Paper 1 - Glaciers

Intro

Earth entered its newest ice age approximately 2.6 million years ago, marking the beginning of the Quaternary period, which continues to this day. An ice age is a prolonged period of time during which global temperatures drop significantly, leading to the expansion of ice sheets and glaciers across continents. Geologists call the time we are currently in in Holocene Epoch, starting roughly 11,000 years ago.

Glaciers are sheets of ice that move slowly down a river valley under the influence of gravity

This period is characterised by cyclical shifts between glacial periods (colder phases where ice advances) and interglacials (warmer phases where ice retreats).

Glacial Movements

Basal sliding

  • The weight of the ice increases pressure at the base of the glacier.

  • This increases warmth at the base of the glacier

  • This in turn increases melting meaning meltwater is present

  • This melt water provides lubrication allowing the glacier to slide over the surface

  • Gravity causes the movement to be downhill

  • This is known as basal sliding

Glacial Processes

  • Plucking: This occurs when meltwater at the base of the glacier freezes into cracks in the bedrock. As the glacier moves, it pulls out large chunks of rock.

  • Abrasion: Rocks embedded in the base of the glacier scrape against the bedrock like sandpaper, smoothing the surface but also leaving behind scratches called striations.

  • Freeze-Thaw Weathering: Water enters cracks in rocks, freezes and expands by approximately 9%, exerting pressure that pushes the rock further apart. This happens repeatedly eventually breaking the rock.

Landforms of Erosion

Corries (Cirques)

Characteristics

  • Steep back walls: Formed by intense plucking.

  • Deep hollow: Created by the rotational slip of the ice.

  • Armchair shape: With high ridges on three sides.

  • Rock Lip: A raised edge at the front of the hollow caused by reduced erosion at the glacier's snout.

  • Tarn: A circular lake that often fills the corrie after the ice melts.

Formation

  1. Snow falls down onto the mountain, over time turning into glacial ice.

  2. As the glacier moves down, the processes of plucking and abrasion, along with freeze-thaw weathering starts to erode the back wall, creating a steep back wall.

  3. The glacier keeps falling downwards till there is a deep crevasse and stays but due to gravity causes it to move in a rotational motion. This movement, combined with abrasion, deepens the floor of the hollow.

  4. After the glacier melts, a deep, armchair-shaped corrie is left behind with a rock lip.

Arêtes and Pyramidal Peaks

  • Arête: A sharp, knife-edged ridge formed when two corries erode back-to-back toward each other to form a mountain.

  • Pyramidal Peak: A sharp, pointed mountain peak (like the Matterhorn) created when three or more corries erode backwards toward the same central point.

Glacial Troughs (U-Shaped Valleys)

  • Formation: Glaciers occupy pre-existing V-shaped river valleys. Because glaciers are massive and rigid, they cut through the interlocking spurs and widen/deepen the valley floor.

  • Characteristics: Steep sides and a wide, flat floor, transforming the profile from a "V" to a "U".

  • Hanging Valleys: Tributary valleys that were not eroded as deeply as the main glacial trough. After the ice melts, they are left high above the main valley floor, often resulting in waterfalls.