A caldera is a large, bowl-shaped depression formed when a volcano erupts and collapses. This geological feature occurs after a massive eruption empties the magma chamber beneath the volcano, causing the ground above to sink. Calderas can vary in size and may contain lakes, hot springs, or even new volcanic activity. Calderas are often found in volcanic regions and can be significant for studying geological processes. Famous examples include the Yellowstone Caldera in the United States and the Santorini Caldera in Greece. These formations provide valuable insights into the history and behavior of volcanic systems.