What is karst, how does it form and what are the effects on the economic environment?
Some of you might already know the white sharp and tall rocks, enormous caves or sinkholes, but karst has many more (subtle) faces than that. A lot of these landscapes are not visible because they develop beneath the surface. To learn more about karst, lets ask some basic questions.
What is it?
Let's start with the most basic question, what is karst? Karst is a general name for landscapes where the surface consist of a rock that is easily erodible by slightly acidic water. Common rocks to form karst landscapes are limestone, dolomite and sometimes gypsum. The CO2 in the atmosphere reacts with precipitating water, forming the acid H2CO3. This acid percolates into the soil, where it dissolves the rock.
H2O+CO2 --> H2CO3
CaCO3+H2CO3 --> Ca2+ +2HCO3
The water is transported trough cracks dissolving the surrounding rock and further deepening the joints. These cracks, or joints continue to deepen until they form cave systems or underground rivers. When these cave systems continue to expand over time, a collapse can occur when the remaining terrain becomes unstable. The depression formed by this collapse is what we see as a sinkhole.
The name "karst" comes from the Slovenian region where the first paper on this landscape was published. The name has been adopted by the scientific community ever since.
what does karst look like?
As mentioned earlier, karst landscapes are formed by water erosion deepening joints and cracks. Landscape features we could expect from this are caves, sinkholes, underground rivers as mentioned in the previous part, but also large towers, limestone pavement, vertical shafts, dolines, disappearing and reappearing rivers.
When an entire area is under the influence of this depression forming process, poljen can be formed. these are large flats as a result of multiple sinkholes merging in one big depression. On a flat we would expect the formation of river channels, but since there is an underground river network, we do not see these on the surface. This is one way to recognize a polje.
The following illustration shows different types of karst features really well.
where do we find it?
Basically, we find karst landscapes wherever water erodible rocks comes at the surface. Here is a nice map illustrating where carbonate rocks (most common karst forming rock) covers the surface.
What are the effects on the social economic space?
A convenient effect is that sinkholes and sudden collapses of the soil pose a danger to people living on that surface. This can be confirmed by the many news articles of sinkholes damaging infrastructure or buildings.
When the rocks erode they leave behind a residue of impurities that can form a soil. When enough impurities are present, the resulting soil can be farmed, even with the lack of surface water and thus result in social economic activities. In some cases however, the karst elements can cause precipitation to disappear in underlying groundwater systems too fast, making it inaccessible for domestic use.
Another effect is the susceptibility of rainwater for pollution. Since karst topography is characterized by caves and underground flow, it is very permeable, resulting in less opportunities to filter pollution by the underlying formations.