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Forces the Shape the Earth
8.6.5 Explain the concepts of
continental drift and plate
tectonics.
New Zealand Earthquake
• The earthquake that
devastated a city in New
Zealand tore open a new 11ft
faultine in the Earth’s surface.
• The 7.1-magnitude quake
which hit Christchurch, the
country’s second-largest city,
destroyed about 500 buildings
and caused an estimated
£930million of damage.
• But hundreds of lives were
saved by tough building rules,
it was claimed. Only two
injuries were reported.
New Zealand Earthquake
Seismograph
New Zealand Earthquake
New Zealand Earthquake
• The quake was caused by the
continuing collision between
the Pacific and Australian
tectonic plates, said Professor
Mark Quigley, of Canterbury
University.
• ‘One side of the Earth has
lurched to the right ... up to 11ft
and in some places been
thrust up,’ he said. ‘We went
and saw two houses that were
completely snapped in half by
the earthquake.’
The Pacific plate is gradually being pushed beneath the
Australian plate, which caused Friday's massive
earthquake
New Zealand Earthquake
Earth’s Major Plates
• The map of the Earth is always changing;
not only are the underlying plates moving,
but the plates change in size. Also, the sea
level changes over time (as the
temperature on Earth varies and the poles
melt or freeze to varied extents), covering
or exposing different amounts of crust.
Earth’s Major Plates
• The current continental and oceanic plates
include: the Eurasian plate, AustralianIndian plate, Philippine plate, Pacific plate,
Juan de Fuca plate, Nazca plate, Cocos
plate, North American plate, Caribbean
plate, South American plate, African plate,
Arabian plate, the Antarctic plate, and the
Scotia plate. These plates consist of
smaller sub-plates.
1. Earth’s Major Plates
PLATE TECTONICS
• PLATE TECTONICS
The theory of plate tectonics (meaning
"plate structure") was developed in the
1960's. This theory explains the movement
of the Earth's plates (which has since been
documented scientifically) and also
explains the cause of earthquakes,
volcanoes, oceanic trenches, mountain
range formation, and many other geologic
phenomenon.
2. Earth’s Crust
TYPES OF PLATE MOVEMENT
• TYPES OF PLATE MOVEMENT: Divergence,
Convergence, and Lateral Slipping
At the boundaries of the plates, various
deformations occur as the plates interact; they
separate from one another (seafloor spreading),
collide (forming mountain ranges), slip past one
another (subduction zones, in which plates
undergo destruction and remelting), and slip
laterally.
3. Convergent Boundaries
• The plates move in three
different ways. One way
they move is together
→←. Convergent
boundaries are places
where two plates come
together. When two
plates move together, one
can expect to find a great
deal of volcanoes,
earthquakes and
mountain building. One
can also see subduction
zones, places where one
plate is slipping below
another plate
4. Divergent Boundaries
•
Another way plates move is apart
↔. Places where the plates move
apart are called divergent
boundaries. When plates move
apart, sometimes land will split
apart. For instance, Iceland is
located over a divergent boundary
and eventually the island will split
in half. One can also find rift zones
at divergent boundaries. When two
plates move apart, it forms a rift, or
crack, in the Earth’s crust. From
this rift flows molten hot lava from
beneath. This can result, over time,
in a mountain range. When the
molten lava flows from an
underwater rift, it produces new
seafloor. One well known rift zone
is The Mid-Atlantic Ridge, located
in the middle of the Atlantic Ocean.
In this location, the seafloor is
expanding as we speak.
5. Transform Boundaries
• Plates can also grind
against one another ↑↓.
Places where this occurs
are called transform
boundaries. When plates
rub against one another,
they can produce a fault.
A fault is a crack in the
Earth’s crust. The San
Andreas Fault is an exam
of a transform boundary.
6. "Hot Spots"
• The exception to this
arrangement are "Hot Spots"
which are plumes of hot
material (rather than belts) in
the middle of plates. These
spots stay stationary while the
plate moves above it. The spot
melts through the plate like a
blow torch and produces a
volcano above it. As the plate
moves, the spot melts through
another spot producing a chain
of volcanic islands. Hawaii is
an example of a hot spot island
chain.
1. What type of boundary?
2. Types of Plate Boundaries
3. Evidence of Continental Drift
•
•
•
•
1. Puzzle Fit of the continents to form Pangaea
2. Fossil Evidence
3. Glacial Evidence (see below)
4. Coal in Antarctica- coal is formed in tropical
swamps. Coal was formed when Antarctica was
closer to the equator.
• 5. Magnetic Stripes on the ocean floor
• 6. Mountain Chains appear where they should if
continents are colliding
4. Fossil Evidence
• Fossil Evidence- in
the picture above,
fossils of many landliving have been
found on opposite
shores. When
Pangaea is reassembled, the fossils
match up.
4. Fossil Evidence
• Glossopteris – A
Fern
• Cynognathus – A
Land Reptile
• Lystrosaurus – A
Land Reptile
• Mesosaurus – A
freshwater reptile
5. Glacial Evidence
• when Pangaea is reassembled, there is
evidence of a single ice
sheet affecting many of
the southern continents.
When viewed this way,
this sheet leaves
consistent evidence of a
single glacier. When
viewed on the current
continents, it is
inconsistent and even
highly improbable. For
example, India, which is
north or the Equator, has
glacial evidence coming
from the south!
5. Glacial Evidence
• Rocks and sediments
are added to glaciers
through various
processes. Glaciers
erode the terrain
principally through
two methods:
abrasion and
plucking
5. Glacial Evidence
• As the glacier flows over the
bedrock's fractured surface, it
softens and lifts blocks of rock
that are brought into the ice.
This process is known as
plucking, and it is produced
when subglacial water
penetrates the fractures and
the subsequent freezing
expansion separates them
from the bedrock. When the
ice expands, it acts as a lever
that loosens the rock by lifting
it. This way, sediments of all
sizes become part of the
glacier's load. The rocks frozen
into the bottom of the ice then
act like grit in sandpaper.
The Baltoro Glacier in the
Karakoram Mountains, Pakistan
The ice calving end of the Perito
Moreno Glacier, in the western
Patagonia of Argentina
Icebergs breaking off glaciers at
Cape York, Greenland
Magnetic Stripes on the ocean floor
• When the molten rock
hardens, the magnetic
minerals in the rock align
themselves with the Earth's
magnetic field. Scientists
discovered that the Earth's
magnetic field has reversed
itself many times, at intervals
of roughly every 100,000
years. The pattern they
observed makes sense if the
ocean floor is being formed
at the ridge and gradually
pushed outward in both
directions
6. Mountain Chains
• 6. Mountain Chains
appear where they
should if continents
are colliding