What Lies Beneath: Karst

It took millions of years to create the special geology that is now Birmingham – and now it’s slowly dissolving away. Jones Valley is part of a sub-region characterized by valleys with limestone and dolomite bedrock, and the thick layers of rock are prone to chemical erosion. Both kinds of rock are made up of minerals like calcium carbonate – which also makes chalk – that dissolve when exposed to acid. Because rainwater is naturally acidic, the limestone and dolostone that touch water underground are slowly eaten away, leaving behind karst, a terrain riddled with springs, underground streams, and even caves. Those caves are home to animals that have specifically adapted to cave life, including bats, salamanders, spiders, fish and crayfish. Animals that are so specialized for cave life that they cannot live outside – some are blind and completely lacking in pigment, for example – are called troglobites, and Alabama has more kinds of them than almost anywhere else in the world.

Besides providing an abundance of flux for the city’s blast furnaces, Jones Valley’s karst provides a year-round supply of clean spring water in its streams. This benefited the city’s early settlers and later the entrepreneurs who harnessed the valley’s abundant waters for industrial use. But on the down side, every so often the roof of an underground cavern collapses and a sinkhole forms at the surface.  Watch your step!

– Scot Duncan