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Earth Notes
Chapter 2 ~ Section 2
Forces of Change
The Earth’s Interior

Inner Core –
about 4,000 miles
below the surface
of the Earth

Outer Core –
1,400 miles thick,
temperature
reaches 8500°F
Earth’s Interior (con’t)

Mantle: layer of hot, dense rock – MAGMA
Earth’s Interior (con’t)

Crust: rocky shell forming Earth’s surface.
 The
crust is broken into slabs of rock called
plates.
 Natural
forces interact with the crust,
creating landforms on the surface of the
earth.
 Below
the oceans, the crust is about 5 miles
thick. Below the continents it averages 22
miles in thickness.

Earth’s Interior (con’t)
Plates - float on a melted layer in the upper mantle
- carry the earth’s oceans and continents
Internal
Forces of
Change
The Plate Tectonic Theory

The lithosphere — the earth’s crust and
upper layer of the mantle — is broken into
a number of large, moving plates.
The Plate Tectonic Theory



The plates slide very slowly over a hot,
pliable layer of mantle.
The earth’s oceans and continents ride
atop of the plates.
It’s along the plate boundaries that
most earthquakes and volcanoes occur
due to friction and pressure that
produces heat.
Plate Movement
Plate movement: creates oceans
and mountain ranges
Plate
Movement
 Continental
Drift: the
theory that the
continents
were once
joined and
then slowly
drifted apart
Plate Movement
Pangaea: gigantic super
continent which eventually
broke apart
Observe an animation
of the breakup of
Pangaea

http://www.classzone.com/books/earth_scienc
e/terc/content/visualizations/es0806/es0806pa
ge01.cfm?chapter_no=visualization
Examine an
animation of plate
movement predicted
for the future

http://www.classzone.com/books/earth_science/terc/
content/visualizations/es0807/es0807page01.cfm?chap
ter_no=visualization
Ring of Fire

A circle of volcanic mountains surrounding
the Pacific Ocean

It is one of the most earthquake-prone &
volcano-prone areas on the planet.

Hot Spots are hot regions deep within the
mantle that produce magma, which rises to
the surface. Volcanic island chains form as
oceanic plates drift over the hot spot.


Example: Hawaiian Islands
http://www.classzone.com/books/earth_science/terc/content/visualizations/es
0904/es0904page01.cfm?chapter_no=visualization
Volcanoes

Form when magma inside the earth
breaks through the crust. Lava flows
and may produce a large, cone-shaped
mountain

They often form along plate
boundaries

Magma splits the earth’s surface when
Fault—a break in the earth’s
crust. Movement along a fault
can send out shock waves,
causing an earthquake.
San Andreas Fault
San Andreas Fault
A devastating fire followed the 1906
earthquake in San Francisco
The San
Fernando
earthquake
of 1971
collapsed
freeway
overpasses
in southern
California
Converging/Collision Zone
 Plates
collide and push slowly against
each other and form a collision or
converging zone.
 If
2 oceanic plates collide, 1 slides under
the other. Islands often form this way.
 If
2 continental plates collide, mountains
are formed. Example: Himalayas
Continental Crush / Collide
Spreading Zone
Plates pull away from each other and
form a spreading zone.
These areas are likely to have
earthquakes, volcanoes, and
rift valleys (a large split along the
crest of a mountain).
http://www.classzone.com/books/earth_science/te
rc/content/visualizations/es0804/es0804page01.c
fm?chapter_no=visualization
Spreading Zone
Subduction
They meet, or CONVERGE and form a
subduction zone.
*If an oceanic plate collides with a
continental plate, the heavier oceanic
plate will slide under the lighter,
continental plate.
This results in volcanic mountain
building and earthquakes.
Subduction
External
Forces of
Change
External Forces

What other forces can create landforms?
 Weathering
– a process that breaks down
rock at or near the surface into smaller pieces.
- This is a VERY slow process – thousands to
millions of years.
Mechanical
(or Physical) Weathering
occurs when rock freezes – it can cause
Frost Wedging, a crack in the rock caused
by freezing.
Chemical Weathering –
alters the rock’s chemical
makeup by changing the
minerals. This can actually
change one kind of rock into another.
 Important forces in Chemical Weathering
are moisture and carbon dioxide.

 Through

this process caves are created.
Acid Rain causes another type of chemical
weathering that destroys forests, pollutes
water and kills wildlife.


Over thousands of years, areas
with limestone rocks can develop
caves.
Groundwater dissolves a network
of tunnels in the rock. If the water
table is lowered by a change in
climate or tectonic uplift of the
area, groundwater drains out of
the tunnels, leaving the caverns
exposed to air.
http://www.classzone.com/books/earth_science/terc/content/visualizat
ions/es1405/es1405page01.cfm?chapter_no=visualization
EROSION
Erosion is the
movement of
weathered materials
including gravel,
soil and sand.
 The most common
agents of erosion
are water, wind and
glaciers.

WATER AND EROSION

Moving Water (rain, rivers, streams and
oceans) is the greatest agent of erosion.

Sediment – small particles of soil, sand,
and gravel - is carried by the moving water
and works like sandpaper to grind away
rocks.
Erosion
Sullivan Falls
Rickett’s
Glen State
Park
Pennsylvania
Sediment

Sediment from the
River Rhône flowing
into Lake Geneva.
Sediment

http://www.classzone.com/books/earth_scienc
e/terc/content/visualizations/es0604/es0604pa
ge01.cfm?chapter_no=visualization
Sediment creates new landforms
such as floodplains & deltas.
Floodplains
Deltas form at the
mouth of a river
Wind Erosion

The second major cause of
erosion is wind, especially
where there is little water and
few plants.
 Wind Erosion can
devastate one area while
benefiting another –
HOW?
 Loess – windblown
deposits of mineral-rich
dust
GLACIERS CAUSE EROSION?
Glaciers are
slow
moving
sheets of
ice that are
formed
over many
years.
GLACIERS

How do they cause erosion?
 The
movement cuts through land creating lakes.
 They
melt away and then rebuild again over
thousands of years.