Landform Detective: Glaciers

The shape is the evidence

Ice has been gone from Britain for about 11,700 years, and you can still tell exactly where it was, how thick it was and which way it moved. Every glacial landform is a record of the ice that made it, which is why identifying one is detective work rather than memory. You are reading the evidence back. Start with height, because it decides which half of the system you are looking at. Where the ice was thick and moving it carved, so the erosional landforms sit high in steep ground: the hollows, the knife-edged ridges, the straight-sided valleys. Where the ice thinned, stopped and melted it let go of everything it was carrying, so the depositional landforms sit lower on gentler ground: mounds and banks of unsorted material. Getting that one decision right first is what the examiners flag most often, because a candidate who names a landform before looking at its position can end up putting a mound of dropped debris on a mountain top. Then read the direction, which finishes the identification. In Britain the hollows face mostly north and east, because that is the shaded side where last winter's snow survived the summer. A sharp ridge has a hollow on each side of it, which is what made it sharp. A valley that runs unnaturally straight does so because ice cannot bend round an obstacle the way a river does, so it cut the ridge ends off square instead. And a smooth mound with one blunt end and one tapered end is pointing at the ice that shaped it. The Lake District is the worked example throughout: 2,362 square kilometres, a national park since 1951 and a World Heritage Site since 2017.

Eight landforms, sorted by where they sit

The first five are carved by ice and sit high. The last two are built by ice and sit low. Reading the definitions in that order is itself the identification method.

How a hollow becomes a lake

Six stages turn a shaded mountainside hollow into a corrie holding water. Put them in order.

• Snow collects in a shaded hollow facing north or east and survives the summer
• Layer on layer compresses the snow into ice, which deepens year on year
• The mass becomes thick enough to move, rotating within the hollow
• The back wall is steepened and the floor is deepened into a rock basin
• Less erosion occurs at the front edge, so a rock lip is left standing there
• The ice melts and water collects behind the lip, held in the basin

Why check the height first?

A description gives you a landform made of unsorted angular material with no clear layering. Which reasoning identifies it most reliably?

• Unsorted and angular means it was dropped by ice rather than sorted by water, which puts it in the depositional half of the system, so it belongs on lower, gentler ground. Then the shape decides which one it is: a smooth oval mound aligned with others is a drumlin, whereas a ridge lying across the valley is a moraine marking where the ice stopped.
• Unsorted material is always moraine, so no further check is needed.
• Angular fragments indicate erosion, so the landform is erosional.
• It must have been deposited by meltwater, since that is what moves loose material.

Carved high, built low

The content map calls the confusion between these two groups the common error on this topic. Read the third column first in the exam, then use it to place the landform in one of the first two before naming it.

Find the landform the ice built

The image shows an upland area from above. High ground is shaded darker across the left and top, and the ground falls away to gentler country in the bottom right. Tap the feature that was built where the ice came to a halt and dropped everything it was carrying in one place.

Match each description to what it records

Name it, then prove it

Almost every mark lost on this topic comes from stopping at the name. A description says there is a deep bowl in the mountainside holding a lake, a candidate writes "this is a corrie", and that single word is all the credit there is. The landform has been identified and nothing has been explained. Add the proof, and it is usually one clause. Say what the shape shows. The hollow faces north east, which is the shaded side where snow survived the summer. The ridge is narrow because two hollows were cutting back towards each other. The valley runs straight and its ridge ends are square because ice could not bend round them. The mounds all lie the same way because they were moulded under moving ice. Each of those turns a label into an argument, and an argument is what the mark scheme rewards. Two habits worth building. Give a real location wherever you can, since a named place with a figure is worth more than the same point in general terms, and the specification asks for a real upland. And check where the landform sits before you name it, because the commonest outright error is putting dropped material high on a mountain or a carved hollow out on the plain. Finally, a word about the U shape. It is a cross-section and it is fine to mention, but it describes only one view. The plan view carries just as much evidence, and candidates who mention the straightness and the squared-off ridge ends are reading the landscape rather than reciting a diagram.

