Experimental study of caldera formation

International audienceScaled experiments have been carried out on caldera collapse mechanisms, using silicone as analogue magma and dry sand as analogue rock. Experiments were carried out in two and three dimensions using a range of roof aspect ratios (thickness/width 0.2 to 4.5) appropriate for caldera collapse. They reveal a g•neral mechanism of collapse, only weakly dependent on the shape of the reservoir. For low roof aspect ratios (_ 1), multiple reverse faults break up the roof into large pieces, and subsidence occurred as a series of nested wedges (2-D) or cones (3-D). The extensional zone dominates the surface depression. In the case where preexisting regional faults do not play a major role, the collapse mechanics of calderas probably depends strongly on the roof aspect ratio. Calderas with low roof aspect ratios are predicted to collapse as coherent pistons along reverse faults. The annular extensional zone might be the source of the large landslides that generate intracaldera megabreccias. Collapse into magma reservoirs with high roof aspect ratios may be the origin of some funnel calderas where explosive reaming is not dominant