Steep vs. flat subduction over time. The boxed value is the amount of water consumed in mantle hydration during the last time step (normalized to 1 Ma). For steep subduction, the hydration zone (in green) is limited to a small area before the volcanic arc (triangle). The water released by the subducting slab, which is not consumed in mantle hydration, is consumed in mantle melting (in red). On the other hand, in flat subduction, the hydration zone is much more extensive. Additionally, it increases over time, as the volcanic arc migrates landward. Oceanic melting (orange) is also observed.