Types of Moraine: Where Glacial Debris Accumulates
This deep dive covers Types of Moraine: Where Glacial Debris Accumulates within Glacial Processes for GCSE Geography. Revise Glacial Processes in Glacial Landscapes in the UK for GCSE Geography with 15 exam-style questions and 20 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 9 of 17 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 9 of 17
Practice
15 questions
Recall
20 flashcards
🔍 Types of Moraine: Where Glacial Debris Accumulates
A moraine is a ridge or accumulation of till (unsorted glacial debris) deposited by a glacier. Different moraines form in different positions relative to the glacier, and each type tells a different story about the glacier's history and behaviour. Understanding the types of moraine is essential for both OCR B Paper 1 and AQA Paper 1 glaciation sections.
| Type of Moraine | Position | How It Forms | What It Tells Us |
|---|---|---|---|
| Terminal moraine | At the snout (furthest down-valley) | As the glacier advances, it pushes debris ahead like a bulldozer. When the snout is stationary (zero budget), material is continuously delivered to the snout and dropped, building up a ridge across the valley. Marks the glacier's maximum advance. | Shows the furthest extent the glacier reached |
| Recessional moraine | Up-valley from the terminal moraine | As the glacier retreats (negative budget), the snout may pause at a new position for a period before continuing to retreat. Each pause deposits a smaller ridge of till across the valley. Multiple recessional moraines can show the stages of glacial retreat. | Shows pause positions during retreat; helps date glacial history |
| Lateral moraine | Along both valley sides (flanks) | Freeze-thaw debris falls from the valley walls above the glacier and accumulates along the edges of the ice. When the glacier melts, this material is left as a ridge along the valley sides, typically high on the valley walls. | Shows former ice surface level; confirms valley was glacier-filled |
| Medial moraine | Running down the centre of the glacier | When two glaciers join (a tributary glacier merges with a main glacier), their two inner lateral moraines merge together on the surface of the combined ice flow. The result is a dark stripe of debris running down the centre of the glacier, visible from above. | Visible evidence of tributary glaciers joining; seen in aerial photos of active glaciers |
| Ground moraine | Spread across the valley floor | Till deposited beneath the moving ice as the glacier slides over it. Produces a thin, irregular layer of unsorted sediment across the floor of the glaciated valley — sometimes moulded into low, egg-shaped hills called drumlins by the overlying ice. | Shows the glacier's path; drumlins indicate direction of ice flow |
Quick Check: A geologist finds a ridge of unsorted sediment (boulders mixed with clay) running across a valley in the Lake District. What type of moraine is it likely to be, and what does it tell us about the glacier that deposited it?
The unsorted nature of the sediment (boulders mixed directly with clay, no grading by size) confirms it is till — deposited directly by ice, not by meltwater. A ridge of till running across (transverse to) the valley is a terminal or recessional moraine. If it is the furthest down-valley ridge, it is a terminal moraine marking the glacier's maximum advance. If there are ridges further down-valley from it, it is a recessional moraine marking a pause during retreat. Either way it tells us the glacier's snout was stationary at that position long enough to build up a significant accumulation of debris.