Constructive and Destructive Forces

1
Constructive and Destructive Forces

• Processes That Act Upon Earths Surface Features

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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.

3
What Are Surface Features?

• Surface features are landforms and bodies of
  water that cover the Earths surface such as
• mountains
• valleys
• canyons
• gorges
• beaches
• sand dunes
• barrier Islands
• flood-plains
• moraines and drumlins
• volcanoes
• oceans
• lakes
• rivers

4
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 Earths crust through Plate
  Tectonics

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Constructive ForceExamples of Deposition
Constructive Process Surface Feature Force/Agent
Deposition Deltas water / river
Deposition Floodplains water / river
Deposition Beaches and Barrier Islands water / ocean long-shore current
Deposition Sand dunes wind
Deposition Moraines and drumlins Ice / glacier
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Other Constructive Forces
Constructive Process Surface Feature Force
Folding Mountains Plate tectonics
Faulting Mountains Plate tectonics
Earthquake Trench Fault Plate tectonics
Volcanic Activity Mountains Islands Plate tectonics
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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.

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Changing the Earths Surface by a Destructive
ForceExamples 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

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Destructive ForceExamples of Erosion
Destructive Process Surface Feature Force/Agent
Erosion Canyons, Gorges, V-Shaped Valleys Water
Erosion Sea Arches, Sea Stacks Water
Erosion Buttes, Desert Wind
Erosion U-Shaped Valleys Ice
Erosion Mudslide, Sinkholes Gravity
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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

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Visit these sites

• Land Formation

12
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?

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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

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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

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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

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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
• 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

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What Do You Think?
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Deposition is a process that

• Dissolves sediment
• Breaks down rock to form sediment
• Removes sediment from landforms
• Drops sediment to form landforms

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Where do deltas form?

• In desert areas
• At river mouths
• On the banks of rivers
• In valleys formed by glaciers

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Long shore currents help create

• Beaches
• Dunes
• Rivers
• Drumlins

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Volcanoes can create new land when they release

• Lava
• Water
• Faults
• Mud

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What forms moraines and drumlins?

• Wind
• Rivers
• Glaciers
• Volcanoes

23
What landform forms from deposition at the mouths
of rivers?

• a delta
• a floodplain
• a sand dune
• a moraine

24
What is weathering?

• A type of climate
• The transport of sediment
• The breakdown of rock
• The aging of rock

25
Which of these is caused by chemical weathering?

• desert pavement
• formation of U-shaped valleys
• formation of rust
• ice expanding in cracks in rock at is weathering?

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How do earthquakes change the land?

• They transport sediment.
• They form cracks in the surface.
• They release ash and lava.
• They cause chemical weathering.

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A river can form

• Sea arches.
• U-shaped valleys.
• V-shaped valleys.
• Desert pavement.

28
Deposition forms these features on coasts.

• drumlins
• floodplains
• barrier islands
• U-shaped valleys

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What causes V-shaped valleys to form?

• deposition at river mouths
• erosion by rivers
• weathering by wind
• erosion by glaciers

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A dam across a river can cause

• the formation of a delta.
• the carving of a valley.
• the erosion of a beach.
• the formation of a sea stack.

31
Which of these helps prevent the harmful effects
of erosion?

• dams
• volcanoes
• Long-shore currents
• contour plowing

32
In which type of climate are you most likely to
find a sand dune that is not on the coast?

• dry
• humid
• icy
• hot

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What does erosion do?

• breaks down rock physically
• moves broken pieces of rock
• changes rock chemically
• change sediment into rock

34
Beaches that have eroded are reclaimed through

• weathering.
• building of seawalls.
• beach nourishment.
• building of terraces.

35
Which of these is not a way to prevent soil
erosion?

• planting vegetation
• contour plowing
• building windbreaks
• building dams

36
Scientists know where earthquakes will occur
because they know the locations of

• faults
• volcanoes
• mountains
• long-shore currents.

37
Which of these do scientists use to predict when
a volcano is likely to erupt?

• the age of the volcano
• earthquakes beneath the volcano
• temperature of nearby rivers
• the hardness of rock near the volcano