Theory question 305
Underground Water and Karst(a) State three conditions that favour the development of Karst topography. (b) Describe the characteristics and mode of formation of sink hole.
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(a) A thick bed of hard, well-jointed limestone at or near the surface; moderate to heavy rainfall; water table well below the surface; limestone not too porous; plenty of carbon dioxide in rainwater.
(b) Characteristics: a funnel-shaped hole on the surface of limestone; water from surface streams disappears into it; may lead to underground caves; some are large and deep. Formation: rainwater containing carbon dioxide (weak carbonic acid) dissolves limestone along joints; the joints are widened at their intersections; continued solution enlarges the opening into a funnel-shaped hole; roof collapse of caves may also form sink holes.
Mention carbonation-solution.