VII. International Activity

2. Collaborative Study on Volcanic Activity between Indonesia and Japan

In 1993, the Disaster Prevention Research Institute (DPRI), Kyoto University and the Directorate General Geology and Mineral Resources, Ministry of Mines and Energy, Indonesia reached an arrangement for the joint research program in the field of volcanic activity to migrate volcanic hazards in Indonesia and in relation to IDNDR. Kyoto University and Tokyo Institute of Technology have made survey and observations at Indonesian volcanoes in cooperation with Volcanological Survey of Indonesia (VSI). Researchers of VSI have visited Japanese volcano observatories for data analysis and discussion. In 1998, the arrangement of cooperation was extended until 2003. DPRI held International Symposium on Natural Disaster Prediction and Mitigation at Kyoto in December 1997 and Symposium on Japan-Indonesia IDNDR Project, Volcanology, Tectonics, Flood and Sediment Hazards, at Bandung in September 1998 organized with VSI and Research Institute for Water Resources Development.

Guntur Volcano

Guntur volcano repeated eruptions with lava flow, ejection of volcanic bomb and pyroclastic flows until the 19th century. After the last eruption in 1843, no eruption has occurred, however, several tens volcanic earthquakes had been observed per month. In 1994, 3 permanent stations with telemetric system were installed at the south and eastern flank of Guntur volcano under the cooperation project (Sutawidjaja et al., 1998). Temporary seismic observations were conducted by data logging devices in order to supplement permanent stations. Locations of hypocenters of volcanic earthquakes were determined using the data obtained by the observations. The distribution of hypocenters is shown in Fig. 30. The hypocenters of volcanic earthquakes were distributed beneath the summit craters at depths shallower than 5km and were aligned along faults around Kamojang geothermal field at depths of 5-10 km (Iguchi et al., 1996; Suantika et al., 1997). Strike slip focal mechanism was dominant in the volcanic earthquakes around Kamojang. In contrast, the mechanisms beneath the summit crater were normal or reverse faults (Iguchi et al., 1997; Suantika et al., 1998a).

In May 1997, seismic activity at Guntur volcano suddenly increased and the seismicity continued to November. The seismicity was concentrated beneath the summit, especially at depths of 2-4 km, and the hypocenters were aligned from NW to SE, that is, direction of alignment of craters and domes in the summit area (Iguchi et al., 1998a). When the volcanic earthquakes successively occurred, reverse fault type earthquakes were dominant (Iguchi et al., 1998a). Upward tilt toward the summit crater was observed by a tilt meter installed 2km south of the summit crater, associated with the seismicity increase from May 1997 (Suganda et al., 1998). The tilt change suggests inflation of the ground around the summit crater. The inflation of the summit crater was detected by precise leveling along benchmarks on the southeastern and south flanks of the volcano (Hendrasto et al., 1998). Referred to benchmark at southeastern flank, the benchmark closest to the summit was elevated 5 mm during the period from August 1996 to November 1997. The vertical deformation was inverted to deflation in 1998 when seismicity declined. GPS surveys have been repeated surrounding Guntur volcano since 1996 (Abidin et al., 1998). Dilatation and maximum shear in the trilateration network near the summit increased during the period with high seismicity (Suganda et al., 1998). The increase in seismicity and inflation around the summit crater was interpreted to be caused by increase in pressure of a shallow gas chamber beneath the summit (Iguchi et al., 1998a). The cumulative energy of volcanic earthquakes released during the seismicity was estimated. The 1997 seismicity was one of the high-level activities which have been repeated since 1990 with the time interval ranging from one to several years (Iguchi et al., 1998a; b).

Merapi Volcano

The eruptions at Merapi volcano are characterized by lava dome growth at the summit and following pyroclastic flows caused by collapse of the dome. Two tiltmeters have been installed 0.7 km and 0.9 km apart from the summit lava dome since 1993. Inflations of the ground around the summit lava domes were observed by the tiltmeters prior to the big pyroclastic flows in November 1994, November 1995, January 1997 and July 1998. Upward-downward tilt process successively observed from the station (KLA) far from the dome to that (ST3) near the lava dome as shown in Fig. 31. This suggests the location of pressure source causing ground deformation migrated from deep part to shallow one. Prior to the occurrence of pyroclastic flow in 1995, the pressure source moved from the depth of 0.7 km to 0.4 km (Subandriyo et al., 1998). Preliminary experiment to evaluate the activity quantitatively with PC was conducted by using daily number of volcanic earthquakes (A-type, B-type, MP-type and rock-fall) and tilt changes. The algorithm simulates change in activity and the alert level issued by VSI well, and was applicable to the eruption with pyroclastic flows in July 1998 (Hidayati et al., 1998).

The concentration of volatile components in the magma was estimated with chemical data of volcanic gas and lava, and magma extrusion rate. Sulfur contents in the basaltic-andesitic magma of Merapi is 1,240@ppm and 97@% of the sulfur are degassed from magma (Hirabayashi et al., 1997). Apparent equilibrium temperature, which was calculated from chemical composition, concentration of HCl, SO2, H2 and CO, and discharge rate of SO2, is a useful indicator to predict volcanic eruption. Change in CO2/H2O ratio of fumarolic gas is shown in Fig. 32. Decrease in the ratio suggests migration of degassing depth to shallower part (Hirabayashi et al., 1998).

Magnetotelluric survey was conducted crossing volcanoes in Central Java. The two-dimensional resistivity model shows the difference in subsurface structure between basaltic and andesitic volcanoes (Mogi et al., 1997).

