Planet Four Talk

Time lapse of fan formation

  • wassock by wassock moderator

    Watch this vid http://www.youtube.com/watch?v=Hc_o5PF17yY Its from the north pole but shows how fans and cracks form on top of dunes up there. As I see it in this video, the fans from cracks features don't need wind to form. In the example shown here the crack forms on the ridge of the dune slope and the fan simply falls down the hill.

    Does that make these things dunes as well? http://planetfour.org/subjects/standard/50e7418f5e2ed21240003643.jpg

    Posted

  • Paul_Johnson by Paul_Johnson

    Great vid was, she describes it at the beginning as water ice...?

    Also the ice is only 1-2 feet thick she says - we have been working on the ice being 3 feet thick! Very iinteresting vid and the woman had the silkiest voice I've ever heard .....hmmmm.

    Interesting that the material just pours out onto the surface and rolls down-I'm sure there must be similar stuff seen at the South Pole....?

    Posted

  • wassock by wassock moderator

    The vid shows the North pole are where I think the winters are shorter, thus the ice is thinner?

    There are a lot of "fans from cracks" type features in the south but I've always viewed them with wind as the spreading mechanism, will need to revisit maybe

    Posted

  • Portyankina by Portyankina scientist

    Hi everybody!

    wassock: those things are not dunes, they are weird depressions, similar to scalloped terrain (google for images). And it's rather hard to find windless dune field - just to have and keep dunes there you need wind... Unless they are cemented, which is all other story, but let's not get side-tracked here. So it might not need the wind to form the fans, but most of cases there is wind.

    Paul: Serina says that permanent polar cap is made of water ice. This is the same for the southern permanent polar cap - but here we were always speaking about seasonal stuff, which is mostly CO2 in both hemispheres with a bit more water in the north. But by "more" I still mean up to mm-thick layers only.
    The seasonal CO2 ice layer in the South is thicker because the winter is longer, colder and elevation of the hemisphere is generally higher (i.e. pressure is lower). There is much more CO2 frozen in southern winter than in Northern.
    We see similar downslope streaks in couple of locations in the south. I guess, they are more rare because they are made up by sand and there is much less sand in south, while north has the whole dune field around polar cap.
    And I'll pass your words to Serina 😃

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  • wassock by wassock moderator in response to Portyankina's comment.

    The commentary accompanying the video says that they are Dunes, and the title of the whole thing says they are dunes, and they look like dunes? And the commentary says that the dust is flowing down the slope of the dune. Are you telling us that the whole thing is a big fib?

    Can you clarify what the surface underneath the CO2 ice layer is like - I'm getting the picture that where it's not just bare rock there's a permafrost layer of dust CO2 ice and water ice?

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  • mschwamb by mschwamb scientist, translator in response to wassock's comment.

    I think she's referring to the image from the Planet Four site that you linked to http://planetfour.org/subjects/standard/50e7418f5e2ed21240003643.jpg

    Cheers,

    ~Meg

    Posted

  • wassock by wassock moderator

    Dhoooh! Yes think you're right, teach me not to re read me own post when I come back to it after a while.

    Because there's a wind in the summer to blow the dunes about doesn't have to mean that the same wind will be there in the winter/spring does it?

    Without any wind an asymmetric hill of sand which has dust venting from a crack in the ice along its ridge each year, and always falling down the steep side would in principle look like a dune and slowly roll across the countryside?

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  • Portyankina by Portyankina scientist in response to wassock's comment.

    "Without any wind an asymmetric hill of sand which has dust venting from a crack in the ice along its ridge each year, and always falling down the steep side would in principle look like a dune and slowly roll across the countryside?"

    But such a dune would soon ceased to exist. There is many ways to bring sand down the dune but only wind can bring it up.

    Posted

  • wassock by wassock moderator

    Yup, give up on that idea then 😃

    Posted