What are plate margins?
Plate margins are the edges of the plates, where all the power of nature is released in earthquakes and volcanoes. There are three main types of plate margins: -
There are two types of spreading boundary
Ridges, where new rock is formed, pushing the plates apart, and Rift, where the plates pull apart, and the earth between them sinks.
On the ocean floor the plates are spreading. All along the mid ocean ridge, volcanic activity is pouring new lava out onto the seabed. As it hardens, it becomes new rock, gradually pushing the crust, on either side of it away. Another type of spreading boundary is the African Rift Valley. As the two plates are moving apart, the earth between them is becoming stretched. As it stretches it sinks, because it is thinner. It is a little bit like taking a piece of gum, and stretching it out.
The pieces in your fingers stay thick, but the piece in the middle gets thinner and thinner, as it is stretched.
Converging (coming together) Boundaries, are where two plates are banging into each other. What happens when they collide depends on the type of plate they are.
In a subduction zone one plate is being pushed beneath the other. It happens when a lighter plate hits a heavy plate. The lighter plate is pushed under the heavier one. This often happens where continents meet the ocean. As the lighter ocean crust is forced downwards, it takes water with it. The water causes the rock to melt at lower temperatures than normal. The pressure inside the earth is much greater than at the surface, it increases the deeper you go. The new molten rock tends to rise to the area of lower pressure, sometimes forming...