What makes the Mile High City a mile high? (Thinkstock)
What makes the Mile High City a mile high?
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Geologists may finally be able to explain why Denver, the Mile High City, is a mile high. It's water.

A new theory suggests that chemical reactions were triggered by water far below the Earth's surface. They could have made part of the North American plate less dense many millions of years ago. That's when the continents we know today were still forming.

Because plates float on the Earth's mantle, parts of the Western United States might have risen. Think of it like an empty boat next to one with a heavy cargo. It pushed the vast High Plains far above sea level. The theory was formulated by geologists Craig Jones and Kevin Mahan. They work at the University of Colorado-Boulder.

Their work appeared on the website of the journal Geology. It is a big deal for Denver. The 5,280-foot elevation is a point of pride. It also is a big part of the city's identity. At Coors Field, where the Colorado Rockies play baseball, a single row of purple seats interrupts about 50,000 green ones. It marks the mile-high line in the grandstand.

Geologists have long been puzzled. How could the High Plains be so big, so high and so smooth? The plains descend gently from roughly 6,000 feet to 2,000 feet above sea level. They stretch for thousands of square miles, from the Texas Panhandle to southern Montana. And from western Kansas to the foothills of the Rocky Mountains in Colorado.

It's well established that much of the West was still at sea level 70 million years ago. Tectonic shifts don't fully explain the High Plains' altitude. The lifting began long after the ancient Farallon oceanic plate was shoved deep under a vast part of western North America. It settled deep into the planet's mantle over millions of years.

Why?

"Crustal hydration," Jones and Mahan theorize.

They suggest that water that had been locked in minerals in the Farallon plate was released because of pressure from the overlying rock and heat. The higher temperatures came from the Earth's core. The water then rose into the continental plate. That set off chemical reactions. Those turned garnet and other dense minerals into mica and other less heavy minerals. It made vast areas of the crust lighter.

Jones said the Earth's crust under the High Plains "floats higher" over the mantle. It is much like a plank of buoyant balsa wood that rises higher in the water than a plank of dense pine.

Few geological formations appear so uniform on such a vast scale as the High Plains. The only other known location in the world that's similar is in southern Africa, Jones said. The prevailing theory there is different. It involves some other source of buoyance, Mahan said.

The composition of rocks found in the High Plains is strong evidence in favor of the hypothesis, Jones said. But it needs more testing. That was one reason for publishing it.

"Do we think this is 'the' answer? No. Could it be 'an' answer? I suppose it's possible," said Jones.

Not knowing why Denver is a mile high is a little awkward. Jones recalls having to tell a British TV producer a few years ago that he couldn't explain it.

"We probably need to figure this one out guys. Because it's kind of embarrassing," Jones said.

Critical thinking challenge: Why does Denver make such a big deal out of its mile high status?

Assigned 19 times


COMMENTS (6)
  • AlexS1-Jac
    3/19/2015 - 11:14 p.m.

    The topic about the Mile High City is very fascinating. It was very interesting how the Rockies Baseball Stadium has a row of seats that marks the mile in elevation.

  • BaileyB-Kut
    3/22/2015 - 09:49 p.m.

    I think Denver makes such a big deal about there mile high status, because no other state can say they are a mile high. Maybe Craig Jones is right we should try to find out why Denver is a mile high.
    We need to find out if there was a chemical reaction beneath the earths surface.

  • NicholsE-Sua
    4/15/2015 - 09:44 p.m.

    Why does Denver make such a big deal out of its mile high status?
    Denver make such a big deal out of its mile high status because they want people to learn about thing around the world. people like to learn because maybe they can go there one time to see Denver and see how it feels to be at a 5,280 feet high elevation that people say is a point of a pride. Another reason it could be famous and everyone can think that it cool and might be a lot of money. A another reason a lot of people bee the 70 years ago. Those are my reasons why does Denver make such a big deal out of its mile high status.

  • CirilloP-Sua
    4/15/2015 - 10:21 p.m.

    Denver makes such a big deal about mile high status. They make such a big deal because it is so busy. It is also such a big deal because it is so high. Mile high is a very good place to live. That is why mile high is such a big deal.

  • KerrF-Sua
    4/15/2015 - 11:44 p.m.

    Denver makes such a big deal out of its "mile high" status because Denver is the only city in North America to be a mile high. They use the quote "mile high" to attract travelers to come to Denver. And we all know it is not something we see everyday, getting that high above sea level. Denver is using its quote "mile high" as a popular attraction for their city around the country.

  • ShecklenZ-Sua
    4/16/2015 - 01:46 a.m.

    people are proud of there city and how it is 5,280 feet high and how baseball is there.


    1. a single row of purple seats interrupts about 50,000 green ones.

    2. They think 5,280-foot elevation is a point of pride.

    3. and in the story it says " it is much like a plank of buoyant balsa wood that rises higher in the water than a plank of dense pine."

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