A depression formed when a buried block of glacial ice melts is called a kettle, or kettle hole.
Kettles usually form after a glacier retreats and leaves behind chunks of stagnant, or “dead,” ice. Meltwater streams spread sand and gravel across an outwash plain, burying the ice blocks. When the buried ice eventually melts, the sediment collapses or settles into the empty space, leaving a rounded depression.
Some kettles fill with water. A water-filled kettle is commonly called a kettle lake when it is connected to groundwater or surface water; smaller water bodies may be described as kettle ponds or wetlands. Kettles can also form when sediment-rich ice blocks are buried during the sudden drainage of an ice-dammed lake, known as a jökulhlaup.
The other choices describe different glacial landforms. An esker is a winding ridge of sediment deposited by meltwater beneath or within a glacier. A cirque is an amphitheatre-shaped hollow near a glacier’s head, while a tarn is a mountain lake, often occupying a cirque basin. Kettles are generally shallow, and many eventually fill with sediment or vegetation.