A steep-sided valley formed by a waterfall as it retreats.

A steep-sided valley formed by a waterfall as it retreats.

• A. Levees
• B. Flood Plain
• C. Meander
• D. Gorge

Answer: (D)

A steep-sided valley formed by a waterfall as it retreats is called a gorge. This happens when a river erodes vertically at a waterfall, undercutting the rock and causing the rock above to collapse. As the waterfall wears back upstream, the exposed valley becomes narrow and deep with very steep sides—the gorge. The key idea is that the shape and formation come from headward erosion driven by the waterfall retreat. Levees are raised banks formed by sediment deposited during floods, not by waterfall retreat. A flood plain is the broad flat area built up by repeated flooding, rather than a steep valley. A meander is a winding bend formed by lateral erosion on the outer banks of curves, not a steep, narrow valley created by a retreating waterfall.

A steep-sided valley formed by a waterfall as it retreats is called a gorge. This happens when a river erodes vertically at a waterfall, undercutting the rock and causing the rock above to collapse. As the waterfall wears back upstream, the exposed valley becomes narrow and deep with very steep sides—the gorge. The key idea is that the shape and formation come from headward erosion driven by the waterfall retreat.

Levees are raised banks formed by sediment deposited during floods, not by waterfall retreat. A flood plain is the broad flat area built up by repeated flooding, rather than a steep valley. A meander is a winding bend formed by lateral erosion on the outer banks of curves, not a steep, narrow valley created by a retreating waterfall.