Glaciation Flashcards
4 periglacial landforms
Ice wedges
Patterned ground
Pingos
Loess
Ice wedge polygons
- downward narrowing masses of ice between 2-3m wide at base and extend below ground up to 10m
- formed by refreezing of active layer during winter causing soil to contract and cracks open. During melting in summer cracks fill with meltwater and sediment then freeze the following winter, widening and deepening the crack
Patterned ground
- covers features like: nets, polygons, steps and stripes
- formed by movements resulting from frost action:
- frost push caused by hydrostatic pressure propels stone upwards, whilst frost heave causes stones to migrate outwards to form circles - this provides basis for all patterns
- up doming of circle crested by heaving mean larger stones roll outwards due to gravity, leaving finer sediment in centre
- as a result, a stone polygons are elongated into nets/stripes which has clear relationship between type of patterned ground and slope angle
- beyond 30 degrees angle, patterned ground can no longer form and rock avalanches may occur
Pingos
-ice cored hills between 30-70m high and diameter between 100-500m
- growth of ice cores forces up overlying sediments, causing dilation cracks, once the ice core is exposed it melts which causes top of Pingo to collapse, forming a crater
- most Pingos circular in shape
- smaller Pingos tend to have curved top
- large usually have exposed ice at top and melting of this often forms crater which are sometimes filled with water to cause a lake
7 macro features (<1km)
- Cirque/corrie/cŵn
- Arête
- Pyramidal peak
- Truncated spur
- U-shaped valley
- Hanging valley
- Ribbon lake
4 meso features (10m-1km, usually found in macro features)
- Whalebacks
- Crag and tail
- Roche moutonneees
- Knock an’ Lochan
3 micro features (few metres and less)
- Chatter marks
- Striations
- Crescentic gouges
Milankovitch theory
(Long term climate change)
Earths orbit varies every 100,000 years. Elliptical to more circular
Means amount of solar radiation in summer and winter changes, impacts seasonal changes
Low eccentricity = low seasonality = glaciation, as a result temps at high latitudes in northern hemisphere decrease
Axil tilt = obliquity
(Long term climate change)
Varies between 21.8-24.4 degrees, does this over 41,000yr timescale
Impacts intensity of light received at the poles, so effects seasonality
Less tilt = warmer winters + cooler summers = glaciers don’t melt and advance = more solar radiation reflected so variations in ice volume.
Low obliquity = low seasonality so promotes glacation
Precession - wobble
(Long term climate change)
Earth wobbles on it’s axis over 21,000 year cycle, changing when earth is nearest to sun, increasing variation of irradiation of northern hemisphere
This impacts summer and winter temps which impact ice volume.
Glacation favored when direction of tilt means n. Hemisphere summers are at the largest earth-sun distance
Compressional flow
Ice mass thickens as slope gradient reduces and movement slows.
Potential for erosion increases
Extensional flow
Ice mass thins and movement increases when slope gradient gets steeper.
Erosion potential decreases
Factors controlling glacier movement
Lithology
Altitude
Slope angle
Size/thickness
Mass balance
Ice temp
Processes contributing to glacier movement
Basal sliding
Internal deformation
Regelation creep
Extensional and compressional flow
Rotational flow?
Basal sliding
- temp water freezes at decreases under pressure
- glacier moves and exerts pressure so there’s melting at base
- meltwater acts as lubricant allowing glacier to move
