GEOLOGY AND HYDROGEOLOGY OF LUMANJULU REGION, TOBA SAMOSIR DISTRICT, NORTH SUMATERA.

• Main Author: Alam Maulana, Sabda
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/70155
• Institution: Institut Teknologi Bandung

The research area is located in Lumbanjulu, Porsea, Uluan, and Bonatualunasi Districts, Toba Samosir Regency, North Sumatera. Geographically, the research area is located at UTM coordinates UTM 506000 – 515000 mE and 272000 – 282000 mN in the 48 north zone. The research area is 90 km2 (9 km x 10 km). Based on BMB classification, the research area can be divided into five units, Sihiong Fault Block Ridge Unit, Nalela Denudation Hills Units, Amborgang Denudation Plain Unit, Panamean Caldera Wall Unit, and Alluvial Plain Unit. The research area is in young - mature geomorphic stage. Stratigraphically, the research area can be divided into four non-formal rock units which were formed during Late Carboniferous – Recent. The sequences, from old to young, are Slate Unit, Tuff Unit, Sandstone Unit, and Alluvial Unit. The Tuff Unit, Sandstone Unit, and Alluvial Unit were formed in lake to fluvial environment. Geological structures in the research area are Sihiong Normal Fault, Sosornaga Dextral Fault, Lumbandolok Dextral Fault, and Aek Parik Normal Fault. Sihiong Normal Fault was interpreted as the result of the first eruption of Toba Volcano in the Early Pleistocen Age, while the other structures were formed after Sandstone Unite were deposited. Aquifer in the research area is in the weathered Slate Unit, Tuff Unit, Sandstone Unit, and Alluvial Unit. These aquifers form an unconfined aquifer system. All water from the springs and dug wells in the research area are suitable for drinking according to PERMEN No.492/MENKES/PER/IV/2010 based on pH and TDS value criteria. The pH value ranges from 7 – 7.62 while the TDS value ranges from 38 - 206 mg/L.