Do Now:
Weathering
1. How does the sun play a role in weathering?
2. Describe the similarity between the ways tree roots
and ice mechanically weather rock.
EQ- How do rocks and minerals break
down?
Weathering
EQ- How do rocks and minerals break
down?
GPS: S6E5. Students will investigate the scientific view of how
the earth’s surface is formed
d. Describe processes that change rocks and the surface of the
earth.
f. Explain the effects of physical processes (plate tectonics, erosion,
deposition, volcanic eruption, gravity) on geological features including
oceans (composition, currents, and tides).
h. Describe soil as consisting of weathered rocks and decomposed
organic material
Weathering
http://safari.glynn.k12.ga.us/?a=6856&d=02323AA
 Mountains wear down over
time.
 Due to the Sun’s energy,
wind, and water,
mountains begin to
crumble as soon as they are
formed.
Weathering
 The Smokey Mountains are much older than the
Rocky Mountains.
Weathering

At one time, the Smokies were as tall as the Rockies
and also had sharp peaks.
Weathering
 Weathering is simply the chemical and/or physical
breakdown of a rock material--weathering involves
specific processes acting on rock materials at or near
the surface of the Earth
Weathering
 In other rocks, minerals may slowly dissolve.
 Eventually the surface of ALL rocks crumbles, or
weathers.
Types of Weathering
 Mechanical Weathering(physical)
 Takes place when rock is split or broken into smaller
pieces of the same material without changing its
composition.
Example: Breaking of a rock cliff into boulders and
pebbles
Weathering
Mechanical
 Common weathering processes:
 Frost action
 Wetting and drying/Wind
 Action of plants and animals
 Loss of overlying rock and soil
Rate of Weathering
 The type of rock and climate determine how fast a rock
will weather.
Types of Weathering
 Chemical (decomposition)
 takes place when the rock’s minerals are changed into
different substances.
 Water and water vapor are important agents of chemical
weathering.
Example: Formation of clay minerals from feldspar
Types of Weathering
 The two processes of weathering, mechanical and
chemical seldom occur alone!
 Since water vapor is present in the air everywhere
means that chemical weathering occurs everywhere.


Changing conditions of wetness and dryness cause rocks and
minerals to break down.
Weathering occurs quickly when running water knocks
rocks against each other.
Types of Mechanical Weathering
 Frost action or Ice Wedging:
 Water takes up about 10% more space when it freezes.
 This expansion puts great pressure on the walls of a
container.
 Water held in the cracks of rocks wedges the rock apart
when it freezes.
 Often occurs in places where temperatures vary from
below the freezing point of water to above the freezing
point.
Types of Mechanical Weathering
 Frost action or Ice Wedging con’t
 Occurs mostly in porous rocks and rocks with cracks
in them
 Bare mountaintops are especially subject to ice wedging.
Types of Mechanical Weathering


Changing conditions of wetness and dryness cause
rocks and minerals to break down.
Weathering occurs quickly when running water
knocks rocks against each other.
Repeated wetted and drying
 Especially effective at breaking up rocks that contain clay.
 Clays swell up when wet and shrink when dry.
 Causes rocks that contain clay, such as shale, to fall apart.
Types of Mechanical Weathering
 Plants cause weathering
when their roots grow into
small cracks in a rock.
 Animals cause weathering
when they dig into soil or
burrow underground.
 Action of plants and animals:
 Lichens and mosses grow on rocks


They wedge their tiny roots into
spores and crevices.
When the roots grow, the rock splits.
Types of Mechanical Weathering
Types of Mechanical Weathering
 Action of plants and animals:
 Larger trees and shrubs may grow
in the cracks of boulders.
 Ants, earthworms, rabbits,
woodchucks, and other animals
dig holes in the soil.

These holes allow air and water to
reach the bedrock and weather it.
Types of Mechanical Weathering
Exfoliation
 Exfoliation is a weathering
process that results in rock
layers peeling away as they
expand or contract.
 Loss of Overlying Rock and Soil
 Sheet jointing on a granite outcrop
produces cracks in the rock, thereby
exposing more of the rock surface to
weathering.
Types of Chemical Weathering
 Chemical weathering is the chemical breakdown of
rocks. Results mainly from the action of rainwater,
oxygen, carbon dioxide, and acids of plant decay.
 Moss and lichens on rocks
will eventually cause them
to break down because of
chemicals they release.
Agents of Chemical Weathering
Oxidation
 The chemical reaction of oxygen with other substances
is called oxidation.
 Oxidation is when the element iron combines with
oxygen and water to make rust.
Agents of Chemical Weathering
Acid Precipitation
 Carbon dioxide dissolves easily in water.
 It forms a weak acid called carbonic acid
 This is the same compound that is in carbonated drinks.
 Attacks many common minerals such as feldspar,
hornblende, augite and biotite mica.
 The original mineral is changed into a clay mineral.
Agents of Chemical Weathering
 Hollows out great caverns in limestone bedrock.
Agents of Chemical Weathering
 Acids are formed from the decay of plants and animals.
 These acids are dissolved by rainwater and carried
through the ground to the bedrock.
Agents of Chemical Weathering
 Carbon dioxide and sulfur compounds released by
industries unite with water in the atmosphere to form
acid rain.
 Increasing amounts of acid rain in the environment
increase the rate of chemical weathering.
Factors that affect weathering
 Weathering is slowest in dry,
cold climates.
 Running water speeds up mechanical weathering
and chemical weathering.
 The kind of minerals found in a rock also affects
how fast it weathers.
 The greater the surface area of a rock or mineral
compared to its volume, the faster it will weather.
Weathering
The process of breaking down rock.
Chemical
Weathering
Mechanical
Weathering
exfoliation
frost
wedging
root
wedging
wind
running
water
rock
fall
changes in
rock
minerals
rust
Activity:
Imagine that you are a tin can-shiny, new, and
clean. But something happens, and you don’t
make it to a recycling bin. Instead, you are left
outside at the mercy of the elements. In light of
what you have learned about physical and
chemical weathering, write a story about what
happens to you over a long period of time. What
is your ultimate fate?
Erosion
Do Now:
Define chemical weathering and
describe its causes.
EQ- How do rocks and minerals break
down?
Chemical weathering occurs when
chemical reactions dissolve the minerals
in rocks or change them into different
minerals. This type of weathering
changes the chemical composition of
the rock, which can weaken the rock.
Erosion
EQ- How do rocks and minerals break
down?
GPS: S6E5. Students will investigate the scientific view of how
the earth’s surface is formed
d. Describe processes that change rocks and the surface of the
earth.
f. Explain the effects of physical processes (plate tectonics, erosion,
deposition, volcanic eruption, gravity) on geological features including
oceans (composition, currents, and tides).
h. Describe soil as consisting of weathered rocks and decomposed
organic material
Erosion
 Erosion is the process of
moving pieces of rock and
sediment by wind, water,
ice, or gravity.
Erosion
Moving Sediment
 Weathering breaks rock into
bits and pieces called
sediment.
How does sediment get from a
mountain peak to a beach?
Erosion


