Weathering
 Weathering processes cause the breakup of rock materials in the Earth's uppermost layer. Some of
these processes are mechanical, for example the expansion and contraction caused by sudden, large
changes in temperature, the expansive force of water freezing in cracks, the splitting caused by
plant roots, and the impact of running water. Roads in PEI need constant repair because of
weathering. In spring and fall. Water may enter cracks in a road's surface. When this water
freezes overnight, it expands and widens the cracks. In time, the surface will break up. The
same process happens in rocks. Several other types of weathering affect rocks. Usually in forests,
roots of plants reach into cracks in rocks by their penetration and growth, and have the same effect as freezing and thawing;
burrowing animals also contribute to the decomposition of earth materials.
Differences in temperature between very hot days and cold nights cause rocks to expand and
contract. In time this too helps break them up.
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Other weathering processes are chemical, for example oxidation, hydration, carbonization, and
loss of chemical elements by solution in water. Construction materials for buildings and roads
are subject to weathering by water, carbon dioxide, aerosol gases, freeze-thaw cycles, and salt.
Salt weathering, by the growth and thermal expansion of salt crystals in rock and soil,
is important in coastal zones, and possibly in polar desert areas like those of our
Canadian Arctic. Some chemicals in certain rocks dissolve in water as rain pours on the rocks over the centuries.
The remaining rock may crumble into smaller and smaller pieces, like a nail that rusts when left
outside. In dry areas, winds carry sand that, much like sandpaper, can wear down solid rock.
Weathering alone cannot wear down mountains and level the earth's surface; the broken-up rock
must also be carried away.