Mars Water Debate Rages (archival thread reposting #4)

[serak_the_preparer]

<br />spaceseed<br />(<font color="#66ccff"><b>B</b></font>)<br />02/21/03 05:34 PM<br /><br />Are these pictures at the same scale? They do not look similar to me. The water source (if it is water) in the Martian picture is a uniform horizontal strip, below the top of the crater. It is hard to see how snow deposits would form that pattern. It sure looks like water seeping out from under the ground.<br /><br />I assume the shortness of the gully tracks is because of the more rapid rate of evaporation on Mars.

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />02/21/03 05:53 PM<br /><br />Martian gully system is ~2 km acorss, while it is 0.6 km across on the Devon Island's system, according to the paper of P. Lee et al.<br /><br />I think liquid water will be protected by thin layer of ice on top. Rapid evaporating and cooling could form film of water ice for short term (1-2 hour/day) stability of liquid water on Mars.

 

[serak_the_preparer]

<br />rlb2<br />(<font color="#ffcc66"><b>G</b></font>)<br />02/21/03 09:39 PM<br /><br />voragerwsh<br /><br />"the relationship to layering, and why two craters of similar size can occur within a few kilometers of each other, yet one has gullies and the other (Bond Crater) does not..."-<br /><br />rlb2<br /><br />There may be several different reasons this might occur. This may not be the same reasoning but here goes.<br /><br />One reason may be that it might have something to do with the altitude of the two craters.<br /><br />Another reason may be one of the craters is in a sheltered area and the other one isn't. I lived up the Washougal River about 15 miles from Vancouver WA. In Vancouver they would get 45 inches of rain a year and we would get about 65 inches. I use to live on the snow line and I remember days where there were 12 inches of snow on the ground in one place and 1/2 mile up the road there would be none. Now the snow line I lived at wasn't directly due to elevation. I was farther up the valley at the same elevation, so here even the elevation had nothing to do about it. It was more about the area I lived in being more sheltered.<br /><br />Another reason is that snowdrifts could accumulate in one place more than another. This may depend on the wind blowing in a certain direction.<br /><br />I agree with you that both of these papers show more evidence for water ice. Snow packed together is under pressure. With pressure water ice if heated can form water.<br /><br />Lot of stuff to think about there. I like the idea that the global dust storms play an important role in all this. Every two years there is a global dust storm on Mars that increases its atmospheric pressure and heats the atmosphere up. Thus the density of the atmosphere increases. These global dust storms last for

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />02/24/03 11:17 AM<br /><br />rlb2<br /><br />Interesting reasonings you post above, "the altitude of the two craters" could be something to think about.<br /><br />But due to the proposed 104 to 105 years snow accumulation and melting mechanisms, small percipitation differentiations among two nearby craters (Bond & Hale) would also exhibit similar gullies over this long time span, wouldn't they? Interestingly, according to the paper of K. Edgett et. al, gullies of regional clusters may all face in a certain deirction and much more south-faced gullies in northern hemishere, perhaps that would suggest same directional wind- drift snow percipitation and melting uner solar heat absorption in certain Mars' obliquity.<br /><br />Perhaps age of the gullies could tell the difference from two models' credentials, unfortunately, I am not aware of any new gullies being observed by reimages of MOC/MGS in the same spot.

 

[serak_the_preparer]

<p><br />rlb2<br />(G)<br />02/26/03 03:18 AM<br /><br />Most the time on the subject of Mars I have many more questions then I have answers. I haven't read everything about these theories behind why this would happen in one place rather than another. However right now I have more answers and not enough questions than one should post here. Not any one of them may be right but here goes.<br /><br />To me there seems to be so many different reasons this can happen. Some of these already were stated above. This is not my field of expertise and some of these ideas may have already been mentioned.<br /><br />Another thought is it could be water ice melting in an underground artesian type spring when the water reaches the surface it turns into vapor then cools instantly into snow crystals. This could have a snow effect in localized areas then it would build up over time in sun-sheltered places. In places not sheltered from the sun the surface water ice would eventually dissipate into vapor and the thin dry Martian atmosphere.<br /><br />Another factor could be a comet or asteroid breaking up before entering the Martian atmosphere. The ice would instantly be vaporized when it entered the Martian atmosphere then would form ice crystals and fall to the surface as snow. Then it would pile up in windy areas as snowdrifts.<br /><br />Yet another reason is more straightforward. Mars simply has occasional snowstorms. Even very dry places like the Antarctica have a snow storm every once in a while. In the sun-sheltered areas on Mars it may not vaporize and then collects into snowdrifts similar to the sand dunes does in a desert. Here is a new picture from Odyssey that shows Ice clouds close to the northern polar region.<br /><br /></p>

