The cryptic summit graben of Mt. Etna volcano

Murray, John B. (2019). The cryptic summit graben of Mt. Etna volcano. Journal of Volcanology and Geothermal Research, 387, article no. 106657.



Previous studies have inferred the likelihood of a summit graben at Mt. Etna, but until now there has been no direct observation or evidence of such a feature. Here, the results of 43 years of deformation measurements at the summit are reported, in which the presence of an actively forming north-south graben 1.5 km wide is evident, with a maximum subsidence of nearly 4 m in 43 years. Its bounding faults have in most places been hidden by the eruptive deposits of 190 summit eruptions, but horizontal measurements across these faults show a maximum value of nearly 9 m of east-west extension. Most of the subsidence and extension has taken place during the injection of eruption feeder dykes, with extreme values for single events of −1.7 m subsidence during the injection of the 2002–2003 dyke, and 4.4 m extension across the 1989 feeder dyke, but subsidence and extension continues to take place slowly during inter-eruptive periods. Analogue modelling indicates that its origin is probably a consequence of the gravitational spreading and downslope sliding of the Etna edifice on its clay-rich substrate, aided by magmatic pressure from feeder dykes intruded into individual faults, and by downward pressure from surface loading of erupted lava. This study clarifies the way in which the mechanism of gravitational spreading is maintained throughout the lifetime of this and other spreading volcanoes and rifts on Earth and Mars.

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