Magmatic model for the Mount St. Helens blast of May 18, 1980

Journal Article · Fri Sep 10 00:00:00 EDT 1982 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB087iB09p07727· OSTI ID:5912450

Eichelberger, J C; Hayes, D B

Analytical and numerical solutions to the hydrodynamic equations of motion, constrained by physical properties of juvenile ejecta in the Mount St. Helens blast deposit, were used to investigate magmatic conditions required to produce the initial devastating blast phase of the eruption of May 18, 1980. Evidence that the blast was magmatic includes equivalence in volume of juvenile blast ejecta to preeruption inflation of the cone, substantial vesicularity of this ejecta, and continued vesiculation of large juvenile clasts after eruption. Observed or inferred ejecta velocities of 100 to 250 m/s are shown to require 0.2 to 0.7 wt% water vapor preexisting in magma unloaded by a landslide 200 to 900 m thick. These conditions imply total magmatic water contents of 0.7 to 1.7 wt%, respectively. Such low required water content suggests that volcanic blasts may be regarded as a normal consequence of magma intrusion into an unstable edifice.

• Research Organization: Sandia National Laboratories, Albuquerque, New Mexico 87185
• OSTI ID: 5912450
• Journal Information: J. Geophys. Res.; (United States), Vol. 87:B9
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
MT ST HELENS
ERUPTION
GEOLOGIC MODELS
EQUATIONS OF MOTION
HYDRODYNAMICS
MAGMA
SEISMICITY
CASCADE MOUNTAINS
DIFFERENTIAL EQUATIONS
EQUATIONS
FEDERAL REGION X
FLUID MECHANICS
MECHANICS
MOUNTAINS
NORTH AMERICA
PARTIAL DIFFERENTIAL EQUATIONS
USA
WASHINGTON
580202* - Geophysics- Volcanology- (1980-1989)