Sand drift

“ It is the steady prevalence of moderately strong winds that causes the extension of sand-drifts. The wind of to-day deposits the sand at a certain distance from the shore. The wind to-morrow starts the accumulated sand from that depot to form a new deposit about equidistant; and thus by slow degrees the dunes are formed by a succession of mounds, conveyed onwards by an unchanging force; but the maximum power of a gale would be unable to carry thousands of tons of heavy sand to form a hill-range at the extreme distance from the original base of the material. ”

“ The irresistibility of drift sand is well seen where isolated hills lie in the path of the dunes. When such hills are narrow, and elongated in a north and south direction, they generally act as a wedge, divide the wind, and force any sand it may be carrying to pass on either side. ”

“ Especially destructive are they when, by any accident, a cavity is opened into them to a considerable depth, thereby giving the wind access to the interior, where the sand is thus first dried, and then scooped out and scattered far over the neighboring soil. The dune is now a magazine of sand, no longer a rampart against it, and mischief from this source seems more difficult to resist than from almost any other drift, because the supply of material at the command of the wind is more abundant and more concentrated than in its original thin and widespread deposits on the beach. ”

“ The spring floods find their way, through openings in these higher banks, into the hollow centres of the islands, carrying with them a vast quantity of drift timber, which, being left there, becomes water-soaked, and, finally, firmly impacted in the mud. The young willows, which spring up rapidly, contribute much towards raising the borders of the stream, by intercepting the drift sand which the wind sweeps from the margin of the shallow ponds as they dry up in summer. ”

“ Where the desert touches a river-valley or oasis, the sand is in a continual state of drift from the wind, and it is this drift which is the real cause of the barrenness of such portions of the desert at least as abut upon the fertile land. For under the rain, or by infiltration of the river, plants often spring up through the sand, and there is sometimes promise of considerable fertility. It never lasts. Down comes the periodic drift, and life is stunted or choked out. ”

“ The cart must have crushed the pebbles deeply into the soft sand on which they lay, and the ruts thus formed rapidly filled up again with drift sand during the first sandstorm, showing as two conspicuous white lines, owing to the absence along the tracks of the darker pebbles, and forming marks that might easily last for a century, unless they happened to be situated in a part of the desert where the sand erosion was gradually wearing away the surface of the ground. ”

“ The worst results occur where the littoral drift is almost wholly in one direction, so that the projection of a solid breakwater out from the shore causes a very large accretion on the side facing the exposed quarter; whilst owing to the arrest of the travel of sand, erosion of the beach occurs beyond the second breakwater enclosing the harbour on its comparatively sheltered side. ”

“ Long-shore drift involves erosion and deposition of sediment. Formation of new islands depends on the amount of sand deposited being greater than the amount of erosion.
Erosion by rivers: the strength and speed of flowing water is able to wear away the material of the riverbank and bottom, and carry it as sediment, in smaller or larger particles. The action of the moving sediment itself acts as an abrasive which may accelerate further erosion downstream. When the river slows down sufficiently, the sediment is dropped ”

“ Longshore drift spreads it to the East and West, where it joins sediment contributed by lesser river systems such as the Imo and the Osse (Ovia) .
The sand spreads as a band of islands along the coast. They are mostly 'true islands', completely surrounded by water, be it the Atlantic itself or the water of lagoons and of the creeks that twine their way around islands formed further inshore. Where they form in the mouth of an estuary, they may be called sand bars.
Sand thus thrown up by the Atlantic often forms a high beach, behind which streams running from inland may form a lagoon. ”

“ As usual, we began our onward march at four o’clock in the afternoon. Our road now led us somewhat away from the sea. The country round about consists wholly of flat sand drifts. Nowhere can one see farther ahead than a distance of about four hundred meters. Hardly has one sand hill been passed, before another looms up to shut out the view. ”

“ Our life sweeps onward like a river, brushing in here a little sand, there a few rushes, till the accumulated drift-wood chokes the current, or some larger tree falling across it turns it into a new channel. ”

“ When, under the vertical rays of the never-clouded sun, the carbonized turfy covering falls into dust, the indurated soil cracks asunder as if from the shock of an earthquake. If at such times two opposing currents of air, whose conflict produces a rotary motion, come in contact with the soil, the plain assumes a strange and singular aspect. Like conical-shaped clouds, the points of which descend to the earth, the sand rises through the rarefied air on the electrically-charged centre of the whirling current, resembling the loud water-spout, dreaded by the experienced mariner. ”

“ He who has witnessed a storm along a rocky coast-line, has marked the breakers battering against the weather-bleached cliffs, and heard the thunder-like rattle of the shingle at the recoil of every wave, needs not to be told how vast an amount of sediment must in this way be formed. The pebbles of the beach are ground down still smaller, the sand produced by their friction finds its way to a lower level, while the finer particles taken up by the water are borne out to sea, and if a current traverse the locality may be transported for leagues, till they at last settle to the bottom. ”

“ Placing a stick into the ground, in a few moments a heap of sand would accumulate on the windward side. These sand storms fill up all the mouths of the Alt, and pile the sand up in big banks. If there was no correcting force these sand storms would quickly fill up the shallow shores and destroy their capacity to impound the tidal water which assists the scouring power of the main stream; but at high water with a westerly gale the waves churn up these deposits of sand, and the ebb tide carries them out to sea. ”

“ A variation in the direction of winds of successive storms may be responsible for the piling up of the beach sand in a peculiar “plunge and flow” or “cross-bedded” structure, a structure which is extremely common in littoral deposits, though simulated in rocks of eolian origin.
The order of deposition during a transgression of the sea.—Many shore lines of the continents are almost constantly migrating either landward or seaward. When the shore line advances over the land, the coast is sinking, and marine deposits will be formed directly above what was recently the “dry land.” ”

