1. Weathering & Mass Movement

Before we even talk about the river itself, we need to understand what shapes the valley around it. Two different sets of processes are at work in a river landscape, and it's easy to mix them up:

The Three Types of Weathering

• Physical weathering — rock is broken into smaller pieces by temperature changes. The classic example is freeze-thaw weathering: rainwater seeps into a crack, freezes overnight and expands (ice takes up about 9% more space than water), which widens the crack. Repeat this enough times and the rock eventually splits apart.
• Chemical weathering — rocks dissolve or disintegrate when they react with slightly acidic rainwater (rain is naturally slightly acidic because it absorbs CO₂ from the air).
• Biological weathering — plant roots grow into cracks and physically prise the rock apart as they get thicker.

Mass Movement

Once weathering has loosened material, gravity takes over and moves it downslope towards the river. There are two types you need to know for river valleys:

• Slumping — happens when the river erodes and undercuts the base of a slope. This is common where a softer, less resistant rock lies underneath a harder, heavier one — the soft layer gives way and a large chunk of material slides down in one go, often leaving a curved scar.
• Soil creep — a much slower process where gravity causes individual weathered particles to inch their way down the slope over a long period of time.

Factors Affecting Weathering & Mass Movement

2. The Process of Erosion

Here's a fact that surprises most students: a river spends about 95% of its energy just overcoming friction with its own bed and banks. Only the small amount left over is available for erosion and transportation. This is why the upper course of a river — which is shallow, narrow, and full of large rocks — has so much friction that very little energy is left for erosion, even though the water is often turbulent-looking.

The Four Erosion Processes

Vertical vs. Lateral Erosion

This distinction is crucial for understanding why river valleys look so different upstream versus downstream:

• Vertical erosion — dominant in the upper course. The river erodes downwards, deepening the river and valley. This is why upper courses have steep V-shaped valleys.
• Lateral erosion — dominant in the middle and lower course. The river erodes sideways, widening the river and valley. This is why meanders form further downstream.

3. Transportation & Deposition

Once material has been eroded, the river has to carry it somewhere. How it carries each piece depends entirely on how heavy that piece is.

The Four Transportation Processes

Deposition

Deposition is simply what happens when a river runs out of energy to keep carrying its load — so it drops it. This can be caused by:

• Reduced discharge (less rainfall, or water being taken out upstream — "abstraction")
• A decrease in the gradient (the river slows down as the slope flattens)
• Slower flow on the inside of a river bend
• The river entering a sea, lake, or ocean, where it suddenly loses all its forward momentum

4. Changes in River Characteristics

Every river changes shape from source to mouth. Geographers describe this using two different types of profile — don't get them confused, because they show completely different things.

The Long Profile

The long profile shows how the river's gradient (steepness) changes as you travel along its entire length, from source to mouth. Most rivers have a concave long profile — think of the curved inside of a bowl, laid on its side:

• Upper course: steep, uneven surface, close to the source (usually in an upland area)
• Middle course: gradient decreases noticeably
• Lower course: gradient decreases even further, almost flat by the mouth

Cross Profiles

A cross profile is completely different — it's a slice straight across the river valley from one bank to the other, at one particular point along the river. It shows you the shape of the channel and valley at that spot.

5. Case Study: The River Tees

You need a real named example for the exam — the River Tees in North-East England is the go-to case study because it shows every stage of a river's journey in one place.

Upper Course

• Land use: moorland with peat soil, mainly used for sheep grazing
• Climate: over 2,000mm average annual rainfall
• Geology: mostly limestone and sandstone
• Channel: narrow, shallow, large angular bedload, high friction, dominated by vertical erosion, steep gradient
• Landforms: High Force waterfall — formed where hard rock (dolerite, also called whinstone) overlies softer rock (limestone and sandstone); a steep-sided gorge left behind as the waterfall retreats upstream; rapids; V-shaped valleys; interlocking spurs
• Human activity: several dams and reservoirs (e.g. Cow Green) supply water to urban areas and help control discharge downstream

Middle Course

• Land use: mainly farmland as the valley widens; settlements like Barnard Castle increase in size
• Climate: rainfall drops to around 1,000mm
• Geology: still limestone and sandstone
• Channel: wider and deeper, gentler gradient, smaller/rounder bedload, decreasing friction, dominated by lateral erosion
• Landforms: meanders, which develop due to increased lateral erosion

Lower Course

• Land use: arable farming, large settlements (Middlesbrough, Stockton-on-Tees), industrial areas
• Climate: rainfall drops further to around 773mm
• Channel: widest and deepest, very gentle gradient, small sediment, dominated by lateral erosion then deposition near the tidal mouth
• Landforms: large meanders, ox-bow lakes, levees, floodplains
• Human activity: flood prevention schemes in Yarm; the Tees Barrage (prevents flooding at high tides); river straightening downstream of Stockton for navigation; the Mandale Loop — a meander that was artificially cut off to shorten shipping routes by 4km; industrial developments on the floodplain near the estuary

6. Upland Landforms

In the upper course, vertical erosion dominates. This produces a distinctive set of dramatic, steep-sided landforms.

