Geology
The island originated from a volcano located near its center. Igneous rocks make about 85% of its surface with occasional limestone, sandstone and dolomite. The soil in low-lying coastal areas is mainly alluvial, with a predominance of sand and gray clay. At altitudes of 10–30 meters above sea level, older alluvial accretions show up as horizontal layers of brown clay, and the higher areas are dominated by red-brown laterite.
The area is considered seismically active, with frequent tremors which are companied by landslides. The island has deposits of coal and onyx which are being mined from the early 2000s. There are oil and gas fields in the underwater shelf around the island, which are among the largest in Indonesia. Their development started in the 1960s and is being conducted now by the national company Pertamina and several foreign companies.
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