“ Where no such barrier exists, the waves in a winter storm sweep all the sand clean off, and lay bare the clay, and tumbling upon it with mighty shocks, sometimes wear it down a foot in the course of a tide. By this lowering of the base, the saturated soil above, deprived of support, topples over, leaving a huge gap, which only facilitates further encroachments; and in the course of a few tides the fallen mass is drifted away to enlarge the shoals in the estuary of the Humber. ”

“ Our knowledge of the mode of their first accumulation is derived from observation of the action of wind and water in the few instances where, with or without the aid of man, new coast dunes have been accumulated, and of the influence of wind alone in elevating new sand-heaps inland of the coast tier, when the outer rows are destroyed by the sea, as also when the sodded surface of ancient sands has been broken, and the subjacent strata laid open to the air. ”

“ It is easy to be conceived how the sand, conveyed and accumulated by the wind in one part, can again be taken up by the same wind and carried farther, and that the sand can thus advance into and cover the country while the mine which furnishes it continues unexhausted; for without this the sand, by advancing, would always diminish in height, and would cease its destructive ravages. Now it is but too possible that the sea throws up or deposits new sand in the place from whence the wind raises it up, and therefore the dreadful effects may long continue. ”

“ Here the travellers were obliged to pass one day, and all through that day and all through the night the wind blew with steady, persistent force, carrying with it the sands of the plain, which it piled up here and there in great dunes and then lifted again and carried on to some other point. The sandhills were constantly shifting and being tossed backward and forward, as restless and inconstant as the waves of the ocean. Often the sand is piled high upon the sparse vegetation, and again it is carried away so that the roots of that vegetation are uncovered. ”

“ The sheet of drift was once more continuous and extensive than it is now, and the localities in which we find these crops of boulders are spots where the tide has eaten into the drift, wearing away the finer materials, or the paste in which the larger fragments were imbedded, and allowing them to fall to the bottom, or where the same result has been produced by the action of rivers cutting their way through the drift, and thus finding an outlet to the sea. ”

“ One of the peculiarities of those terrible and fatal sands is, that the first approach of those entering tides, which come on, not with the ordinary roll and thunder of billows and flash of snowy surf, but swift and silent as the pestilence that flies by night, is harbingered by no outward and visible sight or sound, but by the gradual and at first imperceptible conversion of the solid sands into miry and ponderous sludge, into moving quicksand, into actual water.
When the sounds and sights are heard and seen, it is too late to make an effort. Death is at hand, inevitable. ”

“ The wind does much to help the waves in their patient beating on rocky shores. If the wind blows from the ocean and the tide is landward, the two forces combine, and the loose rocks are thrown against the solid beach with astonishing force. Even the gravel and the sharp sand are tools of great usefulness to the waves in grinding down the resisting shore. Up and back they are swept by the water, and going and coming they have their chance to scratch or strike a blow. Boulders on the beach become pockmarked by the constant sand-blast that plays upon them. ”

“ When the north wind, which blows continuously for months, comes into conflict with currents from the south, or yields them the mastery, the traveller suddenly sees the sand become alive, rising in huge pillars as thick as they are high, which whirl more or less rapidly over the plain. The sun’s rays sometimes lend them the ruddy gleam of flames, at another time they seem almost colourless, yet again, portentously dark, the furious storm weakens them and strengthens them, splits them and unites them, sometimes merging two or more into one huge sand-spout which reaches to the clouds. ”

“ Many streams that intersect the different routes across our continent are broad and shallow, and flow over beds of quicksand, which, in seasons of high water, become boggy and unstable, and are then exceedingly difficult of crossing. When these streams are on the rise, and, indeed, before any swelling is perceptible, their beds become surcharged with the sand loosened by the action of the under-current from the approaching flood, and from this time until the water subsides fording is difficult, requiring great precautions. ”

“ At low tide the green-gray and blackened bulk of the larger boulders was exposed, cluttered with shell and weed-growth, and making the scene even more somber than when the tide had thrust itself up and around the sand, nosing between rocks and overspreading like a sentient invader. ”

“ A sufficient testimony to the dangers of the sands is found in the fact that those who have known them best have ever been the ones to most dread them and the “cruel crawling tide” that with the shifting of the wind can readily change from a crawl to a hissing seething gallop across the perilous flats. ”

“ It is as though some great monster of fabled size and unearthly power were puffing out these hurtling blasts of sand upon the traveler’s head. The sound is that of a giant hand drawing rough fingers in regular rhythm across tightly stretched silk.
When the sand-storm comes there is nothing to do but to push doggedly on. Around any stationary object, whether it might be a post, a camel, or a man, the eager sands swiftly gather, piling up and up until there remains only a smoothly rounded heap. If it is torture to go on, it is death itself to halt. ”

“ A third cause of the change on the surface of the globe, are impetuous winds. They not only form downs and hills on the sea shores, but they often stop and choak up rivers, and change their directions; they tear up cultivated land, destroy trees, overthrow edifices, and cover entire countries with sand. We have an example of these inundations of sand on the coasts of Britany in France: the history of the Royal Academy at Paris, anno 1722, makes mention of it in the following terms. ”

“ The energies of the atmosphere mechanically applied, bring before us a group of results, not perhaps so nearly universal, but even more tangible and conspicuous. Many agents are at work producing mineral materials of such fineness that the winds can carry them. Oriental travelers and explorers know the sand storm as one of the most distressing and sometimes deadly visitations. In the desert mechanical disruption of rocks goes on rapidly and there is little moisture or plant life to hold the fragments down. ”