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Constructive and
Destructive Forces
Processes That Act Upon Earth’s
Surface Features
What are Constructive and
Destructive Forces?
• Constructive Force
– A constructive force is
a process that raises
or builds up the
surface features of the
Earth.
• Destructive Force
– A destructive force is a
process that lowers or
tears down the surface
features of the Earth.
What Are Surface Features?
– Surface features are landforms and bodies of
water that cover the Earth’s surface such as:
•
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•
•
•
•
•
•
•
•
•
•
mountains
valleys
canyons
gorges
beaches
sand dunes
barrier Islands
flood-plains
moraines and drumlins
volcanoes
oceans
lakes
rivers
How Can a Surface Feature be
Changed by a Constructive Force?
– Natural forces such as wind, water, ice,
through the process of deposition.
• Deposition is the process of dumping sediment,
dirt, rocks, or particles in one place.
– The movement of the Earth’s crust through
Plate Tectonics
Constructive Force
Examples of Deposition
Constructive
Process
Deposition
Surface
Feature
Deltas
Floodplains
Beaches and
Barrier Islands
Sand dunes
Moraines and
drumlins
Force/Agent
water / river
water / river
water / ocean
long-shore
current
wind
Ice / glacier
Other Constructive Forces
Constructive
Surface
Process
Feature
Folding
Mountains
Faulting
Mountains
Earthquake
Trench
Fault
Mountains
Islands
Volcanic
Activity
Force
Plate
tectonics
Plate
tectonics
Plate
tectonics
Plate
tectonics
How Can a Surface Feature be
Changed by a Destructive
Force?
– Physical or Chemical Weathering
• Weathering is the breaking down of rock into
sediment.
– Natural forces such as wind, water, ice,
through the process of erosion.
• Erosion is the movement of sediment from one
place to another.
Changing the Earth’s Surface by a
Destructive Force
Examples of Weathering
• Mechanical / Physical
Weathering
– Temperature ChangeFreezing and thawing of
Rock
– Ice Wedging-Water
freezing and expanding
in cracks of rock
– Impact of organisms
• Root Pry
• Animals burrowing
• Chemical Weathering
– Oxidation / rusting
– Carbonic Acid / acid
rain
• Caverns
– Impact of organisms
• Secretion of acid from
Lichen
Destructive Force
Examples of Erosion
Destructive
Process
Erosion
Surface
Feature
Force/Agent
Canyons,
Gorges, VShaped Valleys
Water
Sea Arches,
Sea Stacks
Buttes, Desert
Water
Wind
U-Shaped Valleys Ice
Mudslide,
Gravity
Sinkholes
Other Destructive Forces
• Volcanic Activity
– Movement of Earths Crust (Plate tectonics)
• Reshaping of Mountains
• Earthquakes
– Movement of Earths Crust (Plate tectonics)
• Trenches
– cracks in the Earth Curst
Visit these sites
• Land Formation
Controlling Constructive and
Destructive Forces
• How can constructive and destructive
forces be controlled through the use of
technology?
• How does technology affect constructive
and destructive forces?
• What are examples of technology used to
control constructive and destructive
forces?
Effects on the Control of
Constructive Forces
• Dam – a structure built across a river to
control its flow
– Positive Effect
• Flood Control
• Hydroelectric Power
– Negative Effect
• Holds back sediment
– Prevents deposition of flood plains, deltas, and beaches
Effects on the Control of
Destructive Forces
• Prevention of beach erosion
– Groin – a structure built perpendicular to the beach.
• Positive Effect
– Traps sand that moves along the shore and causing the beach to
build up.
• Negative Effect
– Beach Erosion down stream is worse.
– Seawall – a structure built parallel to the shore
• Positive Effect
– Protects land behind if from ocean the ocean waves
• Negative Effect
– Ocean side beach will erode
– Beach Nourishment – sand from ocean or nearby rivers are
pumped onto the beach
Effects on the Control of
Destructive Forces
• Prevention of soil erosion
– Contour Plowing – method in which farmers plow across the
sided of hill instead of down
– Terracing – the planting of corps on terraces (steps) built
into steep hillsides.
– Windbreaks – rows of plants or fences.
• Slow down wind and limit the distance it can carry soil.
– Vegetation – used to hold soil in place
– Storm drain management – a system of drains
• Prevents flooding and soil erosion
Can Volcanoes and Earthquakes
be Controlled?
• Volcanoes and Earthquakes can not be
controlled;
– However scientist have ways to determine when
and where these they might occur.
• Volcanoes –
– instruments are used to detect changes in volcanoes
• Earthquakes –
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Detailed maps show major faults
Safety Education
No new buildings on or near faults
Building codes to resists earthquakes
Seismographs – measures earthquakes on a rector scale
What Do You Think?
Deposition is a process
that…
A.
B.
C.
D.
Dissolves sediment
Breaks down rock to form sediment
Removes sediment from landforms
Drops sediment to form landforms
Where do deltas form?
A.
B.
C.
D.
In desert areas
At river mouths
On the banks of rivers
In valleys formed by glaciers
Long shore currents
help create…
A.
B.
C.
D.
Beaches
Dunes
Rivers
Drumlins
Volcanoes can create
new land when they
release…
A.
B.
C.
D.
Lava
Water
Faults
Mud
What forms moraines
and drumlins?
A.
B.
C.
D.
Wind
Rivers
Glaciers
Volcanoes
What landform forms
from deposition at the
mouths of rivers?
A.
B.
C.
D.
a delta
a floodplain
a sand dune
a moraine
What is weathering?
A. A type of climate
B. The transport of sediment
C. The breakdown of rock
D. The aging of rock
Which of these is
caused by chemical
weathering?
A.
B.
C.
D.
desert pavement
formation of U-shaped valleys
formation of rust
ice expanding in cracks in rock at is
weathering?
How do earthquakes
change the land?
A.
B.
C.
D.
They transport sediment.
They form cracks in the surface.
They release ash and lava.
They cause chemical weathering.
A river can form …
A.
B.
C.
D.
Sea arches.
U-shaped valleys.
V-shaped valleys.
Desert pavement.
Deposition forms these
features on coasts.
A.
B.
C.
D.
drumlins
floodplains
barrier islands
U-shaped valleys
What causes V-shaped
valleys to form?
A.
B.
C.
D.
deposition at river mouths
erosion by rivers
weathering by wind
erosion by glaciers
A dam across a river can
cause…
A.
B.
C.
D.
the formation of a delta.
the carving of a valley.
the erosion of a beach.
the formation of a sea stack.
Which of these helps prevent
the harmful effects of
erosion?
A.
B.
C.
D.
dams
volcanoes
Long-shore currents
contour plowing
In which type of climate are
you most likely to find a sand
dune that is not on the coast?
A.
B.
C.
D.
dry
humid
icy
hot
What does erosion do?
A.
B.
C.
D.
breaks down rock physically
moves broken pieces of rock
changes rock chemically
change sediment into rock
Beaches that have eroded are
reclaimed through…
A. weathering.
B. building of seawalls.
C. beach nourishment.
D. building of terraces.
Which of these is not a way to
prevent soil erosion?
A. planting vegetation
B. contour plowing
C. building windbreaks
D. building dams
Scientists know where
earthquakes will occur
because they know the
locations of …
A. faults
B. volcanoes
C. mountains
D. long-shore currents.
Which of these do scientists
use to predict when a volcano
is likely to erupt?
A.
B.
C.
D.
the age of the volcano
earthquakes beneath the volcano
temperature of nearby rivers
the hardness of rock near the
volcano