Mysteries of the Libyan Desert

by W. J. Harding King

Mr. H. Ll. Beadnell,[23] who carried out a series of weather observations over a considerable time in Kharga Oasis, estimated that the sand blew from a northerly direction for five days out of six in this district. Violent sandstorms are unpleasantly common, by far the greatest number of them coming from the predominating northerly direction. The result of this uniformity in the direction of the winds is clearly seen on the plateau. The swirling clouds of sand, driven by the furious desert gales, have in many places not only shaped the hard limestone into long ridges running up and down wind, but have even cut grooves in the ridges themselves, as though with a gigantic gouge, forming a type of desert known to the natives as kharashef. These ridges rise sometimes twenty feet above the level of the plateau, but more usually are only three or four feet in height, producing a surface somewhat resembling a rough sea—a very uncomfortable type of desert to have to cross with a caravan. A diminutive form of this—kharafish—in the shape of small ridges, often with a cutting edge, is also frequently seen, and works havoc with the soles of the soft-footed camels. Besides these forms a flat rock surface with very shallow groves, known as rusuf, is occasionally met with.

Some of the limestone boulders lying on the surface of the plateau are perforated in the most extraordinary way. The driving sand apparently eats its way into the softer portions of the stone, boring holes into its surface. Small pebbles are often to be seen which have been blown into these holes. These fly round and round in the excavation under the influence of a strong wind, and presumably continue the erosion of the sand blast, in the same way as a stone wears a pot-hole in a stream. In course of time the whole boulder becomes so riddled with holes as to resemble a gigantic sponge.

In several places are large patches of desert more or less closely covered with round boulders up to a foot in diameter, a type of erosion known to the natives as battikh, or water-melon desert.

In other places in the desert perforated rocks and small natural arches are to be seen; while near Farafra village were a number of fine “mushrooms” and table stones cut out of the chalk by wind-driven sand. Similar “mushrooms” of sandstone were, moreover, met with near the centre of the desert.

In Kharga Oasis there is an area several square miles in extent covered by curious clay ridges. These, which seemed all to be under twenty feet high, were evidently formed by the erosion of the earth by the wind-driven sand, for they all ran roughly from north to south, in the direction of the prevailing wind.

Apparently, as the sand wore away and lowered the surface of the desert, it encountered here and there harder portions of the clay which resisted its erosive action. These consequently remained protruding above the surface of the desert as the surrounding clay was eaten away by the sand blast, and consequently acted as a protection to the earth immediately to leeward of them, which remained intact above the level of the desert in the form of a ridge running in the direction of the prevailing northerly wind. I have found similar forms to the west of Dakhla and in that oasis itself.

While in the central part of the desert in my first season, I found embedded in a sand dune two short pieces of dried grass much frayed and battered;[24] so, as has already been mentioned, on leaving the camp next day, we followed the line of the sand belt, to the north as showing the direction of the prevailing wind, and so found the place from which the dried grass embedded in the dune had come.

The occurrence of this grass so far to windward of the piece I had picked up among the dunes is only another illustration of the great part the strongly predominant character of the northerly wind plays in this desert. Had we continued marching towards the north, along the same bearing as we had during the day, we should have found the oases, or hattias, of Bu Mungar, Iddaila and Sitra, all on the same line. The original seed, of which the grass we found were the descendants, were probably specimens carried by the wind from Sitra to Iddaila, where they took root and produced seed that was similarly carried to Bu Mungar and from thence—perhaps through another hattia, or oasis—to the place where we found it growing. Very probably the line of plantations of the grass may even reach to the Sudan, should there be any places along it where the seed could germinate.

ERODED ROCK, SOUTH-WEST OF DAKHLA.