Choose the best answer.

Stacks are formed by _______________.

Erosion and deposition are also caused by the actions of ocean waves. It is an important agent for the creation of many geographical features. Stacks are an important feature as a result of the erosion by sea waves. Stacks are the remaining parts of the sea arch that has been completely collapsed by the action of the waves. The remaining seaward portion of the arch in the upper part is the stack. The Old Man of Hoy in Scotland is an important sea stack.