UK Landscape Case Studies: Geomorphic Processes and Landforms

Coastal Case Study: The Jurassic Coast

Imagine walking through 185 million years of Earth's history in just $155\text{ km}$. The Jurassic Coast stretches from East Devon to Dorset, featuring Triassic sandstone, Jurassic clays, and Cretaceous chalk.

• A concordant coastline has rock bands running parallel to the sea. It does not have alternating headlands and bays (e.g., Lulworth Cove, where the sea breached hard Portland Limestone to hollow out softer clays behind).
• A discordant coastline has rock bands running perpendicular to the sea, allowing differential erosion to create headlands and bays (e.g., Swanage Bay).

How Old Harry Rocks (a stack) formed:

1. Destructive waves exploit faults in the chalk headland.
2. Hydraulic action and abrasion enlarge the faults into caves.
3. The caves break through the headland to form an arch.
4. Sub-aerial weathering weakens the arch roof until it collapses under gravity, leaving an isolated pillar called a stack (Old Harry).
5. The base of the stack is undercut by waves until it collapses into a stump (Old Harry's Wife, which collapsed in 1896).

River Case Study: The River Wye

Starting high in the Welsh mountains and ending in the Severn Estuary, a river changes its entire physical character as it flows downhill. The River Wye is $210\text{ km}$ long, descending $700\text{ m}$ from its source in the Cambrian Mountains.

• Upper Course: Features hard, impermeable shale. Vertical erosion creates V-shaped valleys and waterfalls.
• Middle Course: Features softer mudstones. Lateral erosion creates wide floodplains and meanders.
• Lower Course: The river cuts through Carboniferous Limestone to form the $120\text{ m}$ deep Symonds Yat gorge.

How Cleddon Falls (a waterfall) formed:

1. The river flows over a layer of hard rock that sits on top of softer rock.
2. The soft rock is eroded more quickly by hydraulic action and abrasion, creating a step.
3. Continuous undercutting leaves a hard rock overhang and creates a deep plunge pool at the base.
4. The overhang loses support and collapses; the waterfall retreats upstream leaving a steep-sided gorge.

How the Glasbury Oxbow Lake formed:

1. The thalweg (fastest current) swings to the outside bend of a meander, eroding the river cliff.
2. Slower water on the inside bend deposits sediment to form a slip-off slope.
3. Continuous erosion narrows the neck of the meander.
4. During a high-energy flood event, the river cuts straight through the narrow neck.
5. Deposition seals off the old loop, leaving an isolated oxbow lake (this happened at Glasbury in January 2005).

Estuary Landforms of the River Wye

Where a freshwater river meets the salty sea, a unique chemical reaction builds entirely new land. At the Severn Estuary near Chepstow, the Wye forms extensive mudflats and salt marshes.

• As freshwater meets saltwater, fine clay particles clump together in a process called flocculation.
• These larger, heavier particles sink and are deposited in the low-energy estuary waters, forming mudflats.
• Pioneer plant species known as halophytes (like glasswort) colonize the mud. They trap more sediment, raising the land level so other species can grow, eventually forming a stable salt marsh that acts as a natural carbon sink.

Analysing Human and Physical Interactions

Human attempts to control nature often create a domino effect, where altering one physical process dramatically changes the landscape character.

• Coastal Management at Swanage: To protect the town from erosion, humans installed 18 timber groynes in 2005-06. These groynes interrupt longshore drift (a physical process), trapping sediment to build a wider beach. This human-induced wider beach absorbs wave energy, reducing hydraulic action at the cliff base and slowing the natural rate of retreat.
• River Management in the Wye Basin: Agriculture dominates 90% of the basin, contributing up to 74% of phosphate pollution. To combat flood risks to over 9000 properties, humans use afforestation (tree planting). Trees increase interception and infiltration (physical processes), which reduces surface runoff. This has been shown to reduce flood heights by 20%, decreasing the river's erosive power and altering floodplain formation.

Calculating Coastal Change

Geographers use formulas to quantify how quickly a landscape is changing.

Worked Example A section of a discordant coastline retreated by 48 m between 1944 and 2024. Calculate the mean rate of retreat.

Step 1: Identify the values.

• $\text{Total Distance} = 48\text{ m}$
• $\text{Total Time} = 2024 - 1944 = 80\text{ years}$

Step 2: Substitute into the equation.

• $\text{Mean Rate of Retreat} = \frac{48}{80}$

Step 3: Calculate and state units.

• $\text{Mean Rate of Retreat} = 0.60\text{ m/year}$