Gazette & Herald today
Threat to the hill
SILBURY Hill is at risk of an internal collapse, says leading Wiltshire archaeologist Mike Pitts, unless urgent remedial work is carried out on an exploratory tunnel.
The tunnel into the south west slope of the 5,000 year old hill claimed to be the largest man-made mound in Europe was dug in 1969 by a team led by Professor Richard Atkinson from Cardiff University.
The dig was filmed by the BBC whose reporter at Silbury Hill for the Chronicle series was Magnus Magnusson, later the Mastermind host.
Mr Pitts, of Marlborough, the only living archaeologist to have directed excavations at both Avebury and Stonehenge, told the Gazette that a survey has shown a gaping cavity where Atkinson's shaft was backfilled.
He said that unless the hole is filled or shored-up it could lead to a further collapse.
The Gazette was the first to reveal in 2000 that a 225-year-old vertical shaft at the core of the hill had collapsed, leaving a hole on the summit.
That revelation led to a major survey of the hill by English Heritage, which manages it on behalf of its absentee owner Lord Avebury.
English Heritage employed specialist Swedish civil engineers Cementation Skanska to drill survey boreholes from the top of the hill to the bottom to see if any further voids could be found.
A camera lowered into one of those bore holes revealed that the Atkinson tunnel backfill had been inadequate, said Mr Pitts.
After studying some of the pictures sent back from the bottom of the bore hole Mr Pitts said large voids can be seen in the Atkinson tunnel.
He said: "The whole hill appears to be stable, which is good news.
"The bad news is that inside the hill Richard Atkinson's tunnel is collapsing."
Mr Pitts said "It is collapsing inside the hill at the moment but unless something is done it will reach the surface."
The archaeologist said "absolutely unique ecological deposits" within the hill could be harmed if the side of the hill gave way, allowing the air to reach them.
Modern thinking by archaeologists including English Heritage's own experts is that the Atkinson tunnel should never have been allowed to be dug in the way it was, said Mr Pitts.
He said: "It is evident that the tunnel was never properly backfilled and that has led to voids being created inside the hill."
Three possible solutions are being discussed, said Mr Pitts, who is editor of British Archaeology magazine, which reveals the problems with Silbury Hill in its latest edition, due out on Christmas Eve.
One would be to use the bore hole to pump in a chalk slurry to fill the void.
Another would be to re-open the Atkinson tunnel and back-fill it properly.
The third and most exciting alternative, the archaeologist said, would be to open up the tunnel, shore up the roof and sides properly and leave it open for archaeologists to examine.
Mr Pitts said re-opening the excavation would allow archaeologists to examine the structure of the hill and take samples from its interior.
He said Prof Atkinson had not completed his report on the Silbury dig by the time he died and most of the samples he took had been lost.
English Heritage confirmed that voids had been found in the hill in the area of the Atkinson dig and that methods of dealing with them were being examined.
Mr Pitts said: "If nothing is done the collapse will eventually reach the surface."
English Heritage still has to repair the collapsed central shaft that left a crater in the top of the hill in 2000.
It was given a temporary filling of polystyrene with a final layer of chalk the material originally used to build the hill but no decision has been taken yet about a permanent solution.
Since the collapse of the shaft dug in 1776, the hill has remained closed to the public and new fences around its base were recently erected.
