Essay
Assess the factors affecting the type and rate of weathering
- Module
- Unit 1 - Core Geography
- Institution
- CIE
CIE A1 geography essay, rocks and weathering: Assess the factors affecting the type and rate of weathering
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BeckyAssess the factors affecting the type and rate of weathering (15)
Weathering is the decay and disintegration of rocks involving biological, chemical, and
physical processes. Climate has the most profound effect on the rate and type of
weathering, however rock type and structure and vegetation do still have an impact on the
rate.
Climate effects both the rate and type of weathering. As shown in Peltier’s diagram,
weathering is related to the moisture availability and average temperature of an area. The
rate of chemical weathering is heavily influenced by temperature, for example carbonation
occurs more frequently and at a faster rate in warmer temperatures due to this heat
speeding up the rate of reactions by 2-3 times for every 10 degrees increase in temperature.
In addition to this the weak carbonic acid in rainwater along with the other atmospheric
pollutants dissolved in it such as sulphur dioxide and nitrous oxides cause this chemical
weathering. This demonstrates how both precipitation and temperature hugely affect the
speed and occurrence of chemical weathering. Climate also impacts physical weathering,
but more so in terms of temperature. For example, freeze thaw weathering occurs because
of a large diurnal temperature range, causing the water which has seeped into the joints of
rocks to freeze at night when the temperature drops, thereby expanding, and thawing again
when warmed by the sun. This expansion weakens the joints and cracks in the rocks
resulting in weathering, demonstrating the effect of temperature on the type of weathering
as well as the moisture content within the rocks. Similarly, diurnal temperature differences
cause the rocks to heat up during the day, causing expansion, and cool again at night,
causing contraction. Due to the different rates of expansion and contraction of the different
minerals present within the rocks, complex stresses form resulting in disintegration. Salt
crystallisation is another example of physical weathering heavily affected by temperature.
This occurs when salt solutions in the pores and joints of rocks crystalise, expanding and
forcing the rock apart. This process is particularly effective at temperatures around 27
degrees C, when temperature fluctuations can cause a 3000% expansion rate. Therefore,
climate is the most crucial factor in affecting the type and rate of both chemical and physical
weathering.
Rock structure also plays a part in the type and rate of weathering. For example, joint
patterns within the rocks exert a strong control over water movements within the rock,
acting as lines of weakness and thereby creating differential resistance within the same
rock, increasing the rate of weathering. The orientation of the bedding planes may also
impact the type of weathering that takes place. For example, if the bedding planes are
horizontal and pressure from rock above is released, the removal of the weight from the
previously deeply buried rocks results in the expansion of the upper layers. This, in turn,
allows cracks to form parallel to the ground, known as pseudo-bedding planes. These new
weaknesses will speed up the rate weathering due to the new established joints for water to
enter. This shows how the orientation of the bedding planes allows for dilation to occur, and
how this in turn can increase the rate of other physical and chemical processes due to
creation of the pseudo-bedding planes. Grain size also influences the rate of weathering, as
coarse-grained rocks weather quickly due to the large pores between the grins allowing
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