How Long Ago Was The Bottom Rock Of The Grand Canyon Formed

Slopes of Dox Formation virtually Unkar Creek

How was it formed?

The truth is that no ane knows for sure though in that location are some pretty good guesses. The chances are that a number of processes combined to create the views that you lot see in todays Grand Canyon. The most powerful forcefulness to take an impact on the Grand Canyon is erosion, primarily by water (and ice) and second past wind. Other forces that contributed to the Canyon'southward formation are the form of the Colorado River itself, vulcanism, continental drift and slight variations in the earths orbit which in turn causes variations in seasons and climate.

Water seems to have had the nigh bear upon basically because our planet has lots of it and it is always on the move. Many people cannot understand how water can have such a profound impact considering that the Canyon is basically located in a desert. This is one of the biggest reasons that water has such a big touch here. Because the soil in the Grand Canyon is baked by the sun it tends to get very hard and cannot absorb h2o when the rains to come. When it does rain the h2o tends to come down in torrents which merely adds to the problem. The plants that grow in the Grand Canyon tend to accept very shallow root systems then that they can grab every bit much h2o as possible on those rare occasions when it does rain. Unfortunately these root systems exercise naught to deter erosion by holding the soil in place. Now you've got lots of water, no place for it to go, just down to the Colorado River, and cipher property the soil and stone in place. The result is ofttimes a flash flood roaring down a side canyon that can move boulders the size of automobiles, buses and even small houses. If automobiles, buses and small houses are in the manner then it will take them too. Luckily no one builds houses in the 1000 Canyon so that's not a problem but in that location are a few autos, vans and buses sitting at the bottom of the Colorado. This mass that moves down a side coulee during a flash flood is more like a fast flowing physical than water and it can be very dangerous. You lot should always exist well informed of weather condition conditions when you are hiking through side canyons in the Thou Canyon.

After erosion by liquid water the adjacent most powerful force is probably its solid form, ice. In the colder months, especially on the north rim, water seeps into cracks between the rocks. These cracks can be acquired by seismic activeness, or past the constant soaking and drying of the rocks. When the water freezes it expands and pushes the rocks autonomously and widens the cracks. Eventually rocks near the rim are pushed off the edge and autumn into the side canyons. These rocks sometimes striking other rocks and are stopped only on occasion i fall by a large rock will cause a cascading effect and create a rock fall that will modify the landscape drastically in the side canyon. Debris from rock falls piles up at the bottom of the side canyons and is then carried down to the Colorado River the next time there is a wink flood. Rock falls ofttimes take out sections of trail in the G Canyon requiring the Park Service to close these trails until they can be repaired.

Once the ice had pushed the rocks off the border and the water in the wink floods has carried them down to the river, then the Colorado itself takes over. The erosive action of the Colorado has been severely constrained by the building of the Glen Canyon Dam, which concluded the annual jump floods, but there is still a lot of water flowing relatively quickly through a very narrow gorge. Before edifice the dam the Colorado River had leap floods that would exceed a flow rate of 100,000 CFS. All of that snowfall melting in the Colorado Rockies came pouring down through the Grand Canyon in May and June, every year, like clock-work. These spring floods were considerably larger than todays "trickle" of 8,000-10,000 CFS at low water and even the 20,000 CFS peak flow rates.

The Colorado'south spring floods used to conduct away all of the debris that was deposited in the main channel by the wink floods, just todays mediocre flow rates have a tough time doing the job. It yet gets washed to some extent, it merely takes a lot longer. In the process of moving the rocks and sediment down the river to the Pacific Ocean the bed of the river is scoured past all of this fast moving droppings which slowly eats away at the banks and bed of the river. This causes the river to widen and cut downward deeper into the lower stone layers. Some other cause for the slowing of the erosive force of the Colorado River is the fact that it is at present trying to cut through harder granites and schists constitute at the lesser of the Canyon instead of the softer limestones, sandstones and shales nearly the top. This rock takes a lot longer to erode and a slower moving river ways it takes even longer.

Where did all of the rock come up from?

Geologists have this question pretty much wrapped upwardly, aside from some missing layers, or unconformities, that have been completely eroded abroad. Once more at that place were a number of forces at work and this is where continental drift, vulcanism and climatic change come into play.

The fact that the Earth'due south continents are not fixed in place but rather float on a sea of molten rock, means that they movement around quite a bit, relatively speaking. The surface of the Earth is composed of about xx of these "plates" which class its chaff. Seven of these plates are very large and consist of entire continents or sea floors and the residual are smaller in comparing. The plates are average out to be about 50 miles or 80 kilometers thick and float on top of the Earth'south mantle. The plate which contains the One thousand Canyon, the Northward American plate, was at i time considerably further south than its present location and therefore had a much unlike climate. In time information technology has gradually moved northward and rotated near ninety degrees to its present location and configuration.

The continents in move, the red dot indicates the approximate location of the Grand Coulee region.

Click here or on the image above for more data on the continental drift theory.

