What is the fundamental difference between Glacial Till and Fluvioglacial Outwash?

Till is deposited directly by ice and is unsorted and unstratified. Outwash is deposited by meltwater, meaning it is sorted by size and stratified into layers due to water energy variations.

How do Eskers and Drumlins differ in their formation and composition?

Eskers are winding ridges of sorted sand/gravel formed by subglacial meltwater streams. Drumlins are teardrop-shaped hills of unsorted till molded by the movement of the ice itself.

What distinguishes a Terminal Moraine from a Recessional Moraine?

A terminal moraine marks the maximum forward advance of a glacier. A recessional moraine forms behind the terminal moraine during a period of stability or a temporary halt during glacial retreat.

What is a common error when identifying the direction of ice flow from a Drumlin?

Students often mistake the steep side for the direction of flow. In reality, the steep 'stoss' side faces the direction the ice came from, and the gentle 'lee' slope points in the direction the ice was moving.

Why is it incorrect to assume all mounds in a glacial landscape are Moraines?

Many mounds are actually Kames, which are formed by meltwater and contain sorted, stratified sediment. Moraines are composed of unsorted till, and the internal structure must be checked to distinguish them.

What mistake is made regarding the 'sorting' of sediment in an Esker?

Learners often think ice-contact features are always unsorted. However, because Eskers are formed by subglacial streams (water), they are highly sorted and stratified despite being located 'under' the ice.

Define 'Lodgement Till'.

Lodgement till is subglacial material that is physically plastered or 'lodged' onto the bedrock by the pressure of the overlying moving ice, often resulting in highly compacted sediment.

A sandur, or outwash plain, is a broad, flat area of sorted sediment deposited by meltwater streams in the proglacial zone (in front of the glacier snout).

Erratics are large boulders transported by glaciers that are geologically different from the bedrock of the area where they are eventually deposited.

How does a Kettle Hole form in a depositional landscape?

A block of 'dead ice' becomes buried in outwash sediment; when the ice block eventually melts, it leaves a depression in the ground that often fills with water to form a lake.

Glacial Deposition Landforms & Landscapes | Pearson Edexcel A-Level Geography

Glaciated Landscape & Change

Glacial Deposition Landforms & Landscapes

Summary

Glacial deposition occurs when a glacier loses the energy required to transport its load, resulting in the accumulation of sediment known as drift. This process creates distinct landforms categorized by whether the material was deposited directly by ice (ice-contact) or by glacial meltwater (fluvioglacial). Understanding these landforms allows geoscientists to reconstruct past ice extent, flow direction, and climatic conditions.

1. Definition & Core Concepts

Glacial Drift: This is the collective term for all sediment transported and deposited by glaciers, further subdivided into till and outwash.
Glacial Till: Material deposited directly by the ice; it is typically unsorted (containing everything from clay to boulders) and unstratified (lacking layers).
Fluvioglacial Outwash: Sediment deposited by meltwater streams; it is sorted by size and stratified into layers due to the seasonal variations in water energy.
Deposition Context: Landforms are classified as ice-contact (formed against or under the ice) or proglacial (formed in front of the glacier snout).

Cross-section of a glacial landscape showing ice-contact features like drumlins and terminal moraines, alongside proglacial outwash plains.

2. Underlying Principles of Deposition

Lodgement Processes: Occurs at the base of a moving glacier where high pressure and friction force subglacial debris into the underlying bedrock, creating compact, aligned deposits.
Ablation Processes: Occurs when the ice melts (ablates) and drops its internal (englacial) or surface (supraglacial) load in situ, resulting in loose, chaotic mounds of debris.
Energy and Sorting: Meltwater energy dictates sediment size; high-velocity streams transport gravel and cobbles, while low-velocity water in proglacial lakes allows fine silts and clays to settle.
Hydrostatic Pressure: In subglacial tunnels, water under immense pressure can transport sediment uphill, which explains the winding, ridge-like paths of certain landforms.

3. Ice-Contact Landforms

Moraines: Linear ridges of till. Terminal moraines mark the furthest extent of the ice, while recessional moraines mark temporary halts during retreat.
Drumlins: Elongated, teardrop-shaped hills of till with a steep stoss side facing the direction of ice origin and a gentle lee side pointing in the direction of flow.
Erratics: Large boulders that differ in lithology from the local bedrock, having been transported long distances by ice and deposited upon melting.
Lateral and Medial Moraines: Ridges formed along the sides of a glacier (lateral) or where two glaciers merge (medial), concentrating debris in the center of the ice flow.

4. Fluvioglacial (Meltwater) Landforms

5. Key Distinctions

6. Exam Strategy & Tips