Modes of sector collapse of volcanic cones: insights from analogue experiments

Many volcanic edifices are subject to sector collapse. Analogue models are here used to better understand specific modes of collapse. Four sets of experiments have been performed with a cone (volcano analogue) of dry sand (87% in volume) and flour (13%) simulating collapse through: A) basal failure, due to the horizontal sliding of a basal plate; B) unbuttressing, due to the horizontal movement of a lateral wall; C) summit growth, due to the addition of sand and flour on the top of the cone; D) injection, due to the intrusion of silicone (magma analogue). Sets A and B show common results, highlighting the influence of topography on the dip and strike of the collapse surfaces. In set C, the location and direction of collapse are controlled by the cone shape and occurrence of pre-existing collapses. In set D, if the silicone is injected eccentrically, it induces collapse on the nearest slope; this process leads to repeated collapse on the side of a pre-existing scarp, possibly triggering a feedback mechanism between magmatic activity and topography. In general, sets A and B induce deeper and wider collapse, whereas shallower and narrower collapse is observed in set C; set D shows intermediate geometries. Comparison with natural examples shows an overall similar distribution in the geometry of the sector collapses and their known triggering mechanisms. Similarities and discrepancies between each experimental set and corresponding cases in nature are discussed.