Tearing Down (Erosion):
* Plucking: As a glacier flows over bedrock, it melts slightly at its base. This meltwater seeps into cracks and crevices in the rock, freezing and expanding. The expansion exerts pressure, breaking off pieces of rock and incorporating them into the ice.
* Abrasion: The embedded rocks and debris within the glacier act like sandpaper, grinding and scraping against the bedrock as the glacier moves. This process polishes and smooths the rock surface, creating striations (parallel scratches) and grooves.
* Erosion of Valleys: Glaciers carve out U-shaped valleys with steep sides and flat bottoms, contrasting with the V-shaped valleys created by rivers. This distinctive shape is a result of the glacier's erosive power and ability to move and scour rock.
* Cirques: Glaciers can create bowl-shaped depressions called cirques at the head of a valley. These form as the glacier erodes the bedrock, creating a steep, amphitheater-like structure.
* Aretes: When two cirques erode back-to-back, they form a sharp, jagged ridge called an arete.
* Horns: When three or more cirques erode a mountain peak, they create a pointed, pyramid-shaped peak called a horn.
* Fjords: In coastal areas, glaciers can carve deep, narrow inlets called fjords. These are often filled with seawater, creating stunning landscapes.
Building Up (Deposition):
* Moraine: As glaciers move, they transport sediment and rock debris. When the glacier melts, it deposits this material at its edges and terminus, forming mounds called moraines.
* Lateral moraines: Form along the sides of the glacier.
* Medial moraines: Form in the middle of the glacier when two glaciers merge.
* Terminal moraines: Mark the furthest point of the glacier's advance.
* Outwash Plains: Meltwater from glaciers carries sediment downstream, depositing it as the water slows down. These deposits create outwash plains, often characterized by gravel and sand.
* Drumlins: Streamlined hills of glacial till (unsorted sediment) that are shaped by the flow of ice.
* Eskers: Long, winding ridges of sand and gravel deposited by meltwater streams flowing within or beneath the glacier.
* Kettles: Depressions in the landscape formed when blocks of ice are buried by glacial sediment and melt, leaving behind a hole.
Overall, glaciers are powerful agents of change, shaping the landscape through both erosion and deposition. Their impact is evident in many of the distinctive features we see in mountain ranges, valleys, and coastal areas around the world.
