Abstract
We produced new multi-temporal Digital Elevation Models (DEMs) of the April 2007 summit collapse at Piton de la Fournaise from previously unused aerial photographs. This dataset revealed the precise temporal evolution of collapsed volume and caldera morphological changes. Four days after the onset of an eruption at an unusually low elevation, the summit started to collapse (20:48 UTC April 5th). During the first 30 hours, collapsing was relatively fast (840 m3 s-1 average), and continued for at least the following 12 days, at a slower rate (46 m3 s-1 average). On April 19th, the collapse reached 96% of its final volume, while the remaining 4% were probably attained by May 1st (end of lava emission at the vent). The post-collapse hydrothermal activity in the caldera is closely associated with the main ring faults evidenced as active during the collapse, which are now preferential paths for fluids to reach the surface.
Highlights
In volcanic systems, rapid withdrawal of large magma volumes from reservoirs can lead to the formation of calderas – broad depressions at the top or on the sides of volcano flanks
Except in the case of the A.I.G.L. campaign, the photographs were acquired manually by different operators (Table 1) from an ultralight airplane flying roughly between 200 and 600 meters above the caldera rim
There was a clear difference in behaviour between the northwest of the caldera and the south and east
Summary
Rapid withdrawal of large magma volumes from reservoirs can lead to the formation of calderas – broad depressions at the top or on the sides of volcano flanks. These large but recurring events pose multiple hazards to neighboring communities (e.g. caldera collapses, summit instabilities, high gas fluxes, ash plumes, ash deposits, rapid and extended lava flows in distal areas). Detailed measurement of the collapsed volumes and precise mapping of ring faults during and after the caldera formation is of paramount importance when determining the precise geometry and location of an underlying magma reservoir.
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