Post by L Roebuck on Sept 5, 2006 10:35:01 GMT -5
GEOLOGY
Time, elements combined to create unique Ohio Caverns
Tuesday, September 05, 2006
DALE GNIDOVEC
Sometimes it’s the things in your own backyard that you don’t see.
I’ve been to many U.S. geological sites — the Grand Canyon, Rocky Mountains, Devil’s Tower, La Brea Tar Pits — but I had never been to Ohio Caverns until last weekend, when an organization meeting there asked me to give a talk on the caverns’ origin.
The geological story of the Logan County attraction has three chapters. The first begins 380 million years ago, when the land we call Ohio was under an ocean. Currently, 40 degrees north of the equator — the 40-degree parallel runs through the Ohio State University campus, near the Main Library — but 380 million years ago, Ohio was 15 degrees south of the equator.
That means Ohio was about where northern Australia is today, so Ohio was like the Bahamas.
That ocean teemed with life: some familiar to us, such as clams, snails and corals, and some odd, such as crablike trilobites, squidlike cephalopods and giant armored fish.
Most of the shellfish had shells composed of calcium carbonate — lime. Their shells settled to the bottom, became deeply buried and eventually hardened into a thick layer of limestone. The first chapter was complete.
Now fast forward, past 250 million years ago, when the landmass Pangaea began splitting into the continents we know today; past 225 million years ago, when dinosaurs appeared; past 65 million years ago, when dinosaurs became extinct; to 1.8 million years ago, when Earth’s climate cooled and we entered the Pleistocene Epoch, or Ice Age.
The limestone was near the surface but below the water table. The limestone was porous, with many voids. Rainwater, which becomes slightly acidic when it comes in contact with carbon dioxide in the air, flowed through through cracks, slowly dissolving the limestone and forming caves. Chapter two was finished.
Tens of thousands of years ago, the water table dropped, leaving the caves empty. Water percolating from above carried dissolved lime. Upon reaching the cave, a drop would loose carbon dioxide, becoming less acidic and less able to hold lime. The lime precipitated, starting a stalactite.
A drop that dripped to the floor also lost acidity, starting a stalagmite. Eventually, the two met in the middle to form a column.
Beautiful stalactites and stalagmites make Ohio Caverns one of the prettiest caves I’ve seen. I highly recommend it.
Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University.
gnidovec@geology.ohio-state.edu
Article
Time, elements combined to create unique Ohio Caverns
Tuesday, September 05, 2006
DALE GNIDOVEC
Sometimes it’s the things in your own backyard that you don’t see.
I’ve been to many U.S. geological sites — the Grand Canyon, Rocky Mountains, Devil’s Tower, La Brea Tar Pits — but I had never been to Ohio Caverns until last weekend, when an organization meeting there asked me to give a talk on the caverns’ origin.
The geological story of the Logan County attraction has three chapters. The first begins 380 million years ago, when the land we call Ohio was under an ocean. Currently, 40 degrees north of the equator — the 40-degree parallel runs through the Ohio State University campus, near the Main Library — but 380 million years ago, Ohio was 15 degrees south of the equator.
That means Ohio was about where northern Australia is today, so Ohio was like the Bahamas.
That ocean teemed with life: some familiar to us, such as clams, snails and corals, and some odd, such as crablike trilobites, squidlike cephalopods and giant armored fish.
Most of the shellfish had shells composed of calcium carbonate — lime. Their shells settled to the bottom, became deeply buried and eventually hardened into a thick layer of limestone. The first chapter was complete.
Now fast forward, past 250 million years ago, when the landmass Pangaea began splitting into the continents we know today; past 225 million years ago, when dinosaurs appeared; past 65 million years ago, when dinosaurs became extinct; to 1.8 million years ago, when Earth’s climate cooled and we entered the Pleistocene Epoch, or Ice Age.
The limestone was near the surface but below the water table. The limestone was porous, with many voids. Rainwater, which becomes slightly acidic when it comes in contact with carbon dioxide in the air, flowed through through cracks, slowly dissolving the limestone and forming caves. Chapter two was finished.
Tens of thousands of years ago, the water table dropped, leaving the caves empty. Water percolating from above carried dissolved lime. Upon reaching the cave, a drop would loose carbon dioxide, becoming less acidic and less able to hold lime. The lime precipitated, starting a stalactite.
A drop that dripped to the floor also lost acidity, starting a stalagmite. Eventually, the two met in the middle to form a column.
Beautiful stalactites and stalagmites make Ohio Caverns one of the prettiest caves I’ve seen. I highly recommend it.
Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University.
gnidovec@geology.ohio-state.edu
Article