Click here to visit the USGS site This Dynamic Earth: the Story of Plate Tectonics

The North American Plate is moving due west and is colliding the Pacific Plate which is moving towards the northwest. The Pacific Plate is also expanding from its middle and its eastern border is being subducted beneath the North American Plate every bit it comes into contact with it. Oceanic plates are typically subducted beneath continental plates because they area heavier. As pressure increases while they are beingness subducted they tend to get heavier still and to some extent they start to fall and pull more plate along with them. As the Pacific Plate moves beneath the Due north American Plate the stone of which information technology is composed is superheated and h2o is released and begins to rise. This water, which is extremely hot, causes lighter minerals to melt and forms lava which feeds the chain of volcanoes on the eastern edge of the Pacific Rim which runs from Alaska to Chile.

The disharmonize between the plates is also frequently responsible for mountain building activity. Equally the plates are forced together they sometimes buckle which causes mountain ranges to be formed along the contact point. This is how the Rocky Mountains, the Sierra Nevada and the costal mountains of California were formed and how the Aleutian Island are existence formed today. A much older range of mountains, which geologists suspect were much higher than todays Rocky Mountains and may even have rivaled the Himalayas, now forms the base of the Chiliad Canyon. The rocks that made up these mountains are nearly one.seven billion years old, or about one-third the historic period of our planet. These mountains take long since eroded away and sedimentary deposits have covered them over.

The sediments that covered the roots of these aboriginal mountains were deposited past a series of advancing and retreating ocean coast lines. Every bit the climate of our planet warms and cools the median ocean level of the planet rises and falls due to the melting and freezing of the polar caps. When the sea level rises, land areas which are close to the declension and relatively low in altitude are sometimes submerged. This was the case with the land area of the Grand Canyon and is why so many unlike sedimentary rock layers be. Each of these was formed past a different period in which the ocean moved in and covered the land, stayed for a while, and then retreated over again. Limestone deposits are created when the ocean moves in and slates, shales and mudstone deposits are created when the body of water moves out and the area is covered past silts washing into the retreating ocean.

How do we know this?

Well, the fact is that almost of the rock in the One thousand Coulee is composed of sedimentary rock which tin can but exist formed at the lesser of the ocean or in shallow coastal plains. The Kaibab Limestone which is the electric current top of the Yard Coulee is composed generally of a sandy limestone, with some sandstone and shale thrown in for expert measure. This ways that it was probably formed in a shallow sea about the coast. The fact that it contains fossils of creatures that used to live in the ocean, like brachiopods, coral, mollusks, sea lilies, worms and fish teeth, only tends to reinforce this conventionalities. The intrusion of sandstone and shales into this later means that at times the layer was as well in a higher place the surface of the water but nevertheless very close to the border. Sandstones are solidified sand which are typically fields of sand dunes or beaches, and shales are solidified mud which are common to river deltas. By dating the fossils found in the stone of the Kaibab Limestone, geologists have determined that it is approximately 250 million years one-time, and this is the youngest layer.

So where are the younger rocks?

The younger rocks have already been eroded away past the forces of nature, at least in the immediate vicinity of the Grand Canyon. Some of the younger layers, like the Navajo Sandstone of which the Vermilion Cliffs and the stone of Zion National Park are composed, can be plant in the region north of the Yard Canyon. Going even further n results in even younger rocks every bit can be seen in Bryce Canyon. The area from Bryce Coulee down to Grand Canyon is typically referred to as the Grand Staircase.

Cantankerous sectional view of the Colorado Plateau
showing the Grand Staircase

Why does it expect like it does?

The reason that it looks the way does is due to the sequence in which the events that help to create information technology happened. We already know that in that location was once a very tall chain of mountains in the area that occupied the Yard Canyon. These mountains were, over many millions of years, somewhen eroded away to form a level apparently. Fluctuations in climate then caused the oceans to move in over successive periods and each time a new rock layer was deposited. The rock layers were deposited one on top of the other and sometimes there were long periods in between in which some of the upper layers were eroded abroad, sometimes completely.

And at present the Colorado River comes into play. The ancestral "Colorado River" came into beingness when the Rocky Mountains to the east of the K Canyon were formed, at sometime around 60-70 1000000 years ago, as the master western drainage for these mountains. Over millions of years the course of this ancestral river changed its class a number of times as the terrain around it was altered. The course of the bequeathed Colorado River probably started in Colorado and at ane betoken it entered the region of Marble Canyon, but that is about all that tin be agreed upon at this indicate.

Some geologists believe that very young rock layers to the west of the G Canyon, dated at just 5 and ten million years sometime, and through which the Colorado at present flows, indicate that the river could not take been flowing there prior to that time. The river had to cut through these layers after they were deposited. The search for some other exit for the Colorado River from the Grand Coulee has been a hotly debated issue. Some geologists believe that it flowed out of Marble Coulee where the Little Colorado at present enters, others believe that it exited virtually present solar day Diamond Creek and still others believe that it exited through massive caves in the Redwall Limestone. The most likely go out at this point seems to exist up through Kanab Creek which would have had the ancestral river flowing back up into Utah and and then across Nevada and California to the Pacific.