Complete the glacial landform figures

The lake in the hollow below Helvellyn lies at about _____ metres, while the summit above it reaches 950 metres and the ridge alongside runs for roughly _____ kilometres. Down in the valleys, the deepest lake in England reaches _____ metres, lying in a straight trough about 5 kilometres long, and the longest stretches for around 17 kilometres. On lower ground the mounds left beneath the moving ice stand _____ to 50 metres high and lie in swarms pointing the same way. All of it was left when the ice finally went, about _____ years ago.

Spot the three sound landform statements

Select the THREE statements that could stand as they are in an answer.

• British hollows of this kind face predominantly north and east, because those are the shaded slopes where snow lasted through the summer and could build into ice.
• Ridge ends along the valley have been cut off square, which shows ice filled the valley, since a river would have wound between them instead.
• The mounds lie in a swarm with every blunt end facing the same way, which records the direction the ice was travelling when it moulded them.
• The material in the ridge is well sorted, with the coarsest fragments at the base, which is typical of deposition directly from ice.
• The valley is U-shaped, which is all that needs saying to identify it as glacial.
• Mounds of unsorted material are commonly found on the highest ground, where the ice was thickest.

A 6-mark identification, marked

Using a named upland area, explain the formation of two landforms of glacial erosion. [6 marks] In the Lake District, Red Tarn lies in an armchair-shaped hollow at roughly 718 m on the north eastern side of Helvellyn, whose summit is 950 m. It formed because snow collected on that shaded side and survived the summer, so layer compressed layer into ice until the mass was thick enough to rotate within the hollow. Rotation steepened the back wall and deepened the floor into a rock basin, while less erosion at the front edge left a rock lip standing, which is why water is held there now that the ice has gone. The north eastern aspect is not incidental detail: it is the reason the ice could form at all, since a south facing slope loses its snow each summer. Striding Edge, about 1.5 km long, runs alongside that hollow and is a knife-edged ridge with steep ground falling away on both sides. It is narrow precisely because it was attacked from two directions at once: a second hollow was being cut back on the far side at the same time, and the ridge is what survived between them. That makes the two landforms a single story rather than two separate ones, since the process that deepened the hollow is the process that sharpened the ridge. What earned the marks: a real named upland with heights and a length attached; each landform explained as a sequence rather than described; the aspect used as evidence rather than mentioned in passing; and the second landform linked causally to the first instead of being started again from scratch.

Find the two that would cost marks

Five sentences from answers about glacial landforms. Two would lose credit, one for a claim that is the wrong way round and one for stopping short of an explanation. Tap those TWO.

• Swarms of smooth mounds are found on the highest ground, since that is where the ice was thickest and dropped most of its load.
• The hollow faces north east, the shaded side, which is why snow survived the summer there and could compress into ice.
• This landform is a glacial trough, as you can tell because it is U-shaped.
• The ridge ends stop square rather than interlocking, showing that ice rather than a river filled this valley.
• The lake is far longer than it is wide because it lies along the floor of a valley the ice straightened.

Build the identification sentence

Assemble a sentence that names a landform and proves it in the same breath.

Four descriptions, four identifications

Each description is the kind you get on an exam resource. Work out what it records before naming anything.

• A narrow ridge runs between two deep hollows on the same mountain, and the land drops away sharply to either side of it.
• A group of low, smooth oval mounds of unsorted material sits on a lowland plain, each one blunt at the same end.
• A valley has a wide flat floor, steep sides, and ridge ends along both sides that stop abruptly rather than interlocking.
• Beyond the end of a valley lies a spread of rounded pebbles, graded from coarse near the valley to fine further out.

Explain two landforms

Using a named upland area, explain how one landform of glacial erosion and one of glacial deposition were formed. [9 marks]

• A height, depth or length attached to each landform
• Stages, not what it looks like now
• The carved landform sits high where ice was thick and moving; the built one sits lower where it stopped
• Shape records: the aspect of a hollow, the alignment of a swarm of mounds
• Unsorted material separates it from anything meltwater left