Umlando Wokwakheka Kwezwekazi LaseMelika
Izwekazi laseMelika lingenye yezindawo ezinkulu kakhulu emhlabeni, kusukela eNyakatho Pole kuya cishe eNingizimu Pole. Kodwa-ke, ukuma kwalo okude, izintaba ezinkulu njenge-Andes ne-Rocky Mountains, kanye nokuba khona kweziqhingi ezinkulu njengeGreenland akuyona into eyenzeka ngengozi. Konke lokhu kuwumphumela wenqubo ende kakhulu ye-geological—amakhulu ezigidi kuya ezigidigidini zeminyaka—ehilela ukunyakaza kwamapuleti e-tectonic, umsebenzi wezintaba-mlilo, ukwakheka kolwandle, ngisho nezinkathi zeqhwa. Lesi sihloko sihlola kafushane kodwa ngokuningiliziwe umlando wokwakheka kwezwekazi laseMelika.
1. Umhlaba Oguquguqukayo kanye Nendima Ye-Plate Tectonics
Ukuze siqonde ukwakheka kweMelika, kumelwe siqonde isimiso esiyisisekelo sesayensi ye-geology yesimanje: ubuso bomhlaba bakhiwe ngamapuleti e-tectonic ahamba phezu kwengubo eshisayo, yepulasitiki. Lawa mapuleti angasuka komunye nomunye (ahlukane), ashayisane (ahlangane), noma asheleleke adlule komunye nomunye (ashintshe). Kungale ndlela yokuxhumana lapho amazwekazi akha khona, ahlukane, ahlangane kabusha, futhi ashintshe isimo.
INyakatho Melika iphezu kwePlate yaseNyakatho Melika, kanti iNingizimu Melika iphezu kwePlate yaseNingizimu Melika. Ezinhlangothini zawo ezisentshonalanga, womabili amazwekazi asebenzisana namapuleti olwandle njengePlate yasePacific, iPlate yaseNazca, iCocos Plate, kanye namapuleti amancane amaningana. Lokhu kuxhumana okuyinkimbinkimbi kuyisihluthulelo ekwakhekeni kwezintaba kanye nemingcele yezwekazi.
2. Ukuqala: Ukwakheka Kwengxenye Eyinhloko Yezwekazi Lasendulo
Umlando wamazwekazi uqala ngokwakhiwa kwamatshe amadala kakhulu akha "umnyombo" wamazwekazi, aziwa ngokuthi ama-craton. ENyakatho Melika, i-craton enkulu, ebizwa ngokuthi i-Canadian Shield, yakhiwe ngamatshe amadala kakhulu, aneminyaka engaphezu kwezigidigidi ezingu-2,5 ubudala. Lesi kwakuyisisekelo sokuqala esizinzile lapho iNyakatho Melika kamuva "yakhula" khona ngokungezwa kwezinto ngezinqubo ze-tectonic.
ENingizimu Melika, umongo wezwekazi nawo umdala kakhulu, isibonelo eGuiana Shield naseBrazilian Shield. Lezi zifunda ezimbili ziqukethe amatshe asendulo akha uhlaka oluyinhloko lwaseNingizimu Melika.
Lawa ma-craton afana “ne-skeleton” yamazwekazi: awashintshi kakhulu njengemingcele yezwekazi esebenzayo. Kodwa asebenza njengezikhungo zokwengeza izindawo ezintsha zomhlaba ngokuhamba kwesikhathi.
3. I-Supercontinent Era: Ukusuka eRodinia kuya ePangea
Kuwo wonke umlando woMhlaba, amazwekazi ahlangane abe amazwekazi amakhulu izikhathi eziningana. Elinye lamazwekazi amakhulu anjalo asendulo kwakuyiRodinia (cishe eminyakeni eyizigidi eziyinkulungwane eyedlule). Phakathi nalesi sigaba, izingxenye ezazizoba yiMelika zazisesimweni esihlukile kakhulu kunanamuhla. Lapho iRodinia ihlukana, izingcezu zezwekazi zahamba, zakha izilwandle ezintsha, zabe sezihlangana kabusha zaba elinye izwekazi elikhulu.
