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LadyAstronomer
Bookworm
Reged: 11/15/07
Posts: 2951
Loc: Library of Congress
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ESA’s Venus Express has detected varying levels of the volcanic gas sulphur dioxide which may suggest active volcanoes.
Press release is here: Volcanoes on Venus
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"I do not know what I may appear to the world, but to myself I seem to have been only a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me." -- Sir Isaac Newton
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10475
Loc: Amargosa Valley, NV, USA
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Hasn't this idea been kicked around since at least the Magellan radar mission?
Considering the temperature and density of Venus' atmosphere, and the probable dryness of the volcanic gases, I suspect that an active vent on the surface would look nothing like its earthly counterpart. I wonder how we would recognize a volcano if we were to catch it in mid-eruption?
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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LadyAstronomer
Bookworm
Reged: 11/15/07
Posts: 2951
Loc: Library of Congress
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Quote:
Hasn't this idea been kicked around since at least the Magellan radar mission?
Yup, Magellan detected many, many volcanic remnants, primarily shield volcanoes (for those unfamiliar with shield volcanoes, they are the type of volcanic cones found in the Hawaiian Islands), pancake domes (features formed by a viscous lava flow, they look like pancakes with a central, bowl-shaped vent), and others. The most unusual of these are "tick-like" structures that are similar to pancake domes, but are surrounded by small ridges that look much like legs. In fact, the planet's surface is primarily basaltic. However, this is the first evidence that there might be current activity.
Quote:
Considering the temperature and density of Venus' atmosphere, and the probable dryness of the volcanic gases, I suspect that an active vent on the surface would look nothing like its earthly counterpart. I wonder how we would recognize a volcano if we were to catch it in mid-eruption?
Good question, Dave! Maybe some type of thermal emission, but as you pointed out... Given the Venusian atmosphere that may be a long shot. The calibration alone could be somewhat of a nightmare.
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"I do not know what I may appear to the world, but to myself I seem to have been only a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me." -- Sir Isaac Newton
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10475
Loc: Amargosa Valley, NV, USA
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On Earth, water vapor supplies a huge proportion of the energy of a volcanic eruption. Water dissolved in magma also lowers the melting temperature and decreases the viscosity.
It's hard to imagine an explosive eruption without water. Dry, flowing lava would have to be much hotter than in any earthly eruption in order to make flow channels -- but we see them, so those super-hot volcanoes must exist.
I would guess that the absence of water in the Venusian crust slows down the heat transfer from the interior, allowing for hotter rock closer to the surface. That's in addition to the greenhouse heat already present.
Because of all this, I'm thinking that volcanic outgassing there would be a slower, gentler, and possibly more steady background process on Venus than Earth. This, I suppose, is why its been hypothesized that, in the absence of plate tectonics, volcanic resurfacing of Venus takes place in rare episodes of global "overturning", interspersed by long periods of slow outgassing.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10022
Loc: Chaville, France
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What would "overturning there"? An episode where the "whole" planet experiences massive lava flows, while on earth it is more contained to our small volcanoes, like the safety thingy on a pressure cooker?
And wouldn't there be something to learn from Io's volcanoes? I know little about Io's surface makeup, but it looks like there the volcanoes are barely holes in the ground, compared to Olympus Mons or Mt St Helens.
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Matt
CI700 mount with various scopes on top.
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2472
Loc: tacoma wa
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Explosive eruptions on Venus: "...the high atmospheric pressure at the Venusian surface (about 90 bar)... gases that would ordinarily escape freely from the magma remain trapped within it, leading to explosive eruptions."--New Solar System, RS Saunders
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Mardi
4" achromat, ETX-70.
