1. Deep sea trench
By Grace & Emma

2. Deep sea trenches are formed when two plates collide
Deep sea trenches are formed when two plates collide. They can also be known as subduction zones.
Ocean Trenches are deep water areas that run along a coastline which has a destructive plate margin. 
They are created by subduction, and mark the point where the Oceanic crust is being pushed under the Oceanic crust.
sometimes a volcanic island arc such as Japan or the Aleutian Islands can be found in between the trench and the continental shelf.

3. Ocean Trenches
Marianas trench
Trenches form in some areas when two oceanic plates converge forming a subduction zone. The Pacific Plate is subducting under the Mariana Plate forming Mariana Trench.

4. Continental oceanic
When tectonic plates with different densities collide, the denser plate sinks beneath the other: a process known as subduction. This happens, for example, when a plate carrying a continent (less dense) rides over an oceanic plate (more dense). The boundary between the two plates forms a trench that can be several miles deep and tens of miles wide. Because plates are so huge, a single trench can be thousands of miles long. All the trenches on Earth are found in oceans.

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