Loess: The Yellow Earth

186/© Blackwell Science Ltd, GEOLOGY TODAY, September–October 1996

Loess: The Yellow EarthIAN SMALLEY & CHRIS ROGERS

A wind-deposited silt forming large deposits in China and middle America, loess is the basis of much grade-one agricultural land.

What have the following in common? –Buckingham Palace, the collapse of the

Teton Dam in Idaho in 1976, the origins of theChinese civilization, the ‘dustbowl’ of the1930s in middle America, the economy of NewZealand, and the great 1920 earthquake inGansu Province in China. The answer is loess,a yellow soil or sediment that is essentially silt-sized (20–60 µm) and deposited by the wind. Itused to be said that everybody who had sur-vived a high-school geography course knewthree things about loess: it was yellow, depos-ited by the wind and found in China. The factsare still true; the spread of knowledge may belacking.

Loess grows good crops (Iowa is virtuallycovered in loess) and makes good bricks. Buck-ingham Palace is made of bricks from the loessdeposits in North Kent. The locals call itbrickearth, but it is true loess. The 90-m-highTeton Dam in Idaho was made of loess, whichis not good dam construction material, and thedam failed as the reservoir was being filled. TheChinese civilization, the only one of the ancient

civilizations to survive to today, developed inthe loess lands of northern China (Fig. 1).Loess suits simple agriculture, and 4000 yearsago the loess lands were wetter than now andgrew good crops. The loess, having blown intoposition, can blow away again and this is whathappened across the mid-West in the 1930s.Desperately dry conditions and less than per-fect farming practices allowed the surface ofsome of the valuable land to blow away; luckilymuch remained, as a major national resource.New Zealand has loess and rain in abundance,and as a result it grows sheep, grapes and treesand survives in a difficult trading world. Thegreat 1920 earthquake in Gansu province mo-bilized the loess ground into huge flowslidemovements; the area in motion was about thesize of the island of Ireland. Many thousands ofpeople who lived in the easily excavated cavesin the loess were killed. In terms of loss of life, itwas the worst natural disaster ever to occur.

HistoryWe need to look at two beginnings of the loessstory, an ancient beginning and a compara-tively recent beginning. The ancient Chinesewere well aware of the loess and its remarkableproperties. They observed the Yellow Riverwith its huge suspended load of loess material(about 40% solids) and noted the vertical fea-tures and cemented nature of the material. The‘Yellow Earth’ (Hwang tu) was important and,indeed, yellow became the Imperial colour. Butthere is no record of an ancient land-form sci-ence; the Chinese were astronomers and engi-neers but not, apparently, geomorphologists.The poets took note of the material. The Tangpoets of around the eighth century, writing inthe Imperial capital at Chang-an, wrote often ofdust. The loess dust was everywhere. The dustappears in Chinese poetry as often as waterdoes in English poetry. Chang-an is now Xianand is the site of the Xian Laboratory for Loessand Quaternary Geology (XLLQG), a recententerprise of the Chinese Academy of Sciencesand one of the great centres of loess research.

Yellow dust and clear water beneath the FairyMountainsChange places once in a thousand years whichpass like galloping horses.When you peer at far-off China, nine puffs ofsmoke;

Fig. 1. Loess-coveredhills near Lanzhou innorth-west China(Gansu Province).Even at great heights,cultivation terraces areconstructed. (Photo:Tom Dijkstra.)

© Blackwell Science Ltd, GEOLOGY TODAY, September–October 1996/187

And a single pool of the ocean has drainedinto a cup.

Li Ho

Alas, alas that the ears of common menShould love the modern and not love the old.Thus it is that the lute in the green windowDay by day is covered deeper with dust.

Po Chu-I

My feet shod with stout pilgrim-shoes,My hand grasping my old holly staffLooking again beyond the dusty worldWhat use have I for a land of empty dreams?

