Tombolo's are ridges of sand and shingle which join the mainland to an island. Tombolo's are created through the process of longshore drift. Where there is a change in the shape of the land, a spit...
Well this is part of it..... Continental islands are bodies of land that lie on the continental shelf of a continent.
a island isformed by a volcano that is a dumb answermore detail?add it yourself
underwater volcanoes
Volcanoes under the sea created them. (and are still underneath them)