HR: 10:50h
AN: V42A-03 INVITED     [Abstracts]
TI: Experimental Volcanology: Fragmentation and Permeability
AU: * Spieler, O
EM: spieler@lmu.de
AF: Earth & Environmental Sciences, LMU Muenchen, Theresienstr. 41, Muenchen, 80333 Germany
AB: An increasing number of scientists design new experiments to analyse processes that control the dynamics of explosive eruptions. There research is mostly coupled to numerical models and aims toward its controlling parameters. The fragmentation process, its threshold and the speed of the fragmentation wave as well as the energy consumed by the fragmentation are some hot spots of the experimental volcanology. Analysing the fragmentation behaviour of volcaniclastics as close to the natural system as possible, we found a number of physical constrains. Identifying the porosity as determining factor of the threshold, we realised that neither threshold nor the speed of the fragmentation process are solely controlled by the rock density. The later results of the shock tube type apparatus lead to the analysis of the specific surface area and permeability as direct links to textural features. Permeability analysis performed in a modified shock tube type apparatus, show two clear, distinct trends for dome rock and pyroclastic samples. The specific surface determined by Argon sorbtion (BET) as well as textural features of pumices from Campi Flegrei, Montserrat and Krakatoa (1883) give in contrary evidence of a more complex story. Large spherical, or ellipsoidal bubbles around fractured crystals prove that the high permeability of the pumice has partially developed after the fixing of the bubble size distribution. This puts up the question, if permeability measurements on pyroclastic samples reveal relevant numbers! The surface tension controlled 'self sealing' behaviour of surfaces from foaming obsidian hinders in situ measurements. Close textural investigations will have to clarify how the 'post process' samples deviate from the syneruptive conduit filling.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8430 Volcanic gases
DE: 8434 Magma migration and fragmentation
DE: 8445 Experimental volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005