Han Shan

The recent beginning takes place in Heidelbergaround 1830. Karl Caesar von Leonhard(Fig. 2) named the material ‘Löss’. He ob-served it in the bank of the Neckar river andconsidered it interesting and distinctive enoughto deserve a name. This was a great scientificleap; once the material was named, its natureand mode of formation could be investigated.An interesting coincidence occurred at thispoint. Charles Lyell, who was engaged in writ-ing one of the seminal works in the Earth sci-ences, The Principles of Geology, having just gotmarried, set out for a honeymoon trip down theRhine. He met von Leonhard in Heidelberg,was shown the loess, and was so impressed by itthat he included a loess section in Volume 3 ofthe Principles. The Lyell book proved to be ahuge success and its wide distribution meantthat news of loess spread around the world. The

‘loess problem’ for nineteenth-century scholarswas ‘how was the material deposited’, and arange of opinions was proffered.

By 1880 a theory of loess deposition was wellin place. Baron Ferdinand von Richthofen hadsuccessfully promoted the idea that loess mate-rial was transported by aeolian mechanisms –i.e. that the wind blew the loess into place. Thistheory was soon widely accepted, particularly inNorth America. There is only one major maver-ick diversion that needs to be identified: L. S.Berg, in the early days of the Soviet Union, pro-moted the idea that loess formed in situ by asort of ‘loessification’ process. He especiallydenied any validity to the aeolian hypothesis.The Berg hypothesis can now be seen to derivedirectly from the basic soil-forming ideas for-mulated by V. V. Dokuchaev in the late nine-teenth century. The in-situ theory was a trulyRussian theory, and in the chauvinistic days ofthe early Soviet state was inevitably accepted.As might be expected in the hierarchical struc-ture of Soviet science, a theory, once accepted,became very difficult to adjust and correct. TheBerg theory, operating from, say, 1920 to about1960, was echoed by R. J. Russell in Louisianain the mid-1940s, but he was probably the onlyinfluential western supporter.

Interest in deposit formation mechanisms isnow limited. The key areas of interest in theworld of loess scholarship are currently the useof thick deposits to indicate past climates, theengineering problems of soil-structure collapseand slope failure, the problems of silt-particleformation and problems of conservation anderosion prevention. Loess has participated insome real environmental tragedies. For exam-ple the recent misguided attempts to irrigatethe loess soils along the Amu-Darya and Syr-Darya rivers in Kazakhstan (for purposes ofgrowing cotton) have all but destroyed the AralSea. Loess is a major soil resource that needs tobe appreciated, conserved and used responsi-bly.

Loess investigators are supported, and loessinvestigation is encouraged, by the INQUALoess Commission. INQUA stands for Inter-national Union for Quaternary Research and isthe international body which deals with re-search and investigation into the Quaternaryperiod (roughly the last two million years). Itoperates via a series of Commissions, one ofwhich is the Loess Commission. The current

Fig. 2. (left) KarlCaesar von Leonhardas a young man. Hefirst named the ‘Löss’in the early years of thenineteenth century. Hedescribed the site atHaarlass, nearHeidelberg, which isnow the ‘LocusTypicus’ of loess.

Fig. 3. Vladimir Afanas’evich Obruchev. Probablythe most important Russian loess investigator; he iscredited with introducing the concept of ‘desertloess’ which is still being discussed. On thecentenary of his birth in 1963, the Sovietgovernment issued a commemorative stamp.Obruchev appears to be the only loess investigatorso honoured.


Commission president is An Zhisheng atXLLQG. Loess investigation is worldwide,there being major institutions in the USA, NewZealand, Russia (Fig. 3), China, France, Ger-many, Britain, Slovakia, Tadjikistan (for exam-ple) where loess studies are being conducted,and there is a vast multilingual literature. PaulWoldstedt described the loess literature as‘ungeheuer’, which we can translate as ‘mon-strous’.

