Lesson 8 periglacial processes and their landscapes and landforms

Ice heave, frost push and other periglacial processes explained as well as the action of freeze thaw and the features it presents

1. Periglacial Processes and their landscapes and Landforms Lower Sixth

2. What we’ll learn today There are 4 basic processes that help cause the landscapes we see There are various types of landforms and features we need to know That mass movement, snow, wind and meltwater have a key role in the formation of landscapes That many of these can be seen within the UK as Relict features

3. Distinctive Landscapes These areas develop distinctive Geomorphology because of FOUR basic processes Water expands by 9% upon freezing which can cause Frost shattering creating scree and block fields The contraction and cracking of rapidly freezing soils in which ice wedges form as well as frost heaving which creates patterned ground Migration of sub surface water to the ‘freezing front’ via suction causing segregated ice to form leading to ice lens and pingos Mass movement of the active layer downslope via Solifluction leading to lobes and terraces Other processes such as wind and fluvial action also exist but are not exclusive to periglacial areas

4. Periglacial areas and Permafrost Periglacial literally means ‘edge’ of glacial. They are found on the fringes of polar environments They contain permanently frozen ground (Permafrost) During the brief warmer summers the surface of the ground thaws Periglacial environments are not permanently covered by ice.

5. Remember how climate changes slowly POLAR CONDITIONS WARMER CONDITIONS

6. Permafrost Within permafrost there are three layers the top layer is the active layer as it melts and freezes with summer and winter temperature changes Beneath this is the permafrost zone where temperatures are too cold to ever melt and then there is the unfrozen ground due to the geothermal gradient of the planet

7. Distribution Periglacial distribution is straight forward FOUND on the fringes of polar regions In-between polar and boreal conditions Sub Arctic conditions

8. Frost Action – Ice wedges Freeze thaw action is one the most important parts of Periglacial and glacial activity. We know this as frost shattering Explanation In extremely low temperatures the ground contracts and cracks develop During the summer meltwater fills these cracks In the winter they expand by 9% making them able to hold more water in the summer. This cycle continues

9. Ice Wedge Polygons - >>WATCH<<

10. Ground Ice Features Ice wedge polygons Downward narrowing masses of ice that are between 2 to 3 metres wide at the base and extend below the ground surface up to 10 metres Explanation Formed by the refreezing of the active layer during winter causing soil to contract and cracks open. During the melting of the summer the cracks fill up with meltwater and sediment then refreeze the following winter which will widen and deepen the crack

11. Patterned Ground - Explanation They are formed by a series of movements resulting from frost action Frost push (caused by hydrostatic pressure) propels the stones upwards, whilst frost heave causes stones to migrate outwards to form circles The up doming of the circle created by the heaving mean that larger stones roll outwards due to gravity leaving finer sediment in the centre As a result stone polygons are elongated into stone nets and stripes which has a clear relationship between the type of patterned ground and slope angle Beyond 30 degree angle patterned ground can no longer form and rock avalanches may occur

12. Rock Stripes

13. Frost Heave - >>WATCH<<

14. Pingo Formation - >>WATCH<<

15. Pingos Description Ice-cored hills with a height between 30 to 70 metres and a diameter between 100 to 500 metres Most pingos are circular in shape. Large ones usually have exposed ice at their top and the melting of this ice often forms a crater. Sometimes the craters are filled with water forming a lake. Explanation The freezing of water in the upper layer of soil creates ice lens and leads to the expansion of ice The growth of the ice core forces up the overlying sediments, causing dilation cracks, once the ice core is exposed it melts causing the top of the pingo to collapse forming a crater.