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />02/26/03 10:36 AM<br /><br />RLB2,<br /><br /><i>"...when the water reaches the surface it turns into vapor then cools instantly into snow crystals..."</i><br /><br />That would qualify into the paper by Gilbert Levin et al. "...The (water) vapor condenses, then freezes, and, along with any falling ice crystals and upwelling sublimate, deposits on the surface..."--Liquid water and life on Mars<br /><br />Also, interesting question on "Does it Snow on Mars". There is compelling evidence of contemporary frost/snow on Mars., and frost in Viking 2 area was new in the winter of 1977.<br /><br />Perhaps, shallow aquifers or snow ice melting are the two most promising models to predict the martian gullies. There could be huge groundwater deposit and seasonal and diurnal percipitation on surface of Mars, my own perspective.

 

[serak_the_preparer]

<br />AlexBlackwell<br />(<font color="#ccffff"><b>A</b></font>)<br />02/26/03 03:22 PM<br /><br />voyagerwsh wrote:<br />Perhaps, shallow aquifers or snow ice melting are the two most promising models to predict the martian gullies. There could be huge groundwater deposit and seasonal and diurnal percipitation on surface of Mars, my own perspective.<br /><br />Alex writes:<br />I'm beginning to favor this intermediate position (i.e., the gullies probably represent manifestations of both subaerial and subsurface origin). I read the Christensen paper in the Advanced Online Publication (AOP) version of Nature, which I admit offered some fairly seductive reasoning, though I'm not sure if I'm completely won over. To be sure, Christensen provides a very plausible alternative to subsurface aquifers or aquicludes, though I was interested in seeing how he addressed two other salient aspects regarding the martian gullies, namely their observed affinity and association with specific subsurface strata, even when the layers are disrupted by faulting or other unconformities, as well as their observed spatial (regional) clustering.<br /><br />For me, I'm not sure if Christensen adequately addresses the first issue, though he does discuss an "upslope boundary" to the widely observed tongue-like, lobate deposits, which occur at varying elevations on the pole-facing side of different features. He further writes that "[t]he position of the upslope boundary is significant to this model, and probably represents the highest point on the pole-facing slope where ice-rich material is stable under solar illumination." If he (or anyone else) can explain how the insolation can be related to strata at different elevations, then I would probably accept his model without reservation.<br /><br />However, as t

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />02/27/03 02:09 PM<br /><br />Perhaps, one way to investigate the gullies formation may go the the volatile source. During winter season, some craters tend to accumulate frost in the rims and bases. [1]<br /><br />The source might come from groundwater in the bottom of each depression or craters, as the groundwater emerges, vapors and rapid freezes in the cold and thin atmosphere, it gradually drift upslope and condensed [2] or "pasted-on" near the rim and strata in certain hemispheric fall and winter. As season progresses into spring and summer, the accumulated snow/ice packs melt and trickled down the crater wall to carve the gullies.<br /><br />References<br /><br />[1]. The Frosted Craters of Northern Spring and Southern Autumn, NASA/JPL/Malin Space Science Systems<br /><br />[2]. Metastability of Surface Water on Mars, (The Obvious Model), Michael Hecht, Jet Propulsion Laboratory

 

[serak_the_preparer]

<br />PeteB<br />(<font color="#000000"><b>void</b></font>)<br />02/28/03 01:55 PM<br /><br />rlb2:<br /><blockquote><font class="small">In reply to:</font><hr /><p>Some calculations say there is an increase in the atmospheric temperature of as much as 20C during these dust storms. Therefore with the dust in the atmosphere, the increase in temperature with the increase in the pressure, the density of the atmosphere is much higher during these storms.<br /><br /><br /><br /><br />PeteB:<br />I thought that the temperature increase is only at the top of the dust clouds and that the surface cools during these global storms.</p></blockquote>