US loess‘Everybody ought to thank God for loess’, ex-claimed Bob Ruhe in a famous National Geo-graphic article (September 1984). It certainlyprovides the rich agricultural heart of the USA.Ruhe, from Iowa and then Indiana, was a nota-ble loess scholar, one of a distinguished groupof investigators and author of a well-knownbook on the Quaternary Landscapes of Iowa.Iowa is classic loess country and one of thegreat loess regions of the world (Fig. 4). Theloess is essentially glacial loess. The particles,with a mode size of around 30 µm and a largelyquartz mineralogy, were produced in the northby glacial grinding, carried to the south by largerivers and moved over the last small stage byaeolian transportation.

The great rivers gathering material fromacross the continent carried some down to formthe Mississippi Valley loess in Mississippi andLouisiana. This loess provided the most inter-esting scholarly event in US loess history. R. J.Russell, of Louisiana State University, writingin 1944, produced a revolutionary theory ofloess formation. He suggested, as L. S. Berghad done earlier in Russia, that the loess formswhere you find it. The process is essentially asoil-forming process, turning the ground intoloess by loessification. This idea was completelycontrary to the prevailing view in the USA,which was that loess was an aeolian sediment.The Russell proposals provoked a large reac-tion, the community of loess scholars was gal-vanized, interest in loess was renewed and awhole series of papers (overwhelmingly in fa-vour of the aeolian theory) appeared.

Perhaps more controversial theories shouldhave been published, because the loess inNorth America has not been studied as thor-oughly as it deserves. In fact, its enormous dis-tribution is still not fully appreciated: thePalouse soil in the north-west is loess; theMississippi–Missouri river system has spreadloess to all the parts it reaches, and concen-trated material into the lower valley; and thearid regions have their adobe/loess deposits. InCanada, poorly defined loess is found inPalliser’s triangle, in the southern parts of Al-berta, Saskatchewan and Manitoba. However,the real loess in Canada will be found in the farwest, being mountain loess from the Rockies.The adobe in New Mexico is loess from thesouthern Rockies. The northern Rockies haveproduced a lot of Canadian silt, much of whichhas yet to be recognized as loess. There is amajor deposit at Kamloops, but a lot more in-vestigation is needed in this region.

Nebraska provides the setting for one of themost interesting loess systems in the USA. Likethe neighbouring state of Iowa, large parts ofNebraska are covered by loess, but it is that bitfurther westward than Iowa, that bit nearer tothe Rocky Mountains, and as a result it has afairly well defined layer of ‘mountain’ loess ontop of the much more widespread ‘ice-sheet’loess. Alan Lutenegger, of the University ofMassachusetts at Amherst, has investigated theBrady soil in Nebraska, which is dated at about8000 BP (before present). On top of the Bradysoil is a loess deposit which has its source in theRockies, as opposed to the Canadian glaciers.As the glaciers were melting and retreating, theRockies remained very cold and mountain loesscontinued to be produced for a significant pe-riod after the glacial retreat. Material was car-ried down the Platte River and made a beautifuldeposit in Nebraska.

Large amounts of ice-sheet loess are foundin Nebraska and Iowa, formed from materialcarried by the Missouri. Bob Ruhe, among oth-ers, showed how deposits thin away from thetransporting rivers and this observation hasbeen elegantly refined and developed byRichard Handy of Iowa State University, whodemonstrated the requirements for loess distri-bution from a source. The wind can blow mate-rial from the Missouri floodplains into bothNebraska and Iowa. Handy also showed thatthe loess in Iowa tended to undergo structuralcollapse when the clay-mineral content waslow, so a simple soil analysis allows structuralbuilding failures to be avoided. Iowa really isthe state for the loess enthusiast (of whichHandy is one) and examination of the biblio-graphical records shows more papers aboutIowa loess than that in any other state. Ne-braska comes second, and Illinois third.

Fig. 4. (far left)Richard Handy of IowaState University relaxesin Turin, Iowa. Loessprovides the basis forthe Iowa farmeconomy.


local loess. Idaho is not a major loess region andperhaps the constructors did not realize justhow widespread the North American loess is.Unfamiliarity with this strange and interestingmaterial might therefore have clouded judge-ments on its behaviour.

