systems and processes in glaciers and glacial landscapes Flashcards
Ablation
the natural removal of snow or ice from the surface of a glacier or snowfield. this can occur through melting, sublimation or calving
calving
breaking of ice chunks from the edge of a glacier
sublimation
Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage.
accumulation
the addition of snow or ice
snow line
the lowest elevation on mountains where snow remains year-round
Adret slope
the side of the mountain that is exposed to sunlight
ubac slope
the side of a mountain that is not exposed to direct sunlight
firn/neve
it is when lower levels of snow are compresses by the upper levels as snow accumulates making it very compact (forms after two seasons of accumulation). solid ice develops after 20-40 years after all the air has squeezed out.
zone of accumulation
the upper part of the glacier where inputs exceed outputs and therefore more mass is gained than lost over a year.
zone of ablation
where outputs exceed inputs in the lower part of the glacier, and mass is lost rather than gained
the boundary between the zone of accumulation and ablation
where net gain and net loss is balanced - the equilibrium line.
net balance
difference between total accumulation and total ablation in 1 year.
Glacial advance
When accumulation exceeds ablation - Snout moves downwards
Glacial retreat
When ablation exceeds accumulation - Snout move upwards
Glacials
Cold periods in Earth’s history when glaciers have advanced and ice sheets increased in size
Interglacials
The warm periods that occur during ice ages or between ice ages
Glacial area in europe
6,500km squared
Are most glaciers retreating?
Yes but some in Alaska and the Himalayas are advancing.
3 types of glaciers
Temperate/warm based, polar/cold based and sub-polar
Where are warm based glaciers located?
In temperate and alpine regions with high winter snowfall rates and spring/summer temperatures high enough to cause rapid summer melt rates.
Where are cold based glaciers located?
Found in areas of high latitude within the Arctic and Antarctic circles and in cold areas of Alaska and Canada. Low precipitation and aid conditions
The characteristics and development of temperate/warm based glaciers
Large amounts of meltwater which acts as a lubricant, faster rates of movement –> more erosion, transportation and deposition. The surface (thin layer - few metres) melts rapidly and insulates the layers of ice beneath it. Lower melting point at base of glacier due to high pressure (pmp). Temperate glaciers can be relatively thin so more ice influenced by geothermal heat
Pressure melting point (pmp)
The temperature at which ice under pressure will melt. At the base of a 2000m deep glacier the melting point is -1.27C
The characteristics and development of polar/cold based glaciers
Little accumulation, virtually no melting. Ice at base can be 100,000 years old. All ice except the most upper surface layers that can be exposed to summer temperatures is below the melting point. Little meltwater due to little geothermal and atmospheric heat. Most ice loss is due to sublimation and ice calving. Frozen to bedrock to v slow movement (mainly internal flow) - little erosion, transportation and deposition
Sublimation
A change directly from the solid to the gaseous state without becoming liquid.
Weathering
The breakdown and/or decay of rock at or near the earth’s surface creating regolith (debris) that remains in situ until it is moved by later erosional processes. Can be chemical, mechanical or biological (very little in cold environments due to low temps)
Frost action (freeze-thaw action) - frost shattering
Occurs when temps exceed 0C during the day but drop below freezing at night. Water enters cracks in rock and freezes overnight and expands by <10% which exerts pressure on surrounding rock. This process repeats which widens cracks and breaks off rock. This can collect at the bottom of a slope (scree slope) with scree at the bottom
Moulin
A vertical or nearly vertical shaft in a glacier, formed by surface water percolating through a crack in the ice.
Nivation
Series of processes that operate underneath patches of snow in hollows. Freeze-thaw action and chemical weathering causes underlying rock rock to disintegrate. As some of the snow melts in spring the weathered particles are ‘flushed out’ of the hollow and moved downslope by meltwater and solifluction. This repeated process forms nivation hollows which can be the beginnings of a corrie
Ice has great rigidity and strength, but under steady pressure it behaves as a …….. ………… body
plastic (mouldable)
What happens when ice is put under sudden compression/tension?
It will break or shear apart
Rigid zone
Upper part of glacier where ice is brittle, breaking apart to form crevasses
Zone of plastic flow
The lower zone of a glacier which has steady pressure and meltwater and friction with bedrock enables a rapid plastic flow
Internal deformation including creep
Occurs when stress builds up allowing the ice to behave with plasticity and flow. This is common when obstacles meet. Internal flow. Main feature of the flow of a cold based glacier
Internal flow
It involves ice crystals orientating themselves in the direction of the glaciers movement and sliding past each other
Rotational flow
Occurs within a corrie. Ice moving downhill cn pivot around a point, producing a rotational movement. This combined with increased pressure within the rock hollow leads to greater erosion and an over deepening of the corrie floor
Compressional flow
Occurs when there is a reduction in the gradient of the valley floor leading to deceleration and a thickening of the ice. Ice erosion is at its maximum
Extensional flow
Occurs when the valley gradient becomes steeper. The ice accelerates and becomes thinner, leading to reduced erosion
Basal sliding
Occurs because as the glacier moves the bedrock there is friction. The lower levels of ice are also under a great deal of pressure and this combined with friction results in some melting and the meltwater acts as a lubricant enabling the ice to move faster
Glacial surges
Occurs when an excessive build up of meltwater under the glacier leads to the ice moving rapidly forward, perhaps as much as 250m in one day
Where in the glacier does the ice move the fastest?
