Download Weathering and Erosion

Bryce Canyon National Park
Bryce Canyon National Park
Weathering and Erosion
Weathering and Erosion
Sheer cliffs, rocks balanced on one small
is one example of physical weathering.
Sheer cliffs, rocks balanced on one small
is one example of physical weathering.
tip, massive underground caves, and giant
Physical weathering occurs when large rocks
tip, massive underground caves, and giant
Physical weathering occurs when large rocks
sand dunes: what do all these things have in
are broken into smaller rocks of the same
sand dunes: what do all these things have in
are broken into smaller rocks of the same
common? These and other spectacular and
kind. The sand you made was still the same
common? These and other spectacular and
kind. The sand you made was still the same
fascinating landforms around the world are
material as the larger piece of granite, only
fascinating landforms around the world are
material as the larger piece of granite, only
the result of the processes of weathering
smaller. The granite may have broken into
the result of the processes of weathering
smaller. The granite may have broken into
and erosion. Weathering and erosion also
the minerals that make it up, such as quartz
and erosion. Weathering and erosion also
the minerals that make it up, such as quartz
create (and can destroy) the soils we depend
and feldspar, but they are the same minerals
create (and can destroy) the soils we depend
and feldspar, but they are the same minerals
on to grow the food we need to survive.
that made up the original granite.
on to grow the food we need to survive.
that made up the original granite.
How can weathering and erosion do all
You saw that shaking the granite pieces
How can weathering and erosion do all
You saw that shaking the granite pieces
that? Let’s look at the investigations you have
made them more rounded than the pieces of
that? Let’s look at the investigations you have
made them more rounded than the pieces of
done so far to get some clues about these
fresh granite. The sharp edges and corners
done so far to get some clues about these
fresh granite. The sharp edges and corners
processes. Remember, physical weathering
wore away as they hit other rocks. This occurs
processes. Remember, physical weathering
wore away as they hit other rocks. This occurs
is the breaking down of rock into smaller
naturally when rocks are hit by windblown
is the breaking down of rock into smaller
naturally when rocks are hit by windblown
pieces. The smaller pieces are called sediment.
sand or rock particles in moving water. The
pieces. The smaller pieces are called sediment.
sand or rock particles in moving water. The
Erosion is the process of transporting
name for this type of physical weathering
Erosion is the process of transporting
name for this type of physical weathering
sediment to a basin by water, wind, or ice.
is abrasion. Abrasion also happens when
sediment to a basin by water, wind, or ice.
is abrasion. Abrasion also happens when
Physical Weathering and
Round Rocks
When you shook the granite in a jar,
little pieces broke off to become sand. This
falling rocks hit other rocks, causing them to
break apart.
When you observed beach sand or sand in
a riverbed, you could see smooth, polished
sand grains. Waves and flowing water rolled
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Physical Weathering and
Round Rocks
When you shook the granite in a jar,
little pieces broke off to become sand. This
falling rocks hit other rocks, causing them to
break apart.
When you observed beach sand or sand in
a riverbed, you could see smooth, polished
sand grains. Waves and flowing water rolled
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Blowing sand (sand abrasion) helped carve
and smooth this sandstone canyon.
Talus is evidence of a rock fall at the base
of a cliff.
Blowing sand (sand abrasion) helped carve
and smooth this sandstone canyon.
Talus is evidence of a rock fall at the base
of a cliff.
these sand grains around, causing them to
Ice Wedging and Rock Falls
these sand grains around, causing them to
Ice Wedging and Rock Falls
hit each other. You observed sand particles
in the stream table bouncing and hitting
other grains of sand as they moved along.
The water carries rocks that bump off the
rough edges on other rocks. The farther the
sediment is carried by water, the smoother
the sand grains get.
No water is involved when wind transports
sediment. The sand grains bang into each
other, creating a frosted surface (a surface that
is dull instead of shiny). Beach sand, river
sand, and dune sand are all similar in at least
one way—the farther the weathered rocks
travel and the more they get banged around,
the smaller they become.
When ice freezes, it expands with
hit each other. You observed sand particles
in the stream table bouncing and hitting
tremendous force. You saw what happened
other grains of sand as they moved along.
when water in a jar froze and expanded.
