Torres Strait
The islands are a mix of island types. Some of the islands near New Guinea are low lying islands made from soil washed down from the rivers. The hilly and steep  granite islands in the west were once the tops of mountains which became islands when the sea levels rose 8,000 years ago. The islands in the centre are mostly coral cays. The islands in the east of the strait were made by submarine volcanos which grew above the surface of the ocean.