In the Pits

Because of their morphometry, man-excavated surface depressions or 'pits' (usually created during the extraction of minerals) tend to have high relative depths. Following mineral extraction, unused pits usually fill with groundwater and runoff water. When a water body has a small surface area, and yet is relatively deep, its 'relative depth' tends to be high and such water bodies may have a 'predisposition' to meromixis. The 'relative depth' Zr, regarded as the ratio of the maximum depth (Zm) (in meters) to the square root of the mean diameter of the lake surface area (Ao) in square meters can be quantified by the formula: Zr = (50 Zm)(V"p)/^Ao) or Zr = (Zm x 88.6)/ (v^Ao), which converts directly into percentages.

There are large numbers of water bodies around the world that are located in pits, probably many more than generally realized. We cannot possibly cover here all examples of meromixis in water-filled pits. However, the following examples illustrate some variations in depths and locations of just six different pits containing meromictic bodies of water: (1) Island Copper Mine (>400 m deep) on Vancouver Island, Canada; (2) Goitsche Lignite Mine (47 m deep) in Germany; (3) St. Louis Coal Mine (60 m deep) in France; (4) Ravlidmyran Zinc/Silver Mine (29 m deep) in Sweden; (5) Fountain Pond Iron Mine (~90 m deep) in Michigan, USA; (6) Wausau Granite Quarry (~21 m deep) in Wisconsin, USA.

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