Silbury Hill, one of Europe's most significant ancient monuments, has become dangerously unstable after heavy rain caused a gaping hole to open in its surface. The 12m (40ft) deep hole, which measures 1.8m (six feet) across, appeared in Silbury Hill, the oldest earthen mound in Europe and part of the World Heritage Site at Avebury, Wiltshire (England). The National Trust, which manages the monument, was working urgently to cap the hole to prevent injury to the public and stabilise the mound to avoid further archaeological damage.
      Experts believe that extreme wet weather caused the collapse of the upper part of a 30.5m (100ft) deep shaft dug in the 1776 in an attempt to discover if the hill was a burial site. Silbury Hill was built in three phases about 4,500 years ago with chalk dug from nearby quarry pits. It covers five acres and pre-dates both Stonehenge and the stone circles at Avebury.
      Visitors have been prohibited from climbing the 39.6m (130ft) high, steep-sided hill since the Seventies because of fears that it would be damaged. But a small number of people persist in climbing the fences to walk on the mound. However, it was a tourist, one of Avebury's 350,000 annual visitors, who reported the appearance of the hole to local people on 29 May. They then passed on the information to the National Trust.
      Chris Gingell, the trust's property manager, said: "The hole is extremely dangerous and our first concern must be public safety. We have to cap the hole securely to make it impossible for anyone to fall into it. We then have to work out how to prevent further deterioration. The real worry is that the vertical sides of this shaft could slump, causing a bigger collapse. Parts of the monument that have not been examined could then be lost. In a sense the real archaeological damage was done in the 18th century when the shaft was dug. Among the questions we have to try and answer now is whether the lower part of the shaft, another 18m (60 feet), is solid."

Source: The Daily Telegraph (31 May 2000)