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Plate Boundaries ~ Plate Movement ~ Plate names ~ Types of
landforms/Effect of plate boundaries ~ Names of landforms Maps
& Information
Slide 3
Plate Boundaries: The point at which two tectonic plates meet
is called a plate boundary. It is at these locations where tectonic
activity results in earthquakes, volcanoes and the formation of
mountain ranges due to the movement of the plates.
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This map shows 15 of the largest plates. Note that the
Indo-Australian Plate may be breaking apart into the Indian and
Australian plates, which are shown separately on this
map.Indo-Australian Plate
Slide 6
World map showing plate boundaries (blue lines), the
distribution of recent earthquakes (yellow dots) and active
volcanoes (red triangles). Courtesy of NASA.
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The diagram below shows the major plates and their boundaries.
The arrows indicate the direction of movement at each plate. It is
the direction of movement as well as the difference in crust which
determine the variations in processes and landforms at the
different plate boundaries. (animation from USGS)
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At the edges of the plates we see the ridges and trenches that
gave the first clues to Plate Tectonics. There are a few theories
that control what happens along these edges, or plate boundaries as
they are called. http://geography-
site.co.uk/pages/physical/earth/tect.htmltheorieshttp://geography-
site.co.uk/pages/physical/earth/tect.html
Slide 17
Map showing the global distribution of tectonic plates and
plate boundaries. The black arrows and numbers give the direction
and speed of relative motion between plates. Speed of motion is
given in mm y 1. (Adapted from Bott, 1982)
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Interactive Map of Plate Boundaries & Types of Boundaries
Source: http://www.learner.org/interactives/dynamicearth/plate.html
http://www.learner.org/interactives/dynamicearth/plate.html Use the
interactive map at the weblink below to see where the three
different types of plate boundaries are found throughout the world.
First, find the KEY in the green box located in the lower
right-hand corner of the map. Then, roll your mouse over each
boundary name in the KEY to see its location.
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GREAT RIFT VALLEY The red line on this map shows the eastern
and western faults of the Great Rift Valley, which travels 4,500
miles from southern Africa, under the Red Sea, and into Syria in
southwestern Asia. The red star is Nyiragongo volcano.
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Constructive plate boundaries cause mid-ocean ridges, volcanoes
and earthquakes, though often less violent than those on
destructive plate boundaries. Volcanoes can form along the edges of
the plate boundary due to the rising magma. These volcanoes are
called shield volcanoes. Example: the North American plate moving
away from the Eurasian plate formed the Mid-Atlantic Ridge and
created Iceland through volcanic activity. Constructive Plate
Boundaries (aka Divergent or Tensional) When two plates move away
from each other creating a gap between them. Molten rock (magma)
rises from the mantle to fill the gap forming a mid-ocean
ridge
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Destructive Boundary aka Convergent Movement Movement: Two
plates moving towards each other (continental and oceanic crust)
(note where two oceanic plates meet one will be subducted and an
island arc will form) Processes: an island arc The denser oceanic
crust is subducted underneath the continental crust forming a
subduction zone and oceanic trench. As it is subducted it melts due
to heat and pressure. The heat sources are friction between the two
plates and from the earth's interior. Melting of the subducting
plates creates magma which is lighter than the mantle and therefore
rises resulting in the formation of volcanoes. Earthquakes also
occur at this type of boundary due to the friction and pressure
during subduction. Landforms Created: Fold Mountains and Ocean
Trench Example: South American and Nazca Plates (forming the Andes
and a deep sea trench (Peru-Chile trench))
http://geobytesgcse.blogspot.com/2007/01/plate-boundaries.html
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Constructive Boundary aka Divergent Movement Movement: two
plates moving away from each other Processes: As the two plates
separate, hot magma is able to rise to fill the 'gap' creating new
crust. As magma continues to build up, new mountain ranges form
under the sea creating a mid-oceanic ridge. Where rising magma
continues to build up above the ocean surface, a volcanic island is
formed (for example Surtsey, Iceland). Both earthquakes and
volcanoes occur at this type of boundary. Landforms Created: Ocean
Ridge; Volcanic Islands Example: North American and Eurasian Plate
- (forming the Mid- Atlantic Ridge)
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Movement: two plates moving away from each other (animation
courtesy of USGS)
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Key Term Check Constructive Boundary (Divergent) - where two
plates move away from each other resulting in new crust being
formed. Destructive Boundary (Convergent) - where two plates move
towards each other - in the case of a plate consisting of
continental crust meeting a plate consisting of oceanic crust, the
oceanic crust will be subducted and destroyed as it is less dense.
