Chapter 113
Volcano Deformation Monitoring in Indonesia:
Status, Limitations and Prospects H.Z. Abidin, H. Andreas, M. Gamal, M.A. Kusuma Department of Geodetic Engineering, Institute of Technology Bandung, J1. Ganesha 10, Bandung 40132, Indonesia, E-mail :
[email protected] M. Hendrasto, O. K. Suganda, M.A. Purbawinata Directorate of Vulcanology and Geological Hazard Mitigation, J1. Diponegoro 57, Bandung, Indonesia F. Kimata, Irwan Meilano Research Center for Seismology and Volcanology and Disaster Mitigation (RCSVDM), Nagoya University, Japan
Abstract. Indonesia has 129 active volcanoes.
With a population of approximately 200 million, and the fact that the most populated island in Indonesia (i.e. Java) has the largest number of active volcanoes, then it is obvious that the Indonesian people live under the very real threat of volcanic eruptions. Monitoring volcanic activities can be done by using several methods, of which one of them is the deformation method. In Indonesia volcano deformation has been monitored using Tiltmeter observations, EDM measurements, Levelling Surveys, and Repeated or Continuous GPS Survey techniques. This paper will describe and discuss the implementation status of the GPS survey method for deformation monitoring of Indonesian volcanoes, along with their limitations and prospects. The obtained results and experiences will be presented to illustrate the discussions. Keywords. Volcano deformation Indonesia, GPS survey
monitoring,
1 Introduction Indonesia has 129 active volcanoes and 271 eruption points as a consequence of interactions and collisions among several continental plates. With a population of around 200 million, and the fact that the most populated island in Indonesia (i.e. Java) has the largest number of active volcanoes, then it is obvious that the Indonesian people live under the very real threat of volcanic eruptions. According to (Katili & Siswowidjojo, 1994), around 10% of Indonesians live in areas endangered by volcanic eruptions, and several million of them live in the danger zones. This fact alone suggests that in Indonesia the monitoring of volcano activity should be performed not only
routinely, but should also be done as reliably as possible. In relation to the deformation of a volcano, it is already well known that explosive eruptions are usually preceeded by relatively large inflation of its body [Scarpa and Gasparini, 1996, Scarpa and Tilling, 1996]. In the case of a volcano that has been 'quiet' for sometimes, the deformation of its body is one of the reliable indicators of its reawakening phase. Moreover, according to Van der Laat (1996) and Dvorak & Dzurisin (1997), the deformation of a volcano body, represented by the point displacement vectors and their velocity vectors, could provide information on the characteristics and dynamics of the magma chamber. Monitoring the deformation of the volcano itself can be done using several methods. In Indonesia, volcano deformation has been monitored using Tiltmeter observations, EDM measurements, Levelling Surveys, and Repeated or Continuous GPS Survey techniques. This paper will describe and discuss the implementation status of the GPS survey method for deformation monitoring of the Indonesian volcanoes.
2 Deformation Monitoring of Indonesian Volcanoes Monitoring volcanoes in Indonesia is continuously and routinely conducted by the Directorate of Vulcanology and Geological Hazard Mitigation of Indonesia. Up to now, the seismic and visual methods are the most used methods for monitoring Indonesian volcanoes. The deformation method is also widely used. The Department of Geodetic Engineering, Institute of Technology Bandung (ITB), in cooperation with the Directorate of Volcanology
Chapter 113 • Volcano Deformation Monitoring in Indonesia: Status, Limitations and Prospects
and Geological Hazard Mitigation, has conducted several GPS surveys in order to study the deformation of several volcanoes in Indonesia. 105-"
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Locations of the volcanoes being studied are shown in Figure 1. The characteristics of these volcanoes are explained in DVMBG (2003).
Fig. 1 I_acation of studied volcames
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The study of volcano deformation using GPS methods has yielded results and experiences that have been reported in Abidin et al. (1998a, 1998b,
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GPS Su r ~ y s
Processing of all GPS surveys data is done using BERNESE 4.2 scientific software (Beutler et al., 2001). Processing is done in radial mode from a certain reference station. The reference station is assumed to be stable for the deformation study, and its coordinates are computed in relation to Indonesian IGS stations in Bakosurtanal, Cibinong, Bogor. For all computations, the precise ephemeris is used, and residual tropospheric and residual ionospheric biases are estimated. All cycle ambiguities are successfully resolved and the final position solution is obtained using the narrow-lane signal [Hofmann-Wellenhof et al., 1994].
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Several GPS surveys have been conducted in the studied volcanoes, as summarized in Table 1. The GPS surveys were conducted using dualfrequency geodetic-type receivers. For all surveys Vd cano
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the typical length of sessions was around 10 to 24 hours. The data were collected with a 30 second data interval, and elevation mask was set at 150 for all stations. Vd cano
GPS Su Reys
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