SlideShare utilise les cookies pour améliorer les fonctionnalités et les performances, et également pour vous montrer des publicités pertinentes. Si vous continuez à naviguer sur ce site, vous acceptez l’utilisation de cookies. Consultez nos Conditions d’utilisation et notre Politique de confidentialité.
SlideShare utilise les cookies pour améliorer les fonctionnalités et les performances, et également pour vous montrer des publicités pertinentes. Si vous continuez à naviguer sur ce site, vous acceptez l’utilisation de cookies. Consultez notre Politique de confidentialité et nos Conditions d’utilisation pour en savoir plus.
What is weathering?Different types of weathering. Effects of weathering.
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earths atmosphere,biota and waters. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves themovement of rocks and minerals by agents such as water, ice, wind, and gravity.
1.Mechanical weathering or Physical weathering. 2.Chemical weathering. 3.Biological weathering.
A form of weathering where the grains of a rockbecome loosened. Grains fall out to leave a pitted,uneven surface. Granular disintegration may be the result of freeze-thaw, hydro-fracturing, thermal expansion, or salt weathering.
Exfoliation is the process in which rocksweather by peeling off in sheets rather than eroding grain by grain.
This processes include frost shattering, frost- wedging and freeze-thaw weathering. This type ofweathering is common in mountain areas where the temperature is around the freezing point of water.Certain frost-susceptible soils expand or heave upon freezing as a result of water migrating via capillary action to grow ice lenses near the freezing front
In daytime, intense solar heating causes rocks toexpands. At night, the temperature falls so rocks cool and contrasts. Repeated expansion and contraction produces stress along joints. Joints are then widened and deepened and finally break down the rocks block by block.
Chemical weathering changes the composition of rocks, often transformingthem when water interacts with minerals tocreate various chemical reactions. Chemicalweathering is a gradual and ongoing processas the mineralogy of the rock adjusts to the near surface environment.
Salt crystallization may also take place when solutions decompose rocks (for example,limestone and chalk) to form salt solutions ofsodium sulfate or sodium carbonate, of which the moisture evaporates to form their respective salt crystals
Mineral hydration is a form of chemical weatheringthat 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. Forexample iron oxides are converted to iron hydroxides and the hydration of anhydrite forms gypsum.
Oxidation affects the iron minerals found in a large variety of rocks, when iron comesinto contact with oxygen in the presence of water it "rusts" and takes on the familiar red colour
Carbonation occurs on rocks which containcalcium carbonate, such as limestone and chalk. This takes place when rain combines with carbon dioxide or an organic acid to form a weak carbonic acid which reacts with calcium carbonate (the limestone) and forms calcium bicarbonate.
Living organisms may contribute to mechanical weathering (as well as chemical weathering, see biological weathering below). Lichens and mosses grow on essentially bare rocksurfaces and create a more humid chemical microenvironment. The attachment of these organisms to the rock surfaceenhances physical as well as chemical breakdown of the surfacemicrolayer of the rock. On a larger scale, seedlings sprouting in a crevice and plant roots exert physical pressure as well as providing a pathway for water and chemical infiltration.
Weathering might be considered the gradual deterioration of "stuff".It is part of a natural process of erosion, and deterioration of plant and animal matter as well as minerals which then becomes nutrients for the next generation of plants.Unfortunately when these natural cycles hit our homes and items we wish to be "permanent", it can be a big pain withneeding to repaint or otherwise repair weathered paint, andwood. Roofing wears out and leaks or needs replacing. Cars oxidize, or rust.Many people do like the looks of weathered wood as it often looks somewhat muted over the pristine freshly cut wood.I suppose that without weathering and deterioration, that we would be in bad shape. Think of what it would be like if garbage, litter, and discards would just last forever.