Solid Earth Discussions www.solid-earth-discuss.net 1869-9537 2 1 2010 10.5194/sed-2-19-2010 http://www.solid-earth-discuss.net/2/19/2010/ http://www.solid-earth-discuss.net/2/19/2010/sed-2-19-2010.html http://www.solid-earth-discuss.net/2/19/2010/sed-2-19-2010.pdf 19 42 2010-02-19 Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna D. Giordano dgiordan@uniroma3.it M. Polacci P. Papale L. Caricchi Dipartimento di Scienze Geologiche, Università di Roma Tre, L.go S. Leonardo Murialdo 1, 00154 Rome, Italy Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Via della Faggiola 32, 56126 Pisa, Italy Institut des Sciences de la Terre d'Orleans, UMR 6113 CNRS, Universite d'Orleans, 1A rue de la Ferollerie, 45071 Orleans Cedex, France In the period from January to June 2000 Mt. Etna exhibited an exceptional explosive activity characterised by a succession of 64 Strombolian and fire-fountaining episodes from the summit South-East crater. Textural analysis of the eruptive products reveals that the magma associated with the Strombolian phases had a much larger crystal content >55 vol% with respect to the magma discharged during the fire-fountain phases (~35 vol%). Rheological modelling shows that the crystal-rich magma falls in a region beyond a critical crystal content where the small addition of solid particles causes an exponential increase of the effective magma viscosity. When implemented into the modelling of steady magma ascent dynamics, the large crystal content of the Strombolian eruption phases results in a one order of magnitude decrease of mass flow-rate, and in the onset of conditions where small heterogeneities in the solid fraction carried by the magma translate into highly unsteady eruption dynamics. 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