Sunday, August 28, 2011

Sed Structure Sunday - Real Rivers!

As a continuing service provided by this blog, we'll be using this edition of Sed Structure Sunday to illustrate some of the characteristic features of that strange and mysterious geomorphological entity known as a "RIVER", which apparently has befuddled some folks.  Here's a picture of the Green River, Wyoming, showing that most characteristic of river attributes, THE SUBAERIAL CHANNEL, i.e., the big ass declivity through which the water flows.

Note the difference between this sort of water/sediment transport system, and say, tiny adhesive droplets of water flowing at low Reynold's numbers through interstitial pore-space.  Pretty much not at all the same thing.  Pretty goddamn different beasts all together, when you get right down to it.

Here's a picture of a little bank-attached barform, accreting laterally into the channel.  You can also see, to the left of the little point bar, a spot where lower flows cut into the toe of the bar, leaving behind a coarse-grained lag (predominately made up of oil shale weathered off the slopes).

Here's some rad current-ripples on the barform surface, showing flow to the right of the picture (hammer for scale).

  And here's a close-up of the same.  Neat, huh!  Note the muddy drapes present, left behind during the very end of the falling stage of last flow to come through here.  Thus are mud rip-ups born!

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