文本讲义笔记geologyii

1、TPO1-GroundwaterTPO2-Desert FormationTPO3-Depletion of The Ogallala AquiterTPO12-Waterhe DesertTPO20-Fossil preservationTPO24-Lake WaterTPO27-The Formation of Volcanic IslandTPO28-Ground waterGroundwaterGroundwaterwatert saturates(使饱和)the ground, filling all the available spares···the

2、 most abundant(丰富的)type of ground water meteoric water(大气水；天落水)the groundwatert circulates as part of the water cycle·soakedo the ground from the surface, from precipiion and fromlakes and streamshe "solid" ground underfoot the commonest spaspace·among the particles-sand grains a

3、nd tiny pebbles-of loose,ounconsolidated(没有的) and and gravel（沙砾）· found wherever fast rivers carrying loads of coarse(粗糙的) sediment once flowedexample·the great iheetst covered Normerica during the last iceageladen(载满了) with pebbles, gravel and sand known as gla outwash(冰水沉积)l··d

4、eited as the flow slowed downa sediment-laden river or stream from mountain valley onto relatively fl spread out fanwise(扇形的)anddeit the sedimenthe form of a smooth, fan-shd slopewhere a river slow on entering a lake or the seain lowland countryonce the bed of a rivers sinceebelow the water's up

5、per surface(the water table)The gravels and sands of the former riverbed, and its sand bars(沙洲) will be saturated with groundwater···unconsolidated sedimentsconsolidated(or cemented)的 sedimentscontaillions of minute water-holding pores(孔)this is because the gaps among the original gra

6、ins are often not totally plugged with cementin chemicalsparts of the original grains may groundwaterSandstonee dissolved by percolating(过滤，渗透)as porous(多孔的) as the loose sand from which it was formed crystalline(晶体的) rocksmore solidexception-basalt(玄武岩)··a form of solidified volcanic lava

7、full of tiny bubbles porosity(多孔性)t make it very porousthe proportion of empty space in a rock premeability(渗透性)measure the ease with which water can flow through a material depend on the sizes of the individual cavities(孔洞) and the crevilinking themsurface ten(缝隙)The total column of water as consis

8、ting of water pore sizehe saturated sample must therefore be thought oft can, and watert cannot, drain away.··small size The waterhem will exist as thin fi, too light toe theforce of surface tenholding them in placeDepletion of the Ogallala Aquifer(蓄水层)the cast grasslands of the High Plain

9、she centra a semiarid(半干旱) climateited Ses···a low-ensity( 密集的， 密集度 ) agricultural economyof cattleranching(放牧) and wheat farming he early twentieth centurya huge aquifera rock layer containing large named after the Ogallala Sioux····ties of groundwater nsSioux n.，

10、美洲土著印第安人的一支，a sandstone formationfrom northwester Texas to Southern South Dakota enough water to fill Lake Huronrates of addition to the aquifer are minimal····aboulf a centimeter a yearduring the drought years of the early 1930sThewells were drilledo the Ogallalathe ensuing(继续,跟

11、着发生) ra from the 1950s onwardexpanof irrigation agriculturetransformed the economy of the regiona landscdominated by geometric patterns of circular green islands of cropssupply significant amount of the cotton, shum(高粱), wheat and corngrownhe United Ses40% of American grain-fed beef cattleunpreceden

12、ted development of a finite(有限) ground water resource wi almost negligible(可忽略的) natural recharge raten·····no natural water source to replenish(补充) the water supply the drastic(戏剧性的) fall of water tablesthe periodic deepening of wellsthe use of ever-more-erful pumpswill run

13、 dry within 40 yearsinevitable(不可避免的) depletion(下降) of the Ogallalathe reaction ormersattempt to conserve water by irrigating less frequently or by switching tocropst require less wateradopt the philosophyt it is best to use the water while it is silleconomically profitable to do so concentrate on h

14、igh-value cropch as cottonThe incentive(刺激) of the farmers who wish to conserve water is reduceda number of grandiose(宏大的) schemes to transport castties of waterby cor pipelineincrease pumcostseast tenfoldrelease capillary(毛细管的) water above the water taby injectingcompressed airo the groundwaterhe s

15、oiltriple water costs genetic engineering(工程)new strains of drought-resistant cropsDesert Formation the desertoccupy approximay a fourth of the Earth's land surfaceincrease at desertificationarming paceIs been estimatedt an additional one-fourth of the Earth's land surfaceis threatened by th

16、is pro desertificationsthe loss of stabilizing natural vegeion(植被)the subsequent(紧随而来的) accelerated ero waterof the soil by wind andThe loose soil is blown compley away, leaving a stony surface.The finer(细的)particles may be removed, while the sand-sized particles areaccumulated to form mobiills or r

17、idges of sand.the loss of the soil's ability to absorb substantial(大量的) the impact of raindrops on the loose soilties of watertransfer fine clay particles seal(封) themo the tiniest soil spaproduce a surfacet allows very little watenetrationWater absorption is gre Runoff is increasedy reducedacce

18、lerated ero further loss of vegerates iona cycle of progressive(进步，进程) surface deterioration( a trend toward drier climatic conditionscontinued gradual global warming an increase in aridity(干旱的)causehuman activities natural proshuman activities expanding populations)preres to provide food and fuelDu

19、ring the dry periods, the prere on the land is often far in exs(超过，多余) of its diminished(减少)capacity, and desertification resultsmajor contributors(导致) to the desertification prosesovercultication(过度种植) overgrazing(过度放牧) firewood gathering(搜集柴火) overirrigation(灌溉)The raising of cropsnesie(是成为必要) the prior removal of the natural vegeioncrop failuresextensive(广泛的) tracts(田) of land devoid of(缺乏) a plant cover susceptible to wind and water eroThe raising of livestockGrasses are generally the dominant type of natural vegeionan exsive(多余的) number of livestock grazing in an ar