The Lesser Sunda Islands consist of two geologically distinct archipelagos. The northern archipelago, which includes Bali, Lombok, Sumbawa, Flores and Wetar, is volcanic in origin. A number of these volcanoes, like Mount Rinjani on Lombok, are still active while others, such as Kelimutu on Flores with its three multi-coloured crater lakes, are extinct. The northern archipelago began to be formed during the Pliocene, about 15 million years ago, as a result of the collision between the Australian and the Asian plates. The islands of the southern archipelago, including Sumba, Timor and Babar, are non-volcanic and appear to belong to the Australian plate. The geology and ecology of the northern archipelago share similar history, characteristics, and processes with the southern Maluku Islands, which continue the same island arc to the east.