Which statements explain what happens at deep-ocean trenches? check all that apply.

crust is formed.
mountains are formed.
seafloor spreading occurs.
crust becomes molten rock.
denser plates slide under lighter plates.

Options 3,4 and 5

Explanation:

As the oceanic or the continental crust undergoes subduction i.e the denser plate gets subducted beneath the lighter one, deep ocean trenches are formed, and with futher pushing the plate at greater depth, the crust gets consumed into the mantle and at some places, sea floor spreading takes place in order to keep the lithospheric plate in equilibrium.

                       Deep oceanic trenches results in the convergent plate boundary such as oceanic-oceanic convergent and oceanic-continental convergent.

Options (4) and (5)

Explanation:

The oceanic trenches are formed in a convergent type of plate boundary. In this type of plate boundary, two plates move towards each other. Due to this motion, the denser plate goes down below the lighter plate, as a result of which a subduction zone is created above which the deep oceanic trench lies. This marks the boundary of separation between the two distinct plates. In this region, as the heavier plate goes down, it initiates partial melting and the melt is again mixed with magma. This slowly pushes the magma upward due to the convection current, which gives rise to the formation of volcanoes or volcanic or island arcs in the over-riding plate. This results in the changing of the solid hard crust into molten rock (magma).

Thus, the correct answers are options (4) and (5).

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