Following on from my post on Tuesday of my walk along part of the Wolds Way from Fridaythorpe in the Yorkshire Wolds, I am here in pen and (st)ink to try to explain the formation of these peculiar valleys took place.
During the last ice age there was a glacier that came down from Scotland through the Vale of York butting up against the North York Moors and the Yorkshire Wolds. The deep crater that was squeezed between this glacier (to the west) and the ice sheet(to the east) that covered the North Sea (originating in Scandinavia) was then filled with water and was known (although I don't know who exactly was around at that time to call it or know it by anything in fact - whoever they are they will for sure be very old by now and should they not have shaved will have a very large and thick beard - more impressive than those sported even by ZZ Top I would say) as Lake Pickering (with the Moors to the north and wolds to the south).
The aforementioned monstrous slab of Scandinavian ice then started to encroach on Lake Pickering causing its contents to displace through the Yorkshire Wolds. This motion of the running water caused all the soil to run off off with it as it made it's way away from Lake Pickering in the north to the south and into what was Lake Hull. It was this movement of water that eroded the soil and created the valleys as it went.
As the ground is so permeable once the ice age slowly but surely came to an end and the permafrost melted (which previously prevented the water soaking into the ground) the water permeated into the soil. With the water settled the silt that had been carried down from the hill tops as Lake Pickering had overflowed.
This is why the valley bottoms in Thixendale and the surrounding valleys of the Yorkshire Wolds look so perfect yet are dry bottomed and are as flat as they are. This is a unique feature due to the unique series of events that came together in order to make the Yorkshire Wolds appear the way that they do. Good eh!
Below is a map showing the glacier on the western side of Lake Pickering and the ice slab of the North Sea to the eat. The northern and southern shores of Lake Pickering are marked by the North Yorkshire Moors and the Yorkshire Wolds respectively. The arrows show the movement of water following the displacement of the Lake.
View Yorkshire Wolds Formation and Lake Pickering in a larger map