Tamsyn Mather

So in the case of Mount St.

Helens, it's what we call a strata volcano.

It's been made up of layers of lava and ash and other volcanic products that have been erupted.

So, yes, in the case of Mount St.

Helens and many other volcanoes, the mountains have been built by the volcanic activity.

That's an excellent question.

It's not something we fully understand.

So in some cases, we do have a really good understanding.

So Hawaii, for example, is fed by a hot spot underneath the volcanoes.

So again, it's down in the Earth's mantle.

And as the rigid Pacific plate rides over that hot spot, it actually takes the volcanoes away from that source of magma.

So Kilauea and Mauna Loa are the active volcanoes at the moment.

But as you go over to the west along the Hawaiian chain, the volcanoes become extinct.

And that's because they've actually moved away from the source of the molten rock that fed them.

Well, that turns out not to be quite correct.

But actually, in a funny way, it's where we started, where the science started.

So hundreds of years ago, people thought basically that's what volcanoes were.

They thought that that was where Earth's internal fires found their way to the surface, very much like your...

Your idea there, people had these ideas of the bigs of chimneys for earths in a fire.

And then even when Christianity took a hold, people thought of them as being gateways to hell even.