Show Sand Dunes Remain Puzzle Of Nature Sand dunes seem not to know the rules Most move but some dont They can be lifeless or verdant Some turn to stone I and others sing Natures Nature's sand piles come in only a few basic geological forms but an infinite variety of delicately sculptured forms They range in size rom inches- inches high ripples on a desert floor to foot tall foot tall crescents in Great Sand Dunes National Monument Colorado the National National National Na Na- Geographic Society says These d dunes are among the highest in the world Dunes can form a wasteland as as big as Texas the forbidding forbidding forbidding forbid forbid- ding Empty Quarter of Saudi Arabia where not even Bedouin Bedouin Bedouin Bed Bed- and camel can find sub sub- Yet the dune country country country coun coun- try on the southern shore of Lake Michigan supports a wondrous botanical paradise w where re arctic reindeer moss mingles amicably with cactus from the American Southwest NOT FOR SHEIKS Contrary to popular notion dunes and deserts do not necessarily necessarily necessarily go together Only a ninth of the Sahara which covers square miles is blanketed in the golden smooth sharply crested dunes suitable as a film setting for sheiks legionnaires and camel caravans As a ph phenomenon of nature dunes seem to be alive breathing breathing breathing breath breath- ing growing bu busy y changing They are complex creations whose mechanism is still not fully understood by In parts of the world the pale shifting sands make mysterious mysterious mysterious mys mys- unexplained noises likened to sirens organs drums trombones and the twanging of monstrous harps Of dunes in the great Gobi t M roo co Polo wrote Sometimes you shall hear the sounds of musical instruments and still stillmore stillmore more commonly C th the sound of drums arums It would seem obvious that thata a dune comes into being when wind begins piling sand up against an obstacle a stone boulder plant post or what shave have you Some geologists are of the opinion however that dunes may be brought into existence by irregularities in wind currents Once a dune has been born it tends to maintain itself increase increase increase in in- crease its size migrate and take a special form influenced by wind climate vegetation and the amount and type of sand There are five general types the beach dune the wavelike ridge of deserts that forms at a right angle to the wind the longitudinal sand dune that parallels the winds wind's direction the shaped U-shaped dune whose open end faces windward windward windward wind wind- ward and the barchan the photographically ideal lunar crescent whose horns point downwind Most beach dunes are quartz sand Those in Great Sands National Monument are gritty the dunes in New Mexico's White Sands National Monument Monument Monument ment are the products of the worlds world's largest known deposit of white milky powder-fine powder gypsum sand In Bermuda dunes of coral sand have cemented cemented cemented ce ce- themselves into stone VILLAGE BURIED UNDER DUNE Dunes cart carl be deadly Like armies invading from the sea coastal dupes duties in Europe and the eastern United States have marched across nearby farms and woods A small village on Germanys Germany's Baltic coast was slowly buried burled over 30 years then just as quietly disinterred over the next year 30 span But man has recently learned learned learn learn- ed that coastal dunes have a definite purpose in natures nature's scheme the protection of shorelines Massachusetts law prohibits any tampering with dunes and a massive dune rehabilitation job was undertaken undertaken undertaken under under- taken by the thc National Park Service on North Carolinas Carolina's Outer O Banks n In the Ironically the worlds world's most famous Kill dune dune Kill Devil Hill has ceased t to be one While the Wright Brothers were experimenting experimenting experimenting ex ex- with their air machine machine machine ma ma- chine Kill Devil Hill Hlll was marching steadily southward I at about 20 feet a y year ar Then in 1929 it was permanently immobilized with woods debris debris debris de de- de- de bris planted with grass and tamed into graceful submission submission submission sion with curlicues of park- park like walks and drives Depending on height and size dunes seem to move at roughly the same rate whatever whatever whatever what what- ever their geographical loca loca- tion North Carolinas Carolina's barch- barch ans s shift ift at the same pace of those in Africa's Libyan Desert Desert Desert Des Des- ert about 20 feet a year SOME SOl REMAIN STABLE In Africa's Sahara however some dunes seem not to have moved noved in the memory of man Geologists suspect that these sand dunes are mantles of sand anchored somehow to an irregularly contoured region of stone The ability of most dunes to change position fascinates geologists For wind cant can't push along an entire dune It must be done grain by grain a caroming effect as in bil bil- bil- bil Normally a sand grain is not lifted into the air by wind It is bounced One grain hits another causing it to ricochet ricochet ricochet rico rico- chet and hit others Soon the theair theair air is filled with hopping bobbing bobbing bobbing bob bob- bing grains of sand But even when the wind is strongest a single bit of sand in a dune rarely travels more than three or four feet T Geologists can reconstruct ancient wind systems from traces of dunes that have been destroyed by erosion It is only in recent years that man has come to appreciate elate sand dunes as a significant significant i- i cant and purposeful creation of nature The United States government has set aside two areas the Great Sand Dunes National Monument in Colorado Colorado Colorado Colo Colo- rado and New Mexico's White Sands National Monument for permanent protection and enjoyment en en- |