Geologically , the area of modern Indonesia appeared from under the Southeast Asian seas as the result of the Indian and Australian plates colliding and slipping under the Sunda Plate , sometime in the early Cenozoic era around 63 million years ago . This tectonic collision created Sunda volcanic Arc that has produced chains of islands of Sumatra , Java and the Lesser Sunda Islands . The active volcanic arc creating supervolcano that today become Lake Toba in Sumatra . The massive eruption of Toba supervolcano that occurred some time between 69,000 and 77,000 years ago instigated the Toba catastrophe theory , a global volcanic winter that caused a bottleneck in human evolution . Other notable volcanoes in Sunda Arc are Mount Tambora and Krakatau . The region is known for its instability due to volcano formations and other volcanic and tectonic activities as well as climate changes ; resulted in lowlands drowned occasionally under shallow seas , the formation of islands , the connection and disconnection of islands through narrow land-bridges , etc
Toba catastrophe theory
Toba catastrophe theory
Prehistoric Indonesia