Ingqophamlando edume kakhulu "yobunye" bezwekazi kwakuyiPangaea, eyakhiwa eminyakeni engaba yizigidi ezingu-335 edlule futhi yaqala ukuhlukana eminyakeni engaba yizigidi ezingu-200 edlule. Ngaphakathi kwePangaea, izifunda ezazizoba yiNyakatho neNingizimu Melika zazinamathele e-Afrika naseYurophu endaweni eyodwa enkulu. Ukuhlukana kwePangaea kwakuyisinyathelo esibalulekile ekwakheni ikusasa laseMelika yanamuhla.
4. Ukuhlukana kwePangaea kanye nokuzalwa koLwandlekazi i-Atlantic
Njengoba iPangaea yaqala ukuhlukana, amazwekazi amakhulu ahlukana aba amaqembu amabili amakhulu: iLaurasia enyakatho (eyandulela iNyakatho Melika, iYurophu, ne-Asia) kanye neGondwana eningizimu (eyandulela iNingizimu Melika, i-Afrika, i-Antarctica, i-Australia, ne-India).
Ngokuhamba kwesikhathi, uqhekeko oluhlukanisa iMelika ne-Afrika neYurophu lwanda, lwakha uLwandlekazi i-Atlantic. Le nqubo yenzeka ngokusabalala kolwandle eMid-Atlantic Ridge. I-Magma yaphakama, yaqina yaba uqweqwe olusha lolwandle, futhi yahlukanisa kancane kancane amazwekazi. Kuze kube namuhla, i-Atlantic iyaqhubeka nokwanda ngamasentimitha amaningana ngonyaka.
Lokhu kuhlukana kwakubalulekile: ngaphandle kokuvulwa kwe-Atlantic, iMelika ngabe ayibanga “yizwekazi ngokwalo” njengoba silazi namuhla.
5. Ukwakheka Kwezintaba Ezinkulu zaseNtshonalanga Melika
Ohlangothini olusentshonalanga yeNyakatho Melika, kwenzeka inqubo ehlukile. Esikhundleni sokuhlukana, lesi sifunda sabhekana nokushayisana okuningi kanye nokuncipha kwamapuleti olwandle ngaphansi kwamapuleti ezwekazi. Eminyakeni eyizigidi, ipuleti lolwandle eliminyene lancipha ngaphansi kwezwekazi, laqala umsebenzi we-magma futhi lakha izintaba-mlilo kanye nezintaba.
Esinye isikhathi esiyinhloko sokwakheka kwezintaba kwakuyi-orogenesis, eyakhiqiza izingxenye zezintaba zaseRocky. Ngaphezu kwalokho, izindawo ezinkulu zamaphutha njengeSan Andreas Fault eCalifornia zakhiwa ukushintshashintsha phakathi kwePacific kanye neNorth American Plates. Ngenxa yalokho, ugu olusentshonalanga yeNyakatho Melika luyisifunda esisebenza kakhulu ekuzamazameni komhlaba esinendawo ehlukahlukene kakhulu.
6. Ukuzalwa Kwezintaba zase-Andes kanye Nokuvela KweNingizimu Melika
INingizimu Melika inesinye sezici zemvelo ezimangalisayo kakhulu eMhlabeni: izintaba zase-Andes, okuyizintaba ezinde kakhulu eziqhubekayo emhlabeni. Ama-Andes akhiwa ngokuyinhloko ngokuncishiswa kweNazca Plate (ipuleti lolwandle) ngaphansi kweSouth American Plate. Lokhu kuncishiswa kwaholela ku:
1. Ukuphakanyiswa koqweqwe lwezwekazi ukuze kwakheke izintaba eziphakeme
2. Ukuqhuma okukhulu kwentaba-mlilo ebhande lase-Andean
3. Ukuzamazama komhlaba okunamandla okubangelwa ukungqubuzana kwamapuleti
Le nqubo ibilokhu iqhubeka iminyaka eyizinkulungwane eziningi futhi iyaqhubeka yenzeka nanamuhla. Ngenxa yalokho, amazwe afana neChile, iPeru, ne-Ecuador atholakala "ePacific Ring of Fire," isifunda esinokunyakaza okukhulu kokuzamazama komhlaba kanye nezintaba-mlilo.
