Seminar Bendungan Besar Asahan: Sejarah Geologi Tufa Toba

Between Barumun and Wampu River in North Sumatera there exist a topographic culmination marked by contour lines of 100 and 1000 m, called batak Tumor by van Bemmelen (1939). The top of this culmination, on the NE side of the Sumatera fault zone, is crowned by Lake Toba which measures on its NW-SE side axis 87 km. The area of lake including Samosir island is 1.776,5 sq.km. Samosir is 640 sq.km and Pardapur near the southern shore is 7 sq.km, so that the free water area of the lake measures 1.130 sq.km. The volcano-tectonic history of the Toba area has attract many scientist.

The author proposed the foolowing sequence of formation : culmination or forming of the Batak Tumor; deposition of pre-Toba dacite which age was dated 1,9 m.y.; post-Toba welded Tuff which is 1,2 m.y. old; formation of lake deposit in the Samosir island and surrounding area; upper tuff which age is 0,1 and 0,075 m.y.; then the uppermost pumice tuff which was dated 30.000 years old. The distribution of the first three phase is exposed in the area surrounding Toba Lake. Each phase activity contained several cooling units which distribution is not uniform for the whole area. Tuffs younger than 0,1 m.y. seems to be more explosive and was oirborn distributed in a very broad area, from Tampan in Malaysia to the SW part of Ceylon in the Indonesian Ocean.

More

Share this: