Transcript http://www.pbs.org/wgbh/aso/tryit/tectonics/#

Dynamic Earth
This unit will cover: layers of
the earth, plate tectonics,
volcanoes, earthquakes
Earth’s Internal
Structure:
Compositional
Layers
1. Crust:
Continental
Oceanic
crust
crust
2. Mantle

Largest section
Includes the asthenosphere
toward the top

Solid part and semi-liquid
parts to it

3. Core

Inner core (Solid—Iron)

Outer Core (Liquid)
Internal Structure of Earth
Upper Mantle
Crust
Lower Mantle
Outer
Core
Inner
Core
“Asthenosphere”
The Lithosphere contains the crust and the solid
mantle
Early observations of the world
• Alfred Wegener proposed an idea for
CONTINENTAL DRIFT.
• Continental Drift= proposed that the
world’s continents were stuck together
• He called his super continent PANGEA.
Rejected…..
• Alfred Wegener idea of Pangea was
rejected after his death in 1930.
• The use of Seafloor spreading was a new
idea that was promoted.
Technology used in Seafloor
Spreading
• Sonar—uses sound waves to measure the
depth of the bottom of the ocean
• Magnetometer—is a device to measure
the changes in magnetic fields.
Sonar
Antarctic- using
magnetometer
Results…
• Map Generated Topographical Maps that
showed the deep sea trenches and ocean
ridges.
Picture of
California’s
Coast
Blue—water
Green, brown-land
Theory of Plate Tectonics
• Which states that the Earth’s crust and
rigid upper mantle is broken into plates
• The plates move in different directions and
different rates over time.
Different Plates Around the World
Ring of
Fire
Plate Boundaries
• Divergent Boundaries
– Places where plates are coming apart
• Convergent Boundaries
– Places where plates crash or crunch
together
• Transform Boundaries
– Places where plates slide past each
other
Divergent Boundary
–Places where plates are coming apart
Convergent
Boundary
With Subduction
Plate
Plates crash into
each other
Transform Boundary
–Places where plates slide past each other
San Andres Fault, California
Plate Motions
• Assume plates are rigid (no internal
deformation: bending or flexing)
• Obtain plate motion:
– Directions
– Rates of movement
Convection Cell— that regulates the
flow of magma. There are also
convection cells in the atmosphere
for our weather.
What do plate tectonics form?
• Earthquakes
• Hotspots
• Volcanoes
Earthquakes
Earthquakes
Most destructive forces on Earth.
But it is buildings and other
human structures that cause
injury and death, not the
earthquake itself
1988 - Soviet Armenia: magnitude 6.9, 25,000
people died
1985 - Mexico City: magnitude 8.1, 9500 people
1989 - Loma Prieta, CA: magnitude 7.1, 40 people
died
1995 - Kobe, Japan: magnitude 7, ~6000 people died
Where do earthquakes occur?
• They occur when plates are diverging,
sliding past each other, colliding or going
underneath each other.
• There are three types of faults
– Strike-Slip Fault
– Normal Fault
– Reverse Fault
• Thrust Fault
3 types of faults
Strike Slip Fault
• Occurs horizontally when
two plates slide past each
other
• San Andres Fault in
California
• Causes Rail roads to
bend
Normal Fault
• Occur vertically and when the plates are
diverging
• Happen where the lithosphere is being
pulled apart
Reverse Fault
• Occurs vertical, the
plates collide together
pushing the rock
upward
• Example—thrust
– In the ocean causes
tsunami
PARTS OF EARTHQUAKES
• HYPOCENTER—LOCATIONS OF
EARTHQUAKE UNDERNEATH THE
GROUND.
• EPICENTER—LOCATION OF
EARTHQUAKE ON THE SURFACE
epicenter
hypocenter
Transform fault
P and S Wave
Body Waves
P waves:
• Pressure or compressional waves. Vibrate parallel to
direction of wave travel like a slinky.
• Fast travel: 4-7 km/sec (15,000 mph)
• P is primary, or first wave to arrive at recording
station
S waves:
• Shear waves. Vibrates perpendicular to direction of
