What is a caldera?

A caldera is defined as a large hollow that is formed following the collapse of a volcano after a violent eruption. This occurs when the magma chamber beneath the volcano empties, and the ground above it can no longer support its weight, leading to a significant depression at the summit. Calderas can be quite expansive and unique in their geographical features, often filled with water to become a lake as seen in places like Crater Lake in Oregon or Yellowstone Lake in Wyoming. This characteristic distinguishes calderas from other geological formations, as it specifically involves volcanic activity resulting in a large crater-like structure.

The other options do not accurately describe the features associated with a caldera. Volcanic islands and mountains formed by tectonic activity, while related to geological processes, do not encompass the specific collapse structure that a caldera represents. Similarly, a depression formed by erosion typically indicates a different process and context. Understanding this definition helps in grasping the broader implications of volcanic activity and the resultant landforms.