Divergent
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.




There is still much disagreement on how divergent plates develop. The problem is a chicken and egg situation. Some scientists feel that rifting thins the crust, reducing pressure, causing more pressurized rocks to ascend, causing uplift ("Types of Plate Boundaries"). The opposing argument is that pretty much the backwards argument, the uplift causes the the rifting. One of the more interesting things about geology is just how much uncertainty is still present in the theories.