What is a Divergent Plate Boundary?
Earth’s outer shell consists of large, rigid tectonic plates that constantly move across the planet’s surface. A divergent plate boundary marks a location where two of these plates actively pull apart from each other, creating new crustal material between them.
How Divergent Plate Boundaries Work
The underlying mechanism driving the separation of tectonic plates at divergent boundaries is mantle convection. Within Earth’s mantle, heat from the core creates convection currents where hotter, less dense material rises and cooler, denser material sinks. This circulating motion drags the overlying tectonic plates along, causing them to move.
As magma rises from the mantle, it intrudes into the gap created by the separating plates, a process known as seafloor spreading. This molten rock solidifies, forming new oceanic crust and effectively pushing the existing plates further apart. This continuous upwelling of magma and subsequent solidification ensures the widening of ocean basins over geological timescales.
Landforms and Phenomena
Divergent plate boundaries feature distinct geology. Oceanic divergent boundaries are marked by mid-ocean ridges, extensive underwater mountain ranges. This elevated topography forms as rising magma cools, creating new, thermally expanded crust that is higher than older crust.
On continents, divergent boundaries create rift valleys, large depressions formed as the crust stretches and thins. Blocks of land may drop along faults, forming the characteristic valley shape.
Both oceanic ridges and continental rifts are sites of significant volcanic activity. Volcanism is typically effusive, with magma flowing gently rather than erupting explosively, often forming pillow lavas when cooling rapidly in seawater. Shallow earthquakes also occur, caused by crustal fracturing as it stretches and moves apart.
Global Distribution and Examples
Divergent plate boundaries are found globally. The Mid-Atlantic Ridge is a prime example of an oceanic divergent boundary, extending for thousands of kilometers down the center of the Atlantic Ocean. New oceanic crust continuously forms along this submarine mountain range, causing the Atlantic Ocean to gradually widen.
On land, the East African Rift Valley represents a notable continental divergent boundary. Here, the African Plate is slowly splitting apart, creating a series of valleys, volcanoes, and lakes. Geologists anticipate this rifting could eventually lead to the formation of a new ocean basin, similar to how the Atlantic Ocean formed.