Final answer:
A caldera forms by the draining of a magma chamber beneath a volcano during an eruption, leading to the surface collapsing and creating a large crater-like depression.
Step-by-step explanation:
A caldera forms by the draining of a magma chamber beneath a volcano during an eruption. When an eruption occurs, the significant amount of magma within the chamber is expelled onto the surface, which can cause the surface above to collapse due to the evacuated space below, thereby creating a large crater-like depression that we refer to as a caldera. These geological phenomena are a result of the dynamic processes involving tectonic plates moving over hotspots in the mantle which produce extreme heat and volcanic activity. One classic example is the Yellowstone Caldera, formed above the Yellowstone hotspot. Unlike other geological features such as lava flows or land alterations from glacial retreats and landslides, a caldera specifically arises due to the unique volcanic process of a collapsed magma reservoir.