Science Saturday - Why Do Volcanoes Exist?

As a matter of fact ...

The Mount Ontake volano erupted in Japan today. The last time it erupted was 2007. Although that doesn't seam frequent, I cant imagine living nearby an active volcano and having it erupt twice it 7 years.

Japan is known for having high volcanic activity with over 100 volcanoes a year. My home, the UK, has none. Why is this? Why are some places seemingly packed with volcanoes and in others they are just stories?

The recent Mount Ontake eruption in Japan

Plate friction forcing magma to the surface in the form of a volcanoe

It's all down to tectonic plates. The Earth's surface has 17 of them. They're the huge, hard and rigid surface of the Earth's crust and whenever they diverge, converge and rub against each other, you can be sure to find volcanic activity. The friction from the plates forces the less dense magma from nearer the Earth's core to rise upwards, eventually spewing out onto the surface. This was first notice by Alfred Wagner when he proposed his 'continental drift' theory of moving tectonic plates and landmass over long periods of time.

This concept is best demonstrated using the map below. You can see that sure enough, Japan is sitting right on a tectonic fault line in the top right hand corner. The UK, the the upper middle of the map, is nowhere near a fault line. A convergent line runs right along the northern tip of India and is responsible for creating the Himalayas some 45 million years ago.

Tectonic plate map

See how far you live from a fault line on the map. Who knows, perhaps you might travel to one of the active volcanoes along it and see this awesome power of nature.