Question 8 of 21: Question 3, Part 2: Karst Topography

Question 3, Part 2: Karst Topography (6 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Formation. Karst topography develops where soluble bedrock – overwhelmingly limestone or dolomite, occasionally gypsum or salt – is dissolved by circulating groundwater that has been made mildly acidic by dissolved atmospheric/soil CO₂ (forming weak carbonic acid, H₂CO₃). Water preferentially attacks joints, fractures, and bedding planes, slowly widening them into an interconnected network of solution channels and caves as calcium carbonate is carried away in solution. Over time, cave-roof collapse and surface dissolution produce closed depressions (sinkholes/dolines), and streams may disappear underground (sinking streams) to re-emerge elsewhere as large springs.

Consequences. Karst terrain is characterized by irregular, hummocky topography riddled with sinkholes, disappearing streams, poorly integrated (or absent) surface drainage, caves, and springs. Engineering/hazard consequences include: unpredictable, sudden ground collapse (sinkhole formation) beneath structures and roads; highly permeable, fast conduit-flow aquifers that transmit surface contaminants to water supplies with little natural filtration (making karst groundwater very vulnerable to pollution); difficulty siting reliable water wells or foundations because subsurface cavities are hard to detect; and, in some regions, unique but fragile cave/spring ecosystems requiring protection during land development.