Chapter: Formation of Mountain Ranges

Plate Boundaries

1. Divergent Boundaries

a. In the Oceans (MOR)

First we'll have a closer look at the divergent boundaries. We find those mainly in the oceans, more precisely at the mid-oceanic ridges (MOR). This is a submarine mountain range with a rift valley running along its axis. Underneath the MOR we find a magma chamber which causes magma to flow out of the rift valley and form new oceanic crust. Let us have a closer look at the MOR's we find today. If you move your cursor above the MOR's their name will appear.

What happens with the flown out lava on the seabed?

First it cools down very quickly and forms funny pillow-like shapes, thus the name pillow-basalts. With the formation of such pillows the whole ocean bed is being pushed aside; this process is not visible as the ocean floor just moves a few inches per year. But viewed in geological time – geologists calculate with millions of years – a few inches per year lead to quite a distance. For example 1.2 inches/year give 18.7 miles in one million years.

The Atlantic Ocean grows. How is this possible?

Let's take a look at the earth surface. It has a fixed size of 197 square miles. So if the Atlantic grows this happens at the expense of another ocean or a continent with a convergent boundary.

To b) Divergent Boundaries on Land