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Term
Plate
Asthenosphere
Tectonics
Lithosphere
Folding
Faulting
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Description
a rigid slab of solid lithosphere rock
that has defined boundaries and floats
on the denser rocks of the
asthenosphere
the plastic (part solid, part liquid)
layer of the upper mantle directly
below the lithosphere that can flow
slowly when put under constant
pressure.
the processes that deform the earth’s
lithosphere and the rock structures
and surface features created by these
processes
the solid outer layer of the earth where
the rocks are less dense and more rigid
than those of the asthenosphere
below; includes the top part of the
mantle and all of the crust.
the process that bends and twists rocks
through compression or squeezing
the process by which rocks move past
one another along a fracture or
cracking the earth’s crust, usually
occurring where plates are separating,
sliding past one another, or colliding
Hot Spot
a point on the earth’s surface where
strong upward convection currents or
plumes of hot magma in the upper
mantle push up below the plates of the
lithosphere causing volcanic activity
Converging plate boundary
the boundary between two plates that
are moving towards one another
the boundary between two plates that
are moving apart or separating, at a
mid-ocean ridge
Diverging plate boundary
Transform plate boundary
Subduction zone
the boundary between two plates that
are slipping or sliding past one
another
the zone where an oceanic plate is
sinking below a plate containing
continents at a converging plate
Sea-floor spreading
boundary
The process that creates new sea floor
as plates spread apart or separate at
mid-ocean ridges
Viscosity
The resistance to flow of a liquid, such
as magma or molten rock
Transform Faults
A fault formed by the horizontal
movement of the earth’s crust,
occurring where two plates are sliding
past one another
Fault Scarps
The often straight, continuous cliff
created by the uplift of the earth’s
crust along a fault line
Strike-slip Faults
A fault where two sections of the
earth’s crust move almost horizontally
past each other
Subduction
The downward movement and eventual
melting of an oceanic plate as it sinks into the
asthenosphere along converging plate
boundaries
Volcanic Necks
A block of hard rock left standing above the
landscape when an extinct composite volcano
is eroded away over millions of years.
Composite Volcanoes
A smooth-sloped volcanic peak with a summit crater made
up of alternating layers of ash and lava, formed from
andesitic magma at subduction zones
Anticlines
Rock beds that have been
folded or bent upwards to form
a hill or mountain
Synclines
Rock beds that have been
folded or bent downwards to
form a valley
Andesitic Magmas:
Highly viscous, silica-rich, gaseous, molten rock formed by the melting of subducting oceanic plates in
the asthenosphere that produces violent volcanic activity
Continental Volcanic Arcs:
An arc-like chain of volcanic mountains formed on a continent bordering a subduction zone at a converging plate boundary
Island Arcs:
An arc-shaped chain of volcanic mountains, often rising above sea level as islands, formed on the ocean floor at a subduction zone at a
converging plate boundary
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Cinder Cones:
A steep-sided volcanic peak, with a large summit crater, composed mainly of volcanic ash and rock spewed out of the vent during
explosive eruptions
Dykes:
An intrusion of magma that cuts across the original rock beds and cools beneath the earth’s surface to form igneous intrusive rock
Sills:
An intrusion of magma that follows the layers of the original rock beds and cools beneath the earth’s surface to form igneous intrusive
rock
Laccoliths:
An intrusion that forces apart the local rock beds to form an enlarged, dome-shaped chamber of magma that cools to form igneous
intrusive rock
Batholiths:
A massive, often bottomless intrusion of magma that cools beneath the earth[s surface to form igneous intrusive rock
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Recumbent Folds:
A fold that has been compressed so severely that it falls over or is overturned
Vulcanism: the movement of molten rock, or magma, beneath or above the earth’s
surface
Mid-ocean ridge:
The ridge that marks the boundary between two or more separating plates
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Magnetic Reversals:
A periodic change in the polarity of the earth’s magnetic field from normal (north) to
reversed (south), or vice versa
: Normal Faults:
A fault resulting from the upward movement on one side of a fault line and/or the
downward movement on the other, forming a cliff or fault scarp
Reverse Faults:
A fault where one block of the earth’s crust moves upward against another
Pillow lavas:
A pillow-shaped igneous rock formed by rapid surface cooling of magma in direct
contact with cold ocean water, often at mid-ocean ridges
Horst or Block Mountains:
A steep-sided mountain formed where a block of the earth’s crust has been squeezed
upward between two parallel fault lines; also known as a block mountain
Tilted Block Mountain:
A mountain formed where a block of the earth’s crust moves upward at an angle
between two parallel fault lines
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Shield volcanoes:
A gently rising, smooth-sloped volcanic dome formed from very fluid (low viscosity)
basaltic lava typical of mid-ocean ridges and hot spots.
