OCR A Level GL - 13 OCR A Level GL 2.3b Periglacial landforms and processes 2

Question 1

What are periglacial environments?

Answer 1

areas with permafrost, seasonal temperature variations and freeze-thaw cycles that are found at or near ice sheets.

Question 2

Where are periglacial environments found?

Answer 2

1. High latitude areas - Alaska and northern Canada
2. High altitudes - Plateau of Tibet, Andes and Alps
3. Continental interiors - Siberia

Question 3

What percentage of the Earth’s land surface is covered be periglacial environments?

Answer 3

25%

Question 4

What is permafrost?

Answer 4

perennially frozen ground for 2 consecutive years or more

Question 5

What is the active layer?

Answer 5

thawed surface layer where plants can live for at least part of the year

Question 6

What is freeze-thaw weathering?

Answer 6

1) Water seeps into the cracks of a rock 2) Water freezes and expands by 9% in volume which wedges the rock apart 3) When this repeats, the rock breaks into pieces

Question 7

What is frost heave?

Answer 7

a subsurface process that leads to vertical sorting of material in the active layer.

Question 8

What is patterned ground?

Answer 8

Where rock particles are distributed in a system of polygons and circles.

Question 9

How is patterned ground formed?

Answer 9

Through repeated cycles of freezing and thawing in the active layer (frost heave), larger stones are moved to the surface and the ground surface is domed. These larger stones then move, under gravity to the sides of the domes, forming a network of stone polygons.

Question 10

Typically how big is each stone polygon in patterned ground?

Answer 10

1-2 metres in diameter

Question 11

Give a named example of where patterned ground is found

Answer 11

Barrow, Alaska

Question 12

What are stone garlands?

Answer 12

elongated polygons from patterned ground

Question 13

What conditions are required for stone garlands to form?

Answer 13

slopes to be between 3-50 degrees

Question 14

What conditions are required for stone stripes to form?

Answer 14

slopes to be over 60 degrees

Question 15

What is a pingo?

Answer 15

A dome-shaped, ice-cored mound of earth

Question 16

What are the two types of pingo?

Answer 16

1. Open-system (East Greenland type) 2. Closed-system (Mackenzie delta type)

Question 17

How are open system pingos formed?

Answer 17

1. In an area of discontinuous permafrost and often in valley bottoms.​
2. Water is able to seep into the upper layers of the ground under artesian pressure.
3. Water accumulates in flat, low lying areas between the upper layers of permafrost or soil and frozen ground beneath the water, and then freezes.
4. The freezing ice core expands, thus doming the overlying layers into the classic pingo shape

Question 18

How are closed system pingos formed?

Answer 18

1. In an area of continuous permafrost some deep lakes (over 2m deep) may remain unfrozen in winter.​
2. The permafrost layer is insulated from the cold and thaws above
3. If the lake begins to drain, the lake bed is no longer insulated,​
4. as a result, the saturated bed begins to freeze..
5. Because of the localised differences in pressure between the lake, freezing lake bed and underlying permafrost, the newly freezing water gathers together to form an ice lens that expands,​
6. This expansion pushes the lake-bed sediments above it, forming a classic dome shape.​
7. This ice lens continues to grow as long as there is still unfrozen ground in the lake bed as a source of pressurised water.

Question 19

What are blockfields?

Answer 19

extensive areas of angular rock that have been created by regular freeze-thaw activity fragmenting exposed rock in situ. The material is left strewn across the level ground. ​ Large areas of these blocks are called Felsenmeer. ​ Where this occurs on rock faces on a gradient, scree will be left at the bottom of the slope where talus accumulates.

Question 20

What is solifluction?

Answer 20

Summer melt of water in the upper layers of permafrost leads to large amounts of water which cannot drain away because of the permafrost. ​

Solifluction lobes are created when the saturated active layer of soil is thawed, usually during the summer months. ​

The gradient of the ground is important too as these lobes will only form on slopes. Winter freeze-thaw weathering loosens material while summer thaw melts the ice content and then it will flow down the hill. When the gradient changes again and flattens out, the material flow slows and is deposited in a tongue shape.