Karst
Distinctive topography of karst is created by dissolution of underlying rocks by surface water or ground water. The degree of development of karst landforms varies greatly from region to region. Large drainage systems in karst areas are likely to have both fluvial (surface) and karst (underground) drainage components. The process is following: Water falls as rain or snow and soaks into the soil. The water becomes weakly acidic because it reacts chemically with carbon dioxide that occurs naturally in the atmosphere and the soil. This acid is named carbonic acid. Rainwater seeps downward through the soil and through fractures in the rock responding to the force of gravity. The carbonic acid in the moving ground water dissolves the bedrock along the surfaces of joints, fractures and bedding planes, eventually forming cave passages and caverns. Limestone as a sedimentary rock consisting primarily of calcium carbonate in the form of the mineral calcite is dissolved by the following reaction:
Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.
CaCO3 + CO2 + H2O → Ca(HCO3)2
Cracks and joints that interconnect in the soil and bedrock allow the water to reach a zone below the surface of the land where all the fractures and void spaces are completely filled with water. This water-rich zone is called the saturated zone and its upper surface is called the water table. When these voids are interconnected, water or air (or other fluids) can migrate from void to void. Thus the soil or bedrock is said to be permeable because fluids (air and water) can easily move through them. Permeable bedrock makes a good aquifer, a rock layer that holds and conducts water. If the ground water that flows through the underlying permeable bedrock is acidic and the bedrock is soluble, distinctive karst topography can be created.
Springs
Part of the water that falls in the form of precipitation on the surface flows over the surface and part of it seeps into the ground. The ground water flows through porous or broken rocks down until it reaches the water table or an impermeable layer. Unless the water table is horizontal the water flows as well in lateral direction until it encounters the sloping impermeable layer. Leaking water and the water table may in some places get to the surface - then we call such places as springs. The spring is a name for the seepage from which the water comes from the ground on the surface. The springs can also be below the water level in rivers, lakes or seas.
Groundwater can descend through permeable rocks and in the areas with lower surface it can flow freely. It can overflow to the surface in areas where it faces impervious rock, or it is pressed to the surface by pressure. According to this criteria , the springs are divided into descending and ascending.
Descending springs occur in places where the impermeable layer or water table is leaning in the direction of water seepage and the water flows out by gravity.
The subtypes of descending springs
Valley spring - water flows slowly - Becasue of the drop of the surface in the area the surface is below the water table.
1 - impermeable layer, 2 - permeable layer, a - water table
Debris spring - water flows out slowly. The groundwater level is higher than the spring.
Overflowing spring - The spring is higher than the groundwater level. The water flows out slowly when the grondwater level reaches the spring.
Ascending springs occur in places where water rises opposite to the direction of gravity due to pressure (e.g. caused by gases) or hydrostatic pressure exerted by water, which is located above (the principle of communicating vessels).
Subtypes of ascending springs
Layer spring - It is located higher than the underground water. The water flows out only when it rains, otherwise it does not have enough water.
Fault spring - the water spouts. The impermeable layer is disrupted. The water then come to the surface against the direction of gravity, trying to balance the pressure.
Karst spring
A karst spring is a spring that is part of a karst system. That includes the underground drainage of a much larger area, which means that karst springs often have a very large discharge. Karst springs are usually the end of a cave system at the place where a river cave reaches the Earth's surface. Thus, it is often possible to enter the caves at karst spring and explore them.
Springs in karst areas differ from normal springs: they normally have a much higher production, as they are just the end of a water filled cave system. Also they are highly dependent on the weather. Every rain and, of course, the snow melting leads to increased production. In opposite, karst springs regularly fall dry in dry periods in the summer. Such springs are called Seasonal Spring.
The water quality from the karst springs is often poor! The reason is the water flows rather fast through cave systems, so there is not enough time for microorganisms to clean the water. So karst springs are not good sources for water supply.
The cache
This earthcache is dedicated to one of the springs in Durmitor area - the spring of the river Ljutica. The coordinates will lead you to the place where the river springs.
To log the cache you have to upload the picture of you at the river Ljutica together with your log and to send me the following information via profile:
- What is the type and subtype of the spring you see (choose the most probable alternative from the above mentioned examples) and why?
- What is the approximate length of Ljutica river form its spring to the place where it mouths into the Tara river?
- Would it be possible to enter the underground cave through the Ljutica karst spring's opening in the rock?
- Describe the intensity of the spring discharge, optionally try to estimate it in liters per second.
Please, do not write the answers to the questions in your log.
Access to the cache
The more safe approach is from the Tara river bank. So you need some boat to get there. Rafting trips usually organize a short stop here so you can find this cache while on the trip. It is also possible to get to the cache from the road. You take the road R4 from Durdevica Tara direction Mojkovac. Several meters before the first tunnel it is possible to turn left to the road aiming to the river. You can leave your car at the parking lot and walk back along the road approx. 100 meters where (see additional waypoint) you can find a marked pathway leading to the spring.