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1. Earthquakes, Volcanoes, andEarthquakes, Volcanoes, and
TsunamisTsunamis

2. EarthquakesEarthquakes
• Fault: a break in the Earth’s crust.
• Blocks of the crust slide past each other
along fault lines.
• When rocks that are under stress
suddenly break, a series of ground
vibrations is set off.
• These vibrations are known as
earthquakes.
• Earthquakes are occurring all the time.

3. Focus & EpicenterFocus & Epicenter
• The point beneath the surface where the
rocks break and move is called the focus.
The focus is the underground origin of an
earthquake.
• Directly above the focus, on the Earth’s
surface is the epicenter. Earthquake
waves reach the epicenter first. During an
earthquake, the most violent shaking is
found at the epicenter.

5. SeismologistsSeismologists
• Seismologists study earthquakes. They
can determine the strength of an
earthquake by the height of the wavy line
recorded on the paper.
• The seismograph record of waves is
called a seismogram.
• The Richter scale is used to calculate the
strength of an earthquake.

6. The Richter Scale
• Used by scientists to quantify the amount of
energy released by an earthquake.
• Magnitude: The measure of the energy released
by an earthquake.
• The scale goes from 1.0 to 10.0.
• Each increase of magnitude by one whole
number is ten times greater and releases 31.7
times more energy than the whole number
below it.

7. The SeismographThe Seismograph
• A weight attached to a spring remains
nearly still even when the Earth moves. A
pen attached to the weight records any
movement on a roll of paper on a
constantly rotating drum. The drum moves
with the Earth and affects the line.

9. TsunamisTsunamis
• Earthquakes which occur on the ocean
floor produce giant sea waves called
tsunamis. Tsunamis can travel at speeds
of 700 to 800 km per hour. As they
approach the coast, they can reach
heights of greater than 20 meters.

10. How a Tsunami FormsHow a Tsunami Forms

11. VolcanoesVolcanoes
• A volcano is a mountain built from
magma.
• Magma: melted rock that found beneath
the surface of the earth (called lava when
above earth’s surface)
• Located near tectonic plate boundaries
where plates are sliding or separating from
one another.
• May occur on the land or under sea.

12. Formation of a VolcanoFormation of a Volcano

13. Volcanic EruptionsVolcanic Eruptions
• A volcano erupts when the pressure of the
magma inside becomes so great that it
blows open the solid surface of the
volcano.
• Some volcanoes have magma flowing out
of them all the time so the pressure never
builds up and they never erupt.

14. Types of VolcanoesTypes of Volcanoes
Different types of volcanic eruptions form
different types of volcanoes.
1. Cinder cones
2. Shield volcanoes
3. Composite volcanoes
4. Caldera volcanoes
5. Fissure volcanoes

15. Cinder ConesCinder Cones
• Volcanoes made mostly of cinders and
other rock particles that have been blown
into the air are called cinder cones.
Cinder cones form from explosive
eruptions. Because the material is loosely
arranged, the cones are not high. The
have a narrow base and steep sides such
as Paricutin in Mexico.

16. Cinder Cone VolcanoCinder Cone Volcano

17. Shield VolcanoesShield Volcanoes
• Volcanoes composed of quiet flows are
called shield volcanoes. Because it is
rummy, the lava flows over a large area.
After several eruptions, a dome-shaped
mountain is formed such as Mauna Loa
(4km over sea level) in the Hawaiian
Islands.

18. Shield VolcanoesShield Volcanoes

19. Composite VolcanoesComposite Volcanoes
• Volcanoes built up of alternating layers of
rock particles and lava are called
composite volcanoes.
• Composite volcanoes have another name
called “Strato Volcanoes.” Composite
volcanoes consist of lava that is mixed
with sand or gravel which in turn creates
cinders or volcanic ash.

20. Composite VolcanoComposite Volcano
During the formation of
a composite volcano, a
violent eruption first
occurs, hurling volcanic
bombs, cinder and ash
out of the vent. Then a
quiet eruption, produces
lava flow that covers the
rock particles. After
alternating eruptions, a
cone-shaped mountain
forms such as Mount
Vesuvius.

21. Mount VesuviusMount Vesuvius

22. Mount VesuviusMount Vesuvius
• Images of victims in
eruption of Vesuvius
in 79 AD. Most died
as a result of
suffocation.

23. CalderaCaldera
volcanoesvolcanoes

24. Caldera volcanoes are circular
depressions in the ground over a magma
chamber. Sometimes the depression in
Caldera volcanoes are covered in with lava
and volcanic ash making it hard to
recognize. This type of volcano is easier
noticed from space due to the distance and
view point. When this volcano erupts it can
spew volcanic rocks for miles and miles.

25. FissureFissure
volcanoesvolcanoes

26. Fissure volcanoes are also hard to
recognize from the ground and sometimes
from space. Fissure volcanoes have no
main crater, the ground just splits and lava
pours out through the cracks. After a
fissure volcano erupts and has cooled
because it’s a solid it will look mainly like
the plains.

27. CraterCrater
• There is often a funnel-shaped pit or
depression at the top of a volcanic cone.
This pit is called a crater. If the crater
becomes very large as a result of the
collapse of its walls, it is called a caldera.
A caldera may also form when the top of a
volcano explodes or collapses.

28. Volcanic CraterVolcanic Crater

29. Volcanic ActivityVolcanic Activity
• Volcanoes are rather unpredictable .
Some erupt regularly, others have not
erupted in modern history. Scientists
classify them as active, dormant or extinct.

30. Active VolcanoesActive Volcanoes
• An active volcano is one that erupts wither
continually or periodically such as Mount
Katmai in Alaska and Mount St. Helens in
the Cascade Range.

31. Dormant VolcanoDormant Volcano
• A volcano that has been known to erupt
within modern times but is now inactive is
classified as a dormant volcano. Mount
Rainier in Washington state are example
of dormant volcanoes in the United States.

32. Extinct VolcanoExtinct Volcano
• A volcano not known to have erupted
within modern history is classified as an
extinct volcano. They have been worn
away almost to the level of their magma
chamber. Scientists can be wrong. Mount
St. Helens was considered to be dormant
but erupted after long periods of inactivity.

33. Volcano and Earthquake ZonesVolcano and Earthquake Zones
• Most major earthquakes and volcanic
eruptions occur in three zones of the
world. Scientists believe that there is a
great deal of movement and activity in the
Earth’s crust in these three zones.

34. Ring of FireRing of Fire
• One major earthquake and volcano zone
extends nearly all the way around the
edge of the Pacific Ocean. This zone
goes through New Zealand, the
Philippines, Japan, Alaska and along the
western coasts of North and South
America. The San Andreas fault is part of
this zone.

35. Mediterranean ZoneMediterranean Zone
• A second Major earthquake and volcano
zone is located near the Mediterranean
Zone and extends across Asia into India.
Many countries in the zone, including Italy,
Greece and Turkey, have violent
earthquakes. Many volcanic eruptions
also occur in this zone.

36. Mid-Atlantic Ridge ZoneMid-Atlantic Ridge Zone
• The third major earthquake and volcano
zone extends through Iceland and to the
middle of the Atlantic Ocean. There is
under the ocean a long range of volcanic
mountains called the Mid-Atlantic Ocean
Range. Scientists believe that the volcano
and earthquake activity are due to the
formation of new parts of the Earth’s crust
along the ridge. The volcanic island of
Iceland is part of this zone.

37. Earthquake BeltsEarthquake Belts