Periglaciation & Associated Features THE TUNDRA

Periglaciation Cold environments which experience intense frost action and permafrost. Up to 25% of the land surface of earth is periglacial

Permafrost Ground is permanently frozen. How long does the temperature need to remain below freezing for permafrost to develop? 2 Years

Permafrost ACTIVE LAYER = Up to 4m deep (May thaw in summer) TALIK = Active areas within the permafrost (usually associated with the areas beneath rivers or lakes))

Permafrost Continuous Arctic areas, very cold. Often no thawing. Can reach 1400m deep in Siberia Discontinuous Up to 30m deep. Often with breaks around water features, or in summer Sporadic Temps hover around 0, so spots of permafrost are infrequent

Process = Nivation Feature = Nivation Hollow Remember??? Corries???? Freeze-Thaw and chemical weathering taking place below a patch of snow creating a nivation hollow Using a diagram, show how the process (Nivation) can lead to the feature (Hollow)

Mass Movement - Process Solifluction Slopes over 2 degrees Upper ‘active’ layer becomes saturated Aka gelifluction

Solifluction (AKA Soil Creep) Have a go yourself…. Why might these features occur in the periglacial environment?

Solifluction In summer, the active layers thaws. The permafrost below is impermeable, so the soil above becomes waterlogged. On a slope (as little as 2 degrees), Solifluction lobes will start to occur (Similar to a mudslide)

Frost Creep Gradual downslope movement of individual soil particles due to freeze-thaw of active layer

Terracettes Known as sheep’s tracks Possibly caused by animals in periglacial areas Possibly a combination of frost action and solifluction

Rock Falls Caused by frost shattering Links to freeze thaw in glaciation. Forms scree slopes (slopes) and blockfields (flat)

Process = Frost Heave Features = Patterned Ground. Stone Polygons Process = Frost Heave Features = Patterned Ground Stone Polygons Stone Stripes

FROST HEAVE (See handout) Due to stones rising the ground ends up with little lumps Due to the gradient, the stones fall down the lumps to form stone polygons or stripes (on steeper land) Copy figure 5.5 a and b on P118

Ice Wedges (Ground Contraction) 2 to 3 meters wide at the base and extend below the ground surface up to 10 meters. A seasonal crack in the ground forms in the winter. Cold temperatures can cause soil contraction. At first, the crack is several millimeters wide and about a meter deep. When temperatures warm up in the summer, liquid water from the active layer fills the crack. This water then refreezes because the fracture extends into the sub-zero permafrost. Ice expands (9%) This expansion then increases the width and depth of the fracture.

You can clearly see the ice which has cleaved apart the soil in this exposed profile. Ice wedge

A closer view of arctic polygons A closer view of arctic polygons. These are about 70 feet (20 meters) across, although polygons may be as small as 10 feet (about 3 meters) across.

Ice wedges Intense cooling and contraction of the permafrost in winter may cause polygonal patterns of cracks to form. In summer the cracks fill with meltwater and some loose material and, upon refreezing the following winter, the crack will be enlarged. Such ice wedges may extend to a depth of 3m and reach 1m in width at their surface. Ice wedge polygons differ from those formed by frost heave in that they are larger (30m diameter) (compared with 1-5m) and their edges are slightly higher than their centres (the edge of the ice deforms the adjacent sediments), whereas frost heave polygons are domed. The larger polygons are found where the winter temperature is below –20C. Ice wedges which are 1-2m wide and 8-10m deep can take up to 100 years to form.

The rims on an ice wedge are formed when expansion of sediment during autumn freezing causes material to be pushed upwards as it is forced against the more resistant ice wedge. If the ice wedges melt, they become filled with sediment to form ICE WEDGE CASTS – eg East Anglia

Pingos https://www.youtube.com/watch?v=4_mVhXYc7W4

Pingos Ice-cored hills with a height between 3 to 70 meters and a diameter between 30 to 1000 meters The ice at the core of pingos is thought to accumulate because of cryostatic pressure and artesian groundwater flow.

Closed System Pingo The development of a CLOSED pingo begins with a lake with no permafrost beneath it (talik). The lake then gradually fills in with sediment and invading permafrost isolates the remaining water in the lake's sediments. Continued inward and downward freezing of the old lake sediments generates enough pressure to move pore water upward. This pore water then begins to freeze to form a segregated mass of ice at the core of the developing pingo.

OPEN pingos develop when a supply of groundwater is channeled to a particular location where it freezes just below the ground surface

Ruptured Pingo When the ice core melts, the pingo may collapse to form a collapsed, or ruptured pingo

Therokarst Thermokarst is a land surface characterised by very irregular surfaces of marshy hollows and small hummocks formed as ice-rich permafrost thaws. Small domes that form on the surface due to frost heaving with the onset of winter are only temporary features. They then collapse with the arrival of next summer's thaw and leave a small surface depression

(5 marks)

(15 marks)

Describe Pingos (4 marks) Explain the formation of Pingos (5 marks) Explain the formation of patterned ground (7 marks)