in the upper mantle (lithosphere) our journey guide states that "movement of molten material between the crust and mantle" causes islands, volcanos, and ocean trench. what is this movement? describe how it works

Boundaries between the plates are of three types: divergent (i.e., moving ... Plates are thought to move along the lithosphere-asthenosphere boundary, ... plates include both crustal material and lithospheric mantle material makes it ... crust to the ocean floor where it creates a chain of volcanic islands known as an island arc.

Explanation:

force tends to be low and long diustance masses are high