What is the primary difference between warm-based and cold-based glaciers regarding movement?

Warm-based glaciers move through both basal sliding and internal deformation due to meltwater at the base. Cold-based glaciers are frozen to the bedrock and move only via internal deformation.

How does glacial till differ from fluvio-glacial outwash in terms of sorting?

Glacial till is unsorted because ice carries all particle sizes equally. Outwash is sorted by meltwater, which deposits heavier materials first as its velocity decreases.

What is the difference between accumulation and ablation?

Accumulation refers to all inputs of snow and ice into the glacial system. Ablation refers to all outputs or losses of mass, such as melting, evaporation, and calving.

What is a common misconception about the temperature required for basal melting?

Many assume ice only melts at $0^{\circ}C$. However, due to high pressure at the base of a glacier, the Pressure Melting Point (PMP) can be lower than $0^{\circ}C$, allowing melting in sub-zero environments.

Why is it incorrect to say a glacier 'retreats' by moving backward up the mountain?

Ice always flows downhill due to gravity. A 'retreating' glacier simply means the snout is melting faster than the ice is being supplied from the accumulation zone; the ice itself never flows uphill.

What error is made when identifying the shape of rocks in glacial till versus outwash?

Students often forget that rocks in till are angular because they haven't been eroded by water. Rocks in outwash are rounded due to attrition in meltwater streams.

Define 'Firn' (or Névé).

Firn is partially compacted snow that has survived at least one summer season. It represents the intermediate stage between loose snow and dense glacial ice.

What is the Pressure Melting Point (PMP)?

The PMP is the temperature at which ice begins to melt under a specific amount of pressure. As pressure increases with ice depth, the melting temperature decreases.

What is the 'Equilibrium Line' in a glacial system?

The equilibrium line is the boundary on a glacier where the amount of accumulation exactly equals the amount of ablation over a year.

Why does glacial ice appear blue?

Intense pressure squeezes out air bubbles, creating dense ice that absorbs longer red wavelengths of light and scatters shorter blue wavelengths.

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Summary

Glaciers are dynamic open systems characterized by a mass balance between accumulation and ablation. Their physical properties, including thermal regimes and movement mechanisms, are determined by environmental factors such as temperature, gravity, and the pressure melting point of ice.

1. Definition & Core Concepts

Glaciers as Open Systems: A glacier is defined as a system that receives inputs of mass (snow, avalanches) and loses mass through outputs (melting, calving), with energy transfers occurring throughout the body of the ice.
Formation Process: Glacial ice forms through the compaction of snow over approximately 30 years. Initial snowfall settles into a granular state called firn or névé, which is eventually compressed into dense, air-free glacial ice.
Optical Properties: Glacial ice often appears blue because the high-pressure compaction removes air bubbles, allowing the ice to absorb long-wave red light while scattering short-wave blue light.

Diagram of a glacial system showing the accumulation zone, ablation zone, and equilibrium line.

2. The Glacial Budget

Mass Balance: The glacial budget is the annual balance between accumulation (gains) and ablation (losses). It is expressed by the formula: $Net Balance = Accumulation - Ablation$ .
Zonal Division: Glaciers are divided into the Accumulation Zone (upper part where gains exceed losses) and the Ablation Zone (lower part where losses exceed gains).
Equilibrium Line: This boundary marks the point where accumulation exactly equals ablation. If the line moves up-valley, the glacier is retreating; if it moves down-valley, the glacier is advancing.

3. Thermal Regimes & Movement

4. Transportation & Deposition

5. Key Distinctions

6. Exam Strategy & Tips