🟦 SECTION 1: UNDERSTANDING WATERFALLS

What is a waterfall?

A waterfall is a feature where river water flows over a steep drop in the riverbed.

Waterfalls are associated with the youth stage of a river, where the gradient is steep and vertical erosion is important.

Remember: Waterfalls are associated with the upper course of a river.

What is waterfall formation?

Waterfall formation is the process through which a waterfall develops as a result of erosion and differences in the resistance of rock.

Where harder rock and softer rock occur together, the softer rock can be eroded more quickly. This can create a steep drop in the riverbed.

Key terms:

• Hard rock.

• Soft rock.

• Erosion.

• Plunge pool.

• Overhang.

• Waterfall retreat.

What is the difference between hard rock and soft rock in waterfall formation?

Hard rock:

• Is more resistant to erosion.

• Erodes more slowly.

• Can remain projecting above softer rock.

Soft rock:

• Is less resistant to erosion.

• Erodes more quickly.

• Can become undercut beneath harder rock.

Why does this matter?

The difference in erosion rates can create a waterfall and contribute to its retreat upstream.

does soft rock erode more quickly than hard rock?

Soft rock is less resistant to erosion than hard rock.

As water flows over the rocks, the softer rock is worn away more quickly, while the harder rock remains for longer.

This difference can produce an uneven riverbed and create a waterfall.

Application: If a river flows over softer rock beneath harder rock, the softer rock may become eroded first, leaving the harder rock projecting outward.