Geography
Ancient mystery solved by Portsmouth geographers
Fri, 22 May 2009 12:50:00 BST
The Geography department has been helping solve a mystery that has puzzled archaeologists and residents of Malta for years. The island is covered in pairs of tracks up to two feet deep tracks that are cut into the rock. One area has been dubbed Clapham Junction because of the proliferation of ruts.
Professor Derek Mottershead, of the Department of Geography, followed in the footsteps of generations of scholars to try and unravel these mysteries of the Maltese landscape.
His conclusion was that 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.
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, Derek and his team studied the forces required to make the rock fail.
Derek?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.
According to Derek, ?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 would erode in front of your eyes.?
Derek says, ?The underlying rock in Malta is weak and when it?s wet it loses up to 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. This explains why there are so many ruts criss-crossing the island.
According to Derek, ?There are ruts in other countries, but generally 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 also included Dr Alastair Pearson and Martin Schaefer, also of the Geography department. Their research was published in the journal Antiquity.