The Art of

Subduction…

The Marianas Trench

By Michael Liston

Oceanography 1 - Prof. Wiese

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!

Introduction

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.

The Magic Moment

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-to-Ocean in this case) and is where

the Marianas Trench is formed.

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 mid-ridges and rises) called “Back-Arc

Basins”.

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.

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.

9

ConclusionTypically, 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.

10

References“How the Earth was made”, History Channel - Season 1, Episode 2http://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/earth-environ/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