Adobe and bricksThe word adobe comes from the Arabic ‘at-tub’, meaning mud brick. The word has trav-elled steadily west along the north coast ofAfrica, up into Spain, across the Atlantic, upthrough Mexico and Central America toSouthern California and New Mexico. The lin-guistic separation of ‘adobe’ and ‘loess’ appearsto reflect other separations: the dry south-westfrom the more humid north-east, the area ofnorth European settlement from the area influ-enced by Spanish incursions, and the classicmidwestern loess from the arid zone variety.Adobe is fringe loess, being produced by rela-tively inefficient particle production mecha-nisms and existing in arid regions.

When adobe is thoroughly wetted andmixed, it becomes a very useful building mate-rial. A low-order chemical reaction, the adobereaction, occurs in the wetted mass and thisgives a modest cementing action which confersstrength on the dried artefacts, usually bricks orwalls. This adobe reaction seems to be ratherlike the pozzolanic action which made Romancement so effective and long-lasting. The Ro-mans added fine granular volcanic ash to limemortar and produced a cementing reactionwhich made the set mortar much stronger andlonger lasting. The pozzolanic reaction de-pends on the silica in the volcanic ash reactingwith the lime and water to produce calcium sili-cates, which hydrate to produce, in turn, thecementing action. In adobe, the silica (quartz)particles react with the carbonates in the sedi-ment when the material is thoroughly wettedand left to react. The reaction is not well de-fined, and adobe is not really appreciated as theinteresting and useful material it is.

Bricks are made from loess in many parts ofthe world. Normal loess makes an ideal brickbecause the problems of shrinkage and distor-tion on firing are avoided. The loess has a smallclay-mineral content, but it has enough for thefiring process to give a strong product. Thequartz silt provides the bulk of the brick and itpacks together to form a rigid block (it is thisthat allows the brick to be fired without distor-tion). The classic British bricks were the Stockbricks which were made, on quite a large scale,from the small loess deposits in North Kent andSouth Essex. A beautifully balanced system op-erated in the exploitation of these East Thamesbrickearths. A fleet of sailing barges operated

Illinois is another great loess state. For a longtime, a major loess scholar, John C. Frye, waschief of the Illinois State Geological Survey andunder his leadership loess investigation flour-ished. Frye was one of those who responded tothe Russell ‘loessification in situ’ proposal, andmade a good case for the aeolinists. Good loesswork is still being done in Illinois, but thenumber-one loess state is definitely Iowa,where the centre of gravity of the North Ameri-can loess is located (probably quite close toAmes).

Teton DamGeorge Sowers, the well-known constructionexpert, claimed in a paper published in 1994that the collapse of the Teton Dam in Idaho in1976 was the worst civil engineering construc-tion failure of the twentieth century. He meantthat it was the worst disaster as far as the profes-sion was concerned; there was not a large loss oflife but the loss of confidence in embankmentdam construction was indeed considerable.

The Teton Dam was built on fissuredrhyolite, a very unsafe volcanic rock which wasinevitably going to cause foundation problems,and it was largely constructed from the localIdaho loess. Embankment dams are popular asthey can be built from local ground materialand, if well built, can resist quite a lot of defor-mation. If a well designed clay core is used, theseepage losses can be kept to a minimum. Thisclay core is the critical part of an embankmentdam as it plays the critical role in keeping thewater impounded. It needs to be a fairly plasticclay, which allows it to deform slightly ifstressed (embankment dams can deform andsurvive earthquakes) and to develop fully a rela-tionship with water that prevents water pen-etration. The basis of this close relationshipwith water is the charged nature of the clay-mineral particles and the phenomenon of plas-ticity. Water in a clay-mineral system tends tobe held by chemical forces and is thus immobi-lized. But loess, while it may look superficiallylike a clay soil, lacks these two useful propertiesand thus it is not a plastic material. On the usualengineering scale of plasticity, a dam core couldhave a value of 40–50% and this would be satis-factorily high. When the post-failure plasticitymeasurements were done on the Teton Damloess core, a value of 3 was obtained. This isremarkably low and means that the materialwould require considerable engineering viacarefully constructed filter systems if materialinstability were to be avoided. As failure didoccur, one can only assume that the on-site en-gineers (subconsciously, if not consciously)thought that they were making the dam from aclay soil, when in fact they were using the brittle


