Modelling Shear Bands in a Volcanic Conduit: Implications for Over-Pressures and Extrusion Rates

Alina Jane Hale and Hans Bernd Muhlhaus (2007) Modelling Shear Bands in a Volcanic Conduit: Implications for Over-Pressures and Extrusion Rates. Earth and Planetary Science Letters, : .

Document type: Journal Article
Sub-type: Article
Collection: Temporary duplicates
Attached Files (Some files may be inaccessible until you login with your UQ eSpace credentials)
Name Description MIMEType Size Downloads
ShearBands_AJH_HM_figs.pdf Paper application/pdf 584.49KB 171

Author Alina Jane Hale
Hans Bernd Muhlhaus
Title Modelling Shear Bands in a Volcanic Conduit: Implications for Over-Pressures and Extrusion Rates
Journal name Earth and Planetary Science Letters  (ERA 2012 Listed)    (ERA 2010 Rank A*)
Publication date 2007-08-28
Sub-type Article
Collection year 2007
Subject 260200 Geophysics
260103 Vulcanology
Abstract Shear bands in a volcanic conduit are modelled for crystal-rich magma flow using simplified conditions to capture the fundamental behaviour of a natural system. Our simulations begin with magma crystallinity in equilibrium with an applied pressure field and isothermal conditions. The viscosity of the magma is derived using existing empirical equations and is dependent upon temperature, water content and crystallinity. From these initial conduit conditions we utilize the Finite Element Method, using axi-symmetric coordinates, to simulate shear bands via shear localisation. We use the von Mises visco-plasticity model with constant magma shear strength for a first look into the effects of plasticity. The extent of shear bands in the conduit is explored with a numerical model parameterized with values appropriate for Soufrière Hills Volcano, Montserrat, although the model is generic in nature. Our model simulates shallow (up to approximately 700m) shear bands that occur within the upper conduit and probably govern the lava extrusion style due to shear boundaries. We also model the change in the over-pressure field within the conduit for flow with and without shear bands. The pressure change can be as large as several MPa at shallow depths in the conduit, which generates a maximum change in the pressure gradient of 10’s of kPa/m. The formation of shear bands could therefore provide an alternative or additional mechanism for the inflation/deflation of the volcano flanks as measured by tilt-metres. Shear bands are found to have a significant effect upon the magma ascent rate due to shear-induced flow reducing conduit friction and altering the over-pressure in the upper conduit. Since we do not model frictional controlled slip, only plastic flow, our model calculates the minimum change in extrusion rate due to shear bands. However, extrusion rates can almost double due to the formation of shear bands, which may help suppress volatile loss. Due to the paucity of data and large parameter space available for the magma shear strength our model results can only allow for a qualitative comparison to a natural system at this stage.
Keyword Magma flow
Finite element method
Shear bands
Computational volcanology
Soufrière Hills Volcano
Q-Index Code C1
Additional Notes This is an author version of a forthcoming article in Earth and Planetary Science Letters.
 
Versions
Version Filter Type
Citation counts: Scopus Citation Count Cited 7 times in Scopus
Access Statistics: 149 Abstract Views, 171 File Downloads  -  Detailed Statistics
Created: Wed, 29 Aug 2007, 09:28:53 EST by Alina Jane Hale on behalf of Research Management Office  -  Detailed History