Karst geomorphology, cave development and hydrogeology in the Kashmir valley, Western Himalaya, India

Abstract

Surface and underground karst features, such as karren, dolines, sinking streams, caves and large freshwater and thermal springs are developed in Triassic Limestone in the southern Kashmir Valley. The rock formation has a high hydraulic conductivity (K), up to 1,000 m d-1 and constitutes one of the most productive aquifers in the region. Springs discharging from this aquifer supply pristine water to more than one million people, but the regional karst system is still poorly understood. The present study is really a first and preliminary study of an important but remote and previously unstudied area, with the goal to provide a first overview and inventory of karst phenomena, as a basis for more detailed (and more “scientific”) studies in the future. Results suggest that karstification is developed along tectonic joints and bedding planes. Karstification shows distinct variation with altitude and is more developed towards the valley floor. The study also revealed that erosion of the alluvium along streams pushed karstification downwards and caused drying up of formerly phreatic cave passages. Reconstruction of karst evolution on the basis of geomorphological, geological and climatic conditions of the region suggests that karstification has started during Plio-Pleistocene. The present surface and subsurface karstification is directly related to the tectono-sedimentational history of the Himalaya and the climatic conditions that prevailed after the Himalayan Orogeny. Key words: Triassic Limestone, karstification, freshwater supply, Himalaya, Kashmir Valley. Kraska geomorfologija, razvoj jam in hidrogeologija v Kasmirski dolini, Zahodna Himalaja, Indija Povrsinske in podzemne kraske oblike, kot so skraplje, vrtace, reke ponikalnice, jame ter veliki sladkovodni in termalni izviri, so v južni Kasmirski dolini nastale v triasnih apnencih. Ti imajo visoko hidravlicno prevodnost (K) do 1000 m d-1 in so med najbolj produktivnimi vodonosniki v regiji. Izviri, ki drenirajo ta vodonosnik, prispevajo neoporecno vodo vec kot milijon ljudem. Kljub temu hidrogeologijo regionalnega kraskega sistema se vedno slabo razumemo. Ta studija je prva in preliminarna studija pomembnega, a oddaljenega in predhodno neraziskanega obmocja ter poskusa zagotoviti prvi pregled in popis kraskih pojavov kot podlaga za podrobnejse (in bolj »znanstvene«) studije. Rezultati kažejo, da je zakrasevanje razvito vzdolž tektonskih prelomov in lezik. Zakrasevanje se razlikuje glede na nadmorsko visino in je bolj razvito proti dnu doline. Studija je pokazala tudi, da je erozija aluvija vzdolž vodotokov potisnila zakrasevanje v globino vodonosnika in povzrocila fosilizacijo predhodno freaticnih jamskih kanalov. Rekonstrukcija kraskega razvoja na podlagi geomorfoloskih, geoloskih in klimatskih razmer v regiji nakazuje, da se je zakrasevanje zacelo med Plio-Pleistocenom. Sedanje povrsinsko in podzemno zakrasevanje je neposredno povezano s tektonsko-sedimentacijsko zgodovino Himalaje in podnebnimi razmerami, ki so prevladovale po himalajski orogenezi. Kljucne besede: triasni apnenec, zakrasevanje, oskrba z vodo, Himalaja, dolina Kasmir.