Flow directions inferred from imbrication in the Handa pyroclastic flow deposit in Japan |
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| Authors: | H Kamata K Mimura |
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| Institution: | (1) Geothermal Research Department, Geological Survey of Japan, 1-1-3, Higashi, Yatabe, Tsukuba, 305 Ibaraki, Japan;(2) Geology Dept., Geological Survey of Japan, 1-1-3, Higashi, Yatabe, Tsukuba, 305 Ibaraki, Japan |
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| Abstract: | Flow direction patterns have been determined by imbrication measurements of pumice and lithic fragments of the Handa pyroclastic
flow deposit, in order to estimate the source vent location and to analyze the flow behavior. The pyroclastic flow deposit
studied is dacitic in composition, 2 km2 in volume, and >32,300 Y.B.P. in age. Flow directions from 52 outcrops indicate a source vent located within the area of
recent lava domes of Kuju Volcano. The distribution of the pyroclastic flow deposit and the flow direction patterns determined
by imbrication suggest that the pyroclastic flow accurately followed the topographic relief at the time of eruption. The presence
of imbrication indicates the change of flow-regime from turbulent condition to laminar condition according to the distance
from the source vent. Imbrication is visible within the lower-half reaches of the pyroclastic flow distribution, where the
pyroclastic flow had developed the laminar flow characteristics of a dense gravity current. |
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