Plate Tectonics
1. Basic components of earth
2. Two layers key to plate
tectonics
LITHOSPHERE ASTHENOSPHERE
Hard & Plastic “silly
brittle putty”
Crust & Lower mantle
upper Convection
mantle current that
“Plate” carries the
plates
3. Most common rock in crust
Silicon dioxide SiO2
Found in magma or igneous rocks the
most common rock
4. How is convection like a
lava lamp?
Convection cells in
asthenosphere
5. Two types of crust
Crust
OCEAN crust CONTINENTAL crust
Denser Less dense
Thinner Thicker
Eventually is Rarely/never
subducted subducted
Relatively young Oldest crust on
Earth
6. Evidence supporting
Theory of Continental Drift by
Alfred Wegner
Fit of S. America to Africa
Fossil evidence
Geological evidence
What is evidence gathered after
WW2 that lead to Theory of plate
tectonics ---- Seafloor
spreading---
7. Theory of Plate Tectonics
a.The plates move across the surface
b.Current idea is that plates move because of
convection cell motion under the crust in the
upper levels of the mantle---plume theory
c.3 kinds of plate boundaries are : divergent,
convergent and transform
d.Topography (surface shape) of earth is
formed by uplift and weathering/erosion
e. Different from Alfred Wegnener’s Theory of
Continental Drift ( he could not explain
HOW they moved)
8. IN plate tectonics the earth is broken into major plate
9. What impact does Plate
tectonics have on Earth?
Splitting of continents creates isolation
opportunities for evolution (biodiversity)
Uplift of mountains creates new air &
precipitation patterns new habitats
(ecosystems)
EQ’s destroy human construction:habitation
and hwys
Volcanoes eruptions produce new land, rich
soil
10. The evidences that show
how plates move?
Magnetism
Seafloor spreading
Depth of marine sediments
Ring of fire
Comparing oceans
Hawaiian hot spot
A. Magnetic field lines
While magma cools, it
is imprinted with the
magnetic field lines.
Periodically the
magnetic poles reverse
directions. N becomes
S & S becomes N.
New magma will be
imprinted with the new
magnetic field lines.
Mirror image of stripes either
side of spreading zone
Depth of marine sediments &
age of marine sediments
Thin sediments by ocean ridge
Thicker sediments by trenches
What kind of plate boundary is
the Ring of Fire?
A) diverging ocean plate
B) converging ocean & continental
plates
C) converging ocean & ocean plates
D) transform fault zone
What’s the answer?
Ring of Fire– add this into notes
Subduction zones around Pacific Ocean
volcanoes
major earthquakes
Hawaiian Hot spot
What is does this show us?
Which is the youngest and oldest island?
Comparing Oceans
Pacific Ocean is Atlantic Ocean is
shrinking widening
Subduction zones Spreading zones
Oldest sediments Oldest sediments
are farthest from are farthest from
spreading zone spreading zone
11. 3 types of Plate
Boundaries
1) diverging, spreading plates
2) collision, colliding, converging plates
3) sliding beside, transform faults
Guess!!
Divergent boundary
As the crust separates, the gap is filled
in with basalt.
There may hydrothermal vents
There may be a ridge
Overall the crust is young in this region
Diverging Zones aka spreading
center
CONTINENT OCEAN
Rift zone Creates new ocean
Valley w/ basalt floor
flows Mounds of basalt
E.g. Red Sea, Rift E.g. Mid-Atlantic
Valley in Africa Ridge, East Pacific
Rise
Convergent Ocean-Continent
Denser ocean crust is subducted under
Deep trench, strong earthquakes
Volcanic Mt range on continent
E.g. Andes Mts, Cascade Mts
Guess!!
Convergent Continent-
Continent
Piles & piles of crumpled, folded crust
= tall mountains
Thick crust, earthquakes
E.g. Himalayan Mts, Appalachian Mts,
Alps
Convergent Ocean-Ocean
Slower plate is subducted under
Deep trench, strong earthquakes,
tsunamis
Volcanic island archipelago
E.g. Aleutian Islands, Japanese Islands,
Indonesian Islands, Caribbean Islands
Transform Faults
2 plates sliding beside each other
Valleys, roads, fences offset
Lots of earthquakes
E.g. San Andreas Fault, Mendocino
Fracture zone
Right-transform Fault
Just a reminder…
California will not “fall” into the sea.
California is being divided into 2 pieces.
So. Calif is traveling northwesterly
towards Alaska on the Pacific Plate
Transform Faults
Permit differential spreading over the
spherical shape of Earth
12.earthquakes
EQ –seismic event
A movement in earth’s crust that
generates energy
EQ are caused by movement of a fault
Seismic Waves- p, s, l waves
Offset road
Offset stream, Carrizo Plain
13. How to find
an epicenter
The interval
between P and S
is used to
determine the
distance from an
epicenter.
3 s-p and 3
locations.
Triangulation
14. How they measure EQ
Mercalli scale
Richter Scale
Measure the amount
Measure the energy release
from a seismic event of ground shaking or
The number on the Richter scale goes up local damage
exponentially. Meaning that a 2 one the
Richter scale would be a 100, a 3 one the
Richter scale would be a 1000 and so on.
So a 6 is 1 000 000 while a 5 is 100 000 so
it is ten times the power.
15. Lava flows
fissure
a crack in the
crust
Eg. Iceland
Hot Spot
A weak point near middle in the crust
where lava erupts
E.g. Hawaiian Islands
Global volcanic hot spots
Types of Volcanos
Shield volcano Cinder cone Composite
volcano
Huge, shallow sided Small steep sided Mid sided cone
cones cone thicker and alternating lava and
Form from fast, thin sediment layers
slower
lava Mixture lava such as
Non explosive Rhyolite tends andesite
No gas pressure plug the cone A lot gas pressure
Flows like ketchup and build up Very explosive
Divergent or hot spot pressure Subduction
Ex. Hawaiian islands Ex Mt. St Helens
or iceland
Tsunami
caused by EQ in or near ocean
Tidal waves are caused by storms like
hurricanes
Satellite buoy for people in low lying
areas
The End
Of Plate
Tectonics
Presentation