How are glacial landforms developed Flashcards
Weathering
- happens everywhere
- significant in formation of glacial landforms
- uses heat energy to produce chemical altered materials
Physical/mechanical weathering - Freeze-thaw
- water enters cracks and joints and expands when it freezes
- causes rock to split further and for pieces to break off
Physical/mechanical weathering - Frost shattering
- water becomes trapped in rock pores and freezes and expands causing rock to disintegrate
Physical/mechanical weathering - Pressure release
- known as dilation
- weight of the overlying glacier is lost because of continued erosion
- causes vertical pressure release
- upper layers of rock expand producing disintegration of rock masses
Chemical weathering - Oxidation
- some rock minerals react with oxygen (iron)
- becomes soluble in acidic conditions destroying original structure
Chemical weathering - Carbonation
- rainwater combines dissolved CO2 from the atmosphere and produces carbonic acid
- reacts with calcium carbonate in rocks (limestone) to produce calcium-bicarbonate which is soluble
Chemical weathering - Solution
- some salts are soluble in water
- other minerals (iron) are soluble in very acidic water
any process by which a mineral dissolves in water is a solution
Biological weathering
Tree Roots
- roots grow into cracks
- outward pressure exerted causes rocks to split and break
Organic Acids
- produced during plant and animal litter decomposition
- causes soil and water to become acidic causing them to react with minerals
- “Chelation”
Mass movement
- when forces keeping material on a slope exceed forces pushing material off a slope
- main mass movements are on steep slopes
- adds material to glacier for abrasion
- input to a system
- causes erosion and landscape change
Mass movement - Rock fall
- slopes of 40 degrees or more
- rocks can be detached by physical weathering
- transport removes material
- material may accumulate as a straight lower angle scree slope
Mass movement - Slides
- movement along a slip plane or a rotational slide
- rotational slides are known as “slumps”
- slides may occur due to steepening and undercutting of valley sides at the base of the slope
- slumps are common in weaker rocks (clay is weak and heavy when wet)
Erosion - Abrasion
- when the glacier moves along the floor and sides of the valley there is lots of friction
- rocks and debris scrapes along the surfaces creating striations (sandpaper)
-if debris is small and fine there I a polishing effect as it removes jagged rocks - the debris that wears down creates rock flour which can colour meltwater streams milky white
Erosion - Plucking
- meltwater gets into cracks in the valley floor and side
- meltwater freezes and becomes attached to the glacier
- when the glacier moves the rock moves and is plucked out the valley
- when pressure melting point is reached it aids basal plucking
- plucked rocks provide material for abrasion
How does presence of basal debris affect glacial abrasion
- pure ice cannot carry out abrasion
- basal debris is essential for abrasion
- when basal debris increases erosion increases
How does debris shape and size affect glacial abrasion
- embedded particles extert downwards pressure proportional to their weight
- larger debris is more effective and causes more abrasion
- finer debris has a polishing effect on the - sharp debris erodes in a more concentrated area
How does hardness of particles and bedrock impact glacial abrasion
- more erosion when basal debris is hard and bedrock is weak and soft
- if bedrock is harder than basal debris, friction is too great, no erosion takes place
