The Changing Earth
Chapter Fourteen: Weathering
and Erosion
• 14.1 Weathering
• 14.2 Erosion
• 14.3 Rivers Shape the Land
Investigation 14B
Human Impacts on Coastal Erosion
• How do people
living and working
in coastal areas
affect erosion?
14.2 Erosion
• Erosion is the
process of moving
pieces of rock and
sediment by wind,
water, ice, or gravity.
14.2 Moving Sediment
• Weathering breaks
rock into bits and
pieces called
sediment.
How does sediment get from a
mountain peak to a beach?
14.2 Moving Sediment
• Weathering breaks rock into bits and
pieces called sediment.
• Wind erodes mountains and moves
sediment, but not as well as flowing
water.
14.2 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, and
– how rocky or smooth the land is.
14.2 Moving sediment
•
•
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.
14.2 Moving sediment
•
•
•
A greater volume of water
can move a lot of soil or
sediment at once.
Rocky landscapes can
trap sediment so the
sediment will not travel as
far.
A smooth river bed might
mean sediment will be
carried a long way.
14.2 Sorting 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.
14.2 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 direction of
younger layers.
14.2 Interpreting layers of sediment
• Cross bedding, is easy to recognize in
sedimentary rocks where one layer ends
and another layer passed over it.
14.2 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.
14.2 Moving sediment by ice
14.2 Moving sediment by 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.
14.2 Moving sediment by 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.
14.2 More on moving sediment
• Glaciers are formed
from accumulation of
snow over hundreds
or thousands of
years.
• As snow piles up and
pressure increases,
it changes into ice.
14.2 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.
14.2 More on moving sediment
• Mass wasting is the
downhill movement
of large amounts of
rock and sediment
due to the force of
gravity.
14.2 More on moving sediment
• A landslide occurs
when a large mass
of soil or rock
slides down a
steep slope.
14.2 More on moving sediment
• Slumping describes
what happens when
loose soil becomes
wet and slides or
“slumps”.
• Slumping can
happen after a period
of very heavy rainfall.
14.2 Erosion by people
• In the 1930s, the
Great Plains of
North America
experienced
serious wind
erosion events.
What was this region’s knickname?
14.2 Erosion by people
• Farming practices that protect sediment
and soil from erosion include installing
windbreaks, planting ground cover, and
using contour plowing for farming.