Lesser Sunda Islands
Geology

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 Ilikedeka on Flores, 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.

There is a long history of geological study of these regions since Indonesian colonial times; however, the geological formation and progression is not fully understood, and theories of the geological evolution of the islands changed extensively during the last decades of the 20th century.

Lying at the collision of two tectonic plates, the Lesser Sunda Islands comprise some of the most geologically complex and active regions in the world. The province of Bali is the only part of Nusa Tenggara located on the Sunda Shelf and that is not within the Wallacea region and that is west of the Wallace Line.

There are a number of volcanoes located on the Lesser Sunda Islands.
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