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Ice circles - and now their jungle cousins

  1. Aug 31, 2016 #1

    DaveC426913

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    The article below is tainted with the silliness of woo, but the phenomenon is quite natural - and way cool.

    It's a tropical verson of an ice circle.

    I found ice circles hard to believe at first, but I watched a small-scale simulation on an artificial river with just the right flow rate and just the right temperatures for ice accumulation. Indeed, it forms just as expected.

    But now, it seems ice isn't the only substance that can perform this feat. It appears floating vegetation can result in the same phenomenon.

    Here it is on Google (zoom way in):
    https://www.google.com.ar/maps/@-34.2520409,-58.831072,874m/data=!3m1!1e3?hl=es

    So, a slow-moving river is surely flowing through this pond, and vegetation has piled up on its surface. The "island" has been accumulating flotsam, (and possibly growing, I don't know). As it turns, protrusions are discouraged by brushing against the shoreline, whereas empty spaces are free to fill with growth (or accumulation). The result is a floating, slowly rotating island.

    As I said, I've left this link till the end because it's tainted with woo.
    http://mysteriousuniverse.org/2016/08/the-search-for-the-mysterious-round-island-that-moves/
     
  2. jcsd
  3. Aug 31, 2016 #2

    Bystander

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    How so?
     
  4. Sep 1, 2016 #3

    DaveC426913

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    Excerpt from that article:
    Pretty much every story I can find about it seems to be authored by wooists.
     
    Last edited: Sep 1, 2016
  5. Sep 2, 2016 #4

    Bystander

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    Did a little looking and got similar results.
     
  6. Sep 2, 2016 #5

    DaveC426913

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    If you can wade thought some woo, this video contains some great footage from the initial expedition of:
    - flyover shots from the plane
    - satellite photos showing the rotation (below)
    - foot forays onto the island itself



    the-eye.jpg
     
  7. Sep 3, 2016 #6

    BillTre

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    Pretty cool.

    There are places in the Upper Peninsula of Michigan where the terrain is mostly sand in mounds, left as the glaciers melted. This makes an irregular surface over porous soil. There are a lot of lakes and ponds in the low points where the water table is higher than the sand. Small ones can have pine needles and debris fall on the surface and build up a floating mass. Eventually you can end up with a pit in the land, with a flat bottom with ferns bushes and maybe small trees on it and no exposed surface water. If you walk out on them, your feet can go through the surface and only have water under them.
    If this kind of thing started out spinning, I could see this kind of thing happening easily.
    Having a hard bottom underneath, which they mentioned, would help keep any roots from vegetation making anchors from the floating island to the substrate.

    There are floating islands in the islands Okefenokee swamp too: pix

    It also reminds me of the round holes (pot holes, pix) you can get in the rock bottom of a river when the flow makes a reproducible vortex and there is a good supply of pebbles to get caught in the vortex and drill into the bottom.
     
    Last edited: Sep 3, 2016
  8. Sep 6, 2016 #7
  9. Sep 6, 2016 #8
    I've seen this before. Amazing. But I'm confused about your theory DaveC426913. I don't see any river attached to the floating island.
     
  10. Sep 6, 2016 #9

    jim mcnamara

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    The entire mat surrounding the circle and the circle itself are like what you see in temperate bogs: floating mats of vegetation. You can walk on them - when you jump on them you can feel small waves created from your impact. Except that underneath there is a large slow moving river instead of a landlocked pond.

    Google 'plant succession in a bog' - here is a slide show: http://www.slideshare.net/jayarajgr/succession-8212591
     
  11. Sep 6, 2016 #10

    DaveC426913

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    Exactly. I don't either.

    I think it's got to be there though:

    I find it implausible that the island is moving randomly via wind-power alone.
    1] There would be no reason for it to be round. Wind isn't going to spin it. If the wind is just pushing it back and forth, then there's no shear force to grind it circular.
    2] It could easily sit long enough for detritus and creepers to permanently join it to the mainland.

    I predict that they will find an underground stream. (Though I find that pretty implausible too. An underground should manifest itself in the surface growth and geography of the surrounding land).
     
  12. Sep 6, 2016 #11

    BillTre

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    I like the idea of the bog succession (2nd picture on the 5th slide of the slide set).

    Bust off one of the sides and you get floating island.
    The water underneath can flow along, imparting energy to the overlying debris layer. It doesn't have to be a big flow.
    The video made a point about how swampy the place was. Seems there could easily be a slow flow going through the whole area, even if its not a submerged open water space.
    If the current is hitting one side more strongly or has it in a vortex, a detached floater could be made to spin.
    Frequent abrasion on the sides of something rotating will tend to round off the edges.
     
  13. Sep 7, 2016 #12

    jim mcnamara

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    After as small literature search:
    Okovango river delta sub-circular floating vegetation island from :
    http://www.jstor.org/stable/40979854?seq=1#page_scan_tab_contents Note: %$**# paywall.

    First photographed in 1944: The one @DaveC426913 is looking at is on the Parana river delta. Brian Wilson's publication is 1990.
    You can see it by:
    Code (Text):

    get into google maps, enter "S 18 40.000  E 22 12.000"
    Change over to Earth view - the box on the lower left.
    Zoom in as much as it will allow.
    To the right of the red pointer blob you can discern the circle - distance =  the max width of the blobject pointer.
     
    This may work for you:
    https://www.google.com/maps/place/1...e3!4m5!3m4!1s0x0:0x0!8m2!3d-18.6666667!4d22.2

    Note what slow moving river deltas in the tropics look like - dense swampy floating mats of vegetation covering vast areas. Getting into one of these places is expensive and hazardous. Which might explain why they are not commonly documented. Been there done that - never again - not looking for circles, for plants.
     
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