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The geography of Sumatra is dominated by a mountain range called Bukit Barisan (lit: "a row of hills"). The mountain range spans nearly 1,700 km (1,050 mi) from the north to the south of the island, and it was formed by movement of the Australian tectonic plate.[8] The plate moves with a convergence rate of 5.5 cm/year which has created major earthquakes on the western side of Sumatra including the 2004 Sumatra-Andaman earthquake.[9][10] The tectonic movement has been responsible not only for earthquakes, but also for the formulation of magma chambers beneath the island.[8]

Only one of the 35 active volcanos, Weh, is separated from the Sumatran mainland. The separation was caused by a large eruption that filled the lowland between Weh and the rest of the mainland with sea water in the Pleistocene epoch. The largest volcano of Sumatra is the supervolcano Toba within the 100 km (62 miles) × 30 km (19 miles) Lake Toba, which was created after a caldera collapse (est. in 74,000 Before Present).[2] The eruption is estimated to have been at level eight on the VEI scale, the largest possible for a volcanic eruption. The highest peak of the mountain range is Mount Kerinci with an elevation of 3,800 m (12,467 ft).