Most of Indonesia's volcanoes are part of the Sunda arc, a 3,000-km-long line of volcanoes extending from northern Sumatra to the Banda Sea. Most of these volcanoes are the result of subduction of the Australia Plate beneath the Eurasia Plate. Volcanoes in the Banda Sea result from subduction of the Pacific Plate under the Eurasia Plate. Black "teeth" are on the overriding plate. Arrows show direction of movement along major transform faults. Simplified from Lee and Lawver, 1995, Tectonophysics, v. 251, p. 85-138.
About one-fourth of Indonesia's volcanoes are north of the Sunda arc in an area with complex tectonics. Several small plates have produced mostly north-south trending subduction zones. The volcanoes of Sulawesi, Halmahera, and Sangihe are the result of these subduction zones. Simplified from Hamilton (1979).
The distribution of earthquakes in the subducted plates can be used to make a cross-section of the Molucca Sea area. Most of the Molucca Sea Plate has been "consumed" (subducted) by the Halmahera subduction zone in the east and by the Sangihe subduction zone in the west. The volcanoes of Sulawesi, Sangihe, and Halmahera are fed by magma generated in the asthenospheric mantle that has been modified by fluids derived from the subducted Molucca Sea Plate. In a few million years, all of the Molucca Sea Plate will be subducted and the Sangihe and Halmahera plates will collide, shutting off volcanism. Simplified from Hamilton (1979).
Indonesia has 76 volcanoes that have erupted in historic time - the largest number for any volcanic region. These volcanoes have had at least 1,171 eruptions, placing Indonesia second (after Japan) for the region with the most dated eruptions.
Indonesia has had the highest number of eruptions that:
Hamilton, W., 1979, Tectonics of the Indonesian region: U.S. Geological Survey Prof. Paper 1078.
Neumann van Padang, M., 1951, Indonesia. Catalogue of the Active Volcanoes of the World, International Association of Volcanology, 1, Rome, Italy, 271 p.
Neumann van Padang, M., 1983, History of volcanology in the former Netherlands east Indies: Scripta Geol, v. 71, p. 1-76.
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.