Indonesia is located between two continental plates: the Eurasian Plate (Sunda Plate) and Australian Plate (Sahul Shelf); and between two oceanic plates: the Philippine Sea Plate and Pacific Plate. The subduction of the Indian oceanic plate beneath the Eurasian continental plate formed the volcanic arc in western Indonesia, one of the most seismically active areas on the planet with a long history of powerful eruptions and earthquakes. This chain of active volcanoes formed Sumatra, Java, Bali, and Nusa Tenggara islands, most of which, particularly Java and Bali, emerged within the last 2-3 million years. The Pacific and Australian plate movements controlled the tectonics of the eastern portion of Indonesia and formed the unique feature of Banda Arc.
As the tectonic plates in Indonesian region actively move against each other they form a complex geological setting. The cluster of islands in Eastern Indonesia also reflect the impact of the tectonics.