Glacial Deposition (Till & Moraines)

Glacial Deposition Overview

Glacial deposition is the process where glaciers drop or leave behind the material they have been carrying. This material, called sediment, is deposited as the glacier melts or loses energy. Deposition happens because glaciers can only carry so much material, and when they slow down or melt, they drop this load.

The main difference between erosion and deposition is that erosion involves the glacier picking up and removing material from the landscape, while deposition is about the glacier dropping or depositing material it has transported.

Glacial deposition shapes the landscape by leaving behind various sediments and landforms, which are important features in the UK's glacial landscapes.

For instance, if a glacier deposits a mixture of clay, sand, and boulders all mixed together, this is till. It is different from river deposits, which are sorted by size because flowing water separates materials by weight.

Till Characteristics

Till is the unsorted material directly deposited by a glacier. It is sometimes called glacial till or boulder clay. Till is made up of a mixture of clay, sand, gravel, and boulders all jumbled together without any layering or sorting.

Because till is deposited directly by ice, it is unsorted and unstratified. This means the particles vary widely in size and are mixed randomly. The texture is often dense and compact because the ice presses down on the sediment.

Till is deposited beneath the glacier or at its snout (end) as the ice melts. It forms a blanket of material over the landscape, filling valleys and smoothing out irregularities.

For example, in parts of the Lake District and the Pennines, thick layers of till cover the ground, affecting soil types and drainage.

Moraines Types

Moraines are accumulations of till that form distinct ridges or mounds at or alongside glaciers. They are important depositional landforms and come in three main types:

• Lateral moraines: These form along the sides of a glacier. As the glacier moves, it scrapes material from the valley walls and deposits it as ridges parallel to the glacier’s edge.
• Medial moraines: These form when two glaciers meet and their lateral moraines join in the middle of the combined glacier, creating a ridge of debris down the centre.
• Terminal moraines: These form at the furthest point reached by a glacier. They mark the maximum advance of the ice and appear as ridges of debris left when the glacier melts back.

Moraines form because glaciers carry debris picked up by erosion and deposit it as the ice melts or slows. The position of the moraine depends on where the material is dropped.

For example, the terminal moraine at the end of a glacier can form a natural dam, creating a lake behind it.

Learning example: Imagine two glaciers flowing down adjacent valleys. Each has lateral moraines along their edges. When they merge, the lateral moraines join to form a medial moraine running down the centre of the combined glacier.

Landforms from Glacial Deposition

Till and moraines play a key role in shaping the UK's glacial landscapes. Deposited till forms thick layers that influence soil type and drainage. Because till contains fine clay particles, it often creates poorly drained soils, leading to waterlogged areas.

Moraines create ridges and mounds that add relief to the landscape. Terminal moraines can dam valleys, leading to the formation of lakes such as those found in the Lake District. Lateral and medial moraines add features to valley sides and floors.

Examples in the UK include:

• The Lake District: Terminal moraines form ridges that trap water, creating ribbon lakes like Windermere.
• The Scottish Highlands: Lateral moraines mark the sides of former glaciers, visible as ridges along valleys.
• The Pennines: Thick deposits of till cover large areas, affecting farming due to poor drainage.

These depositional features influence land use because soils formed on till are often heavy and wet, making farming difficult. Drainage can be poor, requiring artificial drainage systems for agriculture.