Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna

Abstract

Abstract. In the period from January to June 2000 Mt. Etna exhibited an exceptional explosive activity characterized 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 firefountain phases (∼35 vol%). Rheological modelling shows that the crystal-rich magma falls in a region beyond a critical crystal content where small addition of solid particles causes an exponential increase of the effective magma viscosity. When implemented into the modeling of steady magma ascent dynamics (as assumed for the fire-fountain activity), a large crystal content as the one found for products of 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. We argue that crystallization on top of the magmatic column during the intermediate phases when magma was not discharged favoured conditions corresponding to Strombolian activity, with fire-fountain activity resuming after removal of the highly crystalline top. The numerical simulations also provide a consistent interpretation of the association between fire-fountain activity and emergence of lava flows from the crater flanks.

The rheology of crystal-bearing basaltic magmas from Stromboli and Etna

“…It controls eruption dynamics and affects physico-chemical processes such as degassing and crystallization in magmas (e.g., Caricchi et al, 2007;Giordano et al, 2008Giordano et al, , 2010. The viscosity of naturally-occurring magmas can span in fact more than 15 orders of magnitude (10 À1 -10 14 Pa s) primarily in response to variations in melt composition (X), volatile content, temperature (T), pressure (P), as well as variation in the proportions and distributions of suspended solids and vesicles (Webb and Dingwell, 1990;Dingwell et al, 1992;Dingwell, 1996;Papale, 1999;Llewellin et al, 2002;Llewellin and Manga, 2005;Vetere et al, 2006;Ardia et al, 2008;Giordano et al, 2009).…”

Magma convection and mixing dynamics as a source of Ultra-Long-Period oscillations

“…Magma properties and gas-liquid phase distribution, gas composition, and liquid-gas density and viscosity, are computed as a function of the local P-T-X conditions, by employing composition-dependent modeling and parameterizations (Papale 2001;Papale et al 2006;Giordano et al 2008). Non-Newtonian behavior of multiphase magma at high strain rates, which can be relevant during the rapid ascent of magma along volcanic conduits and fissures (Caricchi et al 2007;Costa et al 2009;Giordano et al 2010), is not accounted for.…”

Dynamics of a lava fountain revealed by geophysical, geochemical and thermal satellite measurements: The case of the 10 April 2011 Mt Etna eruption

“…Such activity is accompanied by the formation of dispersal ash plumes and fall‐out deposits, which often pose severe hazards to aviation and repeated temporary closures of the Catania international airport [e.g., Scollo et al , 2009; Bonaccorso et al , 2011b]. Several studies have been conducted using different mono‐disciplinary approaches, such as volcanic tremor analyses [ Alparone et al , 2003], geochemical analyses of volcanic gases from remote sensing spectroscopy [ Allard et al , 2005], tilt changes [ Bonaccorso , 2006], acoustic records [ Vergniolle and Ripepe , 2008], studies on fallout deposits, on compositional/textural features of the erupted product [ Andronico and Corsaro , 2011] and on the rheological properties of magma [ Giordano et al , 2010]. More recently, multi‐disciplinary approaches have been undertaken at Mt Etna to better investigate lava fountaining phenomena Aiuppa et al [2010]…”