The Lesser Sunda Islands is a small archipelago which, from west to east, consists of Bali, Lombok, Sumbawa, Flores, Sumba and the Timor islands; all are located at the edge of the Australian continental shelf. Volcanoes in the area are formed because of oceanic crusts and the movement of the shelf itself. Some volcanoes completely form an island, for instance, the Sangeang Api island. Mount Tambora, on Sumbawa island, erupted on 5 April 1815, with a scale 7 on the VEI and is considered the most violent eruption in recorded history.