Flashcards
Periglacial processes and landforms
Flashcards do conjunto (24)
- 1What is permafrost?This is permanently frozen ground with a top layer that can melt in the summer. (called the active layer). It is impermeable (water cannot flow through it).
20-25% of the earth's land surface is permafrost. - 2What are the different types of permafrost?Continuous (all the ground is frozen)
Discontinuous (only patches of the ground is frozen) - 3What is needed for discontinuous permafrost to form?Th mean annual temperature needs to be below 0 degrees for at least two years.
- 4What is needed for continuous permafrost to form?The mean annual temperature needs to be below -5 degrees.
- 5What is solifluction?When the temperature gets above 0 degrees in the summer, the active layer melts but the water cannot go anywhere. This means that the active layer gets waterlogged and will easily flow wherever there is a gradient.
- 6What is frost contraction?When temperatures drop very low in the winter, the ground contracts and cracks form in the permafrost.
The permafrost layer is still frozen so the water freezes in the cracks- the ice filled cracks formed in this way are called ice wedges.
Frost contraction in following years can reopen cracks in the same place splitting the ice wedge. More water seeps in and freezes widening the ice wedge. The ice wedge gets bigger each time this happens. - 7How is frost heave formed?Water freezing in the ground can make humps on the surface. When the active layer freezes in winter the ice forms a lens shape.
In fine grained soil (like silt or clay) the ice lifts (heaves) up the surface layers of the soil. This is called frost heave. - 8Where else do ice lenses form and why?Ice lenses also form underneath stones because stones lose heat faster than the soil around them, so when temperatures drop it is colder beneath the stone.
As the ice lenses expand, they push the stones upward towards the surface of the ground. The ice lenses underneath the stones stop the stones from slipping back down. If the ice thaws, fine material fills in the space where the ice was so the stones don't fall down. Eventually the stones rise above the surface of the ground. - 9What is patterned ground?This is when stones on the surface of the ground are arranged in circles, polygons or stripes.
- 10How is patterned ground formed?Either by frost heave or by frost contraction.
- 11Explain how patterned ground is formed by frost heave?Stones get pushed to the surface by frost heave. Once they reach the surface, they roll down to the edges of the mounds that are formed, so they form circles around them (polygons form when the mounds are close together). If the mounds are on a slope, the stones roll downhill and form lines.
- 12Explain how patterned ground is formed by frost contraction?Frost contraction causes the ground to crack in polygon shapes. The cracks get filled in with stones, forming polygon patterns on the surface.
- 13How does nivation make hollows deeper?When snow gets into a hollow in the ground, it can increase the size of the hollow. The temperature in periglacial environments often fluctuates around 0 degrees so a lot of freeze thaw occurs. every time the ice freezes it expands, so frost shattering eventually breaks bits off the rock at the base of the hollow. When the snow melts, the meltwater carries the broken bits of rock away .
- 14How does nivation make hollows deeper? (II)Slopes collapse as they are waterlogged and eroded. The material is washed away by meltwater.
Eventually, the hollow becomes deeper and wider. The processes that cause this are collectively called nivation. - 15What are hollows formed by nivation called?Nivation hollows (these can be the beginning of a corrie).
- 16How does solifluction produce lobe formations?The waterlogged active layer of soil flows easily over the frozen impermeable layer beneath. Solifluction produces lobe formations where one section of the soil is moving faster than the soil around it e.g. because it is on steeper ground, so it flows down further to create a tongue shape.
- 17What is a Pingo?This is a conical hill with core of ice which can be as large as 80m high and 500m wide.
If the ice thaws, the bingo collapses leaving behind a pond of meltwater, surrounded by ramparts. (walls of soil) - 18What are the two types of Pingo?Open system and closed system.
- 19How do open system pingos form?These form where there is discontinuous permafrost. Ground water is forced up through the gaps between areas of permafrost (from unfrozen layers lower down). The water collects together and freezes forming a core of ice that pushes the ground above it upwards.
- 20How do closed system pingos form?These from in areas of continuous read of permafrost where there is a lake at the surface. The lake insulates the ground so the area beneath it remains unfrozen. When the lake dries up, the ground is no longer insulated and the permafrost advances around the area of unfrozen ground. This causes water to collect in the centre of the unfrozen ground, the water eventually freezes and creates a core of ice that pushes the ground above it upwards.
- 21What relict (past) features are associated with periglacial?Dry valleys- river valleys without rivers- common on chalk or limestone as they became impermeable due to permafrost. Erosion occurred due to spring melt. At the end of the periglacial period water sank into permeable rocks and valleys are left dry.
- 22What relict (past) features are associated with periglacial?Misfit rivers - small rivers or streams that occupy large valleys. during the periglacial phase, rapid runoff from snowmelt would have allowed these rivers to carve steep, over deepened valleys - nothing like the small streams now.
- 23What relict (past) features are associated with periglacial?Scree slopes -slopes composed of large quantities of angular fragments of rock. Th angle of the slope is stable- no further mass movements will occur.
- 24What relict (past) features are associated with periglacial?Loess - a deposit laid down by the wind. it consists of mostly of unstratified, structureless silt but also angular pieces.
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- AS - Level Geography (Cold Environments) FlashCards sobre Periglacial processes and landforms, criado por Tom Baker em 02-05-2016.
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