Download Volcanoes and earthquake - SIGNAL HILL SECONDARY

VOLCANOES AND
EARTHQUAKES
Caribbean Studies
Objectives
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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.
What are Earthquakes?
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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
Anatomy of an Earthquake
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Focus (or hypocentre): the center of energy release.
Epicentre: the point on the ground surface
immediately above the focus (closest point on the
surface to the focus).
Two kinds of waves from earthquakes
• P waves (compressional) 6–8 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 through liquids.
Tectonic activity in the Caribbean
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The amount of damage created by an earthquake
depends on several factors.
 The
earthquake’s 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
Seismologists
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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.
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
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
What are
volcanoes?
What is a Volcano?
A volcano is a weak spot in the crust where
molten material comes to the surface
 Magma reaching the surface is called lava.
 A volcanic eruption is the process wherein
volcanic materials such as lava, fragmented
rocks or gases are emitted or ejected through
a crater, vent or fissure on to the earth's
surface to form new deposits.
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Volcanic Terms
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A volcano not known to have erupted within modern
history is classified as an extinct volcano.
A volcano that has been known to erupt within
modern times but is now inactive is classified as a
dormant volcano.
An active volcano is one that erupts wither
continually or periodically
Structure of volcano
Where do volcanoes occur?
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Volcanoes occur most frequently at plate boundaries.
Some volcanoes, like those that form the Hawaiian
Islands, occur in the interior of plates at 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.
Why do volcanoes occur?
Temperatures in the mantle are hot
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, pressure
decreases allowing trapped gasses
to expand and propel the magma
through openings in the Earth’s
surface causing an eruption.
What causes volcanoes?
What causes volcanoes?
Hot Spots
Types of Volcanoes
Shield volcano
Cinder cone volcano
Composite volcano
What Erupts from a Volcano?
Pyroclastic material
• Rock fragments created by
eruptions
•magma explodes from volcano and solidifies in the air
•existing rock is shattered by powerful eruptions
Lapilli
Volcanic bombs
Volcanic blocks
Volcanic ash
Volcanoes in the Caribbean
QUESTIONS