The water carries rocks that bump off the
The force shattered the jar! Ice expansion
rough edges on other rocks. The farther the
naturally causes physical weathering when
sediment is carried by water, the smoother
water gets into tiny cracks in a rock. At night,
the sand grains get.
temperatures fall, and the water freezes,
No water is involved when wind transports
expands, and presses against the surrounding
sediment. The sand grains bang into each
rock. The crack gets bigger. During the day
other, creating a frosted surface (a surface that
as the temperature rises, the water thaws
is dull instead of shiny). Beach sand, river
and seeps farther down into the crack. Night
sand, and dune sand are all similar in at least
comes; the water again freezes. With repeated
one way—the farther the weathered rocks
freezing and thawing, the crack becomes
travel and the more they get banged around,
larger, and eventually pieces of the rock break
the smaller they become.
off. Ice wedging can break rocks off the side
temperatures fall, and the water freezes,
expands, and presses against the surrounding
rock. The crack gets bigger. During the day
as the temperature rises, the water thaws
and seeps farther down into the crack. Night
comes; the water again freezes. With repeated
freezing and thawing, the crack becomes
larger, and eventually pieces of the rock break
off. Ice wedging can break rocks off the side
piece broke off. You may have seen the results
piece broke off. You may have seen the results
of ice wedging: damaged concrete sidewalks
of ice wedging: damaged concrete sidewalks
and curbs, and flaking bricks.
and curbs, and flaking bricks.
Plant roots can also cause weathering by
Round, smooth river rocks
the plant grows, breaking the rocks apart.
growing into cracks. The roots expand as
the plant grows, breaking the rocks apart.
Investigation 2: Weathering and Erosion 17
Investigation 2: Weathering and Erosion 17
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water gets into tiny cracks in a rock. At night,
because a tiny crack kept enlarging until the
because a tiny crack kept enlarging until the
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naturally causes physical weathering when
found at the base of cliffs. These rocks fell
found at the base of cliffs. These rocks fell
growing into cracks. The roots expand as
The force shattered the jar! Ice expansion
falls in the piles of jagged rocks called talus
falls in the piles of jagged rocks called talus
Round, smooth river rocks
when water in a jar froze and expanded.
of a cliff. You can see evidence of these rock
of a cliff. You can see evidence of these rock
Plant roots can also cause weathering by
When ice freezes, it expands with
tremendous force. You saw what happened
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called carbonic acid. Although this acid is too
called carbonic acid. Although this acid is too
weak to make limestone fizz, each slightly
weak to make limestone fizz, each slightly
acidic raindrop dissolves a few molecules of
acidic raindrop dissolves a few molecules of
limestone. Over thousands of years, limestone
limestone. Over thousands of years, limestone
will slowly wear away because of chemical
will slowly wear away because of chemical
weathering.
weathering.
Decaying plant material, lichens, and plant
Decaying plant material, lichens, and plant
roots also produce carbon dioxide and other
roots also produce carbon dioxide and other
weak acids. These acids dissolve in rainwater
weak acids. These acids dissolve in rainwater
as it moves through soil and into cracks
Ice causes bricks to flake apart.
Tree roots break rocks.
You have probably seen tree roots that lifted
in rock. Limestone caves such as Carlsbad
as it moves through soil and into cracks
Ice causes bricks to flake apart.
in rock. Limestone caves such as Carlsbad
Caverns in New Mexico and Mammoth Cave
Caverns in New Mexico and Mammoth Cave
in Kentucky formed as chemical weathering
in Kentucky formed as chemical weathering
dissolved limestone over millions of years.
dissolved limestone over millions of years.
This weathering creates landforms called
This weathering creates landforms called
karst topography. Sinkholes and caves are
karst topography. Sinkholes and caves are
karst landforms and are found in many
karst landforms and are found in many
areas, including Kentucky and Florida. The
areas, including Kentucky and Florida. The
limestone pinnacles found in China are
limestone pinnacles found in China are
also examples of karst topography. Since
also examples of karst topography. Since
the formation of acids requires moisture,
the formation of acids requires moisture,
karst topography is found in rather humid
karst topography is found in rather humid
environments. In more arid locations,
environments. In more arid locations,
limestone tends to form steep cliffs, like the
limestone tends to form steep cliffs, like the
ones in the Redwall Limestone in the Grand
Canyon.
Weak acids will even weather granite,
Tree roots break rocks.
You have probably seen tree roots that lifted
ones in the Redwall Limestone in the Grand
Canyon.
Weak acids will even weather granite,
and broke a sidewalk or even cracked the
though at a much slower pace than limestone.
and broke a sidewalk or even cracked the
though at a much slower pace than limestone.
foundation of a house.
Granite is made of several common minerals,
foundation of a house.
Granite is made of several common minerals,
Chemical Weathering
Physical weathering is not the only way
mainly quartz, feldspar, and hornblende.
