Earth’s tectonic plates move, and they move a LOT. But, their movements vary. The movement occurs along plate boundaries (where two plates meet). When tectonic plates pull away from each other, they are diverging. Therefore, we call the lines where two plates separate divergent boundaries.
How Divergent Boundaries Occur
Convection currents move in a circular pattern. Sometimes the currents rise and then move in opposite directions. This causes the plates above to separate.
What Happens When Plates Pull Apart
Several things can result from divergent boundaries. Depending on where the boundary is, either a valley or a mid-ocean ridge can occur.
Valleys form when plates pull apart above water. The earth’s crust thins as it is pulled in opposite directions. This creates a region where the crust is lower than surrounding areas. This area usually fills with water, forming a river. We call these continental divergent boundaries.
If the crust is stretched thin enough, pieces of land can break off from one another. When this happens, an island is created.
If a divergent boundary occurs under the surface of water, it creates a ridge. Ridges are what cause the ocean floor to spread. When plates pull away, they allow the mantle’s molten rock to rise. The molten rock fills the gap, spreads, and then hardens. As this process repeats, the ocean floor expands. This is known as an oceanic divergent boundary.
The most well known divergent boundary is the Great Rift Valley. It is a continental divergent boundary in Africa that runs 4,000 miles long. The Great Rift Valley includes some of Africa’s most important geographical features such as the Dead Sea, the Jordan River, and the Red Sea. A vast number of volcanoes and hot springs are scattered all along the valley.
The biggest oceanic divergent boundary is the Mid-Atlantic Ridge. This ridge divides the Atlantic Ocean in two places: between the North American and the Eurasian plates in the north and the South American and African plates in the south. It contributes to seafloor-spreading and is what most likely causes continental movement.
Other Great Resources
Kids Fun Science on Divergent Boundaries: http://www.kids-fun-science.com/divergent-boundary.html