Thursday, March 06, 2008

Sinkholes


Scattered throughout the Ozark Highlands, in areas underlain with carbonate rock, rest deep, rounded depressions called sinkholes. Typical of karst landscapes, sinkholes occur when bedrock dissolves and the land above collapses into an underlying cavity. Considering that the Ozarks were formed billions of years ago, sinkholes can be found throughout the region in various stages. Because of the moisture content and cooler temperatures afforded by the deep depression, some sinkholes that were formed thousands of years ago support glacial relics: ferns, mosses, and salamanders that were present throughout Missouri during the Pleistocene. Other sinkholes, like the ones pictured below, were formed in the past 3, 10, 50 years, long after we built roads, homes and shopping malls on top of eroded bedrock. Recent collapses remind us that the ancient Ozark Highlands continue to evolve, sometimes even despite our actions.

The steep slopes leading down into ancient sinkholes are often covered in mosses and ferns, thriving on the weeping limestone or dolomite walls. Within the deep depression, moisture levels remain high year round and temperatures are traditionally lower than the area above. Soils are generally rich, supporting wild hydrangea, white oaks and maples. Four-toed salamanders live here, appreciating the same temperatures and moisture that was present before the glaciers retreated. A rare shooting star (Dodecatheon amethystinum) population is found in one nearby sinkhole, one of only a handful of populations that remain in Missouri (pictured above). Several years ago, I found no fewer than 50 morels here.

Sinkholes can also support a rather distinct terrestrial community similar in characteristics to upland flatwoods. Called, appropriately, sinkhole flatwoods, soils here drain slowly, which can impact the understory flora. Sedges grow here, and if the soils are particularly acidic, not much else will. Undisturbed sinkhole flatwoods are pretty rare, though they traditionally occurred in the lovely Current River Hills, the Central Plateau, the Springfield Plain and the Outer Ozark Border. Many of these communities which range in size from one to (rarely) 30 acres were drained and heavily grazed by livestock.

Because sinkholes open up in the Springfield area every few years, developers are now able to consult geologists to determine if land is situated on top of a cavity. However, a few years ago, during road construction in Springfield, workers discovered a vast cave system, complete with Pleistocene skeletons and tracks. The road was rerouted, obviously, and, sadly, the cave was vandalized mere days after discovery. Ancient sinkholes are special, delicate places, rich in biodiversity. The more recent ones are, I guess, filled with asphalt, fescue, and housing material.

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