Classification of glaciers based on temperature

Glaciers are classified into two main types based on the temperature at their base, which affects their behaviour and interaction with the surrounding environment.

Types of glaciers by basal temperature

• Cold-based glaciers:
  • Found in extremely cold regions like parts of Greenland, where the base remains far below the melting point of ice.
  • These glaciers experience minimal melting, resulting in very little movement and limited erosion of the underlying landscape.
• Warm-based glaciers:
  • Located in relatively milder climates, where the base is at or above the melting point due to frictional heat or geothermal activity.
  • The presence of meltwater acts as a lubricant, facilitating greater movement and leading to significant erosion of the terrain beneath and around the glacier.

Mechanisms of glacier movement

Glaciers move under the influence of gravity, but the way they move depends on factors such as temperature, terrain, and the presence of meltwater.

Key mechanisms of glacier movement

• Basal sliding - Occurs primarily in warm-based glaciers where meltwater at the base reduces friction, allowing the glacier to slide over the ground. Increased pressure around rock protrusions causes more melting, and this water may refreeze further downstream where pressure drops.
• Rotational flow - Happens when a glacier moves in a curved, arc-like manner within a hollow or basin.
• Internal deformation - Predominant in cold-based glaciers, this involves ice crystals within the glacier sliding past one another, enabling slow movement even without meltwater.
• Extensional flow - Found at the glacier's head where the valley is steep. Tension causes the ice to break into layers that slip downwards.
• Compressional flow - Occurs lower down the glacier where faster-moving ice presses against slower-moving ice, creating high pressure that leads to fracturing and forward slipping of ice layers.

Weathering processes in glacial environments

Weathering in glacial regions breaks down rocks through physical processes driven by temperature fluctuations and the presence of water.

Main weathering processes in glacial areas

• Nivation:
  • A collective term for processes that deepen hollows in the landscape through cycles of freezing and thawing.
  • Snow accumulates in hollows, and as temperatures hover around 0°C, repeated freezing and thawing cause frost shattering, breaking rocks apart.
  • Meltwater then removes the debris, while waterlogging can cause slope collapse, forming features known as nivation hollows.
• Frost action (freeze-thaw weathering):
  • Takes place where moisture is present in rock joints and crevices, and temperatures fluctuate above and below freezing.
  • Water freezes and expands when temperatures drop below 0°C, exerting pressure on the rock.
  • Over time, repeated cycles weaken the rock, causing fragments to break off and fall away.

Processes of glacial erosion

Glacial erosion shapes landscapes by removing material from valley floors and walls as the glacier moves. This process is more pronounced in warm-based glaciers due to their greater movement and the presence of debris.

Primary methods of glacial erosion

• Plucking - Occurs when ice slightly thaws and then refreezes around protruding rocks. As the glacier moves, it pulls these rocks away from the bedrock, incorporating them into the ice mass.
• Abrasion - Involves debris embedded in the glacier scraping against valley walls and floors, wearing away the underlying material.

Factors influencing erosion rates

• Rock resistance - Softer, less resistant rock erodes more quickly than harder materials.
• Glacier thickness - Thicker glaciers exert more pressure, increasing erosion.
• Glacier speed - Faster-moving glaciers cause more abrasion and plucking due to greater force.
• Debris volume - A higher amount of debris within the glacier enhances abrasion.
• Debris hardness - Harder debris materials are more effective at scraping and eroding the landscape.

Transport and deposition of glacial debris

Glaciers transport vast amounts of material eroded from the landscape, carrying it over long distances before eventually depositing it.

Methods of debris transport by glaciers

• Supraglacial transport - Material, such as rock fragments, is carried on the surface of the glacier.
• Englacial transport - Debris is embedded within the body of the glacier, carried along as the ice moves.
• Subglacial transport - Material is moved along at the base of the glacier.

Processes and types of glacial deposition

• Till - A general term for the unsorted mix of material deposited directly by a glacier, ranging from large boulders to fine clay. Sometimes referred to as boulder clay, till aligns with the direction of glacier flow.
• Lodgement till - Deposited on the valley floor by an actively moving glacier.
• Ablation till - Material dropped by the glacier as it melts, typically near the glacier's snout where ice loss is greatest.
• Moraines - Distinct landforms created from deposited till.