Rift valley:
A steep sided valley formed when a block of the earth’s crust falls down getween two
parallel fault lines; also know as a graben.
1. What sets the continental plates in motion? Describe the process.
Convention currents (heat rising) in the asthenosphere expand and migrate to the
surface while cooler material flows to fill the void.
2. Briefly explain the difference between Converging, Diverging and Transform
Fault boundaries. (3 marks)
Converging…plates moving together (collide or slide under the other)
Diverging….plates separate from each other
Transform Fault….plates slide past each other
3. What evidence of sea-floor spreading do scientists have?
A pattern of magnetic variations on either side fo the ridge revealed a striped pattern
that was parallel. The pattern also showed a mirror image on both sides of the ridge.
A second discovery of magnetic reversals of rock on either side of the ridge. The
farther from the ridge, the older the rock. Scientists learned that over time, the
magnetic polarity of rock changes or reverses from north to south and back.
4. Give 2 reasons why diverging tectonics are less violent than converging
tectonics?
 The lithosphere is thinnest near the mid-ocean ridges
 The plates are spitting apart, allowing hot magma from the upper mantle to
move easily toward the earth’s surface
 The low viscosity of the magma
5. What causes the narrow valleys along a fault line?
As the plates slide past one another, the pressures shatter the rocks along the fault
line. The shattered rocks are eroded to create the valley.
6. What is fault creep?
Short movements along the fault that gradually release pressure. This creep an release
of pressure means earthquakes are lower in magnitude and less destructive.
7. Explain what it means when the plates are locked. What is the result then?
Where the rock surfaces are rough, the plates get stuck on each other. The pressure
continues to build up eventually to be released as an earthquake. The longer the
pressure builds, the stronger and more destructive the earthquake.
8. How do laser sensors, seismographs and strain gauges help scientists detect and
predict earthquakes?
By measuring the movement of the earth they can determine if the fault plates are
locked or creeping steadily and also measure the amount of movement of the plates.
This will help them generate their predictions.
9. What are the two types of converging plate boundaries?
Subduction zones (where an oceanic plate is slipping below a continental plate)
Collision zones (where two continental plates are meeting)
10. Describe how it is possible for one plate of rock to descend beneath another. Ie,
what are the elements necessary to allow that to happen?
-thin ocean plates with heavy basaltic rock descent into the plastic asthenosphere beneath lighter, thicker
granitic rocks of continental plates
-Descending plates are cooler so they sink down. That is subduction.
11. Briefly describe what happens when two plates collide and neither of those plates
is able to descend beneath the other?
-two continental plates collide
-rocks of the continental plates are lighter and less dense than those of the asthenosphere…don’t sink
-rocks collide to create massive mountain ranges of twisted rocks (Himalayas, Appalachian, Alps)
12. Explain why some volcanoes are more spectacular and destructive than others.
Cooler materials of the andesitic magmas, with silica and gases, tend to clog up the vents of
volcanies leading to the build up of pressure. When the pressure becomes great enough, a
major explosion hurls magma onto the earth’s surface and into the atmosphere.
13. What is the difference between continental volcanic arcs and island arcs?
Same thing, but the only difference is where the arcs are found. Continental arcs are located in
continents while island arcs are formed from volcanoes build on the ocean floor.
14. Scientists speculate ocean floor rock is much younger that continental rocks. Why
would ocean floor rocks be younger?
Because of the subduction. The rocks at subduction zones are consumed as they migrate to the ansthenosphere. Continental rocks on
the other hand are lighter and are not consumed at subduction zones, allowing them to stick around much longer.
15. Cratons are described as the roots of mountains. Explain.
They are actually what is left from millions of years of erosion, so they are called the roots of the
mountains.
16. Briefly describe the process of accretion.
The edges of continents are often plate boundaries and are active zones of mountain building. This is one way continents increase in
size.
Another way they increase in size is through erosion of the mountains, depositing eroded material at the
edge of the continent.