Aim: How can weathering change rock?
Do now: Look at these rock formations.
How do you think they were formed?
Weathering
Weathering
• Weathering is the process of breaking
down of the materials of Earth’s crust into
smaller pieces.
Two Types Of Weathering:
1) Physical weathering is breaking rock by force.
• The rock material is the same but smaller.
– Cracking
– Pounding
– Scraping
2) Chemical weathering is where the rock material
is changed into another substance by reacting
with a chemical.
Physical Weathering
• Process by which rocks are broken down
into smaller pieces by external conditions.
• Types of Physical weathering
– Frost heaving and Frost wedging
– Plant roots
– Friction and impact
– Burrowing of animals
– Temperature changes
Frost Wedging
•Frost wedging is the process of
splitting rock as the results of
water expanding inside a crack
as it freezes.
•The stress created by the
expanding ice forces the crack to
widen.
•As the crack widens, more water
fills the crack, forcing the crack to
widen as this new water freezes
Frost Heaving
•Frost heaving is similar
to Ice wedging except
ice form under rocks
causing the rock to
move out of its original
position.
•This could cause
erosion under the rock
to occur.
Plant Roots •Sometimes seeds fall into cracks of
rocks.
•When the seed grows, its roots
secret a chemical which breakdown
rocks, so that the root have room to
grow.
Friction and Repeated Impact
•Friction and repeated impact can occur in
three ways.
•Moving water
•Moving Ice
•Move air (wind)
Friction and Repeated Impact -
Water 1. As water moves across rock,
the water molecules rub
against the rock, slowly
grinding the rock down.
2. Sometimes hard materials
are mixed in with moving
water. These materials may
smash against rock, chipping
away at it.
3. Since water is heavy,
sometimes the pressure of
water is enough to push
through rock.
Friction and Repeated Impact -
Ice • In very cold regions of the world, glaciers form as the
results of thousands of years of snow pile up onto itself.
• These thick sheet on ice are very heavy and begin to
move down mountain sides.
• As they move material trapped in the ice begin to move
with the glacier- grinding along the bottom against the
ground. Scraping at the rock.
Friction and Repeated Impact -
Wind 1. As wind moves across
rock, the air molecules
rub against the rock,
slowly grinding the rock
down.
2. Sometimes hard
materials (like sand) are
mixed in with moving air.
These materials may
smash against rock,
chipping away at it.
Burrowing of Animals
Many animal will dig
holes and tunnels in
the ground for
shelter and a way to
move safely from
one place to
another.
Earthworms secrete
a chemical with help
breakdown rocks so
they can move
through the ground.
Chemical Weathering
• The process that breaks down rock
through chemical changes.
• The agents of chemical weathering
– Water
– Oxygen
– Carbon dioxide
– Living organisms
– Acid rain
Water
• Water weathers rock by dissolving it
Water - Caves
• Caves are the results of
water dissolving limestone
resulting from underground
streams or seepage from
the surface.
Water - Sinkholes • Sinkholes are the results
of the roof of a cave
collapsing.
Oxygen
• Iron combines with oxygen in the presence of water in a processes called oxidation
• The product of oxidation is rust
Carbon Dioxide
• CO2 dissolves in rain water and creates
carbonic acid
• Carbonic acid easily weathers limestone
and marble
Living Organisms
• Lichens that grow on rocks produce weak
acids that chemically weather rock
Acid Rain
• Compounds from burning coal, oil and gas
react chemically with water forming acids.
• Acid rain causes very rapid chemical
weathering
Rates of weathering will be influenced by
3 main factors:
1. Surface area exposed
2. The type of mineral the rock is made of
3. Environmental Climate
Rates of weathering will be influenced
by: Surface area exposed
Surface area exposed - weathering only
occurs on the surface of rock. 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 greatest surface area exposed. The interior can now be attacked.
• Mineral composition- some minerals are
more resistant than others.
• Some materials are very hard, so they
ware down slowly.
