HR: 10:35h
AN: V12B-02    [Abstracts]
TI: Numerical Reconstructions of Volcanic Tephra: Using Tomography and Two-Point Correlation Functions to Determine Magma Permeability
AU: * Davis, M A
EM: davis923@umn.edu
AF: University of Minnesota Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455,
AU: Walsh, S D
EM: sdcwalsh@umn.edu
AF: University of Minnesota Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455,
AU: Saar, M O
EM: saar@umn.edu
AF: University of Minnesota Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455,
AU: Roberts, J J
EM: roberts17@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550,
AB: Understanding the processes that cause volcanic eruptions to be either effusive or explosive is vital to improve predictability and minimize hazards associated with volcanic eruptions. Explosivity appears to be linked to gas pressure build-up within magma, which is in turn affected by the degree of degassing of magmatic volatiles through permeable bubble networks or fractures in the magma. Magma permeability inside a volcano conduit is typically estimated experimentally by measuring the permeability of small pumice clasts (e.g., Klug and Cashman, Bull. Volcanol., 1996). However, permeability has been shown to be very scale-dependent (e.g., Hyun et al., Water Resor. Res., 2002), leaving substantial uncertainty in magma permeability-dependent calculations, such as magmatic volatile degassing rates. The objective of this study is to up-scale the permeability and microstructure (bubbles and crystals) of volcanic ejecta, and related magma degassing rates, to volcano-conduit scales. This is achieved by creating a numerical reconstruction method using X-ray tomography images of pumice clasts and two-point correlation functions. These numerical reconstructions reproduce the statistics of the spatial relationships of bubbles found in a given pumice clast. Once the bubble network is reconstructed, we are able to determine the porosity, tortuosity, and specific surface area of the bubble networks in the numerical reconstruction. In addition, lattice-Boltzmann simulations can be employed to numerically determine the bubble network's permeability.
DE: 0545 Modeling (4255)
DE: 8404 Volcanoclastic deposits
DE: 8428 Explosive volcanism
DE: 8430 Volcanic gases
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting