Tafkin karkashin kasa

Tafkin karkashin kasa ko tafkin karkashin kasa ya kasance wani tabki ne da ke karkashin saman duniya. Mafi yawan tafkunan karkashin kasa ana samun su ne a wuraren da ake yi na karst topography,   inda aka kawar da dutsen farar ƙasa ko wani dutse mai narkewa, yana barin kogon da ruwa zai iya gudana kuma ya taru.

Tafkunan karkashin kasa na halitta abu ne da ba a saba gani ba. Mafi sau da yawa, ruwan karkashin kasa yana taruwa cikin tsari kamar magudanan ruwa ko maɓuɓɓugan ruwa .

HBabban tafkin karkashin kasa mafi girma a duniya yana cikin kogon numfashi na Dragon a Namibiya,  mai fadin kusan  ;  na biyu mafi girma shine Tekun Lost, dake cikin Craighead Caverns a cikin Tennessee, Amurka, tare da fadin  

 Halaye 
Tafkin karkashin kasa shi ne duk wani ruwa wanda yayi kama da girman tafkin saman kuma ya kasance mafi yawa ko kuma gaba daya a karkashin kasa; ko da yake, ainihin ma'anar kimiyya na abin da za a iya ɗauka a matsayin "tafki" ba a kafa shi ba tukuna.  Ana iya rarraba tafkunan karkashin kasa a matsayin ko dai "tafkuna" ko "tafkuna", ya danganta da girman girman, kamar fili da/ko zurfin da aka fallasa.

Rashin ƙarancin tabkunan ƙarƙashin ƙasa ana iya danganta su da yadda ruwa ke gudana a ƙarƙashin ƙasa. A ƙasan saman duniya, yawan matsi da ake yi a kan ruwan ƙasa yana ƙaruwa, yana sa ya shiga cikin ƙasa. Iyakar da akwai isassun matsa lamba na ƙasa don cika ƙasa da ruwa gaba ɗaya ana kiran teburin ruwa . Wurin da ke sama da teburin ruwa ana kiransa da "unsaturated zone," yayin da yankin da ke ƙasa shi ake kira "saturated zone".   A cikin cikakken yanki, matsa lamba ya zama ƙarfin farko da ke motsa ruwa. Tafkuna suna farawa da farko a ƙarƙashin ƙarfin nauyi - an ja ruwa zuwa ƙasa mafi ƙasƙanci a cikin yanki, kuma yana taruwa cikin tafkin. Duk wani ruwa da ke ƙasa da teburin ruwa zai kasance cikin matsi, don haka ba ya samar da tafkin; a maimakon haka, ya samar da ruwa mai ruwa .

Tafkunan karkashin kasa da ke faruwa a dabi'a na iya samuwa a yankunan karst, inda yanayin yanayi na duwatsu masu narkewa ya bar bayan koguna da sauran wuraren buɗe ido a cikin ƙasa.  Ruwan saman yana iya samun hanyarsa ta ƙarƙashin ƙasa ta waɗannan wuraren buɗewa  kuma ya taru a cikin manyan kogo don samar da tafkuna.

Hakanan ana iya samar da tafkunan karkashin kasa ta hanyar tafiyar mutane, kamar ambaliya na ma'adinai . Misalai biyu sune tafkunan da aka samu a cikin ma'adinan ma'adinai a Blaenau Ffestiniog, irin su Croesor quarry,  da tafkin da ke cikin Ma'adinan Gishiri na Hallein a Ostiriya. 

 Misalai 

 Craighead Caverns, a cikin Tennessee, Amurika
 Cross Cave, a cikin Slovenia
 Kogon Numfashin Dragon, a Namibiya
 Kow Ata, in Turkmenistan
 Lake Neuron, a Albania
 Moqua Well, in Nauru
 Tafkin karkashin kasa na Saint-Léonard, a Switzerland 

 Manazarta