Transcript Weathering and Erosion

4.3
 Weathering is the process through
which rocks or other materials are
broken down.
 As water freezes, it expands. This forces the
cracks to become larger.
 In chemical weathering, the rock is worn down by the
effect of chemicals such as acid rain, which is the
product of gases from factories. In physical
weathering, the rock is worn over time by rubbing,
gravity, and temperature changes, among other things.
 Physical weathering
 Chemical
 Caused by pushing,
weathering
 Occurs when
chemicals break
down rocks
pulling, rubbing, or
temperature
 Water freezes in cracks of rocks and causes them to
spread apart.
 Tree and plant roots can push against the walls of
cracks in a cliff and break apart rock.
 Gravity can pull pieces of rocks down a slope. As the
rocks bump other rocks, they can break off.
 Wind blows and picks up small particles of sand and
dirt. These particles rub against rock and this can wear
away the surface of the rock.
 Groundwater can break up underground rock causing
caves to form.
 Stone or metal statues may have features that have
been worn away or pitted. Color changes can also
occur.
 As metal and stone wear away, pieces may crumble and
be taken away by the wind and precipitation.
 Acid rain can cause statues to become
pitted, worn away, or changed in color as a
result of the acid reacting with the material
in the statue.
 Physical weathering is caused by
mechanical forces. Chemical
weathering is the result of chemical
changes in the material being
weathered.
 Erosion is the process through which
weathered rock is moved from one place to
another.
 When a tree root splits a rock, what happens to the





pieces of rock?
They probably stay where they are.
When water freezes and splits a rock, what happens to
the pieces of rock?
They probably stay where they are.
What might move the broken pieces of rock to another
location?
Wind, gravity, flowing water
 The movement of a large amount of wet soil
and rocks down a slope.
 A landslide is the movement of a large amount of rock
and soil down a slope.
 Earthquakes or volcanic eruptions can cause a
landslide.
 A glacier is a large mass of slowly flowing
ice.
 A glacier can carry away weathered pieces of
rock as it moves.
 A cirque is a steep bowl-shaped hollow that
is formed as bits of rock wear away the
ground at the beginning of the glacier.
 People could cultivate plants on the hill
to keep the soil and rocks from being
carried away by the mudslide.
 A lake would be formed.
 Deposition is the process by which eroded materials




are dropped off in another place.
What things can carry pieces of rock?
Wind, moving water, and moving ice
What eventually happens to these particles?
They are dropped off in a new location.
 Water can wash away soil and erode rock as it flows
down hills.
 More deposition occurs in slow-moving water than in
fast-moving water.
 Meanders are gentle loops that can form in rivers with




slow-moving water.
The water moves slowly around the inside of a
meander.
As the water moves, it can carry particles. These
particles are called sediment.
Sediment can deposit on the inside of a meander and
eventually build new land.
Water moves faster on the outside edge of a meander.
Sediment will travel farther downstream.
 As waves wash sand off beaches, the sand can be
deposited in the water. As this occurs over time,
enough sand may be deposited and a strip of sandy
land can form. This strip is called a sandbar.
 Wind can:
-wear away rocks
-move sand and sediment from one
place to another
 The ocean can flood the beach and carry
away sand and buildings too near to a beach.
 How does gravity deposit materials?
 Gravity causes landslides to deposit rocks
and soil at the bottom of a hill or cliff. The
newly deposited rock and soil become new
land.
 What things would you find at a shoreline?
 Sand, water, waves, wind, grass, shells, gulls,
crabs
 Which of these might change the form of
the shoreline over time?
 Water, waves, and wind
 A barrier island takes the force of waves
from a storm first. This protects the beach
from erosion by waves.
 A flood occurs when water collects on land that is
normally dry.
 Floods can occur when Water overflows banks or beaches
 Rainfall is heavy
A floodplain is a place that is easily flooded when river
water rises.
 Wetlands absorb water and thereby protect the land
farther away from the shore. If wetlands are drained,
this land will not be protected from floods and storms.
 The dunes shelter inland areas from
storm waves and winds.
 What three things can cause the erosion of a
shoreline?
 Running water, waves, and wind
 Plants have roots that hold the sand in
place.
 You should consider the entire
shoreline because a prevention or
reduction of erosion in one part of
the shoreline can cause erosion in
another part.