as the Riau Islands, Nias and the Bangka-Belitung group), it now covers ten of Indonesia's 37 provinces, which are set out below with their areas and populations. Geography The longest axis of the island runs approximately northwest–southeast, crossing the equator near the centre. At its widest point, the island spans . The interior of the island is dominated by two geographical regions: the Barisan Mountains in the west and swampy plains in the east. Sumatra is the closest Indonesian island to mainland Asia. To the southeast is Java, separated by the Sunda Strait. To the north is the Malay Peninsula (located on the Asian mainland), separated by the Strait of Malacca. To the east is Borneo, across the Karimata Strait. West of the island is the Indian Ocean. The Great Sumatran fault (a strike-slip fault), and the Sunda megathrust (a subduction zone), run the entire length of the island along its west coast. On 26 December 2004, the western coast and islands of Sumatra, particularly Aceh province, were struck by a tsunami following the Indian Ocean earthquake. This was the longest earthquake recorded, lasting between 500 and 600 seconds. More than 170,000 Indonesians were killed, primarily in Aceh. Other recent earthquakes to strike Sumatra include the 2005 Nias–Simeulue earthquake and the 2010 Mentawai earthquake and tsunami. Lake Toba is the site of a supervolcanic eruption that occurred around 74,000 years ago, representing a climate-changing event. The most important rivers in Sumatra belong to the catchment area of the South China Sea. Heading north to south, the Rokan, Siak, Kampar, Indragiri, Batanghari flow into the Malacca Strait, while the island's largest river, the Musi, flows into the sea at Bangka Strait in the south. To the east, big rivers carry silt from the mountains, forming the vast lowland interspersed by swamps. Even if mostly unsuitable for farming, the area is currently of great economic importance for Indonesia. It produces oil from both above and below the soil – palm oil and petroleum. Sumatra is the largest producer of Indonesian coffee. Small-holders grow Arabica coffee (Coffea arabica) in the highlands, while Robusta (Coffea canephora) is found in the lowlands. Arabica coffee from the regions of Gayo, Lintong and Sidikilang is typically processed using the Giling Basah (wet hulling) technique, which gives it a heavy body and low acidity. Sumatra is a highly seismic island, huge earthquakes have been recorded throughout history, in