Answer:
Magma fills in the gap where the plates move apart.
Explanation:
The tectonic plates are in constant motion because of the convection currents below them. This motion makes the plates move across the globe and form different types of boundaries between them. One of the types of plate boundaries is the divergent plate boundary, a plate boundary where the plates move away from each other.
At divergent plate boundaries, as the plates move away from each other, they open up a gap between them. The gap makes the crust much thinner, so the magma from below manages to break through very easily. As the magma breaks through, it fills in the gap, creating an underwater chain of mountains, and occasionally volcanic islands. A good example of this is the Mid-Atlantic Ocean Ridge as well as the island of Iceland.
