Download tectonic plates.

Plate Tectonics
And Their Effects on the Earth
What are tectonic plates?
• Remember that the lithosphere is made of
plates of crust (both oceanic and continental).
• We call these plates of crust tectonic plates.
– The tectonic plates float on the liquid mantle
– Plates have boundaries (edges) that come into
contact with neighboring plates, causing
earthquakes and/or volcanic activity
How did tectonic plates form?
• Over time, smaller plates combined to
form larger plates. The thinnest parts of
the larger plates split to form the “edges”
we see today.
What are Subduction zones?
Areas where
oceanic plates
collide with
continental
plates
The oceanic crust
is pulled under
the continental
plate, where it
melts in the hot
magma.
What is Continental Drift?
• Proposed by Alfred Wegener in 1915
• States that the continents were once connected as a
larger land mass, before they were pulled apart. They are
still moving today.
• This theory was not accepted until we discovered
seafloor spreading years later.
Evidence for Alfred Wegener’s Theory
a. South America and Africa would
fit remarkably well, shoreline to
shoreline.
b. If the Americas were moved
next to Africa and Europe, there
would be a match of ancient
continental rocks and tectonic
(fold and fault) structures.
c. Pangaea – when Wegener placed
all the continents together like a
puzzle, it formed a large
landmass which he called Pangaea.
Fossil Evidence
Why do the plates move?
Plates move because heat is
being released from deep
inside the earth.
Convection currents causes
hot material to rise and
expand (plates diverge)
and cooler material to
sink and contract (plates
converge).
How does new crust form?
• Hot magma from the mantle spews out of
specific areas of the earth
• The magma cools, turning to rock
Three Types of Tectonic Plate
Boundaries
1. Divergent Boundries
2. Convergent Boundaries
3. Transform Plate Boundaries
Divergent Boundries
“pulled apart” AKA “rifting”
• Divergent plate boundaries are locations where
plates are moving away from one another.
• The rising current pushes up on the bottom of the
lithosphere, lifting it and flowing laterally beneath it.
This lateral flow causes the plate material above to
be dragged along in the direction of flow.
• At the crest of the uplift, the overlying plate is
stretched thin, breaks and pulls apart producing a
mid-ocean ridge
Consequences
Ex. Krafla Volcano in
northeastern Iceland.
Existing ground cracks have
widened and new ones
appear every few months.
From 1975 to 1984,
numerous episodes of
rifting (surface cracking)
and volcanic eruptions
took place along the Krafla
fissure zone.
Before erupting, the ground
would gradually rise 1-2 m
before abruptly dropping,
Between 1975 and 1984, the
displacements caused by
rifting totaled about 7 m.
East Africa
East Africa may be the site of
the Earth's next major
ocean.
Plate interactions in the region
provide scientists an opportunity to
study first hand how the Atlantic
may have begun to form about 200
million years ago.
Geologists believe that, if spreading
continues, the three plates that
meet at the edge of the presentday African continent will separate
completely, allowing the Indian
Ocean to flood the area and
making the easternmost corner of
Africa (the Horn of Africa) a large
island.
Convergent Boundaries
“plates colliding together”
• Two plates meet and push
on one another, until the
pressure gives way
• Responsible for forming
mountains, and producing
volcanic activity
• Biggest contributor towards
earthquakes
• Subduction zones occur
at convergent boundaries
Convergent plates can occur:
1. Between an oceanic and a
continental plate
2. Between two oceanic plates,
causes the formation of a trench,
subduction zone
3. Between two continental
plates, causes the formation of
mountains, the crust tends to
buckle and be pushed upward or
sideways.
Subduction Zones
• When two oceanic plates collide, the younger of the
two plates, because it is less dense,* will ride over the
edge of the older plate.
•The older, heavier
plate bends and
plunges steeply
through the
athenosphere, and
descending into the
earth, it forms a
trench that can be as
much as 70 miles
wide, more than a
thousand miles long,
and several miles
deep.
Trenches and Subduction
• Trenches are the deepest parts of the ocean floor
and are created by subduction.
• If we could pull a plug and drain the Pacific Ocean,
we would see a number of long narrow, curving
trenches thousands of kilometers long and 8 to 10
km deep cutting into the ocean floor.
Formation of Volcanoes
When subduction occurs
over millions of years,
the erupted lava and
volcanic debris pile up
on the ocean floor until
the volcano rises above
sea level to form an
island volcano.
Such volcanoes are
typically strung out in
chains called island
arcs. Volcanic island
arcs, which closely
parallel the trenches,
are generally curved.
Two Continental Plates Colliding
• Example: The Himalayan mountain
– 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.
– The Himalayas, towering as high as 8,854 m
above sea level, form the highest continental
mountains in the world.
Transform Plate Boundaries
“sliding across”
• The zone between two plates sliding
horizontally past one another
• Most transform faults are found on
the ocean floor.
• They commonly offset the active,
divergent spreading ridges, producing
zig-zag plate margins, and are
generally defined by shallow
earthquakes.
• However, a few occur on land
– Example - the San Andreas fault zone in
California
– This fault connects the East Pacific Rise,
a divergent boundary to the south, with
the South Gorda -- Juan de Fuca -Explorer Ridge, another divergent
boundary to the north.
San Andreas Fault
• The San Andreas fault zone is
about 1,300 km long and, in
places, tens of kilometers wide
• It slices through two thirds of the
length of California.
• Along it, the Pacific Plate has been
grinding horizontally past the North
American Plate for 10 million years,
at an average rate of about 5
cm/yr.
• Land on the west side of the fault
zone (on the Pacific Plate) is
moving in a northwesterly direction
relative to the land on the east side
of the fault zone (on the North
American Plate).
Earthquakes
• 80% of all earthquakes occur along the rim
of the ring of fire
• Most earthquakes occur at fault zones,
where tectonic plates collide or slide
against each other
• Immense stress builds up between plates.
When the stress is released quickly, it
sends massive vibrations to the surface
Ring of Fire
Tsunamis
• A series of ocean waves
that sends surges of water
onto land
• Caused by large, undersea
earthquakes at tectonic
plate boundaries
• When the plate rises or falls
suddenly, it displaces the
water above it, forming
rolling waves that will
become the tsunami
Hotspots
Hotspots
An area of volcanoes that form in the middle of a
tectonic plate
As the plate moves, the volcanoes on the surface move
with it and are eventually cut off from its magma
source
According to the hotspot theory, the
volcanoes of the Hawaiian chain should
get progressively older and become more
eroded the farther they travel beyond the
hotspot.
Kauai
5.5 million
years old
Hawaii
.7 million
years old
YELLOWSTONE
• Here are several calderas (large craters formed by the
ground collapse accompanying explosive volcanism) that
were produced by three gigantic eruptions during the
past two million years, the most recent of which occurred
about 600,000 years ago.
Yellowstone
• The thermal energy of the presumed Yellowstone hotspot fuels
more than 10,000 hot pools and springs, geysers (like Old
Faithful), and bubbling mudpots (pools of boiling mud).
• A large body of magma, capped by steam and hot water, still
exists beneath the caldera.
• Recent surveys demonstrate that
parts of the Yellowstone region rise
and fall by as much as 1 cm each
year However, These ground
movements are most likely caused by
hydrothermal pressure changes and
do not necessarily mean it will erupt
any time soon.