MadSci Network: Astronomy

Re: What are ice volcanoes?

Date: Fri Nov 18 15:18:29 2005
Posted By: Gene Marlin, Undergraduate, Geosciences/Geology, Mississippi State University
Area of science: Astronomy
ID: 1131547076.As

  Hi Rebecca,

  On Earth, we think of a volcano as a kind of vent along which molten 
rock (of basalt-like or granite-like composition, or at some point in 
between) is released at the surface. It is powered by the fact that the 
molten material is less dense and less viscous than the cooler country 
rock it travels through, so bouyancy forces drive it to the surface. As 
the magma body reaches the surface depths, pressure exerted drops rapidly 
and, especially if it has a more granitic composition, gasses trapped in 
the magma are released rapidly, giving an explosive "kick" to the 

  At different temperatures, pressures, and crustal composition, solids 
other than what we generally think of as rock can be involved in 
volcanism, including ices. An ice volcano is therefore only a volcano 
that emits liquids that freeze into ices. In fact, the distinction 
between Earth volcanoes and ice volcanoes is somewhat blurred when it is 
considered that ices are technically minerals, since they are non-
biological, naturally occuring, crystalline solids and some textbooks 
list water ice as one. Considering that, liquid water, in the right 
geological context, qualifies as a magma or lava every bit as much as 
more traditional lavas we see on Earth. 

On Triton there seem to have been three kinds of ice volcanism:

(1) The type associated with "Cantaloupe terrains", where the surface is 
cracked by faults and slushy fluids (thought to be water or mixes of 
water and ammonia or methane) that flowed viscously across the surface, 
creating a texture that resembles the skin of a cantaloupe. 

(2) The type associated with the volcanic plains, in which a less viscous 
molten material than that in (1) (probably water at a higher temperature 
with or lesser amounts of ammonia and/or methane) formed lava lakes and 
depressions interpreted as volcanic calderas. 

(3) The active volcanoes or geysers generating dark streaks in Triton's 
atmosphere during the Voyager 2 flyby. The explosive agent here is 
believed to be methane or liquid nitrogen that forms at very shallow 
depths. The liquid ascends to the surface because it is less dense than 
the ice, but vaporizes as pressure drops. Because this is a fairly 
shallow phenomenon that is mostly powered by vaporization, it may be more 
accurate to call these geysers. 

Only the phenonmenon in (3) is known to be happening today. Triton may 
have long-since cooled past the point where it could support the 
other two types of volcanism, leaving "fossil" landforms behind as 

(Reference: "Exploring the Planets" by Christiansen and Hamblin. Prentice-
Hall, 1995.)

--Gene Marlin 

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