Project Description
The objectives of this research project are to determine the grain size of explosive tephra deposits from cinder cone volcanoes that make up the Sand Mountain Volcanic Field in central Oregon and to determine the matrix glass compositions of the tephra fragments. Cinder cone volcanoes are monogenetic with very short life spans of a few months to a few years. The Sand Mountain Volcanic Field consists of 23 vents that were active over a few decades about 3 ka (three thousand years ago). Trenches up to 2 m deep were dug proximal, intermediate and distal from the N-S trending chain of cinder cones and the main tephra layers sampled for grain size analysis and matrix glass compositions. The grain size of the ash layers will be determined by a Malvern Mastersizer 2000 in the Department of Geosciences. The Malvern Mastersizer 2000 is laser diffraction particle size analyzer that measures grain size based on light scattering when a laser beam passes through dispersed particulate sample. Grain sizes from 002-2000 μm (microns). The matrix glass composition of the ash particles will be determined by electron microprobe at the University of Wisconsin-Madison. The electron microprobe provides major element compositions of the glass in addition to volatiles such as sulfur and chlorine.
Tasks and Responsibilites
The student will undertake both the grain size analysis and electron microprobe analysis of the matrix glass. The student will measure about 40 samples for grain size on the Malvern Mastersizer 2000. The student will add about 0.25 grams of ash to an Erlenmeyer flask, then add 20 ml of Sodium Metaphosphate solution to the flask, cover with parafilm and let sit for at least 24 hours. The solution is then run on the Malvern Mastersizer 2000. The student will also make a sample mount of tephra fragments for electron microprobe analysis. The student will drill 15 holes in 1-inch aluminum disk and place ash in the holes to fill them. Then the student will add epoxy and let the mount cure overnight. The student will then polish the mount and then travel to Madison to analyze the matrix glass in ash samples on the electron microprobe. The student will make preliminary interpretations on what the data means.