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Large parallel slashes through topography

  1. Nov 21, 2008 #1
    Large parallel "slashes" through topography

    What causes these huge (dozens of miles long) parallel "slashes" through topography like seen in this photo??:
    [​IMG]

    Here is another one:
    [​IMG]

    The pattern is so regular, it looks like someone took 50 mile wide comb and scratched the earth's surface with it. You can see the slash marks cut through the "more natural" river flows too.
     
    Last edited: Nov 21, 2008
  2. jcsd
  3. Nov 21, 2008 #2

    matthyaouw

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    Re: Large parallel "slashes" through topography

    Hard to tell on these pictures alone... On the top picture it looks like a lot of the river valleys are follwing lines of weakness. Can't tell what the weakness is, but it could be igneous dykes or a faults. I can't quite get my head round the topography on no.2 but it looks like two sets of ridges & furrows running at right angles. I'm more inclined to think dykes than faults because I can't see any displacement where they cross.
    I don't know the area's geology so I can't tell you any more.

    Could you link to the second on google maps? I wouldn't mind a closer look.
     
  4. Nov 21, 2008 #3
    Re: Large parallel "slashes" through topography

    Ok after a little research, these look like transform faults qualitatively:
    [​IMG]

    But the thing is the previous pictures are in Utah, which is nowhere near a tectonic plate boundary.
     
  5. Nov 21, 2008 #4

    matthyaouw

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    Re: Large parallel "slashes" through topography

    You get faults everywhere, not just near boundaries. I still wouldn't rule out dykes.
     
  6. Nov 21, 2008 #5
  7. Nov 21, 2008 #6
    Re: Large parallel "slashes" through topography

    Pretty amazing features, showing that we still have a long way to go before understanding and it also suggest that things we think we know for sure, aint so.
     
  8. Nov 21, 2008 #7

    matthyaouw

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    Re: Large parallel "slashes" through topography

    On google earth you can see that it is a canyon that has exploited two sets of lines of weakness at right angles to one another. My bet is still faults or dykes but I can't confirm. See if you can find the area on this geological map: http://geology.utah.gov/maps/geomap/parkmaps/pdf/M-87.pdf
     
  9. Nov 23, 2008 #8
    Re: Large parallel "slashes" through topography

    Where can I find more background on geological dikes? Right now what I find basically says "dikes are intrusions that cut across a geological body". Well that's kind of circular - it doesn't explain what causes these formations to occur in the first place. Thanks.
     
  10. Nov 23, 2008 #9

    matthyaouw

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    Re: Large parallel "slashes" through topography

    Basically, when molten magma is on the move within earth it squeezes upwards through the pre-existing rock. When it sets below the surface to form an igneous rock it is known as an intrusion. It can come in all kinds of shapes and sizes, and it's known as a dyke where it is tabular in shape and cuts through beds of rock, rather than following the bedding planes. If the dyke is harder than the surrounding rock it will often stand up as a ridge. If softer, it will erode more easily and form a furrow, valley etc....

    Does that clear things up?
     
  11. Nov 23, 2008 #10
    Re: Large parallel "slashes" through topography

    Err, but what causes it to be in straight lines like this?
     
  12. Nov 23, 2008 #11
    Re: Large parallel "slashes" through topography

    I'm certainly no expert on geomorphology, but I'd say they are faults.

    If they are dykes, then they are probably still faults because dykes are basically just igneaus intrusions along pre-existing lines of weakness which are usually faults anyway.

    Also, I would normally expect dykes to form ridges, because they tend to be composed of stuff that is more resistant to weathering than the surrounding "country" rock. To me those lines of weakness look like topographic lows, or valleys, although I am aware that to the untrained eye these images can be deceiving, so, I'd guess they are faults.
     
  13. Feb 3, 2009 #12
    Re: Large parallel "slashes" through topography

     
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