on the river until about the end of the nine-teenth century, transporting garbage out of thecity and carrying bricks back up to the builders.The garbage was used by the brickmakers; itwas mixed with the brickearth and as the brickwas fired the garbage burned and contributedits share of the required thermal energy. In thisway garbage was destroyed and it positivelycontributed to the production of the usefulbricks. Much of Victorian London was builtwith these yellow Stock bricks. Early brickbuildings in England (say pre-1500) are con-centrated in the south-east, near to the readilyavailable and easily worked brickearths.

Bricks are still made from the North Kentloess, but on a very small scale. The trade mayrevive, however, as bricks tend now to be usedas facings rather than structural units and thedemand for quality and variety is rising.

HydroconsolidationHydroconsolidation, a long and somewhat in-accurate word, has been chosen by the loessengineers to describe the process of soil-struc-ture collapse that occurs in a loess when it isloaded and wetted. Of all the loess lands aroundthe world, this is probably more of a problem inCentral Europe than anywhere else, and cer-tainly most of the literature on loess collapseand subsidence comes from this part of theworld (Fig. 5). The practical problem is simply

how to strengthen the loess ground so thatbuildings may be constructed on it. It has beensaid that the Russians have devised 24 differentmethods for strengthening loess ground, butonly a few are actually used. In some cases theground can be flooded and will then collapseunder its own weight. It can then be drainedand constructed on without further settlement.Alternatively, huge weights may be dropped onthe ground, causing a simple mechanical struc-ture collapse (dynamic consolidation), or largeunder-reamed piles can be used, or chemicalscan be injected which react to give greater rigid-ity, or gas heaters can be lowered down drillholes to bake the ground, or …

The scientific problems of collapse mecha-nisms are still being studied, and they touch onone very fundamental problem. The process isa structural phenomenon in which the structureof the loess collapses – i.e. an open packing ofloess particles collapses to form a closer pack-ing. To describe the process we need to de-scribe and manipulate soil structure at thesingle particle level, and this cannot be done.Notwithstanding that the description of soilstructure is a critical problem in both agricul-ture and foundation engineering, its solutioncontinues to evade us. A famous soil scientist,D. J. Greenland, was driven to write: ‘It is a re-flection on the values of … this century thatwhile our knowledge of physics and technologydeveloped to the stage where we are now able tofly to the Moon, we failed to develop the skillsthat allow us to measure the structure of thesoil.’ Greenland wrote from an agriculturalviewpoint, but what he says is applicable to thesoil engineering situation. It would be useful ifwe could measure the structure of the loess be-fore collapse and after collapse, and it would bealso useful if we could find some way of repre-senting the collapse process, that transitionfrom an open packing to a much closer packing.

It looks as though the collapse process iscontrolled by small amounts of clay, which areconcentrated at the contact points of the silt-sized quartz particles. The clay tends to stabi-lize the metastable airfall structure, but when itis wetted allows (plastic) deformation in thecontact region and this enables the major struc-ture to deform and collapse. There must be afairly small amount of clay in the system be-cause a larger amount would make the wholematerial plastic and it would respond to stressin a totally different way. In the world of soilmechanics, loess is classified as a ‘collapsible’soil, the collapsibility being a consequence ofthe open airfall structure that is maintained bysome (albeit relatively weak) cementing action.Explaining collapse via the Berg/Russell loesstheory was very difficult.

Fig. 5. A house inBratislava, Slovakia.Subsidence is a majorproblem in easternEurope; many housesbuilt on loess developthese characteristiccracks.


