Constraining the Magmatic System at Mount St. Helens (2004–2008) Using Bayesian Inversion With Physics‐Based Models Including Gas Escape and Crystallization

Physics‐based models of volcanic eruptions track conduit processes as functions of depth and time. When used in inversions, these models permit integration of diverse geological and geophysical data sets to constrain important parameters of magmatic systems. We develop a 1‐D steady state conduit mod...

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Bibliographic Details
Published in:Journal of geophysical research. Solid earth 2017-10, Vol.122 (10), p.7789-7812
Main Authors: Wong, Ying‐Qi, Segall, Paul, Bradley, Andrew, Anderson, Kyle
Format: Article
Language:English
Subjects:
Bayes theorem
Bayesian analysis
Constants
Constraint modelling
Crystallization
Datasets
Earthquakes
Extrusion rate
Fluctuations
Flux
Friction
Friction resistance
Gas transport
Geophysical data
Geophysics
GEOSCIENCES
inverse theory
Inversions
Lava
Magma
Magma chambers
Mass flux
Mathematical models
Moisture content
Mount St. Helens
Natural gas
Overpressure
Parameter estimation
Parameters
Permeability
Physics
physics-based models
Porosity
Pressure
Probability theory
Rocks
Seismic activity
Steady state models
Transport
Viscosity
Viscous flow
Volatiles
Volcanic eruption effects
Volcanic eruptions
volcano conduit
Water content
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Summary:Physics‐based models of volcanic eruptions track conduit processes as functions of depth and time. When used in inversions, these models permit integration of diverse geological and geophysical data sets to constrain important parameters of magmatic systems. We develop a 1‐D steady state conduit model for effusive eruptions including equilibrium crystallization and gas transport through the conduit and compare with the quasi‐steady dome growth phase of Mount St. Helens in 2005. Viscosity increase resulting from pressure‐dependent crystallization leads to a natural transition from viscous flow to frictional sliding on the conduit margin. Erupted mass flux depends strongly on wall rock and magma permeabilities due to their impact on magma density. Including both lateral and vertical gas transport reveals competing effects that produce nonmonotonic behavior in the mass flux when increasing magma permeability. Using this physics‐based model in a Bayesian inversion, we link data sets from Mount St. Helens such as extrusion flux and earthquake depths with petrological data to estimate unknown model parameters, including magma chamber pressure and water content, magma permeability constants, conduit radius, and friction along the conduit walls. Even with this relatively simple model and limited data, we obtain improved constraints on important model parameters. We find that the magma chamber had low (
ISSN:2169-9313
2169-9356
DOI:10.1002/2017JB014343