16. Two types of Pingos occur Open System Hydraulic pingos (E. Greenland) found in the discontinuous zone of permafrost or valley floors. Freely available groundwater is drawn towards expanding ice core so the pingo grows from beneath the ground

17. Pingos Closed System Hydrostatic pingos (Mackenzie delta type) associated with low lying flat areas in zones of continuous permafrost. Form from downward growth of permafrost, often after a small lake is enclosed with sediment

18. Water under the ground is under pressure and is forced up to the ice front (ice lens) causing it to freeze and expand the ice Formed on the site of a lake infilled with sediment. meaning the ground is insulated, water collects beneath the sediment. In the winter the sediment freezes, and expands. This confines the water and increases pressure. It then freezes and expands, pushing the sediment above it upwards forming a mound. During the summer the ice core melts causing the mound to cave in on itself leaving a dip.

19. Frost Shattering Freeze–thaw weathering puts pressure on any cracks in rocks and can shatter them Whilst this is not unique to periglacial areas it does occur with greater severity than elsewhere and the features it produces are important. Block fields Scree or talus slopes

20. Blockfields Caused by in situ freeze thaw action

21. The Role of Mass Movement Periglacial landforms and Processes

22. Mass Movement Comes in two types mainly Frost Creep Very slow form of movement, material moves downslope by just a few cms per year even on steeper slopes Solifluction – Occurs in regions with permafrost during the summer the active layer melts forming a mobile water saturated layer This can create stone banked or turf banked lobes on slopes of 10 – 20 degrees On more gentle slopes terraces or benches occur The resulting deposits collect at the bottom of the periglacial valleys and are known as ‘head’ or coombe rock The rocks themselves shows downslope orientation and both angular and sub angular shapes

23. Solifluction This is the slow downhill flow of saturated soil. It is common in periglacial environments It is where the active top layer provides enough water to allow flow to occur. As saturated soil slumps downhill during the summer it forms solifluction lobes

24. Solifluction in the Cairngorm A number of features of the Cairngorm environment contribute to active solifluction : frequent freeze-thaw cycles saturated soils and regolith (loose soil covering rock), after snow melt and heavy rainfall frost-susceptible materials, with significant contents of silt and clay extensive regolith across a range of slope angles

25. Asymmetric Valleys Differential rates of Solifluction and frost creep lead to one side of the valley being significantly steeper than the other. For instance in the northern hemisphere south facing slopes are more exposed to the sun and so thaw more frequently thus increasing soil moisture and promoting mass movement, leading to less steep slopes

26. The Role of Snow Periglacial landforms and Processes

27. Nivation This localised process occurs when both weathering and erosion takes places around or beneath a snow patch It is common in periglacial areas and leads to nivation hollows which form at the base of slopes and can initiate the formation of cirques at times It is geomorphic activity enhanced by snow that persists into the melt season

28. The Role of Wind and Meltwater Rivers Periglacial landforms and Processes

29. Wind Action Due to periglacial areas generally suffering from extreme aridity due to moisture being locked up in ice, the lack of flora means that wind can play a large role During the Pleistocene Ice ages deposits of fine silt and sediment formed extensive outwash plains (Sandurs) These sediments were blown southwards and deposited as loess over large areas of Europe and N. America which formed soils of high agricultural potential Similarly the winds of the Gobi desert are blowing fine material to the loess plateau in N. China (So therefore not unique to periglacial areas

30. Role of Meltwater Water erosion is highly seasonal occurring in spring or summer Due to melting of the active layer this leads to short periods of high discharge This causes typically braided rivers due to the high amount of material carried during higher discharge This though is not unique to periglacial regions and can be seen on many rivers in mountainous areas which suffer high discharge

31. Relict Periglacial Features Periglacial landforms and Processes

32. Periglacial features can form distinctive relict forms when the climate begins to warm In Paraglacial conditions (Rapidly changing landscapes which were once periglacial but now moving towards non glacial) after the rapidly melting permafrost a thermo- kast landscape can occur containing large surface depressions and irregular shaped lakes In areas of the UK it is only comparatively recently that many of the mysteries features have been credited as periglacial often by comparing and surveying areas of present day periglaction (Principle of Uniformitarianism)

33. Questions: Explain 2 ways in periglacial processes have contributed to upland landscapes (6) Assess the contribution of periglacial processes to upland landscapes (12)