Constructive &

Destructive

Forces

Intro:

• Constructive Forces

– Processes that create landforms.

• Destructive Forces

– Processes that destroy landforms.

Intro:

• Constructive Forces

– Volcanoes

– Deposition

– Landslides

– Floods

• Destructive Forces

_Weathering/Erosion

– Volcanoes

– Landslides

– Earthquakes

– Floods

Weathering:

• Process that breaks down rock &

other substances at the Earth’s

surface

• Temperature, water, wind, and plants

all contribute to weathering

2 Types of Weathering:

1. Physical

2. Chemical

Physical Weathering:

• Rock is physically broken into

smaller pieces.

• Small pieces have same

composition as the original rock.

• Very slow

Chemical Weathering:

• Breaks down rock through chemical

changes

• Rock particles have different mineral

make-up than original rock

Erosion:

• Process by which natural forces move

weathered rock & soil from one place to

another (by wind, water, waves, ice, &

gravity)

• Sediment

• Material moved by weathering/erosion

Deposition:

• Deposition is the dropping, or depositing,

of sediments by water, wind, or ice.

• Deposition builds up new land on Earth’s

surface, like a delta at the end of a river or

the pile of a sand dune in the desert.

• Shells on the beach are deposition by

ocean waves.

Creep:

• Very slow downhill movement of rock

& soil

Earthquakes:

• Earth is made of layers.

• The crust is the thinnest layer.

• The crust is made up of giant slabs of

rock called plates.

• When plates move, earthquakes may

occur.

Earthquakes:

• Earthquakes are movements in

Earth’s crust that are caused by a

sudden shift of Earth’s plates.

• Destructive force

• Mountains and volcanoes form as

plates move.

Where Earthquakes Happen:

• Most earthquakes occur near the

edges of Earth’s plates.

• There is an area around the Pacific

Ocean where some of Earth’s plates

meet.

• It is here that most earthquakes

happen.

What causes an earthquake:

• Plates are always moving.

• Sometimes, they move slowly.

• At other times, the motion is sudden.

• The energy released by the sudden

motion of plates shakes the crust.

• It can set a large earthquake in

motion.

What is a Tsunami?

A tsunami – is a giant ocean wave.

• Tsunamis are usually caused by

earthquakes on the ocean floor.

• A few are caused by underwater

landslides and volcanoes.

• Can move faster than 700 m/hr.

Effects of a Tsunami

• Tsunamis can destroy land and

cause great damage if they come

ashore.

Volcanoes:

• Destructive AND Constructive

• Weak spot in the crust where molten

material from the mantle comes to the

surface

• Magma – Below ground, Higher temp.

• Lava – magma that reaches the

surface

What is a volcano?

• A volcano is a mountain that builds up

around an opening in the Earth’s

crust.

• Sometimes, melted rock, gases, and

pieces of rock are forced out of the

volcano.

• This is called an eruption.

Where do volcanoes begin?

• When Earth’s plates move, sometimes they bump into each other.

• As a result, one plate is pushed down deeper inside the Earth.

• When this happens, magma is pushed to the surface.

• This can cause a volcanic eruption.

Volcanoes:

• May not always include magma

reaching the surface

• Hot Springs

• Geysers

Locations of Volcanoes:

• There are many volcanoes along the

edge of the Pacific Plate.

• Ring of Fire – Major belt of volcanoes

that encircles most of the Pacific

Ocean

Parts of a Volcano

Crater – bowl shaped

area that forms around a

central vent

Vent – opening

through which

molten rock & gas

escape

Side Vent Pipe – long tube

through which

magma moves

from the magma

chamber to the

surface

Magma

Chamber

– pocket

beneath a

volcano where

magma

collects

Effects of Volcanic Eruptions:

• The lava and ash can destroy forests

and bury fields.

• Volcanic eruptions can even change

Earth’s weather patterns.

Volcanic Eruptions on the

Ocean Floor:

• Volcanic eruptions, called seamounts,

can also occur under the oceans.

• These volcanoes that are built up are

called seamounts.

• If the seamount rises above the

ocean surface it is called a volcanic

island (for example Hawaii or Japan.)

Types of Volcanic Eruptions:

2. Explosive –

- Thick & sticky magma plugs up the

pipe where pressure builds up

- Breaks lava into pieces that quickly

cool & harden

- Ash, cinders (pebbles), & bombs hurled out

- Mt. Saint Helens

Volcano All-Stars:

• Kilauea –

- Hawaii

- Most active volcano in world

Volcano All-Stars:

• Krakatoa –

- Pacific Island

- 1883 eruption heard 2000 miles away

Volcano All-Stars:

• Mt. Saint Helens –

- Washington state

- Erupted May 18, 1980

- Leveled trees for 25 miles (Pyroclastic

flow)

Volcano All-Stars:

• Olympus Mons –

- Mars

- Largest Mtn./volcano in Solar System

- Size of Ohio

Mass Movement:

• Caused by gravity

• Process that moves sediment downhill

• 4 types

– Landslide - Slump

– Mudslide - Creep

Landslide:

• Most destructive

• When rock & soil slide quickly down a

steep slope

Landslide:

• Landslides are mass movements of

land due to gravity.

• Landslides can cause buildings to fall,

or power and gas lines to break.

• Landslides even occur on the

continental slope in the ocean.

Mudflow:

• Rapid downhill movement of H2O,

rock, and soil

• Often occurs after heavy rains

Slump:

• A mass of rock & soil suddenly slips

down a slope (in a large mass/clump)

Flood:

• A large amount of water covers the

land. It can cause rapid erosion

(destructive), but also deposition

(constructive).

Flood:

• Flood occurs when a large amount of water covers land that is usually dry.

• When the flood occurs, rapid erosion can take place and move soil and sediments away.

• When the flood recedes, new sediment is left behind and can build up rich soil deposits.