The unsorted rock debris carried and deposited by a glacier is called:

Moraine is the unsorted mixture of rock fragments, boulders, gravel, sand and clay carried and deposited directly by a glacier. The material itself is also called glacial till.

How moraines form:

• As a glacier moves, it plucks and scrapes rock from the valley floor and sides, and also collects rocks that fall onto it from the slopes above.
• This debris is carried within, on top of and beneath the ice.
• When the ice melts, the debris is dropped, forming ridges and mounds of moraine.
• Because the ice drops material of all sizes together, moraine is unsorted and unlayered, unlike river deposits.

Types of moraines:

• Lateral moraine: ridges of debris deposited along the sides of a glacier.
• Medial moraine: formed down the middle of a glacier when two glaciers meet and their lateral moraines join.
• Terminal (end) moraine: a ridge marking the farthest point reached by a glacier, at its snout.
• Recessional moraine: ridges left behind as the glacier retreats and pauses.
• Ground moraine: a sheet of debris spread beneath the glacier over the valley floor.

Moraine-dammed lakes:

• Terminal moraines can block valleys, holding back meltwater to form lakes.
• If such a moraine dam breaks, it can cause a sudden, destructive flood called a glacial lake outburst flood (GLOF).
• Many such lakes exist in the Himalayas, and their monitoring is important for disaster management.

Other glacial deposits:

• Drumlins: oval hills of till.
• Eskers: winding ridges of sorted sand and gravel deposited by meltwater streams.
• Outwash plains: sorted sand and gravel spread in front of the glacier by meltwater.
• Erratics: large boulders carried far from their place of origin.

Why not the other options?

• ✗Loess is fine, wind-blown dust deposited in thick layers, as in northern China.
• ✗Alluvium is material deposited by rivers.
• ✗Scree (talus) is broken rock that collects at the foot of cliffs because of weathering.