The effects of rock heterogeneities on dyke paths and asymmetric ground deformation: The example of Piton de la Fournaise (Reunion Island)

During pre-eruptive periods and eruptions, Piton de la Fournaise volcano shows an asymmetric magma-induced pattern of deformation. The origin of this asymmetry is not well constrained and the pre-eruptive deformation does not have a satisfactory explanation. Here we present data on the past history and complex structure of the volcano. We also provide new field data on exposed dykes in the volcano. The field data confirm that the eruptive centre has migrated through time. Our field data indicate average dyke dips of about 80 degrees. By contrast, inferred dips of recent feeder dykes using geodetic data are 53 degrees-75 degrees. We explain this difference as being partly due to the models used to infer the dyke dips from geodetic data, which assume the host rock to be homogeneous and isotropic. When fractures and the other heterogeneities are taken into account in the models, the inferred dyke dips become similar to those of the exposed dykes. New numerical models indicate that when the complex internal structure of the volcano is taken into account, part of the asymmetry of the ground deformation can be explained. Part of the deformation asymmetry, however, is due to the curved structure of the rift system, resulting in the injection of curved dykes, and the dyke dips. (C) 2008 Elsevier B.V. All rights reserved.