托福阅读tpo2desertformation沙漠的形成原题解析

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1、阅读原文：Thedeserts,whichalreadyoccupyapproximatelyafourthoftheEarth’slandsurface,haveinrecentdecadesbeenincreasingatanalarmingpace.Theexpansionofdesertlikeconditionsintoareaswheretheydidnotpreviouslyexistiscalleddesertification.Ithasbeenestimatedthatana

2、dditionalone-fourthoftheEarth’slandsurfaceisthreatenedbythisprocess.沙漠己经占据了地球陆地面积约四分之一，而且最近几十年正以惊人的速度扩张。沙漠化是指类似沙漠的环境漫延到原本并非沙漠的区域。裾估计，地球表而另外四分之一的地方正面临沙漠化威胁。Desertificationisaccomplishedprimarilythroughthelossofstabilizingnaturalvegetationandthesubsequ

3、entacceleratederosionofthesoilbywindandwater.Insomecasestheloosesoilisblowncompletelyaway,leavingastonysurface.Inothercases,thefinerparticlesmayberemoved,whilethesand-sizedparticlesareaccumulatedtoformmobilehillsorridgesofsand.沙漠化主要通过以下过程实现：首先自然植被不断减

4、少，随后风力和雨水加速了土壤的腐蚀。有的时候松散的土壤全部被风刮走，留下石质化的表层；其它情况下细小的沙粒可能会被吹走，而正常沙粒大小的砂子不断堆积，从而形成移动的沙丘或者沙脊。Evenintheareasthatretainasoilcover,thereductionofvegetationtypicallyresultsinthelossofthesoil’sabilitytoabsorbsubstantialquantitiesofwater.Theimpactofraindropson

5、theloosesoiltendstotransferfineclayparticlesintothetiniestsoilspaces,sealingthemandproducingasurfacethatallowsverylittlewaterpenetration.Waterabsorptionisgreatlyreduced;consequentlyrunoffisincreased,resultinginacceleratederosionrates.Thegradualdrying

6、ofthesoilcausedbyitsdiminishedabilitytoabsorbwaterresultsinthefurtherlossofvegetation,sothatacycleofprogressivesurfacedeteriorationisestablished.即便是在保留了土壤表层的IX域，植被减少也已成为土壤大量吸取地下水的能力下降的典型因素。雨水对松散土壤的冲击会把细小的粘土颗粒冲到土壤空隙屮，封闭了土壤并降低土地表层水的渗透率。地表对水的吸收急剧减少，大量水资

7、源流失，因此土壤的腐蚀率也随即增加。地表吸收水分的能力进一步弱化使得土壤越发干燥，导致植被的进一步流失，于是便形成了土壤沙漠化的恶性循环。Insomeregions,theincreaseindesertareasisoccurringlargelyastheresultofatrendtowarddrierclimaticconditions.Continuedgradualglobalwarminghasproducedanincreaseinaridityforsomeareasovert

8、hepastfewthousandyears.Theprocessmaybeacceleratedinsubsequentdecadesifglobalwarmingresultingfromairpollutionseriouslyincreases.在一些地方，沙漠面积的扩大很大程度上归因于干燥的气候条件。在过去的儿千年里，不断增加的温室效应使得一些地方干旱问题愈发严重。倘若空气污染带来的温室效应继续恶化，沙漠化进程会在未來数十年内加速实现。Thereislittledoubt,howeve