What geological feature can effectively create an 'island' inland, leading to internal adaptive radiation?

Answer

The formation of a large, deep lake.

A large, deep lake, such as Lake Victoria, can present an array of distinct aquatic niches within one boundary, acting similarly to an isolated island environment for cichlid fish.

What geological feature can effectively create an 'island' inland, leading to internal adaptive radiation?
Ecologyevolutionradiationtriggerspeciation