Influence of magma composition on the eruptive activity of Mount St Helens, Washington
Date of Original Version
The relation of eruptive intensity with magma composition and viscosity has been investigated for Mount St Helens where eruptive activity has ranged from basaltic lava flows to dacitic Plinian eruptions. The Plinian eruptions have varied in eruptive intensity from 10 6 to 10 8 kg/s, yet all erupted dacitic magma. These dacites, however, differ greatly in temperature, water content, and crystallinity, and thus magma viscosity varies by two orders of magnitude. The variation in viscosity is correlated inversely with intensity. In addition, more mafic magmas erupted at lower intensities, showing that the wide range in eruptive behavior is linked to magma composition. Changes in composition result mainly from mixing of basaltic and dacitic magmas and occur in cycles. The rate of change during a cycle depends upon the length of the preceding repose period and the flux of basalt to the reservoir. -from Authors
Publication Title, e.g., Journal
Gardner, J. E., S. Carey, H. Sigurdsson, and M. J. Rutherford. "Influence of magma composition on the eruptive activity of Mount St Helens, Washington." Geology 23, 6 (1995). doi: 10.1130/0091-7613(1995)023<0523:IOMCOT>2.3.CO;2.