Question

When glaciers retreat, they leave behind huge blocks of ice. When these ice blocks melt, they can form kettle lakes. Why is it important for sediment to build up around the ice blocks in order for kettle lakes to form?

Responses

Without the sediment, the water in the lake would dry up.
Without the sediment, the water in the lake would dry up.

Without the sediment, the water would not stay contained.
Without the sediment, the water would not stay contained.

Without the sediment, vegetation would not be able to grow.
Without the sediment, vegetation would not be able to grow.

Without the sediment, the ice blocks would not warm enough to melt.
Without the sediment, the ice blocks would not warm enough to melt.

Answer 1

Correct answer: "Without the sediment, the water would not stay contained."

Explanation: When a buried ice block melts it leaves a depression. Sediment (glacial till, sand, gravel) building up around and above the ice forms the basin walls or rim that traps meltwater. Without that surrounding sediment the meltwater would simply run off or drain away instead of collecting to form a kettle lake. The other choices are incorrect: sediment doesn’t cause vegetation to be required for lake formation, and in fact sediment can insulate ice (not make it melt faster).