The centre surface ice moves faster than the base and the sides. This means ice cracks producing crevasses on the surface. These also occur where extending flow speeds up the flow of the ice, where the valley widens or the glacier flows from a valley on to a plain like a piedmont glacier
Piedmont glacier
Piedmont glaciers occur when steep valley glaciers spill into relatively flat plains, where they spread out into a fan-shaped glacier
Abrasion
Occurs where the material in the glacier is carrying rubs away at the glacier floor and sides. The coarser material leave scratches (striations) and the smoother material polishes the rock surface. The debris involved is often worn down into rock flour (very fine). This is taken away from the glacier by subglacial meltwater streams, turning them into a milky colour
Plucking
It involves the glacier freezing onto and into rock outcrops. As the ice moves forward it pulls away masses of rock .Only found at base of glacier where there is a low pmp and meltwater
Supraglacial debris
Material transported on the surface of the glacier
En-glacial debris
Material transported within the glacier
Sub-glacial debris
Material transported at the base of the glacier
Glacial deposition sorted or unsorted?
Unsorted
Fjord
A long, steep-sided glacial valley now filled by seawater
Ribbon lakes
A LANDFORM formed through EROSION Ribbon lakes are long, thin lakes that form after a glacier retreats. They form in hollows where softer rock was eroded more eg Windemere, Lake District
Misfit stream
Small stream flowing in the much larger valley created by a glacial melt
Sub-glacial stream characteristics
High velocity and turbulent flow due to high hydrostatic pressure enabling water to travel uphill. Stratified (due to seasonal variations) and sorted deposition
Which meltwater channels leaves an erosional trace om the post-glacial landscape?
Only those in contact with the bedrock
Pro-glacial lakes and overflow channels
During deglaciation, lakes develop on the edges of the ice, some occupying large areas. Overflows from these lakes which cross the lowest points of watersheds will create new valleys. When the ice damming these meltwater lakes totally melts, many of the new valleys are left dry, as drainage patterns revert to the pre-glacial stage. In certain cases the postglacial drainage adopts them creating new drainage patterns
Permafrost
Permanently frozen ground
When does permafrost occur?
In areas where temperatures below the ground remain below 0C continuously for more than 2 years
How much of the Earth’s surface is covered by permafrost?
20-25%
Talik
Unfrozen ground below permafrost
Areas where periglacial conditions occur
North in northern hemisphere - e.g. Alaska, Canada, northern Russia and high mountainous areas such as the Alps
Active layer
The upper surface layer of permanently frozen soil that thaws briefly during the summer. The thickness depends on local conditions
Continuous permafrost
It refers to an environment where more than 80% of the ground is permafrost. Occurs in very cold regions e.g. Siberia (1500m deep permafrost)
Discontinuous permafrost
It refers to an environment where 30-80% of the ground surface is underlain by permafrost. On average the frozen area will reach 20-30m underground occurs in warmer areas than continuous permafrost
Sporadic permafrost
Found where mean annual temperatures are around 0C. Permafrost only occurs in isolated spots where the local climate is cold enough to prevent complete thawing of the soil during summer
Solifluction
The slow, downslope flow of soil saturated with water in areas surrounding. It occurs when summer temperatures rise enough to melt the huge amounts of ice in the upper layers of permafrost. The water cannot drain due to the impermeable permafrost below and the little evaporation making this layer very wet. Excessive lubrication reduces the friction between the soil particles. On even slopes at 2 degrees the saturated layers become mobile and the soil moves downslope. When related to freeze-thaw this is called gelifluction
Frost creep
Gradual downslope movement of individual soil particles due to the alternating freeze-thaw cycles within the active layer
Blockfield
A substantial area covered by boulders, without soil cover and often with little or no vegetation; common in Arctic and Alpine regions. Also known as a rock sea or felsenmeer
Rock falls
Loose rocks fall down a steep slope (in relation to freeze-thaw action)
Open talik
Talik that exists directly below a lake
Through talik
Only found under large deep lakes that provide enough heat for the talik to reach down
Closed talik
Closed taliks can develop when lakes fill in with sediment and become bogs. With the removal of the open water, summer solar radiation is now being received by a surface with a lower specific heat and poor vertical heat transfer. As a result, soil near the surface begins to freeze solid encasing a zone of unfrozen soil in permafrost
