How are cryovolcanoes different to magma volcanoes?

05 July 2016

Question

I heard recently that there may be cryovolcanoes on Pluto. This was explained to me as ice-volcanoes where instead of magma, molten rock, there is water. But what is the difference between ice and rock? Ice is frozen water.... Rock is frozen magma. Right? Is there a fundamental difference?

Answer

Chris Smith put this to Professor Marian Holness, geologist from the University of Cambridge...

Marian - No, there isn't. Let's just step back a bit and talk about Pluto for a minute. These messages that are coming pixel by pixel for the last year or so. So Pluto is extremely cold. Its surface is about minus 200 degrees centigrade. So, what's the surface of Pluto got on it? Well, it's ice essentially. There's water ice which is fairly rigid. It's like the bedrock of Pluto is water ice. And then there are some ices that move around a lot. There's nitrogen ice and there's carbon monoxide ice. And then moving around, they're sublimating and then they're condensing somewhere else. The reason I'm telling you all of this is because if you look at the topography on Pluto, there are mountains and ridges and bumps, and lumps. If they're old, they've got craters on them. That's how we know they're old. They must be made of bedrock. There are these two mounds which they found. They're not mountain ranges. They're just isolated circular mounds and they're about 150 kilometres across and they're about 6 kilometres high. Now that's a pretty big mound. We've got some things vaguely similar to that like Hawaii on Earth - the biggest volcano on Earth. Anyway, there are these things. Because they're really big, they must be made of something strong. So they're probably made of water ice. They've got a central depression in the middle. They look just like a volcano, a really big hole in the middle which is what a volcano looks like. And their surface has not got many craters on it. so they're quite young, but it's got a very curious sort of hummocky texture. That's essentially all we know. It's pure speculation. We're just saying the shape of these things looks like a volcano but we don't know any more than that. It's just very exciting science.

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