Lecture 18: Permafrost and Glaciers Comprehensive Notes

Glaciers

  • About 77% of Earth's freshwater is frozen.
  • Definition: A glacier is a large mass of ice resting on land or floating as an ice shelf in the sea adjacent to land.
  • Movement: Glaciers move slowly in stream-like patterns.

Stages of Glacier Formation

  • Stage 1: Snow survives the summer.
  • Stage 2: In the following winter, old snow is pressured and re-crystallized into firn.
  • Stage 3: After many years, dense glacial ice is formed as snow and firn are pressed and re-crystallized.

Types of Glaciers

1. Alpine Glaciers

  • Found in mountain ranges.
  • Subtypes:
    • Cirque glacier: located in a bowl-shaped recess at the head of a valley.
    • Valley glacier: found in steep-walled valleys.
    • Piedmont glacier: located at the base of a mountain range.
    • Tidewater glacier: ends in a body of water influenced by tides.

2. Continental Glaciers

  • A continuous mass of ice covering a large area.
  • Major ice sheets include the Antarctic and Greenland ice sheets.
  • Types:
    • Ice caps: roughly circular, covering less than 50,000 km².
    • Ice fields: elongated patterns of ice cover.

Glacial Mass Balance

  • Accumulation zone: area where ice gains exceed losses (positive balance).
  • Ablation zone: area where losses exceed gains (negative balance).
  • Equilibrium line: the line where the gain and loss are equal.

Glacial Movement

  • Lubrication: Water presence in the basal layer can facilitate glacial movement.
  • Ice regelation: speeds up movement due to frozen rock debris reducing friction with the bedrock.

Glacier Erosion

  • Glacial plucking: process where glaciers mechanically pick up rock material and carry it away.
  • Abrasion: glaciers scrape the land, polishing the surface of exposed rock.

Glacial Erosional Landforms

  • Roche moutonnée: an asymmetrical hill of exposed bedrock, polished on one side and steep on the other.
  • Glacial valleys: transformed from V-shaped valleys into U-shaped troughs.

Fjords

  • Formed as glaciers retreat, flooding troughs that create deep, steep-sided valleys filled by seawater.

Depositional Landforms from Alpine Glaciation

  • Glacial Drift: all glacial deposits; can be sorted (stratified drift) or unsorted.
  • Types:
    • Moraines: accumulations of glacial debris.
    • Till Plains: flat areas covered by till.
    • Glacial Outwash: material deposited by meltwater.

Moraines

  • Lateral moraine: on each side of a glacier.
  • Medial moraine: formed when two glaciers with lateral moraines join.
  • Terminal moraine: deposits at the glacier's farthest advance.

Glacial Outwash Features

  • Eskers: ridges formed by meltwater streams beneath glaciers.
  • Kames: mounds of sorted sand and gravel on glacier surfaces.
  • Kettle lakes: depressions formed from melted ice blocks.

Periglacial Landscapes

  • Occupy over 20% of Earth's land surface, found in subarctic and polar climates.

Geography of Permafrost

  • Definition: Permafrost is permanently frozen ground, with temperatures below 0°C for over two years.
  • Types:
    • Continuous permafrost: found in the coldest regions, depth can exceed 1000 m.
    • Discontinuous permafrost: scattered patches that become less dense towards warmer areas.

Permafrost Behavior

  • Talik: unfrozen ground found within or below the permafrost.
  • Active layer: the seasonally frozen layer above the permafrost, thickness varies with latitude.

Periglacial Processes

1. Frost Action

  • Ground ice: frozen water in permafrost.
  • Frost heaving and frost thrusting: movements caused by freezing water in soils and rocks.
  • Ice wedges: formed when water enters cracks in permafrost and freezes.

2. Patterned Ground

  • Formation of distinct shapes in the ground due to frost action and the movement of soil particles.

Impact of Humans on Periglacial Landscapes

  • Heat effects: human activities can alter permafrost stability due to heat generation and insulation changes.