How do volcanoes create new land on the ocean floor at mid-ocean ridges?

At mid-ocean ridges, tectonic plates diverge and hot mantle material rises to fill the gap. As pressure drops, the mantle partially melts and produces basaltic magma. That magma erupts or intrudes into cracks, then cools to form new oceanic crust. This process continuously renews the seafloor and creates the longest mountain system on Earth, the global mid-ocean ridge network. Much of this volcanism happens underwater and is invisible from the surface, but it is the main source of new ocean crust.