Glacial erosional landforms are features on the Earth’s surface that have been shaped and sculpted by the movement and erosion of glaciers. Glaciers are massive bodies of ice that flow slowly under the influence of gravity, carrying rocks, sediment, and debris with them. As glaciers move, they exert tremendous erosional power, carving, sculpting, and smoothing the landscape. Here are some common glacial erosional landforms:
- U-shaped Valleys (Glacial Troughs): Glaciers erode existing river valleys into distinctive U-shaped troughs. They widen and deepen these valleys by plucking rocks from the valley floor and walls, and abrasion as the ice grinds against the bedrock.
- Cirques: These are steep, bowl-shaped hollows or basins located near the heads of glacial valleys. They are formed as glaciers carve away the mountain slope.
- Arêtes: Arêtes are sharp, narrow ridges that form when glaciers erode both sides of a mountain ridge, leaving a knife-edge ridge in between.
- Horns: A horn is a pointed mountain peak formed when glaciers erode all sides of a mountain, creating a sharp, jagged pinnacle at the summit. The Matterhorn in the Swiss Alps is a famous example.
- Tarns: Tarns are small, circular, mountain lakes that occupy cirques after the glacier has retreated.
- Roche Moutonnées: These are bedrock outcrops that have been smoothed and polished by the passage of glaciers. The upstream side is typically smooth, while the downstream side is plucked and roughened.
- Glacial Striations: Glacial striations are scratches or grooves on bedrock surfaces caused by the abrasive action of rocks and sediments carried by the glacier. These scratches indicate the direction of glacial movement.
- Erratics: Erratics are large boulders that have been transported by glaciers and deposited far from their source. They often stand out in areas with different types of rock.
- Fjords: Fjords are deep, narrow inlets of the sea that have been carved by glaciers as they flowed into the ocean. They often have steep, glacier-carved walls and are found in regions like Norway and Alaska.
- Hanging Valleys: These are smaller valleys that intersect with larger U-shaped valleys but are higher in elevation. They form when smaller tributary glaciers erode their own valleys, which are later left “hanging” above the main glacial valley.
These glacial erosional landforms bear witness to the powerful and transformative force of glaciers. They provide valuable insights into the Earth’s geological history and the dynamic processes that shape our planet’s surface.