A volcano that appears to be a large sunken depression is called a caldera.

Here's why:

* Formation: Calderas form when a large volcanic eruption empties the magma chamber beneath the volcano. Without the support of the magma, the overlying rock collapses inward, creating a large, bowl-shaped depression.

* Size: Calderas can be incredibly large, sometimes several kilometers in diameter.

* Examples: Famous examples of calderas include Yellowstone National Park in the United States and the Lake Toba caldera in Indonesia.

Let me know if you have any more questions!