HR: 1340h
AN: V43B-1426    [Abstracts]
TI: Volcano Instability and Dike Swarms Controlled by Local Stress Field
AU: * Otaki, O
EM: tacky@eps.nagoya-u.ac.jp
AU: Fujii, N
EM: fujii@seis.nagoya-u.ac.jp
AB: Hotspot volcanoes in the Hawaiian, Canary, and the Reunion islands have two or three directions of dominant rift zones, which are highly developed. Rift zones in those islands are normally underlain by a sequence of basalt flow units, and consist of dike swarms which are elongated to a specific direction (with several kilometers length). In oceanic volcanic islands(Kilauea, Mauna Loa, Piton de la Fournaise) with rift zones, many large landslides have been generated during the past hundreds of years. Most of such landslides are presumably caused by lateral failures. Destabilization of volcanic edifices resulting from internal and external factors (such as local Stress field by dike intrusions, surface loading by eruption erosion, and seismic activities) should contribute to lateral fracturing and collapsing. In this study, the mechanisms of lateral collapse on the have been examined by numerical and analogue analyses of volcanic edifices with highly developed rift zones. We have conducted analogue experiments on the re-distribution of stress field with which associated the growth of a lift zone by using of the _eanalogue cone_f as a simulation of polygenetic volcano, In the analogue experiments, we will reveal the relationship between fracture distribution and failure (open cracks) developments. First, the gelatin cone was placed on a PVC plate with several holes for the injection of fluid and covered all over with the mixture of starch powder and pulverized soybean. The former is a simulate of thicker outer brittle part that consist of eruption fragments, and the latter is simulated for the underlying inner ductile part that consists of the relatively high temperature material near the magmatic dikes (or fissures). We made a series of experiments by changing of above indicated parameters. Second, the obtained results are compared with the varieties of developed rift zones. Finally, we show that distributions of open cracks produced by intruded dike swarms cause the lateral collapse, although their parameters are greatly affected by the thickness of cumulative fragmentations and inclination of edifice. For the volcanoes with non-dominant rift zones, the lateral collapse on the flank seems hardly generated due simply to the non-heterogeneous distribution of the local stress.
UR: http://epp.eps.nagoya-u.ac.jp/~tacky/
DE: 8409 Atmospheric effects (0370)
DE: 8414 Eruption mechanisms
DE: 8168 Stresses--general
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting