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Improved constraints on the estimated size and volatile content of the Mount St. Helens magma system from the 2004–2008 history of dome growth and deformation
Author(s) -
Mastin Larry G.,
Lisowski Mike,
Roeloffs Evelyn,
Beeler Nick
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl039863
Subject(s) - geology , magma , overpressure , magma chamber , dome (geology) , petrology , volume (thermodynamics) , lava dome , lateral eruption , bubble , volcano , mineralogy , seismology , mechanics , geomorphology , explosive eruption , thermodynamics , physics
The history of dome growth and geodetic deflation during the 2004–2008 Mount St. Helens eruption can be fit to theoretical curves with parameters such as reservoir volume, bubble content, initial overpressure, and magma rheology, here assumed to be Newtonian viscous, with or without a solid plug in the conduit center. Data from 2004–2008 are consistent with eruption from a 10–25 km 3 reservoir containing 0.5–2% bubbles, an initial overpressure of 10–20 MPa, and no significant, sustained recharge. During the eruption we used curve fits to project the eruption's final duration and volume. Early projections predicted a final volume only about half of the actual value; but projections increased with each measurement, implying a temporal increase in reservoir volume or compressibility. A simple interpretation is that early effusion was driven by a 5–10 km 3 , integrated core of fluid magma. This core expanded with time through creep of semi‐solid magma and host rock.