Title: Weathering
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2Weathering
3- Weathering is the physical and chemical breaking
down of rock material into smaller fragments due
to exposure to processes that occur at Earths
surface - Weathering occurs when rocks in the lithosphere
are UPLIFTED and is exposed to the atmosphere,
hydrosphere, and biosphere
4Weathering
- The most important agent involved in the
weathering of material is WATER
5Two Types OF Weathering
- 1) Physical weathering is breaking rock by force
into smaller pieces of the SAME material - ex hitting, scratching, cracking
- 2) Chemical weathering is the chemical reaction
of water and water vapor breaking down rock by
changing its chemical composition - The minerals that make up the rocks are changed
into another substance
64 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! - Water seeps into small cracks in rocks.
- When the water freezes it expands creating great
pressure. - The crack widens and allows water to seep deeper
into the rock. - Alternating Freezing and Thawing
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8Examples of Frost Wedging Potholes
9- 2) Plant action
- tree roots grow into small fissures or wedges
and expand rock - Tiny root hairs seek out small cracks and pits in
rock. - Once the root hairs find a place they grow and
expand. - The expansion causes great pressure and cracks
the rock.
10- 3) Exfoliation
- the peeling of rock due to release of pressure
experienced when rock was formed - 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
11Water (especially in streams
- 4) Abrasion-
- collision of rocks with one another
- Scraping, grinding, and wearing away other rocks
during erosion (movement)
WIND
12Types of Chemical Weathering
- Oxidation
- Hydrolysis (water)
- Carbonation (acid rain)
13- Oxidation
- rocks with metallic elements combine with oxygen
(in air and water) and rust away (rust stains the
rocks REDDISH BROWN) - ex. rusting
14- Water (hydrolysis)
- Minerals are dissolved in water when they react
with it - ex. Feldspar reacts with water to form kaolinite
- Much of the time these minerals will end up as
clay
15- Acid-Carbonation
- 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?
16- Acid Rain Sulfur Dioxide in the atmosphere
dissolves in rain water forming a strong acid
(sulfuric acid).
17NOTE chemical weathering typically results in a
rounded appearance of the landscapejust like
here in the Catskills!
18Carbonation Stalagtites and Stalagmites (karst
topography)
19Carbonation Karst Topography
- Karst Topography is the name given to a region
where the bedrock is easily chemically weathered - This leads to the rock weathering away and
forming sinkholes, caverns, disappearing streams
20Karst Topography
21Differential Weathering
- Masses of rock do not weather uniformly due to
regional and local factors - Results in many unusual rock formations
- Example Bryce Canyon
22Bryce Canyon National Park
23Rates 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.
24A smashed piece has greatest surface area
exposed. The interior can now be attacked.
A full, solid block has the least surface area.
The interior is safe from exposure.
25Rates 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.)
26Rate of Weathering will depend on
- 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 groundwhere they are
quickly exposed to lichens, moss, trees,
rainfall, ice, and animals!
27Rate of weathering will depend on
- Topography higher elevations tend to be colder
and experience more freeze-thaw cycles
28Where is the rock more resistant to weathering?
F
A
C
E
B
D
29Where is the rock least resistant to weathering?
F
A
C
E
B
D
30You might also see it like this
31You might also see it like this
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33Rates of Weathering will depend on
- Climatic Conditions
- 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 wildly.
34Soil - The product of weathering
- 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 horizons.
35Soil 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, etc.) - 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
36Soil Horizons