These are the Travertine Dams of Slade Brook, near St Briavels, and have the distinction of being the best Travertine Dams in the country. Impressive, eh?
Having never heard of a Travertine Dam before, nor ever knowingly seen one, (and therefore utterly failing to be as impressed as you may just have been) I went in search of information. It turned out to be fairly simple really. Anyone familiar with the tufa deposits in limestone areas such as Malham (North Yorkshire) will know the principle. The spring of Slade Brook emerges through limestone and in the process absorbs quite a lot of that mineral. When the water flows over obstructions in the stream the turbulence releases dissolved carbon dioxide, causing the limestone to come out of solution and deposit itself. In time these deposits build up to form the 'dams' we see today.
Slade Brook is on a pleasant walk I recently did from St Briavels, a few miles from my home. It started with lovely views of the Wye Valley.
The River Wye flows along the far side of the valley. According to my walk book, the low-lying cultivated ground in the middle distance was once within a meander of the river, which became incised when the river straightened itself. I remember learning this stuff for Geography O-Level, a long time ago, and it's nice to see it 'for real'. Those old text books would have drawn an oxbow lake where the old river bed had been, but that has long since disappeared.
I searched in vain to discover when all this happened; presumably some time in the last 10,000 years or so, after the last ice age had receded.
So there you have it — chemistry, geology and a picturesque countryside walk, all in one post.
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P.S. For an interesting sequel to this post, and some more photos of the travertine dams, click this link.
I'm still on holiday, but a lesson like this is a tonic! I've spied a few tall waterfalls in thd Lake District, but they were too far off to impress.
ReplyDeleteLucy