Glacial Landforms of Deposition (Moraines)

Definition of Moraines

Moraines are landforms created by the deposition of material (called till) directly from a glacier. Till is an unsorted mixture of clay, sand, gravel, and boulders transported by the ice. When the glacier melts or retreats, this material is left behind, forming moraines.

There are four main types of moraines:

• Lateral moraines: Ridges of till deposited along the sides of a glacier.
• Medial moraines: Ridges of till formed where two glaciers meet and their lateral moraines join.
• Terminal moraines: Ridges of till deposited at the furthest point reached by the glacier, marking its maximum advance.
• Ground moraines: Sheets or layers of till deposited beneath the glacier as it moves.

Formation Processes

Moraines form from material carried by glaciers. As glaciers move downhill, they pick up rocks and soil from the valley floor and sides. This material is transported within the ice, on top, or at the base of the glacier.

When the glacier melts or slows down, it loses the energy needed to carry this load, so the material is deposited. The location of deposition depends on the glacier’s movement:

• At the edges, material accumulates as lateral moraines.
• Where two glaciers merge, their side moraines combine to form medial moraines.
• At the glacier’s snout (terminus), material builds up as terminal moraines.
• Material deposited beneath the glacier forms ground moraines.

The shape and size of moraines depend on the volume of material carried and the glacier’s speed and melting rate.

Types of Moraines

Lateral Moraines

Lateral moraines are ridges of till found along the sides of a glacier. They form as the glacier erodes the valley sides, and debris falls onto the ice. This debris is carried along the glacier’s edges and deposited when the ice melts.

They often appear as long, linear mounds running parallel to the valley sides.

Medial Moraines

When two glaciers meet, their adjacent lateral moraines join and are carried along the centre of the combined glacier. This creates a medial moraine, a ridge of debris running down the middle of the glacier.

Medial moraines are visible as dark lines of rock and sediment on the glacier surface.

Terminal Moraines

Terminal moraines mark the furthest advance of a glacier. They form when the glacier’s snout remains in one place for a period, depositing material pushed forward by the ice.

These moraines often form curved ridges across valleys and can dam meltwater, creating lakes.

Ground Moraines

Ground moraines are widespread sheets of till deposited beneath the glacier. As the ice melts, this material is left as a gently rolling or flat landscape.

Ground moraines are less obvious than other moraines but cover large areas, often forming fertile soils.

Learning example: For instance, lateral moraines can be seen as ridges along the sides of a glacier valley, while terminal moraines form prominent ridges at the valley mouth.

Examples of Moraines in the UK

The UK’s glacial landscapes provide excellent examples of moraines formed during the last Ice Age (the Devensian glaciation, which ended around 10,000 years ago).

Lake District Moraines

The Lake District contains many well-preserved moraines. For example, terminal moraines can be found at the end of glacial valleys like Borrowdale. These ridges mark the maximum extent of glaciers that once filled the valleys.

Lateral moraines are visible along valley sides, showing where glaciers once flowed.

Scottish Highlands

In the Scottish Highlands, moraines are common in glaciated valleys such as Glen Coe. Terminal moraines here form ridges that trap water, creating ribbon lakes.

Ground moraines cover large upland areas, creating gently rolling landscapes with fertile soils.

Snowdonia Moraines

Snowdonia in Wales features many moraines, especially lateral and terminal types. For example, the Nant Ffrancon valley shows clear lateral moraines along its sides and terminal moraines at its mouth.

These moraines are important for understanding the extent and movement of Welsh glaciers during the Ice Age.