Science Questions

How are cryovolcanoes different to magma volcanoes?

Tue, 5th Jul 2016

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Amanda Adams asked:

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?


Chris Smith put this to Professor Marian Holness, geologist from the University of Pluto, in false colourCambridge...

Marian - No, there isn't. Letís 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, itís ice essentially. There's water ice which is fairly rigid. Itís 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, theyíve got craters on them. Thatís 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. Weíve got some things vaguely similar to that like Hawaii on Earth Ė 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. Theyíve 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 itís got a very curious sort of hummocky texture. Thatís essentially all we know. Itís pure speculation. Weíre just saying the shape of these things looks like a volcano but we donít know any more than that. Itís just very exciting science.


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Exploding plumes of material (a volcano) relies on material which is heated sufficiently to turn into a liquid and/or gas, but then cools down into a solid, close to the source.

Farther from the Sun, it gets much colder, and different substances can be in this solid/liquid/gas zone.

So the main difference between volcanoes and cryovolcanoes is how hot (or cold) the liquid is.
Earth has many active magma volcanoes;
Venus shows the marks of more volcanoes than Earth
Olympus Mons on Mars is a massive shield volcano
Earth has water volcanoes - we call them geysers. But in most places on Earth, the water will remain liquid and run away, or evaporate, rather than forming an ice mountain.
Jupiter's moon Io has volcanoes spewing lava and clouds of sulphur over 100km into space, before falling down and solidifying on the surface.
Saturn's moon Enceladus has plumes of water vapor streaming from tiger stripes at the south pole. Much of this water ends up in Saturn's rings, rather than building a mound on the surface.
Neptune's moon Triton has volcanoes of water and ammonia
Pluto's cryovolcanoes are thought to be powered by liquid nitrogen or ammonia.
Comets have gasses such as water, carbon dioxide, carbon monoxide exploding from vents on the surface as they approach the Sun. But because the comet has virtually no gravity, they keep going, and are lost to the comet's tail.

Look for volcanoes as "tectonic" or "cryovolcano" here: evan_au, Tue, 19th Jan 2016

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