This is how canyons are formed
Standing on the edge of the enormous canyons scattered across the southwest United States, one is consumed with an overwhelming sense of awe. The Grand Canyon in Arizona… Canyonlands National Park in Utah… Canyon de Chelly… canyon after canyon dot the landscape of the high plateau. All those enormous gashes carved into the earth’s surface somehow defy every sense of logic we possess as we ask ourselves how?
So how did these marvelous displays of Mother Nature’s handiwork manage to appear anyway?
To understand the formation of the canyons, all you have to remember is DUDE.
D – the first “D” in DUDE stands for DEPOSITION. Many millions of years ago, the whole area now covered by the high desert plateau used to be covered by a gigantic ocean. On the bottom of the ocean was a bunch of sand and mud. Eventually, the ocean dried up, but left behind all the sand and mud.
Stream beds then covered the area, and left behind their own layers of sediment – more sand and more mud. This sand and mud was a bit different from the sand and mud from the bottom of the ocean though.
Time passed and the area changed into a desert – complete with sand dunes.
As the millennium passed, more and more layers of sediment piled on top of one another. In other words, we could say – the layers were DEPOSITED on the earth’s surface.
Those layers were covered by more layers and eventually, the underlying layers were compressed into stone – lots of layers of stone. Each layer was unique because it was formed by very different circumstances from the layers above and below it.
However – all those layers shared one important characteristic. They were all deposited at sea level.
U – Once all the rock layers were formed at sea level, they had to be UPLIFTED. That means that the whole area was somehow lifted up way above sea level. Nobody is sure exactly how that process happened – but everybody agrees that it was a pretty remarkable event.
Usually, when rock layers get lifted up, they end up crumpled and folded into mountains. But the area now known as the Colorado Plateau was not. The entire region simply lifted straight up – as though someone put a great big plate underneath it and gently lifted it up. All the rock layers are still intact and are in the same order they were deposited – they are just way up above sea level now.
D – The second “D” in DUDE stands for DOWNCUTTING. Once the layers of the plateau had been lifted up, the rivers started flowing over them and cutting down into them.
As the rivers flowed, they carried away tons of small pieces of rock – creating a big hole in the ground with steep sides.
Some of the canyons in the region are still very narrow – like Canyon de Chelly. These canyons are basically DUD canyons, because they haven’t had the “E” act on them very much yet – only the downcutting.
E – After the river has cut a canyon into the rock layers, EROSION takes over to make the canyons wider. Every time it rains or the wind blows, small and large pieces of rock are washed or blown off the sides of the canyon. In winter, water seeps into cracks and expands – which breaks big chunks of rock off the canyon walls. Rain storms send thousands of gallons of water rushing over the edges of the canyons – forcing rocks down into the canyon itself.
Over millions of years, the canyons widen as more and more rock from the canyon walls fall into the canyon and is washed away by the river in the bottom.
So – to understand how the canyons of the southwest formed, all you have to do is remember:
D – deposition of rock layers
U – uplifting of rock layers
D – downcutting through the rock layers
E – erosion of rock from the sides of the canyons
This process is still happening today – the rivers are still cutting the canyons deeper and rock is still falling from the canyon walls making the canyons wider and wider. If you could come back to visit in a couple thousand years, you would see noticeable changes in the canyons of the southwest!