involves physical, chemical and biological processes, but the two major type is
(mechanical) and chemical
strictly a physical process, involving no change of chemical composition
or frost wedging:
penetrates easily into the openings of the rocks from rain or melting snow, than
when freezes expands (stress is about 110 kg/cm2= to drop a 98 kg
iron ball from a height of 3m).
period of time the rock will be literally hammered apart.
these we need:
1. enough moisture
2. falling, rising temperature
3. rocks with cracks or weakening (problem on highways)
formed under confining pressure, when eroded up to the surface got released from
the pressure and tend to expand. This internal pressure will break the rocks
into fragments. Expansion joints will form parallel to the surface, and the
process is called sheeting.
rocks taken away --- sheeting can cause problems rock slumping)
temperature cycle, in hot deserts
chemical weathering rocks are decomposed, the internal structures of minerals
are destroyed, and new minerals are created.
is the primary source of chemical weathering
-as part of the weathering or
-as carrying material for dissolved ions
on the other hand it removes the weathered particles, to expose the next
fresh rock layer
degree and the rate of chemical weathering is essentially influenced by the
amount of precipitation.
chem w. is not that imp. in deserts.
imagine dissolution easily
or sugar in water)
water-soluble mineral is Halite. This is caused by the mineral structure, and
the fact that the water has polar molecules.
mineral are insoluble in dest. water, this fact is abruptly changing by the
presence of different weak acids:
HCl: think of acid test
from such a dissolution makes the water HARD
hard water reacts with soap and makes insoluble compound (not desired)
chemical union of water and a mineral is called HYDROLYSIS.
not an adsorption process as the pores of a sponge sucks up water, but a
specific chemical change where a new mineral is forming.
hydrolysis the ions of the mineral react with H+
and OH- ions of the water to produce
NaAlSi3O8 (Na plagioclase)
to weather this we need: CO2
and of course the feldspar
will react with the water to form carbonic acid
18H2O = 4Na+ + 4HCO3-
8H4SiO4 + Al4Si4O10(OH)8
can see the clay mineral has no Na+ in
it, on the other hand it contains (OH) in its structure.
original framework silicatestucturewill become sheet silicate. Some silica is also released from the feldspar, which in the
water forms weak acid, and may then be carried away from the site of reaction.
in an other word is called rusting.
involves every process where cations loose electrons from their outer electron
shell to Oxygen.
oxidation most of the time the Cation was released from a silicate structure by
coal mining or volcanic area pyrite is exposed it will go through oxidation
+ 4H2O= 2FeO(OH) + 2H2SO4
problem with soils around these mines. Acidifying
activity of chemical weathering rises with rising temperature.
is most intensive in warm hot tropical weathering
OF ROCK INTEGRATION
Mechanical breakdown and the shape of the weathered rocks are usually inherited
from the pattern of joints, bedding, and cleavage of the original rocks,
usually the edges and faces became weathered
this PROCESS successive shells will separate down from the rock (spelling off)
of different rocks
Check in headstones in old cemetery!
Quartz is very stable
olivine, pyroxene very unstable
Stability of minerals is the OPPOSITE of BOWEN REACTION
Texture is also very important (porosity, permeability)
3.Topography (Amount of rocks exposed)
Feldspar - clay min Ca goes first,
pyroxene-amphib. mica - clay + Limonite
Quartz remain unaltered (light redish soil)
Soon goes into clay and iron oxides (red-brown soil)
dissolves away easily, cave systems
resistant, forms cliffs
away quickly because it is fine grained and soft. However it is not changing,
probably just transported away.
rock masses weather very differently.
resistant zones will make cliffs, and stand out as ridges. The weaker zones tend
to become walleyes or depressions
is coming from the Greek word REGO
It is a
layer of soft desintegrated rock material formed in place and covers the fresh
rock underlies beneath it.
thickness of the regolith is variable from some cm to hundreds of meters, dep.
on the composition of rocks, climate, + the length of time the weathering takes
UPPERMOST LAYER OF REGOLITH IS
Composed of rock fragments, minerals and decomposed organic matter (HUMUS)(50%), and pore space filled by
air and water
is very important, because it helps to retain the water in the soil zone. On the
other hand it provides the nutrients for plants.(5%)
Soil water: is not pure water, but contains lots
very important ions, nutrients (25%)
Soil air: supply the oxygene plants need (25%)
formed in place are termed:
developed on unconsolidated deposits are termed:
of the upper surface of the soil down to the bedrock.
Profile contains a constant sequence of layers, or horizons, distinguished by
composition, color and texture.
thin surface of leaf mold (forest)
topsoil layer, light leached layer (zone of leaching) (ions and fine
grained parts are washed out downward) ELUVIATION
Subsoil, contains Fine clays washed down from the topsoil. This is the zone
of accumulation and commonly reddish. ILLUVIATION
and B together is called solum or true soil
Zone of partly
disintegrated and decomposed bedrock, It is gradually grades into the fresh
soils which has no well developed zones are immature
type of zones, and the thickness of soil is essentially depend on the following
2.Parent rock material
3.Plants and animals
Desert, arctic region:
Physical weathering major,
Organic matter is minimal (no humus)
SOIL: thin, mostly rock fragments
Chemical weathering is dominant
Thick soil develops rapidly (60m).Rarely it
Quartz sandstone: thin infertile soil
organic decay----humus (mostly plants)
Swamp almost 100%
It effects the rate of erosion and drainage
Slope:On steep slope no too much soil, few water, not
TYPES IN THE US
of Fe, and Al-clays, mostly occurring underneath of forests in mid-latitude
areas, with more than 65 cm annual rainfall (acidic conditions (from organic
of calcium carbonate
climate, grasslands smaller amount of clay, bec. dry climate
caCO3 layer arid-semi-aride climate
wet climate of the tropics
amount of silica is dissolved---
in soil management
More dangerous lately, bec. of forest destroying
(plants are protective)
removement can happen by:
Eroded soil is moved to lakes rivers,
shrink the reservoir capacity
Pollution carried by soil into reservoirs drinking water