Transcript Plate Tectonics

Plate
Tectonics
By Nadine Kummer
Alfred Wegner’s
theory of
continental drift &
Supercontinent
theory
Continental drift
Wegner’s theory
Stamp from
Austria
His theory was that all the
continents like we know them
today were one big
Supercontinent.
He thought about it because
some continents have similar
shapes and he compared that
with a newspaper. He called
that the torn newspaper
analogy. It means to put
together all the pieces and see
if they have same
characteristics
Evidence
he explained it by showing
the similarity between the
land lines of south america
and africa.
It also explained some
mountain chaines.
Problems with theory
the biggest problem was the
supporting evidence. It was
only a theory and he his only
evidence were the landforms.
Nothing scientific.
Only seafloor spreading was
the supporting evidence
The Supercontinent
Supercontinent cycle
The supercontinent cycle
is a prediction about how
the continents will move in
the future, based on how
they moved in the past.
Pangaea was the last
existing supercontinent in
earth history (300-150 Ma
years ago)
Panthalassa was the ocean
that surrounded Pangaea.
Accretion is the increase
of the size of the
tectonic plate by
addition of material
along a convergent
boundary.
Rifting is development of
a rift, which is a linear
zone where earths crust
and lithosphere are
pulled apart.
How plate movements alter
climates and evolution
Climates:
More land at higher latitude…
Different ocean locations and
therefore heat transport
Different global atmospheric
circulation
Overland more glaciers,
higher albedo and cooler
temperatures
Evolution
Because there are different
continents with different
climates, a lot of different
animals developed. It all
depended on the climate.
Even if it was the same animal
on Pangaea, it is now
transformed and has the right
conditions for the climate on
the continent.
For example the mammoth.
Because of plate movements
they lives in hotter areas and
lost their fur. That is what we
know today as elephants.
Theory of plate
tectonics
Lithosphere
The lithosphere is the outer shell
of a rocky planet. On Earth, it
comprises the crust and the
portion of the upper mantle
that is elastically on time scales
of thousands of years or
greater.
Asthenosphere
The asthenosphere is the
mechanically weak and
ductilely-deforming region of
the upper mantle of the Earth.
It lies below the lithosphere
How plates move
Plates at our planet’s
surface move because of
the heat inside the Earth’s
core that causes molten
rock in the mantle layer to
move. It moves in a pattern
called a convection cell.
These form when warm
material rises, cools, and
sinks down. As the cooled
material sinks down, it is
warmed and rises again.
Three types of plate
boundaries
Divergent
boundaries
 Convergent
boundaries
 Transform
boundaries
for explanation look
at picture on the left

