The student knows that plate tectonics is the global mechanism for major geologic processes and that heat transfer, governed by the principles of thermodynamics, is the driving force. The student is expected to:

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TEK 10 Solid Earth
The student knows that plate tectonics is the
global mechanism for major geologic processes and
that heat transfer, governed by the principles of
thermodynamics, is the driving force. The
student is expected to

• C) Explain how plate tectonics accounts for
  geologic processes and features, including
  sea-floor spreading, ocean ridges and rift
  valleys, subduction zones, earthquakes,
  volcanoes, mountain ranges, hot spots, and
  hydrothermal vents
• E) distinguish the location, type, and relative
  motion of convergent, divergent, and transform
  plate boundaries using evidence from the
  distribution of earthquakes and volcanoes

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How Plate Tectonics Accounts For
Sea-Floor Spreading

• Sea-Floor Spreading is the process in which the
  ocean floor is extended when two plates move
  apart.  As the plates move apart, the rocks break
  and form a crack between the plates. 
• Earthquakes occur along the plate boundary. 
• Magma rises through the cracks and seeps out onto
  the ocean floor like a long, thin, undersea
  volcano.

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How Plate Tectonics Accounts For
Ocean Ridges and Rift Valleys

• As magma meets the water, it cools and
  solidifies, adding to the edges of the plates. 
• As magma piles up along the crack, a long chain
  of mountains forms gradually on the ocean floor. 
  This chain is called an oceanic ridge. 
• When these boundaries form on the continents,
  they are called Rift Valleys.
• The boundaries where the plates move apart are
  'constructive' because new crust is being formed
  and added to the ocean floor. 

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. 
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How Plate Tectonics Accounts For
Hydrothermal Vents
As weve already learned, the Earth's tectonic
plates can move apart, collide, or slide past
each other. The Mid-Ocean Ridge system - the
Earth's underwater mountain range - arises where
the plates are moving apart. As the plates part,
the seafloor cracks. Cold seawater seeps down
into these cracks, becomes super-heated by magma,
and then bursts back out into the ocean, forming
hydrothermal vents.
These hydrothermal vent communities have evolved
some of the most interesting communities of
organisms on Earthperhaps showing us the place
where life on Earth originated.
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How Plate Tectonics Accounts For
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. Oceanic
plates grow more dense as they cool and move
further away from the Mid-Ocean Ridge
The older, heavier plate plunges steeply through
the athenosphere, and descends into the Earth,
where it forms a trench that can be as much as 70
miles wide, more than a thousand miles long, and
several miles deep.
The Marianas Trench, where the enormous Pacific
Plate is descending under the leading edge of the
Eurasian Plate, is the deepest sea floor in the
world. The Challenger Deep at the trenchs
southern end measures nearly 7 miles deep. If
Mount Everest was set down in the Pacific at this
place, there would still be well over a mile of
water left above it.
Only three descents into the trench have ever
been achieved. The first was the manned descent
by Trieste in 1960. This was followed by the
unmanned ROVs Kaiko in 1996 and Nereus in 2009.
Convergent boundaries are referred to as
destructive.
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How Plate Tectonics Accounts For
Earthquakes
One need only look at a map of tectonic plates,
and one of earthquake activity, to see the close
association. If we were to remove the clutter of
the minimal earthquakes, and only show those
equalling 7 or higher on the Richter scale, you
can see that all major earthquakes have been
centered along tectonic boundaries.
An earthquake, also known as a quake, tremor or
temblor, is the result of a sudden release of
energy in the Earth's crust that creates seismic
waves. Earthquake intensity is measured most
commonly in terms of the Richter Scale, where
each increase in whole number, yields a10-fold
increase in intensity. So, a magnitude 7
earthquake is 10 times stronger than a 6, and 100
times stronger than a 5etc.
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How Plate Tectonics Accounts For
Volcanoes
Volcanoes are generally found where tectonic
plates are diverging or converging. A mid-oceanic
ridge has examples of volcanoes caused by
divergent tectonic plates pulling apart the
Pacific Ring of Fire has examples of volcanoes
caused by convergent tectonic plates coming
together.
By contrast, volcanoes are usually not created
along transform boundaries, but they may form
where there is stretching and thinning of the
Earth's crust in the interiors of plates, such as
in the East African Rift, and the Rio Grande Rift
in North America. This type of volcanism falls
under the umbrella of "Plate hypothesis"
volcanism. Volcanism away from plate boundaries
has also been explained as mantle plumes. These
so-called "hotspots", for example Hawaii, are
hypothesized to arise from upwelling of magma
from the core-mantle boundary, 3,000 km deep in
the Earth.
A volcano is an opening, or rupture, in a
planet's surface or crust, which allows hot
magma, volcanic ash and gases to escape from
below the surface
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How Plate Tectonics Accounts For
Hot Spots
Although Hawaii is perhaps the best known
hotspot, others are thought to exist beneath the
oceans and continents. More than a hundred
hotspots beneath the Earth's crust have been
active during the past 10 million years. Most of
these are located under plate interiors, but some
occur near diverging plate boundaries. Some are
concentrated near the mid-oceanic ridge system,
such as beneath Iceland, the Azores, and the
Galapagos Islands.
A few hotspots are thought to exist below the
North American Plate. Perhaps the best known is
the hotspot presumed to exist under the
continental crust in the region of Yellowstone
National Park in northwestern Wyoming. There 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 was 600,000 years ago.
As you can see from prior ash layers, the area
affected by a volcanic eruption would be immense.
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How Plate Tectonics Accounts For
Mountain Ranges
When two continents carried on converging plates
ram into each other, they crumple and fold under
the enormous pressure, creating great mountain
ranges. The highest mountain range in the
world, the snow-capped Himalayas, is an example
of a continent-to-continent collision. This
immense mountain range began to form when two
large landmasses, India and Eurasia, driven by
tectonic plate movement, collided. Because both
landmasses have about the same rock density, one
plate could not be subducted under the other.
The pressure of the colliding plates could only
be relieved by thrusting skyward.
The existence of linear mountain chains on the
Earth makes the Earth unique in the solar system.
Although there is volcanism on Venus and Mars
and on some of the larger moons, there is no
evidence of linear mountain chains. Linear
mountains suggest the movement of a plate
boundary and the existence of active plate
tectonics
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Convergent, Divergent, and Transform
Weve already shown evidence of convergent and
divergent boundaries by looking at the
earthquake/volcanic activity maps. What about
transform boundaries?
Since transform boundaries are sliding past one
another, they are obviously a place of great
earth movement, and areas of high earthquake
activity.
Many earthquakes occur along transform plate
boundaries.
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Transform Faults

• Three types of transform faults
• Ridge-ridge
• Ridge-trench
• Trench-trench

are by far the most abundant. The active
displacement on these faults occurs only between
the ridge segments, as shown above. No movement
occurs along the rest of the fracture zone.
are much less common. They form an important
connection between diverging and converging
plates. The longest transform faults are all of
this kind.
are also rare. These faults appear to connect
trenches together.
Transform faults can connect convergent and
divergent plate boundaries in various
combinations. In all cases, the trend (or
movement) of a transform fault is parallel to the
direction of relative motion between plates.