Weathering is the breakdown of rocks and minerals at their location through contact with the atmosphere, water, and organisms. It occurs through both physical and chemical processes. Physical weathering includes thermal stress from temperature changes, exfoliation from pressure release, and abrasion where particles are reduced in size by water, ice, and wind. Chemical weathering includes hydrolysis where minerals react with water, oxidation where substances react with oxygen, and dissolution where acids from carbon dioxide and pollutants break down minerals. Erosion is the movement of weathered rocks and minerals by gravity, wind, water, ice, or glaciers to other locations.

2. WEATHERING is the breaking
down
of rocks, soil and minerals as
well as wood and artificial
materials through contact with
theEarth's atmosphere, waters
and biological organisms.
Weathering occurs in situ (on
site), that is, in the same place,
with little or no movement, and
thus should not be confused
with erosion, which involves the
movement of rocks and minerals
by agents such as water, ice,
snow, wind, waves and gravity
and then being transported and
deposited in other loc

3. WEATHERING/MEC
HANICAL
WEATHERING
Physical weathering, also recognized
as mechanical weathering, is the class
of processes that causes the
disintegration of rocks without
chemical change. The primary
process in physical weathering
is abrasion (the process by
which clasts and other particles are
reduced in size). However, chemical
and physical weathering often go
hand in hand. Physical weathering
can occur due to temperature,
pressure, frost etc. Physical
weathering is also called mechanical
weathering or disaggregation.

4. HEATING AND COOLING
Thermal stress weathering (sometimes
called insolation weathering)[2] results from
the expansion and contraction of rock,
caused by temperature changes. For
example, heating of rocks by sunlight or
fires can cause expansion of their
constituent minerals eventually cause the
rock to crack apart.
Thermal stress weathering comprises two
main types, thermal shock and thermal
fatigue. Thermal stress weathering is an
important mechanism in deserts, where
there is a large diurnal temperature range,
hot in the day and cold at night.[3] The
repeated heating and cooling
exerts stress on the outer layers of rocks,

5. EXPOLIATION is weathring of rocks due
to release of pressure on rock surface . It is
also known as sheeting shearing . Before
expoliation rocks are under tremendous
pressure because of the overlying rock
material and atmosphere. When erosion
removes the overlying rock material, these
intrusive rocks are exposed and the pressure
on them is released. The outer parts of the
rocks then tend to expand. The expansion
sets up stresses which cause fractures
parallel to the rock surface to form. Over
time, sheets of rock break away from the
exposed rocks along the fractures, a process
known as exfoliation. Exfoliation due to
pressure release is also known as
"sheeting“………………………….

6. ABRASION
The primary process in physical
weathering is abrasion . It is the
process by which clasts and other
particles are reduced in size.
Abrasion by water, ice, and wind
processes loaded with sediment
can have tremendous cutting
power, as is amply demonstrated
by the gorges, ravines, and valleys
around the world. In glacial areas,
huge moving ice masses embedded
with soil and rock fragments grind
down rocks in their path and carry
away large volumes of material.

7. WETHERING
Biological effects on mechanical
weathering
Living organisms may contribute to
mechanical weathering (as well as
chemical weathering, see 'biological'
weathering
below). Lichensand 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.

8. 10/29/2016 8

9. Hydrolysis
There are different types of chemical
weathering. Let's start with a discussion
of hydrolysis, which is the chemical
breakdown of a substance when
combined with water. You can recall this
term by remembering that the prefix
'hydro' means 'water' and the suffix 'lysis'
means 'to break down.'
With chemical weathering of rock, we
see a chemical reaction happening
between the minerals found in the rock
and rainwater. The most common
example of hydrolysis is feldspar, which
can be found in granite changing to clay.
When it rains, water seeps down into the
ground and comes in contact with
granite rocks. The feldspar crystals
within the granite react with the water
and are chemically altered to form clay
minerals, which weaken the rock.

