Transcript Weathering and Erosion ppt

Weathering is the breakup of rock due to
exposure to the
atmosphere.
Erosion
Remember: Erosion involves
removal and transport.
Weathering involves two
processes that often
work together to
decompose or break
down rocks.
Chemical and Mechanical
Weathering!
Chemical weathering, or
decomposition, takes place
when at least some of the
rock’s minerals are changed
into different substances.
Chemical processes include
rain, acid etching by plants,
oxidizing, and demineralizing
by water.
5 Agents of Chemical Weathering
Common agents of chemical weathering are
water, acids, and air.
These agents weaken the bonds between
minerals grains of the rock.
1. Water – can cause rock to be broken down
and dissolve. Can take thousands of years to
take place.
2. Air – the process of oxidation is a chemical
reaction in which an element (iron) combines
with oxygen, causing rust.

(Weak Acids) - acid precipitation, acids in
groundwater, acids in living things.
Three Sources of Weak Acids
3. Acid Precipitation – rain, sleet, or snow
that contains a high concentration of acid.
Normal precipitation is acidic, acid
precipitation contains more acid than normal.
4. Acids in Groundwater – carbonic acid or
sulfuric acid reacts with rocks in the ground,
causing a chemical reaction, eating away at
the rock.
5. Acids in Living Things – Lichens produce
acids that slowly break down rock.
Chemical
Weathering
Types of Chemical Weathering:
Dissolution
H2O + CO2 + CaCO3 --> Ca+2 + 2HCO3water + carbon dioxide + calcite dissolve
into calcium ion and bicarbonate ion
Dissolution is very common in areas that
have a great deal of limestone. Acidic
waters (from pollution or natural) dissolve
limestone allowing for additional water to
gain entrance. Can cause sinkholes and
dissolution of statutes and grave stones.
Hydrolysis
Hydrolysis takes place when acid rain reacts
with rock-forming minerals such as feldspar to
produce clay and salts that are removed in
solution.
The only common rock-forming mineral that is
not affected is quartz, which is a chemically
resistant mineral. This is why quartz and clay
are the two of the most common minerals in
sedimentary rocks.
The weird shapes form as water attacks
the rock along joints and cracks, leaving
rounded lumps of un-weathered rock.
The iron-rich minerals in the rock have also
oxidised to a brown “rusty” colour.
Rusting: The Transfer Of
Electrons So finally, what is rust?
It is the product of the transfer of
electrons from the metal (loss of
electrons is called oxidation) to the
oxygen molecules (gain of
electrons is called reduction).
Batteries take advantage of this
process of natural decay of
metals. However, instead of
allowing the metals to decay
immediately, they make the
electrons travel to the other end of
the battery first, and so the current
can be made to pass through a
circuit.
Mechanical weathering, or
disintegration, involves physically
breaking rocks into fragments
without changing the chemical
make-up of the minerals within
them.
There are four main sources of power
for mechanical weathering.
Gravity, Water, Wind, & Waves
Of these, water appears to be the
leader in changing the surface.
If a particle is loosened by
weathering, but stays put, its
just weathering. If it starts
moving, its Erosion.
Remember this!: You’ll be
quizzed soon!
Mechanical weathering
processes, many of which
are erosional, include
some of the following.
Frost Wedging
Frost Wedging
is the freezing
and thawing of
water in
cracks.
Mechanical Exfoliation
Mechanical
Exfoliation is the
peeling off of
sheets of rock as
they expand and
crack.
Crystal Growth Wedging
Crystal Growth
Wedging
involves salt
crystals growing
from salty
waters.
Crystal Growth Wedging
Crystal Growth
Wedging usually
occurs near
coastlines as it
has on this
granite.
Root Penetration
Plant roots have to be strong to
survive the elements.
Root Penetration
Powerful plant
roots grow into
rock cracks and
cause fractures.
Abrasion
Both wind and
water can
cause abrasion
as rock
fragments
bounce off
each other.
Abrasion
This “moon
looking” picture
of an Antarctic
rock, shows
weathering
from the wind
blown sands.
Glacial Weathering
Glaciers and avalanches can
cause weathering as ice and
rock interact.
Other Agents of Weathering
Things like flash
floods, mud
slides,
landslides, and
other forms of
mass wasting
can cause
weathering.
Erosion
Remember: Erosion involves
removal and transport.
Erosion
Rain, wind, and streams are all
agents of erosion.
Can you think of any others?
Get out a piece of paper and
identify if the following
involve weathering, erosion,
both, or neither.
Ready?
1.Waves are crashing on a sand
beach.
2.Water expands as it freezes in
the cracks of rocks.
3. Pebbles move down a stream
with the current.
4. Acid rain causes the
decomposition of a statue in New
York.
5. A man shovels dirt to plant a tree.
6. A Glacier slowly moves down a
mountain.
7. A tree’s roots grow into the
cracks of rocks.
8. A major volcano erupts.
9. A boy takes out the garbage
for his mother.
10. A shovel is left outside and
begins to rust.
Once you’ve answered these,
discuss you’re answers with the
rest of the class before you go
on.
Let’s Discuss The Questions.
1. As the sand is moving there
is definitely erosion; there is
also abrasion from the sand
gains colliding. Both
2. This is frost wedging so it’s
mechanical weathering. There
is no mention of movement.
Weathering
3. There is probably some
weathering, but there is
definitely erosion. Erosion or
Both
4. Acid rain on a statue is
chemical weathering. This is
mainly Weathering.
5.Since the man is transporting
Earth materials, it’s Erosion.
6. A glacier moving down a
mountain would have both
weathering and erosion. Both
7. A tree’s roots growing into
cracks of rocks would be
weathering. Weathering
8. A major volcanic eruption
would involve both weathering
and erosion. Both
9. Unless the garbage has
“Earth Material” or dirt in it
there is probably no erosion or
weathering. Neither
10. The rusting of a shovel is
oxidation. This is chemical
weathering. Weathering
Think you understand
the difference?