At last, a theory about why Denver is a mile above sea level

March 13, 2015 byDan Elliott
A marker carved in one of the west steps of the State Capitol denotes the "one mile above sea level" elevation in Denver on Friday, March 13, 2015. In an article published in March 2015, geologists from the University of Colorado suggest chemical reactions triggered by water far below the Earth's surface could have made part of the continental plate less dense. Because the plate floats on the Earth's mantle, the lighter portion might have risen like an empty boat next to one with a heavy cargo -- lifting the vast High Plains far above sea level. (AP Photo/David Zalubowski)

Geologists may finally be able to explain why Denver, the Mile High City, is a mile high: water.

A new theory suggests that chemical reactions, triggered by water far below the Earth's surface, could have made part of the North American plate less dense many millions of years ago, 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, like an empty boat next to one with a heavy cargo, pushing the vast High Plains far above , according to the theory formulated by geologists Craig Jones and Kevin Mahan at the University of Colorado-Boulder.

Their work appeared last week on the website of the journal Geology, and is a big deal for Denver, where the 5,280-foot elevation is a point of pride and 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, marking the mile-high line in the grandstand.

Geologists have long been puzzled by how the High Plains could be so big, so high and so smooth. The plains descend gently from roughly 6,000 feet to 2,000 feet above sea level as 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, and that 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 and then 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 emanating from the Earth's core. The water then rose into the continental plate, setting off that turned garnet and other dense minerals into mica and other less heavy minerals, making vast areas of the crust lighter.

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

The reason crustal hydration happened where and when it did has to do with how steeply the oceanic plate descended, Jones said. At some point, the angle at which the plate was descending became shallower, enabling the released water to rise for reasons that remain unclear, he said.

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, involving 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, and 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, who is also a fellow at the Cooperative Institute for Research in Environmental Sciences, a partnership of CU and the National Oceanic and Atmospheric Administration.

The theory has merit, according to Ken Dueker, a professor of geology and geophysics at the University of Wyoming.

"It's a plausible hypothesis that has some data to support it," said Dueker, who was not part of the team that devised it. One unanswered question, which Jones and Mahan raised in the journal Geology, is what channeled the water up into the North American plate, Dueker said.

The Farallon plate also helped form the Rocky Mountains just west of Denver, which soar as high as 14,433 feet. As it moved under the continent, friction caused the North American plate above to compress horizontally, like a rug that bunches up if a foot is dragged across it, geologists say.

Cracks opened from that horizontal pressure, and one side was shoved higher than the other, creating the Rockies.

Not knowing why Denver is a mile high is a little awkward for Colorado geologists. 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.

Explore further: Researchers propose a novel mechanism to explain High Plains elevation

Related Stories

New insights on the origin of the Rocky Mountains

February 28, 2011

( -- The formation of the Rocky Mountains in Colorado has always puzzled scientists. Some 600 miles inland and far removed from the nearest tectonic plate, the only comparable inland mountain range is the Himalaya, ...

The North American Cordillera: Constructive collisions

April 3, 2013

The mountain ranges of the North American Cordillera are made up of dozens of distinct crustal blocks. A new study clarifies their mode of origin and identifies a previously unknown oceanic plate that contributed to their ...

Is there an ocean beneath our feet?

January 27, 2014

( —Scientists at the University of Liverpool have shown that deep sea fault zones could transport much larger amounts of water from the Earth's oceans to the upper mantle than previously thought.

Recommended for you

The full story on climate change requires the long view

December 17, 2018

The science is clear that human activities over the last century have contributed to greenhouse-like warming of the Earth's surface. Much of the global conversation around climate change fixates on what individual countries ...

Does saving energy save the climate?

December 17, 2018

To stop climate change, saving energy matters less than switching to renewable energy. Indeed, says Anthony Patt, it isn't clear whether saving energy makes much of a difference at all.

Do you know the carbon footprint of your food choices?

December 17, 2018

Shoppers greatly underestimate the difference their food choices can make to climate change, but they'll favour items with a lower carbon footprint if they're given clear information on the label, according to new research ...


Adjust slider to filter visible comments by rank

Display comments: newest first

2.3 / 5 (9) Mar 14, 2015
Geologists may finally be able to explain why Denver, the Mile High City, is a mile high: water.

Specifically, because the amount of water in the oceans is just enough to fill up the earth to one mile below the height of Denver, Denver is exactly one mile above the water!
Scientists are proud of their discovery.
1 / 5 (1) Mar 14, 2015
Why is Denver so high? Because they smoke so much pot.
1 / 5 (9) Mar 14, 2015
And When are we going to drill from 1 end of this planet to the other end of it?
Are there any such plans on the table?
Is it like cutting the tree branch on which you are sitting?
How long it may take once the drilling is initiated?
Why not DO IT TO MOON?
1 / 5 (7) Mar 14, 2015
"And When are we going to drill from 1 end of this planet to the other end of it?"
i.e Follow
Don't Just go upwards - Go Downwards too Motto!
Just like Everyone grows up as much as possible from Infancy & then goes Downwards reaching that 6'X2' Tomb.
5 / 5 (4) Mar 14, 2015
And When are we going to drill from 1 end of this planet to the other end of it?
Are there any such plans on the table?
We aren't. There aren't. No.
The deepest borehole ever drilled is 40,230 ft at the Kola Superdeep Borehole in Russia. The target depth was 49,000 feet, but they were unable to make the equipment work that deep in the crust. If you can figure out a better way, and justify the return over the immense cost, knock yourself out.
1 / 5 (1) Mar 15, 2015
...might have risen, like an empty boat next to one with a heavy cargo...

Other than in Billy's bathtub or within the locks on canals, where in the world do boats act like this?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.