Education and Careers

Q: Can the slow movement of tectonic plates make much of an impact on human society?

From Anon (November 2009)

Reply By Dr Ted Nield

You are correct in saying that the tectonic plates move very slowly, but it is important to remember that these rates are average figures. The spreading centres of the Atlantic Ocean and others, where new crust is made, tend to widen at about the speed your fingernails grow (others, which open more slowly, open at the speed of your toenails). The range is from one or two centimetres per year, to up to about 15cm.

However because the Earth is not getting bigger, in other places the crust must be destroyed by processes that must operate at roughly the same rate. The problem is that the Earth is not a smoothly oiled machine and things get stuck. While the system in places where plates are destroyed (by one diving back into the Earth) is locked, strain builds up and energy is stored like in a leaf-spring. The same thing happens where plates move past one another - as at the San Andreas Fault in California. Eventually the strain becomes too much for the rocks to bear (rocks only have a finite amount of strength, and hence can store up only a certain amount of energy) and the fault moves catastrophically. This movement might then amount to several metres, being the accumulation of many years of strain.

When this happens, human societies are very much affected, as the release of energy, which of course is an earthquake, can be immensely destructive!