6) Glaciated landscapes- periglacial processes and landforms

Active layer

The top layer of soil in permafrost environments that thaws during summer and freezes during winter. thawing and freezing occurs from surface downwards. a warming climate will deepen it.

patterned ground

Unique to periglacial areas. Includes a range of features e.g. circles, nets, polygons, steps and stripes. Surface accumulation of coarse and fine debris. Ice crystals form beneath stones and push them to the surface by the process of frost heave. The stones then roll into position by gravity.

Ice wedge polygons

Unique to periglacial areas. The process of frost cracking creates areas of irregular polygons which are found on the valley floor and are usually 5-30m across. When the active layer thaws, ice wedges begin to form as water flows down into cracks and subsequently freezes and contracts meaning the ice wedges can build up over time.

blockfield

a large expanse of boulders strewn across a level surface, often in mountainous areas

fossil (relict) features

features that have been separated from the forces and processes that created them. they are old and can degrade in form

frost heave ground (Humocky ground)

ground pushed up by frost heave

Loess Plateau

large areas of deposited Aeolian derived loess. these can develop into substantial areas and thicknesses. northern China 90m thick

stone polygon (stone stripe)

nets or patterns of stones which have rolled under gravity as a result of central uplift from frost heave

periglacial and their characteristics

non-glacial cold climate areas with a high range of different high latitude and high altitude environments which may or may not contain glaciers. they occur around the edge of polar regions in the Northern Hemisphere intense frosts in winter and on any snow-free ground in summer. highest average temp range from 1°C to -4°C (annual). daily temp below 0°C for at least 9 months and below-10°C for at least 6 months. temp rarely rise above 18°C even in summer. Low precipitation under 600mm per year

permafrost

soil and rock that remains frozen as long as temps don't exceed 0°C in summer months for at least 2 consecutive years. continuous permafrost: forms in the coldest areas of the world where the mean annual air temp are below -6°C. it can extend downwards for 100s of meters. discontinuous permafrost: more fragmented and thinner than continuous permafrost sporadic permafrost: occurs at the margins of periglacial environments and is usually very fragmented and only a few metres thick. it often occurs in shady hillsides

ground ice

soil moisture freezes. can take many forms

Thermokarst

surface depressions produced by thawing of ground ice an periglacial areas. these depressions can often fill with water.

Ognip

the circular ramparts that are left when the ice core within a pingo melts and the mound collapses. these can be filled with a small lake

freeze thaw

the mechanical action caused by repeated freezing and thawing of water in pores, fissures and cracks that forces rock or other material apart

frost heave

the predominantly upward movement of soil due to expansion as water freezes within it. processes are magnified under some stones where ice lenses are formed. contributed to solifluction if on slope and there is a frequent freeze thaw cycle

ventifacts

the unique shaped rock forms created as wind blown sand erodes boulders. erosion greater at base of boulder

talik

unfrozen ground found under permafrost or in pockets. can occur under small ponds and lakes

pingo

unique to periglacial areas. a large dome shaped hill on a flat pain which often has a crater like depression on top. they are ice core mounds, which are 30-70m in height. ground frost freezes as permafrost advances to make an ice core (segregated ice), which causes overlying sediments to buckle upwards

tundra

vast treeless plains located at high latitudes above the coniferous forest belt. dominated by mosses, grasses and small shrubs

hydrostatic pressure

water experts pressure on surrounding water

ground contraction

when frozen ground continues to cool it contracts. this can causes cracking

segregated ice (similar to ice lense and ground ice)

when ice forms in a single body. can be as small as ice lenses under individual stones or as big as an ice core forming a pingo. open system: Are hydraulic or East Greenland type. they are found in the discontinuous zone of permafrost or valley floors and freely available groundwater is drawn towards the expanding ice core so the pingo grows from below the ground. closed system: are hydrostatic or Mackenzie Delta type. they form in continuous permafrost zone and are associated with low lying flat areas. they form from the downwards growth of permafrost, usually after a small lake is gradually enclosed with sediments. the loss of the lake allows permafrost to advance that traps the water putting it under hydrostatic pressure

Aeolian processes

wind has energy and can therefore erode, transport and deposit sediment. this is particularly important in periglacial environments where there is much small sediment and little vegetation to anchor it down