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Geology
Earth’s Interior, Plate Tectonics,
Earthquakes & Volcanoes
Earth’s Interior
1.Earth’s interior is divided into the:
a. Crust
b. Mantle
c. Outer core
d. Inner core
surface
center of earth
2. The lithosphere includes the crust and the
rigid upper layer of the mantle.
3. The asthenosphere lies below the lithosphere
and is made up of the soft layer of the mantle.
Earth’s Interior
Plate Tectonics
1. Plate – lithosphere is broken into separate
sections called plates
2. Alfred Wegener developed the idea that the
continents were once joined and have since
drifted apart. The once giant land mass was
known as Pangaea.
3. The Theory of Plate Tectonics explains the
plates constant, slow motion, driven by
convection currents in the mantle. It
combines the theories of continental drift and
sea-floor spreading.
Sea-Floor Spreading Diagram
Sea-Floor Spreading is the process by which molten material
adds new oceanic crust to the ocean floor driven by convection
currents in the mantle.
C
A = Molten magma rising –Mid-Ocean Ridge forming
B = Sea-Floor spreading by convection currents
C= Convergent Boundary leading to subduction – trench forming
Plate Tectonics
a. Plates move in the following ways:
i. Transform Boundaries - slip past one another/No change in
elevation (stress = shearing)
ii. Divergent Boundaries - move apart/may cause a change in
elevation (stress = tension); found at mid-ocean ridges; created
by sea-floor spreading (2 oceanic plates); can create a rift valley
on Earth when 2 continental plates move apart.
iii. Convergent Boundaries - come together/may cause a change
in elevation (stress = compression); 2 oceanic plates or 1 oceanic
plate & 1 continental plate converge – subduction occurs and a
trench is formed; 2 continental plates converge – a mountain is
formed
Plate Tectonics/Plate Boundaries
Diverging Plate Boundary
Converging Plate Boundary
Transform Plate Boundary
Earthquakes
A. Description
1. An earthquake is the shaking and
trembling that results from the movement of
rock beneath Earth’s surface
2. Earthquakes occur because of stress built
up in rock. Stress is a force that acts on a rock
to change its shape or volume. These stresses
cause faults (a break or crack in Earth’s
lithosphere (underground) along which the
rocks move). There are three types:
a. Shearing – Strike-slip Fault
b. Tension – Normal Fault
c. Compression – Reverse Fault
Plate Tectonics & Faults
Tension
Normal Fault
Compression
Earthquakes
B. Measuring Earthquakes
1. Seismic Waves – vibrations that travel through
Earth carrying the energy released by an earthquake.
a.
Primary Waves – P waves arrive first
move by compression and expansion
b.
Secondary Waves – S waves arrive
second - move side to side and up and down
c.
Surface Waves – when P and S waves
meet the surface – move in different
directions
2. Epicenter – center of the earthquake ON Earth’s
surface; in order to find the epicenter of an
earthquake, you need data from 3 cities
3. Focus – the point UNDER ground where the
Earth’s breaks under stress and causes an earthquake
Earthquakes
C. Earthquake Hazards
1. Soil Conditions/Shaking
2. Liquefaction – violent shakes turn loose, soft soil into mud
3. Aftershock – earthquake that occurs after a big earthquake in the same
area
4. Tsunamis – large wave caused by an earthquake on the ocean floor
D. Earthquake Safety
1.
2.
3.
Location – some places are more prone to earthquakes
Construction – earthquake-proof buildings/houses (base-isolated buildings)
Drop, cover and hold
E. Earthquake Detecting Devices – 4 fault monitoring devices
1. Creep Meters – uses a wire across a fault to measure horizontal
movement of the ground
2. Laser-ranging Devices – uses a laser to measure horizontal movement
3. Tiltmeters – measures tilting or raising of the ground
4. Satellite Monitors – uses GPS from outer space to monitor changes in
elevation as well as horizontal movement along a fault
5. Seismographs – collects data (seismic waves) from earthquakes
Volcanoes
A. Description
1. A volcano is an opening in Earth’s Surface
where magma escapes from the interior.
Magma is the liquid inside a volcano. When
magma reaches earth’s surface it is called
lava.
2. Most volcanoes occur near the boundaries
of Earth’s Plates and along the edges of
continents above subduction zones, in
island arcs, or along mid-ocean ridges
(under water mountain ranges)
Earthquakes & Volcanoes
Volcanoes
B.Volcanic Landforms
1. Shield Volcanoes – Hawaiian Islands; quiet
eruptions, lava flows, wide base, not very tall –
usually created over hot spots
2. Cinder Cone Volcanoes – Paricutin in Mexico;
explosive eruptions of cinders/rock/gases – tall,
narrow base
3.Composite (Strato) Volcanoes – alternating
quiet/explosive eruptions – alternating layers of
lava and ash; Mt. Hood, Mt. St. Helen’s, Mt.
Ranier – usually created at subduction zones
Volcanoes
C. Volcano hazards
1.Pyroclastic flows
2.Damage from ash
3.Lava Flows
4.Avalanches of mud
5.Flooding
6.Deadly gases
Volcanoes
D.Volcano Benefits
1. Fertile Soil
2. Increased Tourism
3. Energy source