The word ‘Karst’ comes from the Krs Plateau in Slovenia, where karst environments were first studied closely. The Slav people use ‘Krs’ to refere to ‘bare stony ground’. More specifically geomorphology refers to karst as a type of terrain characterised mainly by caves, sinkholes and complex drainage networks. The majority of karst formations occur in soluble rocks such as limestone and dolomite (although recent discoveries have revealed karst formations in more resistant rocks such as quartz, but are rare) and the reason for this is connected to the underlying processes. The two chief processes responsible for the weathering of rocks are physical weathering and chemical weathering, but it chemical weathering that is particularly present in soluble rocks (Christopherson 2012). Around 25% of the earth’s surface is composed of limestone and almost 15% of the earth’s surface contains karst features. Considering the potential hazards of karst features together with their significant proportions it is no surprise that karst environments are highly studied. These hazards include sinkholes, sinkhole flooding and the contamination of groundwater. This essay will also discuss the impact humans have had on karst landscapes.
Figure 1: Karst landscapes and limestone regions (Christopherson 2012) 2. Karst Processes
2.1 Brief Description
The hydrological cycle is very important in the process of karst formations. The formation of karst starts with precipitation that often reacts to carbon dioxide to form carbonic acid. When the water reaches the earth it percolates through very permeable limestone. The water will erode the limestone along cracks and over long periods of time these cracks increase in size to form caves and other karst features. In many instances tectonic processes are responsible for the exposure of limestone. As uplift takes place and as the limestone starts bulging cracks start to appear making the rock more vulnerable to erosion along these cracks. As mentioned before the principle process of weathering in soluble rocks is the dissolving of minerals by water. The process of dissolving is a rather simple concept, however several conditions are needed for the formation of karst topography (Blair 1986).
Figure 2: Hydrological Cycle in Karst Regions (American Geological Institute) 2.2 Lithology
The solubility of rocks is determined by the amount of calcium they contain. The higher the concentration of calcium becomes the higher the chances of karst forming. Karst topography can form in rocks that constitute less than 80% carbonates but the development of karst favours rocks with higher concentrations of carbonates. Consequently the majority of karst landforms appear in limestone and dolomite(Jennings 1985). Any rock that contains concentrations of calcium carbonate (CaCO3) greater than 50% is considered to be limestone. Pure limestone contains at least 90% and in places such as Jamaica and Slovenia the limestone is at least 95% pure. Dolomite rocks contain at least 50% calcium-magnesium carbonate, also known as dolomite ((CaMg)(CO3)2), while pure dolomitic rocks (also called dolostones) contain at least 90% dolomite (Huggett 2011). Additionally the thickness of the bed rock as well as the nature of the bed influence the degree of karsification. For instance in the Dinaric Mountains the soluble rock is quite shallow before it meets insoluble rock, resulting in broad flat floors in the caves.
Figure 3: Limestones close to Dover (Lutgens 2011)
The limestone, or other soluble rock, needs to have complex patterns of joints in order for water to enter the rock. Water will slowly erode the rock to form subterranean drainage channels that could later on increase in size and form caves. Vertical karst features, such as pinnacle karst, are formed where the limestone is exposed at the surface. Tectonic processes also have an important impact since tectonic forces can uplift and deform...