Quartz is very resistant to chemical
weathering; feldspar is more susceptible.
Chemical Weathering
Physical weathering is not the only way
mainly quartz, feldspar, and hornblende.
Quartz is very resistant to chemical
weathering; feldspar is more susceptible.
rocks can be broken down. Remember how
Acid slowly breaks down feldspar into clay
rocks can be broken down. Remember how
Acid slowly breaks down feldspar into clay
the limestone fizzed when you put a drop of
particles. Without feldspar to hold the granite
the limestone fizzed when you put a drop of
particles. Without feldspar to hold the granite
acid on it? During that chemical reaction,
together, the quartz crystals fall out and
acid on it? During that chemical reaction,
together, the quartz crystals fall out and
acid dissolved a tiny amount of rock. This
become sand. The durability of quartz is the
acid dissolved a tiny amount of rock. This
become sand. The durability of quartz is the
same process takes place naturally. Tiny
reason so much sand is composed mainly
same process takes place naturally. Tiny
reason so much sand is composed mainly
amounts of carbon dioxide in the air dissolve
of quartz.
amounts of carbon dioxide in the air dissolve
of quartz.
in falling raindrops to form a very weak acid
in falling raindrops to form a very weak acid
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Bryce Canyon National
Park, Utah
Bryce Canyon National
Park, Utah
Vie
Bl e Ridge Parkway,
Park a
View from the Blue
North Carolina
Grand Canyon National Park, Arizona
Vie
Bl e Ridge Parkway,
Park a
View from the Blue
North Carolina
Grand Canyon National Park, Arizona
Badlands National Park
Park, South Dakota
Badlands National Park
Park, South Dakota
Yangshuo, China
Yangshuo
Yangshuo, China
Yangshuo
Investigation 2: Weathering and Erosion 19
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Investigation 2: Weathering and Erosion 19
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behind. Much of the scenery in the Grand
behind. Much of the scenery in the Grand
Canyon is due to differential erosion. Devils
Canyon is due to differential erosion. Devils
Tower in Wyoming consists of hard rock that
Tower in Wyoming consists of hard rock that
was once covered and surrounded by softer
was once covered and surrounded by softer
rock. Over the past 1 to 2 million years,
rock. Over the past 1 to 2 million years,
the softer rock weathered and eroded away,
the softer rock weathered and eroded away,
leaving the column of hard rock standing.
leaving the column of hard rock standing.
Niagara Falls on the New York–Canada
Niagara Falls on the New York–Canada
border is another example of differential
border is another example of differential
erosion. The water going over the falls erodes
erosion. The water going over the falls erodes
the edge of the thick, soft shale layer under
the edge of the thick, soft shale layer under
a hard limestone layer. This undercuts the
a hard limestone layer. This undercuts the
limestone, causing it to give way. This photo
limestone, causing it to give way. This photo
of the American Falls, one part of Niagara
of the American Falls, one part of Niagara
Falls, shows huge limestone boulders that
Falls, shows huge limestone boulders that
have fallen. For the past 10,000 years, the
have fallen. For the past 10,000 years, the
falls have continued to move upstream,
falls have continued to move upstream,
eroding the rock at the higher part of the
eroding the rock at the higher part of the
river, at an average rate of about 1 meter (m)
river, at an average rate of about 1 meter (m)
a year.
a year.
The surrounding sedimentary rocks have
eroded away to expose the resistant igneous
rock that forms Devils Tower in Wyoming.
The surrounding sedimentary rocks have
eroded away to expose the resistant igneous
rock that forms Devils Tower in Wyoming.
Differential Erosion
Differential Erosion
Some of the most dramatic scenery in
Some of the most dramatic scenery in
the world occurs where soft rock erodes
the world occurs where soft rock erodes
more quickly than harder rock. You saw
more quickly than harder rock. You saw
differential erosion in action when
differential erosion in action when
you watched the multimedia stream tables
you watched the multimedia stream tables
that had a layer of clay between two layers
that had a layer of clay between two layers
of sand. The water easily eroded away the
top layer of sand, but the clay layer resisted
The Niagara River tumbles over a hard layer of
limestone to form a fall 50 m high.
erosion. As long as the clay layer was intact,
the bottom layer of sand was protected. This
is called differential erosion, because the
layers erode at different rates.
Differential erosion happens any time
soft rock is eroded away, leaving harder rock
of sand. The water easily eroded away the
top layer of sand, but the clay layer resisted
The Niagara River tumbles over a hard layer of
limestone to form a fall 50 m high.
erosion. As long as the clay layer was intact,
Wind Erosion and Rain Forests
How could erosion in Africa help the
Amazon rain forests, all the way across the
Atlantic Ocean? Windstorms on the Sahara
desert carry dust high into the atmosphere.
