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GEOMORFOLOGIE - · PDF fileGEOMORFOLOGIE TUTORE CURS: Conf. univ. dr. Marian Ene AGENŢI ŞI PROCESE GEOMORFOLOGICE

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  • GEOMORFOLOGIE

    TUTORE CURS: Conf. univ. dr. Marian Ene

    AGENI I

    PROCESE GEOMORFOLOGICE

  • METEORIZAREA reprezint un ansamblu de procese fizice i

    chimice prin care are loc distrugerea rocii. Eroziunea i

    transportul nu sunt obligatorii, astfel nct n acest caz cea

    mai mare parte a materialului rezultat rmne n locul n care

    roca a fost distrus;

    Meteorizarea creeaz produse (materiale) de meteorizare;

    www.web/karin/mechanical-weathering-diagram&docid http://www.canadiangeographic.ca/atlas/glossary

  • acest proces se realizeaz la contactul atmosferei terestre

    cu roca, determinnd transformarea acesteia prin intermediul

    unor procese superficiale dintr-o stare stabil ntr-o stare

    mobil uor de dislocat de agenii exogeni;

    n funcie de mecanismul prin care se realizeaz i de

    transformrile pe care le sufer roca, aceste procese sunt de

    dou feluri: meteorizare mecanic (a) i meteorizare chimic

    (b).

    http://www.limestone-pavements.org.uk

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  • meteorizarea mecanic (dezagregarea) se produce n

    urma tensiunilor externe; fragmentarea rocii se produce fr

    schimbarea compoziiei chimice a acesteia;

    meteorizarea presupune, ns, existena unor fisuri iniiale n

    masa rocii, fisuri n interiorul crora se vor produce ulterior

    tensiuni laterale determinate de modificarea unor factori

    atmosferici;

    http://dawnssedstrat.blogspot.com/2012/02/weathering-and-erosion.html

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  • agenii care determin procese de dezagregare sunt legai de

    dinamica factorilor climatici (temperatur, umiditate) care pot s

    genereze n interiorul fisurilor, porilor din roc tensiuni tangeniale

    puternice, care vor duce la frmiarea rocii;

    aceste procese sunt impuse de: insolaie, nghe-dezghe,

    umezire-uscare, presiunea rdcinilor plantelor http://suhow.info/30256-definition-of-differential-weathering.html

    http://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.htmlhttp://suhow.info/30256-definition-of-differential-weathering.html

  • insolaia; este fenomenul ce determin modificrile termice de la

    suprafaa rocilor, provocnd dilatarea i contractarea termic a

    mineralelor ce intr n compoziia acestora; eficiena ei este cu att mai

    mare cu ct roca este mai puin protejat de nveliul vegetal sau de sol;

    exist regiuni lipsite de vegetaie (deerturi) unde , ca urmare a insolaiei

    puternice, temperaturile diurne oscileaz ntre 0C i 50 70C, uneori mai

    mult; n timpul nclzirii are loc o dilatare a mineralelor din roc, iar n timpul

    rcirii o contractare a acestora; aceste tensiuni produc crpturi a cror

    profunzime este limitat de slaba conductibilitate termic a rocii; efectul

    insolaiei este superficial i se produce pe adncimi de la civa milimetri la

    civa centimetri (dezagregare prin descuamare); efectul tensiunilor termice

    este mai mare cu ct componena mineralogic a rocilor este mai neomogen

    (exemplu: mineralele mai nchise la culoare se nclzesc mai repede i se

    rcesc mai greu); formele de relief rezultate sunt diverse, cum ar fi blocurile de

    roc rotunjite devenite aproape sferice (cpnile de zahr din M. Mcinului

    sau din jurul oraului brazilian Rio de Janeiro);

  • http://www.portervillecollege.edu/richardgoode/Death%20Valley%20Pictures.htm

    http://www.portervillecollege.edu/richardgoode/Death Valley Pictures.htm

  • ngheul i dezgheul produce tensiuni laterale n interiorul fisurilor i

    porilor rocii datorit creterii n volum (cu circa 9%) a apei n urma

    ngheului acesteia; procesul de dezagregare prin nghe-dezghe este

    eficient doar atunci cnd fisurile i porii rocilor sunt umplui cu ap ntr-o

    proporie de peste 90%;

  • umezire uscare: dezagregarea se poate datora i presiunii de

    cristalizare a srurilor; soluiile concentrate cu anumite sruri produc procese de

    cristalizare a srurilor pe suprafee de strat, n fisuri, n porii rocilor n urma

    evaporrii apei. O sare n momentul cristalizrii i mrete volumul i preseaz

    asupra rocii (tensiuni de cristalizare);

  • http://www.papplewick.org/holgate/fieldwork/Processes/weathering&slopes.htm

    http://www.papplewick.org/holgate/fieldwork/Processes/weathering&slopes.htm

  • presiunea rdcinilor plantelor exercitat n timpul creterii rdcinilor;

    determin pstrarea dislocaiilor i chiar mrirea acestora (A), ceea ce duce la

    creterea volumului i suprafeei pe care pot s acioneze agenii externi;

    rdcinile plantelor superioare au un efect de dislocare n timpul balansrii lor de

    ctre vnt (B).

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  • meteorizarea chimic (alterarea) reprezint ansamblul de procese prin care are loc

    descompunerea substanelor i elementelor chimice din compoziia rocilor i formarea unor

    noi combinaii chimice:

    A + soluia A B + soluia B

    Alterarea chimic este prezent n mod deosebit n rocile metamorfice i magmatice, roci

    neomogene ce conin numeroase elemente chimice ce se combin uor cu cele din aer i ap, cum

    ar fi O2 i H2O. Intensitatea de aciune a apei este condiionat de temperatur i pH-ul su;

    condiiile de alterare sunt impuse de:

    de alctuirea mineralogic (i chimic) a rocilor;

    de gradul de fisurare i porozitate a rocilor, ceea ce determin creterea suprafeei de

    contact cu apa i aerul (mediul atmosferic);

    de clim i vegetaie.

    Rezultatele

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