Figure 12.6 Stages in the evolution of karst topography. Karst topography is the

Question

Figure 12.6 Stages in the evolution of karst topography. Karst topography is the result of dissolution of water-soluble bedrock, which is usually limestone or dolostone but can be evaporite (e.g., gypsum or halite) A. Early stage of karst development Streams common Large lakes Springs Small caves filled with water Water table near land surface B. Mid-stage of karst development Small lakes Sinkholes Few streams Large caves filled with water in basal Thin cave roofs C. Late (advanced) stage of karst development Solution Disappearing streams Sinkholes Very large caves only partly fillecd with water Water table well below land surface Thin cave roofs

Explanation / Answer

A.

1. The water accesses the deeper layers of soil along the fractures and linear features of the karst topography. The plants thus grow along such features.

2. The groundwater can be accessed by drilling along the lines of growth as it will be along the direction of fractures where water is accumulated.

3. A matured or an advanced stage of karst development links the two figures. Such a stage allows the dissolution of limestones to a great extent and leads to the deep penetration of water and the formation of sub-surface caves where stalactites form.

B.

1. B is the most hazardous as it is situated exactly above a well-developed cave in an advanced stage of karst topography development.

2. A is the least hazardous as it is situated above a relatively less fractured zone within a mid-stage karst development.

3. For finding out a potential hazard, one must dig the ground to find out if there are any excavations or not and that the water table is relatively deeper so as to ensure the least amount of chance of cave formation by percolating water.

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