Checking 4700 yo ancient monument for tunnels, seismic activity, etc.
Leslee
** Ancient monument needs hi-tech rescue**
Archaeologists turn to engineers to save Silbury Hill, one of the world's most spectacular prehistoric sites, from collapse after 5,000 years
** Maev Kennedy, arts and heritage correspondent**
Guardian
** Monday April 2, 2001**
A hi-tech engineering solution is being sought urgently, to help archaeologists deal with the disastrous consequences of the wettest winter since records began, and the aftermath of centuries of curiosity about the largest manmade hill in Europe.
The mound, which is within sight of the great henge and stone circle at Avebury, is over 4,700 years old, but archaeologists have no idea why it was built.
It is estimated to have taken 35m baskets of chalk rubble and earth, and up to a century to build, but its purpose remains an enigma.
Despite a wealth of legends, including one of a great king buried on horseback, no trace of any chamber or burial has ever been found.
A shaft dug by an 18th century amateur archaeologist collapsed last year, and although it has partly filled up with soil and rubble it has also widened.
Further cracks have been detected during the past winter, and archaeologists now fear that the mound, which is pitted with the remains of other holes and shafts, is dangerously unstable.
"It is not good," said Amanda Chadburn, an ancient monuments inspector at English Heritage. "It is causing us concern. You and I might think that you could simply backfill the shaft and close the hole, but our expert engineering advice is that that might just make the whole thing more unstable."
Ms Chadburn and her team have been climbing to the top of the 40 metre hill every week throughout the winter to monitor its condition, and are alarmed at the evidence of movement.
In the 1960s a controlled archaeological excavation seemed to show that the hill was stable and that the largest shaft had been securely backfilled. "I fear now we took false comfort from that," Ms Chadburn said.
"It could be that what we have here is a sort of Swiss cheese, full of holes which cannot be seen from outside, and the danger is that the whole thing could almost implode," said Elspeth Henderson, of English Heritage.
English Heritage is about to seek tenders for a seismic survey, usually used in major engineering projects, which will cover the entire hill with a web of monitors linked to computers, and produce a three dimensional image of the 21,000sq metre hill, revealing the stress areas and mapping for the first time any tunnels and voids inside it.
It will be the first time the engineering technique has been applied to an archaeological site.
Any repair work will probably have to be done by helicopter: apart from the instability of the site, it is officially classified a site of special scientific interest.
The bonus is that the tomographic survey may also finally answer the question of whether there is a burial chamber in Europe's most famous pyramid. But no scientific answer is likely to end the legends and conspiracy theories: everything from links with Pharaonic Egypt to the resting place of the Ark of the Covenant has been suggested for Silbury.
While other field monuments were overgrown and lost, Silbury has been unmissable for almost 5,000 years: the arrow-straight neighbouring stretch of the A4, following the route of a Roman road, jinks to avoid the hill.
Silbury Hill in Wiltshire, one of the most spectacular and puzzling prehistoric monuments in the world, is in danger of collapse.
http://www.guardian.co.uk/Archive/Article/0,4273,4163359,00.html