Rivers are powerful forces that shape our landscapes. They start as small streams high up in the mountains and gradually grow as they flow downhill to the sea. Along the way, they create amazing landforms through the processes of erosion, transportation and deposition. In this guide, we'll focus on how rivers work and the special features they create in their upper course (the part closest to the source).
Key Definitions:
Rivers are part of the water cycle. Rain falls on high ground, flows downhill in small streams that join together to form larger rivers. The upper course of a river is steep and fast-flowing, with lots of energy for erosion. As rivers flow downstream, they gradually lose height and energy, changing how they shape the landscape.
A river's ability to erode and transport material depends on its energy. This energy comes from:
Rivers shape the landscape through three main processes: erosion, transportation and deposition. In the upper course, erosion is the most important process due to the river's high energy.
Rivers erode the landscape in four main ways:
This is the force of water hitting the river banks and bed. Fast-flowing water forces its way into cracks in the rock, compressing air which can create a mini-explosion effect, breaking off pieces of rock. This is the most powerful type of erosion in the upper course.
Also called corrasion, this is when rocks and pebbles carried by the river scrape against the bed and banks, wearing them away like sandpaper. It's like the river using the rocks it carries as tools to carve the landscape.
This is when rocks being carried by the river knock against each other, gradually becoming smaller and smoother. This doesn't directly erode the landscape but creates the rounded pebbles often found in rivers.
Also called corrosion, this is when river water dissolves soluble rocks like limestone. Slightly acidic rainwater can dissolve minerals in the rock, carrying them away in solution. This is especially important in areas with limestone bedrock.
Rivers transport eroded material in four ways, depending on the size of the particles and the energy of the river:
Large, heavy materials (like boulders) are rolled along the riverbed.
Pebbles and small stones bounce along the riverbed in a hopping motion.
Small particles like silt and clay are carried within the flow of the water.
Dissolved minerals are carried invisibly in the water.
The upper course of a river creates several distinctive landforms through erosion processes. Let's explore the main ones:
One of the most recognisable features of the upper course is the V-shaped valley. These form through a combination of river erosion and weathering of the valley sides.
1. The river cuts downwards (vertical erosion) using hydraulic action and abrasion
2. As the river cuts down, it creates steep valley sides
3. These steep sides are weathered by rain, frost and gravity
4. Material falls into the river and is carried away
5. Over time, this creates the distinctive V-shape
Waterfalls are spectacular features where a river falls vertically from a height. They often lead to the formation of gorges - deep, narrow valleys with steep sides.
1. Rivers flow over alternating bands of hard rock (resistant) and soft rock (less resistant)
2. The soft rock erodes faster than the hard rock, creating a step in the river
3. Water plunges over the step, increasing erosion at the base through hydraulic action
4. This creates a plunge pool at the base of the waterfall
5. The hard rock is undercut and eventually collapses
6. This process repeats, causing the waterfall to gradually retreat upstream
1. As a waterfall retreats upstream, it leaves behind a steep-sided valley
2. This deep, narrow channel is called a gorge
3. Gorges have very steep, almost vertical sides
4. They're formed by the intense vertical erosion of the river
5. Over time, they may widen through weathering and mass movement
High Force on the River Tees in northern England is one of the UK's most impressive waterfalls. It formed where the river flows over a hard band of dolerite (called the Whin Sill) which overlies softer limestone and sandstone rocks. The waterfall is about 21 metres high and continues to retreat upstream as the softer rock beneath the dolerite is eroded, eventually causing the hard rock to collapse. Downstream from High Force is a spectacular gorge that has been created by this process of waterfall retreat over thousands of years.
In the upper course, rivers often flow through landscapes with interlocking spurs - ridges of land that extend into the valley from alternate sides, creating a zig-zag pattern.
1. In upland areas, rivers don't have enough energy to erode sideways
2. They take the easiest route downhill, winding around higher ground
3. This creates a series of ridges (spurs) that project into the valley
4. These spurs 'interlock' like fingers from opposite hands
5. From above, the river appears to snake between these projections
Interlocking spurs are important because:
Rapids are sections of fast-flowing, turbulent water caused by a steeper gradient or by large boulders in the river channel. They're common in the upper course where the river flows over bands of resistant rock. The intense erosion in rapids can create potholes - circular holes in the riverbed formed when stones are swirled around by the current, gradually drilling into the rock. The Strid on the River Wharfe in Yorkshire is a famous example where the river narrows dramatically, creating powerful rapids that have eroded deep potholes, making it one of the most dangerous stretches of water in Britain.
As a river flows from source to mouth, its characteristics change. The upper course features we've explored are just the beginning of the river's journey.
The long profile of a river shows how its gradient changes from source to mouth. In the upper course, the gradient is steep, giving the river high energy for vertical erosion. This creates deep, narrow features like V-shaped valleys, waterfalls and gorges. As the river moves into its middle and lower courses, the gradient becomes gentler and different processes and landforms become dominant.
In the upper course:
The upper course of a river is characterised by high energy, steep gradients and dominant erosion processes. This creates distinctive landforms including:
These features are the result of the four erosion processes (hydraulic action, abrasion, attrition and solution) and show how powerful rivers can be in shaping our landscapes, especially in their upper course where energy is highest.
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