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Ancient mystery solved by geographers

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Mon, Apr 20, 2009

The mystery of how two-foot deep tracks were cut into the rock of Malta which has long puzzled locals, scientists and tourists may have been solved by British scientists.

The ruts were almost certainly caused by the passage of carts because the rock was not strong enough to support the wooden wheels of loaded carts.

Professor Derek Mottershead, of the University of Portsmouth’s Department of Geography, followed in the footsteps of generations of scholars to try and unravel the mysteries of the Maltese landscape.

The ruts are up to two feet deep and more than 30km of them run in pairs criss-crossing the island. But instead of concentrating on the shape and distribution of the ruts, as previous researchers had done, they studied the forces required to make the rock fail.

Professor Mottershead’s team came up with a design of a cart to fit the field evidence, estimated its weight and calculated the stresses involved. They discovered that in some places the rock was so soft that after heavy rainfall a single passage of a cart could cause the rock to fail.

Professor Mottershead said: “The ruts have been studied and talked about for centuries and though it is obvious they are related to vehicles nobody understood how they were made or even when.

“We decided to reverse-engineer a cart to fit the ruts and then calculate the stresses it would have imposed. The limestone could withstand cart wheels when it was dry but after heavy rain it erodes in front of your eyes.”

In one area, known locally as Clapham Junction because of the proliferation of ruts, the rock was so soft it would have eroded after the passage of a single unloaded cart.

Professor Mottershead said: “The underlying rock in Malta is weak and when it’s wet it loses about 80 per cent of its strength. The carts would have first made tracks in the soil but when that eroded, the cartwheels ran directly on the bedrock, making it easier for other carts to follow the same tracks.”

But the ruts would quickly become too deep and the carters would have had to continually find new routes, which explains why there are so many ruts criss-crossing the island.

Professor Mottershead said: “There are ruts in other countries, but in less resistant sandstones and clays. Good examples are the American wagon trails formed during the settlement of the west, and at Arbroath, Scotland, formed during quarrying, and at Robin Hood's Bay in Yorkshire.

“What is unique to Malta is the sheer number of ruts. For years they have attracted the attention of archaeologists but until now we didn’t have a convincing explanation of the mechanics of how they could have been formed.”

The research team included Dr Alastair Pearson and Martin Schaefer, also of the University of Portsmouth. Their research was published in the journal Antiquity.