High energy (10^11+ eV) atmospheric muons are a natural probe for geophysical studies. They can travel through hundreds to kilometers of rocks allowing for a radiography of the density distributions within large structures, the like mountains or volcanoes. A collaboration between volcanologists, astroparticle- and particle physicists, TOMUVOL, has been formed in 2009 to study tomographic muon imaging of volcanoes with high-resolution, large-scale tracking detectors. We report on two campaigns of radiographic measurements of the Puy de Dôme using Glass Resistive Plate Chambers (GRPCs) developped for Particle Physics R&D, within the CALICE collaboration.