Glacial landforms of erosion

1. Snow collects in a hollow on a mountainside, often facing north-east, where it is shaded and melts least.
2. Over years, the snow is compacted into ice.
3. Plucking steepens the back wall, and freeze-thaw weathering adds loose rock.
4. Rotational slip and abrasion deepen the hollow into an armchair shape.
5. Where the ice is thinner at the front, there's less erosion, so a rock lip is left.
6. When the ice melts, water can collect behind the lip in a small lake: a tarn.

Arêtes:

1. Two corries form back to back or side by side on a mountain.
2. As they are eroded backwards, by plucking and freeze-thaw, the land between them gets narrower.
3. A sharp, knife-edged ridge is left between them: an arête.

Pyramidal peaks:

1. Three or more corries form on different sides of one mountain.
2. Each is eroded backwards towards the summit.
3. A sharp, pointed peak is left, with arêtes running down from it: a pyramidal peak.

1. Before the ice age, a river flowed in a V-shaped valley, winding between interlocking spurs.
2. A glacier filled the valley. Being much bigger and heavier than the river, it eroded the bottom and sides by plucking and abrasion.
3. The glacier couldn't wind round the spurs, so it cut straight through them, leaving steep cliffs: truncated spurs.
4. When the ice melted, a wide, deep valley with steep sides and a flat floor was left: a glacial trough, or U-shaped valley.

A small river now flows along the wide floor: a misfit stream, far too small for its valley.

Hanging valleys:

1. Small glaciers in side valleys flowed into the main glacier.
2. The main glacier, being bigger, eroded its valley much deeper.
3. When the ice melted, the side valleys were left high above the main valley floor: hanging valleys. Their streams fall into the trough as waterfalls.

Ribbon lakes:

1. The glacier eroded some parts of the trough floor more deeply, where the rock was softer or where tributary glaciers added more ice.
2. When the ice melted, water filled these hollows, making long, narrow ribbon lakes.

Some ribbon lakes are also dammed by moraine left across the valley.

On this extract, every 50 m contour is drawn, as glaciated uplands are steep:

• Thorns Dale is a glacial trough: steep sides, where the contours crowd together, and a wide, flat floor with almost none.
• Long Water, on its floor, is a ribbon lake.
• The stream joining from the west (grid square 3215) falls steeply out of a hanging valley.
• Blackcombe Tarn sits in a corrie, a hollow with a steep back wall.
• Harrow Edge is an arête, where contours run close together on both sides of a narrow ridge.
• Harrow Pike (1028 m) is a pyramidal peak.