Wednesday 24 August 2005

G7
1515-1700 hours

309
Modeling eruption column of the 2000 Miyakejima volcano eruption (Japan)
using residual GPS data
Darmawan, Dudy¹, Kimata, Fumiaki², Hirahara, Kazuro², Abidin, Hasanuddin¹
1 Department Of Geodetic Engineering, Institute Of Technology Bandung, Indonesia
2 Graduate School Of Environmental Studies, Nagoya University, Japan
Author email: hzabidin@indo.net.id
Miyakejima volcano island is an active basaltic andesite stratovolcano located about 200 km south of Tokyo, in the Izu-Bonin volcanic chain. The recent intense seismic activities occurred during the period from June 26 to September 4, 2000, which were accompanied by some eruption events. The largest eruption occurred on August 18, 17:00-19:00 JST, producing an eruption column higher than 10 km. The total amount of volcanic ash and lapilli ejected by such eruption was about 8x109 kg, which covered the whole area of the volcano. The aim of this research is to model the eruption collumn of the August 18, 2000 eruption using GPS data. GIPSY-OASIS II package is employed to process GPS data. Epoch by epoch analysis of the zero-differenced residual data clearly shows that the signal's travel was delayed. GPS measurements on August 18 indicate that during 2-hour eruption the recorded GPS signals seemed to have been significantly disturbed by the ejected volcanic materials, for especially the signals that traveled over the caldera. The presence of hot volcanic materials inside the eruption column is mainly considered to be the cause of these delays. According to the residual increment, the delays exceeded as large as 15 cm in some cases. In contrast, the residual is negative (decrease) if the signal did not travel over the caldera. The result from residual analysis can obviously be an important information about the state of the eruption column. In this paper we make two simple eruption column models, the fixed and expanded models. By applying the forward modeling of tomographic approach, the residual for each model is generated and compared with the observed one. The fit test analysis shows that the expanded model is more reliable than the fixed one, since it can capture characteristic the observed residual.

Return to Oral Presentations