Which mechanism is most closely associated with plate motion at mid-ocean ridges?

• A. Slab pull
• B. Ridge push
• C. Convection in the mantle
• D. Slab suction

Answer: (B)

Mid-ocean ridges push plates apart mainly through a gravity-driven mechanism acting on the newly created lithosphere. The ridge crest is elevated and hot—the lithosphere here is buoyant. As fresh material forms and then moves away from the crest, gravity causes it to slide toward the cooler, denser flanks. That gravitational sliding effectively pushes the tectonic plates away from the ridge, driving seafloor spreading.

Slab pull involves the sinking of a cold subducting plate and pulls the rest of a plate toward subduction zones, which isn’t the process at ridges. Slab suction is a related subduction-zone effect from mantle flow. Convection in the mantle provides the overall driving background for plate tectonics, but the specific mechanism most closely linked to ridge-related spreading is ridge push.