Wednesday 8 December 2021

It a bit of erosion "news"

Very heavy overnight rain continued all day driven by a strong west wind which only started to ease by late afternoon.

I tried a walk along the south shore, but there was little to see in difficult viewing conditions (MD).
Shelduck 11 braced against the wind on the mud. The rain had eased slightly and I thought at the time, this might be my only photo opportunity today - I was right!
Wigeon 95 on the lee side of No.1 outflow on the way out, there seemed more on the way back, but the rain was particularly harsh then, so not counting weather.
Rock Pipit 1 on saltmarsh 
Greenfinch 3 on Red Nab
Shag - a small pot bellied bird flying out of the harbour was almost certainly a shag, but didn't get a good enough look to be sure.

Blackbirds 5 particularly plump birds were catching worms on the water logged grass in the Nature Park. They were briefly joined by a 
Redwing, don't know if it was also after worms or just seeing what was going on.

That's the end of the bird news, unless someone else was daft enough to be out today. The rest of this post is just a bit of skear history. I've been saving the pictures for this article for a rainy day, not done bad, it's over a year!
On 12th October 2020 I explained how the skears were once two tree covered islands on top of boulder clay, left from the last ice age (if you want to read any historic posts there is a date selection option on the side bar to the right). The islands were still there in the late 17th century, possibly lasting as late as the great storm of 1703. 
Today, I want to demonstrate, that without any historic records, it is still easy to deduce that the islands have not been gone for long.
Boulder clay as the name suggests is a collection of rocks and clay amassed together by a glacier. When the islands were destroyed the surface clay would have been washed away, leaving the rocks and boulders to rest on the current surface. This first shot is of the inner skear, you can see a range of size and shaped boulders resting where they settled.
Boulders on the inner skeer
Although the inner skear is covered by the sea twice a day, and is subjected to weathering due to rough seas, it is a slow and pretty much a random process.
It's a different story on the outer skear, there are no large rocks present at all. The difference is the speed and power of the, particularly ebbing, tides has completely eroded any large rocks. But, to me, the interesting area is the middle skear, where the erosion can be seen in progress. 
There are still a lot of large rocks on the middle skear, but at they all appear to be a similar shape, triangular. This is a typical middle skear rock, when it's not encrusted with honeycomb worms or mussels.
Middle skear rock, the clue to its shape can be seen at its base where it is eroding
This is not the shape of the rock that first settled here. You can see at its base the fast tides are driving stones and mussels against it and undermining the rock. This has already happened to it at least once, the peak at the top was once its side. This next picture shows one that has just toppled over.
Recently toppled middle skear rock
You can see how the undermining has caused it to be top heavy and it has fallen on its side. The process begins again immediately. 
Sometimes the base gets so thin that they end up, upside down, as these three.
Three recently toppled middle skear rocks, now upside down
The process is surprisingly quick, I have walked on the skear for many years and have watched them erode and topple (although you never actually see them topple, the currents do that). I'm not talking months, but definitely decades not centuries. It is easy to see that in a few hundred years there will be very few large rocks on the middle skear, as is the case now on the much harsher environment of the outer skear.
There are exceptions of course, the rocks above are sandstone, there are also limestone rocks whose erosion is somewhat more erratic. A few granite rocks showing no obvious sign of erosion and the largest rock of all Conger. This is also sandstone, I think, but its huge size makes the process relatively slower. Even so, you can see the undermining process at the base of conger, but I'll not see it topple!
Conger rock, not ready to topple yet.

Hopefully a bit more wildlife news tomorrow