Constructive Plate Margin – Tectonic plate margin where two plates are moving apart
The construction (constructive) of a bridge was necessary when the two cliffs moved apart.
Plate margins are the boundaries or edges of tectonic plates.
With constructive plate margins, the two tectonic plates move apart or diverge from each other. This can occur both on land and in the ocean.
Convection currents of magma (liquid rock) in the earth's mantle (the layer below the earth's crust) move in opposite directions and force the two tectonic plates apart.
This does happen under the ocean too.