Conservative Boundary - where two plates move alongside each other
- although crust is neither created or destroyed here, earthquakes
usually occur here. Collision Boundary - where two plates of
continental crust move towards each other creating fold mountains.
Volcano - a vent through which lava, ash etc. is erupted (often,
but not always cone-shaped) Earthquake - a sudden ground
movement
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Collision Boundary Convergent Boundary Movement: two plates
moving towards each other (both continental crust) Processes: As
both plates consist of continental crust they both resist
subduction and buckle and fold, being forced upwards to create fold
mountains or a mountain range, such as the Himalayas. Although
there is no volcanic activity at these locations, due to the forces
of collision major earthquakes often occur here. Example:
Indo-Australian and Eurasian Plate (forming the (Himalayas)
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Convergent Boundary Convergent Boundary click on title for
website information
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Types of Convergent Boundary Oceanic-Continental Convergence
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. Even though the oceanic plate as a whole sinks
smoothly and continuously into the subduction trench, the deepest
part of the subducting plate breaks into smaller pieces. These
smaller pieces become locked in place for long periods of time
before moving suddenly and generating large earthquakes. Such
earthquakes are often accompanied by uplift of the land by as much
as a few meters. Oceanic-Oceanic Convergence 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. Oceanic-oceanic plate
convergence also results in the formation of undersea volcanoes.
Over millions of years, however, the erupted lava and volcanic
debris pile up on the ocean floor until a submarine volcano rises
above sea level to form an island volcano. Such volcanoes are
typically strung out in chains called island arcs.
Continental-Continental Convergence 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.
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Convergent Boundary Places where plates crash or crunch
together are called convergent boundaries. Plates only move a few
centimeters each year, so collisions are very slow and last
millions of years. Even though plate collisions take a long time,
lots of interesting things happen. For example, in the drawing
above, an oceanic plate has crashed into a continental plate.
Looking at this drawing of two plates colliding is like looking at
a single frame in a slow- motion movie of two cars crashing into
each other. Just as the front ends of cars fold and bend in a
collision, so do the "front ends" of colliding plates. The edge of
the continental plate in the drawing has folded into a huge
mountain range, while the edge of the oceanic plate has bent
downward and dug deep into the Earth. A trench has formed at the
bend. All that folding and bending makes rock in both plates break
and slip, causing earthquakes. As the edge of the oceanic plate
digs into Earth's hot interior, some of the rock in it melts. The
melted rock rises up through the continental plate, causing more
earthquakes on its way up, and forming volcanic eruptions where it
finally reaches the surface. An example of this type of collision
is found on the west coast of South America where the oceanic Nazca
Plate is crashing into the continent of South America. The crash
formed the Andes Mountains, the long string of volcanoes along the
mountain crest, and the deep trench off the coast in the Pacific
Ocean.
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Divergent Boundary Movement: two plates moving way from each
other () Places where plates are coming apart are called divergent
boundaries. As shown in the drawing above, when Earth's brittle
surface layer (the lithosphere) is pulled apart, it typically
breaks along parallel faults that tilt slightly outward from each
other. As the plates separate along the boundary, the block between
the faults cracks and drops down into the soft, plastic interior
(the asthenosphere). The sinking of the block forms a central
valley called a rift. Magma (liquid rock) seeps upward to fill the
cracks. In this way, new crust is formed along the boundary.
Earthquakes occur along the faults, and volcanoes form where the
magma reaches the surface.
Slide 35
Divergent Boundary Movement: two plates moving way from each
other () Processes: Where a divergent boundary crosses the land,
the rift valleys which form are typically 30-50 kilometers wide.
Example 1:: include the East Africa rift in Kenya & Ethiopia,
and the Rio Grande in New Mexico. Where a divergent boundary
crosses the ocean floor, the rift valley is much narrower,
only