Question

Which landform is typically created by the erosional action of rivers over geological time scales?

• A. Moraine
• B. Mesa
• C. Delta
• D. Fjord

Hint:

• Rivers cause erosion (e.g., V-shaped valleys, canyons), transport sediment, and deposit sediment (e.g., floodplains, deltas).
• A delta is a depositional landform at the mouth of a river, formed from sediment eroded and transported by the river from its drainage basin.
• Moraines are glacial deposits.
• Mesas are erosional remnants in arid regions, shaped by various erosional agents.
• Fjords are glacially eroded valleys drowned by the sea.
• While a delta is depositional, its existence is a direct consequence of extensive river erosion upstream.

Answer 1

The Correct Option is B

A mesa is a landform typically created by the erosional action of rivers over geological time scales. This process involves the wearing away of rock layers through hydraulic action, abrasion, and the transportation of sediment, eventually resulting in a flat-topped, steep-sided structure. Below is an explanation of why a mesa is the correct answer relative to the options provided:

• Moraine: Formed by the accumulation of glacial debris (till) and is not related to river erosion but rather to glacial action.
• Delta: Created by the deposition of sediment at the mouth of a river, where it slows and enters a standing body of water like an ocean or a lake. It is not a result of erosion but deposition.
• Fjord: A deep, glacially carved valley flooded by rising sea levels. It is formed by glacial activity and not directly by river erosion.
• Mesa: Erosion of soft rock layers beneath a more resistant caprock leads to the mesa's characteristic flat top and steep sides, commonly seen in arid environments where river and wind erosion dominate over time.

Thus, a mesa is directly attributable to the erosional action of rivers, making it the correct answer.