Temporal and Spatial Strain Distribution Derived from GNSS Network in Volcanic Area, the Case Study of Piton De La Fournaise

Abstract:

Basaltic volcanoes are amongst the largest volcanic edifices on Earth. These huge volcanoes exhibit large deformation areas such as rift zones, and strong ground displacements with more or less mobile flanks, which respond to long-lasting stress field conditions (gravitational stress, magmatic processes and/or regional tectonics...). Piton de la Fournaise (La Réunion, Indian ocean) is one of the most active basaltic volcano in the world and displays all of these features. We study the dynamics and the origin of Piton de la Fournaise deformation through the observation of temporal and spatial strain distribution. With the densification of the volcano observatory permanent GNSS network in 2009 and thanks to their high sampling rates, for the first time we have calculated strain maps derived from GNSS displacements on this volcano. We present temporal and spatial distribution of strain on Piton de la Fournaise, on the whole edifice from the summit to the coastline, during both eruptive and rest periods. Main deformation allows us to distinguish four main sectors displaying distinct behaviors in response to volcanic and rest activities: (1) the summit, (2) the terminal cone, (3) the base of the cone, and (4) the eastern flank. Principal strains are maximal on the terminal cone -with an antagonist pattern between the summit and the slope of the terminal cone where the strains are one order of magnitude lower than on the summit-, while decay rates of compressive strain is observed in the eastern flank up to the coastline. Even if the strains are low in the eastern flank, we evidence compressive strain there, whereas the coastline appears to be more stable. The eastern flank sliding damps with the distance, suggesting stress accumulates in the slopes of the Grandes Pentes/Grand Brûlé areas. This evaluation provides new insights for the assessment of potential hazards associated with edifice instabilities, and especially the generation of future flank destabilizations, but also with the propagation of large distal eruptions.