Rarraba kankara

Rarrabawar kankara shine abin da ya faru na yanayin ƙasa wanda aka samar ta hanyar samar da ruwan tabarau na kankara, wanda ke haifar da rushewa lokacin da danshi, ya bazu a cikin ƙasa ko dutse, ya tara a cikin yanki. Da farko kankara tana tarawa a cikin ƙananan ƙuƙwalwar da aka ɗora ko tsagewar da ta riga ta kasance, kuma, muddin yanayin ya kasance mai kyau, yana ci gaba da tattarawa a cikin kankara ko ruwan tabarau na kankara, yana rarraba ƙasa ko dutse. Gilashin kankara suna girma a layi daya da farfajiyar kuma da yawa centimeters zuwa da yawa decimeters (inches zuwa feet) zurfi a cikin ƙasa ko dutse. Nazarin tsakanin 1990 da yanzu sun nuna cewa fashewar dutse ta hanyar rarrabewar kankara (watau, fashewar duwatsu marasa lalacewa ta hanyar ruwan tabarau na kankara wanda ke girma ta hanyar jawo ruwa daga kewaye da su a lokacin yanayin zafi mai ɗorewa) tsari ne mai tasiri fiye da tsarin daskarewa wanda tsofaffin matani suka ba da shawarar."Periglacial weathering and headwall erosion in cirque glacier bergschrunds"; Johnny W. Sanders, Kurt M. Cuffey, Jeffrey R. Moore, Kelly R. MacGregor and Jeffrey L. Kavanaugh; Geology; July 18, 2012, 

Gilashin kankara suna taka muhimmiyar rawa a cikin fashewar dutse da sanyi da ke haifar da ƙasa, waɗanda ke da mahimmanci ga yanayin yanayi a yankuna masu sanyi. Gudun sanyi yana haifar da tarkace kuma yana tsara shimfidar wurare cikin tsari mai rikitarwa. Ragewar dutse a yankunan periglacial (alpine, subpolar da polar) sau da yawa ana danganta shi da daskarewa da fadada ruwa da aka kama a cikin pores da cracks. Koyaya yawancin ƙanƙara da ƙanƙarar dutse suna haifar da rarraba kankara a cikin ruwan tabarau na kankara a yankunan da ke kusa da ƙasa. Rarrabawar kankara tana haifar da karyewar dutse da kuma hauhawar sanyi.

 Bayani game da abubuwan da suka faru 

 Yaduwar sanyi 
Frost lift shine tsari wanda daskarewa na ƙasa mai cike da ruwa ke haifar da lalacewa da turawa sama na ƙasa. Wannan tsari na iya karkatarwa da fashewa, lalata tushe na gine-gine da kuma kawar da ƙasa a cikin alamu na yau da kullun. Rashin ruwa, ƙasa mai kyau a wasu Yanayin zafi yana da saukin kamuwa da ƙanƙara.

 Gilashin kankara a cikin tundra 
Yankin sanyi ya zama ruwan dare a cikin tundra na arctic saboda permafrost yana kiyaye ƙasa a cikin zurfi kuma yana hana dusar ƙanƙara da ruwan sama daga zubar. A sakamakon haka, yanayin sun fi dacewa don samar da ruwan tabarau mai zurfi tare da babban tarin kankara da kuma canjin ƙasa mai mahimmanci.

Yanayin sanyi daban-daban wanda ke samar da alamu masu rikitarwa zai faru idan akwai yanayin da ya dace. Ra'ayoyi daga sanyi na shekara guda yana da tasiri sosai a cikin shekaru masu zuwa. Misali, karamin karuwa a cikin nauyin zai shafi zurfin ƙanƙara da haɓaka a cikin shekaru masu zuwa. Misalai masu dogara da lokaci na sanyi sun nuna cewa a cikin dogon lokaci rikice-rikicen gajeren lokaci ya ragu, yayin da rikice-rikice na tsakiya ke girma kuma ya mamaye wuri mai faɗi.

