We posed this question to Chris Kilburn from University College London...

Chris K -  There are about 600 to 1,000 volcanoes for which we have records of eruption, that have actually been observed, but using radioactive dating techniques we think there are about 10,000 that have been active in the last 10,000 years, and have the potential to erupt again.

We posed this question to Hazel Rymer from the Open University...

Hazel -   It does depend on what you mean by substantially change and what sort of eruption, but yes, some of the largest volcanic eruptions have profoundly affected the climate, and could do so again in the future.

Chris -   Thank you.  I think there’s evidence that the legacy of Krakatoa from 1880 is still there in the sea.  The ocean level is still a bit lower than it would otherwise have been because the Earth cooled because of the stuff ejected into the atmosphere.  I think there was a paper published in Nature a few years ago on that.

Hazel -   Yup.  You can see these effects for an extraordinarily long period of time.

We posed this question to Hazel Rymer from the Open University...

Hazel -  Pyroclastic means literally broken by fire.  It means broken up and exploded rocks.  So when a volcano explodes, it forms a pyroclastic flow and what’s so nasty about it is that they are often very, very hot, and they are clouds of very hot ash that go bellowing very, very rapidly along the ground, engulfing everything in their path. If you've ever been to Pompeii or Herculaneum, and seen the devastation, that’s why they're so dangerous.

We posed this question to Chris Kilburn from University College London...

Chris K -  Sometimes it appears to be the case.  For example, Hawaii and other midplates of volcanic chains have evidence that the activity migrates in a particular direction with time over geological timescales.  In other volcanic areas, you don't actually see the same process.  So, it can be observed, but it doesn’t have to be.

We posed this question to Hazel Rymer from the Open University...

Hazel -  Well, there’s no gas right inside the centre of Earth because the pressure is much too high.  It only comes out as gas when it finally gets to the surface. The magma that comes out of a volcano is really only sourced several kilometres beneath the surface.  I mean, it’s really just beneath the skin effectively.

We posed this question to Chris Kilburn from University College London...

Chris K -  Well, to be honest, I suppose because "active" means we have to have seen this erupting, we have evidence that it was likely to, I’d guess we still have to stick with the Earth, and so that would be Hawaii. But volcanoes such as Olympus Mons on Mars for example are considered to be the largest volcanic edifices in the solar system.  And some of the Jovian satellites, there is evidence of volcanic activity, but I'm afraid I don't know how big those volcanoes are.  But certainly, I think we’ll stick for Hawaii now.  Of course the Martians may have some interesting activity, should we ever finally set foot on Mars, you never know!

We posed this question to Hazel Rymer from the Open University...

Hazel -  No.  Luckily, there isn’t.  There’s plenty more "stuff" to replace it.