Great Gibraltar Sand Dune
| Great Gibraltar Sand Dune | |
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 Location of the Great Sand Dune within Gibraltar.
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| Coordinates | 36°08′03″N 5°20′36″W / 36.134166°N 5.343221°WCoordinates: 36°08′03″N 5°20′36″W / 36.134166°N 5.343221°W |
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| Topo map | OS Gibraltar |
The Great Gibraltar Sand Dune is an ancient sand dune in the British Overseas Territory of Gibraltar. It forms part of the Upper Rock Nature Reserve and dominates the eastern cliffs of the Rock of Gibraltar. It was once used to capture rainwater which was contained in underground tanks within the Rock to satisfy the population's potable water needs.
The prehistoric dune is made from yellow, windblown sands lacking the red component of the sands on the west side of the Rock. It is made of the same sand that once formed part of a vast savanna of the late where Neanderthals hunted. The levant winds of prehistory continuously blew sand from this savanna westwards, accumulating against the eastern cliffs of the Rock, reaching from the base of the cliff right down to sea level (at that time there was no road where Sir Herbert Miles Road is today). The occasional rockfall from the precipice above added boulders to the dune so the formation seen today is a consolidated composite of rocks and windblown sands. The upper limits of the dune were scarped by the British garrison for two reasons - to avoid soldiers deserting the place and to prevent surprise attacks by Spanish troops. The Great Sand Dune was constantly shifting right up to the late 19th century when corrugated iron sheets were laid over the dune for the collection of rainwater.John White described this 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."
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