Modalities of flank collapse of volcanic edifices through analogue models.

Volcanic edifices are commonly subject to the collapse of their flanks. In order to better understand the modalities of flank collapse of volcanoes, as well as the possible triggering factors, we used analogue models. The length ratio between model and nature (˜10-4) requires, according to the scaling procedure, the combined use of dry quartz sand (87%) and flour (13%) to adequately simulate the behaviour of the volcanic edifice. Several modalities of sector collapses have been tested on circular and elongated cones: a) the basal failure of a cone, simulating the effect of an active extensional structure at the base of a volcano; b) the lateral removal of material from a cone, simulating the lack of lateral confinement of a volcano; c) the addition of material on the top of a cone, simulating the increase of mass on the summit of a volcano during repeated effusive eruptions; d) the injection of Newtonian silicone within the cone, simulating flank instabilities during the inflation of a volcano; e) the effect of a layer of silicone at the base of a cone, to simulate the effect of the basal spreading of a volcano over a weak substratum. The most important features controlling the modalities of flank collapse, as well as the similarities with the 2002 collapses at Stromboli and Etna, are highlighted.