Calderas are depressions on the Earth's surface that are formed as a result of volcanic activity. When a particularly large volcanic eruption happens, a large volume of magma is removed from under the Earth's surface as lava. This leaves a large empty void underground where the magma was called the magma chamber. If the chamber is large enough and the overlying rock is heavy enough, the chamber can collapse as the rock above it falls in. This causes a depression to form on the Earth's surface called a caldera. The caldera often fills with water and becomes a lake. Crater Lake in Oregon in the US is an example of a caldera lake.