10. Oxidation
Another type of chemical weathering
is oxidation. Oxidation is the
reaction of a substance with oxygen.
You are probably familiar with
oxidation because it is the process
that causes rust. So just like your car
turns to rust through oxidation, rocks
can get rusty if they contain iron.
You may have noticed that rusted
metal on your car is somewhat fragile;
you could even poke your finger
through a rust patch if it's big enough.
This is because when iron reacts with
oxygen, it forms iron oxide, which is
not very strong. So when a rock gets
oxidized, it is weakened and crumbles
easily,

11. DISSOLUTION AND
CARBONATION
Dissolution and carbonation[edit]
A pyrite cube has dissolved away from host rock, leaving gold behind
Rainfall is acidic because atmospheric carbon dioxide dissolves in
the rainwater producing weak carbonic acid. In unpolluted
environments, the rainfall pH is around 5.6. Acid rain occurs when
gases such as sulfur dioxide and nitrogen oxides are present in the
atmosphere. These oxides react in the rain water to produce stronger
acids and can lower the pH to 4.5 or even 3.0. Sulfur dioxide, SO2,
comes from volcanic eruptions or from fossil fuels, can
become sulfuric acid within rainwater, which can cause solution
weathering to the rocks on which it falls.
Some minerals, due to their natural solubility (e.g. evaporites),
oxidation potential (iron-rich minerals, such as pyrite), or instability
relative to surficial conditions (see Goldich dissolution series) will
weather through dissolution naturally, even without acidic water.
One of the most well-known solution weathering processes
is carbonation, the process in which atmospheric carbon dioxide
leads to solution weathering. 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. This process speeds up
with a decrease in temperature, not because low temperatures
generally drive reactions faster, but because colder water holds more
dissolved carbon dioxide gas. Carbonation is therefore a large feature
of glacial weathering.
The reactions as follows:
CO2 + H2O → H2CO3carbon dioxide + water → carbonic acidH2CO3 +
CaCO3 → Ca(HCO3)2carbonic acid + calcium carbonate → calcium
bicarbonate

12. Erosion and Transport
Erosion
Erosion is the process by which soil
and rock particles are worn away
and moved elsewhere by gravity, or
by a moving transport agent –
wind, water or ice.
Transport refers to the processes by
which the sediment is moved along
– for example, pebbles rolled along
a river-bed or sea shore, sand
grains whipped up by the wind,
salts carried in solution.

13. EROSION BY
GRAVITY
Mass–wasting is the down-slope
movement of loose rock and soil
due to gravity. Whilst processes
such as soil creep are very slow,
landslides can be very sudden, and
may cause loss of life.
Mass-wasting is often aided by
water, so landslides and mudflows
frequently occur after heavy rain

14. EROSION BY WIND
Wind erosion and transport is a
serious environmental problem in the
driest parts of the world, removing
soil from farmland and covering
whole towns with sand and dust.
A strong breeze (wind speed 20
km/h) can easily pick up dry dust and
fine sand. The lightest particles are
swirled up into the air and carried in
suspension for hundreds of
kilometres, whilst sand grains bounce
along the surface by saltation. Small
pebbles can be moved along with the
sand, a process called creep.

15. EROSION BY WATER
Around the world, moving water picks
up and transports millions of tonnes of
sediment every day, along rivers, coasts,
and even in the deep oceans.
Sediment, whether picked up by flowing
water or by waves, is moved along in one
of four ways:
Traction is the rolling or dragging of
large grains along a river bed or shore,
aided by the push of the smaller grains
(below).
Saltation is the bouncing of sand grains
as they are picked up, carried along, and
dropped repeatedly by flowing water.
Fine particles (silt and clay) are carried in
Suspension in the water – they will only
settle out if the water is still.
Soluble salts are carried in Solution in
the water – the sea is obviously salty, but
rivers contain dissolved salts, too.

16. EROSION BY ICE OR
GLACIER
A glacier is a river of ice formed
from compacted snow. They are
most common in the Polar regions
(e.g.Antarctica) and in mountain
regions like the Alps and
Himalayas. Glaciers move slowly
down valleys (at speeds up to a few
metres per day), but have
enormous erosive power. Glaciers
erode the surface of the Earth.