雅思阅读材料2Word格式文档下载.docx
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雅思阅读材料2Word格式文档下载.docx
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sthroatand,7metresdown,sawa"
choke-point"
lessthan10centimetreswide.Belowthatwasacavernaboutthesizeofasmallcar.Butthecameracouldn'
tgodeeperthan14metresbecauseoftheviolentchurnofboilingfluids.
Now
JeanVandemeulebrouck
oftheUniversityofSavoieinLeBourgetduLac,France,andcolleagueshaveanalysedseismicdatacollectedinthe1990s.Usingamodernacoustictechniquemorecommonlyusedtolocatewhalesorsubmarines,theyanalysedthenoiseofthepoppingbubblesinsidethegeyser–capturedintheseismicrecord–toreveala60-cubic-metrecavern15metresdown,andofftothegeyser'
sside.
Thissidecavityactsasacompressiblereservoir,makingthewaterinthesmallermainventbobupanddownlikeaspring.Theoscillationsaffectthewaterpressureandhelpthegeysertoboilintheearlystagesoferuption.
Thesidecavern"
totallychangesourperspectiveofthephysicsofhowgeyserswork"
says
ShaulHurwitz,ahydrologistwiththeUSGeologicalSurveyinMenloPark,California,whohopestheinnovativeacoustictechniquecanbeappliedtovisualisingtheinsidesofvolcanoesaswellasgeysers.
2.NewYorkathighriskofalieninvasions
∙17:
3407May2013by
FredPearce
∙Magazineissue
2916.
Subscribeandsave
Aliensdon'
tstrikeeverywhereinequalmeasure.Thefirstcomprehensiveassessmentoftheriskposedbyballastwaterhasidentified20hotspotsthatareparticularlyvulnerabletobeinginvadedbyspeciesstowedawayinsidethebowelsofcargoships.
SanFranciscoBay,NewYork,LosAngeles,HongKongandDurbaninSouthAfricaareonthelist,whichcouldhelpfocuscounter-measures.
Emptyshipsroutinelytakeonseawaterasballastbeforetheysetsail,tokeepthemstablewhileatsea.Theylaterdumpitintheportwheretheytakeoncargo.Atanyonetime,anestimated7billiontonnesofballastwateriscrossingtheoceans–almostallofitcarryingseeds,spores,eggs,larvae,bacteriaandplanktonnativetowhereverthewaterwasloaded.It'
sprobablythetopcauseofalieninvasionsworldwide.
ThesebiologicaltimebombsweremeanttobedefusedbyaUNtreatyagreedin2004requiringbigshipstofilteranddisinfectballastwaterbeforedumpingit.But
notenoughnationshaveratifiedthetreatyforittocomeintoforce.
Nowateamledby
BerndBlasius
oftheUniversityofOldenburginGermanysaysthatmostofthethreatistoahandfulofports.Ofmorethan1400portsstudied,theyestimatethatjust20carry39percentoftheriskofinvasions.Theriskformostotherportswasnegligible.
Theauthorsmappednearly3millionshipjourneysandassessedthedangertheirballastwaterposed.Analieninvaderismostlikelytobereleasedifthejourneyisnottoolong–inwhichcasethecrittermaydieenroute–andnottooshort–inwhichcaseitmayalreadybepresentlocally.Theriskiestjourneysturnouttobebetween8000and10,000kilometres–roughlythedistancefromShanghaitoSanFrancisco.
Invasionsarealsomorelikelyifthestartpointisinwarmwater,whichusuallycontainsmorespecies,andifthewateratbothportsisofsimilartemperatureandsalinity.Thatflagsupbusytropicalportshandlinglong-distancecargo,withSingaporeandHongKongtopoftheat-risklistalongsidetheSuezandPanamacanals.
Thepredictionsmatchdatafromportsthathaveknownproblemswithalieninvasions.ThatincludesSanFranciscoBay,wherethemajorityofinhabitantsarealienspeciessuchasChinesemittencrabs,NewZealandseaslugsandJapanesegobies–allbroughtbyballastwater.TheteamexpectsrelativelyfewalienspeciestosurvivedischargeatcolderportslikethosearoundtheNorthSea,butcautionthatthiscouldchangewithglobalwarming.
DavidSmithatthePlymouthMarineLaboratoryintheUKsaysthestudyissolidbutfearsthatbypointingoutthatmostportsarenotsovulnerable,"
itcouldbeusedasareasonfornotratifyingthetreaty"
.Hewarnsthattheteamdidnotlookat
bacteria,whichmightposedifferentrisks.
Thefindingscouldhelptargeteffortstosteminvasions,saysstudyco-authorHannoSeebensoftheUniversityofOldenburg."
Usuallyportauthoritiescannotcheckallships,"
hesays."
Ourmodelcanhelpinspectorsidentifytheshipswiththehighestprobabilityofcarryingpotentiallyinvasivespecies."
3.Wheremeltingicemeansretreatingseas
∙06May2013by
StephenBattersby
2915.