7. Ukwakheka kwe-Isthmus yasePanama: Ukuxhumanisa Amazwekazi Amabili
Esinye sezenzakalo ezibaluleke kakhulu ze-geology emlandweni waseMelika kwaba ukwakheka kwe-Isthmus yasePanama eminyakeni engaba yizigidi ezintathu edlule. Ngaphambilini, iNyakatho neNingizimu Melika zazihlukaniswe ulwandle oluhlanganisa uLwandlekazi iPacific ne-Atlantic.
Ukuphakama kwezwe lasePanama kwakungenxa yokuhlanganiswa kwemisebenzi yentaba-mlilo, ukushayisana kwamapuleti amancane eCaribbean, kanye nokuphakanyiswa kolwandle. Umthelela wawujulile:
– Ukuxhumanisa amazwekazi amabili nokuvumela ukufuduka kwezilwane (i-Great American Biotic Interchange)
- Ukushintsha imisinga yolwandle yomhlaba wonke ngokuvala umzila wolwandle phakathi kwePacific ne-Atlantic
– Kuthinta isimo sezulu, okuhlanganisa nokuqinisa iGulf Stream ethinta isimo sezulu saseNyakatho Atlantic
Lesi senzakalo kwakungesona nje kuphela “ukuvela kwebhuloho lomhlaba”, kodwa futhi kwakuyishintsho ohlelweni loMhlaba ngezinga lomhlaba wonke.
8. Inkathi Yeqhwa Nokwakheka Kwesimo Sesimanje
Eminyakeni eyizigidi eziningana edlule, amazwe aseMelika abe nomjikelezo wezinkathi zeqhwa (i-glacial-interglacial). ENyakatho Melika, iqhwa elikhulu lalimboze iCanada kanye nengxenye enkulu yenyakatho ye-United States. Leli qhwa:
– Ukuguguleka kwamadwala, kwakha izigodi namachibi
– Ukubeka izinto ezidakayo, kwakha ithafa elibanzi
– Wadlala indima ekwakhiweni kwamaGreat Lakes
Njengoba iqhwa lincibilika, amazinga olwandle akhuphuka futhi akha izindawo ezisogwini zanamuhla, okuhlanganisa amatheku, ama-delta emifula, kanye namathafa asogwini.
INingizimu Melika nayo yabhekana nemiphumela yeNkathi Yeqhwa, ikakhulukazi e-Andes nasezifundeni eziseningizimu njengePatagonia. Izinguzunga zeqhwa zakha izigodi ezimise okwe-U, ama-fjords, namachibi asezintabeni achaza lesi sifunda.
9. IMelika "Isakhiwa"
Ngisho noma kuzwakala njengomlando wesikhathi esidlule, ukwakheka kweMelika akukayeki. Amapuleti e-Tectonic asahamba:
– I-Atlantic isakhula
– Indawo esentshonalanga isakha izintaba futhi ibangela ukuzamazama komhlaba.
- Imisebenzi yokuguqula efana neSan Andreas iyaqhubeka nokushintsha izindawo zomhlaba
– Isifunda saseCaribbean sisalokhu siyinkimbinkimbi ngokushayisana kwamapuleti amancane
Lokhu kusho ukuthi ukuma kwezwekazi laseMelika kungase kuhluke esikhathini esizayo. Eminyakeni eyizigidi ezayo, izingxenye zezwekazi zingase ziphakame, zicwile, noma zishintshe kakhulu ezindaweni zazo zamanje.
Isiphetho
Umlando wokwakheka kweMelika uyindaba ende yokushintsha okuqhubekayo koMhlaba. Kusukela ekwakhekeni kwezindawo zasendulo zezwekazi (ama-craton), kuya ekuhlanganeni kwamazwekazi amakhulu njengePangaea, kuya ekuqhekekeni okwadala uLwandlekazi i-Atlantic, kuya ekwakhekeni kwezintaba ezinkulu zasentshonalanga, kuya ekuphakameni kwe-Isthmus yasePanama kanye nomthelela wezikhathi zeqhwa—konke lokhu kwabumba iMelika njengoba sizazi namuhla. Ukuqonda lezi zinqubo kusisiza sibone ukuthi amazwekazi awamile, kodwa kunalokho angumphumela wokuguquguquka kwamaplanethi aqhubeka nokusebenza namuhla.
Uma ungathanda, ngingenza futhi inguqulo yalesi sihloko ngendlela elula kubafundi, noma ngengeze umugqa wesikhathi we-geology (unyaka nonyaka) ukuze kube lula ukufunda.
