ee.2.1 Glacial landscapes

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Key terms

• Arête
  • The name given to a narrow, knife-edged ridge with steep sides found in glaciated upland regions. Results from the formation of cirques.

• Cirque
  • This is a semi-circular hollow high up at the head of a glacial valley on the flanks of a glacial mountain. It was formerly a massive collecting ground for ice that flowed into a glacial valley below. It has a steep headwall to the rear, a bowl-shaped rock basin in its centre and a rock lip at its lower end.

• Englacial
  • “Within” the ice.

• Erratic
  • The name given to a rock which has been transported by a glacier and deposited in an area of different geology than that of its source.

• Frost shattering
  • A glacial process that occurs when water enters cracks in rocks and freezes. As the water freezes, it expands and puts pressure on the rock, causing it to break or shatter. Over time, this process can break down and erode large rock formations into smaller pieces, which the glacier can then transport.

• Glacial abrasion
  • A type of glacial erosion that occurs when rocks, sand, and other particles carried by a glacier act like sandpaper, grinding and scraping against the underlying rock and soil. This abrasive action wears away and erodes the surface, sculpting and shaping the landscape. Over time, the repeated grinding and scraping of the glacier can result in the formation of smooth, polished rock surfaces, and the creation of glacial landforms such as U-shaped valleys and cirques.

• Glacial deposition
  • The process by which glaciers drop, lay down or leave behind the sediment, rocks, and other material that they have transported. This occurs as the ice melts, slows down, or changes direction, causing the material to be deposited in a variety of landforms, including moraines and drumlins.

• Glacial erosion
  • Involves the removal and transport of bedrock or sediment by three main processes: quarrying (also known as plucking), abrasion, and melt water erosion.

• Glacial lake
  • A body of water that is formed by the melting of a glacier. These can form in various ways, such as by the accumulation of meltwater in depression in the landscape created by glacial erosion or by the damming of a valley by a glacial moraine. Ribbon lakes are a type of glacial lake that are long and narrow in shape, and are formed when a glacier erodes a valley and then melts, leaving a lake in its place.

• Glacial till
  • A type of sediment that is deposited directly by a glacier. It is a mixture of rock fragments, sand, gravel, and clay, that has been picked up and carried by the ice as it moves - often deposited in a random and unstratified manner, meaning that the different sizes and types of sediment are mixed and not sorted by size or type. This results in a heterogeneous mixture of sediment different from other sediment types, such as river deposits or beach sand.

• Glacial transportation
  • Relates to the movement of ice and rock debris from one place to another by glaciers. The ice in a glacier acts as a conveyor belt, transporting and depositing sediment and rocks in various landforms and depositional environments.

• Glacial troughs
  • This is a steep-sided, wide and flat-bottomed valley that was previously occupied by a glacier.

• Glacifluvial material
  • Sediment that has been transported and deposited by glacial meltwater. This material can include a range of sediment types, including rock fragments, sand, gravel, and clay, that have been carried by meltwater streams and deposited in areas such as outwash plains, river valleys, and deltas. Glacifluvial material is different from glacial till in that it is sorted by size and type, meaning that larger rock fragments are typically found at the bottom of the deposit and smaller, finer material is found at the top.

• Glacigenetic sediment
  • A term is used to describe sediment deposited or re-deposited by a glacier. This sediment can include a wide range of materials, including rock fragments, sand, gravel, and clay, as well as meltwater deposits like outwash plains. Can be deposited in a variety of environments, including on the surface of a glacier, at the base of a glacier, and in areas where glaciers have retreated or melted.

• Lateral moraine
  • A type of glacial moraine that is formed along the sides of a glacier. It is composed of rock fragments and other debris eroded and transported by the glacier as it moves. As the glacier moves it pushes the rock fragments and other debris to the sides, where they accumulate to form ridges of material that run parallel to the glacier.

• Medial moraine
  • A type of glacial moraine that is formed when two glaciers meet and merge together. When two glaciers merge, their lateral moraines are also combined, resulting in a strip of moraine material that runs down the centre of the combined glacier.

• Plucking
  • Also known as quarrying, is a type of glacial erosion that occurs when a glacier pulls or lifts pieces of rock out of the ground as it moves. This occurs when the glacier freezes onto the rock and, as it moves, the rock is pulled away from the surrounding soil and rock.

• Pyramidal peaks
  • Formed when three or more adjacent cirques develop on the side of a mountain leaving a sharp mountain peak with steep sides and aretes radiating from a central peak.

• Rotational movement
  • Refers to the rotating action of a glacier as it moves over a steep rock face or cliff. As the glacier moves and rotates, it erodes the rock face through abrasion, plucking, and freeze-thaw weathering. The glacier's repeated rotation and erosional action can create a deep, steep-walled basin with a flat floor, known as a cirque basin or corrie, at the head of a glacial valley.

• Subglacial
  • Beneath the glacier. Includes basal sediments and the basal layers of ice.

• Supraglacial
  • On the surface of the glacier.

• Terminal moraine
  • A type of glacial moraine that is formed at the end of a glacier. When a glacier reaches its farthest point of advance, it drops its load of material, forming a ridge of debris that marks the furthest extent of the glacier.