Geography of Indonesia - Mountains and Tectonics

Mountains and Tectonics

Most of the larger islands are mountainous, with peaks ranging between 3,000 and 3,800 metres (9,843 and 12,467 ft) meters above sea level in Sumatra, Java, Bali, Lombok, Sulawesi, and Seram. The country's tallest mountains are located in the Jayawijaya Mountains and the Sudirman Range in Papua. The highest peak, Puncak Jaya (4,884 metres (16,024 ft)), is located in the Sudirman Mountains.

Tectonically, Indonesia is highly unstable. It lies on the Pacific Ring of Fire where the Australian Plate and the Pacific Plate are pushed under the Eurasian plate where they melt at about 100 km deep. A string of volcanoes stretches from Sumatra to the Banda Sea. While the volcanic ash has resulted in fertile soils, it makes agricultural conditions unpredictable in some areas. A string of volcanoes runs through Sumatra, Java, Bali and Nusa Tenggara, and then loops around through to the Banda Islands of Maluku to northeastern Sulawesi. Of the 400 volcanoes, approximately 150 are active. Between 1972 and 1991, twenty-nine volcanic eruptions were recorded, mostly on Java. The two most violent volcanic eruptions in modern times occurred in Indonesia; in 1815 Mount Tambora in Sumbawa erupted killing 92,000 and in 1883, Krakatau, erupted killing 36,000.