A caldera is a large, bowl-shaped depression that forms after a volcanic eruption. When a volcano erupts, it can empty its magma chamber, causing the ground above to collapse. This creates a wide, often circular area that can be several kilometers across. Calderas can fill with water, forming lakes, or remain dry. Calderas are often associated with explosive volcanic activity, such as that seen in the Yellowstone National Park in the United States. They can also be sites of future volcanic activity, as magma may still be present beneath the surface, leading to the formation of new volcanic features over time.