Weathering & Erosion

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Transcript Weathering & Erosion

Weathering is the physical and
chemical breaking down of rock
material into smaller fragments
due to exposure to processes that
occur at Earth’s surface
Weathering occurs when rocks in the
lithosphere are UPLIFTED and is
exposed to the atmosphere,
hydrosphere, and biosphere
 The most important agent involved in the
weathering of material is WATER
Two Types OF Weathering:
1) Physical
weathering is
breaking rock by
force into smaller
pieces of the SAME
ex: hitting,
2) Chemical
weathering is the
chemical reaction
of water and
water vapor
breaking down
rock by changing
its chemical
 The minerals that
make up the rocks
are changed into
another substance
4 Types of Physical Weathering
1) Frost action
 (ice wedging)- water seeps into cracks,
freezes, expands and wedges the rock apart!
 –Water and ice are more powerful than rock over time!
1.Water seeps into small cracks in rocks.
2.When the water freezes it expands
creating great pressure.
3.The crack widens and allows water to
seep deeper into the rock.
4.Alternating Freezing and Thawing
Examples of Frost Wedging :
2) Plant action
 tree roots grow into
small fissures or wedges
and expand rock
1.Tiny root hairs
seek out small
cracks and pits
in rock.
2.Once the root
hairs find a
place they grow
and expand.
3.The expansion
causes great
pressure and
cracks the rock.
3) Exfoliation
the peeling of rock due to
release of pressure
experienced when rock was
Rocks formed deep in
the Earth are made
under high pressure.
When the pressure is
released the rocks
expand & crack.
May also be caused by
alternate heating and
cooling of rocks by
weather conditions.
This is basically the
“peeling away” of rock
(especially in
4) Abrasion-
collision of rocks with
one another
 Scraping,
grinding, and
wearing away
other rocks
during erosion
Types of Chemical Weathering
 Oxidation
 Hydrolysis (water)
 Carbonation (acid rain)
rocks with metallic
elements combine with
oxygen (in air and
water) and rust away
(rust stains the rocks
ex.: rusting
Minerals are
dissolved in
water when they
react with it
ex.: Feldspar
reacts with
water to form
Much of the time
these minerals
will end up as
carbon dioxide from air
reacts with water to
create carbonic acid
which breaks down rocks
(especially limestone,
marble, etc.)
Why? What mineral
does these rocks have
in them?
Acid Rain:
Sulfur Dioxide
in the
dissolves in
rain water
forming a
strong acid
(sulfuric acid).
NOTE: chemical weathering typically results in a rounded
appearance of the landscape…just like here in the Catskills!
Carbonation – Stalagtites and
Stalagmites (karst topography)
Carbonation – Karst Topography
 Karst Topography is the name given to a region
where the bedrock is easily chemically
 This leads to the rock weathering away and
forming sinkholes, caverns, disappearing
Karst Topography
Differential Weathering
 Masses of rock do not weather uniformly due to
regional and local factors
 Results in many unusual rock formations
 Example: Bryce Canyon
Bryce Canyon National Park
Rates of weathering (how fast rocks
break down due to physical or chemical
processes) will be influenced by:
1) Surface area exposed weathering occurs on the
surface. The more surface
exposed, the faster the
weathering will occur.
A full, solid block has
the least surface area.
The interior is safe
from exposure.
A smashed piece has
surface area exposed.
The interior can now be
Rates of Weathering will depend on:
2) Rock and Mineral composition- some
minerals are more resistant than others.
Sedimentary rocks are generally soft and weather fast.
–Limestone is easily dissolved by acids.
–Igneous and metamorphic rocks are usually dense, hard, and
more resistant to weathering.
–Any rock containing quartz (hardness of 7) will generally be
resistant to weathering (conglomerate, quartzite, granite, etc.)
Rate of Weathering will depend
 Exposure to surface: rocks exposed at surface
weather much more quickly than buried rock.
 –Rock Outcrops are places where rock layers
actually stick out above ground…where they are
quickly exposed to lichens, moss, trees, rainfall,
ice, and animals!
Rate of weathering will depend
 Topography – higher elevations tend to be
colder and experience more freeze-thaw cycles
Where is the rock more resistant to
Where is the rock least resistant to
You might also see it like this…
You might also see it like this…
Rates of Weathering will depend on:
 Climatic
Cold and/or dry climates favor
physical weathering.
Warm and wet climates favor
chemical weathering.
Frost action works best in areas
where the temperature fluctuates
Soil - The product of
 Soil-Soil is the result of weathering of rock,
which produces smaller pieces called fragments,
which combine with organic matter, air, and
water to comprise soil. •Soil = rock fragments,
humus (decayed plant and animal material), air
and water
 Soil forms layers of different
characteristics called
Soil Horizons
Soil separates over time into distinct layers as follows:
A horizon (Topsoil): the upper layer of dark brown soil
containing humus and plenty of animal activity (bugs, worms,
B horizon: also called “subsoil”, containing many more minerals
leached down by water infiltrating through the A horizon, so often
stained red by oxidation of iron minerals
C horizon: made of weathered bedrock (parent material)
•Usually contains larger particles and rock fragments
Bedrock: the underlying rock that is still mostly un-weathered
Soil Horizons