What causes linear rilles?

[Leovinus]

<i>What could cause a long indentation on the Moon? First discovered over 200 years ago with a small telescope, rilles (rhymes with pills) appear all over the Moon. Three types of rilles are now recognized: sinuous rilles, which have many meandering curves, arcuate rilles which form sweeping arcs, and straight rilles, like Ariadaeus Rille pictured above. Long rilles such as Ariadaeus Rille extend for hundreds of kilometers. Sinuous rilles are now thought to be remnants of ancient lava flows, but the origins of arcuate and linear rilles are still a topic of research. The linear rille below was photographed by the Apollo 10 crew in 1969 during their historic approach to only 14-kilometers above the lunar surface. Two months later, Apollo 11, incorporating much knowledge gained from Apollo 10, landed on the Moon.</i> <div class="Discussion_UserSignature"> </div>

 

[killium]

Don't you see ? Its a runway for ET <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> </div>

 

[aaron38]

Could they be fault lines? Early after the Moon's formation there must have been technonic activity. That looks like it could be an area where two crust areas spread apart.

 

[JonClarke]

The general concensus is that linear rills are fault lines. Faults are simply fractures in rocks along which movement has occurred, you don't need plate tectonics. Faulting can be caused by impact, compaction, cooling, intrusion, and possibly by tidal stresses.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[earth_bound_misfit]

I find it hard to believe that these are fault lines. If this was the case i wouldn't expect to see that lump in the middle of it, running from the crater.<br />But hey, i'm no expert on these matters. <div class="Discussion_UserSignature"> <p> </p><p> </p><p>----------------------------------------------------------------- </p><p>Wanna see this site looking like the old SDC uplink?</p><p>Go here to see how: <strong>SDC Eye saver </strong>  </p> </div>

 

[silylene old]

Welcome back Jon! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[summoner]

My first thought is also fault lines. Either from impact or even during its formation. If the moon was truley formed from a chunck of the Earth, that intial ejection had to form some faults. <div class="Discussion_UserSignature"> <p> </p><p> </p><p> </p><p> <br /><table cellpadding="0" cellspacing="0" style="width:271px;background-color:#FFF;border:1pxsolid#999"><tr><td colspan="2"><div style="height:35px"><img src="http://banners.wunderground.com/weathersticker/htmlSticker1/language/www/US/MT/Three_Forks.gif" alt="" height="35" width="271" style="border:0px" /></div>

 

[JonClarke]

Nice to be missed (and back)!<br /><br />The lunar crust dates from after the probable formation of the moon by a giant impact. As the moon cooled it had a global magma ocean. The plagioclase scum on the surface of the ocean (plagioclase floats in ultramafic and mafic magmas, like water ice) formed the primordial anorthositic crust at about 4.5 Ga. The rills are in the mare basalts, somewhat younger again (as young as 3 Ga, I think). So the faults that form linear rills are still younger than that (although still billions of years old)<br /><br />Cheers<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[exoscientist]

Some channels on the Moon are also believed to have been carved by lava flows.<br /> Reminds me of a question I'm investigating.<br /> A report by Peter Mouginis-Mark in 1990 in Icarus argued there were channels cut in Tharsis that had the appearance they were water carved rather than lava carved and they were geologically recent. This report was based in Viking imaging. I looked in the same area for such channels using MGS imaging and I think I found some examples. Here is one:<br /><br />Sample Tharsis plain <br />http://ida.wr.usgs.gov/html/e02005/e0200557.html<br /><br /> The question is: are these water carved rather than lava carved?<br /> The depth and width of the channels might help to resolve the question since water carved channels would be expected to be shallower and thinner.<br /> The channels whatever their cause also give the appearance of relative youth.<br /><br /><br /> Bob Clark<br /> <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

Hi Bob<br /><br />Yes, lunar sinuous rills are thought to be lava channels formed by fluid lava.<br /><br />My understanding too is that lava channels tend to have simpler internal geometry, and are associated with exclusively volcanic features. Although determining this from satellite imagery alone can be difficult, as lava channels can be sinuous, leveed, and form deltas when they intersect water.<br /><br />Cheers<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[btimsah]

It's been my experience that anything that can be potentially "alien-made" is almost always ruled as created by lava or volcanoes. So if you're looking for an alternate explanation (other than natural) you won't find it. However, if you're looking for non-natural structure's go to my site below! I am studying images which in total prove there are indeed some strange structures NASA has photographed.

