2- Introduction
- The disintegration
and decomposition of rock at or near the surface of the earth. It affects
the rocks in place and no transport is involved. This distinguishes
weathering from erosion.
- Weathering
takes place anywhere that water and/or air can penetrate Human processes
such as pollution, which can be a large factor in acid rain, . It produces
altered material that is more stable at the Earth's surface than the original
parental material, and provides the material that becomes soil or sedimentary
rock. The driving forces for weathering are:
1.
Solar
energy - causes circulation of the atmosphere (weather) and determines
climate and vegetation.
2.
Earth's
internal energy - forces within the Earth uplift deeply
buried rock and expose it to weathering.
3-Rock
Type and Structure-
Different rocks are
composed of different minerals, and
to weathering.
For example a sandstone consisting only of quartz is already composed of a
mineral that is very stable on the Earth's surface, and will not weather at all
in comparison to limestone, composed entirely of calcite, which will eventually
dissolve completely in a wet climate.
Bedding
planes, joints, and fractures, all provide pathways for the entry of
water. A rock with lots of these features will weather more rapidly than
a massive rock containing no bedding planes, joints, or fractures.
If there are large contrasts in the
susceptibility to weathering within a large body of rock, the more susceptible
parts of the rock will weather faster than the more resistant portions of the
rock. This will result in differential weathering
Slope - On steep
slopes weathering products may be quickly washed away by rains. On gentle
slopes the weathering products accumulate. On gentle slopes water may
stay in contact with rock for longer periods of time, and thus result in higher
weathering rates.
Climate- High
amounts of water and higher temperatures generally cause chemical reactions to
run faster. Thus warm humid climates generally have more highly
weathered rock, and rates of
weathering are higher than in cold dry climates. Example:
limestones in a dry desert climate are very resistant to weathering, but
limestones in a tropical climate weather very rapidly.
Animals- burrowing organisms like
rodents, earthworms, & ants, bring material to the surface were it can be
exposed to the agents of weathering.