Weathering breaks rock into bits and pieces
called sediment.
Wind erodes mountains and moves sediment,
but not as well as flowing water.
Erosion
 Running water, wind and ice are all involved in moving
sediment. Sediment generally moves downhill because
of the force of gravity.
 Running water- like that found in rivers, streams, and
waterfalls carries sediment.
- a river is a large, flowing body of water
-a stream is a small river.
-a channel is the path that a river or stream follows
Erosion
Running water moves sediment
The process of depositing sediment after it has been
moved by water, wind, or ice is called deposition.
The amount of sediment carried and deposited by
water depends on many factors:



the volume of water,
the slope of the land,
how rocky or smooth the land is.
Erosion
Volume:
The volume of running water affects how much
sediment can be carried. When the volume of flowing
rainwater is small, some sediment is moved. After a
heavy rainfall, the greater volume of water can move
a lot of soil or sediment from yards.
Slope:
Slope refers to how steep the land is, another word for slope is
gradient. The steeper the slope, the faster the water and
sediment will move over land. Faster water means that larger
particles can be moved and more particles can be moved at
one time.
Rocky vs. Smooth:
Rocky landscapes can trap sediment causing the sediment not to travel far.
A smooth landscape or river bed might mean that sediment can be carried a long
way.
Erosion

A stream table can model how water flows over
the land.
 The steeper the slope, the faster the water and
sediment will move over land.
Erosion
Sorting sediment:
How fast water moves is directly related to how much energy it has.
Both the speed of water and its energy are directly related to how big a
piece of rock can be moved. Fast, high energy water can move big pieces of rock.
Slow-moving water can only move fine sediment.


You can tell the speed of flowing water by the size of the
rock pieces found on a stream bottom.
The grains settle in order, making a pattern called graded
bedding.
Erosion
Erosion
Interpreting layers of sediment:
 Sedimentary rocks hold
clues to their past.
 If you know the up
direction, you know the
direction of younging —
this is the directions of
younger layers.
Erosion
When sediment is carried by the wind or running water, it often forms a pattern
of alternating beds where it is deposited, this pattern is cross bedding.
 Cross bedding, is easy to recognize in sedimentary rocks where
one layer ends and another layer passed over it.
Erosion
Moving sediment by ice:
 Particles that are trapped in
ice or suspended in water can
cause weathering.
 As the ice of a glacier flows
down a valley, it grinds the
valley floor with pieces of
rock caught up in the ice.

As the ice of a glacier
flows down a valley, it
grinds the valley floor
with pieces of rock
caught up in the ice.


Glaciers are formed from
accumulation of snow over
hundreds or thousands of
years.
As snow piles up and
pressure increases, it
changes into ice.

The fine rock powder
that results from
glaciers is called
“rock flour.”

Rock flour can be
washed into lakes
and make them a
milky blue color.
Types of glaciers
Alpine Glaciers
(Valley Glaciers)
- small to medium
glaciers formed in
mountains where
the temperature is
low enough to
prevent snow from
melting during the
summer.
- Flow slowly down
mountain slopes
and valleys eroding
as they go.
U-shaped
Valleys
Alpine glaciers typically follow
a river bed and cut the deep
V into a smoother but larger
U-shape as they move down
the mountain. The sides of
the U-shaped valleys are
much steeper and rugged
than when they were shaped
by a river. The ice in a glacier
is much more destructive to
the land than the running
water in rivers.
Continental Glaciers
Huge continuous
masses of ice that form
from layers of snow that
compact and freeze into
ice.
How do Glaciers
move?
Glaciers move by two different
methods:
• when ice at the bottom of the
glacier melts due to the weight of
the glacier the glaciers begins to
slide on the melted water.
•when ice crystals within the glacier
slip over each other
Glacial Erosion
 As glaciers move they break off pieces
of rock and sediment, pick them up
and carry them with them. As the
glacier begins to melt the sediment is
deposited on land.
More on moving sediment



Wind can move
particles of sediment
from one place to
another.
Beach dunes hold
large amounts of wind
deposited sand.
Loess is another
wind-blown deposit
of fine sediment.
More on moving sediment

Mass wasting is the
downhill movement of
large amounts of rock and
sediment due to the force
of gravity.