Friday Rock Blogging: Mud

Picture courtesy reader Martin. Or maybe Martin doesn’t actually read this blog, and it’s just Wren. Anyway, thanks, Wren and Martin!

Today’s rock is a geopuzzle: What’s up with these ridges? How did they get there, and what determines their size?

I don’t actually know the answer, so this is the best hint you’re going to get out of me.


  1. Ellery wrote:

    Based on your clue, this is clearly a strange phenomenon that exists only along the border of Wales and England, possibly due to a secret EM fence between them :)

  2. cope wrote:

    Could it be that a tidal bore moves up this waterway and when the tide drops, these ridges of sediment result from erosion?

  3. delagar wrote:

    No comment, since I have no clue — I just love Friday rock blogging.

  4. chezjake wrote:

    Just guessing here, but looking at the raised edges and their shadows, I’m wondering if this is mud that has run over a tilted slate bed, or some such similar structure.

  5. Ben wrote:

    Overbank flood deposit? Control: duration and size of flood


    A semi careened off the m48 and into the water and created a big wave. Control: Size of semi.

  6. Ron Schott wrote:

    Well geez, let’s bring the entire aviary in on this! I think these waveforms are actually mimicking the wingbeats of an unladen swallow. The real question is… African or European?

  7. Owen wrote:

    I wonder if the pylons of the bridge there play some role in the formation.

  8. Laura wrote:

    Ooo! The M48! The road that takes me home. This picture is making me homesick for the Severn, there’s some great fossil hunting to be done along there… *sigh*

    Anyway. Before I saw the larger picture I was going to say that they were current formed ripples as there is definite bifurcation on some of those crests.

  9. BrianR wrote:

    hmmm…at first glance, the features have an erosional rather than depositional look to them … I might have to agree with cope above…something along those lines.

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