 

[btimsah]

A rile is an alien made race track where they hold their "Summer race to end cancer". Okay, okay just kidding. :-D

 

[JonClarke]

btimsah wrote: "It's been my experience that anything that can be potentially "alien-made" is almost always ruled as created by lava or volcanoes." And it has been my experience that perfectly unremarkable geologic features are attributed to alien activity by people who have no idea of geology. The posted image is a case in point. A pefectly normal but slightly blurry and some jpeg artefact-ridden image of the moon is supposed sto show "windows"!<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Polarwander<br /><br />Please list 8 points of congruence between lunar linear rills and features caused by glacial erosion or deposition.<br /><br />Nice link BTW. There will always bee some features we do not understand or about which our ideas evolve. But just because we do not know everything does not mean we know nothing. <br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[alexblackwell]

<i>Please list 8 points of congruence between lunar linear rills and features caused by glacial erosion or deposition.</i><br /><br />Wow, Jon! Now you're handing out assignments. Are you polarwander's new faculty adviser? ;-)

 

[JonClarke]

Hi polarwander<br /><br />Subglacial striations and entrainment features are a good start and examples of glacial erosion. Where you get erosion you must also get deposition, glacial deposition generates its' own set of landforms. Once you have a few of those, point to some lunar features you believe match them.<br /><br />In addition to the internet would try a local library. Any book on geomorphology with have a chapter on glacial processes. You may even find an entire book devoted to glacial geomorphology.<br /><br />Cheers<br /><br />Jon<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Keep in mind that gouges and stratiations are all small to medium scale features, you would not expect to see them in satellite images. <br /><br />Cheers<br /><br />jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[silylene old]

<i>Nevertheless, during polar wander movement, boulders of great size might be entrained along the way.</i><br /><br />Thus, the boulder should <i>remain</i> at the end of the Rille <i>after</i> the polar ice has melted. Do you have any examples of huge boulders at the terminus of a rille? Such boulders would need to be present. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[JonClarke]