• Some materials are very soft, so they ware
down quickly. • ex.:Quartz is resistant to chemical and physical
weathering.
Rates of weathering will be influenced
by: Mineral composition
• 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.
Rates of Weathering will depend
on: Climatic Conditions
Soil - The product of weathering
• Soil- rocks, minerals (mainly sand and
clay), and organic material (regolith and
organic matter)
• Soil forms layers of different
characteristics called horizons.
• Soil formation is important because
complex plants can grow.
Erosion
Erosion • The process by which water, ice, wind or
gravity moves fragments of rock and soil
from one area to another..
LANDSCAPES ARE SHAPED BY
EROSION OR DEPOSITION
Erosion – The transport of sediment. Occurs
naturally, wind water or gravity.
Deposition – The drop off of sediment to a
new location.
Water Erosion • Rivers, streams, and runoff cut into rock
and soil creating depression in the
surface.
• Fast moving currents move materials to
areas where the current is slower, there by
dropping them at a new location.
Evidence of water erosion • Rock and land that are cut by water tend to have
deep V-shaped valleys.
• This is because usually in the middle of a stream or
river, the water is moving much faster than the
water on the sides.
• The faster the water moves, the faster it erodes
rock.
• Where currents slow down, sediments are dropped.
• Sediment is arranged or sorted with the largest
particles on the bottom layer and the smallest
particles on the top layer.
Evidence of water erosion
OCEAN - EROSION
• CLIFFS
• The Ocean is
constantly moving.
• Tides causes the
oceans to rise and
lower, changing the
environment that the
rock is exposed to.
• Waves repeatedly
pound against rock,
causing them to chip
and break.
Ice Erosion • As Glaciers form
materials get trapped
in the ice and as the
glacier moves so
does the trapped
materials (sand, rocks
boulders)
Evidence of Ice Erosion • Glaciers are very heavy.
• In general, Glaciers move very slow and
uniformed.
• Glaciers cut U- shaped valleys.
• When glaciers begin to melt, large boulder are
released and deposited.
• Deep parallel groves are cut into rock in the
direction of glacier movement.
• The sediment is unorganized or unsorted. Large
and small particles are mixed together.
Wind Erosion • As strong wind blows across
land and rock, some
materials are lifted up and
move to other areas (sand,
rocks).
• When the wind calms down,
these material drop down.
Evidence of Wind Erosion • Wind moves in variable
speeds. Sometimes very
fast and sometimes not
at all.
• This difference in wind
speed can cause unique
rock formations.
Mass Movements
• Landslides, mudslides,
slump and creep.
• Landslides occur as the
result of a layer of soil or
soil under ground
becomes unstable.
• The weight of the surface
material becomes too
great, causing a large
section of land to shift
downhill.
landslide clip.mpeg
Possible Mass Movement
Problem • http://www.youtube.com/watch?v=3jlaiJRw
U6Q&feature=related
Deposition
• What does deposition look
like?
How is Sediment Deposited? • Energy is needed to move
sediments from one area to
another.
• The more energy, the larger the
sediment that can be moved.
• Once the energy begins to
decrease, larger sediments
begin to settle.
GLACIAL DEPOSITS
Sediments deposited as a glacier melted
Erratic boulder - there are no other rocks like it the area.
Moraine – sediments left behind from a glacier are unsorted (different sizes)
GROUND WATER DEPOSITS
Stalactites – (rock icicles)
• Form from dissolved minerals sediment that drip from cave ceilings.
• They form from the top and grow toward the floor.
Stalagmites – (upside down rockcicles)
• Sediments deposit as undeposited minerals drip from stalactites.
• Take hundreds of years to form.
WIND DEPOSITS Sediment eroded by wind and deposited in
new location.
SAND - DUNES CLAY - LOESS
OCEAN DEPOSITS • Ocean currents can
move sand from one
area of beach to
another.
• Creating sand bars,
new beach and even
islands.