How are mid-ocean ridges formed?

• A. By erosion
• B. By the upwelling of magma at divergent boundaries
• C. By subduction at convergent boundaries
• D. By volcanic arcs at hot spots

Answer: (B)

Mid-ocean ridges form at divergent boundaries where tectonic plates move apart. As the plates separate, mantle rock rises toward the surface, partially melts, and magma upwells to fill the gap. This magma cools and solidifies to create new oceanic crust, building an underwater mountain range with a central rift where the spreading occurs. The continual creation of new crust along the ridge drives sea-floor spreading, pushing older crust away from the boundary over time. Erosion would wear down existing features rather than form new ones. Subduction at convergent boundaries consumes crust and creates trenches and volcanic arcs, not ridges. Hotspots produce volcanic islands or chains away from plate boundaries, not the mid-ocean ridges themselves.