Mechanical Weathering Processes

Mechanical (physical) Weathering:

• Mechanical weathering occurs when exposed rocks are physically broken down into smaller pieces, called Regolith.
• This takes place at areas of weakness such as joints, cracks or spaces between the grains of the rock.
• It mainly takes place in areas of extreme temperature with large changes in temperature, such as desert or mountainous regions.

Freeze-thaw action:

• Can also be called frost shattering/frost action/frost wedging
• It is the most common type of physical weathering
• It is common in upland areas where there is a plentiful supply of precipitation and temperatures fluctuate above and below freezing point
• It is most effective on areas of exposed rock
• Water fills the cracks during the day, when temperatures are warmer
• At night time, temperatures drop below freezing point
• The water in the crack's freezes, turns to ice and its volume expands by 9%
• This widens the crack, putting the rock under pressure
• This process continues over time, repeatedly freezing and thawing until eventually fragments of rock (scree) break off
• Large piles of scree can accumulate on the lower slopes of mountains due to the influence of gravity
• It occurs in mountainous Irish areas during winter
• However, it happens all year round in higher areas such as the Alps or Himalayas due to the climate in these areas
• Scree can be seen on the side of the Great Sugar Loaf mountain in Co. Wicklow

Exfoliation:

• Can also be referred to as onion layer weathering/onion peeling as the pieces of the rocks surface peel away layer by layer
• It is another example of mechanical/physical weathering as it occurs in areas with a large diurnal temperature range
• In some places the temperature change between day and night can be up to 40 °C
• In very hot areas, such as desert regions, rocks are heated during the day as there is no cloud cover to protect them from the heat of the sun
• The rocks expand as a result of this heat
• As there are still no clouds at night to keep the heat in, temperatures drop dramatically
• The rocks cool and contract/shrink
• This does not occur evenly throughout the rock as the outer layers cool quicker than the inner layers
• This puts pressure/stress on the rock and fractures eventually appear over time
• Eventually the outer layers of rock peel off like the layers of an onion
• This mainly occurs in areas of Sedimentary rock as these rocks have strata