A divergent boundary is exactly what it sounds like, a plate boundary where the plates diverge. Plates in a divergent boundary undergo a tensional tectonic force known as tension stress ("Types of Plate Boundaries"). This is a puling force that rips apart the plates at a boundary. The central block at the spread can drop down and form a geologic characteristic known as a graben. Volcanism is quite common along the rift's faults causing even more spreading to occur. Today's active divergent boundaries are midoceanic ridges. These sea floor spreading centers create underwater mountain ranges formed from the magma present at the spread.