Myth: Tectonic plates move because volcanism pushes them apart.
Reality: Older edges of a tectonic plate are cooler and denser, causing them to sink into the mantle where they’re recycled. Where two plates are being yanked apart by this sinking, ocean ridges appear. That’s where the tectonic plate is being built — by a hot, buoyant rock that convects upward and emerges from the stretched-out weak point. The resulting volcanism isn’t what pulls two plates apart.