Rocks & Weathering Flashcards
Carbonation- solution
Rocks with calcium carbonate ie. Chalk, limestone
Rainfall combines with dissolved carbon dioxide or organic acid to form a weak carbonic acid
Hydrolysis
Occurs on rocks with orthoclase feldspar ie granite
Feldspar reacts with acid water and forms kaolin, silicic acid and potassium hydroxyl
Acid and hydroxyl removed leaving behind kaolin containing quartz and mica
Hydration
Certain minerals absorb water, expand and change
Oxidation
Occurs when iron compounds react with oxygen to produce a reddish- brown coating
Van’t Hoff’s Law
Rate of chemical weathering increases 2-3 times for every increase of temperature of 10*C
Chemical weathering increases with
Moisture and heat
Efficiency of freeze - thaw, salt crystallisation and insolation weathering is influenced by …
Critical temperature changes
Frequency of cycles
Seasonal variations in temperature
(4) Rock type influences weathering due to …
Chemical composition
Nature of cements in sedimentary rock
Joints and bedding planes
Grain size
Chemical weathering - 4
Carbonation - solution
Hydrolysis
Hydration
Oxidation
Process that affects limestone the most
Carbonation solution
Limestone features are best developed on carboniferous limestone because of
Greater strength
Low porosity
Lower permeability
(6) Amount and rate of limestone solution is affected by
Amount of CO2 in atmosphere, soil and groundwater
Amount of water in contact with limestone
Water temperature
Turbulence of water
Presence of organic acids
Presence of lead, iron sulphides, sodium or potassium
(6) Accelerated solution happens when …
Impermeable rocks join limestone Solution by rivers Solution by mixture (waters of different hardness mix) Margins of snow and ice fields Rainfall and runoff increase When limestone is under soil cover
Limestone pavements
Large areas of bare exposed limestone
Dolines
Large depressions formed by the solution or collapse of limestone
Swallow hole / sink
Basically a hole / depression
River can disappear down the hole
Resurgent streams
Limestone is underlain by an impermeable rock, such as clay
Stalactites
Develop from the top of the cave
Stalagmites
Develop from the bottom of the cave
Speleothems
Cave deposits formed by precipitation of dissolved calcium carbonate
Granite
Igneous, impermeable, crystalline rock Very strong Resistant to erosion Contain quartz, mica and feldspar Freeze thaw and hydrolysis main processes of weathering for granite
Equifinality
Different processes can produce the same end result
Tors
Remaining outcrop of rock after the surrounding rock has been weathered away
Formation of Tors
Igneous rick ie granite covered with regalith
During warm interglacial period, water infiltrates and percolates through to reach the granite
Water goes into the joint
Hydrolysis: hydrogen ions combine with the felspar mineral to produce kaolinite (china clay)
End of ice age: regalith removed
Tors left behind
Hillslope
Area between the watershed and base
Inputs to slopes
Energy: insolation
Mass: water and sediment
Outputs
Energy : redradiated heat
Weight: mass, regolith
Open system
See diagram
Regolith
Superficial and unconsolidated material found at the Earths surface
Slope controls : Aspect
Direction in which a slope faces
Facing south - subjected to more cycles of freeze thaw
Results in asymmetric valleys
Slope controls : vegetation
Can decrease overland runoff through interception and storage
Can increase chance of major landslips
Forests reduce surface wash, cause a build up of soil between the trees , deepens regolith
Deforestation : exposed to more erosion and gullying
Mass movement
Movement of material downslope under gravity
OR
large scale movement of the Earth’s surface that is not accompanied by a moving agent such as a river, glacier or wave
