Distinctive Landforms

• An arete is a knife edge ridge. It is formed when two neighbouring corries run back to back. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower. For example, Striding Edge found on Hewellyn in the Lake District.
• A pyramidal peak is formed where three or more corries and aretes meet. The glaciers have carried away at the top of a mountain, creating a sharply pointed summit. For example: Mont Blanc, The Matterhorn and Mount Everest
• Aretes are typically formed when two glaciers erode parallel U-Shaped valleys. Aretes can also form when two glacial cirques erode headwards towards one another, although frequently this results in a saddle shaped pass called a col

When a glacier moves across the underlying rock, the process of abrasion wears it away. It is the fragments of rock held in the ice that do the abrading, scraping across the rock surface like nails across a wooden desktop. Larger rock fragments leave deep scratch marks behind them. These scratch marks are straight parallel lines that reveal the direction of ice movement

Freshly exposed strations have a preferred orientation of the rock grains. By lightly running a finger along the striation, it is possible to discover that when moving one way along it, the rock feels smooth, but when moving the other way it feels more coarse. The moving ice leaves the rock aligned with the direction of movement, so when the striation feels smooth, your finger is moving in the direction of ice flow. When the striation feels rough, you are moving against the ice flow. This test doesnt always work, and wont work on striations that have been exposed for a long period of time.

• Glaciers cut distinctive u-shaped valleys with a flat floor and steep sides. The glacier widens, steepens, deepens and smoothens v-shaped river valleys, such as Great Langdale Valley in the Lake District.
• Just like rivers, glaciers have tributaries. As the main glacier erodes deeper into the valley, the tributary is left higher up the steep sides of the glacier. U-shaped valleys ending with a waterfall at the cliff-face are called hanging valleys.
• When a river erodes the landscape, ridges of land form in its upper course which jut into the river. These are called interlocking spurs. A glacier cuts through these ridges leaving behind truncated spurs.

Definition

• A roche mountonnee is a rock hill shaped by the passage of the ice to give a smooth up-ice and a rough, plucked and cliff-girt surface on the down-ice slide. The upstream surface is often marked with striations

Formation

• Stage 1: As the glacier moves over the rock, its weight applies a lot of pressure on the base. This causes the glacier's base to melt, creating meltwater.
• Stage 2: The meltwater allows the glacier to move over the rock. It stays as meltwater due to the pressure. The uphill part of the rock ends up getting smoothed
• Stage 3: After the glacier has moved uphill, pressure decreases and less energy is needed to travel
• Stage 4: This causes the meltwater to freeze again as there is not the presence of the pressure
• Stage 5: The frozen water then freezes to the back of the rock and plucks it as the ice moves forward, leaving cracks in the back.

Features and Characteristics

• All the sides and edges have been smoothed and eroded in the direction of the glacier that once passed over
• The rough and craggy down-ice (leeward) side is formed by plucking
• Roche mountonnees occur widely in granite and metamorphic rocks.
• Roche mountonnees are aligned roughly parallel to ice flow
• Low-level ones show only shallow weathering pits, indicating significant erosion by the last ice sheet
• High-level ice-moulded rock surfaces have deep weathering pits indicating formation before the last ice sheet.

Examples

• Roche mountonne near Myot Hill, scotland
• Roche Mountonnees surface at Great Slave Lake, Northwest Territories, Canada