Explanation

(a) Conditions that favour the development of karst topography:

- Limestone should be the dominant surface rock

-presence of joints/cracks/fissures/ bedding planes on existing rocks

- The area should receive moderate to abundant and regular rainfall

- The limestone area should be underlain by resistant rock

- soluble rocks e.g. dolomite, gypsum, limestone

- Surface relief should be low -tectonic activity will create cracks and joints

Characteristics and mode of formation of sinkhole

Characteristics

- found in limestone regions

- saucer-shaped or shaft-like depression

- steep sided

- could be shallow or deep

- can be as deep as 20 meters or more

- usually links the surface to the underground streams

- water passes through it to the underground

- can be 6 meters wide or more at the surface

- varies in size and depth

- Examples are found in the Atlas of Morocco, Ghyll in Yorkshire

Mode of formation

- formed in the karst region

- presence of a large area of limestone with many cracks and joints

- rain water mixes with carbon dioxide t • form carbonic acid

- Acid dissolves the limestone along the cracks

- The acidic run off passes through the limestone joints and cracks

- The racks continue to deepen and widen.

 - The cracks are further deepened to become depressions called sink holes

- two or more sink holes can be merged to form a do line

Alternatively, the formation could also be sudden

- Underground caves and voids are common in the limestone region

- The roof of the cave may continue to recede or wear out

- The recession continues for a long time

- The cave roof collapses to form a hollow

- This hollow is called  a sinkhole

- Moreover, mining activities could create a hole linking the surface to an Underground void or cave

- Other human activities could cause the Substance of the cave roof to form sinkhole 

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