Divergent Boundaries

Another type of plate boundary is a divergent plate boundary. Divergence occurs when extention takes place. You can remeber that divergence sound like divide. At theses boundaries a ridge will occur. It may look like there is mountain build but that happens with compression. As the plates split, the crack is filled in with underlying magma, which solidifies when it comes in contact with the cold ocean water, making new oceanic crust. This process continues and the older crust proceeds away from the ridge. As it gets older and cools down, it becomes more dense and sinks even lower into the Earth. These boundaries can also occur on land as well as under the ocean. Part of the mid-Atlantic ridge goes through part of Iceland. Another rift valley that is occuring is in the eastern part of Africa. As that rift valley splits it will eventually sink below sea level and be split off from the rest of Africa.
Another Selection For Your Gee Wiz Collection:
If the Earth did not experience plate tectonic, the land would never replenish itself. The land would evenually be all weathered away and eroded to to the oceans and there would be no land to live on.