This is one of the most unexpected and most interesting finds I think I have ever come across. While walking along the River Severn today, I spotted these bizarre cuts in the mud on the path, almost as if a person had come along and scratched the surface with a knife. I ruled out this theory of an anthropogenic origin, as these small splits continued along the entire exposed mud surface of the small riverside path.
My theory for their formation:
I believe that these slits are stress fractures in the mud, caused by its contraction as it begins to dry and lose moisture content. Straight after the flood event, this mud was deep and behaved much like a liquid.
This picture is of the very same mud during the dry period of April 2020. As you can see, the mud was heavily scarred with deep cracks, caused by its contraction as it lost its moisture content.
Due to the mud's formation (deposited in an extremely wet environment), it is particularly susceptible to contraction as it dries, due to its high water content in the first place.
Considering these cracks must begin somewhere, these slits are quite probably the very first step in this process, caused by the sediment contracting so much that it actually pulls itself apart.
Another interesting spot on my walk today:
Along the riverbank, all the trees and banks had a wet band around 50 cm above the water surface, as seen below. A quick look at the river level graph confirmed this to be the high water mark from the morning's tidal surge, caused by the almost-full moon creating spring tides out at sea, which worked their way up the river all the way to Tewkesbury.
I explain how these tidal surges in the Severn work on my YouTube channel:
Finally, I also came across a lovely bivalve specimen, with both valves still attached, in the middle of the path, on the embankment alongside the Severn. I didn't think to snap a picture, but I never expected to find something normally associated with a beach on the Gower in a muddy field in northern Gloucestershire!
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