Silbury Hill
Sequence of photos showing each collapse.

The first collapse. May 2000

English Heritage, National Trust & local archaeologists fence off
the hole and post guards and signs for people to keep out.

EH place a tin cover over the hole to stop further collapse from rain damage.
Unfortunately Bert Janssen, Janet Ossebaard and friends Dave & Rob
dug under the cover to gain entry.
They then abseiled down the tunnel under cover of night and dragged the lid
down into one corner by anchoring their rope to the scaffolding.
The angled cover then channeled rain water into one spot weakening that side.

Which resulted in the cover being taken away to stop it sliding into the ever
widening hole.

Eventualy the bad weather caused a 3 rd collapse

Resulting in a huge hole.