 

[serak_the_preparer]

<br />rlb2<br />(<font color="#ffcc66"><b>G</b></font>)<br />02/28/03 04:46 PM<br /><br />PeteB<br /><br />I thought that the temperature increase is only at the top of the dust clouds and that the surface cools during these global storms.<br /><br />rlb2<br /><br />I had to find a reference from where this was stated on the web. I remember reading a paper about the atmosphere heated by the Martian dust storms and wrote down the resulting temperature variation from my memory bank. Here is something that says it may be even higher.<br /><br />"As the dust has expanded the atmosphere has warmed dramatically, reaching temperatures more than 20C higher than pre-storm levels. The warming in the southern hemisphere is due to direct heating of the dust as it absorbs sunlight. This warm air rises moves across the equator into the northern hemisphere, much as warm air rises in the tropics on Earth and moves to the sub-tropics where it descends to create the Earth's hot, dry desert zones. As a result, the martian atmosphere is warming in the northern hemisphere in advance of the expanding dust storm."<br /><br />http://tes.la.asu.edu/webdata/dust_mov/dust_mov_sm.html<br /><br />"Second, dust clouds don't raise the temperature of air on Earth as they do on Mars. "The temperature of Earth's atmosphere is controlled by the latent heat of water vapor," explains Christensen. "Airborne dust can't compete." On Mars, however, sunlight-absorbing dust can substantially heat the dry, thin atmosphere -- raising winds and, of course, more dust. "The global air temperature on Mars is now about 30 degrees C higher than it was before this dust storm began," notes Christensen."<br /><br /><br /><font color="black">Tomorrow begins today and never ends<fon></fon></font>

 

[serak_the_preparer]

<br />farmer<br />(<font color="#ffcc66"><b>G</b></font>)<br />02/28/03 09:41 PM<br /><br />Alex:<br /><br />My name is John and have been a Farmer all my life.<br /><br />Just a note about Water.<br /><br />I live hear in the Madera, Calif. of San Jouaquin Valley.<br /><br />I bet you didn't know that under ground about 200-300 Feet under the soil in the farming belt are ( Live FISH ).<br /><br />We knew this long ago about under ground in the Aquafir water table are open ( Caverns ) of flowing water.<br />These open caverns are laced from the Sierra's down to the central valley.<br />Dureing millions of years of heavy saturation of rain wash out these caverns.<br />As for live Fish 200-300 Foot dept? ( We have proof ).<br /><br />Our old wells were were installed with the caseing down to blue clay at 200 foot. Then we had the cable tool go down another 100 Ft. of open hole as to cut cost.<br />Our bowls were set at little over 250 feet with a 10 foot open pipe we didn't screw on a coned screen.<br /><br />Over many years once in a while a FISH would plug the venturi to the impeller. And to clear out the live fish , we had to stop and start our pumps to clear it.<br /><br />We have frozen samples of shreaded fish meat, scales and air bags.<br />Other well drillers also encountered RED WOOD in the coble stone layers which have to be relocated away from the ancient stream of coble stones.<br /><br />We have our farm across the farm of madera ranch.<br /><br />ENRON was banned from setting up a Water Bank by Madera County.<br />These Caverns run from the sierras under Metropolitan cities and extraction wells number to 150 wells.<br /><br />There are other info . of Fish in the 200-300 Foot depts.<br /><br />What this info. is all about.<br />We are mapping MARS for surface Water and Gully wash outs.<br />Under

 

[serak_the_preparer]

