Transcript unit 3 plate tectonics_ volcanoes and

Unit 3 Plate Tectonics, Volcanoes
and Earthquakes
Please add this information to your notes
and diagrams.
What is Plate Tectonics?
Attica
A theory
that
explains the
movement
of the
earth’s
crust.
Crust is broken into sections called plates.
Float in Mantle like pieces of ice float on a lake.
Do you think the continents fit
together?
Evidence of Plate Tectonics
 Several continents fit together.
 Rock formations on South America and Africa
match up. See example 1
 Glaciers once covered Africa, India, and South
America. See example 2
 Mountains on the east coast of US, Scotland,
Greenland and Northern Europe are the same
age. See example 3
Evidence of Plate Tectonics
 Same fossil species found on widely separated
parts of the world. See example 4
 All the continents fit together into one large land
mass called Pangaea. See example 5
 Pattern of earthquakes and volcanoes. See
Example 6
Rocks on South America and Africa
South America
Africa
Jurassic Period
135 mya.
Rocks of same age and sequence (order) found on
both continents.
Same minerals found on both also.
back
Glacial Evidence
South America
South Pole
Africa
India
Australia
Glaciers covered parts of these continents around 300 myo.
We find U-shaped valleys and scratched and polished bedrock
located in the southern parts.
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Mountains created when Pangaea was
formed.
Mountains found here are the same age and
structure, about 300 myo.
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Fossil Evidence
Lystrosaurus – 250
mya, Land reptile
Cynognathus –
200-250 mya, Land
reptile
Mesosaurus – 270
mya, Freshwater
reptile
Glossopteris – seed fern
back
Continental Drift
225 million years ago
200 million years ago
Continental Drift
135 million years ago
65 million years ago
Continental Drift
Changes for the future.
•Central America will pull away from South America.
•Africa will start to split apart.
•Australia will move closer to Asia.
•India will continue its northward motion.
India’s Long Journey
India started at 50° S latitude and is
now at 20° N latitude. The result
is…..
The tallest
mountain
range on any
continent.
back
Earthquake and Volcano Patterns
90% of all earthquakes occur here.
Many famous
volcanoes
•Mt. Katmia
•Mt. St. Helens
•Mt. Pinatubo
Plate Boundaries
Here you will learn about how the plates of the earth’s crust
interact. Write down the examples in your notes and turn to
page 5 in your Reference Table to see this diagram.
General Motion of Plates
Mantle Convection
Currents cause the plates
to move.
Divergent Boundary
Where two plates are
being pulled apart.
 Usually occurs at a midocean ridge.
 New sea floor is formed.
 Youngest rock along the
ridge.
 Age increases as you
move away from ridge

examples
Divergent
 Same pattern on both sides of the ridge.
example
 Iron in the magma is magnetized to show the
magnetic field of the earth.
example
 Many earthquakes and volcanoes occur along
the mid-ocean ridges. Example
 Also happens on land.
Convergent Boundary
 Plates are moving together.
 Two types:
Collision and Subduction
 Collision
converging plates both carry continents
lithosphere pushed upward into mountain ranges
examples
Convergent Boundary
 Subduction
one plate plunges below another plate
most noticeable feature is a deep sea trench
usually have deep earthquakes
lithosphere is melted and recycled
 Subduction of two ocean plates (example)
deep sea trench with a chain of volcanic islands
 Subduction of one continent and ocean plate
deep sea trench with Mt..range and volcanoes
example
Sliding Boundary
 Also called a Transform Fault
 Plates are sliding past each other.
 San Andreas Fault, best example.
Mid Ocean Ridge
Back to notes
Youngest Rock
Rocks get older as
you move away
from the ridge.
Mid Atlantic Ridge
Back to notes
Evidence of Underwater Volcanoes
These are found along mid
ocean ridges
Pillow Lava
Back to notes
Black Smokers
Magnetic Patterns in Igneous Rock
Reversed magnetic
polarity means that
the earth’s
magnetic field has
flipped directions.
Discovered by
looking at the iron
atoms in basalt.
Back to notes
East Africa Rift Valley
Back to notes
Collision Boundary
Back to notes
Subduction of Two Ocean Plates
Back to notes
Subduction of Continent and Ocean
Plate
Where are these boundaries found?
Back to notes
Which type of subduction is this?
