Distribution of the Heavy Minerals in the Downwind Tephra Lobe of the May 18, 1980 Eruption of the Mount St. Helens (Washington, USA)

Etienne Juvigné & Susan Shipley
Quantitative analysis of heavy minerals from tephra samples of the May 18 eruption of Mount St. Helens shows variations in the total content of heavy minerals as well as in the ratio hypersthene/hornblende. Both decrease along the lobe with increasing distance from the volcano and from the lobe margins to the axis. The basal dark-grey layer contains more hypersthene than the overlying light-grey layer. The observed sorting is a function of the specific gravity of...