<br />borman<br />(<font color="#ccffff"><b>A</b></font>)<br />03/01/03 06:27 PM<br /><br />Is the evolution of a “crustal” dichotomy upon Europa prevented by strike-slip faults?<br /><br />The gas torus in Europa’s orbit has been recently reported:<br />http://www.jhuapl.edu/newscenter/pressreleases/2003/030227.htm<br />http://www.spaceflightnow.com/news/n0302/27jupiter/<br />If you have free registered with Nature to read abstracts:<br />http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v421/n6926/abs/nature01431_fs.html&dynoptions=doi1046540531<br /><br />Jupiter offers the source radiation that impacts upon the atmosphereless ice of Europa to knock off about as much gas as Io does from its volcanoes. If the same face of Europa always faces Jupiter, tidal lock, it would suffer more erosion if the Europa’s own magnetic field is not strong enough to offer enough deflection. Is the ice crust connected to the core and so in synch with its tidal lock or is it free floating upon an ocean below its surface?<br />The tracking of strike-slip faults seems to indicate that the surface does moves some relative to core causing some polar wander of about 30 degrees over the past few million years:<br />http://spaceflightnow.com/news/n0112/02europapoles/<br /><br />As yet, no volcanoes have been observed to extrude through Europa’s ice crust that might anchor the surface to the core. There may be indirect evidence for volcanoes as opposed to 100-kilometer tall heat cyclones from smokers located upon the ocean basin:<br />http://www.spacedaily.com/news/life-03l.html<br />http://spacedaily.com/news/jupite

 

[serak_the_preparer]

<br />borman<br />(<font color="#ccffff"><b>A</b></font>)<br />03/01/03 08:29 PM<br /><br />Martian relic magnetic field<br /><br />Voyagerwsh,<br />Further study, primarily of the 4-page Purucker paper, http://denali.gsfc.nasa.gov/research/purucker/GL10901W01.pdf , and its better map of the fields, together with more recent ideas regarding Martian stratigraphy brings up at least three critical flaws with the idea that the needed Curie heat comes from an impact event.<br /><br />1) Stratigraphy: Only the most massive impacts have erased the fields. This suggests that the fields were inscribed early in Mars’ history. However Mars has many smaller craters subsequent to the big events that did not destroy the imprints. The observation is that Mars is not only cratered but is a cratered whole to a certain depth. Are we to believe that after an impact that large expances of the planet will be protected from further bombardment until the fields are safely buried by other than impact proccesses which will protect the fresh field from subsequent small impact destruction? The depth of the field may go down to 50 km.<br />2) Differing strengths of magnetisation: The blue or –nT readings only go to about –400nT whereas the red goes up to 666nT. If the Curie heat comes from a one-time event, very short in geological time, why should the poles be so different and not the same? How can a North magnetic pole be so much stronger than a South Magnetic pole at the same time? It is asking too much to have a pole reversal happen at the same instant of an impact.<br />3) Field contours: The Purucker map shows not a simply striped map of alternating fields but some rather complicated structure that can not be justified from just one

 

[serak_the_preparer]

<br />PeteB<br />(<font color="#660033"><b>nebula</b></font>)<br />03/02/03 10:57 PM<br /><br />rlb2:<br />"I had to find a reference from where this was stated on the web. I remember reading a paper about the atmosphere heated by the Martian dust storms and wrote down the resulting temperature variation from my memory bank. Here is something that says it may be even higher. "<br /><br /><br />PeteB<br />OK, I was wrong about the extent of heating of the atmosphere during the global storms. E.g, this abstract talks about a "large vertical range" but doesn't give specific altitudes. It turns out that I am acquainted with one of the authors and will try to get more information next week.<br /><br />But I also found some infomation about actual temperature measurements from Viking which show ~20-25 degree drops at the surface during a global storm in 1977.<br /><br />At this page look at the second graph labeled Mars Temperatures (scroll down about 80% of the way on the page) . Air temperatures measured about 1.5 m above the ground at both V1 and V2 show temperature drops coincident with the start of a dust storm on Sol 210. Als<br /><br />Also a companion page on pressures points out that the amount of sunlight reaching the surface during a global dust storm is reduced by 95-99% . My understanding is that direct solar insolation heating the ground surface materials is mainly responsible for surface temperatures. So if the isolation is intercepted by dust particles high in the atmosphere, where the direct

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />03/03/03 11:09 AM<br /><br />Solar visible light would penetrate CO2 better than dust particles in the atmosphere, surface temperature should decrease accordingly without the visible light imput. I think CO2 and CH4 are much better than dust storms in green house effect. Surface materials take mostly visible light, then radiate back with IR.

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />03/03/03 11:50 AM<br /><br />Borman,<br /><br />Perhaps, we need local geothermal sources to keep the salty water body or slush floating and convecting. Key words for the remnant martian magnetic strips might be salt and subterranean geothermal locales, I guess.

