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Fraser
2006-May-24, 04:33 AM
SUMMARY: This photograph shows one of Mars' three great shield volcanos: Pavonis Mons. The image was taken by ESA's Mars Express spacecraft, and shows a top view of the extinct volcano as it rises 12 km (7.5 miles) above the surrounding plains. Scientists believe the linear features are lava tubes that were created when the volcano was active. Similar to here on Earth, lava forms a crust on top while molten rock continues to flow under the surface. The longest tube extends over 59 km (37 miles).

View full article (http://www.universetoday.com/am/publish/lava_tubes_pavonis_mons.html)
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GBendt
2006-May-26, 10:54 PM
I don´t think that the structures that are visible on the picture represent collapsed lava tubes.

Firstly, the structures all become narrower from their start to their end. This feature is quite untypical for lava tubes.
Secondly, the structures are far too wide to be lava tubes. To produce a lava tube with a diameter of kilometers (look at tha scale in the picture!), lava flows of 4 million m³ per second are required. This is a lot. If such flows occurred on mars, where did that all lava go, and why should it flow through a tunnel that became narrower and narrower without any indication of it breaking out of that tube, and without clogging that narrow section?
Thirdly, collapsed lava tunnels look different than these structures, they have no gentle valley slopes like the ones on the picture.

I think that it is not lava tunnels what we see there, but traces of outbreaking flowing water. While it flowed, it boiled up into the martian atmosphere, as the air pressure on mars is too low to maintain liquid water. Thus, while the water flowed, the flow became thinner and thinner, as more and more water turned into steam and disappeared into the martian atmosphere. I think this is the reason why the valley we see becomes narrower, the greater the distance to the well is from which it came.

Regards,

Günther

JonClarke
2006-May-27, 05:39 AM
According to the the depressions are 280-1.9 km wide. Similar scale lava channels have been reported on earth. The width of the collapse depression depends on the degree to which the channel drained. The down-flow portions of the channel are less drained than the up flow parts, which is why they are narrower.

Jon

JESMKS
2006-May-27, 07:23 PM
There are a number of lava tubes in the picture that appear as a series of open pits created by the partial roof collapse. There are also a number of open channels with smooth sides that appear to be lava troughs that may never have had a roof. There is also a strange band or trough that runs north-south (assuming north is at the top of the picture) that transects about four channels in the sw quadrant of the picture.
Jack

JonClarke
2006-May-27, 10:54 PM
A rift system, perhaps?

Jon

GBendt
2006-Jun-03, 10:58 PM
The valleys we see here are at the outskirts of the Pavonis Mons volcano, just where this volcano´s slope passes into the surrounding plaines. The picture spans roughly 90 km, the whole volcano has a base diameter of 200 km, and the large and wide central crater of the volcano is beyond the border of the picture.
If the valleys are collapsed lava pipes, a lot of lava must have flown in these pipes. But the picture doesn´t give an indication of any lava flows emanating from the end of these pipes.
If you look at the picture carefully, you will realize faint curved structures which seem to be something like a sequence of little pits. Such pits might represent steam vents.

Mars is an icy cold planet, and the many pictures provided by NASA and ESA satellites have proven that the soil of mars contains a lot of ice. Glaciers have been detected in various areas, even on Olympus Mons. If ice is heated by a volcano, it melts and will produce water and steam.

Close to a volcano, the bedrock has to suffer from quakes, as well as from the pressure caused by the volcano´s high tension gases and its body of liquid lava. This has an impact on the structure of the ground. Rift systems are most likely in such an environment. But I don´t think that these valleys are rift systems. Rifts usually are less curved than these valleys. And rift systems do not have rounded ends.

On a planet like Mars, the volcanism is different from the volcanism on our planet. On Mars, gravity is less, so volcanos grow much higher than they do on earth. The mass of Mars is only one tenth of the mass of earth, so the energy supply from this mass in order to maintain volcanism on Mars is much less. It may be too low to produce lots of liquid lava, but it may be hot enough to produce lots of high-pressurized boiling water. Water may play (or may have played) a role on Mars like lava does (or has done) on our planet.
On Mars, the air pressure is much lower, so water cannot be liquid on Mars and thus is much more easily converted into steam. Steam under pressure can blow up a landscape. I think if the volcanos on Earth would act in an atmosphere which has such a low pressure than has the atmosphere on Mars, their water would not flow out in whispering fountains, but burst out more powerful in hissing steam.

Regards,

Günther

JonClarke
2006-Jun-03, 11:23 PM
The valleys we see here are at the outskirts of the Pavonis Mons volcano, just where this volcano´s slope passes into the surrounding plaines. The picture spans roughly 90 km, the whole volcano has a base diameter of 200 km, and the large and wide central crater of the volcano is beyond the border of the picture.

The plains are also probably lava as well


If the valleys are collapsed lava pipes, a lot of lava must have flown in these pipes. But the picture doesn´t give an indication of any lava flows emanating from the end of these pipes.

This is quite common for terrestrial tubes. they are subsurface, not surface flow features. Their discharge points are presented by the plains.


If you look at the picture carefully, you will realize faint curved structures which seem to be something like a sequence of little pits. Such pits might represent steam vents.

Possibly. Of they could be small lava tubes undergoing incipient collpase or collapse along faults.


Mars is an icy cold planet, and the many pictures provided by NASA and ESA satellites have proven that the soil of mars contains a lot of ice. Glaciers have been detected in various areas, even on Olympus Mons. If ice is heated by a volcano, it melts and will produce water and steam.

Close to a volcano, the bedrock has to suffer from quakes, as well as from the pressure caused by the volcano´s high tension gases and its body of liquid lava. This has an impact on the structure of the ground. Rift systems are most likely in such an environment. But I don´t think that these valleys are rift systems. Rifts usually are less curved than these valleys. And rift systems do not have rounded ends.

On a planet like Mars, the volcanism is different from the volcanism on our planet. On Mars, gravity is less, so volcanos grow much higher than they do on earth. The mass of Mars is only one tenth of the mass of earth, so the energy supply from this mass in order to maintain volcanism on Mars is much less. It may be too low to produce lots of liquid lava, but it may be hot enough to produce lots of high-pressurized boiling water.....

The evidence is that Mars has produced lots of liquid throughout its history. The energy of this comes from radioactive decay, not graviational collapse. hyprothermal activity is a byproduct of this.

Jon