That Sinking Feeling

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Sinkhole formationSource: Florida Dept. of State Geology Dept.

Sinkhole formation
Source: Florida Dept. of State Geology Dept.

I’ve written here and here about carbonate organisms which are sensitive to raised levels of acidity in water and rain. Everyone knows the effects of acid rain on trees. Until recently, though, I hadn’t given much thought to the effects of acid rain on rock formations. Specifically, on the porous limestone that underlies much of Florida. Sinkholes are, as I have learned, a part of life in that part of the world. The limestone foundation beneath Florida forms much of its water aquifer system, and sinkholes are important elements of the ecosystem for a vast array of creatures.

There are two kinds: collapse sinkholes and solution sinkholes. Solution sinkholes form in areas where sandy sediment overlays bedrock. When the sand shifts due to water movement, it fills in bedrock cracks and the soil above gradually sinks in response. As I understand it, it is a mainly top-down process.

Collapse sinkholes, on the other hand, occur where clay soil sits atop limestone bedrock that contains cavities below the top bedrock layer. If the bedrock is compromised by water flow, especially acidic water flow that dissolves the carbonate structure of the limestone, a cavity can grow until the roof no longer supports the weight of the clay layer above. A sort of bottom-up disintegration that leads to sudden and sometimes disastrous sinkholes.

Some of Florida’s lakes and waterways have a naturally occurring level of heightened acidity. I haven’t been able to discern why this is in my brief research, something to do with natural acidity in mangrove swamps. What I find interesting is that data tracking acid rain levels in Florida doesn’t seem to be readily available. What I’ve found are studies that state that there are other areas with higher levels of acid rain than Florida (notably the Northeast of the United States), that acid rain levels have decreased with increased emissions regulations, and that Florida has a lack of baseline information due to a lack of extensive monitoring equipment. There were numerous articles back in the 1980s regarding new acid rain studies (here, here and here). Since then, not much, at least not online. Puzzling, in a heavily populated region so sensitive to the effects of acidity.

When I was a kid in California, amongst all the psychedelic posters my parents had used to plaster our walls was one that said Goodbye California. It was an irreverent tip of the hat to a fact of daily life. California is earthquake country, and the real Big One still hasn’t hit. But there are always medium-sized reminders of the earth’s instability. Maybe sinkholes are so routine in Florida that they are il_fullxfull.171271510accepted as inevitable., even if some of them could be delayed or prevented.

Any further insights would be welcome.

More:

Encyclopedia of Earth – Acid Rain

2010 University of Illinois study on acid rain

1999 Florida League of Conservation Voters  study: Acid Rain/Air Pollution: The Situation in Florida and the Southeast

2013 – Sinkhole swallows man in Tampa, Florida

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