3.3.2 Fluvial Landforms - Caused by Erosion

Waterfalls

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Formation: Development:

As water goes over the step, it erodes more of the softer rock.
A steep drop is eventually created, called a waterfall.
Hard rock is eventually undercut by erosion, becoming unsupported and collapsing.
Collapsed rocks are swirled around at the foot of the waterfall, eroding the softer rock by abrasion and creating a deep plunge pool.
Over time, more undercutting causes more collapses. The waterfall retreats, leaving behind a steep-sided gorge.

Location: In the upper course of a river, most erosion is vertical, creating steep valley sides.
Characteristics:
Rivers aren't powerful enough to erode laterally (sideways), so they wind around high hillsides that stick out into their paths.
The hillsides that interlock with each other like a zip as the river winds around them are called interlocking spurs.

Interlocking Spurs

Meanders

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When a river is eroding and depositing material, meanders and oxbow lakes can form.

Meanders: Large bends in rivers that develop in their middle and lower courses.

Faster Current:
- Occurs on the outside of the bend.
- River channel is deeper (less friction to slow it down).
- More erosion takes place on the outside of the bend, forming river cliffs.

Formation of Meanders

Slower Current:
- Occurs on the inside of the bend.
- River channel is shallower (more friction to slow it down).
- Eroded material is deposited on the inside of the bend, forming slip-off slopes.
Thalweg
- The fastest flow of a river through a meander.

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Meanders get larger over time and can eventually turn into an oxbow lake.

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Meander Process 1

Meander Process 2

Meander Process 3