Glaciated landscapes terminology Flashcards
Arete
- Sharp knife-edge ridge
- Where two corries meet
Abrasion
- Type of erosion
- Sediment at base erodes and smooths floor and sides
- Sand-paper like
Bedload
- Sediment dragged along the base of a glacier/ice sheet
- Erodes the ground beneath
Boulder clay
- Aka till,
- Mix of sands, clays, boulders
- Deposited over a large area
Bulldozing
- Material pushed forward by glacier
Calving
- Ice blocks collapse and fall from the snout of the glacier, often into a glacial lagoon
Corrie
- Armchair-shaped hollow
- Formed through glacial erosion, rotational slip and freeze-thaw weathering.
- Depression left when ice melts
Crevasse
- Deep crack found in surface of an ice-sheet or glacier,
- Often buried under snow so can present a hazard
Drumlin
- Deposition of glacial till as a glacier moves,
- Half egg shaped
- Long axis is parallel to direction of ice
Equilibrium line
- Imaginary boundary
- Line between ablation zone and accumulation zone
Erosion
- Material broken down and worn away
- Many ways e.g. abrasion, plucking, freeze-thaw
Erratics
- Rock sediments transported and deposited by a glacier
- Different geology to surroundings
- Up to 3m across
Freeze-thaw weathering
- Aka frost-shattering
- Temperatures near freezing point
- Water enters cracks in rocks, freezes, expand and then break rocks
Glacial trough
- Aka glaciated valley or U-shaped valley,
- Deep, wide shape
Hanging valley
- Tributary valley joins main glacier,
- Too high/ cold for ice to easily move
- Less eroded than main valley
- It often has waterfalls today
Holocene
- Current epoch of geological time
- Began 12,000 years ago (end of Pleistocene)
- Part of Quaternary period
Interglacial
- Time between glacial periods (ice ages)
- Average temperature is higher
Lateral moraine
- Narrow band of debris along sides of a glacier
- Ice erodes valley sides/freeze-thaw weathering
Moraine
- Frost-shattered rock and eroded sediment
- Transported and deposited by glaciers
Outwash
- Sediment deposited by meltwater streams in front of and underneath glaciers
- Sorted and rounded over time,
- Forms outwash plain
Plucking
- Type of erosion
- Meltwater freezes onto rocks and ‘plucks’ and pulls off pieces of rock as ice moves
Pyramidal peak
- 3 or more corries meet at a central point
- A steep pyramid shape
Ribbon lake
- Long, narrow, finger-shaped lakes
- Found in glaciated valleys
- Where glacier had more erosion energy so over-eroded
Rouche moutonnées
- A bare outcrop of rock shaped by erosion
- One side smooth and gently sloping
- Other side is steep, plucked and rough
Rotational slip
- Ice flows in circular motion
- Erodes hollows and bowls in landscape
Scree
- Loose stones broken away from mountain sides by freeze-thaw
- Slopes covered in angular loose stones
Snout
- Aka terminus or toe
- End of a glacier
- Always advancing or retreating
Tarn
- Deep circular lake that forms within corries when ice has melted
Terminal moraine
- Ridge of rock debris deposited at the end of a glacier
- Mix of boulders, sand, gravel and clays
Truncated spur
- Former river valley spur where ends are ‘sliced’ off by a valley glacier
- Steep cliff-like edges
Weathering
- Breakdown of material such as rock by physical (mechanical), chemical or biological processes
Ablation
- Ice loss from a glacier or ice sheet
- Melting, sublimation, evaporation, ice calving, avalanche etc.
