Silbury Hill 180
Image by photobabe

Thanks VBB,

The way you just explained it made it very clear.
So the picture is this? If nothings done soon it will be washed out a bit like a inward landslide, but then in a more serious manner as water and ice are involved and it is not surrounded by supporting earthhills, the process if not taken proper measures will proceed rapid till it's flattened, ... collapsed.

Except for dating material and a cross section of the earth, that can be done with relative ease and nowhere near as distructive as tunnels. There is no need for further investigation to the hill.
And as there is nothing to see on the inside a glass tunnel would be of totally no interest to anyone.

Again thank you for your explanation.

Sorry, had a bit of a delay.

I obviously wasn't that clear - there is no imminent danger of collapse but two things are happenning. One is that the voids above the tunnels are perhaps making their way gradually towards the surface at a very slow pace. If this is happening archaeology is redeposited out of context in a lower position and perhaps broken up and lost - and although this is only a small area it could in very simplistic terms lead to a trench appearing on the surface. The second thing that is happenning is that material underneath Silbury has been damaged by air and water and will be lost unless they go in and get it.

I expect this is clear as chalk

VBB