 Tsarin kankara na karkashin kankara 
An lura da igiyoyin laka ko glacial har sai an lura da su a ƙarƙashin kankara na Antarctic; an yi imanin cewa waɗannan sun samo asali ne daga ruwan tabarau na kankara da ke cikin tarkace. A cikin yankuna masu saurin gudana, kankara yana zamewa a kan ruwa mai cike da ruwa (glacial till) ko kuma a zahiri ana iyo a kan ruwa. Rashin ruwa da ruwa suna aiki don rage rikici tsakanin tushe na kankara da dutse. Wadannan ruwan subglacial sun fito ne daga ruwa na sama wanda a wasu lokutan yakan zubar da ruwa daga narkewa a farfajiya, da kuma daga narkewar kankara.

Girman ruwan tabarau na kankara a cikin dutsen da ke ƙasa da kankara ana tsara shi a lokacin watanni na rani lokacin da akwai isasshen ruwa a gindin kankara. Gilashin kankara za su samo asali a cikin dutse, suna tarawa har sai dutsen ya raunana sosai har ya yanke ko ya fashe. Layer na dutse tare da dubawa tsakanin glaciers da bedrock an sake su, samar da yawancin sediments a cikin wadannan basal yankuna na glaciers. Tunda yawan motsi na kankara ya dogara da halaye na wannan kankara, ana ci gaba da bincike don inganta ƙididdigar abubuwan da suka faru.

 Fahimtar abubuwan da suka faru 
Yanayin asali na rarrabe kankara da ƙanƙara shine kasancewar yanki a cikin ƙasa ko dutse mai ƙuƙwalwa wanda ke da ɗanɗano, yana cikin yanayin zafin jiki wanda ke ba da damar kasancewa tare da kankara da ruwa (a cikin yanayin da aka riga aka narke), kuma yana da yanayin zafin a fadin yankin.

Wani muhimmin abu don fahimtar rarrabewar kankara a cikin ƙasa ko dutse mai laushi (wanda ake kira ruwan tabarau na kankara saboda siffarsa) shine ƙaddamarwa, wanda shine ci gaban fim din ruwa a kan farfajiya da kuma hanyoyin sadarwa a yanayin zafi da ke ƙasa da yawan zafin jiki. Ana amfani da kalmar pre-melting don bayyana raguwa a cikin zafin jiki (a ƙasa da 0 ° C) wanda ke haifar da ƙuƙwalwar ƙasa na kafofin watsa labarai masu ƙuntata ruwa (sakamakon Gibbs-Thomson). Ruwan da aka narke ya wanzu a matsayin wani nau'i mai laushi a saman kankara. A karkashin yanayin narkewa, kankara da ruwa na iya kasancewa tare a yanayin zafi a ƙasa da -10 ° C a cikin matsakaici. Tasirin Gibbs-Thomson yana haifar da ruwa yana ƙaura zuwa ƙasa mai zafi (daga yanayin zafi mafi girma zuwa ƙananan yanayin zafi); Dash ya ce, "...an ɗauki kayan zuwa yankuna masu sanyi..." Hakanan ana iya kallon wannan da kuzari kamar yadda yake son manyan ƙwayoyin kankara akan ƙarami (Ostwald ripening). A sakamakon haka, lokacin da yanayin ya kasance don rarrabe kankara (tsarin ruwan tabarau na kankara) ruwa yana gudana zuwa kankara da aka raba kuma yana daskarewa a saman, yana kauri kan kankara da ya raba.  

Yana yiwuwa a haɓaka samfuran nazari ta amfani da waɗannan ka'idoji; suna hango halaye masu zuwa, waɗanda suka dace da abubuwan lura da filin:

 Tsarin kankara a cikin yadudduka waɗanda suke daidai da saman da ke sama.
 Da farko kankara ta samo asali ne tare da ƙananan ƙananan ƙananan ƙananan abubuwa a layi daya da farfajiya. Yayin da kankara ke tarawa kankara yana girma a waje a cikin abin da ake yawan nunawa a matsayin ruwan tabarau na kankara daidai da farfajiya.
 Ice zai samo asali ne a cikin dutse mai ruwa kamar yadda yake samuwa a cikin ƙasa.
 Idan kankara ta samo asali ne daga sanyaya daga hanya ɗaya (misali, saman) fashewar tana kusa da farfajiya (misali 1-2 cm a cikin chalk). Idan kankara ta haifar da daskarewa daga bangarorin biyu (misali, sama da ƙasa) fashewar tana da zurfi (misali., 2-3.5 cm a cikin chalk).   
 Ice yana samuwa da sauri lokacin da ruwa yake samuwa. Lokacin da ruwa yake samuwa, kankara da aka raba (gidan gashin kankara) yana girma a layi daya da yanayin sanyi da aka fallasa. Yana girma da sauri har sai zafi da aka saki ta hanyar daskarewa ya dumama iyakar ruwan tabarau na kankara, yana rage yanayin zafin jiki kuma yana sarrafa yawan ci gaba da rarraba kankara. A karkashin wadannan yanayi, kankara yana girma a cikin Layer guda daya wanda ke ci gaba da kauri. An kawar da farfajiyar kuma an sake sanya ƙasa ko kuma an karye dutse.
 Ice yana samuwa a cikin tsari daban lokacin da ruwa ba shi da sauƙin samuwa. Lokacin da ruwa ba ya samuwa, kankara mai rarrabewa (gidan gashin kankara) yana girma sannu a hankali. zafi da aka saki ta hanyar daskarewa ba zai iya dumi iyakar ruwan tabarau na kankara ba. Saboda haka yankin da ruwa ke yadawa yana ci gaba da sanyaya har sai wani layin rarraba kankara ya samo asali a ƙasa da layin farko. Tare da yanayin sanyi mai ɗorewa, wannan tsari na iya maimaitawa, samar da yadudduka masu yawa na kankara (gidan gashin kankara), duk suna layi daya da farfajiya. Samun yadudduka da yawa (lens masu yawa) wanda ke haifar da lalacewar sanyi mai yawa a cikin duwatsu ko ƙasa.
 Babu wani kankara a wasu yanayi. A matsin lamba mafi girma kuma a yanayin zafi mai zafi, rarraba kankara ba zai iya faruwa ba; ruwan da ke cikin sararin samaniya yana daskarewa, ba tare da rarraba kan kankara ba kuma babu lalacewar ƙasa ko lalacewar sanyi.

 Girman ruwan tabarau a cikin dutse 
Duwatsu suna ƙunshe da ƙwayoyin ƙwayoyin cuta daban-daban da kuma siffar, ba tare da la'akari da asalin ko wuri ba. Rashin duwatsu sune ƙananan raguwa, kuma suna aiki a matsayin wurin da raguwa zai iya yaduwa idan an sanya dutsen cikin tashin hankali. Idan kankara ta tara a cikin rami ba daidai ba, kankara za ta sanya dutse a cikin tashin hankali a cikin jirgin sama mai tsayi zuwa ga jagorancin tarin kankara. Saboda haka dutsen zai fashe tare da jirgin sama mai tsayi ga jagorancin tarin kankara, wanda ya dace da farfajiya.

Walder da Hallet sun haɓaka samfuran da ke hango wuraren tsiro da ƙimar da ta dace da fashewar da aka lura a fagen. Misali na su ya yi hasashen cewa marmara da dutse suna girma sosai yadda ya kamata lokacin da yanayin zafi ya kasance daga -4 ° C zuwa -15 ° C; a cikin wannan kewayon dutse na iya haifar da fashewa wanda ke rufe kankara mita 3 a tsawon shekara. Lokacin da zafin jiki ya fi girma kankara wanda aka kafa ba ya amfani da isasshen matsin lamba don haifar da tsagewa don yaduwa. Lokacin da zafin jiki ya kasance ƙasa da wannan kewayon ruwa ba shi da motsi kuma tsagewa suna girma a hankali.  

Mutron ya tabbatar da cewa kankara da farko yana samuwa a cikin pores kuma yana haifar da ƙananan microfractures a layi daya da farfajiya. Yayin da kankara ke tarawa, kankara yana girma a waje a cikin abin da ake yawan nunawa a matsayin ruwan tabarau na kankara a layi daya da farfajiya. Ice zai samo asali a cikin dutse mai ruwa kamar yadda yake a cikin ƙasa. Idan kankara ta samo asali ne daga sanyaya daga hanya ɗaya (misali, saman) fashewar dutse tana kusa da farfajiya (misali 1-2 cm a cikin chalk). Idan kankara ta haifar da daskarewa daga bangarorin biyu (misali, sama da ƙasa) fashewar dutse tana da zurfi (misali., 2-3.5 cm a cikin chalk).   

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