- Ablation zone where net loss occurs
Accumulation
- Build-up of glacial mass
- Accumulation zone where there is net accumulation
Albedo effect
- Reflective capacity of material to return incoming solar radiation
- White surfaces have high albedo effect
- Feedback loop: if ice surfaces melt, more dark surfaces exposed, more rapid melting
Basal sliding
- High enough temperatures produce meltwater at base
- Water reduces friction between ice and bedrock
Bergschrund
- Deep crevasse along rear wall of a corrie
- Formed as ice moves away downhill
Cold-based glaciers
- Higher latitudes
- Less seasonal variation in temperature, less meltwater
- Moves by internal deformation
Compressional flow
- When gradient is less steep, or ice moves over a major obstacle, it slows down
- Crevasses close, fractures form in ice
- Thicker ice increases mass and pressure, eroding more
Englacial moraine
- Moraine carried in glacial ice
Eskers
- Long ridge of sediment deposited by meltwater from retreating ice
Extensional flow
- When the gradient becomes steeper, the ice accelerates
- Ice stretches, becomes thinner
- Cracks and crevasses created at 90º to flow
Fluvioglacial
- Term relating to erosion or deposition caused by flowing meltwater from glaciers or ice sheets
Gelifluction
- Form of solifluction in periglacial environments
- Downslope sliding movement of seasonally thawed and saturated soil
- Assisted by permafrost
Glacial budget
- Balance between inputs and outputs in glacial system
- Typically losses mass through evaporation and melting at snout
Internal deformation
- Mostly in cold-based glaciers
- Gravity and pressure in accumulation zone causes crystals to slide over each other, crumple and deform
- Can form crevasses
Kames
- Aka kame terraces
- Steep-sided flat-topped mound of gravel and sand
- Deposited by meltwater from retreating ice
- Terrace forms when sediment accumulates in ponds and lakes
Kettle holes
- Rounded hollow filled by a lake, that forms due to a melting ice mass that is trapped within deposits
Mass balance
The net change in a glacier’s mass over a year; this can be positive, if the glacier accumulates more mass than is lost through ablation, or negative, if there if more ablation that is accumulated
Medial moraine
Weathered rock debris bands that run along the centre of a glacier, forming when lateral moraines from two glaciers merge together
Misfit stream
Once all the ice has melted and a river returns to the deglaciated valley, it can look unexpectedly small in the scale of the wide glacial trough
Moulin
A cylindrical vertical or near vertical shaft within a glacier, formed by surface meltwater percolating through a crack in the ice and scouring
Needle ice
Another form of ground ice, with slice of ice that penetrate down through the soil vertically - crucial to breaking up soil particles to loosen them for erosion and transportation
Nivation
A group of processes such as freeze-thaw and mass wasting serve to carve out depressions and hollows in the ground, which can enlarge over time to form corries
Periglacial
An area adjacent to a glacier or ice sheet that is subjected to repeated freeze-thaw processes, a cold climate that commonly has permafrost, e.g. Canada, Greenland, Siberia
Pingos
Hills that have an ice core, and are usually circular or dome-like in shape; the ice in the centre accumulates due to hydrostatic pressure or groundwater flow
Pleistocene
The most recent epoch during which ice coverage was much greater than it is today, from approximately 2.5 million years ago until 11,800 years ago
Recessional moraine
Similar to terminal moraine, and are deposited wherever the snout remained static for long enough to accumulate debris
Rotational scouring
Layers of rock debris from the valley sides build up on the surface of the glaciers over time, and each successive winter it becomes embedded within the growing ice; bands of slowly rotating frozen rock then scrape over the bedrock to erode when ice moves downhill
Solifluction
A process of gradually moving wet soil or other material down slope, particularly when frozen subsoil acts as a barrier to prevent percolation of water; a form of slow mass movement
Striations
Grooves that are scratched into the bedrock below ice as the glacier moves and transports material down valley; these lines show in what direction the ice flowed
Thermokarst
Irregular land surfaces found in periglacial landscapes that consist of alternating hills and hollows that are formed when permafrost thaws
Till plains
When a large portion of ice becomes detached from the main glacier and melts, any suspended sediment within the ice will be deposited and form a large plain of unsorted till material
Warm-based glaciers
Also known as temperate glaciers, these are found at lower latitudes; temperatures around the glacier are warmer allowing ice to move more rapidly with increased liquid meltwater and basal sliding e.g. The Alps, The Rockies
