LAKE TOBA, A MULTIPLE CALDERA DEPRESSION, NORTH SUMATERA, INDONESIA

A joint research on the geology of Lake Toba and its surrounding was executed by the Kyoto University and Indonesian Institute of Sciences during 1972-1988. The lake origin was explained by van Bemmelen (1949) as a volcano-tectonic depression. Ninkovich (1967) explained that Lake Toba is a caldera produced by a single eruption 70,000 years BC. Geological, geo-chronology, tephra-chronology, and gravity measurements by the Japan-Indonesia surveys revealed a more complex origin, the combined effect of volcanic, tectonic and sedimentation processes starting 1.9 M years ago (Nishimura et al. 1980). Lake Toba water area is 1,129 km² excluding the 647 km² Samosir Island and several other smaller islands in the lake. The morphology formed a topographic depression surrounded by steep cliffs 400 to 1200 m above lake surface. The water is at 904.5 m above sea level, maximum depth 585 m. The joint Japan-Indonesia finding is a strong base for planning a sustainable management for local people, forestry, fisheries, agriculture benefits, industrial developments, hydropower generation, and an everlasting scenic view for tourists