Abrupt conduit geometry changes: a source to geophysical signals near volcanoes?
Abstract
Geophysical signals are the principal tools to forecast eruptive behaviour. In particular, volcano seismicity is largely due to flow processes within the conduit and during dome eruption, it is frequent to record low frequency earthquakes localized at a given depth below the vent (Neuberg et al., 2006). These earthquakes originate at a boundary between a fluid and a solid and propagate along the conduit wall (Chouet, 1988). It has long been assumed that changes in magma rheology might be a cause for this seismicity. However, both field evidences and geophysical studies (Hautmann et al., 2009) showed that it is probable that conduit shape changes from dike to cylindrical conduit at a certain depth, thousands of meters below the surface. Also a previous paper (Massol and Jaupart, 2009) showed that the tensile strength limit of magma may be reached at the exit of the conduit where velocity field changes abruptly from one direction to another. Our goal here is to investigate if this type of conditions may be reached at depth due to an abrupt change in the conduit geometry. We conduct a parametric study using 2-D F.E.M. non-newtonian, conduit flow models and show that if a constriction exists at depth it increases tensile stress values up to order of 10 MPa at that level, overcoming in that case the tensile stress threshold. This might lead to magma breakage and be a potential source for the recorded seismic signals.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.V23F2622M
- Keywords:
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- 8414 VOLCANOLOGY / Eruption mechanisms and flow emplacement;
- 8419 VOLCANOLOGY / Volcano monitoring;
- 8434 VOLCANOLOGY / Magma migration and fragmentation