The topography of the islands of Indonesia varies, but it is mainly composed of coastal lowlands. Some of the larger islands in Indonesia (such as Sumatra and Java) have large inland mountains. Since Indonesia's 13,677 islands are situated on both continental shelves, many of these mountains are volcanic and there are several crater lakes on the islands. For example — Java has 50 active volcanoes.
Natural disasters, in particular earthquakes, are common in Indonesia due to their location. For example, on 26 December 2004, an earthquake of 9.1 to 9.3 magnitudes struck the Indian Ocean, triggering a large tsunami that devastated many Indonesian islands.