Long-Term Subsidence in Lava Fields at Piton de la Fournaise Volcano Measured by InSAR: New Insights for Interpretation of the Eastern Flank Motion
Résumé
Long-term displacement often occurs in lava fields at volcanoes after flow emplacements.
The investigation and interpretation of displacement in lava fields is one of the key factors for the
assessment of volcanic hazards. As a typical Hawaiian volcano, Piton de la Fournaise volcano’s
(La Réunion Island, France) main eruptive production is lava. Characteristics of the lava flows at Piton
de la Fournaise, including the geometric parameters, location, and elevation, have been investigated
by previous studies. However, no analysis focusing on the long-term post-emplacement displacement
in its lava fields at a large spatial extent has yet been performed. One of the previous studies revealed
that the post-emplacement lava subsidence played a role in the observed Eastern Flank motion by
conducting a preliminary investigation. In this paper, an InSAR time series analysis is performed to
characterize the long-term displacement in lava fields emplaced between 1998 and 2007 at Piton de la
Fournaise, and to conduct an in-depth investigation over the influence of post-emplacement lava
subsidence processes on the instability of the Eastern Flank. Results reveal an important regional
difference in the subsidence behavior between the lava fields inside and outside of the Eastern Flank
Area (EFA), which confirms that, in addition to the post-lava emplacement processes, other processes
must have played a role in the observed subsidence in the EFA. The contribution of other processes is
estimated to be up to ~78%. The spatial variation of the observed displacement in the EFA suggests
that a set of active structures (like normal faults) could control a slip along a pre-existing structural
discontinuity beneath the volcano flank. This study provides essential insights for the interpretation
of the Eastern Flank motion of Piton de la Fournaise.
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