When one thinks of volcanoes, images of fiery, molten lava being ejected out of a crater and flowing down a hill fill the mind. Volcanism on other planets and moons, however, looks much different. These volcanoes erupt ice instead of silica magma and emit plumes of methane and ammonia instead of carbon dioxide and sulfur dioxide.
Cryovolcanism
Cryovolcanism is a phenomenon where volcanoes erupt water ice and other frozen liquids, instead of molten rock as the volcanoes on Earth do. There is not a place on Earth where these features exist. There is a regional phenomenon on the southern shores of Lake Superior where water erupts through ice craters along the shoreline, but the origination of the water is from a lake, not from the mantle. However, there are several bodies within the Solar System that are now known, or suspected, to display cryovolcanic activity.
Recent space exploration of the solar system using satellites has identified numerous moons that show evidence of cryovolcanism. The biggest clue is the presence of craters that are emitting substances. Moons where this feature is thought or known to exist are:
- Neptune's moon Titan
- Saturn's moon Triton
- Jupiter's moon Europa
- Jupiter's moon Ganymede
- Uranus's moon Miranda
- Saturn's moon Enceladus
- Saturn's moon Dione
- Pluto's moon Charon
The climate on these moons is very cold - hundreds of degrees below zero - and the atmospheric pressures are extremely low. These conditions create an environment where "hot" material is still frozen and erupted through the moons' crust in the same way as lava is erupted here on Earth.
How Cryovolcanism Works
Volcanism requires a source of heat and something to melt. On Earth, the sources of heat are radioactive decay within the core, frictional heat caused by the Moon's gravity (tidal friction) and left-over heat from the accretionary stage of the Earth's formation. The material that is being melted is the Earth's silica-rich crust, which gets recycled through the mantle and melts to form magma, or lava when it comes to the surface.
Cryovolcanism works much the same way except that the material being melted is water ice, ammonia or methane. Even at "melting" temperatures, these materials are actually still quite frozen and solid, but being warmer and less dense than the surrounding, subsurface material (the moon's "mantle"), the material erupts through craters in the crust.
Although the chemistry involved in cryovolcanism is much different than the chemistry involved with volcanism on Earth, the mechanical and geological processes are similar. Scientists believe the source of heat that causes cryovolcanism is radioactive decay within the moons' core and tidal friction caused by the gravitational pull of the moons' planets.
Sources:
"Icey Volcanoes, Methane Rain", 01/21/05, Astrobio.net
"Icey Volcanoes Likely Shape Saturn's Smooth Moon", by David Powell, 04/24/07, Space.com
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Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
