MAY 18, 1980 ERUPTION OF MOUNT ST. HELENS - 2. MODELING OF DYNAMICS OF THE PLINIAN PHASE.
Document Type
Article
Date of Original Version
1-1-1985
Abstract
The Plinian phase of the May 18, 1980, Mount St. Helens eruption is modeled as a steady state discharge of dacitic magma from a reservoir at 7-10 km depth at a reate of 1. 94 multiplied by 10**7 kg/s. Properties of the magma, including preeruption volatile content (4. 6% in the melt), temperature (920 degree -940 degree C), and confining pressure (190-250 MPa) are constrained by petrologic studies. Mass eruption rate, magma viscosity, and independent estimates of magma ascent velocity suggest a 95-m-diameter conduit at a depth below vapor saturation. Dispersal of pyroclasts indicate a minimum exit velocity of roughly 200 m/s during the Plinian phase. An upper limit of 330 m/s is obtained from the total amount of exsolved volatiles. Model-derived vent diameters based on 0. 1-MPa exit pressure, petrologically inferred magma properties, and known mass eruption rate range from 105 to 135 m with a flared configuration.
Publication Title, e.g., Journal
Journal of Geophysical Research
Volume
90
Issue
B4
Citation/Publisher Attribution
Carey, Steven, and Haraldur Sigurdsson. "MAY 18, 1980 ERUPTION OF MOUNT ST. HELENS - 2. MODELING OF DYNAMICS OF THE PLINIAN PHASE.." Journal of Geophysical Research 90, B4 (1985). doi: 10.1029/JB090iB04p02948.