Isostatsy
Equilibrium in the earth's
crust such that the forces
tending to elevate
landmasses balance the
forces tending to
depress landmasses.
Isostatic adjustments
The movement
of the
lithosphere to
reach isostasy
are called
isostatic
adjustment.
Stress
The force acting on a rock
or another solid to deform
it, measured in kilograms
per square centimeter or
pounds per square inch.
When the stress is really high
and strong solids may deform
Divergent Boundary
Seafloor spreading
The force acting on a rock or
another solid to deform it,
measured in kilograms per
square centimeter or pounds
per square inch.
Mid-ocean ridges
Mid-Atlantic Ridge
An example of an oceanic
ridge is the Mid-Atlantic
Ridge. It is one part of a system
of mid-oceanic ridges that
stretches for 50,000 miles
through the world's
oceans. The underwater
mountains of the ridge may not
be more than two miles higher
than the surrounding sea floor.
Paleomagnetism
is the study of the record of
the Earth's magnetic field in
rocks. Certain minerals in
rocks lock-in a record of the
direction and intensity of the
magnetic field when they
form.
Magnetic reversals
A geomagnetic reversal is a
change in the Earth's magnetic
field such that the positions of
magnetic north and magnetic
south are interchanged
Magnetic Symmetry
The ages of seafloor rocks are
symmetrical, that supported
the theory of seafloor
spreading
Normal faults
Related landforms
Are what helped
Wegener to establish
his theory. He
compared the
landforms of the
continents and found
out that the east
coast of south
America looks like the
west coast of Africa.
Convergent
Boundary
Subduction zone
Regions where portions of
the earth's tectonic plates
are diving beneath other
plates, into the earth's
interior. They are defined
by deep oceanic
trenches, lines of
volcanoes parallel to the
trenches, and zones of
large earthquakes that
extend from the trenches
landward.
Volcanoes
is an opening, or rupture, in a
planet's surface or crust, which
allows hot magma, volcanic
ash and gases to escape from
the magma chamber below
the surface.
Magma
Arenal volcano of Costa
Rica
Piping hot
magma
chamber
is a mixture of molten or semimolten rock, volatiles and
solids[1] that is found beneath
the surface of the Earth, and is
expected to exist on other
terrestrial planets. Besides
molten rock, magma may also
contain suspended crystals and
dissolved gas and sometimes
also gas bubbles.
Three conditions under
which lava forms
Temperature of rock
rises above the
melting point of the
minerals the rock is
composed of.
If enough pressure is
removed from the
rock the melting point
will decrease and the
rock will melt.
The addition of fluids
such as water, may
decrease the melting
point and cause the
rock to melt.
Lava
Lava refers both to
molten rock
expelled by a
volcano during an
eruption and the
resulting rock after
solidification and
cooling. This molten
rock is formed in
the interior of some
planets, including
Earth, and some of
their satellites
Lava flow
Volcano
common
locations
Convergent plate
boundaries
major zone of
active
volcanoes
encircling the
pacific ocean is
the ring of fire
It is the location with the most (75%)
volcanic activity on earth with
over 450 volcanoes
Pyroclastic material
Pyroclastic material is another name for a
cloud of ash, lava fragments carried
through the air, and vapor. Such a
flow is usually very hot, and moves
rapidly. Pyroclastic flows can extend
miles from the volcano, and destroy
life and property within their paths.
viscosity
The resistance of a fluid to flow. Fluids with
a high viscosity resist flow. Fluids with a
low viscosity flow freely.
how magma contents
produce explosive
eruptions
Explosive eruptions are favored by high
gas content & high viscosity magmas.
The explosive bursting of bubbles
fragments the magma into clots of
liquid that cool as they fall through
the air. These solid particles become
pyroclasts or volcanic ash.
Types of volcano
 Composite Volcanoes (also
called strato volcanoes),
Mt. St. Helens, Mt. Rainier,
Pinatubo, Mt. Fuji, Merapi,
Galeras, Cotopaxi
 Shield Volcanoes (also
called shields), Kilauea and
Mauna Loa Fernandina
,Karthala, Erta Ale,
Tolbachik, Masaya
 Cinder Cones, Paricutin in
Mexico. In Iceland, Surter I
and Surter II
 Spatter Cones Isla
Bartolomé, adjacent to the
large island of Santiago,
Galapagos Islands
 Complex Volcanoes (also
called compound
volcanoes). McDonald
Island ,Long Island ,
Guntur ,Dieng ,Dukono ,
Unzen ,Asama ,Iwate
Shield
Shield volcanoes
are huge in
size. They are
built by many
layers of runny
lava flows. Lava
spills out of a
central vent or
group of
vents. A broad
shaped, gently
sloping cone is
formed. This is
caused by the
very fluid,
basaltic lava
which can't be
piled up into
steep mounds.
Cinder cones
A cinder cone is a steep
conical hill formed
above a vent. Cinder
cones are among the
most common
volcanic landforms
found in the
world. They aren't
famous as their
eruptions usually don't
cause any loss of
life. Cinder cones are
chiefly formed by
Strombolian
eruptions. The cones
usually grow up in
groups and they often
occur on the flanks of
strato volcanoes and
shield volcanoes.
Composite volcanoes



Composite volcanoes,
also called strato
volcanoes, are formed
by alternating layers of
lava and rock
fragments. This is the
reason they are called
composite.
Strato-volcanoes
often form impressive,
snow-capped peaks
which are often
exceeding 2500m in
height, 1000sq.km in
surface, and 400km3 in
volume.
Between eruptions
they are often so quiet
they seem extinct. To
witness the start of a
great eruption requires
luck or very careful
surveillance.
Caldera
A caldera is a
cauldron-like
volcanic feature
usually formed by
the collapse of
land following a
volcanic eruption.
They are sometimes
confused with
volcanic craters.
The word comes
from Spanish
caldera, and this
from Latin
CALDARIA,
meaning "cooking
pot".
 Islands
close to
new zealand
Continental+
oceanic crust
When an oceanic plate
pushes into and subducts
under a continental plate,
the overriding continental
plate is lifted up and a
mountain range is created.
This can cause volcanism
and mountain chains
For example islands near
new Zealand
Oceanic+ oceanic
When two oceanic
plates converge
one is usually
subducted under
the other and in the
process a deep
oceanic trench is
formed. The
Marianas Trench, for
example, is a deep
trench created as
the result of the
Phillipine Plate
subducting under
the Pacific Plate.
Marianas trench
Collision zone
Examples:
Philippine Mobile Belt
Molucca Sea Collision
Zone
Carlin Unconformity
A collision zone occurs
when tectonic plates
meeting at a
convergent boundary
both bear continental
lithosphere. As
continental lithosphere
is usually not
subducted due to its
relative low density,
the result is a complex
area of orogeny
involving folding and
thrust faulting as the
blocks of continental
crust pile up above
the subduction zone.
Continental+continental
crust
When two continents meet
head-on, neither is subducted
because the continental rocks
are relatively light and, like two
colliding icebergs, resist
downward motion. Instead, the
crust tends to buckle and be
pushed upward or sideways. The
collision of India into Asia 50
million years ago caused the
Eurasian Plate to crumple up and
override the Indian Plate. After
the collision, the slow continuous
convergence of the two plates
over millions of years pushed up
the Himalayas and the Tibetan
Plateau to their present heights.
Most of this growth occurred
during the past 10 million years.
Compression and
uplift….landforms produced
Transform
boundary
Reverse faults
Along a reverse fault one rocky block is
pushed up relative to rock on the
other side. For example the Sierra
madre, California
Strike-slip faults


