冰山(Icebergs)

详细内容

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icebergsareamongnature＇smostspectacularcreations,andyetmostpeoplehaveneverseenone.avagueairofmysteryenvelopsthem.theyeintobeing-----somewhere------infaraway,frigidwaters,amidthunderousnoiseandsplashingturbulence,whichinmostcasesnoonehearsorsees.theyexistonlyashorttimeandthenslowlywasteawayjustasunnoticed.

objectsofsheerestbeautytheyhavebeencalled.appearinginanendlessvarietyofshapes,theymaybedazzlinglywhite,ortheymaybeglassyblue,greenorpurple,tintedfaintlyofindarkerhues.theyaregraceful,stately,inspiring-----incalm,sunlightseas.buttheyarealsocalledfrighteninganddangerous,andthattheyare----inthenight,inthefog,andinstorms.eveninclearweatheroneiswisetostayasafedistanceawayfromthem.mostoftheirbulkishiddenbelowthewater,sotheirunderwaterpartsmayextendoutfarbeyondthevisibletop.also,theymayrolloverunexpectedly,churningthewatersaroundthem.

icebergsarepartsofglaciersthatbreakoff,driftintothewater,floataboutawhile,andfinallymelt.icebergsafloattodayaremadeofsnowflakesthathavefallenoverlongagesoftime.theyembodysnowsthatdrifteddownhundreds,ormanythousands,orinsomecasesmaybeamillionyearsago.thesnowsfellinpolarregionsandoncoldmountains,wheretheymeltedonlyalittleornotatall,andsocollectedtogreatdepthsovertheyearsandcenturies.

aseachyear＇ssnowaumulationlayonthesurface,evaporationandmeltingcausedthesnowflakesslowlytolosetheirfeatherypointsandbeetinygrainsofice.whennewsnowfellontopoftheold,ittooturnedtoicygrains.soblanketsofsnowandicegrainsmountedlayeruponlayerandwereofsuchgreatthicknessthattheweightoftheupperlayerspressedthelowerones.withtimeandpressurefromabove,themanysmallicegrainsjoinedandchangedtolargercrystals,andeventuallythedeepercrystalsmergedintoasolidmassofice.