Which geological feature is formed when a volcano's summit collapses, creating a large depression?

• A. Caldera
• B. Composite Volcano
• C. Earthquake
• D. Focus

Answer: (A)

This describes how a caldera forms. When a volcano erupts violently, a large amount of magma can be expelled from the underlying chamber, so the support that keeps the summit up is lost. The ground above the emptied chamber can no longer stay perched, so it collapses downward and creates a broad, basin-like depression. That wide depression is a caldera, often many kilometers across, and it can later fill with water to become a caldera lake.

This isn't describing a type of volcano itself—that would be a composite volcano, which is built from alternating layers of lava and ash rather than formed by collapse. And it isn’t about an earthquake or its focus, which are related to seismic activity rather than producing a large surface depression.