HR: 16:15h
AN: V24B-02    [Abstracts]
TI: Earthquake-excited crystal-rich magmas
AU: Davis, M
EM: mast@kingston.ac.uk
AF: Centre for Earth and Environmental Science Research, Kingston University, London, KT1 2EE United Kingdom
AU: Koenders, C
EM: koenders@kingston.ac.uk
AF: Centre for Earth and Environmental Science Research, Kingston University, London, KT1 2EE United Kingdom
AU: * Petford, N
EM: n.petford@kingston.ac.uk
AF: Centre for Earth and Environmental Science Research, Kingston University, London, KT1 2EE United Kingdom
AB: We present the results of a novel set of calculations into the effect of in-situ pressure reduction of a crystal-rich, crustal magma chamber by propagating seismic (P) waves. Three stages in the process are identified. Critically, an instability can arise such that a fluidized, low pressure melt layer develops close to the floor in initially densely packed magma (Φ = 0.6) on near-instantaneous timescales. The role of particle pressure, a newly identified force arising from interactions between adjacent crystals in the magma, is fundamental to the development of the instability, which will not arise in crystal-free liquids. Key variables governing the instability are identified and include the mean particle diameter, the excitation frequency (1-10 Hz), interstitial melt viscosity and melt compressibility. Small penetration depths (high particle pressures) develop most readily in compressible, volatile-bearing magmas at higher frequencies. The quasi-static particle pressure that develops as a result of the spatially-decaying oscillations leads to two effects: 1) a rapid reduction in the interstitial melt pressure (c.0.16 MPa/s) resulting in heterogeneous bubble nucleation, and 2) fluidization of a thin layer at the base of the magma chamber. Both these effects in turn increase the particle pressure. The fluidization effect provides a way of rapidly segregating crystals from interstitial liquid (mechanical differentiation) to produce a potentially unstable melt-rich layer at the chamber floor with a viscosity interval (η) in the range 10² < η <10³ Pa s. A non-linear runaway effect is identified, driven by positive feedback between particle pressure, melt viscosity and degassing.
DE: 8145 Physics of magma and magma bodies
DE: 8428 Explosive volcanism
DE: 8430 Volcanic gases
DE: 8439 Physics and chemistry of magma bodies
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005