Transcript Unit 2 PowerPoint Presentation - e

Plate Tectonics I:
Making Mountains and Earthquakes
GEOSC 10: Geology of the National Parks
Presented by Dr. Sridhar Anandakrishnan
The Pennsylvania State University
Overview
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Death Valley National Park
‣ Spreading apart
‣ Heat within the Earth drives that spreading
Yellowstone National Park
‣ Massive volcanic caldera
‣ Earthquakes, and what they tell us
about the Earth’s interior
GEOSC 10 - Geology of the National Parks
Death Valley National Park
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Eastern CA, near the Nevada border
Lowest (-200ft), hottest (135F), driest (2”/yr)
spot in US.
Evaporation of water leaves behind lots of
minerals - Borax mined for detergent
GEOSC 10 - Geology of the National Parks
Mining
GEOSC 10 - Geology of the National Parks
Death Valley is Spreading
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Pull-apart fault
Block in between
drops down
We can measure the
spreading...
GEOSC 10 - Geology of the National Parks
Death Valley Spreading
Zone...
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Pull-apart fault
continues South to the
Gulf of CA.
Baja & Mexico
separating
GEOSC 10 - Geology of the National Parks
Mid-ocean Spreading Ridges
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QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
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The world’s oceans
have many spreading
ridges.
They look a little like
the seams on a
baseball.
GEOSC 10 - Geology of the National Parks
Heat Drives Plate Tectonics
GEOSC 10 - Geology of the National Parks
What is heat?
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Vibration of Atoms
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What are atoms? The smallest unit of matter. Break
up anything into smaller and smaller pieces - you
get to atoms eventually. Each element (oxygen,
carbon, nitrogen) has a fixed number of protons
(atomic weight).
- Usually, the number of neutrons equals the number of
protons and electrons. If not, we have isotopes.
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At -273C, there is no vibration - absolute zero.
GEOSC 10 - Geology of the National Parks
Moving heat
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Move heat around (i.e., get other atoms to
Don’t do it!
vibrate more)
Skin cancer
‣ Radiation
(like the sun or a tanning booth)
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is bad!
Conduction
Convection
GEOSC 10 - Geology of the National Parks
Heat (cont.)
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Convection is when a heated material
itself =
Density
moves to a new place, carrying heat
with it.
mass/volum
e
Hot things are less-dense
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When you mix less-dense and more-dense
things together, the less-dense will rise.
Heated rocks deep inside the earth rise up...
cool at the surface and then sink down.
This is a convection cell.
GEOSC 10 - Geology of the National Parks
Convection Cell Inside Earth
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Heated rocks rise
(because they are
less-dense)
They cool at the
surface of the Earth.
Then sink back down.
GEOSC 10 - Geology of the National Parks
Convection Drives Plate Tectonics
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Rising rocks push
aside the cool rocks at
the surface.
Those cool rocks
travel sideways, and
will move the
overriding plates with
them.
GEOSC 10 - Geology of the National Parks
Heat (2)
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The heat inside the earth is from radioactive
decay.
‣ Atoms (remember them?) are usually stable, but
sometimes can break apart (changing into other
elements).
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They release heat when they do this. (make a lot of
them do it at the same time - atom bomb).
Some of the heat is from the original formation
of the planet... but most from radioactive decay
GEOSC 10 - Geology of the National Parks
Truth with a T
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In 1897, Lord Kelvin
calculated that Earth
was 24 million years
old, based on how
much heat left over.
Darwin, geologists
said Earth much older.
??
GEOSC 10 - Geology of the National Parks
Truth with a T
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Marie Curie (pictured
here on a visit to
Pittsburgh, 1921)
discovered
radioactivity, which is
the source of the heat.
Geologists right...
GEOSC 10 - Geology of the National Parks
Summary (1)
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Heat inside the earth from radioactive decay
drives convection cells.
The cells move crustal plates (there are 8
major plates and some small ones) around on
the surface of the Earth.
Death Valley is on a pull apart fault... follow it
south and you come to oceanic spreading
ridges.
GEOSC 10 - Geology of the National Parks
Yellowstone National Park
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First National Park (est. 1872).
Washburn expedition documented geysers,
hot spring, and earthquakes.
Huge volcanic caldera (crater left over after
eruption) 30-40 miles across.
‣ Eruptions 1.8 million, 1.2 million, and 600 thousand
years ago
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Each one 1000 times as big as Mt. St. Helens
GEOSC 10 - Geology of the National Parks
Earthquakes
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Elastic rebound
(“stick-slip”)
earthquakes occur
when strain builds up
over time (bottom and
middle)
Eventually the fault
breaks (slips) and an
earthquake occurs
GEOSC 10 - Geology of the National Parks
Earthquake Locations
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Earthquakes occur
where two plates
come together
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When they slide past
each other (San
Andreas Fault)
When they over-ride
each other (subduction
zone)
Sometimes they occur
within a plate
GEOSC 10 - Geology of the National Parks
Earthquake Locations
GEOSC 10 - Geology of the National Parks
Heat Drives Plate Tectonics
GEOSC 10 - Geology of the National Parks
Tsunami
GEOSC 10 - Geology of the National Parks
Earthquake Energy Travels
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When the fault slips, the rocks nearby get
deformed... they deform the next bit of rock...
and so on.
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Grab a rope and shake it...
Two kinds of waves are generated
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P-waves (compressional, “Push”)
S-waves (shear, “side-to-side”) - can’t happen in
water or air or other fluids.
GEOSC 10 - Geology of the National Parks
Seismic Energy
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The energy that
travels away from the
earthquake is called
seismic energy.
Travels right through
the Earth to the other
side (for big
earthquakes).
Outer core is fluid
because no shear
waves
go through it.
GEOSC 10 - Geology of the National Parks
Earthquake Size
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Earthquake magnitude (“Richter scale”) goes
from 1 (small - won’t notice it) to 9 (Sumatra
event).
Going up by 1 number in magnitude (4→5)
means the motion of the ground goes up by
10 times and energy up by 30 times!
True, there are fewer large events, but
because the bigger ones are so much more
powerful, most earthquake energy
is released by a few large earthquakes
GEOSC 10 - Geology of the National Parks
Summary (2)
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Earthquakes mainly occur at plate boundaries
Faults stick, then slip suddenly
The energy from the slip can spread far
away...
‣ Causing destruction near the fault
‣ Can be measured far away to give information about
the structure of the Earth
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Magnitude scale is non-linear
Few large events release most energy
GEOSC 10 - Geology of the National Parks