ZIMSEC O Level Geography Notes: Factors affecting weathering.
- The rate and prvailing type of weathering at any given place is affected by:
- Rock type
- Weathering types are distrubuted according to the prevailing climate of given areas especially when considering.
- Temperature and rainfall have the greatest effect on weathering.
- In cold areas especially regions where temperatures fluctuate around 0°C physical weathering in the form of frost shatter (freeze-thaw) is dominant.
- In hot areas such as deserts where there are large diurnal temperature ranges exfoliation insolation weathering (heating and cooling) is dominant.
- In hot and wet areas like the savannah and rainforest chemical weathering takes place in aided by the easily available moisture and high temperatures which favour chemical reactions.
- In rain forests the decomposition of humus creates humic acid leading to organic weathering.
- Mechanical weathering processes.
- Thus chemical weathering occurs is dominant in hot and humid climate areas
- Climate also indirectly affect weathering by affecting the amount of vegetation and presence of organisms that can lead to chemical weathering.
- Mountain regions have steep slopes which means that in the event of rain they drain quickly leaving the dry.
- As a result physical weathering is dominant at mountain topics especially when considering how some peaks tend to have temperatures that fluctuate around the freezing point even if temperatures are quite higher at the start of the slopes.
- Moisture tends to accumulate at the base of mountains aiding chemical weathering processes.
- Granite regions sometimes lead to the development of vleis which are water logged since granite is impermeable thus favouring chemical weathering in the moist conditions.
- Tree roots penetrate into rocks, widening cracks, release carbon dioxide during respiration resulting in biological weathering. These processes are naturally dominant in areas where there are more trees.
- When tree roots decay humic acids are produced causing biological weathering a process which more readily occurs in areas with dense vegetation cover and moisture such as in rainforests and in the tropics.
- Lichen and moss grow on rock plateaus and domes aided by moisture from rain and at the base of slopes forming acids that eat into rocks.
- Limestone is very soft and porous (being porous is not the same thing as being impervious/impermeable) and therefore more easily affected by processes such as carbonation, more so given the chemical composition of the rock.
- Granite rock is hard and non-porous and thus less susceptible to chemical weathering processes which require a certain amount of moisture in order to occur.
- Different rock types are composed or different chemicals that stand on different places of the reactivity series.
- Chemicals found in limestone readily react with weak acids while granite rocks are more resistant.
- Rocks that are exposed to the surface tend to be weathered faster than bedrock which is covered.
- However mechanical weathering processes such as pressure release can still occur if the overburden is being removed by denudation processes.
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