The material that rises to the surface at a mid-ocean ridge is magma.

Here's why:

* Mid-ocean ridges are divergent plate boundaries. This means that tectonic plates are pulling apart, creating space.

* The space allows molten rock (magma) from the Earth's mantle to rise. The magma is less dense than the surrounding solid rock, so it is buoyed upward.

* As the magma reaches the surface, it cools and solidifies, forming new oceanic crust. This process is called seafloor spreading.

So, the magma rising at the mid-ocean ridge is the source of new oceanic crust and a key driver of plate tectonics.