A Subterranean Water Engine
The Taurus Mountains of southern Turkey are a massive water-storage system. The range is built from thick layers of limestone and dolomite, carbonate rocks formed during the Mesozoic era. These rocks are soluble in the weak carbonic acid of rainwater. Over millions of years, this slow dissolution has carved an immense network of underground channels, caves, and conduits. This geological formation is known as a karst system, and the Taurus range contains the largest and most developed karst area in the entire Mediterranean region.
This subterranean plumbing collects rainfall and snowmelt from a vast area, channeling it deep into the mountains where it is stored in a massive aquifer. Some carbonate rock layers here are more than 1,000 meters thick. The water eventually re-emerges at lower elevations through powerful springs. Major outlets for this system include the Kırkgözler and Düdenbaşı springs. The Düden River, for example, disappears into a sinkhole called Bıyıklı, travels 18 kilometers underground, and re-emerges at the Upper Düden Waterfall. Some springs are so large they form the headwaters of major rivers, like the Manavgat River, which has an average flow of 147 cubic meters per second. Dozens of other springs are submarine, discharging huge volumes of fresh water directly into the Mediterranean Sea from underwater caves.
Water from Another Time
The water emerging from these springs is not from last week's storm. Much of it is ancient, having spent decades or even centuries underground. Scientists can determine the water's "residence time" by measuring the concentration of specific isotopes. One indicator is tritium (³H), a radioactive isotope of hydrogen with a half-life of 12.3 years.
Global tritium levels in the atmosphere spiked dramatically during the nuclear bomb tests of the 1950s and 60s. Water with very low or undetectable tritium levels must have entered the aquifer before this period, making it "pre-modern" water. Analysis of water from the Taurus springs often shows residence times ranging from recent to several decades. This slow, long-term storage makes the aquifer a natural archive. The chemical and isotopic composition of this "paleowater" records past climate conditions and the composition of the atmosphere when the water first fell as rain. The limestone acts as a vast natural filter, so the water emerges with exceptional clarity, though it is high in dissolved minerals like calcium bicarbonate, which gives it a slightly alkaline pH.
The most visible result of this high mineral content is travertine, a form of limestone deposited by the springs. The world-famous terraces of Pamukkale are a type of travertine deposit, and similar, smaller-scale formations are created by the Anatolian karst springs. The Antalya Travertine Plateau, formed by the Kırkgöz springs, is the largest known deposit of its kind created by cool karst groundwater. At the Lower Düden Waterfall, the Düden River plunges 40 meters from a travertine cliff directly into the sea.