Weathering is the breakdown of rocks and minerals at Earth's surface through contact with the atmosphere, biota, and water. There are three main types of weathering: mechanical, chemical, and biological. Mechanical weathering breaks rocks into smaller pieces through processes like exfoliation and frost cracking. Chemical weathering alters the composition of rocks through reactions with water and acids. Biological weathering occurs when living organisms contribute to the breakdown of surface materials.
3. Weathering is the breaking down of rocks, soils
and minerals as well as artificial materials
through contact with the Earth's atmosphere,
biota and waters. Weathering occurs in situ, or
"with no movement", and thus should not be
confused with erosion, which involves the
movement of rocks and minerals by agents such
as water, ice, wind, and gravity.
8. A form of weathering where the grains of a rock
become 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.
9.
10. Exfoliation is the process in which rocks
weather by peeling off in sheets rather
than eroding grain by grain.
11.
12. This processes include frost shattering, frost-
wedging and freeze-thaw 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 or heave upon
freezing as a result of water migrating via capillary
action to grow ice lenses near the freezing front
13.
14. In daytime, intense solar heating causes rocks to
expands. 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.
15.
16. 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
as the mineralogy of the rock adjusts to the
near surface environment.
18. Salt crystallization may also take place when
solutions decompose rocks (for example,
limestone and chalk) to form salt solutions of
sodium sulfate or sodium carbonate, of which
the moisture evaporates to form their
respective salt crystals
19.
20. 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.
21.
22. Oxidation affects the iron minerals found in
a large variety of rocks, when iron comes
into contact with oxygen in the presence of
water it "rusts" and takes on the familiar
red colour
23.
24. Carbonation occurs on rocks which contain
calcium 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.
25.
26. 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 attachment of these organisms to the rock surface
enhances physical as well as chemical breakdown of the surface
microlayer 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.
27.
28.
29. 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 with
needing to repaint or otherwise repair weathered paint, and
wood. 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.
