<P> Subduction zones are important for several reasons: </P> <Ol> <Li> Subduction Zone Physics: Sinking of the oceanic lithosphere (sediments, crust, mantle), by contrast of density between the cold and old lithosphere and the hot asthenospheric mantle wedge, is the strongest force (but not the only one) needed to drive plate motion and is the dominant mode of mantle convection . </Li> <Li> Subduction Zone Chemistry: The subducted sediments and crust dehydrate and release water - rich (aqueous) fluids into the overlying mantle, causing mantle melting and fractionation of elements between surface and deep mantle reservoirs, producing island arcs and continental crust . </Li> <Li> Subduction zones drag down subducted oceanic sediments, oceanic crust, and mantle lithosphere that interact with the hot asthenospheric mantle from the over-riding plate to produce calc - alkaline series melts, ore deposits, and continental crust . </Li> <Li> Subduction zones pose significant threats to lives, property, economic vitality, cultural and natural resources, as well as quality of life . The tremendous magnitudes of earthquakes or volcanic eruptions can also have knock - on effects with global impact . </Li> </Ol> <Li> Subduction Zone Physics: Sinking of the oceanic lithosphere (sediments, crust, mantle), by contrast of density between the cold and old lithosphere and the hot asthenospheric mantle wedge, is the strongest force (but not the only one) needed to drive plate motion and is the dominant mode of mantle convection . </Li> <Li> Subduction Zone Chemistry: The subducted sediments and crust dehydrate and release water - rich (aqueous) fluids into the overlying mantle, causing mantle melting and fractionation of elements between surface and deep mantle reservoirs, producing island arcs and continental crust . </Li>

What is a depression in the seafloor produced by subduction process