Weathering
Weathering is the breaking down of Earth’s rocks, soils and minerals through direct contact with the planet’s atmosphere. Weathering occurs “with no movement”, and thus is different than erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind, and gravity.
In addition, weathering is the effect of atmospheric exposure to man-made structures and materials.
Classifications of weathering —
1- Mechanical or physical weathering Involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure.
2- Chemical or biological weathering, Involves the direct effect of atmospheric chemicals or biologically produced chemicals (also known as biological weathering in the breakdown of rocks, soils and minerals.
Living organisms may contribute to mechanical weathering (as well as chemical weathering, see ‘biological’ weathering below).
Lichens and mosses grow on essentially bare rock surfaces and create a more humid chemical microenvironment.
The Essay on Chemical Weathering Rock Process Rocks
... breaking along mineral borders. The next type of weathering is called chemical weathering. Chemical weathering is "the decomposition of rock by the chemical breakdown of minerals" (Weathering and Soils) which results ... the time and involves little or no movement of the decomposed minerals and rocks. There are two main types of weathering that occur on ...
chemical weathering changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions. Chemical weathering is a gradual and ongoing process
The materials left over after the rock breaks down combined with organic material creates soil. A soil derived from a single rock type can often be less in one or more minerals for good fertility, while a soil weathered from a mix of rock types (as in glacial, or sediiments) often makes more fertile soil
The primary process in physical weathering is abrasion (the process by which clasts and other particles are reduced in size).
Chemical and physical weathering often go hand in hand. Furthermore, the chemical action at minerals in cracks can aid the disintegration process.
Thermal stress
Thermal stress weathering (sometimes called insolation weathering) results from expansion or contraction of rock, caused by temperature changes. Thermal stress weathering is an important mechanism in deserts, The repeated heating and cooling of exerts stress on the outer layers of rocks, which can cause their outer layers to peel off in thin sheets. Moisture can enhance thermal expansion in rock. Forest fires known to cause significant weathering of rocks and boulders exposed along the ground surface.
Frost weathering
This type of weathering is common in mountain areas where the temperature is around the freezing point of water. Certain frost-susceptible soils expand upon freezing Freeze induced weathering action occurs mainly in environments where there is a lot of moisture, and temperatures frequently change above and below freezing point
Pressure release
In pressure release, also known as unloading, overlying materials are removed by erosion, or other processes), which causes underlying rocks to expand and fracture parallel to the surface.
The Essay on Tide and Weathering Chemical Weathering
... has undergone weathering. Physical Weathering Hydrologic Weathering Atmospheric Weathering Chemical Weathering 标记此问题 问题 23 0.8 分 ___________ weathering is more ... weathering by the process of The rock in the photo has undergone extensive weathering by the process ... ______________ must be present in the rock. Minerals Lichen Joints 标记此问题 问题 20 0.8 ... to water by the frictional stress of wind blowing over ...
Over time, sheets of rock break away from the exposed rocks along the fractures. Pressure release is also known as “exfoliation” or “sheeting”;
Hydration
Mineral hydration is a form of chemical weathering that involves the rigid attachment of H+ and OH- ions to the atoms and molecules of a mineral.
When rock minerals take up water, the increased volume creates physical stresses within the rock. For example iron oxides are converted to iron hydroxides and the hydration of anhydrite forms gypsum.
A freshly broken rock shows differential chemical weathering (mostly oxidation) progressing inward.
Oxidation
The most commonly observed is the oxidation of Iron and combination with oxygen and water .
This gives the affected rocks a reddish-brown coloration on the surface which crumbles easily and weakens the rock. This process is better known as ‘rusting’.
Building weathering
Buildings made of any stone, brick or concrete are affected by weathering. Any exposed rock surface. Also statues, monuments and stonework can be badly damaged by natural weathering processes. This is accelerated in areas severely affected by acid rain.
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