How the Great Plains Were Created


Alex Wierbinski's picture

By Alex Wierbinski - Posted on 01 October 2018

GEO NEWS

How the Great Plains Were Created

The origins of the High Plains landscape,
ETH Zurich, September 26, 2018.

MAIN POINTS

WHAT
“Dropping just a few hundred meters over a length of more than 500 kilometres, these plains have only a very gentle gradient and the nearly flat surfaces exhibit unique ecosystems, making them a geological and ecological anomaly.”

UNDER IT
“...the groundwater reservoir known as the Ogallala aquifer. At 450,000 square kilometres, it is the largest aquifer in North America.”

WHEN
“The High Plains were formed 20 million years ago. Earth scientists have recently discovered a zone of unusually hot material in the Earth's mantle that creates a wave of uplift that is slowly shifting from west to east under the continental plate. This wave first uplifted the Colorado Plateau, then the Rockies and finally the plains themselves. This resulted in a steeper gradient of the mountains towards the plains, accelerating erosion. For 15 million years, a massive flow of sediment poured out of the mountains, down the river valleys and into the plains.”

CAPPED
“The surface of these plains sealed with sand, mud and clay, thus making it possible for rain water to remain in sinks to form lakes. Chemical processes eventually led to a calcification of the lakebeds and soils, forming limestone layers up to 10 meters thick. Finally, as it aged, cracks formed in the limestone, allowing water to seep through and feed a groundwater reservoir of vast area and volume, hosted in the gravels shed from the mountains.”

PROCESS
“The flow of sediment finally stopped around three to five million years ago. Since then, the High Plains' surfaces have changed very little (with the exception of human impact). "They are a preserved ancient landscape." ”

"It will take five or ten million years until the High Plains have completely eroded."

 

Bottom Line

We can see a constrained version of this process described above working in the San Joaquin to the West of the Sierra. In our version, our Sierra is different in that it's younger than the Rockies, with its Western sediments trapped in the San J Valley, rather than stretching across the middle of the country.

On the other side of the Range, we can see the sediments eroding off the Eastern Flank of the Sierra for the past few million years have not yet had the time to finally and fully drown the terrain and form a delightful plain, as have the Eastern sediments of the Rockies, but only a rather large stretch of desert running East to the Rockies.

 

Related Research

The high plains aquifer: Can we make it last?

Stream Loss in the Great Plains

 

Ogallala Aquifer Wiki

"Some estimates indicate the remaining volume could be depleted as soon as 2028."

 

 

 

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