Flashcards
Periglacial processes and landforms
Flashcards do conjunto (32)
- 1What is a periglacial area?Refers to area that lie adjacent to glacial environment but they are not glaciated. They are typified but the presence of permafrost. Have tundra vegatation.
- 2What % of the world land is periglacial?25% (another 25% is relict)
- 3What is permafrost?It is permanently frozen ground, its surface may melt in summer this is called the active layer. There are three types.
- 4What are the three types of permafrost?1. Continuous- very cold, no active layer. Very few taliks
2. Discontinuous- little warmer, more noticeable taliks. Have active layer in summer
3. Sporadic- just below freezing, permafrost isolated. Lots of talik and significant active layer - 5What are the 5 reasons affecting distribution and extent of permafrost?1. Proximity to water - water can retain heat for longer so the land in close contact with water remains unfrozen
2. slope angle and aspect - this influence the amount of solar radiation received
3. character of ground surface - different rock and soil types absorb different amounts of solar radiation (dark and compact absorb more while light and loose absorb less)
4. vegetation cover - blocks sunrays from reaching permafrost
5. amount of snow (insulation) - in winter can delay the freezing of the active layer, in spring can delay the thaw - 6What is talik?unfrozen sections within the permafrost
- 7What are the three different types of talik?1. Open talik - occurs upwards from the frozen ground, usually under lakes (insulation) where ground is insulated from above
2. Closed talik - within the permafrost. can occur for 2 reasons. Firstly, as water changes from liquid to solid it releases heat called latent heat. This warms and unfreezes the ground to form talik. Secondly, high pressure = high temperature (ask teacher)
3. sub-permafrost talik occurs beneath peramost zone and is a product of geothermal heating - 8What is frost heave?Causes individual snow particles to move towards the surface. This happens because an ice crystal forms under the stone, the water expands by turning into ice. Therefore, overlying stones are pushed up to the surface by the ice. Particles move parallel to the temperature gradient. During melt the ice thaws and finer material takes places of the previous ice. It is a slow process.
- 9What is freezethaw (periglacial) ?occurs in 2 timescales: annual cycle (Winter freeze/ summer thaw) and diurnal cycle (Night freeze/ daytime thaw). Also known as congelifraction.
- 10What is hydrolysis?Chemical weathering process. Occurs in summer due to abundance of liquid water and vegetation forming acid which weather granite landscapes.
- 11What is carbonation?Occurs as carbon dioxide is more soluble in rainwater at lower temperatures and forms carbonic acid.
It is particularly important in limestone areas as the carbonic acid reacts with calcium carbonate to break this limestone down. Calcium bicarbonate is produced which is then removed in solution. - 12What is nivation (Periglacial)?Nivation is a set of processes that occur beneath a snow patch. Transforms a hollow into an embryo landform. Snow provides meltwater but also insulation leading to interesting combination of processes. Speed of hollow formation depends on intensity of disintegration of bedrock and the speed of removal of the weathered material by melt water.
- 13What is the difference between solifluction and gelifluction?They are both water processes. Gelifluction is when the subsurface is completely frozen whereas solifluction occurs only over a non-frozen surface.
- 14Give 2 qualities of ephemeral streams. Describe how dry valleys are created?Ephemeral streams have high discharge and high erosive power but low duration (around 10 days per year).
Continuous permafrost prevents infiltration of the meltwater so the meltwater flows over the surface. With its high erosive power it creates a v shaped valley. If the permafrost melts the meltwater infiltrates leaving a dry valley (no river). - 15What are solifluction and gelifluction?Soil particles are broken down/ forced apart by ground ice over winter. This broken down soil is called regolith.
In summer the ground ice melts and pore water pressure increases. This adds moisture to the regolith.
The regolith movesdownhill under gravity. WIth the underlying impermeable permafrost acting as a sheer plane (slide).
The amount and speed depends on 3 factors: amount of vegetation (can hold soil together), the amount of precipitation, the gradient .
There has to be lots of ground ice for this to occur. - 16What is frost creep.When water turns into ice the crystals are perpendicular to the ground surface (parallel to the temperature gradient). Therefore (as in frost heave), stones move vertically upwards and downwards (during thaw).
Movement is greatest towards the surface and decreases with depth. - 17How does wind affect periglacial areas?Due to lack of vegetation (tundra) the soil is loose and fine. Periglacial areas are also often in areas of high wind. This cold wind picks up large amounts of material and carries it far beyond its source.