What horns? I only see impact features and lava plains with wrinkle ridges.<br /><br /><br />Cheers<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Polarwander<br /><br />One planet at a time please <img src="/images/icons/smile.gif" />! There is excellent evidence for past and present glaciation on Mars, that is not the issue here. The question is whether lunar features, especially linear rills, are the result of glacial action.<br /><br />That said the wrinkle ridged lava plains of the moon, Mars and Mercury are not basaltic crust. In the case of the moon they are clearly younger than the anorthositic highlands, from crater counts and stratigraphic relations and from radiometric dating. The Martian and Hermian examples are also younger that the primary crust, based on stratigraphy and crater counts. Whether or not the large basin forming impacts are able to generate mantle melting is quite irrelevant to this issue. If they are not, then other mechanisms must be sort, but the fact remains that the basin fills are younger than the crustal basement.<br /><br />Cheers<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Hi Polarwander<br /><br />Please keep in mind that stratigraphy and relative ages from crater counts are two different things. Relative stratigraphic ages are obtained from the geometric relationships between different units. Cross cutting and overlying units are always younger. This is why we know that the fills of large basins on the moon, Mars, and Mercury are youngr that the highland crust into which they have been excavated. Crater counts are a very rough way of comparing relative ages of particular surfaces with or without ecidence of straigraphic relationships, given a flock of essentially uncalibrated assumptions, except in the case of the earth and moon.<br /><br />It is certainly true that covering material which is later removed can protect the underlying substrate from impacts, thus causing a misleading crater density. It need not be ice of course, sediments and water will do just as well. The amount of protection depends on how thick the covering layers are, large enough impactors will punch straight through, as for example has been suggested for a group of putative craters in the Antarctic The presence of such a vanished covering layer can be assertained by looking at the size frequency distribution of craters. There will be a deficiency of smaller craters below a certain size will be present if the area was once covered for a significant time. The inflection point in the size-frequency distribution will allow the thicknes to be calculated, the number of craters larger than this will still give and approximate age for the surface and the number of smaller craters should allow an approximation of how since long the protecting layer disappeared. The caveat is that if the protective cover was present for a very short time the inflection point may not be discernable. If there is evidence of such a dichotomy, then one would look for other evidence, such as geomorphology or stratigraphy, for such a vanished cover, conversely, is such stratigraphic or <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Hi polar<br /><br />Good to see you are still working on it.<br /><br />With respect to U shaped valleys, you first need to demonstrate that linear filles have U-shaped profiles. If they do you then have to show they have other features associated with glaical erosion and deposition. If formed by valley glaciers they should cirques at one end and terminal moraines at the other. <br /><br />With respect to large boulders, these can be formed by a range of processes, such as impact ejecta. We know that the lunar surface has many impacts and so large boulders are to be expected. To determine whether a particular boluder is an eratic you need to look at its association. The Apollo 17 site was well studied and is well documented. Jack Schmitt, the only geologist who went to the moon was LM pilot on Apollo 17. He worked for several years in Alaska and Norway and so would be very familiar with galcial erosion and deposition and would have recongised glical features had they been present. None were reported.<br /><br />With respect to polar accretion of ice and short lived ice sheets I think it is important to distinguish between the presence of ice, which is a possibility on the moon, and glaciers. A glacier is not simply ice, it is a dynamic ice system that has undergone flow. The presence of ice, per se, does not mean you have a glacier. Ice can be present as ground ice, frost, snow without forming glaciers. Therefore to demonstrate glaciers you have to demonstrate flow. Hence the importance of evidence glacial erosion and deposition in the case of former ice. <br /><br />Just thinking about lunar glaciers generally, to get ice to flow you need pressure. On earth about 60 m of ice is needed before it with flow as a glacier. Under lunar gravity you would need a lot more - I would guess six times, say 360 m. this is a lot of ice. Secondly you would need a source of ice. Any ice exposed to lunar sunlight with sublime very rapidly, that is why the polar ice, if prese <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Hi polar<br /><br />My understanding is that the martian caps are mostly water ice with a significant amount of CO2. I have no idea on what impact this would have on the properties of the resulting clathrate.<br /><br />From what I know of Jack Schmitt from his CV I would suggest that he would has recognised glacial evidence had he seen it. Keep in mind the lunar samples are utterly devoid of evidence of water<br /><br />As for the moons of Jupter and Saturn, most of these are surfaced entirely by ice, so are a different kettle of fish altogether.<br /><br />Cheers<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Hi polar<br /><br />Jack Schimtt was not a glacial expert, his field was igenous petrology and geochemistry, as I recall. However he had doneextensive field work in glacial terrains and would therefore had some first hand experience. Plus some training in glacial processes would have been part of his undergraduate training.<br /><br />What do you mean by shaky infilling of lunar features and why does nobody want to believe it?<br /><br />Can your provide images of the features you call of the entrainment gouges on the moon? <br /><br />What do you mean by submerged sand?<br /><br />What is a low pressure clade sliding through regolith?<br /><br />How would you get pure CO2 ice caps? Water is a much more abundant volatile, as I recall, so you would expect ice deposits to be dominated by water, with lesser CO2. <br /><br />What are the inexplicable swirls in circular maria? Can you supply a photo?<br /><br />What is a magnetoshear on the moon?<br /><br />Puzzled<br /><br />Jon<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[silylene old]

Hello Jon and polarwander,<br /><br />Jon: I thank you for your informative, patient socratic style in teaching all of us on this board about geology (us chemists formally are taught very little geology). I admit that I have learned much in this subject from your (and others) posts in this forum because these discussions have inspired me to read books and articles to gain a deeper knowledge.<br /><br />Polarwander: I was reading about the linear gouge marks on the ocean floor formed by the keels of dragging icebergs. Interestingly, these gouge marks look superficially like rilles, and can even be a similar length. Of course, for this to be a mechanism, the moon would have had to have been covered by deep oceans and floating ice (clearly a fantasy). Still fun to ponder. Here's a link:<br />http://www.ig.utexas.edu/people/staff/goff/abstracts/Duncan_icebergs.pdf <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>