Transcript natcie2 - natscie2-5605

WEATHERING
 Weathering is the gradual destruction of rock
under surface conditions. Weathering may
involve
physical
processes
(mechanical
weathering) or chemical activity (chemical
weathering). Some workers also include the
actions of living things (organic weathering),
although these can also be classified as
mechanical or chemical or a combination of
both.
Mechanical Weathering
As stated earlier mechanical weathering
involves the breaking down of rocks due to
a kind of pressure exerted on the rock,
which can be due to various reasons. The
primary method of mechanical weathering
is the alteration in size that the particle
would go through and it would definitely get
smaller
with
weathering..
Types of Mechanical Weathering
1. Ice Wedging= Expansion of H2O and
pushes the cracks wider apart.
2. Sheeting= series of fracture due to
expansion of rock as a result of
removal of overlying material.
Chemical Weathering
Chemical weathering takes place in almost all types of
rocks. Smaller rocks are more susceptible, however,
because they have a greater amount of surface area.
Chemical reactions break down the bonds holding the
rocks together, causing them to fall apart, forming
smaller and smaller pieces. Chemical weathering is much
more common in locations where there is a lot of water.
This is because water is important to many of the
chemical reactions that can take place. Warmer
temperatures are also more friendly to chemical
weathering. The most common types of chemical
weathering are oxidation, hydrolysis and carbonation.
Chemical Weathering
types of Chemical Weathering:
1. Oxidations= oxygen reacts with H2O
iron in mineral forming.
2. Carbonation= Co2+ rainH2O – Carbonic
Acid+ mineral.
3. Hydration= mineral+ H2O ( expand)
4. Dissolution= mineral dissolved in H2O
RATES OF WEATHERING
The speed at which a rock weathers will depend on
the following:
1. The type and hardness of the minerals in the
rock
2. The type of rock
3. The climate
MASS WASTING
 defined
as the down slope movement of
material under the direct influence of
gravity. Most types of mass wasting are aided
by weathering and usually involve sacrificial
(surface) materials. The material moves at
rates ranging from almost imperceptible, as in
the case of creep, to extremely fast as in a
rock fall or slide. Though water can play an
important role, the relentless pull of gravity is
the major force behind mass wasting.
TWO TYPE SOF MASS WASTING
1. ROCK SLIDE -- The usually rapid downward
movement of newly detached segments of bedrock. The
rock mass that has reached its current position through
such a movement.
2. LAND SLIDE--or landslip is a geological
phenomenon which includes a wide range of ground
movement, such as rockfalls, deep failure of slopes and
shallow debris flows, which can occur in offshore,
coastal and onshore environments.
SOIL
Soil refers to the precious
mixture of weathered rock
fragments, minerals grains,
organic debris, and moisture .
E
SOIL PROFILE
Soil Profile refers to the layers of soil; horizon
A, B, and C. If you're wondering what horizon A
is, here's your answer: The litter horizon A
refers to the upper layer of soil, nearest the
surface. It is commonly known as topsoil. In the
woods or other areas that have not been plowed
or tilled, this layer would probably include
organic litter, such as fallen leaves and twigs
.helps prevent erosion, holds moisture, and
decays to form a very rich soil known as humus.
Horizon A provides plants with nutrients they
need for a great life.
What affects soil formation?
Soil characteristics develop as a result of their origin and
environment. Soil begins as a particular rock material and
develops slowly over many years. Each soil is a product of a
combination of the following factors. What affects soil
formation?
Parent material
Climate
Living organisms (biota)
Topography
Time
Parent Material
Alluvium – finely pulverized rock laid down by
running water. Mostly silt and clay particles with
some sand.
Marine Deposits – finely pulverized rock laid
down under sea. This material has been thrust
up by shifts in the earth’s crust.
Loess – salty, floury material laid down by
winds. Mostly silt and clay with little or no sand.
Climate
Physical weathering – results from
mechanical agents, such as heating &
cooling, freezing & thawing, &/or
abrasion.
•Materials are still the same at the
molecular level.
•Materials are classified by the way
they have been moved or scattered
Topography
Topography refers to the “lay of the land” or
the angle & length of the slope.
It affects soil formation because it influences
runoff, drainage, & erosion.
It also may affect the type & amount of plant
growth (biggest factor in determining type &
amount of organic matter)
As soon as material has become loose enough
to hold enough water, air, and nutrients for
plant growth, it is considered a soil.
Soil formation/development may take
place over several centuries or just a few
days.
SOIL EROSION
The denudation of the soil cover and subsequent
washing down is described as soil erosion. The
processes of soil formation and erosion, go on
simultaneously and generally there is a balance
between the two. Sometimes, this balance is
disturbed due to human activities like deforestation,
over-grazing, construction and mining etc., while
natural forces like wind, glacier and water lead to
soil erosion.
What Causes Soil Erosion?
There is no particular soil erosion cause which can be singled out and
assumed as the main cause of soil erosion. The process has many underlying
factors, some induced by nature and some by humans.
Human Induced Causes of Soil Erosion
Human exploitation of nature is perhaps the most hazardous
cause of soil erosion, which has increased over the last
decade. Human activities, such as faulty farming systems,
deforestation caused by overgrazing, clearance of land for
agricultural purposes and construction, dam construction and
diversion of the natural course of river, and mining activities
are just a few among the various human activities which have
either directly or indirectly weakened the topmost layer of
the planet, thus making it vulnerable to excessive wearing away
by the various agents of erosion. For instance, tree roots help
in holding the soil together, and therefore depletion of
vegetation cover is bound to make soil vulnerable to erosion by
running water.
The Effects of Soil Erosion
Soil erosion occurs when wind and water
strips the soil from a given area faster
than it can form. Most of the time, soil
erosion occurs as a result of man-made
issues, such as overgrazing farmland or the
use of unsuitable fertilizers. The effects
of erosion can be felt both on the site
where the erosion takes place and at offsite
locations.