Glacial Erosion and Deposition

Processes of Glacial Erosion

• Plucking

  • Process where glaciers attach to loosened rock and pull or pluck it away.
  • Most effective in well-jointed rocks.

• Abrasion

  • Occurs when rock fragments, which are frozen into the base and sides of a glacier, act like sandpaper as the glacier advances.
  • Erodes the surface underneath the glacier, contributing to landscape modification.

Rate of Glacial Erosion

The rate of glacial erosion is influenced by several factors:

1. Gradient: Steeper gradients increase erosion.
2. Depth of ice: Greater depth causes higher rates of erosion.
3. Resistance of rock: Harder rocks are eroded more slowly than softer rocks.

Key Features of Glacial Erosion

• Cirque/Corrie

  • Basin-shaped hollows in mountains, characterized by three steep sides, often containing a lake known as a Tarn.
  • Considered the birthplace of glaciers.

• Pyramidal Peak

  • Formed by three or more cirques around a mountain top, leaving a steep-sided peak.

• U-shaped Valleys

  • Characterized by wide, flat floors and steep sides, formed from glacial movement.

• Hanging Valleys

  • Smaller glaciated valleys elevated above the main valley floor, typically formed by tributary glaciers.

• Arête

  • A narrow, steep-sided ridge formed where two cirques are adjacent to each other.

• Fjords

  • U-shaped coastal inlets with very steep sides, created by drowned valleys.

• Ribbon Lakes

  • Long, narrow lakes found within U-shaped valleys, often following the path of glacial erosion.

Features of Glacial Deposition

• Boulder clay plains

  • Lowland areas covered in boulder clay, resulting from glacial deposition.

• Erratics

  • Large boulders transported by glacial ice from their original location and deposited elsewhere.

• Drumlins

  • Oval-shaped hills formed from glacial debris.
  • Long axis indicates the direction of ice movement.
  • Often occur in swarms, creating a "basket of eggs" topography.

• Moraines

  • Accumulated debris from glaciers, categorized as:
  • Lateral Moraine: Found at the sides of valleys.
  • Medial Moraine: Located in the middle of the valley.
  • Terminal Moraine: Marks the furthest advance of the glacier at its edge.

Features of Meltwater Deposition

• Pro-glacial lakes

  • Formed in front of ice sheets as they melt.

• Glacial Spillways

  • Overflow channels that form as meltwater drains away.

• Eskers

  • Long, narrow ridges of sand and gravel deposited by meltwater streams flowing beneath glaciers.

• Outwash Plains

  • Flat areas formed by the deposition of sand and gravel from meltwater, often characterized by braided streams.

Geographic Features on Maps

• Cirque

  • Represented by three steep sides surrounding a hollow, may be filled with a tarn lake.

• Pyramidal Peak

  • Depicted as a steep point between three cirques.

• Arête

  • Shown as a steep ridge between two hollows or lakes.

• U-shaped valleys

  • Identified by U-shaped contours surrounding the river.

• Hanging Valleys

  • Characterized by higher contours surrounding the river, indicating a valley elevated above the main valley.

• Ribbon/Paternoster Lakes

  • Long lakes on the valley floor, often appearing connected in series.