Antonius Ratdomopurbo

Deformation and seismic precursors to dome-collapse and fountain-collapse nuees ardentes at Merapi Volcano, Java, Indonesia, 1994-1998

Abstract Following the eruption of January 1992, episodes of lava dome growth accompanied by generation of dome-collapse nuees ardentes occurred in 1994–1998. In addition, nuees ardentes were generated by fountain-collapse in January 1997, and the 1998 events also suggest an explosive component. Significant tilt and seismic precursors on varying time scales preceded these events. Deformation about the summit has been detected by electronic tiltmeters since November 1992, with inflation corresponding generally to lava dome growth, and deflation (or decreased inflation) corresponding to loss of dome mass. Strong short-term (days to weeks) accelerations in tilt rate and seismicity occurred prior to the major nuees ardentes episodes, apart from those of 22 November 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short-term precursors. Because of the combination of populated hazardous areas and the lack of an issued warning, about 100 casualties occurred in 1994. In contrast, the strong precursors in 1997 and 1998 provided advance warning to observatory scientists, enabled the stepped raising of alert levels, and aided hazard management. As a result of these factors, but also the fortunate fact that the large nuees ardentes did not quite descend into populated areas, no casualties occurred. The nuee ardente episode of 1994 is interpreted as purely due to gravitational collapse, whereas those of 1997 and 1998 were influenced by gas-pressurization of the lava dome.

Understanding Merapi-type volcanoes

‘We have to understand volcano science to know what to monitor.” That simple statement by Antonius Ratdomopurbo, director of the Indonesian Center for Volcano Technology [Balai Penyelidikan dan Pengembangan-Teknologi (BPPTK)],captured the spirit and content of a recent workshop about Merapi and Merapi-type volcanoes. Merapi still is experiencing low levels of unrest, following a peak in eruptive activity on 14 June 2006, when pyroclastic flows swept into the evacuated village of Kali Adem and killed two workers who refused to leave. The volcano is an essential element that underlies life in Yogyakarta, Indonesia: It is a constant reminder of the perilous beauty as well as the mystical stature of volcanoes in Indonesia, the worlds most volcanically active country. It also is a proving ground for new technologies and monitoring methods in volcano hazards.