HR: 1340h
AN: V33A-0677    [Abstracts]
TI: Fall-experiments on Merapi basaltic andesite and constraints on the generation of pyroclastic surges.
AU: Schwarzkopf, L
EM: lothar_schwarzkopf@yahoo.de
AF: Earth and Environment, LMU Munich Theresienstr. 41/III , Munich, 80333 Germany
AU: Schwarzkopf, L
EM: lothar_schwarzkopf@yahoo.de
AF: GeoDocCon, Unterpferdt 8 , Konradsreuth, 95176 Germany
AU: Spieler, O
EM:
AF: Earth and Environment, LMU Munich Theresienstr. 41/III , Munich, 80333 Germany
AU: Scheu, B
EM:
AF: Earth and Environment, LMU Munich Theresienstr. 41/III , Munich, 80333 Germany
AU: * Dingwell, D B
EM: Dingwell@lmu.de
AF: Earth and Environment, LMU Munich Theresienstr. 41/III , Munich, 80333 Germany
AB: Pyroclastic surges, hot and gas-rich high-speed particle flows, are probably the largest hazards during volcanic eruptions. In general, surges are generated as either 1) source-related lateral blast-surges, by flank or lava dome collapses or 2) as surges directly associated with a pyroclastic flow. In the latter case, surges are generated from the flow itself, by either entrainment of ambient air at the flow front or interaction between the flow surface and the air. Flow-related surges can also be formed at breaks in slope, e.g. by detachment of the ash-cloud component. Expanding ash clouds at sudden breaks in slopes indicate intensified production of fines and thus fragmentation, and Schwarzkopf et al. (1998) postulate surge generation triggered by sudden and strongly intensified fragmentation at cliffs in the flow path of block-and-ash flows at Merapi. We have now performed fall-experiments with basaltic andesite rock samples from Merapi volcano, using an experimental apparatus designed to use samples heated up to maximum 850°C. Relative pressure changes during impact and fragmentation of the samples were measured by a pressure transducer. From 200°C, dynamic pressure waves were formed on impact and fragmentation. Peak and duration of the pressure signal, and degree of fragmentation were found to depend on the temperature of rock samples, both signal and fragmentation strongly increase with increasing temperature. The pressure waves are most likely generated by the sudden heating of air forcing it to expand. We propose that the observed pressure changes are analogues to pyroclastic surges that may be generated on impact and fragmentation of large blocks during passage of a pyroclastic flow over a steep cliff. We infer that rock temperatures of ca. 400°C are sufficient for this process to occur, a temperature common in pyroclastic flows even in distal reaches.
DE: 8404 Volcanoclastic deposits
DE: 8445 Experimental volcanism
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005