Other Volcanoes

General chemical features of volcanic gases were investigated at Gede, Tangkuban Parahu, Papandayan, Guntur, Galunggung, Slamet, Dien, Muria, Kelud, Lamongan, Ijen and Batur volcanoes. Chemical compositions of volcanic gases indicate high activity of Merapi, Papandayan, Gede and Ijen volcanoes. The CO2 and He in volcanic gases are derived from magma directly at the volcanoes in Java (Hirabayashi et al., 1998).

Hypocenter locations and focal mechanisms of volcanic earthquakes were determined at Anak Krakatau, Gede, Papandayan, Slamet, Sangeanapi and Illi Lewotolo volcanoes. Hypocenters were concentrated beneath the active craters, and the most of focal mechanisms were of normal or reverse fault type (Suantika et al., 1998b).

(Masato Iguchi and Jun-ichi Hirabayashi)

References

Abidin, H.Z., Suganda, O.K., Sukhyar, R., Meilano, I., Kusma, M.A., Setyadji, B., Kahar, J., Tanaka, T. and Rizos, C. (1998) Deformation monitoring of Indonesian volcanoes using repeated GPS survey method: Status and plan. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 39-50.

Hendrasto, M., Suganda, O.K., Yamamoto, K., Eto, T., Ishihara, K., Yosef, H. and Sugiyo (1998) Ground deformation detected by precise leveling at Guntur volcano. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 95-106.

Hidayati, S., Iguchi, M., Ishihara, K., Purbawinata, M.A., Subandriyo, Sinulingga, I.K. and Suharno (1998) A preliminary result of quantitative evaluation on activity of Merapi volcano and its application to 1998 eruption. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 165-180.

Hirabayashi, J., Kadarsetia, E., Ohba, T. and Nogami, K. (1997) Volatile contents in the magma of Merapi and Unzen volcanoes. Proc. Intl. Symp. Natural Disaster Prediction and Mitigation, Kyoto, pp. 239-242.

Hirabayashi, J., Ohba, T., Sukhyar, R. and Sano, Y. (1998) Gas chemistry of volcanoes in Jawa. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 51-56.

*Iguchi, M., Ishihara, K., Tetsuro, T., Suantika, G., Tjetjep, W., Sukhyar, R., Sutawidjaja, I.S. and Suganda, O.K. (1996) Seismic activity at Guntur volcano, West Jawa, Indonesia. Ann. Disast. Prev. Res. Inst., Kyoto Univ., 39B-1, 161-171.

Iguchi, M. Suantika, G. Suganda, O.K. and Ishihara, K. (1997) Increase in seismic activity in 1997 at Guntur volcano, West Jawa, Indonesia. Proc. Intl. Symp. Natural Disaster Prediction and Mitigation, Kyoto, pp. 225-232.

*Iguchi, M., Ishihara, K., Eto, T., Yamamoto, K. Sutawidjaja, I.S., Suantika, G., Suganda, O.K and Hendrasto, M. (1998a) Evaluation of the recent activity at Guntur volcano, West Jawa, Indonesia. Ann. Disast. Prev. Res. Inst., Kyoto Univ., 41B-1, 161-170.

Iguchi, M., Ishihara, K., Sutawidjaja, I.S., Suantika, G., Hendrasto, M. and Suganda, O.K. (1998b) Evaluation of the 1997 activity at Guntur volcano. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 115-122.

Mogi, T., Tanaka, Y., Widarto D.S., and Arsadi, E.M.(1997) Electrical conductivity structure of crust in Central Java, Indonesia, as implication of volcanic activity. Proc. Intl. Symp. Natural Disaster Prediction and Mitigation, Kyoto, pp. 233-237.

Suantika, G., Suganda, O.K., Iguchi, M. and Ishihara, K. (1997) Hypocenter distribution and focal mechanism of volcanic earthquakes around Guntur volcano. west Jawa, Indonesia. Ann. Disast. Prev. Res. Inst., Kyoto Univ., 40, 5-11.

Suantika, G., Iguchi, M., Sutawiddjaja, I.S. and Yamamoto, K., (1998a) Characteristics of volcanic earthquakes around Guntur volcano, West Java, Indonesia - Hypocenter and focal mechanism from 1994 to 1998 -. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 71-80.

Suantika, G., Sulaeman, C., Wildan, A., Sutawidjaja, I.S., Kriswati, E., Kristianto, Solihin, A. and Iguchi, M. (1998b) Improvement of determination capability of hypocenter and focal mechanism at some volcanoes in Indonesia. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 123-136.

Subandriyo, Purbawinata, M.A., Iguchi, M. and Ishihara, K. (1998) Characteristics of tilt changes in association with Merapi eruption during the 1993-1997 activities. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 155-164.

Suganda, O.K., Abidin, H.Z., Iguchi, M., Hariyanto, A.H., Meilano, I. and Kusuma, M.A. (1998) Strain components and tilt vector changes at Guntur volcano, during the increasing of seismic activity in 1997. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 81-94.

Sutawidjdja, I.S., Suantika, G., Hendrasto, M., Suganda, O.K., Iguchi, M., Ishihara, K. and Eto, T. (1998) Observation system at Guntur volcano, West Java under Indonesia-Japan cooperation in volcanology. Proc. Symp. Japan-Indonesia IDNDR Projects -Volcanology, Tectonics, Flood and Sediment Hazards-, Bandung, pp. 65-70.

(* In Japanese with English abstract)


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