The correct answer is sea stack. A sea stack is formed when a sea arch, which is a natural rock bridge over the water, collapses due to erosion or other natural forces. After the collapse, the remaining isolated column of rock is called a sea stack. To find the answer to this question, you could search for information about the different landforms that result from the collapse of a sea arch.
The name of the landform remaining after a sea arch collapses is a sea stack.
