desert weathering processes (chemical and physical)

Hot arid and semi-arid environments generally experience slow rates of weathering
This is largely due to the lack of water, which means that the chemical breakdown of rock is slow
Rock breakdown is, therefore, mainly due to physical weathering, which can be quite rapid due to the absence of soil and plant cover, exposing bedrock over large areas

Also called thermal exfoliation and onion skin weathering - is due to extreme, daily temperature variations
During the day, rocks absorb insolation and expand
At night heat is released and the rock contracts
This process continues (cyclical process 1 in the diagram below) until eventually, fractures form along the surface
These fractured pieces expose the rock beneath and the process continues (cyclical process 2)
Thermal expansion and contraction occur at different rates on different parts of the rock

$thermal-fracturing-in-hot-deserts$

Image of cyclical thermal fracturing in hot deserts

Pressure release exfoliation
This is where overburden is removed through weathering and erosion and the rock beneath is gradually exposed
The removal of the weight of the overburden releases the pressure on the rock beneath and the outer layer splits/fractures apart
Once the fractures develop, water enters and chemical weathering takes place, leading to the formation of new low-density minerals
This enhances the fractures and encourages slabs of rock to detach from the rock surface

Image showing pressure release exfoliation over time

Freeze-thaw weathering is possible where temperatures fluctuate above and below freezing and where there is sufficient moisture
During the day, temperatures rise, allowing water to flow into rock fractures.
At night, temperatures drop, causing this water to freeze.
Water expands as it freezes, exerting pressure on the surrounding rock.
The expansion can create stress along the rock's joints and fractures.
Limited Vegetation: In arid environments, there is often limited vegetation to facilitate moisture retention in the soil. This means more moisture is available for freeze-thaw action in the few instances when it does rain or when moisture is present in the environment.

Salt crystal growth weathering is a process that occurs mainly in porous sedimentary rocks, such as sandstone, and is particularly prevalent in coastal, fog-bound deserts.

Formation of Saline Groundwater: High temperatures result in saline groundwater being drawn up towards the surface. As the water reaches the surface, it undergoes evaporation due to the heat.
Growth of Salt Crystals: As the water evaporates, it leaves behind dissolved salts, which begin to crystallize. These salts can include sodium chloride (table salt) and other minerals.
Infiltration into Pores and Joints: The growing salt crystals infiltrate the tiny pores and joints in the rock, where they can expand as they grow. This expansion exerts pressure on the surrounding rock material.
Granular Disintegration: The pressure generated by the expanding salt crystals can cause the rock to start breaking down into smaller grains or particles, contributing to what is known as granular disintegration.
Block Disintegration: Over time, if the process continues, the integrity of larger blocks of rock can be compromised, leading to block disintegration. This is when significant portions of the rock break away along the natural weaknesses created by the crystallization process.
Repeated Cycles: The process can be cyclic, as further moisture from precipitation can rehydrate the salts, leading to increased crystal growth and further weathering, perpetuating the cycle of destruction of the rock structure.

Well jointed and bedded limestone break into blocks along the natural weaknesses

Minerals in rocks expand when they absorb water, putting the surrounding rocks under more stress
This build up of stress causes the rocks to snap along their joints