A desert is, above all, a vast region that is empty, dry and outside time. T. Monod described it as “the kingdom of absence”. It is a land of surprises, contrasts and oppositions that can occur far apart or close together, sometimes spread out over years, at others separated by barely a few hours. There is the Asian desert, where you broil in summer and freeze in winter, and there is the African desert, where all the days are torrid and all the nights are cold. There is the arid desert, containing opulent oases, while you have a desert enclosed within vegetation. There are deserts that are endlessly flat, as far as the eye can see, and there are plains with rocky islands or bleak mountains. There is the sudden downpour that breaks the monotony of waterless days, and the dry river that swells into a flood. You have the bare desert that transforms, with the rain, into a carpet of flowers. And there is the seemingly uninhabited desert – where as soon as you stop, someone pops up out of nowhere to look at you and to converse.
A desert is also a bare spot that is ideal for contemplation and spirituality, where Man finds himself alone in the face of this immensity, silence and beauty. It is the void, where all fundamental questions arise. It is the Biblical antithesis to the Promised Land. It is the site of fervor, where altars are built and sacrifices made, such as the sacrifice of Abraham; the sacred land where divinity approaches humanity, the land of Moses, Jesus, Mohammed and the Buddha. It is the chosen site for renunciation and retreat, from the medieval monks to the 19th Century Father Charles de Foucauld. It is the site of exaltation, the site of gigantic temples, as can be seen in Babylon, Egypt, Syria, Tibet and in the Andes. It was also the backdrop for adventurers and empire-builders, from Alexander the Great to Genghis Khan, and from the Incans to the conquistadors of the Andes and Mexico. It has served as the arena of war from Libya to Iraq, and the testing ground for the atomic bombs. It is fertile ground for prospectors and operators, the salt-miners of the Sahel and the gold-hunters in the Americas, as well as modern-day oil seekers. Finally, deserts have also served as an observatory for the curious, such as Ibn Battuta and Marco Polo, offered new horizons to explorers, such as Caillé and Barth in the Sahara, Prjevalski and Sven Hedin in Asia, Powell in the Colorado and Eyre in Australia, and been used as a research field for scholars, such as Stein in Chinese Turkestan or Monod in Mauritania.
The desert is also a land of legend, exoticism and dreams, brimming over with fantasies and received ideas. Of course, this aspect of it is slowly diminishing as scientific discoveries and analyses progress and with the increasingly widespread sharing of images from these regions. The Romantics turned the desert into a mysterious land, overwhelmed by light and heat, throwing up strange mirages and sandstorms that could bury entire caravans. It was a hellish land of thirst and wind, of silence and death, that was both fascinating and horrifying. In the colonial period, the desert was always considered a redoubtable and inhuman place, the stuff of myth and legend. It was perilous, meant for military glory (like the French Foreign Legion, whose history waxes eloquent on the legionnaire “feeling the hot sand against his skin”) or for punishment (the African battalions). Even today, several fictional deserts survive, often harsher than the real ones. Dating back to a time when those who traversed the deserts were travelers, merchants or armies (rather than explorers and tourists), these accounts are often embellished with personal impressions and adventures; many are full of exaggerations or even implausible details and many were romanticized or often deliberately falsified in order to win glory, for political reasons, or to distract the competition. And so, for the layman, the desert was a secret region, hostile and populated by unknown beings who were strange and redoubtable. Many writers, carried away by their own lyrical writing or innovations, helped spread a deformed and enduring vision of the desert. For example, there was the French writer Eugène Fromentin’s A Summer in the Sahara (which was actually about the Algerian plains) or Pierre Benoît’s The Atlantide. These dreamlike deserts, “postiches” as they were dubbed by Monod, are a stark contrast to the more realistic and sobering deserts that feature in Westerns and “atmospheric novels” of the modern age, such as the novels about the American West by T. Hillerman and E. Abbey, or A. Upfield’s Australian novels.
1.2.2. Conceptual deserts: deserts that have been experienced
Each desert, considered as an object of study, may be dissected, qualified and quantified. However, this does not result in a homogeneous and unique scientific concept of deserts. A desert cannot be reduced to a concrete, simple and universal formula. To each their own desert, which seems to them more “desert-like and true” than another’s concept. There are, therefore, physical deserts that are objective and measurable by a certain degree of aridity, and then there are psychic deserts, subjective and experienced as a sensation of emptiness and the absence (or, at least, the apparent absence) of human life, and the “true desert” is, in fact, a combination of these two. For Monod, the “true” desert is the “experienced” desert, which one has walked oneself, lived through, feared and admired.
1.3. The world of deserts
In these conditions, it is futile to try and establish a clear definition of a desert that would be applicable in all cases. However, transecting a desert (the Sahara, for instance) from its periphery to its center (or the other way around) could help in revealing the most specific characteristics of the desert state, as is found, to varying degrees, in all deserts around the world.
The characteristic that can be spotted by even the untrained eye is the rapid degradation of any green cover. If someone were flying over it, in just a few minutes the view of greenery from the plane would shift from a clear forest or savanna to a disjointed steppe until it disappears altogether. On land, however, we can see that this degradation involves a gradual decrease in both the number of individual plants as well as the number of species (biodiversity), leading to increasing homogeneity. This is compounded by the unequal distribution of vegetation, spread out on the slopes and interfluves, concentrated in the wadis and showing significant variations in vitality depending on the rainfall, with certain plants rapidly blossoming after a downpour. This decrease in vegetation is accompanied by an equal decrease in the fauna in the region, especially of the animals that are most dependent on vegetation and water.
The hydrographic disruption manifests as the rarefaction of drains and a growing anarchy in water flows. Concentrated drainage divides into independent networks that become fewer and fewer in number and less and less hierarchic, with the water finally forming isolated channels or even disappearing completely. Most channels are dry in all seasons and are only revived during a flood. Apart from the large, exorheic4 allogenous rivers, such as the Nile or the Euphrates, water flow is exclusively local and linked to precipitation, which is itself intermittent and irregular. Between channels, during the rains the surface of an interfluve may often be swept by diffuse flows, in sheets or numerous and changing gullies. All these drains, except for those along the maritime coasts, are endorheic5, that is, they lead to closed basins of all sizes, which are numerous and independent, where they are lost. There is also the extreme case of an arheic region6 where there is a complete absence of water flow.
The morphology of a desert is also formed of unique features of relief, owing to the specific conditions of the desert model. The disaggregation of hydrographic networks reduces the preeminence of valleys in a landscape. The desert is flat until it enters the mountains. The horizontal shapes or shapes with very small slopes, plains, plateaus and glacis7 overpower sharp reliefs or reduce them to eroded tussocks or to small isolated massifs (inselbergs8). And everywhere you have evidence of the wind at work. The sweeping winds shave off the finest elements from the rocky floors and alluvial sheets and accumulate them into dunes, scattered or grouped together (ergs).
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