wave travel. Like snapping a rope
• Slower than P wave: 2-5 km/sec (11,000 mph)
• So S is secondary, or second wave to arrive at
Locating the Epicenter of an
Earthquake
• P, S and surface waves all start out at same
time.
• The further you are away from the quake, the
longer the time span between arrival of P and
S wave.
• The distance of the seismometer to the
earthquake can be determined by the time
between the arrival of P wave and arrival of S
waves.
• Can tell the distance, but not the direction.
• Therefore, multiple sites must be used to find
epicenter.
Richter Scale
• Measures the magnitude of an earthquake
from 1-10
MEASURES MAGNITUDE FROM 0-10
Hotspots
Hot Spots
• Islands associated with hot spots (island chains,
mid-ocean ridges, triple junctions).
• Iceland (mid-ocean ridge).
• Galapagos Islands (triple junction).
• Island of Hawaii (mid-plate volcanic chain; hot
spot trace).
• Linear island chains form as plate moves over
hot spot.
• Hawaiian islands get older in direction of plate
movement (older away from mid-ocean ridge).
VOLCANOES
http://georoc.mpch-mainz.gwdg.de/volcano.gif
Volcanoes
• Basic parts of a volcano
• Crater (depression at the summit of a
volcano, connected by a vent or pipe to the
magma chamber below)
• Caldera (crater more than 1 km in diameter,
formed at the summit of a volcano when
lava is drained from an underground
magma chamber, causing the summit of the
volcano to be unsupported, and to collapse)
Example of Caldera
• Crater Lake in Oregon. This volcano was
so violent that the top of the mountain was
blown off. Now all is left is a beautiful lake.
• Pit crater (collapse features
on the flanks or summit of a
volcano that are smaller
than the main caldera at the
summit of a volcano)
• Vent (pipe-like conduit from
the magma chamber to the
surface)
• Fumaroles (secondary
vents on the flank of a
volcano which emit steam
and other gases)
http://volcano.und.nodak.edu/vwdocs/vw_hyperexchange/parts.html
Types of Volcanoes
1. Shield volcanoes - Hawaii
• Docile lava outpouring. Only minor pyroclastic
material
• Lava forms broad dome with central crater
• Slope is 2-10 degrees, like flattened shield
• Very long lived, very large, massive amounts of
lava (pahoehoe and aa)
Example: Kilauea
Mauna Loa, on the Big Island of Hawaii, is the largest active
volcano in the world. It last erupted in 1984. Mauna Loa erupted 14
times in the 20th Century, and 37 times since 1832. Mauna Loa is
the most massive mountain on Earth, rising to an elevation of 13,677
feet above sea level, or 31,677 feet above the sea floor. Its volume is
10,000 miles3.
2. Cinder cones
• Erupt pyroclastic material
• Steep slopes (30 to 40 degrees)
• Not very long lived.
• Typically small, less than 1000 feet tall
• Often parasitic on larger volcanoes
Examples: Mt. Shasta
Cinder-Cone Volcano
Mt. Shasta--California
3. Composite volcanoes
• Erupt lava and pyroclastic material
• Intermediate slopes because lava acts like
protective coating on pyroclastic layers
• Built up over long periods of time
• Most picturesque, but most violent
Examples: Mt. Vesuvius, Mt. Fuji, Yellowstone
Mount Vesuvius
Mt. Fuji
• Japan’s Highest Mountain, dormant
volcano and last erupted 1708
Yellowstone Caldera
Eruption of Mount Saint
Helens, May 18, 1980
The eruption of Mount Saint Helens was the most
destructive in the history of the United States
 Mount Saint Helens is located in southwest
Washington in the Cascade Range, a mountain
range dominated by periodically active volcanic
peaksIn
 Images include pre-eruption activity and posteruption effects such as the blast area, mud flows,
ash fall, and altered terrain


http://www.ngdc.noaa.gov/seg/hazard/slideset/31/31_thumbs.html