From steep-slope volcano to flat caldera floor

International audienceMost laboratory experiments of caldera collapse have dealt with reservoir emptying below a flat-lying overburden without an overlying analogue volcanic edifice on top. The overload and the role of topography are then neglected so that the final flat floor within the caldera is directly linked to the initial one. In addition, caldera subsidence is commonly attributed to the collapse of the top of a magma chamber linked to eruptions delivering large amounts of volcanic products. Analogue experiments show that the deformation of a weak clay-rich core resulting from the hydrothermal alteration in a volcanic edifice can, in certain conditions, reproduce the structures of a caldera. In particular, it is a way to explain the flat floor of a caldera when resurfacing resulting from new eruptions or destructive processes seems unlikely