It would be a divergent boundary, with the two tectonic plates moving away from eachother.
The name for such a hole is "caldera" which is a word of Spanish origin meaning "a pot" or a "cooking pot" (thing of cauldron!) - and this word is used because it resembles the shape of this hole.
Often the Calderas are filled with water forming lakes and often there is an island in the middle of the water.
Asia is the largest out of the two.
C The coast with lake victoria.
