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VOLCANOES ANDEARTHQUAKES
Caribbean Studies
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Objectives
To explain what are earthquakes and
volcanoes
To identify major area of earthquake and
volcanic activity.
To assess the positive and negative effects of
earthquakes and volcanoes.
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What are Earthquakes?
The shaking or trembling caused by the
sudden release of energy
Usually associated with faulting or breaking of
rocks
Continuing adjustment of position results in
aftershocks
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Anatomy of an Earthquake
Focus(or hypocentre): the center of energy
release.
Epicentre: the point on the ground surface
immediately above the focus (closest point onthe surface to the focus).
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wo n s o waves romearthquakes
P waves (compressional) 68 km/s.
Parallel to direction of movement (slinky), also
called primary waves. Similar to sound waves.
S waves (shear) 4
5 km/s. Perpendicular to
direction of movement (rope); also called
secondary waves. Result from the shear
Strength of materials. Does not pass throughliquids.
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Tectonic activity in the
Caribbean
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The amount of damage created by an
earthquake depends on several factors.
The earthquakes strength
The kind of rock and soil that underlie an area
The population of the area
The kind of buildings in the area
The time at which the earthquake occurs
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Seismologists
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 aseismogram.
The Richter scale is used to calculate the
strength of an earthquake.
I i d M i d f
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Intensity and Magnitude of
Earthquakes
Magnitude
Often measured using the Richter scale
Based on the amplitude of the largest
seismic wave
Each unit of Richter magnitude equates to
roughly a 32-fold energy increase
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Intensity and Magnitude of
Earthquakes
Intensity
A measure of the degree of earthquake shaking
at a given locale based on the amount of
damage
Most often measured by the Modified Mercalli
Intensity Scale
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What arevolcanoes?
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What is a Volcano?
A volcano is a weak spot in the crustwhere molten material comes to thesurface
Magma reaching the surface is calledlava.A volcanic eruption is the process
wherein volcanic materials such as lava,
fragmented rocks or gases are emitted orejected through a crater, vent or fissure onto the earth's surface to form newdeposits.
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Volcanic Terms
A volcano not known to have erupted within
modern history is classified as an extinct
volcano.
A volcano that has been known to erupt withinmodern times but is now inactive is classified
as a dormant volcano.
An active volcano is one that erupts withercontinually or periodically
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Structure of volcano
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Where do volcanoes occur?
Volcanoes occur most frequently at plate
boundaries.
Some volcanoes, like those that form the
Hawaiian Islands, occur in the interior of platesat areas called hot spots .
The greatest number of volcanoes occur on the
ocean floor along spreading ridges.
Over 80% of those on land occur at edges of
continents, or subduction zones, where one
plate dives, or subducts, under another plate.
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Why do volcanoes occur?
Temperatures in the mantle arehot enough to melt rock into
magma magma.
Less dense than the solid rock
around it, magma rises and
some of it collects in magma
chambers magma chambers.
As the magma rises, pressuredecreases allowing trapped
gasses to expand and propel
the magma through openings in
the Earths surface causing an
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What causes volcanoes?
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What causes volcanoes?
Hot Spots
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Types of VolcanoesShield volcano
Cinder cone volcano
Composite volcano
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What Erupts from a
Volcano?Pyroclastic materialRockfragments created by eruptions
magma explodes from volcano and solidifies in the air
existing rock is shattered by powerful eruptions
Volcanic blocks
Volcanic bombs
Lapilli
Volcanic ash
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Volcanoes in the Caribbean
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QUESTIONS