Colluvium: Deposition at Cliff Bases

The question asks to identify the term for unconsolidated rock material deposited by surface wash specifically at the base of a cliff.

Defining Colluvium

• Colluvium refers to loose, unconsolidated sediments that accumulate at the base of slopes or cliffs.
• This deposition occurs primarily due to gravity (mass wasting) and surface runoff or wash, which transport material downslope.
• The description directly matches the definition of colluvium.

Analyzing Other Options

• Alluvium: This is sediment deposited by flowing water, typically in river channels, floodplains, or deltas. It's not specific to cliff bases or deposition by simple surface wash from a cliff face.
• Moraines: These are deposits formed directly by glacial ice, characterized by specific landforms and till composition, unrelated to surface wash at a cliff base.
• Silt: This describes a particle size (sediment grade) between sand and clay. While silt can be a component of colluvium, it is not the term for the deposit itself.

Therefore, colluvium is the correct term for the described deposit.