Strike-slip faults have a different
type of movement than normal
and reverse faults. You probably
noticed that the blocks that move
on either side of a reverse or normal
fault slide up or down along a
dipping fault surface.
The rocky blocks on either side of
strike-slip faults, on the other hand,
scrape along side-by-side. You can
see in the illustration that the
movement is horizontal and the
rock layers beneath the surface
haven't been moved up or down
on either side of the fault. For
example the san andreas fault.
Tension
Stress that stretches or extends
rocks, so that they become
thinner vertically and longer
laterally. Tension may be
caused by divergence or rifting.
Shear stress
Shear stress is the stress
component parallel to a given
surface, such as a fault plane,
that results from forces applied
parallel to the surface or from
remote forces transmitted
through the surrounding rock.
Related landforms
Fault block mountains are very large
blocks of rock, sometimes hundreds
of kilometers in extent, created by
tectonic and localized stresses in the
Earth's crust.
A Graben is a depressed block of
land bordered by parallel faults.
Graben is German for ditch or
trench.
Other related
landforms
Dome mountains
Yosemite national park
These mountains are the result
of a great amount of
melted rock pushing its
way up under the earth.
Over thousands of years
the dome mountains form
in the place where the
earth is pushed up.
Hot spots
Most famous
hotspot on
earth…the
Hawaiian
islands
The places known as hotspots
or hot spots in geology are
volcanic regions thought
to be fed by underlying
mantle that is anomalously
hot compared with the
mantle elsewhere. They
may be on, near to, or far
from tectonic plate
boundaries.
Earthquakes
Elastic rebound
Describes how energy is spread
during an earthquake. Rocks
on opposite sides of a fault and
suffer under force and shift so
that they deform. Than a
sudden movement occurs
along the fault and the
released energy lets the rocks
break and snap back to their
original form
Seismology
Is the study of earthquakes and
different waves that run
through the earth or other
planets. Also included are the
effects of earthquakes, like for
example tsunamis
 Seismograph
Is an instrument used to
measure and record ground
motion.
Focus
It is the point under the earth
surface where the seismic
come from while an
earthquake
Epicenter
Is the location on the earth’s
surface directly above the
focus. This is the location on the
surface where the seismic
energy is the biggest.
Seismic waves
Seismic waves are produced
by the energy released by
earthquakes; the waves
radiate from the quake’s
epicenter
Body waves
A
body wave is a seismic wave that moves
through the interior of the earth, as opposed to
surface waves that travel near the earth's surface.
P and S waves are body waves. Each type of
wave shakes the ground in different ways.
P
waves
is
a seismic body wave that shakes the ground
back and forth in the same direction and the
opposite direction as the direction the wave is
moving.
S
waves

is a seismic body wave that shakes the ground
back and forth perpendicular to the direction the
wave is moving.
Surface waves
is a seismic seismic wave that is trapped
near the surface of the earth.

How seismic waves led
to determination of
earth’s interior
S waves can only go
through solids
P waves can go through
all states of matter
And because you don’t
have any seismic
energy on the other
side of the earth
during an earthquake,
it means that there is a
core and you can also
say where the earth is
liquid and where it is
solid
Earthquakes not resulting from
movement along plate
boundaries
Are also called intraplate
earthquakes. Other than
interplate earthquakes they
occur in a tectonic plate and
not between them. Even today
scientists cannot explain why
these occur. One of the
biggest problems is that they
are not predictbale because
we don’t know anything about
them.
Earthquake in
china
Magnitude
A measure of the
amount of energy
released by an
earthquake, as
indicated on the Richter
Scale.
Intensity
The intensity of an
earthquake at a
particular locality
indicates the violence of
earth motion produced
there by the earthquake.
It is determined from
reported effects of the
tremor on human beings,
furniture, buildings,
geological structure,
etc.


Mercalli scale
The Mercalli intensity
scale is a seismic
scale used for
measuring the intensity
of an earthquake. It
measures the effects of
an earthquake, and is
distinct from
the moment
magnitude usually
reported for an
earthquake (sometimes
described as the
obsolete Richter
magnitude), which is a
measure of
the energy released.
The intensity of an
earthquake is not totally
determined by its
magnitude.
Tsunami
is a series of water waves caused
by the displacement of a large
volume of a body of water,
typically an ocean or a large
lake. Earthquakes, volcanic
eruptions and other underwater
explosions(including detonations of
underwater nuclear devices),
landslides, glacier
calvings, meteorite impacts and
other disturbances above or below
water all have the potential to
generate a tsunami