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GeogOnline... A2GG4b KI2 - Weathering
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		Weathering Processes: KS3 work: This process usually happens in cold, wet areas. Water enters joints / cracks in rocks and freezes. As water freezes it expands, putting pressure on the joint / crack. The water then thaws as the temperature rises above 0°C, releasing the joint / crack. When the temperature drops again, the water refreezes and so on, eventually the rock breaks off from the pressure. The diagram below shows this process in action: The process is sometime called frost shattering. It is a type of mechanical weathering. The cold conditions lead to very limited chemical weathering processes.
The weathered angular rock fragments fall down slopes under the pull of gravity and form scree or talus slopes. The process is most active in periglacial environments where the temperature fluctuates around freezing point. It is the number of cycles of freezing and thawing that matters not the degree of coldness. Permanently frozen polar glacial areas would have little freeze thaw weathering.
Solifluction Process		Periglacial Processes: Mass Movement During the warmer seasons, mass movement can be a common phenomenon in periglacial environments. It usually occurs in four forms: solifluction; gelifluction; frost creep and rockfalls. Solifluction is the slow downslope flow of soil and sediment that is saturated with water. This process can occur on very shallow grades. The common sign of this form of mass movement is the presence solifluction lobes, tongue like semi-mixed surface deposits. In periglacial environments, solifluction is confined to times when temperatures are well above zero and free liquid water is available in the active layer. Solifluction is very common when surface sediments are poorly drained and quite saturated with water.
Gelifluction is a form of solifluction where the moving materials slide over a slick permafrost layer. Frost creep is the slow downslope movement of soil and sediment because of frost heaving and thawing (Figure 11q-5). The process begins with the freezing of the ground surface elevating particles at right angles to the slope. The particles are elevated because cold temperatures causes water in between particles to freeze and expand. In the warm season, thawing causes the ice to convert back to liquid water and the contracting surface drops the particles in elevation. This drop, however, is influenced by gravity causing the particle to move slightly downslope.
		Pressure Release Rocks below the earth surface support the weight of the overlying column of rock. Erosion strips away this overlying rock and decreases pressure on buried rocks. All rocks are slightly elastic, so the buried rocks respond to the reduction of pressure by expanding upwards. This results in the formation of pressure release fractures (cracks) that form parallel to the surface. .
With continued erosion, these rocks are exposed on the surface and slabs of rock break off along the pressure release fractures. This weathering creates bare rock surfaces that may be more resistant than surrounding rocks. These features are termed exfoliation domes; the slabs of rock that break off are termed exfoliation sheets The map opposite shows isostatic rebound in metres for Canada since the Ice Age. The yellow area is over 80 metres rebound and the red is over 100 metres. This uplift caused by Ice Melting and weight removal stimulates weathering and adds to pressure release expansion cracking of underlying layers.