Transcript Plate Boundaries

The Moving Plates
Boundary Interactions and
the Origin of Earth Features
Unit Five: Natural Disasters
Part C
Layers of the Earth:
Inner Core
 Outer Core
 Mantle
 Asthenosphere
 Lithosphere
 The lithosphere is
made of the crust and
rigid upper mantle. It is
broken into about 14
large plates.

Mass:
Percentages From Inside to
Outside:
 Core
32%
 Mantle
66%
 Crust
2%
The Core
 Composed of Iron and Nickel
 Inner Core – solid
 Outer Core – liquid
 High heat originates from gravitational pressure
and radioactivity of heavy, unstable atoms.
 Heat source for convection in the mantle.
Radioactive Decay
 Some atoms are unstable and decay or
breakdown on their own.
They release small particles.
 Certain heavy elements in the core, like
Uranium, decay in such a way that they actually
give off radiation.
 Gamma rays given off by decaying heavy
elements in the core heat it up, like a flame
heats a pot of soup.
Magnetosphere (or E-M Field)
The iron in the Earth’s
core creates a magnetic
blanket around our
planet.
 It protects us from deadly
radiation from the sun,
deflecting it like a shield.

Heat Transfer
Heat moves through different materials in different
ways.
 Conduction = moves through solids by contact.

An example of conduction is burning your forehead with a
curling iron.

Convection = moves through fluids as density changes
hotter = less dense, rises
cooler = more dense, sinks

Radiation = Decay of radioactive materials
Gamma rays, alpha particles, etc.
Heat Transfer cont.
 Heat is generated in the core via radiation.
 The heat in the core moves up through the lower
solid mantle through conduction (or direct
contact.)
 The upper mantle is partially molten and plastic,
meaning it is able to flow. Heat moves through it
by convection.
It is made of fluid rock, known as magma.
Heat Transfer cont.
 The heat from the lower mantle moves into the
upper mantle through convection.
Magma is heated and becomes less dense so it
rises.
When it nears the crust, it cools, becomes more
dense, and begins to sink.
 The rising and falling current is like a conveyor
belt, moving in a circular pattern forever. This
current moves the plates.
Convection in the Upper Mantle
(Asthenosphere):
The Asthenosphere
The mantle is the
thickest layer of the
Earth. It is mostly solid
and very dense.
 The mid to upper layer -the asthenosphere -- is
fluid and supports the
rigid, solid layer above it.

The Lithosphere
The “lithosphere”
contains continental
crust & oceanic crust &
the rigid portion of the
upper mantle
 The lithosphere is the
“plate” in plate tectonics

The Major Plates
Location of Earthquakes and
Volcanoes
Plate Interactions:
Types of Plate Boundaries:
Divergent (tensional force = )
 Transform (shearing force = )
 Convergent (compressional force = )

Continental to continental collision
Continental to oceanic collision
Oceanic to oceanic collision

Subduction (compressional force = )
Continental to oceanic collision

Hot Spots
Divergent Plate Boundary:



Plates move away from each
other.
New crust is formed at the
boundary between the plates
in a central rift valley --> Lava
flows out and is added to
both plates.
Features: mid-ocean ridge,
rift, fissure, rift valley, lava
flows, shallow earthquakes
Ocean Ridges & Rises:
Ridges are the longest chains of
mountains found on Earth,
looking like the seams on a
baseball.
 A rift valley runs down the center
and the ridge is offset along its
length.
 Lava flows out from the central
fissure, adding new sea floor to
the edges of the plates.
 Small earthquakes are frequent
along the ridge’s transform
faults.
 Ex. = Mid-Atlantic Ridge, East
Pacific Rise, Antarctic Ridge,
Mid-Indian Ridge.

Magnetic Polarity:
Magnetic Polarity:
The rocks forming along the edges of
the mid-ocean ridge show a banded
pattern of polarity reversals in the
Earth’s magnetic field.
 The rocks closets to the ridge are the
youngest and the rocks farthest away
are the oldest.
 The age of the rocks near the coasts
of N. America and Europe show that
they formed 200 million years ago-just like Wegener speculated!

Divergent Boundary (cont):
 Divergent boundaries form over time:
Step 1. Continental Bulge -- magma pushes up.
Step 2. Rift Valley -- land rifts apart and new crust is created.
Ex. = East African Rift Valley.
Step 3. Linear Sea -- rift valley floods with ocean water and
becomes a long, thin sea. Ex. = Red Sea.
Step 4. Ocean -- millions of years later, the sea widens to
oceanic proportions. A mid-ocean ridge with a rift valley is found
in the middle. Ex. = Atlantic Ocean.*
*When one ocean opens, another has to close!
Transform Boundary:
At a transform boundary,
plates slide past each
other
 The San Andreas Fault is
an example of a
transform boundary

The North American Plate
is sliding past the Pacific
Plate.
Transform Boundary:




2 or more plates slide past
each other slowly at a fault.
Stress builds up in the rocks
over time and slippage
occurs abruptly. The energy
released causes an
earthquake.
Features: fault, shallow
hypocenter earthquakes
Ex. = San Andreas Fault,
California (N. Am plate +
Pacific plate)
C-C Convergent Boundary:



Continental to continental
convergence creates folded,
non-volcanic mountains.
A period of mountain building
is called an orogeny.
The densities of the two
continental plates are equal,
so they bend upwards. The
heat and pressure created by
the slow, unstoppable plate
motion folds the rock layers.
Syncline
Anticline
Non-Volcanic Mountain Ranges
Mountains form when the
two plates collide and get
shorter and thicker. The tops
are eroded by wind, water,
and ice.
Ex. = Appalachians, Atlas,
Alps, Caucusus, Himalayas,
& Urals
C-O Convergent Boundary:



Continental to oceanic convergence
exhibits the collision of different types
of crust. Ocean crust is most dense &
sinks beneath the continental crust
into the asthenosphere and melts.
Features: subduction zone, oceanic
trench (deepest parts of the Earth’s
surface), deep hypocenter
earthquakes, volcanic coastal
mountains, and volcanic island arcs.
Ex. = Andes (S. America), Cascades
(N. America), Japanese Is., Philippine
Is., Java & Sumatra, Caribbean Is.
C-O Convergent Boundary:
 Most trenches are
named for the country or
islands they parallel; i.e.
Peru-Chile, Japan,
Filipino, Java, Aleutian,
Caribbean, etc.
Deep Earthquakes!
O-O Convergent Boundary
Older plate subducts
beneath younger plate
 Very deep trench
 Part of subducted plate
melts and forms
volcanoes on ocean floor
 “Island Arcs” if volcanoes
rise above ocean

Aleutian Islands, Alaska
The Rocky Mtns Are Weird:



The Rockies formed when
the N. American plate overran the Pacific Plate and the
East Pacific Rise (the Kula &
Farallon Plates).
The heat from the mid-ocean
rift valley created a range of
mountains.
Plutons (bubbles of magma)
pushed up the land, then
were eroded by moving ice
into the jagged peaks visible
today.
Hot Spots:




Hot Spots are volcanic
regions in the middle of
plates, away from edges.
They feature single shield
volcanoes (continental or
island), hot springs and
geysers.
They form as a column of
magma punches through a
plate as it passes over.
Ex. = Hawaii, Bermuda, &
Yellowstone Natl. Park.
Hot Spots of the World:
Earth Features:
Plate Tectonics Cannot Yet
Explain:
-Tectonics of Earliest Earth
-Location of Many Small Plate Fragments
-Future Plate Motions
-Global Pattern of Plates (Is there a geometrical
pattern?)
-How and Where Plates Will Fragment
-Details of Driving Mechanism