HR: 09:15h
AN: V51B-06    [PDF]
TI: The role of magma porosity in explosive magma-water interaction
AU: Trigila, R
EM: raffaello.trigila@uniroma1.it
AF: Universita' di Roma "La Sapienza", Dipartimento di Scienze della Terra, Roma, 00185 Italy
AU: * Battaglia, M
EM: battag@seismo.berkeley.edu
AF: UC Berkeley, Dept of Earth and Planetary Science, 215 McCone Hall, Berkeley, CA 94720 United States
AU: Manga, M
EM: manga@seismo.berkeley.edu
AF: UC Berkeley, Dept of Earth and Planetary Science, 215 McCone Hall, Berkeley, CA 94720 United States
AB: We performed laboratory experimental studies to investigate magma-water mixing and triggering mechanisms in explosive magma water interaction. The experimental facility operates at pressures up to 200 MPa and temperatures up to 1200 /deg C. The goal of our experiments is to investigate magma-water mixing and the triggering of steam explosions. In contrast to previous studies, in our experiments magma-water mixing and vapor film collapse, prerequisites to induce the steam explosion, are self-triggered. That is, they are not induced by any external triggering signal. We keep parameters such as water/melt mass ratio, temperature, and confining pressure nearly constant, but the samples had two different grain sizes: a) a finely grounded powder (grain size approximately 0.05 mm, b) spatter grains 0.8 mm in size. Precautions were taken to make certain that the melt samples were completely dehydrated. The amount of injected water was kept as constant as possible, with a water/melt mass ratio around 0.4.The samples interact with water at a temperature of 800 or 900 /deg C and a confining pressure close to 8 MPa. The main qualitative experimental results are that: (1) No explosive melt-water interaction has been observed for the finely crushed (powder) samples; (2) The magma water interaction shows no obvious dependence on the melt temperature; (3) In the case of the spatter grain sample, data on particle size distribution indicate similar distributions for grains collected in the sample holder or in the gasket, indicating a possible partial melting of the grain ring only. The results of our experiments indicate that a pre-existing permeable/fragmented melt may be sufficient to initiate a phreato-magmatic eruption. Hydrodynamic premixing, a process inhibited by the large viscosity difference between the melt and water, may not be required to initiate an eruption. This is in contrast with experimental studies on pre-mixing of basaltic magma and water or peperites formation where hydrodynamic mixing appears to play an important role.
DE: 8414 Eruption mechanisms
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting