Wednesday, May 27, 2009

It's sedimentary

After all the horrible wet weather today was sunny, calm and even warm. The gulls were back in fine fig, after their stay on the Oval (the local large playing fields), where last week there had been thousands of them puddling about in large areas of standing water.


The tide was out, a long way for this beach. And on the still-wet parts of the sand, could be seen some amazing runnels.


Reminiscent of the tracks made by stones shifting about on salt-flats, there had a weird out-of-this-world appearance.


A closer inspection reveals what is going on. The sea is still draining away, lowering the water table. As it does so it leaves behind the stones, in a miniature braided channel. Like a ladder in a pair of tights, the channel runs backwards up the beach.


Closer still and it becomes obvious that this is an erosion feature. It is very similar to satellite images from deserts showing wadis.


Sometimes the effect can be more or less symmetrical, providing 'antlers' to this black 'nosed' deer!


This one shows the eroded sand being deposited again as mini-deltas just beneath, and to the left of the rock. Just about the whole of erosion and deposition cycle could be seen in miniature.