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.
Arrows show direction of movement along major transform faults.
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. The distribution of earthquakes in the subducted plates can be used to make a cross-section of the Molucca Sea area. 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.