Question

How do erosion and deposition work together to form sand dunes?

Waves cause erosion along coastlines and deposit sand away from the shore.
Erosion occurs as surface water carries sediment and the sediment is deposited near oceans and lakes.
Glaciers cause erosion through the movement of large chunks of ice, which are deposited and form depressions.
Erosion occurs through deflation, and sand that was picked up is deposited against an obstruction.

Answer 1

Correct answer: 4.

Why: Sand dunes form mainly by wind action. Wind erosion (deflation) lifts and removes loose sand particles; most sand moves by saltation (short hops) and surface creep. When the wind slows, or when it encounters an obstruction (vegetation, rocks, a fence, a rise in the ground), it loses the carrying capacity and the sand is deposited. Continued pickup and redeposition builds the pile into a dune. Vegetation, moisture, and wind direction/strength control dune shape and stability.

Why the other choices are wrong or incomplete:
- 1: Waves do erode and move sand on coasts, but dunes themselves are shaped by wind moving sand inland from the beach, not by waves depositing sand “away from the shore.”
- 2: Surface water deposition near oceans/lakes describes deltas and floodplain deposition, not dune formation.
- 3: Glaciers create landforms (moraines, kettles), not typical sand dunes.