Physical Processes & Chemical Processes

What is weathering?
Weathering is the breakdown of rocks in situ, while erosion involves the breakdown of material through movement processes.

Which rocks are least resistant to weathering?
Limestones and sandstones are the least resistant to weathering.

What does physical weathering produce?
Physical weathering produces small, angular fragments of the same rock.

What is freeze-thaw weathering?
Freeze-thaw occurs in cold areas where water freezes in cracks in rocks, expanding 10% and exerting pressure to break the rock.

How does freeze-thaw weathering work?
Water collects in cracks, freezes, and expands. The pressure exceeds the rock’s resistance, causing the crack to widen. When ice thaws, water penetrates deeper, repeating the process.

What is exfoliation?
Exfoliation occurs in hot deserts with large diurnal temperature ranges. Rocks heat up during the day, and outer layers expand, while they cool and contract more rapidly at night, causing stresses that flake off outer layers.

How does salt crystal growth weather rocks?
Salt crystal growth occurs when saline solutions penetrate rock surfaces. As water evaporates, salt crystals form and expand, exerting pressure that causes the rock to disintegrate.

What temperature range is salt crystal growth most effective in?
Salt crystal growth is most effective in temperatures around 27°C, where expansion can reach 300%, particularly with Sodium Sulphate, Magnesium Sulphate, and Calcium Chloride.

What is dilation in weathering?
Dilation is a pressure-release process where overlying rocks are removed by erosion or glaciers, causing underlying rocks to expand and form fractures parallel to the surface.

What happens when horizontal pressure is released in dilation?
When horizontal pressure is released, vertical faults develop, often seen on cliff faces.

How does vegetation root action contribute to weathering?
Vegetation root action can penetrate rocks or prevent rocks from forming or settling in specific places, contributing to weathering.

What does chemical weathering create?
Chemical weathering creates altered rock substances and requires water to occur.

What is hydrolysis in weathering?
Hydrolysis is the breakdown of rocks with feldspar minerals, such as granite, by acidic water, producing kaolin, silicic acid, and potassium hydroxyl.

What does hydrolysis produce?
Hydrolysis produces kaolin (clay), silicic acid, and potassium hydroxyl from the breakdown of feldspar in granite.

What is hydration in weathering?
Hydration occurs when minerals absorb water and expand, causing mechanical and chemical stresses, particularly in shale and mudstones.

How does hydration affect clay minerals?
Clay minerals, such as anhydrite, absorb water and expand, causing them to form hydrates like gypsum, which results in significant expansion and cracking.

What is carbonation in weathering?
Carbonation is the process where acid rain breaks down limestone or chalk. Carbon dioxide dissolves in rainwater to form carbonic acid, which reacts with calcium carbonate in limestone.

What happens during carbonation weathering?
Carbonic acid reacts with calcium carbonate in limestone to form calcium bicarbonate, which is soluble and washed away by water, leading to the removal of limestone.