∙Forsimilarstories,visitthe
ClimateChange
TopicGuide
Itsoundsimpossiblebutit’strue.Thesealevelaroundameltingicecapwillfallevenasdistantshoresareinundated
SITyourselfdownonthechillyshoreofGreenland.Setyourtimemachinetofast-forwardthroughthenextfewcenturies,andwatchasthegreaticesheetaboveyouslowlymeltsandspillsintothesea.Sofar,sopredictable.Butwhathappensasallthismeltwaterpoursintotheseamaysurpriseyou.Whilefarawaycitiesbattlerisingwaters,youfindyourselfhighanddry,lookingdownattheretreatingwaves."
Atyourfeet,sealevelwillfallby100metres,"
saysgeophysicistJerryMitrovica."
It'
scrazy.Crazybuttrue."
Howisthatpossible?
Itisalltodowiththefactthattheseaisnotasflatasitlooksfromadistance.Insteadofbeingaslevelasabathtubofstillwater,itssurfaceismarkedbywateryhillsandvalleys.Theyareinvisibletooureyesbecausetheslopesaresogradual,buttheycanbemanymetreshighordeep.
Thiswaterscapehasremainedessentiallythesameforthepastfewthousandyears,butnowitisbeginningtochange.Astheicesheetsmelt,therewillnotonlybemorewaterintheoceans,butthepositionsofthosehillsandvalleyswillshift.Dependingonwhathappens,BostonandNewYorkmightfacethethreatofanewsummitinthesea.OrthewavescouldretreatfromScotlandtoexposenewland.
Ifyouthinkthissoundsunlikelythenyouareingoodcompany,asevenoceanographershavestruggledtoaccepttheidea.Yetthephysicsbehinditisquitesimpleandthebasicprinciplewasrecognisedasfarbackasthe19thcentury.Thefirstpersontodosowas
RobertWoodward,aphysicistwhoworkedfortheUSGeologicalSurveyatthetimewhenitwasbecomingclearthatmuchofNorthAmericahadbeencoveredbyicenotthatlongago.
Woodwardwasaskedbyhiscolleaguestohelpexplainapuzzlingfinding:
whentheicewaspresent,theshorelineofonelakeappearedtohavebeenmuchhigherononesidethantheother.HerealisedthatanylargemassonEarth'
ssurface,fromacontinenttoanicesheet,exertsasignificantgravitationalpullonanywatersurroundingit,pilingtheliquidagainstitsflanks.Inthecaseofanicesheet,thesewateryfoothillswillsubsideiftheicemelts.In1888,Woodwardpublishedapaperdescribingwaystocalculatetheresultingchangesinsealevel.
Nearlyacenturylater,in1976,WilliamFarrellandJamesClark
factoredintheeffectsofgravity
whentheytriedtoworkouthowsealevelchangedasthegreatnorthernicesheetsmeltedattheendofthelasticeage.Thefollowingyear,ClarkandCraigLingleappliedthesameprinciplestoworkoutwhatwouldhappenifthefragileWestAntarcticicesheetweretothinordisappear.SealevelaroundmostoftheEarthwillrise,theyfound,butinpartsofthesouthernoceanitwillfall,producingadistinctiveglobal"
fingerprint"
.
That1977findingwasnothiddenawayinsomeobscurejournal–itwasinNature
–butremarkablythemessagestilldidn'
tgetthrough."
Theideaofsealevelfingerprintshasalonghistoryofbeingforgotten,"
saysMitrovica,whoisatHarvardUniversity.Oceanographerscontinuedtotalkaboutaveragesealevel,assumingthatameltingicesheetwoulddeliverauniformchangearoundtheglobe.Tothisday,mostmapspurportingtoshowtheeffectsofsealevelrisearebasedonthissimplisticassumption.
Yetithaslongbeenatoddswiththemeasurements.Thetidegaugesmonitoringsealevelathundredsoflocationsaroundtheglobewereshowing
aslowrise
in
averagesealevel,buttherewerelargeregionalvariations."
Thepeoplelookingattidegaugedatasawthatsealevelwaschangingfromplacetoplace,"
saysMitrovica,"
buttheyhadforgottenabouttheeffectofgravity,sotheythoughtthiswasaproblem."
Inthe1990s,theTOPEX/Poseidonsatellitegaveusadetailedglobalviewoftheoceansforthefirsttime,andconfirmedthesepuzzlingvariationsintheseascape(seea
videoshowinghowthestrengthofgravityvariesaroundtheglobe).
Atfirstoceanographerssuspectedahangoverfromthelasticeagewastoblame.Ithasbeenknownsincethe19thcenturythattheweightofanicesheetpushesdowntheEarth'
scrust.Asthecrustsinks,deeprockoozessideways,makingsurroundingareasbulgeupwards.Whentheicemeltsandtheweightislifted,thecrustreturnstoitspreviousshape.Whilethegravityeffectwaslargelyforgotten,post-glacialreboundremainedcommonknowledge.
ThevasticesheetsonNorthAmericaandEurasiaweresoheavythatthelandsurfacebelowthemsankbyasmuchas500metres.Whentheicebeganmeltingaround20,000yearsago,thecrustreboundedpartofthewayveryrapidly."
slikelettinggoofastretchedelasticband,"
saysMitrovica.Afterthat,theprocesscontinuedfarmoreslowly.Someplacesarestillrisingtoday–HudsonBay
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