KARST IN RAS AL-KHAIMAH, NORTHERN UNITED ARAB EMIRATES

Asma Al-Farray, Tadej Slabe, Martin Knez, Franci Gabrovšek, Janez Mulec, Metka Petrič, Nadja Zupan Hajna
2014 Acta Carsologica  
UDC 551.435.8(536. 2) Northern United Arab Emirates This paper presents karstological prospecting of selected areas in Ras Al-Khaimah Emirate, UAE. Several locations in Musandam Mountains have been explored for caves, karst springs and surface karst features. Two karst springs, Khatt and MeBreda, were analyzed for basic physical, chemical and microbiological parameters. Although they are both recharged from karst aquifers, they differ significantly. The first one is a thermal spring in which
more » ... spring in which infiltrated rain water is mixed with more saline and mineralized water from greater depths. The location of the second one at the high altitude of 710 m a. s. l. is conditioned by the existence of a less permeable zone within a carbonate aquifer with a larger share of dolomite. There were increased concentrations of nitrates probably due to grazing goats around the spring but on the other hand there was surprisingly low number of total bacterial counts; however detected Escherichia coli indicated probable fecal contamination. None of the water from any of the tested sites matched the ISO criteria for direct human consumption. Surface rock relief resulted from different karst processes was studied in river beds and side walls of wadis and on the mountain plateaus. The slopes of the wadis are often dissected by large recesses, relatively rare subsoil forms, and karren with microrills and rain flutes. More extensive karren are found on the tops of the mountains. The rocky riverbeds of wadis were shaped by rapid water currents and corrosion at the contact with sediment. In the study area at the northern slopes of mountains no big cave was found. The largest discovered cave was in fact tectonic fracture which was extended due to the gravitational sliding of part of a mountain along a fissure. But several small (10−20 m long) solutional caves have been discovered and surveyed on the wadis slopes. They exhibit relatively simple assemblage of dominantly deadend passages. Caves are vertically distributed at several levels Izvleček UDK 551.435.8(536.2) V članku predstavljamo preliminarne krasoslovne raziskave izbranih območij emirata Ras Al-Khaimah, ZAE. Na več lokacijah v Musandamskem gorovju smo raziskovali jame, kraške izvire in kraško površje. Kemične in mikrobiološke analize voda dveh kraških izvirov (Khatt in MeBreda) kažejo na precejšnjo razliko obeh vodozbirnih območij. Khatt je termalni izvir, za katere je značilno mešanje infiltrirane deževnice in globokih mineraliziranih voda. Izvir MeBreda se nahaja na nadmorski višini 710 m in iztekanje vode je pogojeno z manj prepustno dolomitizirano plastjo. Zaradi gorske paše je v vodi precej nitratov, vendar presenetljivo malo celokupnih bakterij. Priso tnost E. coli vseeno nakazuje verjetno fekalno onesnaženost. Nobena analizirana voda ne ustreza ISO standardom za nepo sredno uporabo za pitno vodo. Na gorskih planotah, pobočjih in kori tih vadijev smo proučevali kraške skalne oblike. Pobočja vadijev so pogosto razčlenjena z velikimi vdolbinami, razmeroma redkimi podtalnimi oblikami ter škrapljami z mikrožlebiči in žlebiči. Obsežnejše škraplje so na vrhovih gora. Kamnite struge vadijev so oblikovali hitri vodni tokovi in korozija ob stiku z naplavino. Na severnih pobočjih obravnavanega območja ni smo našli večjih jam. Največja odkrita jama je v sistemu ra zpok, ki so nastale zaradi gravitacijskega drsenja dela gore v dolino. V dolinah vadijev smo našli več pravih kraških jam (dolžina 10 do 20 m). Največkrat gre za enostavno, slabo ra zvejano geometrijo. Rovi se povsem slepo končajo. Jame so vertikalno razporejene po različnih nivojih glede na dno vadija. Skalne oblike kažejo na paragenetski razvoj. Več jam je povsem ali delno napolnjenih z rumenim klastičnim sedimentom. Našli smo tudi plasti sige ter kristale kalcita in sadre. Mineraloška analiza je pokazala precej podobno sestavo vzorcev. V njih smo v različnih razmerjih določili združbo kremena, sadre, kaolini-ACTA CARSOLOGICA 43/1 -2014 24 ASMA AL-FARRAJ, TADEJ SLABE, MARTIN KNEZ, FRANCI GABROVŠEK, JANEZ MULEC, METKA PETRIČ, NADJA ZUPAN HAJNA above the wadis. The rocky relief of the caves indicates the paragenetic development of the caves. Some of the studies caves were fully and some partially filled with yellow clastic sediments. Also few layers of flowstone, calcite crystals and gypsum crystals were found. Mineralogical analyses shows very similar composition of sediments: different minerals such as quartz, gypsum, kaolinite, smectite, illite, calcite and palygorskite in various proportions. Calcite and gypsum represent precipitates from the cave (crusts, crystals, cements) and the other minerals were brought to the cave most probably by water or wind from eroded rocks and/or soils from wadis catchment areas.
doi:10.3986/ac.v43i1.579 fatcat:b6u4qqsht5c5ramuugz2l7tgtm