HR: 0800h
AN: H11B-0482    [Abstracts]
TI: The Effect of Freezing on the Dynamics of Dike Propagation
AU: Tait, S
EM: tait@ipgp.jussieu.fr
AF: Laboratoire de Dynamique des Fluides Geologiques, Institut de Physique du Globe de Paris, 4, Place Jussieu, Paris, 75252, France
AU: * Taisne, B
EM: taisne@ipgp.jussieu.fr
AF: Laboratoire de Dynamique des Fluides Geologiques, Institut de Physique du Globe de Paris, 4, Place Jussieu, Paris, 75252, France
AB: When magma-filled cracks propagate close to the Earth's surface, host rock temperature is well below the magma solidus. Solidification and substantial increase in magma viscosity can occur, are most pronounced near the propagating tip and can slow or arrest the progress of the dike. Quantitative analysis is required to predict whether a given dike will reach the surface to erupt and the duration of the precursor sequence. This challenging physical problem mixes elasticity, fracture mechanics, heat transfer and fluid flow with strong rheologic gradients due to cooling. We describe the propagation behaviour of such a hydraulic fracture using a laboratory experimental system of a crack fed by a constant flux of paraffin wax from a source reservoir propagating through gelatin below the solidus of the wax. The most novel behaviour is an intermittent regime in which cracks periodically stop advancing due to solidification, then swell at constant length while enhancing the elastic deformation in the surrounding solid before propagation resumes. We present a physical model of this system, based on different balances between driving and resistive forces: the former are elastic stress and liquid buoyancy, the latter are fracture resistance at the tip and viscous resistance. The fracture is represented as a head, behind the propagating tip, connected to the source by a narrow tail. Freezing of liquid close to the tip is assumed to enhance fracture resistance according to a cooling law, and propagation is assumed to occur only when the stress exerted by the liquid is enough to overcome fracture resistance. Our theoretical model reproduces intermittent propagation with precise behaviour depending on the controlling stress balances, and provides a tool to analyse natural systems.
DE: 5104 Fracture and flow
DE: 7280 Volcano seismology (8419)
DE: 8419 Volcano monitoring (7280)
DE: 8434 Magma migration and fragmentation
DE: 8445 Experimental volcanism
SC: Hydrology [H]
MN: 2007 Fall Meeting