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Transcript
Changes to Earth’s Surface
Chapter 9
Vocabulary
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Landform
Weathering
Erosion
Deposition
Landslide
Volcano
Fault
Earthquake
Epicenter
Landforms
• Natural features that
cover Earth’s surface
are landforms.
• Landforms can be
different sizes and
shapes.
• For example, a
mountain is a landform.
Landforms
• Plains are flat
landforms on low
ground.
Landforms
• Plateaus are flat
landforms on high
ground.
Landforms
• Valley, canyons, and
peninsulas are also
landforms.
Landforms
Valley
Peninsula
Weathering
• When rocks are broken
into smaller pieces, the
process is called
weathering.
• http://www.youtube.co
m/watch?v=lyysL02ZvQ
8
Erosion
• When water, ice,
gravity, and wind work
together to move
weathered pieces of
rock, this process is
called erosion.
Deposition
• When rock, soil, organic
matter, or other
material are laid down
on Earth’s surface is
called deposition.
• It often adds to and
creates landforms.
Landslide
• When a large amount of
rock and soil is rapidly
moving downhill, this is
a landslide.
How do weathered materials move?
• Materials that are from rock by weathering
can be carried to a new place, where they
become part of another landform.
• Water, ice, gravity, and wind work together to
move weathered pieces of rock. This process
is called erosion.
Effects of Erosion
• Moving water erodes, or carries away,
materials from landforms.
• Rain picks up loose material from the surfaces
of rocks. As the rain runs into streams, it takes
the loose, weathered material with it.
Effects of Erosion
• Water running downhill wears away rocks and
soil. After many years, the grooves that the
water carves in the land become canyons or
valleys.
Effects of Erosion
• Waves from the ocean constantly change the
shape of a shoreline.
How can Earth’s surface change
rapidly?
• Volcanoes and
earthquakes cause
large, rapid changes to
Earth’s surface.
Volcanoes
• A volcano is a landform
that can cause a rapid
change to Earth’s
surface.
• At 80 to 160 km (50 –
100 miles)
underground, very hot
rock, called magma is
partially melted into
liquid.
Volcanoes
• A volcano forms at a
weak spot in Earth’s
crust where magma is
forced upward because
of gas and it reaches
the surface.
• When the magma boils
onto the surface, the
volcano erupts.
• When magma flows out
of the volcano, it is
known as lava.
Volcanoes
• Sometimes the pressure
builds up, so the gases
in the magma explode.
Hot rocks, gases, and
ash burst into the air
from openings called
vents.
• Sometimes volcanoes
explode, and
sometimes the magma
oozes out.
Active Volcanoes
• An active volcano has
frequent eruptions or
shows signs of future
eruptions.
• In Hawaii, the island
Kilauea began erupting
in 1983 and is
continuing to erupt
today, so it is an active
volcano.
Dormant Volcanoes
• A volcano that has not
erupted in a long time is
dormant.
• Mount Rainier in the
Cascade Mountains in
Washington has not
erupted in about 150 years.
However, scientists consider
it dangerous because if the
magma inside the mountain
were to heat up, it would
explode.
Extinct Volcanoes
• Volcanoes are classified
as extinct if scientists
do not think it will erupt
again.
• Mount Keyna in Africa is
extinct.
• There are extinct
volcanoes all over the
world.
Effects of Eruptions
• Volcanic eruptions can
create a lot of rock and ash.
• Volcanoes can cause major,
rapid changes to Earth’s
surface.
• For example. Mount St.
Helens used to be 9,600 ft
high, but in May 1980, it
erupted and it created an
area 3,300 feet where the
mountain exploded! The
ash from the explosion
went more than 15 miles
into the air!
Before and After
Mount St. Helens Before 1980
Eruption
Mount St. Helens After
Eruption
Question Time!
1. What is magma?
Magma is very hot, partially liquid rock found
under Earth’s crust.
2. What causes a volcano to erupt?
A volcano erupts because of a build up of hot gas
pressure and magma and the Earth’s crust is
weak, so the magma comes to the surface the
the volcano erupts.
3. What is an active volcano?
An active volcano has frequent eruptions or
shows signs of future eruptions.
Earth’s Moving Plates
• Earth’s outer layer, or crust,
rests on top of another
layer called the upper
mantle.
• These two layers, together,
are divided into very large
pieces called plates.
• The plates move all the
time. Most volcanoes are
along or near the places
where plates come
together.
The Plates
The Cause of Earthquakes
• A fault is a break or
crack in rocks where
Earth’s crust can move.
The Cause of Earthquakes
• Sometimes rocks along
the fault get stuck, but
the plates continue
their slow movement.
• If they pressure
becomes strong
enough, the rocks can
break and the plates
move suddenly. The
sudden movement that
causes Earth’s crust to
shake is an earthquake.
The Cause of Earthquakes
• Earthquakes often
cause major, rapid
changes to Earth’s
surface.
The Cause of Earthquakes
• The place underground
where the plates start
to move and
earthquake beings is
called the focus.
• The point on Earth’s
surface above that area
(the focus) is the
epicenter.
The Cause of Earthquakes
• Earthquakes are cause by
plates sliding along each
other and they give off lots
of energy.
• The energy moves in the
form of vibrations, or
waves.
• So people may feel the
earthquake from far away,
but the damage it causes is
usually greatest near the
epicenter.
Effects of Earthquakes
• Earthquakes can cause
tsunamis.
• In 2004, an earthquake
under the ocean off the
west coast of Indonesia
cause tsunamis that
traveled throughout the
Indian ocean. The
tsunamis affected at
least 11 countries.
Effects of Earthquakes
• Earthquakes can cause
damage to buildings,
roads, and bridges.
• In 1906 an earthquake
occurred in San
Francisco. It caused gas
lines to break which
created a fire that
burned for three days!
Effects of Volcanoes
• Volcanoes can cause
damage to cities and can
change our environment.
• In 1815, Mount Tambora in
southeast Asia erupted. The
ash from the volcano filled
the sky.
• Less sunlight could reach
Earth.
• Snow fell in northeaster
United States in June.
• People called it they “year
without a summer.”
Question Time!
1. What are some large-scale effects of volcanoes and
earthquakes?
Some large scale effects of volcanoes are that volcanic ash can
reduce the amount of sunlight reaching Earth’s surface, causing
cooler temperatures. Earthquakes can cause tsunamis.
2. What is one cause and effect of an earthquake?
Cause: a sudden movement of Earth’s plates shakes Earth’s crust
layer. Effect: There are sudden changes in Earth’s surface.
3. Why would it be important to locate the epicenter
of an earthquake?
The epicenter is directly above the earthquake’s focus. The largest
amount of damage may occur at the epicenter.