Nigel Hawkes and Nick Nuttall report from the British Association for the Advancement of Science on Wonderland clues, rising seas and unseen pollution

Oh my ears and whiskers! A geologist has identified the hole in the ground that must have inspired Alice's big tumble as she pursued the White Rabbit.

The cause of her fall, says Tony Cooper of the British Geological Survey, was the soluble gypsum rock that underlies Ripon in North Yorkshire. At regular intervals the dissolving rock causes collapses that create holes large enough to swallow buildings.

Lewis Carroll, the author of Alice in Wonderland, was brought up near Ripon and visited the town many times. Not only must he have been aware of the holes, Dr Cooper told the British Association meeting in Sheffield yesterday, but there is another connection.

Carroll's father had a close friend, Canon Badcock, who lived at Ure Lodge in Ripon. His daughter, Mary Badcock, was later used by Carroll as the model for Alice's appearance. He gave a photograph of her to John Tenniel, the artist who drew the original illustrations, with instructions that this was how he wanted Alice to look.

In Carroll's day there were many collapses in the fields opposite Ure Lodge and it is likely that in 1834 he visited a dramatic hole that opened up about 300 yards northeast of the house. This left a shaft more than 60ft deep and 35ft in diameter, with solid rock exposed at the sides.

"Down, down, down. Would the fall never come to an end!" Alice thought to herself as she fell. In Carroll's time, the holes were indeed believed to be bottomless. Near the village of Croft, where Carroll grew up, was Hells' Kettle, a huge hole filled with water. Prosaically, divers who have plumbed its murky water in recent times have found it is a mere 20ft deep, but that was unknown to Carroll.

The dissolving rock under Ripon is gypsum - chemically, calcium sulphate - originally laid down when the area was under an enclosed sea in tropical temperatures more than 250 million years ago. The evaporating sea left behind the gypsum sheets that lie sandwiched between water-permeable limestones.

Underground streams flow through the gypsum, said Dr Cooper, at depths of 100ft to 350ft. Over the years channels form as the gypsum dissolves. Eventually the rock is so weakened that it can no longer support the overlaying ground. In Carroll's day Ure Lodge was the solid home of a clergyman. But in 1997 a huge hole appeared close to the house, destroying a row of four garages. The house itself has now been demolished.

"The insurance company paid for that," said Dr Cooper. "But it will not take responsibility for the land. So the owners are now facing lawsuits against them for the reinstatement of the land, where a group of houses had been built in the garden of Ure Lodge. And as the hole is large, that is pretty difficult to do."

Fortunately, the belt of gypsum running through Ripon is fairly narrow, no more than a couple of miles wide. Where gypsum occurs elsewhere in Britain, the problems are less serious because the rock is usually sandwiched between mudstones, which water penetrates less easily. Along the Ripon gypsum belt, special building regulations apply to control damage by subsidence.

Bridges on the Ripon by-pass have been specially built so that a collapse of the ground under any of the supporting pillars will leave the bridge standing.

There are also problems abroad. Around Zaragoza, in Spain, collapses are so frequent, Dr Cooper said, that farmers crossing their fields late at night attach long planks across their shoulders so that if the ground opens up beneath their feet they will be left suspended. Curiouser and curiouser, as Alice remarked.