Answer
The characteristic of a slab of oceanic lithosphere that leads to the formation of deep-ocean trenches instead of shallow trenches is its density and ability to undergo subduction.
Oceanic lithosphere is denser than the underlying asthenosphere and continental lithosphere. When an oceanic plate converges with another tectonic plate at a subduction zone, the denser oceanic lithosphere sinks beneath the less dense lithosphere. This downward movement is driven by gravity and the force exerted by the denser lithospheric plate.
As the oceanic lithosphere subducts, it descends into the mantle and forms a steeply inclined subduction zone. The subducting lithosphere continues to sink due to its greater density. This downward motion creates a trench, which is a deep depression on the ocean floor.
The depth of the trench is determined by the angle at which the oceanic lithosphere subducts. If the subduction angle is steep, the trench will be deeper. This is because a steeper angle allows the subducting lithosphere to sink more rapidly and to a greater depth.
In contrast, shallow trenches occur when the subduction angle is more shallow, resulting in a less pronounced depression on the ocean floor. Shallow trenches are less common and are typically associated with younger and less dense lithosphere.
Therefore, the density of the oceanic lithosphere and the steepness of the subduction angle determine whether a deep-ocean trench or a shallow trench is formed at a subduction zone. The denser the lithosphere and the steeper the subduction angle, the deeper the trench will be.
Work Step by Step
The characteristic of a slab of oceanic lithosphere that leads to the formation of deep-ocean trenches instead of shallow trenches is its density and ability to undergo subduction.
Oceanic lithosphere is denser than the underlying asthenosphere and continental lithosphere. When an oceanic plate converges with another tectonic plate at a subduction zone, the denser oceanic lithosphere sinks beneath the less dense lithosphere. This downward movement is driven by gravity and the force exerted by the denser lithospheric plate.
As the oceanic lithosphere subducts, it descends into the mantle and forms a steeply inclined subduction zone. The subducting lithosphere continues to sink due to its greater density. This downward motion creates a trench, which is a deep depression on the ocean floor.
The depth of the trench is determined by the angle at which the oceanic lithosphere subducts. If the subduction angle is steep, the trench will be deeper. This is because a steeper angle allows the subducting lithosphere to sink more rapidly and to a greater depth.
In contrast, shallow trenches occur when the subduction angle is more shallow, resulting in a less pronounced depression on the ocean floor. Shallow trenches are less common and are typically associated with younger and less dense lithosphere.
Therefore, the density of the oceanic lithosphere and the steepness of the subduction angle determine whether a deep-ocean trench or a shallow trench is formed at a subduction zone. The denser the lithosphere and the steeper the subduction angle, the deeper the trench will be.
