Download Earthquakes and Volcanoes

Chapter 21
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They occur mostly at plate boundaries, along
fault lines
Energy is released as seismic waves
As the seismic waves travel through the Earth
they create shaking
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Focus - the exact point within the Earth
where an earthquake originates
Epicenter - a point on the Earth’s surface
immediately above the focus
◦ Damage from earthquakes are usually greatest at
the epicenter
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Energy released is measured as shock waves
Three types of waves generated:
1. longitudinal waves - originate from the focus
and travel through rock faster than other waves
 Also called P-waves or primary waves
 They travel by compressing the crust in
front of it and stretching the crust
behind it
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These waves move more slowly than p-waves
◦ Known as secondary waves or, S-waves
◦ Transverse waves have peaks and valleys like ocean
waves
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Moves only across the Earth’s surface
Combination of up and down motion and
back and forth motion
Longer wavelengths and rolling action can
cause most of surface damage to buildings
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Seismology is the study of earthquakes
Seismograph machines measure ground
motion during earthquakes and record data
about p-waves, s-waves and surface waves
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Seismographs measure p-waves first, then swaves and finally the larger surface waves
The difference in time from the arrival of pwaves and s-waves enables seismologists to
determine the distance to the epicenter
Using distances from three seismograph
stations allows them to find the epicenter
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Because waves change speed and direction as
they travel whenever the density changes,
scientists have used seismograph information
to create a model of the Earth’s interior
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Measure of the energy released by an
earthquake
Each step, on the scale represents a 30-fold
increase in the energy released
An earthquake of magnitude 8 releases 304,
or 810,000 times as much energy as
magnitude of 4
http://video.nationalgeographic.com/video/e
nvironment/environment-naturaldisasters/earthquakes/earthquake-montage/
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Distance from epicenter
Type of bedrock
Type of buildings present
Population
How deep the focus is
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http://www.bbc.co.uk/news/world-asiapacific-12709850
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Any opening in the Earth’s crust through
which magma reaches the surface ( vents )
Volcanoes release molten rock, ash, and a
variety of gases
When magma reaches the Earth’s surface , its
physical behavior changes, and it is called
lava
http://video.nationalgeographic.com/video/e
nvironment/environment-naturaldisasters/volcanoes/volcano-lava/
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Mild eruptions
Magma is rich in iron and magnesium,
creates fluid lava
The buildup of this kind of lava creates a
gently sloping mountain known as a shield
volcano
Mauna Loa, in Hawaii is a shield volcano
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Composed of alternating layers of ash,
cinders and lava
Magma is rich in silica, is more viscous
Gases are trapped in magma, causing
eruptions that alternate between flows and
explosive activity
Japan’s Mount Fuji, Mount St. Helens, Mount
Ranier, Mount Hood and Mount Shasta are
examples
http://www.bing.com/videos/search?q=earthquake+videos
+discovery+channel&mid=149DB76B32D4742F389F149DB7
6B32D4742F389F&view=detail&FORM=VIRE3&adlt=strict
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Smallest and most abundant volcanoes
Large amounts of gas trapped in magma
cause more violent eruptions
Cinders and ash are thrown from the vent
Paricutin in Mexico is a cinder cone
Seamounts – underwater volcano
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Most volcanoes occur along convergent plate
boundaries
75% of active volcanoes are located in these
zones
Volcanoes around the Pacific Ocean lie in a
zone known as the Ring of Fire
These volcanoes often have explosive
eruptions due to the highly viscous magma
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Underwater volcanoes occur at divergent
plate boundaries
Volcanic mountains of the central rift valley
Iceland, in the North Atlantic Ocean, is on the
Mid-Atlantic Ridge
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Some volcanoes occur in the middle of plates
at hot spots
Mantle-plumes of hot rock rise from deep
inside the mantle, melt as they rise, and erupt
to form volcanoes
As the continental plate continues to move
over the hot spot, a series of islands is
created
Hawaiian Islands are an example