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />03/06/03 10:37 AM<br /><br />Supplement with larger image publication, NASA STUDY SHOWS HOW WATER MAY HAVE FLOWED ON ANCIENT MARS<br /><br />Examples comparison: Previous (1) vs Current (1)

 

[serak_the_preparer]

SteveHW33, this is an archival thread, recreated from old files and re-posted to Space.com. That said, I see nothing wrong with adding new material to it. Ideally, I'd try to quickly put up all the old posts, and then people like you and me could add on new posts.<br /><br />But the <i>Mars Water Debate Rages</i> thread was one of the longest-running conversations on the old Space.com, and it will take me awhile to bring as much of it back as I'm able to reconstruct.<br /><br />Short version of the above: Your response is welcome.<br />: )<br /><br />Farmer was the member who is the author of the post you've answered. I'm not sure if he posts much (or at all) to Space.com any longer. (Some of the more ardent conservatives participating in Space.com's Free Space forum went into voluntary exile awhile back when their excesses forced the hand of the moderators, who then began stricter enforcement of the Terms of Service. Farmer may have been among them.) But I will go a short distance in defense of his post.<br /><br />There are subterranean rivers, and living things sometimes inhabit those rivers. I myself am not willing to do the research to prove whether such fish are found very deep underground or not. You wish to prove Farmer over-reached himself, then the burden of proof is on you (since Farmer was not writing for a science journal, where the burden of proof would otherwise be solely on him).<br /><br />A quick search by the Mad Archivist, however, did turn up the following:<br /><br />Karst Landscape and Tourism Exploitation around Fengyu Cave, China by Jiang Zhongcheng (Institute of Karst Geology, Guilin, China 541004, Karst Dynamics Laboratory and Network Center of Guangxi Normal University)<br /><br /><i>The cave has a whole length of 5.3 kilometers and a subterranean river course of 4.1 km long. The main cave passage is usually 6-10 m wide and 3-10 m high, with many large chambers and 10 branches.The biggest ch</i>

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />03/06/03 12:13 PM<br /><br />Borman,<br /><br />Something might be very interesting, Mars may have a liquid core now!( i.e. global geothermal source). It could be a complete liquid iron or liquid outer core with light elements, such as sulfur, according to Dr. Charles Yoder et al. (1)<br /><br />With water ice detected by MO on the upper shelf, Mars may have deeper deposits of ice as well. As water ice burried inside the crust, it could be geothermal heated to groundwater.<br /><br />Reference<br /><br />1. NASA Scientists Say Mars Has Liquid Iron Core

 

[serak_the_preparer]

<br />AlexBlackwell<br />(<font color="#ccffff"><b>A</b></font>)<br />03/06/03 04:21 PM<br /><br />PeteB wrote:<br />My understanding is that direct solar insolation heating the ground surface materials is mainly responsible for surface temperatures. So if the isolation is intercepted by dust particles high in the atmosphere, where the direct heating occurs, the surface is shielded and can only be heated from any dust particles that are carried down through the atmosphere, which would be much less effective in raising temperatures at or near the surface, I think.<br /><br />Alex writes:<br />To first order, yes. Convective heat transfer between the rarefied Martian atmosphere and surface, even during dust storms, is neglible.<br /><br />Alex R. Blackwell<br />University of Hawaii

 

[serak_the_preparer]

<br />AlexBlackwell<br />(<font color="#ccffff"><b>A</b></font>)<br />03/07/03 05:16 PM<br /><br />In light of the recent Christensen paper in Nature, some may be interested in the following paper that was published online today in the Journal of Geophysical Research-Planets:<br /><br />Treiman, Allan H.<br />Geologic settings of Martian gullies: Implications for their origins<br />J. Geophys. Res. Vol. 108 No. E4<br />10.1029/2002JE001900<br />08 March 2003<br /><br />For those who do not have access to JGR-Planets, you're in luck. A few weeks ago I asked Allan to place a preprint online, which can be downloaded as a 756 Kb PDF file.<br /><br />Alex R. Blackwell<br />University of Hawaii

 

[serak_the_preparer]

<br />voyagerwsh<br />(<font color="#ff0000"><b>M</b></font>)<br />03/07/03 06:17 PM<br /><br />Thanks for T. Allan and your kindness to provide preprint online.<br /><br />Just wondering could have eolian dust and silt eroded gullies in crater Wall, Noachis Terra?

