Thanks to Chris Johnson and Tony Marsh for alerting me to this. Thanks also to Geomatics PLC. It's a new LIDAR image of Stonehenge and the Avenue, showing the ground surface contours at 1 ft intervals -- this is very detailed work.
So what does it show us that we did not know before? We have discussed to so-called "periglacial stripes" at great length -- use the search box for the relevant entries. I am happy to admit that I have got it wrong -- I have interpreted the "grain" of earlier LIDAR images as showing that the alignment of the Avenue and the "periglacial stripes" is oblique to the prevailing surface slope. This new image shows that the alignment is in fact perpendicular to the contours. In other words, the Avenue runs pretty well exactly along the "nose" of a very slight ridge, except at its outer end, where it simply keeps going in a straight line to the far end of the spur. So there it is on the flank of the spur rather than on the ridge top.
Tony has added the T-marks on the image so that we can see where averaged perpendiculars are located -- but these are subjective in the sense that the alignment of the downslope line will vary according to the width of the lateral spread of the sampled points. If you see what I mean.......
We are talking about very subtle variations here -- just a degree or two. So the message is that the Avenue has been build along the nose of the ridge, and maybe has nothing at all to do with solar or lunar alignments of solstices. By the same token, the "periglacial stripes" are running pretty well directly downslope, as we would expect them to do in a periglacial environment. But I still don't think they are anything to do with periglacial sorting or patterned ground processes. They are not straight, and because of their internal characteristics I still think they are solutional rills just like the many thousands of others in the Stonehenge landscape. Here -- at the SW end of the Avenue -- they run pretty well parallel to the Avenue sides. To left and to right they probably splay slightly, keeping more or less perpendicular to the contours and running directly downslope so long as there is a sufficient gradient. That is what water does.
The trouble is that nobody has looked for these "insignificant" or "irrelevant" rills systematically, because the focus of attention has always been Stonehenge and the Avenue.