Key Terms: Glacial systems & processes (AQA A Level Geography): Revision Note

Glacial characteristics - key terms

Ablation – The loss of ice or snow from a glacier through melting, evaporation, or calving.

Accumulation – The input of snow and ice to a glacier from precipitation, avalanches, or wind-blown snow.

Ablation zone – The lower part of a glacier where outputs (melting, evaporation) exceed inputs, resulting in a net loss of ice.

Accumulation zone – The upper part of a glacier where inputs exceed outputs, resulting in a net gain of ice.

Dynamic equilibrium – A state where the total inputs and outputs of a glacier are balanced over time, keeping the glacier’s size stable.

Equilibrium line – The boundary on a glacier where accumulation equals ablation; its position moves with changing mass balance.

Firn (or névé ) -Crystalline or granular snow in the upper part of a glacier

Glacial budget – The balance between accumulation and ablation over a year; determines if a glacier advances or retreats.

Mass balance – The overall difference between inputs and outputs on a glacier, indicating growth (positive) or shrinkage (negative).

Positive feedback (glacial) – A process that amplifies change, e.g. ice loss reduces albedo, increasing solar absorption and further melting.

Pressure melting point (PMP) – The temperature at which ice melts under pressure; lower at higher pressures.

Warm-based glacier – A temperate glacier with basal temperatures at or above the PMP, allowing basal sliding and higher erosion.

Cold-based glacier – A polar glacier with basal temperatures below PMP, where ice is frozen to the bed and moves via internal deformation.

Glacial processes - key terms

Abrasion – Erosion caused when rock fragments embedded in ice grind against the bedrock beneath, producing striations and rock flour.

Basal sliding – The movement of a glacier as meltwater at the base reduces friction and allows ice to slide over bedrock.

Carbonation – A chemical weathering process in which acidic water dissolves calcium carbonate in rocks like limestone.

Compressional flow – A type of glacier flow that occurs when the gradient decreases, causing ice to slow, thicken, and increase erosion.

Englacial – Debris that is carried within the body of the glacier.

Extensional flow – A glacier flow type caused by steepening gradients, leading to stretching and thinning of ice and reduced erosion.

Freeze–thaw weathering – Repeated freezing and thawing of water in rock cracks, expanding when frozen and eventually breaking the rock apart.

Glacial till - sediment containing a mix of materials from fine clay to boulders deposited by glaciers.

Internal deformation – Glacier movement caused by ice crystals slipping and deforming internally, especially in cold-based glaciers.

Meltwater – Water produced from melting ice, which can lubricate glacier bases and transport debris.

Nivation – A combination of processes including freeze–thaw and meltwater erosion beneath snow patches, forming hollows.

Plucking – A process where meltwater refreezes around rocks at the glacier base and pulls them away as the glacier moves.

Regelation – The melting and refreezing of ice around obstacles in the glacier base, allowing movement over uneven surfaces.

Rotational flow – Ice movement in a curved path in hollows or corries, often forming the over-deepened floors seen in cirques.

Snout – The glacier’s front edge, where melting and deposition commonly occur.

Striations – Scratches or grooves in rock surfaces made by debris dragged along by glacial ice.

Subglacial – Material transported at the base of the glacier.

Supraglacial – Debris transported on the surface of a glacier.

Till – Unsorted glacial debris deposited directly by ice.

Periglacial features - key terms

Active layer – The surface layer of ground in a permafrost area that seasonally thaws in summer and refreezes in winter.

Blockfield (Felsenmeer) – A surface covered with angular rock fragments caused by intense freeze–thaw weathering.

Continuous permafrost – An area where the ground remains permanently frozen over a vast region, often to great depths.

Discontinuous permafrost – An area with permafrost interrupted by patches of unfrozen ground (talik).

Felsenmeer - areas of the periglacial landscape with angular rocks littered over the surface.

Frost contraction – The process where frozen ground contracts and cracks, often forming ice wedges when meltwater refreezes in the cracks.

Frost heave – A periglacial process where ice lenses form in soil and push stones or particles to the surface.

Ground ice – Ice that exists in the soil or rock of permafrost regions, including pore ice and needle ice.

Ice wedge – A wedge-shaped body of ice that forms in ground cracks and grows with repeated freeze–thaw cycles.

Isolated permafrost – Pockets of frozen ground within a generally unfrozen (talik) landscape.

Needle ice – Thin slivers of ice that grow in soil pores at night and help dislodge particles for erosion.

Periglacial – Areas adjacent to glaciers characterised by permafrost and intense freeze–thaw activity.

Permafrost – Ground that remains frozen for at least two consecutive years.

Solifluction – The downslope movement of waterlogged soil in periglacial regions, especially during the summer thaw.

Sporadic permafrost – Small, scattered areas of permanently frozen ground within a mainly thawed region.

Subsea permafrost – Frozen ground located beneath the seabed, originally formed on land and submerged after sea-level rise.

Talik – Unfrozen ground within permafrost, which can be open (at the surface), closed (surrounded), or through (beneath active layer).

Thaw lake – A water body formed when meltwater collects on the surface due to the impermeable nature of permafrost below.