A Look at the Grand Canyon
A Look at the Grand Canyon
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For over 100 years now, the Grand Canyon has been a treasured national park. But how did such a geological wonder come to be? The history of this great landmark actually spans nearly 2 billion years!
This map provides a good look at the canyon as a whole. Impressive, right? The Grand Canyon is 277 miles long and 18 miles wide. That's bigger than the state of Rhode Island!
Looking at the layers
Looking at the layers
Some may know that the Grand Canyon was formed by water--more specifically, the Colorado River; but that's only a part of the area's immense history. The rocks of the canyon have been around for much longer, with different layers having their own story way before the Colorado River shaped the canyon we know today.
On the left is a picture showing each distinctive layer and their respective point in time. Thanks to the principle of superposition, we know that the rock layers at the bottom are older than the ones above and so on.
On the right is a simplified geologic time chart to use as a reference. Can you find all the points shown in the Grand Canyon graphic? Notice that some of the rocks date back all the way back to the Precambrian (in which the era as a whole actually spans as far back as 4,600 Ma)!
The first foundations
The first foundations
Being the oldest layer, the Vishnu group, or "Vishnu Basement Rocks", is a remnant of the great Vishnu Mountains that once stood there. They formed in the Precambrian era--more specifically, the early Proterozoic eon nearly 2 billion years ago. When two tectonic plates collided, rows of volcanic islands smashed together and formed an incredible mountain range rivaling the Himalayas. But over the next 500 million years, these mountains were eroded away and now only the bases remain. Because of this, the remaining rocks are primarily metamorphic due to previously being underneath an entire mountain range!
After the Vishnu mountains disappeared due to erosion, the land became submerged by a shallow sea, which swept in sediments that later hardened and became rock. These late Proterozoic layers would be collectively named the "Grand Canyon Supergroup," with the oldest section being called the Unkar Group. What's especially interesting about this layer is the angle it sits at. As is the principle of original horizontality, layers of sediment are deposited horizontally; therefore, geologic forces set the Grand Canyon Supergroup at an angle much later. But what happened to the rest of the layer? The top eroded away, but its absence reveals something incredibly mysterious: the Great Unconformity.
A great gap in time
A great gap in time
The Great Unconformity represents an immense gap in the rock record between Cambrian times and the Precambrian. It's as if several entire chapters of a book were torn out! The amount of lost time is different depending on the place (ranging from 250 to 1,200 million years). So in some places of the canyon, over a billion years of geologic history is straight up missing. But what's even more mysterious is the fact that the Great Unconformity can be found everywhere across the globe--not just the Grand Canyon.
The Grand Canyon's story finally picked up again 500 million years ago in the Paleozoic era. Over these hundreds of millions of years, the area was submerged by inland seas over and over again, forming new sedimentary layers of limestones, shales, and sandstones.
At long last, all the rock layers had been built! Though, the area was still at sea level and it took plate tectonics to bring it higher in elevation. Finally, the stage was set for the Colorado River, as it began to cut through the Plateau just 6 million years ago, forming the incredible canyon we know today.
Old rocks, young canyon
Old rocks, young canyon
I feel the geologic history of the Grand Canyon tends to go underappreciated, despite it being such an incredible feat of nature. In the broad perspective of time, the canyon itself has only been around for a few million years--a miniscule amount of time in the grand scheme of things. I feel as human beings, we can't ever grasp the entire scope of this incredible landmark, but that's why we should treasure it all the more.
My 3d Canyon Topographic Map Project
My 3d Canyon Topographic Map Project
For my learning objective on maps, I felt that making a 3d model would be an interesting challenge. My location of interest is Powell Plateau, mainly because it looks quite distinct from the rest of the canyon and I figured it could use some love.
My model is color coded to show certain elevation ranges. Every pixel in height also represents an increase in 500 elevation--much like a contour line!
With an elevation of 7,661 feet, Powell Plateau was named after geologist and explorer John Wesley Powell, who visited it in 1870. His reports had a huge influence in cementing the Grand Canyon's reputation as a national icon and natural wonder. But even though this plateau is named after him, it's worth mentioning that the Anasazi actually lived there during the 11th and 12th centuries.
For my topographic map reference (shown on the right), I used this site to find the exact location I wanted. The contour interval is 500, which is also reflected in my 3d version!
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