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 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.

10 References “How the Earth was made”, History Channel - Season 1, Episode 2 “Deepest Place in the Ocean: Challenger Deep”, Extreme Science, Earth and Environmental Science Home - Hydrothermal Vents, environ/interact01.jspl Vents, Back-arc Basin - Encyclopedia Britannica, Serpentine - Department of Geology aSerpentine - Department of Geology and Planetary Science, Marianas Trench - Oceanography, Trench - Oceanography, Marianas Trench graphic - Astrobiology Magazine,