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 in diameter. Calderas can be found in various locations around the world, often filled with water to form lakes. Some famous examples of calderas include the Yellowstone Caldera in the United States and the Santorini Caldera in Greece. These geological features can lead to unique ecosystems and landscapes, making them important for both scientific study and tourism.