Solid Earth www.solid-earth.net 1869-9510 1869-9529 1 1 2010 10.5194/se-1-61-2010 http://www.solid-earth.net/1/61/2010/ http://www.solid-earth.net/1/61/2010/se-1-61-2010.html http://www.solid-earth.net/1/61/2010/se-1-61-2010.pdf 61 69 2010-07-01 Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna D. Giordano dgiordano@ija.csic.es M. Polacci P. Papale L. Caricchi Institut de Ciències de la Terra Jaume Almera (ICTJA), CSIC, c/Lluís Solé Sabarís s/n, 08028 Barcelona, Spain 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 now at: Department of Earth Sciences, University of Bristol, Queens Road, Bristol, BS8 1RJ, UK 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 fire-fountain 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. Allard, P., Burton, M., and Murè, F. : Spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas, Nature, 433, 407–410, 2005. Alparone, S., Andronico, D., Lodato, L., and Sgroi, T.: Relationship between tremor and volcanic activity during the Southeast Crater eruption on Mt Etna in early 2000, J. Geophys. Res., 108, 2241–2253, 2003. Behncke, B., Neri, M., Pecora, E., and Zanon, V.: The exceptional activity and growth of the Sotheast crater, Mt Etna (Italy), between 1996 and 2001, B. Volcanol., 69, 149–173, 2006. Bouhifd, M. A., Richet, P., Besson, P., Roskosz, M., and Ingrin, J.: Redox state, microstructure and viscosity of a partially crystallized basalt melt, Earth Planet. Sc. Lett., 218, 31–44, 2004 Bourgue, E. and Richet, P.: The effects of dissolved CO₂ on the density and viscosity of silicate melts: a preliminary study, Earth Planet. Sc. Lett., 193, 57–68, 2001. Branca, S. and Del Carlo, P.: Eruptions of Mt Etna during the past 3200~years: a revised compilation integrating the Historical and stratigraphic records, in: Bonaccorso, A., Calvari, S., Coltelli, M., Del Negro, C., and Falsaperla, S., Mt Etna: Volcano Laboratory, AGU Geophys. Monogr. Ser., 143, 1–27, 2004. Coltelli, M., Del Carlo, P., and Vezzoli, L.: Stratigraphic constrains for explosive activity in the past 100 ka at Etna volcano, Italy, Int. J. Earth Sci., 89, 665–677, 2004. Caricchi, L., Burlini, L., Ulmer, P., Gerya, T., Vassalli, M., and Papale, P.: Non-Newtonian rheology of crystal-bearing magmas and implications for magma ascent dynamics, Earth Planet. Sc. Lett., 264, 402–419, doi:10.1036/j.epsl2007.09.032, 2007. Caricchi, L., Giordano, D., Burlini, L., Ulmer, P., and Romano, C.: Rheological properties of magma from the 1538 eruption of Monte Nuovo (Phlegrean Fields, Italy): an experimental study, Chem. Geol., 256, 157–170, 2008. Chong, J. S., Christiansen, E. B., and Baer, A. D.: Rheology of concentrated suspensions, J. Appl. Polym. Sci., 15, 2007–2021, 1971. Costa, A.: Viscosity of high crystal content melts: dependence on solid fraction, Geophys. Res. Lett., 32, L22308, doi:10.1029/2005GL024303, 2005. Costa, A., Caricchi, L., and Bagdassarov, N.: A model for the rheology of particle-bearing suspensions and partially molten rocks, Geochem. Geophy. Geosy., 10, Q03010, doi:10.1029/2008GC002138, 2009. Dingwell, D. B., Courtial, P., Giordano, D., and Nichols, A. R. L.: Viscosity of peridotite liquid, Earth Planet. Sc. Lett., 226, 127–138, 2004. Giordano, D. and Dingwell, D. B.: Viscosity of hydrous Etna basalt: implications for Plinian-style basaltic eruptions, B. Volcanol., 65, 8–14, 2003a. Giordano, D. and Dingwell, D. B.: Erratum to: Non-Arrhenian multicomponent melt viscosity: a model, Earth Planet. Sc. Lett., 208, 337–349, 2003b. Giordano, D., Mangiacapra, A., Potuzak, M., Russel, J. K., Romano, C., Dingwell, D. B., and Di Muro, A.: An expanded non-Arrhenian model for silicate melt viscosity: a treatment for metaluminous, peraluminous and peralkaline liquids, Chem. Geol., 229, 42–56, 2006. Giordano, D., Polacci, M., Longo, A., Papale, P., Dingwell, D. B., Boschi, E., and Kasereka, M.: Thermorheological magma control on the impact of highly fluid lava flows at Mt Nyiragongo, Geophys. Res. Lett., 34, L06301, doi:10.1029/2006GL028459, 2007. Giordano, D., Russell, J. K., and Dingwell, D. B.: Viscosity of magmatic liquids: a model, Earth Planet. Sc. Lett., 271, 123–134, 2008. Giordano, D., Ardia, P., Romano, C., Dingwell, D. B., Di Muro, A., Schmidt, M. W., Mangiacapra, A., and Hess, K.