At around 17 million years ago, while the river was flowing beyond this ancient landscape, the state mass know as todays Colorado Plateau began to uplift. The uplift was caused by pressures deep with the Earth and may have been caused by additional disharmonize betwixt the North American Plates and the Pacific Plates. This process connected until around five million years ago which interestingly enough is the date of the sedimentary layers only w of the plateau. At its greatest hieght the Colorado Plateau was once nearly three miles above sea level. The rise of the plateau probably prevented the seas from submerging it again and instead the topmost layers were eroded away and carried into the bounding main. The most favorable currently accepted theory is that the Colorado River connected to cut through the Colorado Plateau while the land rose around it.

At some point effectually 5 million years ago something happened to cause the Colorado to change its grade and exit via its present route down to the Gulf of California. The most likely cause for the alter in its course was probably due to it being captured by another river, which was draining the western portion of the Colorado Plateau. This other river eroded n along the San Andreas fault, then e and eventually entered the Grand Canyon and joined with the Colorado well-nigh nowadays day Kanab Creek. The Colorado would then have abruptly inverse its class and flowed out this newly formed go out.

Much of the eastern G Canyon was already formed past the time the river inverse its grade. Side canyons had formed forth fault lines in the rock and these were eroded away and the rock within them carried down to the Colorado. The Colorado River took all of the rock that was put into it and carried it off to the Pacific Ocean. Over many more millions of years the erosion along the course of the Colorado continued to widen the Canyon to nowadays the vistas that y'all run across today. Before the Glen Canyon Dam was built the Colorado River used to carry three cubic miles of sediment into the Pacific Ocean every hundred years.

When did all this happen?

The Earth was formed approximately 5 billion years agone.
The roots of the ancient mountain range that now lies at the bottom of the 1000 Canyon were formed nearly 1.vii billion years ago.
There is and so an unconformity of about 450 million year in which the rocks are missing.
At ane.25 billion years ago the first sedimentary layer, the Bass Formation, was laid down. Aboriginal coastal abode colonies of algae known every bit Stromatolites are preserved inside this layer and indicate that the area was coastal at that fourth dimension.
At 1.2 billion years ago the sea retreated leaving mud flats behind which eventually became the Hakatai Shale.
At one.nineteen billion years a similar layer was deposited which is known equally the Dox Formation. This was again formed of mudstones and shales and contains ripple marks too as other features that betoken that it was close to the coast.
Betwixt 1.25 and one.1 billion years ago at that place was also some volcanic activity with the region of the Grand Canyon and this is when the Cardenas Basalts were formed.
Between i billion and 825 meg years ago additional littoral and shallow ocean formations, which are now classified as the Chuar group, were deposited.
There is so another unconformity of nigh 250 million years in which new rock layers were probably laid down simply were completely eroded away.
The Tapeats Sandstone was and then deposited around 550 million years ago along long vanished coastline. There are places in the Canyon in which in which off shore islands have been found imbedded within this layer.
The Bright Angel Shale was deposited effectually 540 million years agone and indicates that the ocean was once again advancing.
The Muav Limestone was deposited effectually 530 million years ago at the bottom of a shallow bounding main.
The thick layer of Redwall Limestone which began to deposited around 330 million years agone indicates that the state was submerged for a great deal of time.
The Supai Grouping which rests atop the Redwall is dated at 300 1000000 years ago and indicates that information technology was formed in an above h2o and coastal environment.
The Hermit Shale which was deposited around 280 million years agone contains many plant fossils which indicate that information technology was also higher up h2o.
The Coconino Sandstone represents the remains of a vast body of water of sand dunes which was diddled downward from the north around 270 one thousand thousand years ago.
The layers plant within Toroweap Germination contains both sandstone and limestone, indicating that it was sometimes coastal and sometimes submerged. These layers date to effectually 260 million years.
The top layer of the Grand Canyon, the Kaibab Limestone, contains many marine fossils which bespeak that it originated at the bottom of the sea. This layer is around 250 1000000 years old.
Rock layers younger than 250 million years have been eroded away and no longer be in the immediate vicinity of the Grand Canyon.
The Rocky Mountains brainstorm to form 60-70 1000000 years ago and at some point after the Colorado River is born.
At this point there are at to the lowest degree two pop theories which describe what happens next:
- Effectually 20 million years ago the Colorado River begins to carve into the K Canyon at its eastern end, Marble Coulee, and probably exiting via Kanab Canyon.
- At 17 million years ago the Colorado Plateau begins to uplift and causes the river to cut deeper.
- Around 5 million years ago the uplift ceases and some other river working its style northward along the San Andreas fault and eastward along the western Colorado Plateau captures the Colorado River.
OR
- Around 35 million years agone the Kaibab Plateau begins to uplift and diverts the bequeathed Colorado, which was already established on a course very similar to that of today, to the southeast. The cut-off western portion, now named the Hualapai Drainage Organisation, contines to drain the western region.
- About 12 meg years ago the Colorado's path to the body of water is blocked and a huge lake, Lake Bidahochi, is formed.
- Eventually the Hualapai cuts dorsum through the southern portion of the plateau and recaptures the Colorado. Lake Bidahochi is drained and becomes the Picayune Colorado River.
  Formation of the Grand Coulee
  
  Click hither or on the epitome above for illustrations.