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1、www.ylongedu.com新托福TPO1阅读原文(一):GroundwaterTPO-1-1：Groundwater Groundwateristhewordusedtodescribewaterthatsaturatestheground,fillingalltheavailablespaces.Byfarthemostabundanttypeofgroundwaterismeteoricwater;thisisthegroundwaterthatcirculatesaspartofthewatercycle.Ordinarymeteoricwa
2、teriswaterthathassoakedintothegroundfromthesurface,fromprecipitation(rainandsnow)andfromlakesandstreams.Thereitremains,sometimesforlongperiods,beforeemergingatthesurfaceagain.Atfirstthoughtitseemsincrediblethattherecanbeenoughspaceinthe“solid”groundunderfoottoholdallthiswater. Th
3、enecessaryspaceisthere,however,inmanyforms.Thecommonestspacesarethoseamongtheparticles—sandgrainsandtinypebbles—ofloose,unconsolidatedsandandgravel.Bedsofthismaterial,outofsightbeneaththesoil,arecommon.Theyarefoundwhereverfastriverscarryingloadsofcoarsesedimentonceflowed.Forexampl
4、e,asthegreaticesheetsthatcoveredNorthAmericaduringthelasticeagesteadilymeltedaway,hugevolumesofwaterflowedfromthem.Thewaterwasalwaysladenwithpebbles,gravel,andsand,knownasglacialoutwash,thatwasdepositedastheflowsloweddown. Thesamethinghappenstothisday,thoughonasmallerscale,wherev
5、erasediment-ladenriverorstreamemergesfromamountainvalleyontorelativelyflatland,droppingitsloadasthecurrentslows:thewaterusuallyspreadsoutfanwise,depositingthesedimentintheformofasmooth,fan-shapedslope.Sedimentsarealsodroppedwhereariverslowsonenteringalakeorthesea,thedepositedsedim
6、entsareonalakefloorortheseaflooratfirst,butwillbelocatedinlandatsomefuturedate,whenthesealevelfallsorthelandrises;suchbedsaresometimesthousandsofmetersthick. Inlowlandcountryalmostanyspotonthegroundmayoverliewhatwasoncethebedofariverthathassincebecomeburiedbysoil;iftheyarenowbelo
7、wthewater’suppersurface(thewatertable),thegravelsandsandsoftheformerriverbed,anditssandbars,willbesaturatedwithgroundwater. Somuchforunconsolidatedsediments.Consolidated(orcemented)sediments,too,containmillionsofminutewater-holdingpores.Thisisbecausethegapsamongtheoriginalgrainsa
8、reoftennottotallypluggedwithcemen
