| Abstract |
The Sembalun Bumbung area is located in the Northñ East of Lombok island. This area is a part of a volcano depression, which has formed a caldera structure by a violent eruption of Mt. Sembalun. Geothermal manifestations, including altered rock occur in Sembalun caldera floor (± 1300 asl), and some hot springs discharge along the NEñSW, WñE, NWñSE trending faults, while 4 hot springs are situated at the foot of Mt. Rinjani. The hot spring waters are of neutral, acid sulphate, and chloride sulphate types. The highest values of Hg, and CO2 are found in soils at Nanggi hill, in ì Sembalun Bumbungî. Results of gravity and geoelectric surveys support the subsurface data interpretation. Gravity data analyzed, suggest that Bouguer, and residual anomalies arround Sembalun represent a caldera structure. Resistivity data for the caldera floor, show low anomaly (< 25 Ÿ m) contour patterns of AB/2=500m, and AB/2=1000 m and are concentrated at Sembalun Bumbung, on the caldera floor. Estimation of the actual resistivity beneath Sembalun Bumbung on line A show that, the thickness of overburden layers is 185 ñ 280 m, the clay cap layer is probably about 550 ñ 1450 m, whereas the thickness of the layer below the clay cap (the maximum penetrated) with resistivity < 10 Ÿ m couldnít be recorded. The layers beneath the clay cap layer are assumed to constitute a liquid or steam reservoir. The best area for developing a small scale geothermal power for supplying electricity demand in Lombok island is presumably in the vicinity of ìNanggi hill in Sembalun Bumbungî on the caldera floor. |