Mariana Trench

Mariana Trench - It is the deepest part of the earth's ocean and the deepest location of the earth itself. Mariana Trench is located in the Pacific ocean, just east of the 14 Mariana Islands near Japan. The trench is about 1580 miles long with the mean width of only 43 miles. It reaches a maximum depth of about 10,924 meters at the Challenger Deep, a small slot-shaped valley in its floor, at its southern end.

Mariana Trench was created by ocean-to-ocean subduction, a phenomena in which a plate topped by oceanic crust is subducted beneath another plate topped by oceanic crust. The deepest part of the Mariana Trench is the Challenger Deep, so named after the British exploration vessel HMS Challenger II. So how come the Challenger Deep is so deep? - Well, the earth's crust is not one solid piece of rock, its really pretty thin. In fact its made up of huge plates of thin crust that float on the molten rock of the earth's mantle. While floating around the mantle the edges of these plates slide past each other, bump into each other and sometimes even crash. The oceanic crust is much heavier than the continental crust so when the plates crash into each other, the oceanic plate plunges downward toward the molten mantle, while the lighter continental plate rides up over the top. The forces driving the two plates are really intense so the underlying oceanic plate creates a trench where it drags the edge of the continental crust down as it descends underneath. This is what is happening on the bottom of the Pacific ocean off the Marianas Islands.

View Source: http://www.extremescience.com/DeepestOcean.htm