The Great Gibraltar Sand Dune
Watercatchments were erected in 1909 as an extension to smaller rainwater collection areas which had been prepared at the end of the nineteenth century on the Upper Rock of Gibraltar. They were prepared on a slope of continuously shifting sand which reached from the base of the cliff right down to the sea, because at that time there was no road where Sir Herbert Miles Road is now positioned. To succeed in anchoring the sheets of corrugated metal, wooden frames were fixed into the sand and the sheets attached onto the wood. The system worked and maintained the population with an, albeit unpredictable, freshwater supply until the development of desalination plants in the 1980s removed the dependence on rainwater. These catchments have now being removed and the sands which were under the sheets are being reseeded with natural vegetation. The method used in reseeding is more effective than nature ever was herself and the green appearance of the sand slopes in the spring now is unparalleled.
The sand slope represents one of nature’s grand achievements, being a prehistoric sand dune. The sand which you see here lacks the red component of the sands on the west. They are yellow, windblown sands. In fact they are the sands that once formed part of the vast sandy plain of the late Pleistocene where the Neanderthals hunted. The east winds of prehistory regularly blew sand westwards and this accumulated against the east cliffs of the Rock. From time to time rock collapses added boulders to the dune so that the formation today is a composite of rock falls and wind-blown sands. These sands were constantly shifting right up to the erection of the sheets. John White describes this side and the efforts to make it inaccessible:
“The Eastern side of the hill consists of an immense sloping bank of whitish sand interspersed with huge fragments of rock, and reaching from the sea nearly to the summit of the rock in some parts not far from the Signal House, and the Middle-hill Guards. These parts were formerly accessible, which made it necessary to keep constant guards there, as well to prevent desertions from within as a surprise from without. Of late years, much labour has been bestowed in making all these parts more abrupt and difficult, yet it is still necessary to watch them, as there are always some hardy adventurers who will wantonly risk their lives down these perilous cliffs, either in attempting to desert or in search of flowers.”
They served to maintain a regular supply of sand on the beaches of the eastern side, especially Sandy Bay (the Little Bay of James) particularly when the sea removed material from the beach. This dynamic nature meant that little vegetation of any significant height could grow on the dune with any permanence as many pre-catchment photographs clearly demonstrate.