Download Mechanical weathering

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eather/weathering/
Chemical weathering is weathering that
changes the chemical makeup of the
rock. It occurs when chemical reactions
dissolve or alter the minerals in rocks
and transform them into different
minerals. It occurs at or near Earth’s
surface.
Usually caused by reactions with
Oxygen, water, or acids.
OXIDATION: occurs when oxygen combines
with another substance and new substances
called oxides are formed
ex: Rust is an iron oxide
Many rocks contain iron and weaken or crumble when
oxidation occurs.
ACIDS: carbon dioxide can dissolve in the rain
to form weak carbonic acid. When this acid
comes into contact with certain minerals, a
chemical change called carbonation occurs.
ex: calcite is changed by this process.
Acids are also formed from certain
green plants, such as moss. Decaying
organisms can produce acids, too.
As acid seeps into the cracks in a rock,
it can break the rock apart.
WATER: most chemical weathering is caused by
water. Water reacting with a mineral that has little
water content is called hydrolysis
ex: feldspar undergoes hydrolysis to become clay
After they have undergone hydrolysis, the rocks may
crumble apart if they are heated or dried even a little!
Mechanical weathering involves only
physical changes, such as alterations
in size and shape. The chemical
makeup of the rock does not change!
Ex:
ripping
a piece
of paper
Also called
“physical
weathering”
Temperature changes: rocks can be
broken by changes in temperature.
-heat causes expansion
-cooling causes the rock to contract
Repeated expansion and contracting can
cause breakage over time
Ice wedging- the repeated freezing and
melting of water in the cracks of rocks
causes ice wedging. When water freezes, it
expands, causing the crack in the rock to
widen.
ex: potholes are caused by ice wedging
Root Action: plant roots search for
minerals and nutrients. They often grow
into cracks in the rock. The pressure of
the growing root causes the rocks to
break apart over time.
-Change in phase
(mineral type) and
composition due to
the action of chemical
agents.
-Usually caused by
reactions with
oxygen, water, or
acids.
-Effects the
structure and
integrity of a
rock
-Breaks down
rock into
fragments
--key stage in
forming soil
-doesn’t change chemical
characteristics
-physical decomposition
of a rock into smaller
fragments, each with the
same properties as the
original.
-examples include frost
wedging, pressure and
temperature changes,
and root damage
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