What term describes a small lake formed when a glacier carves a depression at the bottom of a cirque and then melts?

A tarn is specifically used to describe a small lake that forms in a depression carved by a glacier, typically found in a cirque. During the process of glacial erosion, the glacier carves out a bowl-shaped hollow, and when it melts, water collects in this depression, creating a tarn. This term is distinct and accurate as it highlights the glacial origin of the lake and its specific geographic context.

In contrast, an atoll refers to a ring-shaped coral reef island and is unrelated to glacial processes. A cirque lake is not a formal term commonly used in geography, although it describes a similar formation; however, it lacks the precision of the term tarn. A glacial pool is more of a general descriptor and does not specifically refer to the particular characteristics associated with a tarn. Thus, tarn is the most appropriate term for this specific glacial feature.