Whitepeak Lunar Observatory Website
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10475
Loc: Amargosa Valley, NV, USA
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I'm also not convinced that there are a lot of volatiles available in Venus' crust to even support much outgassing. On Earth, plate tectonics continually recycles water and CO2 back into the deep crust, where it can be reused to power new volcanic eruptions. I know of no recycling mechanism on Venus -- once a gas is in the atmosphere, that's where it stays. That would mean a rocky crust depleted in volatiles, which means volcanic activity would be sparser, less fluid, and requiring higher pressures and tempertures to activate.
--------------------
"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10475
Loc: Amargosa Valley, NV, USA
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Quote:
And wouldn't there be something to learn from Io's volcanoes? I know little about Io's surface makeup, but it looks like there the volcanoes are barely holes in the ground, compared to Olympus Mons or Mt St Helens.
That's a good question. The lava lakes on Io are very hot, but I'm not sure what their composition is. The surface crust is mostly sulphur minerals, which count as volatiles to a certain extent, but I don't what, if any, recycling mechanisms would exist there.
I would think the Io's original composition has been extensively processed and modified during its history.
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10022
Loc: Chaville, France
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Io's eruptions are very sulphur-rich, and from what I understand there is no plate tectonics there, just volcanic flows going <splat> on top of previous lava flows.
What is sure is that because of the atmospheric density and gravity, we would not see on Venus eruptions as spectacular as those on Io.
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Matt
CI700 mount with various scopes on top.
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2472
Loc: tacoma wa
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Quote:
On Earth, plate tectonics continually recycles water and CO2 back into the deep crust, where it can be reused to power new volcanic eruptions. I know of no recycling mechanism on Venus --
One theory for such recycling on Venus is called "delamination". It involves mantle convection expressed in upwelling and subduction at the surface unrelated to plates. The chapter in New Solar system on surfaces and interiors of planets explains ti, and there is an online reference i found, VOLCANISM AND VOLATILE RECYCLING ON VENUS FROM LITHOSPHERIC DELAMINATION. 2005 LPI meeting. Another article (abstract) dealing with the subject of volatile recycling on Venus can be found here: "Volcanism and volatile recycling on a one-plate planet" JOURNAL OF GEOPHYSICAL RESEARCH 2007
Perhaps this is what you meant by 'global overturning"? Anyway, nothing here to contradict the characterization of Venusian volcanism as generally less violent and less frequent compared to Earth's.
There is also more recent interesting info on Venus & volcanism at "VENUS VOLCANISM" from the University of Oxford Venus Express Group if anyone is interested. They seem to infer that 50ppm of h2o is required for eruption (in the past at least) and the present level averages 30ppm but ranges up to 70... Recent analysis of the lower venusian atmosphere from Venus Express "VIRTIS Observations of Venus' Lower Atmosphere" indicates presence of water vapor in the lower atmosphere as well as strong vertical mixing--so i would assume this would mean that this indicates a possibility of reintegration of this gas (as well as others) back into the crust and from there into the mantle...?
Anyway thanks to the OP for the reminder of this fascinating ongoing mission! No end to the surprises waiting out there...
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Mardi
4" achromat, ETX-70.
Whitepeak Lunar Observatory Website
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 10475
Loc: Amargosa Valley, NV, USA
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From the conclusion of Mardi's first link:
Quote:
Venus’s crust is therefore likely to be volatile rich
if the planetary interior is volatile rich. Delaminating
crustal material will therefore carry volatiles into the
mantle. Some of the resulting melt may erupt, but as
pressure rises while the instability sinks liquids will be
trapped by refreezing. Delamination therefore refertilizes
the mantle with volatiles and eclogite and makes
possible a boninite-producing mantle in the absence of
plate tectonics. Through time the mantle’s bulk melting
temperature therefore decreases, encouraging
catastrophic melting and resurfacing events.
Great information, Mardi. I always admire the way you zero in quickly on the most relevant literature!
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"S.O.E." (Sauron's Other Eye) 16" Royce conical mirror: A permanent work in progress.
10" Homebuilt dob, old Coulter mirror
Next Project: The "Eye of Sauron" Observatory!
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