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The
Marianas
Trench
The Art
of
Subduction…
By Michael Liston
Oceanography 1 - Prof. Wiese
Introduction
 With a length that extends 2,542km and a width of 69km the Marianas Trench is known
as having the deepest region on Earth (the Challenger Deep - approximately 11km
deep) stirring the imaginations of both professional earth scientists and amateur
researchers alike.
 At those depths the water pressure is enormous (called hydrostatic pressure) and can
reach up to 16,000 pounds per square inch!
How exactly did it form?
The driving forces behind the formation of the Marianas Trench is the
colliding (convergence) of continental plates.
The Pacific plate, moving from east to west, originates from the East
Pacific rise (closer to Mexico and South America) where new oceanic
lithosphere forms.
How exactly did it form?
As new oceanic lithosphere displaces the old, the western edge of the Pacific plate
collides violently with the Marianas Plate forcing it under and back into the mantle.
The point where these two plates collide is called a “Subduction Zone” (Ocean-toOcean in this case) and is where the Marianas Trench is formed.
The Magic Moment
Unique Features:
As the Pacific plate subducts under the Marianas plate, intense heat from
the recycling of oceanic lithosphere produces magma which rises to the
surface to create volcanic island arcs.
But along with this comes small spreading centers (less intense than midridges and rises) called “Back-Arc Basins”.
Hydrothermal Vents:
These Back-Arc Basins are closely related to the subduction zone/Island
arc systems found in the western part of the Pacific ocean and have also
been found to have hydrothermal vent activity and have a rich biosphere
surrounding those hydrothermal vents.
Seismic Activity:
Throughout years of research of the Marianas Trench, Earth
scientists have wrestled with why there hasn’t been a major
seismic event along this convergent boundary in modern times...
Seismic Activity continued:
This question was answered when researchers discovered hills erupting mud
at the subduction zone.
But this was not any ordinary mud. Researchers found that this mud was in
fact a type of rock called Serpentinite that was acting like a lubricant (because
of its brittleness) as the two plate converged on each other thus minimizing
seismic activity along this subduction zone.
Conclusion
Typically, convergent boundaries are classified as seismic centers for some of the
most violent earthquakes on Earth.
Although not void of seismic activity, the boundary along the Mariana Trench
doesn’t quite fit the mold like its sister subduction zones along the coast of Chile
and the Western United States.
Unique places on our planet like the Marianas Trench and
the activities that help form them will continue to keep us
in awe of the its power and remind us of our place in past
and present history.
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References
“How the Earth was made”, History Channel - Season 1, Episode 2
http://www.youtube.com/watch?v=BYjyGfRp3F4&list=FL04mVa4r9Hg_4DX0nBrhfTg&index=2&feature=plpp_video
“Deepest Place in the Ocean: Challenger Deep”, Extreme Science, http://www.extremescience.com/deepest-ocean.htm
Earth and Environmental Science Home - Hydrothermal Vents, http://www.nsf.gov/news/overviews/earthenviron/interact01.jsp
Back-arc Basin - Encyclopedia Britannica, http://www.britannica.com/EBchecked/topic/1333151/back-arc-basin
Serpentine - Department of Geology and Planetary Science,
http://www.pitt.edu/~cejones/GeoImages/1Minerals/3MetamorphicMineralz/Serpentine.html
Marianas Trench - Oceanography, http://www.marianatrench.com/mariana_trench-oceanography.htm
Marianas Trench graphic - Astrobiology Magazine, http://astrobio.net/articles/images/marianas_trench_lg.jpg
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