-U.: The rheological evolution of alkaline Vesuvius magmas and comparison with alkaline series from the Phlegrean Fields, Etna, Stromboli and Teide, Geochim. Cosmochim. Ac., 73, 6613–6630, 2009. Ishibashi, H. and Sato, H.: Viscosity measurements of subliquidus magmas: Alkali olivine basalt from the Higashi-Matsuura district, Southwest Japan, J. Volcanol. Geoth. Res., 160, 223–238, 2007 Ishibashi, H.: Non-Newtonian behavior of plagioclase-bearing basaltic magma: Subliquidus viscosity measurement of the 1707 basalt of Fuji volcano, Japan, J. Volcanol. Geoth. Res., 181, 78–88, 2009. Lejeune, A. M. and Richet, P.: Rheology of crystal-bearing silicate melts: an experimental study at high viscosities, J. Geophys. Res., 100(B3), 4215–4229, 1995. Métrich, N., Allard, P., Spilliaert, N., Andronico, D., and Burton, M.: 2001 flank eruption of the alkali- and volatile-rich primitive basalt responsible for Mt Etna's evolution in the last three decades, Earth Planet. Sc. Lett., 228, 1–17, 2004. Papale, P.: The dynamics of magma flow in volcanic conduits with variable fragmentation efficiency and non-equilibrium pumice degassing, J. Geophys. Res., 106, 11043–11065, 2001. Pinkerton, H. and Stevenson, R. J.: Methods of determining the rheological properties of magmas at sub-liquidus temperatures, J. Volcanol. Geotherm. Res., 53, 47–66, 1992. Pinkerton, H. and Norton, G.: Rheological properties of basaltic lavas at sub-liquidus temperatures: laboratory and field measurements on lavas from Mt Etna, J. Volcanol. Geotherm. Res., 68, 307–323, 1995. Polacci, M., Corsaro, R. A., and Andronico, D.: Coupled textural and compositional characterization of basaltic scoria: Insights into the transitino from Strombolian to fire fountain activity at Mt Etna, Italy, Geology, 34, 201–204, 2006 Pompilio, M., Trigila, R., and Zanon, V.: Melting experiments on Mt Etna lavas, I The calibration of an empirical geothermometer to estimate the eruptive temperature, Acta Vulcanol., 10, 67–75, 1998 . Roscoe, R.: The viscosity of suspensions of rigid spheres, J. Appl. Sci., 3, 267–269, 1952. Ryerson, F. J., Weed, H. C., and Piwinskii, A. J.: Rheology of Subliquidus Magmas, 1 Picritic Compositions, J. Geophys. Res., 93, 3421–3436, 1988. Saar, M. O., Manga, M., Cashman, K. V., and Fremouw, S.: Numerical models of the onset of yield strength in crystal-melt suspensions, Earth Planet. Sc. Lett., 187, 367–379, 2001. Sato, H.: Viscosity measurement of subliquidus magmas: 1707~basalt of Fuji volcano, J. Miner. Petrol. Sci., 100, 133–142, 2005. Shaw, H. R.: Rheology of basalt in the melting range, J. Petrol., 10, 510–535, 1969. Spilliaert, N., Allard, P., Métrich, N., and Sobolev, A. V.: Melt inclusion record of the conditions of ascent, degassing, and extrusion of volatile-rich alkali basalt during the powerful 2002 flank eruption of Mt Etna (Italy), J. Geophys. Res., 111, B04203, doi:10.1029/2005JB003934, 2006. Villeneuve, N., Neuville, D. R., Boivin, P., Bachèlery, P., and Richet, P.: Magma crystallization and viscosity: A study of molten basalts from the Piton de la Fournaise volcano (La Réunion island), Chem. Geol., 256, 242–251, 2008. Walsh, S. D. C. and Saar, M. O.: Numerical models of stiffness and yield stress growth in crystal-melt suspensions, Earth Planet. Sc. Lett., 267, 32–44, 2008. Whittington, A., Richet, P., and Holtz, F.: Water and the viscosity of depolymerised aluminosilicate melts, Geochim. Cosmochim. Ac., 64, 3725–3736, 2000. Whittington, A., Richet, P., Linard, Y., and Holtz, F.: The viscosity of hydrous phonolites and trachytes, Chem. Geol., 174, 209–223, 2001.