Sahara DesertIs there, or isn’t there, a belt of loess around theSahara desert? This is a current question and ithinges on the problem of finding a naturalmechanism that can operate in the great aridsandy, rocky wastes of the Sahara to produce asubstantial number of loess-sized particles. Alarge amount of geo-energy is required to pro-duce a 30-µm particle and there are not thatmany large suitable sources available in nature.To explain the origin of the bulk of the US loessmaterial is comparatively easy, it was formed byglacial grinding. The large continental icesheets crushed the rocks to silt size and the riv-ers distributed the material through middleAmerica. The large Chinese deposits have theirorigin in the very high lands of the Tibetan pla-teau and the associated ranges. The enormousrelease of tectonic energy in this region, allied tothe temperature-weathering factors caused bythe great mountain heights, produces vastamounts of silt. Again rivers distribute it, and insome places a final aeolian transport phasegives a loess deposit. A deposit at Jiuzhoutaimountain, near Lanzhou, is believed to beabout 400 m thick. The amount of materialproduced in this region is enormous and it iswell called ‘mountain’ loess. The silt output ofHigh Asia (Fig. 6) has produced the rich agri-cultural lands of north India, the loess depositsof China and Central Asia, and the entire na-tion of Bangladesh. Bangladesh is proto-loess,an entire country of silt, even more silt than theNetherlands or Iowa.

But if we invoke ‘ice-sheet’ or ‘mountain’actions to explain the particle-forming mecha-nisms for the world’s large loess deposits, whatabout the Sahara? A collection of ingenious

mechanisms has been proposed to produce theright size of particles, ranging from sand-grainimpact to salt weathering. There is no doubtthat the Sahara is a great producer of dust; Sa-haran dust fell on Charles Darwin as the Beaglemade its way south at the beginning of the fa-mous voyage, but it is largely very fine,aerosolic, dust (< 10 µm), which travels high insuspension and may even reach NorthAmerica.

Albrecht Penck, the famous geomorpholo-gist, stated that the Sahara ‘lacked a loess gir-dle’ and it is true that spectacular deposits aremissing. If there are not efficient particle-pro-ducing mechanisms available, this is not sur-prising. But a collection of relatively inefficientmechanisms operating over a long time canproduce a modest deposit, and this is what ap-pears to have happened. Al-Bashir Assallayfrom the Al Fateh University in Tripoli hasshown that the coastal deposits do have theright size distribution, and show the proper col-lapse behaviour when loaded and wetted. AtGharyan in Libya, and more famously atMatmata in Tunisia, houses have been exca-vated into the loess (Fig. 7). This might be an-other defining factor for loess – one can live init. It has been suggested that Tolkien’s hobbitslived in loess houses in their Shire country. In-deed, we have all seen the Matmata loess dwell-ings as they were inhabited by the Skywalkerfamily at the beginning of the Star Wars saga.They made a suitably other-worldly settingfrom which to launch the great adventure.

Stratigraphy and QuaternaryeventsA current cause of concern is the change in theEarth’s climate. Two factors control thischange: natural oscillations in atmospheric cir-culation and received radiation, and humanfactors such as the release of greenhouse gases.The natural oscillations have left a record in theloess which stretches back for about two million

Fig. 6. The loessaround High Asia. Thissketch map by DrsAlekseev and Dodonovof the RussianAcademy of Sciencesshows loess near thatregion of crustaloverlap which hasprovided the Himalayasand the Tibetanplateau. Enormousenergy release in thisregion has allowedlarge-scale siltproduction. 1, loess; 2sand; 3, land over3000 m elevation –High Asia.

Fig. 7. Slovakian loess used to provide storagerooms. This sort of use occurs wherever fairly thickloess deposits are found. (Photo: AlenaKlukanova.)


years, long enough perhaps to establish thenatural oscillation frequency of climaticchange. A cold climate allows the normal pro-duction of loess material and the formation ofloess deposits. A warmer climate allows soils toform in the system, so that a long loess sectionin a deep deposit shows an alternating patternof loess and soil. These old soils are called pal-aeosols, and they are particularly well devel-oped in the Chinese loess. They are largelyresponsible for the large current amount of in-terest in loess stratigraphy, as they offer arecord of Quaternary events.