Ocean
Crust
Back to notes
Continental
Crust
Transform Boundary
San Andreas Fault in California
Pacific Plate
North
American
Plate
Volcanism and Plate Tectonics
1. Volcanism produces magma
A. Magma
1. Definition – molten rock underground
2. Where?
a. in the asthenosphere
b. at plate boundaries
3. Reaches surface through volcanoes
4. Types of magma
a. felsic – thick, light colored slow
moving, forms rock Granite
b. mafic – thinner, darker flows
more easily, forms rock Gabbro
Volcanism and Plate Tectonics
B. Lava
1. Definition – magma that reached the
surface
2. Mafic – thin and fluid, gases escape easily
a. flows smoothly on surface, forms
rock Basalt
3. Felsic – less fluid, gases can not escape
easily
a. explosive eruptions , forms rock
Rhyolite
Volcanism and Plate Tectonics
4. Aa lava compared to Pahoehoe lava
a. Aa – rough, jagged, slow moving
b. Pahoehoe – smooth, ropelike, fast
moving examples on page 254
5. Solid fragments of lava called tephra
a. ash – fine dust like fragments
b. block and bombs – blocks are solid,
bombs leave as liquid harden when
falling examples
Volcanism and Plate Tectonics
II. Kinds of Eruption
A. Rift Eruptions (divergent boundaries)
1. Occur at long, narrow fractures in
crust
2. Typically flow out smooth and fluid
like
3. In oceans on mid ocean ridges
a. cause pillow lava
Volcanism and Plate Tectonics
4. On land form basalt plateaus
a. East Africa Rift System
b. Columbia Plateau of
Washington, Oregon and Idaho
B. Subduction Eruptions
1. Result of magma that forms at subduction
boundaries
2. Usually explosive, mostly lava fragments
3. Most of world’s active volcanoes found here
a. Cascade Mts of Washington, Oregon
b. Andes of South America
Volcanism and Plate Tectonics
C. Hot Spots
1. Located in middle of plates
2. Similar to rift eruptions
3. Most famous – Hawaiian Islands
4. Islands get older the further away from
Hawaii
a. indicates steady motion of Pacific
Plate
Lava and Tephra
More Lava
back
Cascade Mountains
back
Web site
East Africa’s Volcanoes
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Hawaiian Volcanoes
back
Photo gallery
Rift Eruptions
Last year’s Icelandic volcano
Volcano Types
back
Earthquakes
Pay attention because you never know
when you’ll be in one.
Earthquakes In The USA
Why is the highest Hazard on the West Coast?
A Plate boundary is there.
largest quakes in us
recent and historical quakes
Where do earthquakes take place?
Worst damage occurs at
the epicenter
Movements takes place
at the focus
Most occur on faults
Circles represent
seismic waves that
radiate in all directions
Seismograph – Records Earthquake
Earth shakes and
moves the base.
Weight remains
stationary because of
inertia.
Rotating drum records
the motion
Fault Types
Fault Types
Richter Magnitude Scale
Tells us how much energy is released during an
earthquake.
Scale is based on movement and energy released not
damage.
Created by
Dr. Charles Richter
Comparison to Other Intensity Scales
How is the Richter Magnitude Measured?
First find the
amplitude and the
S – P wave time
difference.
Then look them up
on the chart, where
the line crosses the
magnitude scale,
that’s your answer.
Types of Seismic Waves – P Waves
Four Things to Remember About P Waves
•They are the fastest waves (3 miles/sec.)
•They travel in the same direction as the particles
vibrate
•They travel through solids,liquids and gases
•They travel faster through denser materials
Types of Seismic Waves – S Waves
Four Things to Remember About S Waves
•They are slower than P waves (2 miles/sec.)
•They travel at right angles to the direction the
particles vibrate
•They travel through solids ONLY!!!!!!!!!!!!
•They travel faster through denser materials
Examples of Seismic wave motion
Time Travel Graph
This graph is used to
determine three
things.
1. Travel Time for a P
or S wave.
2. Epicenter distance
based on a travel
time.
3. Epicenter distance
based on arrival
time difference.
Travel Time for a P or S wave.
S wave travel
time = 12 min.
30 sec.
P wave travel
time = 4 min.
15 sec.
Epicenter distance based on a travel time.
Epicenter
distance = 2200
km
Epicenter
distance = 2900
km
Steps to find the Epicenter Distance
Step 1 – Determine the P and S wave arrival
times from the seismogram.
Step 2 – Calculate the Time Difference by
subtracting the P wave arrival time from the S
wave arrival time. Write down the following
examples.
Steps to find the Epicenter Distance
Time Travel Difference Examples
S wave arrival
- P wave arrival
Time Difference
05:49:50
-05:43:20
00:06:30
18:35:40
-18:33:10
00:02:30
12:21:10
-12:18:40
00:02:30
15:20:15
-15:15:30
00:04:45
Remember you have to convert minutes
into seconds when you borrow.
Steps to find the Epicenter Distance
Step 3 – Use the time
difference to find the
epicenter distance on
the Travel Time
Graph on page 11 in
your reference
tables.
Pay attention to
the next two
examples
Steps to find the Epicenter Distance
To do step 3, first
you mark the time
difference on a
sheet of paper.
Example 2 Time
Difference = 6 min
and 30 sec
Steps to find the Epicenter Distance
Now slide the
paper over so the
time marks line up
with the P and S
wave lines.
Read down the line
along the edge of
the paper to the
epicenter distance
scale.
Epicenter Distance
= 4,800 km
Try This One
09:32:25
-09:24:45
07:40
Epicenter
Distance =
6000 km
Earthquake Damage
Comparison of San Francisco Earthquakes
Earthquake Damage
Earth’s Interior
All of this information has been determined
by studying seismic (earthquake) waves.
Shadow Zone
Seismic waves are
refracted (bent) as
they travel through
different density
materials.
No earthquake waves
are recorded here.
The End………. Finally