Mechanical and chemical
forces break down rock
When you are walking in your
neighborhood how do you think the
small rocks are formed?
Mechanical and chemical forces
break down rock
 Weathering,
which
is the process by
which natural forces
break down rock.
Mechanical and chemical forces
break down rock
There are two ways
in which
weathering can
occur.
 Physically broken
apart and
chemically

Mechanical and chemical forces
break down rock



Mechanical weathering
breaks up rock by
physical forces.
Those physical forces
split apart rock
Mechanical weathering
can be caused by ice
wedging, pressure
release, plant root
growth, and abrasion.
Mechanical and chemical forces
break down rock

Ice wedging causes
mechanical weathering.
When water freezes in
the cracks and pores of
rocks, the force of its
expansion is strong
enough to split apart
rock.
Mechanical and chemical forces
break down rock

Pressure release is the
next method. Rock
deep within the
earth’s surface is
under great amounts
of pressure. Over
time the rock is
pushed up to the
surface of the earth.
Mechanical and chemical forces
break down rock

When the rock
reaches the surface
the pressure is
released and the rock
expands. As the rock
expands cracks from
in it causing
weathering.
Mechanical and chemical forces
break down rock

Plant Root growth is
method in mechanical
weathering. When plants
grow in a rock, their
roots can widen the
crack and force the rock
apart. Thus mechanical
weathering takes place.
Mechanical and chemical forces
break down rock

Abrasion is the final
method in mechanical
weathering. Water alone
can wear down rocks,
but they also can move
rocks downstream
causing them to rub
together and wear down
into rounded shapes.
Mechanical and chemical forces
break down rock

When elements
react with water
and air they can
cause the
breakdown of
rocks. This is of
course chemical
weathering.
Mechanical and chemical forces
break down rock

When minerals in
rocks come into
contact with air and
water, some
dissolve and others
react and are
changed into
different minerals.
Mechanical and chemical forces
break down rock
Water is the main
cause of chemical
weathering.
 Water and carbon
dioxide mix with
decaying plants and
breaks down rock
into smaller pieces.

Mechanical and chemical forces
break down rock

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Oxygen is also a major
factor in chemical
weathering.
When minerals dissolve
in water, oxygen in the
air and water combines
with iron to produce iron
oxides or rust.
Mechanical and chemical forces
break down rock


Just like the rock cycle
weathering can take
hundreds, thousands, or
millions of years.
The surface of the earth
will weather at a faster
rate because of the
exposure to air and
water.
Mechanical and chemical forces
break down rock


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Different rocks break
down at different rates
such as limestone and
granite.
Climate can also affect
chemical weathering.
Weathering occurs faster
in hot wet regions than
cold dry regions. Why?
Mechanical and chemical forces
break down rock

Although mechanical weathering can occur
more in cold regions rather than hot. Why?