Changing Earth's Surface - This is Going to Take Some Time!
Grand Canyon - The story begins
Weathering and erosion, earthquakes, uplift and volcanoes mold and change Earth's surface. At the Grand Canyon you can see evidence of it all.
Look at the photo. It tells a story. The rock layers you see were slowly formed over millions of years.
17 million years ago, uplift began to occur in the area. As the land rose, the Colorado River flowed across the area causing weathering and erosion.
Over millions of years the river gradually cut down through the layers of rock.
This process formed the Grand Canyon that you see today.
A brave, geologist named John Wesley
Have you ever been on a whitewater river trip? Perhaps the most exciting river trip ever taken was that of Major John Wesley Powell in 1869.
Major Powell lost an arm while fighting in the Civil War. But, this did not stop him from seeking adventure.
Major Powell was a geologist interested in the geology of the Grand Canyon. He thought the best way to learn about the canyon was to travel by boat on the wild Colorado River that runs through the canyon.
John Wesley Powell was the first white man to explore the 1,000 miles of the canyon. He and the other nine men of the expedition did not know what to expect from the river or the canyon. One day may bring a life threatening rapid, while the next may be spent floating peacefully on calm stretch of river. Sometimes the men had trouble sleeping at night as they listened to the roaring rapids downriver from camp. They knew the next day would be full of adventure whenever they heard the roar of rapids.
Unlike the river trips of today, the men of the Powell Expedition did not have lifejackets. Aside, from not having lifejackets for safety, can you imagine rowing a boat with only one arm?
They faced other challenges; food began to run out and rot. The men often suffered from empty bellies.
John Wesley maneuvered through dangerous rapids during the day and often spent his evenings climbing dangerous canyon walls. On one such occasion, he almost lost his life when he slipped from a ledge. Hanging by his one arm, he was saved when one of his companions used his long underwear as a rope to rescue John Wesley. Major Powell took many risks to learn about the geology of the Grand Canyon.
How long do you think such an expedition would take? It took the entire length of your summer vacation – three months.
Once upon a time - long, long ago (over a billion years in fact!) some volcanoes erupted. This volcanic layer is now at the bottom of the Grand Canyon. The tops of these volcanic mountains weathered and eroded until they became relatively smooth. Next these rocks were buried beneath a calm sea. Rivers carried sand and small rocks to the sea. The particles or sediment settled forming new layers of rock on top of the old volcanic mountains. The process is called deposition, meaning depositing, or laying down material. The seas dried up, leaving new deposits and minerals. Then they came again, and went, and came and went each time depositing new layers of rock.
Around 17 million years ago the area was uplifted. At its tallest, this place was once about 5 kilometers (over 3 miles or 16,000 feet) above sea level! As the land rose, the Colorado River flowed across it weathering and eroding. Over millions of years the river gradually cut down through the layers of rock, leaving the canyon we have today.
Although millions of years sounds like a very long time, geologically speaking it was pretty quick compared to the 1 or so billion years of deposition.
Build up a pile of soil into a formation that looks like a mountain. Now pour the water over your formation, what happens?
Can you make the flow of water resemble a river?
Your running water carries soil with it. After some time, the running water carries away enough dirt to create a small ditch. In much the same way, rivers shape canyons.
As the running water flows over soil and rocks, it slowly wears Earth away until, after millions of years, a canyon is shaped.
The Colorado River shaped the Grand Canyon by slowly wearing away the rock. Scientists estimate that it has taken the Colorado River about 10 million years to create the Grand Canyon.
Today the canyon is 1.6 kilometers deep and 6 to 20 kilometers wide and it is still changing. All the forces that shaped the Grand Canyon in the past are still at work today.
To take a virtual tour ... visit Grand Canyon National Park!