As far as we can determine, loess stratigra-phy was invented just over 100 years ago, by anunlikely discoverer in an unlikely place. JohnHardcastle was a school teacher in Geraldine, asmall town in the South Island of New Zealand.He had a keen interest in natural history andwas a talented observer. In 1889 and 1890 hepresented papers at the Canterbury Institute inChristchurch on loess formation and on theloess as a ‘climate record’. He stood on thebeach at Timaru and observed the loess cliffs,the so-called Dashing Rocks section, and hewas able to see the signs of climate change. Hepublished his observations in the Transactions ofthe New Zealand Institute where they remainedunappreciated until the 1970s.

The 1970s were a time of great excitement inthe world of loess stratigraphy, thanks largely tothe efforts of George Kukla of the Lamont-Doherty Observatory in New York State. Butpossibly the most significant event had hap-pened in 1961. The INQUA Congress that yearwas held in Poland, and there was a specialLoess Workshop at Lodz. Liu Tung-sheng pre-sented some observations from China, in par-ticular a diagram of a 120-m-thick loess sectionat Wucheng which showed 17 palaeosols

(Fig. 8). The workshop papers were published,in Poland, in 1964 and the paper by Liu Tung-sheng and Chang Tsung-hu showed clearlythat a large number of climatic changes hadtaken place, and that they were clearly recordedin the Chinese loess. Liu and Chang were asunlucky as Hardcastle; the Polish volumeswhich contained their epoch making contribu-tion were not widely noticed; and before awidespread publication operation could bemounted, the Cultural Revolution occurredand scientific activity ceased in China for tenyears.

During these ten years the multiple palaeo-sols made another appearance, this time in Eu-rope, at Krems in Austria and Brno inCzechoslovakia. The Middle European loesssections were nothing like as good as the Chi-nese sections, but some determined investiga-tions, in particular by Julius Fink of theUniversity of Vienna and Kukla from the CzechAcademy, revealed an intriguing pattern of cli-mate change. By 1977 they had detected 17-warm periods in the last 1.7 million years.Kukla moved to the USA and has been theleading figure in loess stratigraphy ever since.The topic needed a forceful and imaginativeprotagonist and Kukla fills this role very well.His work and the rapidly increasing concernabout climatic change have helped to pushloess stratigraphy into a very prominent posi-tion in the world of Quaternary studies. And, ofcourse, the opening up of China to scientificendeavours and the development of timely newtechniques (measurements of thermolumines-cence and magnetic susceptibility) have allcombined to promote climate-related loessstudies.

There are other excellent methods for study-ing the intricacies of climate change, such asdeep drilling on the continental ice caps anddrilling for core samples in the deep ocean sedi-ments, but they are relatively expensive and dif-ficult. The huge loess deposits of China andCentral Asia provide the best terrestrial databank relating to climate change in the last twomillion years. The Chinese place the beginningof the Quaternary period at about 2.4 millionyears BP, to coincide with the beginning of loessdeposition. This date also correlates well withthe Gauss-Matuyama magnetic change, whenthe Earth’s magnetic field changed fromnormal to reversed, a useful fixed point(Fig. 9). The change back to today’s normal,the Matuyama–Brunhes event, occurred at730 000 BP and is found in palaeosol S

8 of the

Chinese loess. The Chinese reckon the old soilsfrom the top, so S

8 is not very far down. One

can thus do some approximate calculations toestablish a frequency for climatic change. Re-cent studies suggest that 40 palaeosols exist in

Fig. 8. This is one ofthe most famous andsignificant pictures inthe world of loessscholarship, showingthe loess section atWucheng in Shanxiprovince. LiuTung-sheng showed itto the INQUACongress in Poland in1961. The multiplepalaeosols demonstrateclearly that manyclimatic oscillationsoccurred in Quaternarytime. 1, Malan loess; 2,Upper Lishih loess; 3,Lower Lishih loess; 4,Wucheng loess; 5,Buriedsoils = palaeosols; 6,Lower Plioceneconglomerate; 7,Palaeozoic sandstones.