Waterfalls and Gorges

This is one of the most commonly examined landform formations, so it's worth learning the sequence of steps precisely.

1. A waterfall forms where there is a drop in the riverbed — usually because a band of hard rock overlies softer rock.
2. Hydraulic action and abrasion erode the softer rock much faster than the hard rock above it.
3. This undercuts the hard rock, creating a hollow beneath it called a plunge pool.
4. The hard rock is left jutting out unsupported — this is called an overhang.
5. Eventually, gravity causes the overhang to collapse into the plunge pool below.
6. The fallen rocks increase abrasion in the plunge pool, making it even deeper.
7. This whole process repeats over and over, causing the waterfall to retreat upstream — and it leaves behind a steep-sided gorge where the waterfall used to be.

V-Shaped Valleys

Since vertical erosion is dominant in the upper course, the river cuts down into its bed, deepening the channel. But it's not the river alone that creates the "V" shape — weathering and mass movement attack the valley sides above the river, causing loosened material to collapse and slide down into the channel. The combination of the river cutting down and the valley sides collapsing inward produces the classic steep V-shaped valley.

Interlocking Spurs

In the upper course, the river channel already starts to meander slightly around high points of land. Because the valley sides are so steep and the river doesn't have enough lateral erosive power yet to cut straight through these high points, it has to wind around them instead. Viewed from above, the ridges of land on alternating sides appear to "interlock" like the teeth of a zip — these are interlocking spurs.

7. Lowland Landforms

Further downstream, lateral erosion and deposition take over as the dominant processes, creating wide, gentle, flat landscapes rather than dramatic drops.

Meanders

A meander is a bend in the river. It forms because water doesn't flow at the same speed everywhere across the channel — this is the key insight that explains almost everything about meanders.

• On the outside of a bend, the water flows fastest (this fastest-flow line is called the thalweg). This high energy causes erosion, which undercuts the bank and forms a steep river cliff. Over time the bank collapses and the meander's edge migrates further outward.
• On the inside of a bend, the water flows slowest. With less energy, the river can't carry its load anymore, so deposition occurs here, building up a gentle slip-off slope.

Because one side erodes while the other deposits, the entire meander gradually migrates sideways and downstream across the valley over time — and this migration is exactly what carves out the wide, flat floodplain either side of a lowland river.

Ox-Bow Lakes

As meanders grow larger and larger downstream, this can lead to a dramatic landform in four clear stages:

1. Continued erosion on the outside bends of a large meander narrows the strip of land between two loops — this narrow strip is called the meander neck.
2. During a flood (when the river has extra energy and can rise above its normal channel), the river cuts straight through the neck, creating a new, shorter, straighter course.
3. Water flow entering and leaving the old meander loop is now much slower, so deposition occurs at both the entrance and exit points.
4. This deposition eventually seals off the old loop entirely from the main channel, leaving behind a curved, standalone lake — the ox-bow lake.

Floodplains & Levees

Floodplains and levees are closely linked, and they form together during flood events:

1. The floodplain — a wide, flat area of land either side of the river — is initially created by meanders migrating back and forth across the valley over long periods of time.
2. During a period of high discharge, the river overflows its banks (floods).
3. As floodwater spreads out across the floodplain, much more of it comes into contact with the land surface, which massively increases friction and reduces velocity.
4. With less energy, the river deposits its load right across the floodplain, gradually building up its height and fertility over many floods (this is why floodplains make excellent farmland).
5. The heaviest material is always deposited first, closest to the river channel — over repeated floods, this builds up raised, natural embankments called levees, which grow taller with each flood event.

What to Memorise

Concepts Checklist

Tick off each concept once you can explain it without looking back at your notes.

• I can explain the difference between weathering and erosion
• I can describe the three types of weathering, with an example of each
• I can explain slumping and soil creep, and how they differ
• I can list factors affecting weathering and mass movement
• I know why a river uses ~95% of its energy on friction
• I can name and explain all four erosion processes
• I understand the difference between vertical and lateral erosion
• I can name and explain all four transportation processes
• I can explain what causes deposition and what order material is deposited in
• I can describe the shape of a long profile and explain why it's concave
• I can compare the cross profiles of the upper, middle and lower course
• I can give key facts about the River Tees case study
• I can describe the formation of a waterfall step-by-step
• I can explain how a V-shaped valley forms
• I can explain how interlocking spurs form
• I can explain how a meander forms, including erosion and deposition patterns
• I can describe the four stages of ox-bow lake formation
• I can explain how floodplains and levees form together during a flood

Exam Tips & Common Mistakes