Velika Jeršanova Doline - a Former Collapse Doline

Abstract

Velika Jeršanova dolina (n.m.v.=535 m) leži na površju nad sistemom Postojnskih jam. Njeno poglabljanje je nedvomno prekinilo nadaljevanje Pisanega rova (n.m.v.=535,5 m) proti S. Čez Veliko Jeršanovo dolino poteka teme Postojnske antiklinale v smeri SZ-JV. Prav tako smer ima tudi Jeršanov prelom. Vpad in smer tankoplastnatih turonijskih in cenomanijskih apnencev sta v temenu antiklinale zelo neurejena. Apnenci vpadajo pod kotom 5-25°. Velika Jeršanova dolina danes nima značilne oblike udornice. Kot najpomembnejši vzrok netipične udorne oblike Velike Jeršanove doline zagovarjamo njen nastanek v temenskem delu Postojnske antiklinale, oblikovanje v tankoplastnatih bolj glinastih apnencih, ki so ob Jeršanovem prelomu precej pretrti ter intenzivno korozijsko zniževanje terena. Glede na današnjo oblikovanost pobočij in zunanjih robov je Velika Jeršanova dolina relikt nekdanje izrazite udornice.

The Velika Jeršanova doline (a.s.l.=535 m) is situated on the surface above the Postojnska Jama cave system. Its deepening undoubtedly interrupted the continuation of Pisani rov (a.s.l.=535,5 m) towards N. Through the Velika Jeršanova doline the Postojna anticline crest runs in the direction of NW-SE. The same direction has also the Jeršan fault. Strike and dip of thin bedded Turonian and Cenomanian limestones are disordered on the anticline’s crest. The limestones dip 5-25°. The Velika Jeršanova doline today does not have the typical shape of a collapse doline. The main cause for the untypical collapse shape of Velika Jeršanova doline is its formation in the Postojna anticline crest, its shaping in thin bedded clay - rich limestones and intensive erosional lowering of the area. Regarding the actual shape of the slopes and outer edges, the Velika Jeršanova doline is a relic of a former well shaped collapse doline.