Download Mid-ocean ridges

Lesson 14:
Plate Tectonics II
Geological Oceanography
Last class we learned about Earth’s
plates
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The Earth’s surface is a mosaic of rigid plates all
moving with respect to each other
These movements result in many of the structural
features we see on Earth, like mountains, trenches
and ocean basins
Plate movement also shapes continents, for example
leading to formation of mountains like the Himalayas
Today we’ll learn more about plate
movement or plate tectonics
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As plates moves, they always interact with other plates
The ways that plates interact along their boundaries
shape geological features of Earth’s surface and the
terrain
The terrain of the seafloor includes seafloor (abyssal)
hills, mountain chains (ridges, islands and seamounts),
trenches and great platforms, all formed by tectonic
processes
Map of the ocean floor
This map shows
that the ocean
floor has
underwater
mountain chains
(shown by the
tan lines)
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Photo: NOAA-OE/WHOI
There are three types of plate boundaries
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Divergent Boundary: Two plates move apart,
called Spreading Centers
Convergent Boundary: Two plates collide,
called Subduction Zones
Conservative Boundary: Two plates slide past
one another, called Transform Faults
Divergent boundary
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Two plates move away from each other, pulling crust apart
As crust pulls apart, magma (molten rock) rises up to form new
crust and seafloor, a process called seafloor spreading
The spreading center is raised because of the heat of the
magma and sometimes has a central rift valley, as in the midAtlantic Ridge
Most spreading centers are found within the new seafloor they
are forming
Spreading center
Plate 1
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Plate 2
Magma
Divergent boundaries and mid-ocean ridges
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Mid-ocean ridges are continuous mountain chains
found in all the world’s ocean basins
Mid-ocean ridges occur along divergent boundaries
(spreading centers)
The entire mid-ocean ridge system is the longest
continuous mountain chain on earth!
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Examples of mid-ocean ridges:
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(Over 40,000 miles long and found primarily below 2000 m)
Mid-Atlantic Ridge: runs down center of Atlantic Ocean basin
East Pacific Rise: runs down Pacific Ocean basin, parallel to
South and Central America
Close-up of ocean ridge
This image
shows a midocean ridge
mountain chain
called the East
Pacific Rise
Photo: NOAA-OE/WHOI
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Convergent boundary
Two plates collide with each other
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Oceanic-Oceanic plates: Can form trenches or
island arcs like the Aleutian Islands
Oceanic-continental plates: Oceanic plate gets
subducted, pushed beneath, the continental plate
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Forms oceanic trenches and volcanic mountains on land,
like the Cascade Mountains and the Andes Mountains
Continental-continental plates: Form mountains as
crust folds together, like the Himalayas
Aleutian Islands: A result of plate
tectonics
This map shows the
location of the Aleutian
Islands, which were
created as a resulted of
oceanic-oceanic plate
convergence
Photo: NOAA
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A recent NOAA voyage to the Aleutian Island area
uncovered rarely seen Subarctic oceanic life, like this
snailfish
Conservative boundary
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Two plates slide past one another in opposite
directions, parallel to, and along a transform
boundary, also known as a transform fault
This results in earthquakes, like those in California
along the San Andreas Fault (the boundary between
the Pacific and North American plates)
Plate 1
Plate 2
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Viewing the global terrain
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The plate movement you learned about
results in the geological terrain that makes
up our planet
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Examples include mountains, trenches, valleys
and volcanoes