Importance of Karst Topography - Essay Example

Karst Topography al Affiliation) Key Words: Karst, Topography Introduction Karst is a distinctive topography in which the landscape is largely shaped by the dissolving action of water on carbonate underground rocks, such as limestone, dolomite or marble. The process of development of karst takes place is called karstification (Marshak, 2007). The Process of Carstification Karstification occurs on terrain where the overlying rocks are hard and almost impermeable to water (Larsen, 2003). The overlying rocks must however have cracks and fissures and there should be plenty of rain. Since rain water is slightly acidic, a direct consequence of contact with carbon dioxide in the atmosphere, it readily dissolves rock and washes it away as an insoluble solution. When rain water first flows through acidic soils, it becomes much more acidic and more capable of dissolving superior quality rocks and large volume of the rock. As acidified water percolates through the cracks on limestone, it enlarges them gradually, allowing more water to get through. Continuation of this process with time enlarges the fissures to an extent they can take in entire rain water moments after falling. Underground, the water from the fissures join up to form small underground streams, causing massive and widespread corrosion and dissolution of rocks. These lead to development of underground cavities at varied depths and of different sizes. Notable karst areas include the Nullarbor Plain in Australia and Chocolate hills, Philippines among many others (Larsen, 2003). Effects of Carstification Karstification results in formation of varied features of varied sizes and at different depths. Karst topography has some small sized features on its surface collectively referred to as Karren or Lapiez. Examples of these are: Flutes As acidic rain occurs, it runs on the surface and causes dissolution of limestone or other soluble surface rock. As it keeps running over the surface, it dissolves and sculptures it with each run of water causing grooves and solution flutes on the ground. This causes a vast area of parallel flutes known by their German name Rillenkarren Clints and Grikes Vertical joints and bedding planes in limestone can be widened and enlarged by solutions to form a series of deep elongated slots called grikes. Such larger and fairly deeper features are known as grikes. Medium sized features on the surface of a karst can also result from karstification. These include: Sinkholes/ Dolines These are closed depressions in karst areas, usually circular in outline. Dolines either formed by dissolution of rocks close to the surface or by underground dissolution that forms a cavity whose roof then collapses to expose a hollow depression on the surface. Sinkholes formed by dissolution of rock is are fairly well rounded with smooth funnel shapes while those as a result of sinking roofs often have cliffed and abruptly cascading sides. Steepheads A steephead is a steep sided karst valley. It is generally short and ends abruptly where a stream emerges upstream Foiba This is a type of natural dolines formed fairly deep into the earth surface and is a collapsed portion of bedrock overlying a void. They appear in the form of an absolute vertical opening into a cave or just a shallow depression. Disappearing Streams A disappearing stream is the term used to describe a channel of water flowing rapidly and entirely into a crack or a sinkhole into an underground system especially in a Karst topography. Reappearing Streams This is a point of resurgence where an underground stream reappears from the underground The process of Karstification, also result in formation of some large scale features. These are: Limestone pavements This is a karst landform consists of a flat incised surface of exposed limestone that resembles an artificial pavement. They are formed when advancing deluge of acidic water horizontally corrodes, dissolves and scraps away the overlying burden of top soil to expose a slab of horizontally bedded limestone rock. An example can be found in Stora Alvaret in Oland region of Sweden Poljes A polje is usually a large stretch of plain land in karst regions. A polje is formed where a vast area is eroded and of the top soil burden to expose a vast layer of fairly flat land. The landscape is barely disturbed since most drainage involved water flowing short distances and disappearing in sinkholes. Polges are covered with a layer of thick sediments called terra-rossa and very agriculturally viable. Dry Valleys As ariver flows over a period of time in a karst area, it corrodes and dissolvesits channels. However, as underground dissolution occurs, a cavity develops and when its roof collapses, the river abandons its channel and flows into the hollow in the form of a swallow hole as a disappearing river. What results of its older channel is a gapping dry valley with boulders and pebbles lining its course. This feature is called a dry valley (Williams, P. 2007). Dry valleys sometimes become rivers during periods of heavy rains when the sinkhole can no longer take in the entire river’s water. Places with mature karst terrain can also result into Karst Towers. These are the features formed where more bedrock has been removed away than actually remains, leaving limestone pillars sticking out. These are called karst towers. Karstification also results into complex underground drainages features such as: Karst Aquifers A karst aquifer is a feature formed when water seeps into cracks on the surface of karst region and is channelled into an underground system where it is conserved by a plate of impermeable rock then able to be discharged back to the surface as surface water. An aquifer can have water flowing into the ground just adjacently or travel a long distance off the point where it is discharged (Williams, P. 2007). Extensive Caves One of the ways of their formation is when a river flows into the underground and dissolves away a long and extensive channel which massively widen in time to form a very long feature simply referred to as an extensive cave. Cavern Systems These are formed when large volumes of water seeps into the ground and dissolves off a massive volume of rock masses, leaving a gaping natural cavity below the surface. The point of water entry later widens enough to allow admission for people or animals. Importance of Karst Topography To begin with, karst topography is important for formation of underground water. This results from disappearing streams characteristic of karst topography. Underground water has led to formation of karst aquifers which provide a source of water for entire populations. A classical example is in Texas where two million people obtain drinking water from the Edwards Karst aquifer (Larsen, 2003). Karst topography also has economic value in the form of providing grazing grounds, mostly for sheep. The various wonderful karst features are also a tourist attraction which provides massive financial returns to places they occur. With adequate rainfall, karst areas, especially polges have a great agricultural potency. References Paul, Larsen, 2003.Scientific accounts of a vanishing lake: Janez Valvasor, Lake Cerknica and the New Philosophy, Routlege. Stephen, Marshak, 2007. Earth: Portrait of a Planet. New York.W. W. Norton & Company Ford, D.C. and Williams, P.2007, Karst Hydrogeology and Geomorphology, n.a. John Wiley and Sons Ltd., Read More