcanic terrain.