Question: Has there ever been a flat volcano ? One that you have not known was there until it erupted? Is it possible for the plates to slide as the volcano erupts? Has it ever happened? Many thanks u11bradshawt

Jonathan Stone answered on 22 Mar 2013:

You are totally correct in thinking this – it shows you are a natural scientist. This has probably happened lots of times, but rarely been seen. HOWEVER…there is an incredible example of this happening in Mexico with a volcano called Paracutin.

A farmer was in his field, the ground shook, cracked apart, emitted steam, then ash then lava and a volcano grew in his back garden. Can you imagine that?! Have a read of the story. It is awesome!

http://en.wikipedia.org/wiki/Par%C3%ADcutin

Plate movement does have an effect on where and why volcanoes occur, in that it is most often the reason for having magma there in the first place. But in places where plates are moving apart (so divergent boundaries) like in Iceland or the Mid-Atlantic ridge…there are volcanoes there pretty much because magma from the mantle comes up where the plates are pulling apart/the crust is thin.

In REALLY big eruptions, such as the ones that have occurred at Yellowstone in the past…the amount of magma that has been ejected from under the volcano is so much (many thousands of kilometres cubed) that the crust/ground above where the magma was stored subsides downwards forming a huge crater which we call a caldera. These calderas as so big, and the subsidence of the rock downwards can generate some very large earthquakes even!