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Taum Sauk/ St. Francois Mountains (1.5 Billion Years)

April 24 2002 at 12:03 AM
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Response to Oldest Mountains in America?

 
As a native Missourian I grew up on the belief that Taum Sauk/St. Francois Mountains were among the oldest mountains on earth. This is noted in a geologic museum at the Taum Sauk Pumped Storage Power Plant and which I repeated on my site.

Among the other claims are that Taum Sauk is one of the few peaks not to have been under water (even Everest was under water). This is not quite right but it's been a while.

I will post a follow up on Harney/Black Hills.

My knowledge on both of these were spurred by exhibits at the mountains.

Anyway check out this Missouri DNR citation:
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The St. Francois Mountains of southeast Missouri are among the oldest mountains on earth. We should be proud to have such geologic antiquities in Missouri.
The bedrock of the eroded knobs of the St. Francois Mountains is at least 1.5 to 1.3 billion years old. As with human longevity, it is a complexity not easily explained in a few paragraphs. All mountain ranges are the result of the succession of interplay of fundamental earth forces.
The buried igneous bedrock of the whole Ozarks region is similar to the hard, exposed, igneous rock of the St. Francois Mountains. But only in the counties of St. Francois, Madison, Iron, Carter, Washington, Shannon, Reynolds and Wayne is this ancient rock exposed at the surface. These mountains sit like islands in the vast expanse of younger, softer sedimentary limestone, sandstone and dolomite rocks that lie spread out in all directions from their flanks.
Around 1.4 billion years ago, the foundation of the Ozarks was formed by the eruptions of hundreds of separate volcanoes. Steam, smoke, ash, cinders and lava flows buried the landscape. Intrusions of unseen molten material also swelled beneath the crust but did not reach the surface. This raised the foundation of the Ozarks in southeast Missouri above the rest of the region as well as above the surface of the ancient ocean that covered the land at that time. In so doing, the St. Francois Mountains were born. From ocean floor to peaks, the mountains could have been 10,000 feet high, half of which was above the ocean's surface. It was a cataclysmic period that lasted more than half a billion years.
The buried igneous bedrock of the whole Ozarks region is similar to the hard, exposed, igneous rock of the St. Francois Mountains. But only in the counties of St. Francois, Madison, Iron, Carter, Washington, Shannon, Reynolds and Wayne is this ancient rock exposed at the surface. These mountains sit like islands in the vast expanse of younger, softer sedimentary limestone, sandstone and dolomite rocks that lie spread out in all directions from their flanks.
Around 1.4 billion years ago, the foundation of the Ozarks was formed by the eruptions of hundreds of separate volcanoes. Steam, smoke, ash, cinders and lava flows buried the landscape. Intrusions of unseen molten material also swelled beneath the crust but did not reach the surface. This raised the foundation of the Ozarks in southeast Missouri above the rest of the region as well as above the surface of the ancient ocean that covered the land at that time. In so doing, the St. Francois Mountains were born. From ocean floor to peaks, the mountains could have been 10,000 feet high, half of which was above the ocean's surface. It was a cataclysmic period that lasted more than half a billion years.
Afterwards, the lingering ocean deposited thousands of feet of sedimentary rock atop the old volcanic rock that formed the bed of the ocean. The St. Francois Mountains were probably buried by several thousand feet of sediments. Hundreds of millions of years of geologic uplift followed, raising these deposits and driving away the ocean waters, creating new land surfaces. Surface erosion by streams and subsurface solution of the sedimentary rock by groundwater then carved a hilly topography in the softer sedimentary deposits, giving us our beautiful Ozark landscape.
How do the Ozark Mountains and the St. Francois Mountains relate? The rugged, hilly Ozark Mountains were largely produced by surface erosion and dissolution of the bedrock by acidic groundwater over the past 65 million years. By contrast, the rugged St. Francois Mountains were largely produced by volcanic processes that occurred more than one billion years ago.
To understand the specific geologic events that have given us the St. Francois Mountains, pay them a visit. Explore Johnson's Shut-Ins State Park, Sam A. Baker State Park, Elephant Rocks State Park, St. Francois State Park and Taum Sauk Mountain State Park. Visit with the park staff. Ask them about the origins of the colorful ash-flow tuff, rhyolite, rhyolite porphyry, granite and basalt. With diligence, and some study and field observations, you'll soon decipher the "DNA" of Missouri's oldest mountains and discover why they are aging so gracefully.


http://www.dnr.state.mo.us/magazine/1999_fal/one-last-word.htm

 
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  • correct - M. Libby on Jul 23, 2002
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