Wucheng is the same as today’s loess. Go toArizona State University and ask Troy Péwéabout the loess in Alaska, and he will tell youwhere some was deposited last week; the sameold dust.

Suggestions for further readingBooks

Derbyshire, E., Dijkstra, T. & Smalley, I.J.(eds). Genesis and Properties of CollapsibleSoils, Kluwer, Dordrecht. 413pp.

Rozycki, S.Z. 1991. Loess and Loess-like Depos-its, Ossolineum-Polish Academy of Sciences,Wroclaw. 187pp.

Livingstone, I. & Warren, A. 1996. AeolianGeomorphology, Addison Wesley Longman,Harlow. 209pp.

Pye, K. 1987. Aeolian Dust and Dust Deposits,Academic Press, London. 287pp.

Periodicals

East Asian Tertiary/Quaternary Newsletter. Pub-lished by Centre for Asian Studies, Univer-sity of Hong Kong, Pokfulam Road, HongKong.

GeoJournal, v.36, no.2–3, 1995. Special issueon ‘Loess-paleosol and paleoclimatic investi-gations’.

Loess Letter: the Newsletter of the INQUA LoessCommission. Published twice a year by theCollapsing Soils Research Group, Civil &Structural Engineering Department, Not-tingham Trent University, NottinghamNG1 4BU, UK.

Quaternary Proceedings, no.4, 1995. Special is-sue on ‘Wind blown sediments in the Qua-ternary record’.

Quaternary Science Reviews, v.14, no.7–8, 1995.Special issue on ‘Aeolian sediments in theQuaternary record’.

Articles

Rogers, C.D.F., Dijkstra, T.A. & Smalley, I.J.1994. Hydroconsolidation and subsidenceof loess: Studies from China, Russia, NorthAmerica and Europe, Engineering Geology,v.37, pp.83–113.

Rutter, N., Ding, Z., Evans, M.E. & Wang.Y.1990. Magnetostratigraphy of the Baojiloess-paleosol section in the north-centralChina loess plateau, Quaternary Interna-tional, v.7–8, pp.97–102.

Ian Smalley is Secretary of the INQUA LoessCommission, and teaches soil science at LeicesterUniversity. Chris Rogers is senior lecturer ingeotechnical engineering at Loughborough Univer-sity.

the Chinese loess, indicating 40 oscillations inthe last two million years. That puts one cycleat 50 000 years (on average). This is a remark-ably short cycle. It will include a cold phase anda warm phase, so the warm phase could be25 000 years, during which half will be heatingand half will be cooling. We appear to be in thewarming quarter-cycle; the glaciers retreatedperhaps 10 000 years ago, so we are within2500 years of the turnover from warming tocooling. We must point out that these areballpark figures (a huge ballpark), but 40 estab-lished palaeosols do indicate 40 cycles. Theturnover will be delayed by greenhouse gasemission, but too much interference with thecycle could be dangerous.

Same old dustWe appreciate that the Tang poets used dust asa metaphor for the world. To fall into ‘the net ofthe world’s dust’ was to become totally in-volved in everyday worldly affairs, which thepoets sought to escape. But for a Tang poet,living in Chang-an, the world was a world ofdust; the loess dust was universal. When Li Powrote of ‘the same old dust of ten thousandages’ he referred to the rigours of everyday life,but we can adopt and adapt his phrase. Theloess is the same old dust; the old loess at

Fig. 9. Loess-palaeosolsequence at Baoji onthe Chinese LoessPlateau. The loess andpalaeosol units arenumbered from thetop, and magnetic fieldvariations are shown.Over 30 climaticoscillations since theGauss-Matuyamamagnetic reversal areindicated. Loessdeposition begins as thePliocene ends, at aboutthe time of the G-Mtransition. (After Rutterand others, 1990.)

Loess: The Yellow Earth

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