Weathering Flashcards
Strata are horizontal…
layers of material.
Weathering is a breakdown of…
rock in situ-it is not taken away(erosion).
Physical/Mechanical weathering results in…
disintegration of a rock, producing angular fragments of the same rock.
Biological weathering is a form of…
disintegration(mechanical) and decomposition(chemical). The processes are interrelated.
Chemical weathering involves…
granular disintegration on the particle level, creating altered rock substances.
Freeze-thaw weathering can be found in areas…
of temperature change above or below 0 degrees, which can be either diurnal or seasonal.
Joints are cracks in a rock in…
vertical position.
Lines of weakness are cracks in a rock in…
horizontal position.
During freeze-thaw, water percolate…
into joints and freezes.
The volume of frozen water expands by…
9%.
The expansion of frozen water…
forces the rock apart. Over time, the joints get larger.
Frost shattering can happen if…
the rock is filled with a lot of water-the rock instantly breaks apart.
Salt crystallisation can be found in…
hot desert regions where low rainfall and high temperatures cause salt to accumulate just below the surface.
When water enters joints, salts such as…
sodium sulphate or sodium carbonate can be formed. These salts can expand by about 300%, putting pressure on the joints.
Another form of salt crystallisation can be when…
the water evaporates, salt crystals are left behind.
(salt crystallisation)As the temperature rises, the salt…
expands and exerts pressure on the rock.
Occasionally, salt crystallisation can occur in areas of…
polar regions, when salt is deposited form snowflakes.
The rate of disintegration of rock is related to…
porosity and permeability of the rock.
The combination of freeze-thaw and…
salt crystallisation produces the highest rates of breakdown.
Exfoliation can be found in hot…
desert areas, where there is a large diurnal temperature change.
Rocks are poor conductors of heat, therefore…
exfoliation occurs only in the outer layers.
During a day, there are heavy rates of insolation, causing…
the rock to expand as it heats up. The rock will undergo stress. The lines of weakness will grow inside the rock.
During the night, there is no insolation, causing…
the rock to return to its original shape.
As the rock heats up again, the outer layer…
of rock breaks off, as it starts to expand again.
The exfoliation needs small amount of…
moisture to undergo the weathering, showed by Griggs 1936.
Pressure release is also known as…
dilatation.
Pressure release starts when…
overlaying rocks are removed by erosion. This causes the underlying rock to expand(isostatic change) and lines of weakness are formed to release pressure.
When the rocks come up as the pressure is released,
horizontal pseudo-bedding planes are formed.
Vegetation roots may…
physically break down rocks.
Water is a key medium for…
chemical weathering.
Chemical weathering is most effective…
sub-surface weathering, since percolating water gained organic acids.
Carbonation-solution occurs on rocks with…
calcium carbonate, such as chalk and limestone.
(carbonation)Rainfall combines with dissolved…
CO2 to form a weak carbonic acid. CO2 + H2O = H2CO3
Carbonic acid reacts with…
Calcium carbonate(calcite) and forms calcium bicarbonate, which is soluble and removed by percolating water.
The equation for the formation of calcium bicarbonate:
CaCO3 + H2CO3 = Ca(HCO3)2
Hydrolysis occurs on rocks with…
orthoclase feldspar, mostly granite.
Feldspar reacts with…
acid water and forms kaolinite-china clay, potassium hydroxyl and silicic acid.
The equation for the formation of kaolinite:
2KAlSi3O8(feldspar) + 2H2O = Al2Si2O5(OH)4 (kaolinite) + K2O(potassium hydrxyl) + 4SiO2(silicic acid)
The silicic acid and hydroxyl are…
removed in the solution, leaving kaoline behind as end product.
Other minerals in the granite such as…
quartz and mica remain in the kaoline.
Hydration is the process when…
certain pervious minerals absorb water, expand and change.
During hydration, anhydrate…
absorbs water to become gypsum, it expands by about 0.5 %, creating hydrostatic pressure.
Oxidation happens when…
Fe in rocks reacts with oxygen, resulting in rusting.
After oxidation, ferrous rocks break…
into ferric material-bits of iron breaks off the rock.
To start chelation, dead vegetation…
must be decomposed by microbes.
(chelation)Precipitation mixes with…
nutrients from decomposed vegetation and humic acid is formed, which is very fertile and it is very acidic.
The chelation continues by solution…
weathering, where humic acid reacts with rocks.
The Basal surface of weathering is the maximum…
depth to which weathering penetrates. It makes the boundary between the weathered and unweathered rock.