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the bottom layer of sand was protected. This
is called differential erosion, because the
layers erode at different rates.
Differential erosion happens any time
soft rock is eroded away, leaving harder rock
Wind Erosion and Rain Forests
How could erosion in Africa help the
Amazon rain forests, all the way across the
Atlantic Ocean? Windstorms on the Sahara
desert carry dust high into the atmosphere.
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This large mushroom rock near Lees Ferry
on the Colorado River in Arizona is the result
of differential erosion.
Warning: Rock structures of this kind can be
hazardous. Be careful around them.
Massive dust storms can carry dust across
the ocean.
was created by weathering and erosion. All of
these scenic wonders were once solid rock.
Weathering and erosion produce sediments
This large mushroom rock near Lees Ferry
on the Colorado River in Arizona is the result
of differential erosion.
Warning: Rock structures of this kind can be
hazardous. Be careful around them.
that can form new rocks, create soil, change
Massive dust storms can carry dust across
the ocean.
was created by weathering and erosion. All of
these scenic wonders were once solid rock.
Weathering and erosion produce sediments
that can form new rocks, create soil, change
High-altitude winds carry the dust west across
landforms, and even affect air quality. Think
High-altitude winds carry the dust west across
landforms, and even affect air quality. Think
the Atlantic Ocean, and sometimes to the
about that the next time you feel smooth,
the Atlantic Ocean, and sometimes to the
about that the next time you feel smooth,
rain forests of South and Central America.
rounded sand between your toes at the beach,
rain forests of South and Central America.
rounded sand between your toes at the beach,
The soil in rain forests is normally of poor
see a crack in a rock or a sidewalk, or eat a
The soil in rain forests is normally of poor
see a crack in a rock or a sidewalk, or eat a
quality, but the dust from Africa provides
piece of fruit!
quality, but the dust from Africa provides
piece of fruit!
many of the nutrients that the rain forest
plants need to survive.
There is also a negative side to all this dust.
Some of the dust settles on coral reefs in
many of the nutrients that the rain forest
Think Questions
plants need to survive.
1. Choose one of the photos of rock
Some of the dust settles on coral reefs in
There is also a negative side to all this dust.
Think Questions
1. Choose one of the photos of rock
the sea. The dust carries bacteria and fungi
formations in this article. Make a
the sea. The dust carries bacteria and fungi
formations in this article. Make a
that can kill or weaken the coral. When
sketch of the formation. Label which
that can kill or weaken the coral. When
sketch of the formation. Label which
the dust settles over populated areas, it can
layers you think might be hard rock
the dust settles over populated areas, it can
layers you think might be hard rock
trigger asthma and other respiratory diseases.
and which might be softer. What is
trigger asthma and other respiratory diseases.
and which might be softer. What is
Other places in the world are affected by
your evidence?
Other places in the world are affected by
your evidence?
dust sources other than the Sahara Desert.
2. Describe the processes you think might
dust sources other than the Sahara Desert.
2. Describe the processes you think might
Consider this—dust from China sometimes
have produced the mushroom-shaped
Consider this—dust from China sometimes
have produced the mushroom-shaped
reaches people living in California!
rock in the photo above.
reaches people living in California!
rock in the photo above.
Weathering and erosion created the Grand
Canyon and many spectacular landforms
around the world. The spires and hoodoos of
Bryce Canyon in Utah, the rugged Badlands
in South Dakota, and the rounded Blue Ridge
Mountains extending from West Virginia to
Pennsylvania are all products of weathering
and erosion. Even Mammoth Cave in
Kentucky, the world’s longest cave system,
3. Think about your community. Give at
least one example of where you have
seen:
• Weathering
• Erosion
• Differential erosion
• A landform created by weathering
and erosion
Weathering and erosion created the Grand
Canyon and many spectacular landforms
around the world. The spires and hoodoos of
Bryce Canyon in Utah, the rugged Badlands
in South Dakota, and the rounded Blue Ridge
Mountains extending from West Virginia to
Pennsylvania are all products of weathering
and erosion. Even Mammoth Cave in
Kentucky, the world’s longest cave system,
Investigation 2: Weathering and Erosion 21
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3. Think about your community. Give at
least one example of where you have
seen:
• Weathering
• Erosion
• Differential erosion
• A landform created by weathering
and erosion
Investigation 2: Weathering and Erosion 21
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