HR: 1330h
AN: V42B-0361    [PDF]
TI: Pyroclastic Flows, Rockfalls, and Heightened Magma Flux Associated With the Merapi Volcano Eruption of 1992-1998, Central Java, Indonesia
AU: * Young, K D
EM: kirby@aracnet.com
AF: Dept of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Voight, B
AF: Dept of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
AU: Ratdomopurbo, A
AF: Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian, Direktorat Vulkanologi, Jalan Cendana 15, Yogyakarta, 55166 Indonesia
AU: Andreastuti, S D
AF: Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian, Direktorat Vulkanologi, Jalan Cendana 15, Yogyakarta, 55166 Indonesia
AU: Subandriyo, P
AF: Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian, Direktorat Vulkanologi, Jalan Cendana 15, Yogyakarta, 55166 Indonesia
AU: Suharna, P
AF: Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian, Direktorat Vulkanologi, Jalan Cendana 15, Yogyakarta, 55166 Indonesia
AU: Sajiman, P
AF: Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian, Direktorat Vulkanologi, Jalan Cendana 15, Yogyakarta, 55166 Indonesia
AU: Miswanto, P
AF: Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian, Direktorat Vulkanologi, Jalan Cendana 15, Yogyakarta, 55166 Indonesia
AB: An elevated phase of magma production with respect to the long-term rate for the 20th century characterizes the activity at Merapi volcano, Central Java/Yogyakarta, Indonesia, for the period 1992-1998. During this time, 224,810 recorded seismic events were identified as rockfalls and pyroclastic flows between January 1992 and December 1998. Of these, 820 pyroclastic flows specifically were reported, mainly from field observatory posts. Most of nine large (0.2 - 3.4 x 10$^{6}$ m$^{3}$) dome collapses or dome collapse episodes began to occur during elevated short-term extrusion rates typically 0.2 m$^{3}$ s$^{-1}$ or greater. Large collapses were often preceded by variable inflationary tilt of the crater rim, increasing numbers of rockfalls and their associated seismicity, and intensifying multiphase earthquake activity. In such cycles, a gas-rich volume of magma extruded onto or intruded into preexisting dome lava, leading to rockfalls and eventual dome collapses from the headwalls of developing lava flow fronts. While gas pressure build-up within the dome may have played some role, similar effects may have been generated by intense monsoon rainfall on still hot lava. Multiphase earthquakes, rockfall counts, and amplitude-duration data established from seismic records show varying positive correlations with extrusion rate. Pyroclastic flow and rockfall seismic amplitude-duration data have been calibrated as proxies for collapse volume. When combined with calculations of dome volume estimates over time and deposit volumes from major dome collapses, an overall magma flux of 0.1 m$^{3}$ s$^{-1}$ between 1992 and the end of 1998 has been obtained. This rate is significantly greater compared to the long-term 0.04 m$^{3}$ s$^{-1}$ magma flux calculated for Merapi over the first nine decades of the 20th century (Siswowidjoyo et al., 1995). For the 20th century as a whole, observed magma production rates continue to suggest long-term cycles of ca. 30 years that begin with heightened magma flux over two to eight years with greater potential for explosive eruptive activity, followed by much-diminished mean magma flux in the concluding ca. 25 years of the cycle. If similar cycles continue into the 21st century, activity at Merapi will experience lower magma production compared to the most recent eruptive phase during the next 20-25 years, followed by significantly heightened magma flux over several years to begin the next cycle, accompanied by a greater likelihood of major explosive events.
DE: 7280 Volcano seismology (8419)
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting