River Landforms: Upper Course

The upper course of a river is characterised by steep gradients, turbulent flow, and the dominance of vertical erosion. This creates distinctive landforms including V-shaped valleys, interlocking spurs, waterfalls, and gorges. This lesson examines how each of these landforms is created, with detailed UK examples.

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V-Shaped Valleys

The most characteristic landform of a river's upper course is the V-shaped valley. When viewed in cross-section, the valley has steep sides and a narrow floor, forming a distinctive "V" shape.

How a V-Shaped Valley Forms

1. In the upper course, the river has a steep gradient and relatively low discharge.
2. The steep gradient gives the river high potential energy, which is used for vertical erosion — the river erodes downwards into the bedrock.
3. Hydraulic action and abrasion are the main erosion processes. The river uses rocks and boulders on its bed to scrape and deepen the channel.
4. As the river cuts down, the valley sides above the water level are left exposed.
5. Weathering (especially freeze-thaw in upland areas) breaks down the exposed rock on the valley sides.
6. Mass movement (soil creep, slides, rockfalls) moves the weathered material downslope towards the river.
7. The river then removes this material through erosion and transport.
8. This combination of vertical erosion (by the river) and sub-aerial processes (on the valley sides) creates the steep-sided, narrow V-shaped valley.

Process	Location	Effect
Vertical erosion	River bed	Deepens the channel
Freeze-thaw weathering	Valley sides (exposed rock)	Breaks rock into fragments
Mass movement	Valley sides	Moves fragments towards the river
Transport by river	River channel	Removes material, maintaining steep valley sides

Exam Tip: A common exam mistake is to say the river itself creates the V shape. In fact, the river only erodes vertically (downwards). The V shape is created by weathering and mass movement on the valley sides. Make sure you explain both sets of processes.

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Interlocking Spurs

As the river winds its way through its upper course, it does not have enough energy to erode laterally (sideways). Instead, it flows around obstacles — ridges of hard rock that jut out into the valley from alternate sides. These ridges are called interlocking spurs.

How Interlocking Spurs Form

1. In the upper course, the river follows the path of least resistance, winding around areas of harder rock.
2. The river does not have enough energy for lateral erosion, so it cannot cut through these ridges.
3. Instead, the river weaves between them, creating a pattern where spurs from one side of the valley interlock with spurs from the other — like interlocking fingers.
4. When viewed from above or from the valley floor, the spurs appear to overlap.

As the river gains more energy further downstream (with increased discharge from tributaries), it may begin to erode laterally and eventually truncate (cut through) these spurs, creating truncated spurs — a feature more commonly associated with glaciated valleys, but also found in river valleys.

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Waterfalls

Waterfalls are one of the most dramatic landforms in the upper course of a river. They form where a river flows over a band of hard rock underlain by softer rock.

How a Waterfall Forms

graph TD
    A["River flows over a band<br/>of HARD rock overlying<br/>SOFT rock"] --> B["Softer rock is eroded<br/>faster by hydraulic action<br/>and abrasion"]
    B --> C["The soft rock is<br/>undercut, creating an<br/>OVERHANG of hard rock"]
    C --> D["Water plunges over<br/>the overhang into a<br/>PLUNGE POOL below"]
    D --> E["The plunge pool is<br/>deepened by abrasion<br/>and hydraulic action"]
    E --> F["The overhang becomes<br/>unsupported and<br/>eventually COLLAPSES"]
    F --> G["The waterfall RETREATS<br/>upstream, leaving a<br/>steep-sided GORGE"]
    G --> A

Step-by-step process:

1. The river flows over a layer of resistant (hard) rock which overlies a layer of less resistant (soft) rock. This might be a horizontal band of hard rock on top of soft rock, or a near-vertical boundary between the two.
2. The soft rock is eroded more quickly than the hard rock by hydraulic action and abrasion.
3. The soft rock is undercut, creating an overhang (or ledge) of hard rock.
4. Water cascades over the overhang and crashes into the pool below — the plunge pool.
5. The plunge pool is deepened and widened by the force of the falling water, abrasion (rocks swirling in the pool), and hydraulic action.
6. Over time, the overhang becomes unsupported and eventually collapses under its own weight.
7. The collapsed material falls into the plunge pool and is used as ammunition for further abrasion.
8. The waterfall has now moved upstream — this process of headward retreat continues over thousands of years.
9. As the waterfall retreats, it leaves behind a steep-sided, narrow gorge — the remnant of the valley that once existed below the waterfall.

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UK Case Study: High Force, River Tees

High Force on the River Tees in County Durham is one of England's most spectacular waterfalls and a textbook example of waterfall formation.

Feature	Detail
Height	21 m (one of the highest waterfalls in England)
Rock type (hard)	Whin Sill — a layer of dolerite (a hard, dark, igneous rock) that was intruded as a horizontal sheet approximately 295 million years ago
Rock type (soft)	Carboniferous limestone, sandstone, and shale beneath the dolerite
Plunge pool	A deep plunge pool at the base where the force of the water and abrasion have carved into the softer rock
Gorge	The waterfall has retreated upstream over thousands of years, leaving a gorge approximately 700 m long downstream
Process	The softer limestone and shale beneath the dolerite are undercut; the dolerite overhang becomes unsupported and collapses; the waterfall retreats upstream
Location	Upper Teesdale, County Durham, within the North Pennines AONB

Other UK Waterfall Examples