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Constructive and Constructive and Destructive ForcesDestructive Forces
Processes That Act Upon Earth’s Processes That Act Upon Earth’s Surface FeaturesSurface Features
What are Constructive and What are Constructive and Destructive Forces?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?What Are Surface Features?
– Surface features are landforms and bodies of water that cover the Earth’s surface such as:
• mountains
• valleys
• canyons
• gorges
• beaches
• sand dunes
• barrier Islands
• flood-plains
• moraines and drumlins
• volcanoes
• oceans
• lakes
• rivers
How Can a Surface Feature be How Can a Surface Feature be Changed by a Constructive Force?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 ForceConstructive ForceExamples of DepositionExamples of Deposition
Constructive Process
Surface Feature
Force/Agent
Deposition
Deltas water / river
Floodplains water / river
Beaches and Barrier Islands
water / ocean long-shore current
Sand dunes wind
Moraines and drumlins
Ice / glacier
Other Constructive ForcesOther Constructive ForcesConstructive
ProcessSurface Feature
Force
Folding Mountains Plate tectonics
Faulting Mountains Plate tectonics
Earthquake Trench
Fault
Plate tectonics
Volcanic Activity
Mountains Islands
Plate tectonics
How Can a Surface Feature be How Can a Surface Feature be Changed by a Destructive Changed by a Destructive
Force?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 Changing the Earth’s Surface by a Destructive ForceDestructive ForceExamples of WeatheringExamples of Weathering
• Mechanical / Physical Weathering– Temperature Change-
Freezing 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 ForceDestructive ForceExamples of ErosionExamples of Erosion
Destructive Process
Surface Feature
Force/Agent
Erosion
Canyons, Gorges, V-Shaped Valleys
Water
Sea Arches,
Sea Stacks
Water
Buttes, Desert Wind
U-Shaped Valleys Ice
Mudslide, Sinkholes
Gravity
Other Destructive ForcesOther 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
Controlling Constructive and Controlling Constructive and Destructive ForcesDestructive 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 Effects on the Control of Constructive ForcesConstructive 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 Effects on the Control of Destructive ForcesDestructive 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 Effects on the Control of Destructive ForcesDestructive 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 Can Volcanoes and Earthquakes be Controlled?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 – – 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
Deposition is a process Deposition is a process that…that…
A. Dissolves sediment
B. Breaks down rock to form sediment
C. Removes sediment from landforms
D. Drops sediment to form landforms
Where do deltas form?Where do deltas form?
A. In desert areas
B. At river mouths
C. On the banks of rivers
D. In valleys formed by glaciers
Long shore currents Long shore currents help create…help create…
A. Beaches
B. Dunes
C. Rivers
D. Drumlins
Volcanoes can create Volcanoes can create new land when they new land when they
release…release…
A. Lava
B. Water
C. Faults
D. Mud
What forms moraines What forms moraines and drumlins?and drumlins?
A. Wind
B. Rivers
C. Glaciers
D. Volcanoes
What landform forms What landform forms from deposition at the from deposition at the
mouths of rivers?mouths of rivers?
A. a delta
B. a floodplain
C. a sand dune
D. a moraine
What is weathering?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 Which of these is caused by chemical caused by chemical
weathering?weathering?
A. desert pavement
B. formation of U-shaped valleys
C. formation of rust
D. ice expanding in cracks in rock at is weathering?
How do earthquakes How do earthquakes change the land? change the land?
A. They transport sediment.
B. They form cracks in the surface.
C. They release ash and lava.
D. They cause chemical weathering.
A river can form …A river can form …
A. Sea arches.
B. U-shaped valleys.
C. V-shaped valleys.
D. Desert pavement.
Deposition forms these Deposition forms these features on coasts.features on coasts.
A. drumlins
B. floodplains
C. barrier islands
D. U-shaped valleys
What causes V-shaped What causes V-shaped valleys to form?valleys to form?
A. deposition at river mouths
B. erosion by rivers
C. weathering by wind
D. erosion by glaciers
A dam across a river can A dam across a river can cause…cause…
A. the formation of a delta.
B. the carving of a valley.
C. the erosion of a beach.
D. the formation of a sea stack.
Which of these helps prevent Which of these helps prevent the harmful effects of the harmful effects of
erosion?erosion?
A. dams
B. volcanoes
C. Long-shore currents
D. contour plowing
In which type of climate are In which type of climate are you most likely to find a sand you most likely to find a sand dune that is not on the coast?dune that is not on the coast?
A. dry
B. humid
C. icy
D. hot
What does erosion do? What does erosion do?
A. breaks down rock physically
B. moves broken pieces of rock
C. changes rock chemically
D. change sediment into rock
Beaches that have eroded are Beaches that have eroded are reclaimed through…reclaimed through…
A. weathering.
B. building of seawalls.
C. beach nourishment.
D. building of terraces.
Which of these is not a way to Which of these is not a way to prevent soil erosion?prevent soil erosion?
A. planting vegetation
B. contour plowing
C. building windbreaks
D. building dams
Scientists know where Scientists know where earthquakes will occur earthquakes will occur because they know the because they know the
locations of …locations of …
A. faults
B. volcanoes
C. mountains
D. long-shore currents.
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