Journal of Natural Disaster Science

SEISMIC OBSERVATIONS AND INFRARED THERMAL SURVEYS OF THE 1990-1993 ERUPTION OF UNZEN VOLCANO

Kodo UMAKOSHI*, Hiroshi SHIMIZU**, Norimichi MATSUWO*, Takeshi MATSUSHIMA* and Kazuya OHTA***
*Research Associate, **Associate Professor, ***Professor, Shimabara Earthquake and Volcano Observatory, Faculty of Science, Kyushu University

(Received 20 September 1993 and in revised form 8 February 1994)

Abstract

Mt. Fugen (Unzen Volcano) started to erupt on November 17, 1990, after 198 years of dormancy. Since a lava dome started to grow, there have been frequent pyroclastic flows that have caused severe damage to Shimabara City and Fukae Township. The seismic network operated by Kyushu University had detected precursory seismic activity prior to the eruption. After the first eruption, temporary seismic stations were densely deployed near to and around the peak of Mt. Fugen. In addition, new permanent seismic stations were established. The regional seismicity in and around Unzen Volcano has decreased markedly since the emergence of the lava dome. This is probably because excess magma pressure was released due to the lava extrusion. Summit earthquakes often have increased just before lava extrusion from a new vent. In these cases, it has been possible to determine the growth of new lobes in advance. A thermal survey using an infrared thermal video system was begun after the start of lava dome extrusion. It gives the surface temperature distributions of the lava dome and the pyroclastic flow deposits and has proved useful in ascertaining the extrusion of fresh lava and in discriminating the latest pyroclastic flow deposits from previous ones.

Key words

Unzen volcano, Mt. Fugen, seismic observation, infrared thermal survey, lava dome, pyroclastic flow