HR: 1340h
AN: V53C-1582    [Abstracts]
TI: Rheology of Crystal- and Bubble-Bearing Lava in Uniaxial Compressional Tests
AU: * Lavallee, Y
EM: lavallee@min.uni-muenchen.de
AF: Ludwig-Maximilians Univeristy, Dept. Geo- und Umweltwissensch Theresienstr. 41/III, Munich, 80333 Germany
AU: Hess, K
EM: hess@min.uni-muenchen.de
AF: Ludwig-Maximilians Univeristy, Dept. Geo- und Umweltwissensch Theresienstr. 41/III, Munich, 80333 Germany
AU: Cordonnier, B
EM: cordinnier@min.uni-muenchen.de
AF: Ludwig-Maximilians Univeristy, Dept. Geo- und Umweltwissensch Theresienstr. 41/III, Munich, 80333 Germany
AU: Mueller, S
EM: mueller@min.uni-muenchen.de
AF: Ludwig-Maximilians Univeristy, Dept. Geo- und Umweltwissensch Theresienstr. 41/III, Munich, 80333 Germany
AU: Dingwell, D B
EM: Dingwell@lmu.de
AF: Ludwig-Maximilians Univeristy, Dept. Geo- und Umweltwissensch Theresienstr. 41/III, Munich, 80333 Germany
AB: Modeling of the emplacement and eruption of silicic domes is still hampered by the lack of rheological data for lava hosting crystals and vesicles. We have developed a high-load (0 to 300 kN), high-temperature (25 to 1300°C) deformation apparatus to study in situ the behavior of multi-phase melts. The uniaxial press consists of two pistons which accommodates cylindrical samples with dimensions up to 100 mm in diameter and 100 mm long, and can be used to run at constant strain rate (10^-6 to 10^-2 s) or constant load. Here we investigate the behavior of multi-phase melts from Colima volcano, Mexico. Dacitic samples with dimension of 40 x 40 mm and containing 8 to 32 % porosity and ~50 % crystals (up to 4 mm) were heated up above the calorimetric glass transition temperature to a temperature of ~940°C and deformed at constant pressure. At pressures of 10 and 25 MPa, the strain rates and viscosities of samples with 5-10 % porosity remained constant throughout the experiments. Above 30 MPa minor radial cracked propagated along the sample and the measurements showed decreasing strain rates (non-Newtonian regime) and viscosities (thixotropy) throughout the experiment. In contrast samples with 30 % porosity revealed increasing strain rates (non-Newtonian regime) and viscosities (rheopecty) at a pressure of 10 MPa. The viscosities increased and approached that of equivalent low-porosity melts. The onset of non-Newtonian behavior observed for crystal-rich lava occurs at strain rates which are two orders of magnitude lower than that of crystal- and bubble-free obsidian lava. Insofar our textural analysis allows us to speculate that crystals focus the stress distribution, enhance fracturing and weaken magma. As for the presence of open pores, they close easily upon deformation and a rheopectic non-Newtonian flow regime will dominate until most open pores are annihilated.
DE: 3653 Fluid flow
DE: 8425 Effusive volcanism
DE: 8429 Lava rheology and morphology
DE: 8434 Magma migration and fragmentation
DE: 8445 Experimental volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005