Its deposited in landforms called loess (can be v extensive) - 18What is an involution?It is a folded structure that develops within the active layer. It is always present beneath patterned ground. Repeated freezing and thawing of the water within the active layer causes expansion and contraction of the material. This churns and breaks up the material - this process is known as cryoturbation.
- 19What are ice lenses?Different materials freeze at different speeds (e.g. sand faster than silt). Frozen material becomes isolated and form an ice pocket. Further water is drawn in and frozen to the ice mass. This pushes up overlying sediment causing doming of the ground.
- 20What are ice wedge polygons?Occur in areas of continuous permafrost where soils are poorly drained. During winter ground contraction causes cracks to develop from the surface to the permafrost. These cracks take on a polygon pattern (on surface). During thaw water seeps down these creeks and refreezes, widening the cracks. This allows more water in next time. This repeats. The edge of the polygon can be marked by ridge of stone brought up by frost heave (leaving polygon lower than the sides).
- 21What is patterned ground? How does it form?Stones and other material bought to surface by frost heave. Stones roll outwards thus forming a circle whilst the finer material is left in the centre (this is called frost thrust).
Shape arises depending on gradient. But does not occur in gradients above 30o. As gradient increases (up to 30) the polygons elongate. - 22What are pingos?Large mounds within a permanent ice core. That interrupt flat tundra plain. May have ruptured summit. Usually develop in areas of continuous permafrost.
- 23How do open system (hydraulic pingos) pingos form?/ Where do they occur?Surface water infiltrates in to the upper layers of the ground where it freezes. As it freezes it expands, forming localised mass of ice. This increased pressure forces overlying sediment upwards in to a dome.
They occur in valley bottom where there are areas of discontinuous permafrost. - 24How do closed system (hydrostatic pingos) pingos form? Where do they occur?Water (from lake) insulates ground beneath so it does not freeze (talik). Eventually the lake will disappear so ground is no longer insulated. The talik will begin to freeze and from an ice core. Ice core is pushed up by surrounding permafrost to create a dome.
If ice core melts the pingo can rupture.
Occur in flat lowlying areas with continuous permafrost. Form on sites of small lakes. - 25What is thermokast and how does it form?It is depressions in the ground formed by thawing of ground ice.
Ice wedges and ground ice thaw and the ground above settles unevenly.
Occur in poorly drained areas. - 26What can cause/ increase thermokarsts?Thermokarst occur because ice melts - therefore they are caused by temperature increases.
Natural/ anthropogenic climate change has increased the rate of thermokarst formation.
Locally, central heating from houses, mining, utility pipes and removal of vegetation can increase thermokarsts. - 27What are tors and how do they form?A tor is a dramatic rocky peak often found in upland areas.
They form by both physical and chemical weathering. Physical weathering e.g. freeze thaw, dilution (pressure release from removal of weight above). Chemical weathering e.g. hydrolysis.
It is surrounded by blockfields. - 28What are blockfields?These are an accumulation of frost-shattered stones and boulders on a relatively flat surface. They are created by freeze-thaw and frost heave of jointed rock.
Commonly found on mountains and surround tors. - 29What are scree slopes/ talus (periglacial)?Scree (angular rock fragments from freeze-thaw weathering) . Scree accumulates at the base of the valley and forms a scree slope. The gradient is higher at the upper part and lower at the bottom.
Larger scree tends to accumulate lower down the slope because of its increased mass (and momentum).
Scree slopes can occur anywhere but are most rapidly formed under periglacial conditions. - 30What are gelifluction lobes?They are tongue shaped deposits of material from gelifluction, orientated down slope between 10-20o. They may be stone banked or turf banked depending on the amount of vegetation cover and whether frost heave has occurred before gelifluction.
- 31What are head and coombe deposits?This is when Solifluction/ gelifluction deposits infill valleys (moves downslope). Builds up into deep layers called head deposits. The head deposits contain a mixture of fine sand and frost shattering material. Coombe deposits refer specifically to frost shattered and geliflucted chalk and flint.
- 32How do asymmetrical valleys form?Different sides of valley will receive different amounts of solar insolation. (In N.Hemisphere the south facing receives more sun). The side with more insolation will have more frequent freeze thaw cycles thus there is more what weathering and gelifluction. Therefore on the more insolated side (because of gelifluction) material will move to the base of slope as a lobe. This side will be shallower than the less insolated slope.
A stream at the bottom of the valley may undercut the less-insolated slope and steepen it.
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- A level Geography FlashCards sobre Periglacial processes and landforms, criado por William Holcroft em 29-12-2018.
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- William Holcroft
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