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Chapter 18: Problem 2

The ocean trenches at some subduction zones are relatively shallow. What is one explanation for this?

Short Answer

Expert verified
One explanation for relatively shallow ocean trenches at some subduction zones is the age and temperature of the subducting oceanic lithosphere. Younger and warmer lithosphere tends to subduct at a shallower angle, resulting in a shallower trench compared to older and colder lithosphere that subducts more steeply.

Step by step solution

01

Introduction to subduction zones and ocean trenches

Subduction zones are areas where one tectonic plate moves under another plate, typically an oceanic plate being subducted beneath a continental plate. This process results in the formation of ocean trenches, which are deep linear depressions on the seafloor. The depth of these trenches can vary, and we will explore one explanation as to why some trenches are relatively shallow.
02

Oceanic lithosphere age and temperature

A significant factor that influences the depth of ocean trenches is the age and temperature of the oceanic lithosphere, which is the part of the tectonic plate that gets subducted. As the oceanic lithosphere forms at mid-ocean ridges, it cools down and becomes denser over time. Older lithosphere is colder and denser, and subsequently, it will subduct more steeply into the mantle.
03

The influence of age and temperature on trench depth

The depth of an ocean trench is related to the angle at which the oceanic plate is being subducted. When the subducting lithosphere is older and denser, it gets subducted at a steeper angle, resulting in a deeper trench. In contrast, if the oceanic lithosphere is relatively young and warm or buoyant, it may subduct at a shallower angle, thus making the trench relatively shallow.
04

Conclusion

One explanation for relatively shallow ocean trenches at some subduction zones is the age and temperature of the subducting oceanic lithosphere. Younger and warmer lithosphere tends to subduct at a shallower angle, resulting in a shallower trench compared to older and colder lithosphere that subducts more steeply.

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