Mt. Etna 2001 eruption: New insights into the magmatic feeding system and the mechanical response of the western flank from a detailed geodetic dataset

摘要

In the last decades, the increasing availability of comprehensive geodetic datasets has allowed for more detailed constraints on subsurface magma storage and conduits at several active volcanoes worldwide. Here, by using a large dataset of geodetic measurements collected between early January 2001 and August 2001, we identified at least six different deformation stages that allow us to quantify the surface deformation patterns before, during and after the 2001 Mt. Etna volcanic eruption. Our results are largely in agreement with previous works (e.g. the presence of a deep inflating source and a shallow dike located beneath the north-western and upper southern flanks of the volcano, respectively). However, we provide (1) finer resolution of the temporal activity of these magmatic sources, leading to (2) new evidence related to the evolution of the magmatic system and the mechanical response of the western flank, in particular during the pre-eruptive phase. Results and analysis show a clear change in the ground deformation pattern of the volcano in response to the 20-24 April 2001 seismic swarm that occurred beneath the western flank, evolving from a volcano-wide inflation to a slight deflation of the summit area. We suggest that the source responsible for the volcano-wide inflation, beginning in the fall of 2000, experienced a drastic reduction in the inflation rate in response to this seismic swarm. Moreover, we provide evidence for the presence of a new inflating source located beneath the upper southern flank at a depth of ～7.0 km bsl that triggered both the occurrence of the 20-24 April 2001 seismic swarm and led to the rapid ascent of magma upward to the surface after 12 July (the Lower Vents system was fed by fresh magma rising from this source). The presence of this inflating source is inferred by (1) seismological and volcanological observations coming from the 2001 eruption and (2) seismological constraints coming from a previous similar episode that occurred at Etna during the 1993-1998 period. Furthermore, both shallow deflations observed after the 20-24 April 2001 seismic swarm and during the first day of the eruption also could be due to the deflation of two adjacent portions of the same shallow (～2 km bsl) reservoir. Such reservoirs would feed the activity that occurred at the South-East Crater after January 2001 and the activity of the Upper Vents system during the July-August eruption, in agreement with petrochemical observations. Through an updated revision of the available data, we shed some light on the relevance of pre-eruptive activity patterns, an important element for an effective volcano monitoring.