I want to make an island like this how do I go about creating it?
I might be wrong but I don’t think that you can achieve this in Gaea only ( the “empty” center part from which water is falling to the ground).
But you could mix an eroded island and a volcano with a large mouth, make the erosion as close as possible of the image in Gaea and then export a mesh.
In blender for instance you could perform some boolean opération for the center of your model to get this empty space in the center and add something ( a sculped plane or another flatter terrain exported for Gaea) to figure a ground.
Not sure however if you could use this, once textured, for something else than still images.
A very rough example:
