which is required for karst topography to form? A. Pure water B. Granite C. Basalt D. Carbonic acid
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Answer: D. Carbonic acid
Karst topography is a landscape formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes, dolines, and caves. For karst topography to form, there needs to be the presence of acid in the water, which facilitates the dissolution process. Carbonic acid, which is a weak acid formed by the combination of water and carbon dioxide (CO2), plays a crucial role in this process. Rainwater naturally absorbs CO2 from the atmosphere and the soil, forming a mild carbonic acid solution. This acidified water then seeps through the soil and into the bedrock, slowly dissolving the soluble rock over thousands of years to form karst landscapes.
Extra: Karst topography is a fascinating subject in the study of geology and earth sciences. In a typical karst system, water plays the leading role as an erosive agent. When water combined with carbon dioxide forms carbonic acid, it can dissolve certain types of rock that are prone to acid dissolution, particularly limestone. Limestone is composed primarily of calcium carbonate (CaCO3), which reacts with carbonic acid. The chemical reaction allows the water to carry away the rock components, which eventually creates the unique and often spectacular features of karst landscapes.
The features typically associated with karst include:
1. Sinkholes or dolines: These are depressions or holes in the ground surface where soluble rock has been removed by water.
2. Caves: Caves are natural underground spaces, the intricate passageways within them generally formed by the dissolution of rock.
3. Disappearing streams or reappearing springs: Water in karst areas can flow underground and may vanish from the surface, flowing through a network of caves and voids, only to reappear at a spring further down the valley.
Because karst systems depend on specific rock types and acidic water, they are not found everywhere. Conversely, rocks like granite and basalt mentioned in the question options (B and C) do not typically form karst landscapes because they are silicate mineral-based and much more resistant to dissolution by weak acids such as carbonic acid. Pure water (option A) without the presence of carbon dioxide to form carbonic acid would also not be sufficient to create karst features because it is not acidic enough to significantly dissolve the limestone.