 

[serak_the_preparer]

<br />spaceseed<br />(<font color="#66ccff"><b>B</b></font>)<br />03/11/03 08:58 AM<br /><br />We have had "Blue Mars" and "White Mars"; I would call this paper's suggestion that all the gullies are caused by dry flows of dust "Gray Mars". This is not good for prospects of surface life.<br /><br />The opening statement <blockquote><em>Martian gullies are found on steep slopes of all origins, on all sorts of terrains of all ages, scattered across nearly all of Mars. Gullies are observed on all manner of substrates (layered, massive, shattered, rubble), with or without nearby mantling deposits.</em></blockquote> makes the groundwater hypothesis hard to believe, unless it can be shown that gullies take different forms in different areas. However, it does not rule out the idea that the groundwater comes from snow deposits, which would be independent of landform, and similar to windblown dust patterns. The difference would be in gully shape.<br /><br /><br />I am interested in the meaning of this statement later in the paper:<br /><blockquote><em>If shallow igneous intrusions have been so abundant in the recent geological past as to produce gullies across the globe, it would be reasonable to expect at least one such intrusion to still be warm. Yet no warm spots have been reported from the TES instrument on the MGS spacecraft [Christensen et al., 2001], nor so far in preliminary THEMIS instrument images, reports, and press releases.</em></blockquote> Does this rule out geothermal heating of the sub-suface, or simply indicate that the heat does not reach the surface? Is there enough data to make this statement? Without geothermal heat, a sub-surface biosphere is very unlikely.

 

[serak_the_preparer]

<br />rlb2<br />(<font color="#ffcc66"><b>G</b></font>)<br />03/11/03 08:59 PM<br /><br />I believe in the "Blue Mars" more and more especially after this latest finding on a Martian fluid iron core.<br /><br />To me if it is proven that Mars has a fluid iron core then there should still be thermal vents on Mars. Its surface might be getting enough heat convection from the interior of the planet to have hot spots on Mars. The hot spots may not resemble Earth's because and flow of water to the surface would instantly sublimate into the Martian atmosphere then change into ice crystals.<br /><br />A good place for ape caves (larva tubes), spring water and aquifers on Mars breaking though to the surface is from hill's gullies and mountain cliffs. This would form a buildup of snow in localized areas. The unsheltered places would dissipate the water vapor differently then the sheltered places. Voergerwsh enlightened me about a paper written that covers that scenario.<br /><br /><font color="black">Tomorrow begins today and never ends<font color="black"></font></font>

 

[serak_the_preparer]

<br />exoscientist<br />(<font color="#66ccff"><b>B</b></font>)<br />03/12/03 01:25 AM<br /><br /> Treiman argues in the paper that dry flows could have created the Malin/Edgett gullies.<br />Key aspects of the flows that led Malin/Edgett to argue they were carved by liquid water flow are the dendritic (like a tree branching) and anastomosing (channels that branch off then reconnect with the main channel) features seen in the gullies. Such features are expected<br />with channels cut by liquid flow.<br />Treiman suggests that snow avalanches have shown these features and gives images of snow avalanches where the temperature was below -15 C. He gives blown-up versions of these images at the end of the paper. In the blown-up versions there do indeed seem to be dendritic and anastomosing patterns.<br />However, he states that liquid water exists as thin films even in such cases. He argues that this amount is not important for the development of the avalanche but he offers no support of this claim. If snow avalanches occurred even at temperatures below when such thin liquid films existed that would support his claim. But my understanding of snow avalanches is that in fact some amount of liquid water encourages their formation. I'm also suspicious of the fact that the only images he gives that might show dendritic and anastomosing patterns involves snow in which it is admitted there is some amount of liquid water available.<br />Also the -15 C was measured air temperature. As Christensen argues sunlight can penetrate snow and cause melting subsurface.<br />Treiman argues that other dry flow cases can show features of liquid flow, such as pyroclastic flows as argued by Nick Hoffman. But the images Hoffman has given of pyroclastic flows still do not show the dendritic and anastomosing patterns common to liq