🟧 SECTION 4: GORGE FORMATION

What is a gorge?

A gorge is a deep, narrow valley with steep sides.

In waterfall formation, a gorge can develop as a waterfall retreats upstream through repeated erosion and rock collapse.

How does a gorge form behind a retreating waterfall?

A gorge develops as the waterfall gradually retreats upstream.

The process is as follows:

1. Water erodes the rock at the base of the waterfall.

2. Softer rock is removed more quickly.

3. The harder rock becomes undercut.

4. The overhanging rock collapses.

5. The waterfall moves upstream.

6. The process repeats.

7. A long, steep-sided gorge is left behind.

Key idea: The retreating waterfall leaves a gorge behind it.

Why does a gorge have steep sides?

A gorge develops through repeated erosion and collapse associated with the retreating waterfall.

These processes remove rock from the river channel and leave a deep, narrow valley with steep sides.

What is the difference between a waterfall and a gorge?

Waterfall:

• A place where water flows over a steep drop.

• Can retreat upstream through erosion.

Gorge:

• A deep, narrow valley with steep sides.

• Can develop behind a retreating waterfall.

Remember: The waterfall retreats; the gorge is the valley left behind.

What is the difference between waterfall retreat and headward erosion?

Waterfall retreat describes the backward movement of a waterfall upstream.

Headward erosion describes erosion that extends a river channel or valley backwards towards its source.

The terms are closely connected because waterfall retreat occurs through erosion that extends the channel upstream.