The mysterious rock-cut cart ruts of Malta are here examined by geomorphologists. They find that the ruts could be caused by two-wheeled carts with a gauge of l. 40m carrying moderate loads. In wet weather the carts would gradually cut into the limestone and reach their ground clearance of 0.675m, causing the carriers to try another route--so there are plenty of them.
Keywords: Malta, uncertain age, cart ruts, transport, wheeled vehicles
The Maltese cart ruts are found mainly on the west part of the island, on the uplands formed by coralline limestone (Figures 1 and 2). The earliest reference to them was by Gian Francesco Abela in 1647, and descriptions have since been provided by numerous authors over a considerable period (Zammit 1928; Evans 1934; Gracie 1954; Parker & Rubinstein 1984; Ventura & Tanti 1994), culminating in a meticulous and comprehensive review by Hughes (1999). Trump (1993; 2000) provides further good illustrations. Their age is uncertain: attributions have variously included the later Bronze Age (1500 BC), the Punic occupation (c. 600 BC) and the Roman period (post 218 BC), and ranged as widely as the Neolithic and the Arabic periods (c. 870). Traces of these features are also present in Gozo and elsewhere in the Mediterranean (Parker & Rubinstein 1984). A notable and pioneering venture in experimental archaeology was carried out by the BBC in 1955 (BBC 1955), in which various types of vehicle were run along the cart ruts, although without producing an unequivocal and commonly accepted conclusion.
The ruts were created in soft limestone that, as a soluble rock, is subject to solution under rainfall when directly exposed at the Earth's surface. Their morphological details thus necessarily become degraded through time, obscuring original features and rendering interpretation still more difficult. Erosional forms such as cart ruts must, of necessity, be interpreted on the basis of their geomorphology alone, but this has previously only been attempted by Drew (1996).
The ruts are essentially small-scale erosional landforms incised into surface bedrock outcrops. A major focus of the science of geomorphology is erosion, hence geomorphology is an especially appropriate perspective from which to approach the problem of their formation, and enables a distinctive contribution to the study of these intriguing landforms. Geomorphology deals with landforms at various scales, their spatial patterns and distributions, material properties, surface processes and relationships between processes and forms. Many previous authors have described aspects ofthe form and distribution ofthe ruts, whereas material properties and erosion processes have been hitherto little considered. Here we present observations of properties and process, with a focus on the applied forces required to cause the erosion of the ruts.
[FIGURE 1 OMITTED]
Combining published descriptions with the authors' own field observations, the defining characteristics of the ruts can be identified as follows:
* They occur as paired parallel grooves incised into bedrock, and extending up to several hundred metres in length.
* Each rut pair possesses a constant gauge (distance apart) of c. 1.40m, although this may vary slightly between rut pairs.
* The width of a rut ranges from 0.04 to 0.10m, with depth variable up to a maximum of 0.675m (Gracie 1954).
* In cross-section they are commonly v-shaped channels with a rounded floor; the largest ruts tend to have a rectangular box cross-section.
* Some rut cross sections show multiple grooves, with two or three channel floors, and always replicated in both members of the rut pair.
* Locally they may divert in order to avoid obstacles.
* In the broader context, ruts are often clearly related to major landscape features, such as cols or scarp slopes.
* Concentrations may occur at regional route nodes, especially crossing points of high ground.
* They may be intermittent in plan, often oblique to contours, and exhibit convergent or crossing patterns (anastomosis), or in the case of ancient quarry sites, parallel patterns (Figure 3).
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Whilst there is widespread agreement that the paired ruts are intimately related to the passage of vehicles, there are many unresolved questions concerning their origins. The principal questions are whether they were cut by manual labour to facilitate the passage of vehicles, or eroded by the passage of the vehicles themselves. If the latter, then the question arises as to whether the vehicles were wheeled or travelled on runners, or took the form of inclined shafts strapped to a draught animal (a travois).
The objectives of the present paper are to:
* investigate the material properties of the terrain materials in which the ruts are formed;
* determine the nature and magnitude of applied stresses, as a measure of the erosive forces, required to overcome the resistance of the rock materials; and
* reverse engineer a vehicle to fit the ruts and, with its load, generate sufficient stress to cause rock failure.
This study is based on field observations of ruts at three sites, San Pawl tat-Targa (near Naxxar), Bingemma and Misrah Ghar-il Kbir (popularly and locally known as Clapham Junction), in relation to the geotechnical properties of the local surface rocks.
In order to identify the resistance characteristics of the local rocks, standard geotechnical tests were applied. Rock density was determined from hand-sized samples by dry weighing the sample and determining the volume of fluid (normally water) that it displaces. …