Density tomography with cosmic muons: Applications in volcanology

Density tomography of rock with muons of cosmic origin uses the attenuation of the flux of muons crossing a volume of rock to derive its opacity, i.e. the quantity of matter encountered by the particles along their trajectories. Progress in micro-electronics and particle detectors now make field measurement in harsh environments possible and muon density tomography is becoming more and more popular. We present the telescopes constructed by our teams for the DIAPHANE project. These instruments may be equipped with a variable number of detection matrices, and they are portable autonomous devices able to operate in difficult field conditions encountered on tropical volcanoes. The telescope successfully operate on Mount Etna and on the Soufrière of Guadeloupe volcano. Muon radiographies of the Soufrière lava dome reveal its very heterogeneous density structure produced by an intense hydrothermal circulation of acid fluids which alters its mechanical integrity leading to a high risk level of destabilisation. Small-size features are visible on the images and provide precious informations on the structure of the upper hydrothermal systems. Density muon tomography of the internal structure of volcanoes like the Soufrière brings important informations for the hazard evaluation an is particularly adapted to brought constraints on flank destabilization and hydrothermal circulation models.iew of a cosmic muon telescope in operation on the Soufriere of Guadeloupe volcano. The particle detector matrices are contained in the yellow frames. ensity muon radiography of the Soufriere of Guadeloupe volcano taken in the North-South plane (South is on the left). The less dense areas appear in blue and correspond to hydrothermal reservoirs and altered material. Dense regions (in red) correspond to massive lava scarps.