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

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• Land Formation

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

What Do You Think?What Do You Think?

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.

Which of these do scientists Which of these do scientists use to predict when a volcano use to predict when a volcano

is likely to erupt? is likely to erupt?

A. the age of the volcanoB. earthquakes beneath the volcanoC. temperature of nearby riversD. the hardness of rock near the

volcano