GRAND CANYON
Length: 277 river miles
Width: Average 10 miles. Maximum 18 miles.
Depth: Average 1 mile or 5,280’. Maximum 6,000’
Volume of Rock Eroded: 803 cubic miles
Elevation: North Rim – 8,200’; South Rim – 7,000’
Precipitation: North Rim – 25”; South Rim – 20”; Phantom Ranch – 8”
Annual Visitation: 5 million, 40% from foreign countries.
COLORADO RIVER
Total Length: 1,450 miles
Elevation at: Lee’s Ferry – 3,100’; Phantom Ranch – 2,400’; Lake Mead – 1,200’
Elevation Change within Grand Canyon: 1,900’
Average Gradient within Grand Canyon: 8’
Width – Average: 200-300’; Minimum: 76’. Maximum about 750’ at mile 193.
Depth – Maximum measured: 110’; Average: 35’. The most striking feature is how suddenly depth may change.
Flow Rates – Maximum estimated flow before Glen Canyon Dam: Pre-dam highs may have exceeded 240,000 cfs in the 1800s, and 300,000 cfs in the 400s-800s though flows weren’t accurately measured until 1922. Flow rates fluctuate throughout the day in response to changing demands for hydroelectric power in the West. Lowest flow since GCD – 1,000 cfs in 1977. Highest flow since GCD – 92,000 cfs in 1983
Average annual sediment load before GCD: 168 million tons
Temperature: 46° at GCD, 50° at Phantom Ranch and 60° at Lake Mead. Slightly colder in the winter.
Speed: 10-15 mph at steeper rapids, average 3-4 mph
Drop: Total 1,709’ in 296 miles from GCD to Lake Mead or approximately 8 feet per mile, nearly 25 times that of the Mississippi River.
Though the Colorado River is not particularly large in volume, its name evokes images of whitewater and stunning red rock scenery. The river begins at the continental divide, winds its way across the upland desert known as the Colorado Plateau and deposits not a drop of water at its old terminus, the Gulf of California. The Grand Canyon is an enigma, a puzzle, a mystery. It follows a confusing path in an unlikely location. But it is the crown jewel of the National Park System and arguably the most recognized and beloved landscape in America.
THE COLORADO PLATEAU. This is a large uplift that covers the west part of the state of Colorado, the NW corner of New Mexico, the SE half of Utah, and the NE half of Arizona, centered on the Four Corners area. The total area is equal to Maryland and New Jersey combined or the Netherlands or Switzerland.
The plateau itself in the Grand Canyon is divided into 7 separate plateaus – 4 north of the river, 2 south and one, the Marble Platform to the east. The plateaus were once one continuous feature before being separated by the river cutting the Grand Canyon. The average elevation of the Colorado Plateau is 6,000 feet, has an average range of 5,000 to 9,000 feet and an extreme elevation of 12,000 feet. Here most of the precipitation falls in the winter as snow and then again during the summer monsoon in August/September. The bare rock allows for catastrophic runoff.
The Colorado begins near the continental divide at 14,000 feet in the Rocky Mountains of Colorado and in the Wind River range of Wyoming as the Green River. Together these make up 70% of the water volume. The major tributaries that contribute the rest are the Gunnison, Yampa and Dolores in Colorado, the Escalente and Virgin in Utah, the San Juan in Colorado, New Mexico and Utah, and the Little Colorado in Arizona.
ENVIRONMENTAL THREATS
A range of new proposals have been made, many of them by savvy entrepreneurs operating just outside the canyon’s boundaries in areas that were controlled not by the National Park Service but by the US Forest Service or one of the five Native American tribes whose federally recognized reservations are located around the canyon. The Federal Aviation Administration caps air tours at 93,971 flights a year. This limit doesn’t apply to the Hualapai.
Shortly after it became a National Park in 1919, the Grand Canyon hosted some 37,000 visitors a year. Today, about 5.5 million tourists arrive annually. It’s the second most visited national park, after the Great Smokey Mountains.
1. Tsuayan. A small city composed of a strip of modest tourist motels and gas stations two miles from the park’s main entrance at the South Rim has been taken over by a consortium of investors who want to transfer it into a resort, with potentially thousands of new homes and millions of square feet of commercial space, including luxury hotels, a European-style health spa, and a dude ranch – that is they want to create a city. All of this will require lots of water. The developers, led by an Italian company called Stilo, are looking at ways to bring in water, including by train or a pipeline tapped into the Colorado River. But they also have the right to punch wells through the surface of the arid South Rim to access an aquifer that drives many of the springs and seeps deep within the Grand Canyon. These tiny pockets where water trickles from cracks in the bare rock make up less than 0.01 % of the surface area inside the canyon, but each little oasis supports a web of complex plant and animal life.
In the 6,000 feet between the river and the North Rim, the canyon has five of North America’s “life zones” – more than any other national park. In latitudinal terms, it’s the equivalent of walking from the deserts of Northern Mexico to the boreal regions of Canada, all in the span of a vertical mile. Anything that might taint these springs or induce them to dry up would reverberate throughout the canyon’s biome.
Tusayan backers have already overcome many obstacles, with the last an application for a road easement crucial for the project to go forward. If this final hurdle is cleared, there is little to stand in their way.
2. Hualapai Tribe. A 24-mile stretch of the river corridor at their western end of the canyon is opened to unlimited air traffic by the Hualapai. Thanks to a Federal Aviation Administration rule change requested by the Hualapai, the tribe may operate an unrestricted number of helcopter flights. These are filled with sightseers, many from Las Vegas, and fly below the canyon’s rim from sunrise to sunset. The noise they generate is so intense, and so continuous, the the area is locally known as Helicopter Alley. Helicopter tours drew over a million visitors to Hualapai land in 2015. Busy days see up to 450 flights a day. 262 were counted in one 5-hour period.
Hualapai Skywalk. In 2007, the Hualapai Tribe opened the glass-bottomed Grand Canyon Skywalk on their property, Grand Canyon West. The Skywalk has seen mixed reviews since the site is only accessible by driving down a 10-mile (16 km) dirt road, costs a minimum of $85 in total for reservation fees, a tour package and admission to the Skywalk itself and the fact that cameras or other personal equipment are not permitted on the Skywalk at any time due to the hazard of damaging the glass if dropped. The Skywalk is about 250 miles (400 km) by road from Grand Canyon Village at the South Rim. The skywalk has attracted “thousands of visitors a year, most from Las Vegas”.
3. Uranium Mining The discovery of uranium in the 1940s led to decades of mining in the GC. According to the US Geological Survey data, 15 springs and five wells inside the Grand Canyon area have levels of uranium that are considered unsafe to drink, due in part to incidents in older mines, including Hack Canyon, Orphan Mines, and Horn Creek where erosion and problems with containment have allowed uranium to leach into the groundwater. In 2012, the interior secretary banned new uranium mining claims for 20 years in a million acres of federal lands near the park. A bill before Congress seeks to designate 1.7 million acres of the canyon’s watershed as a national monument, making the ban on new uranium mining claims permanent.
The ban on new uranium mining doesn’t apply to preexisting claims. In 2015, one mine on Forest Service land was restarted by Energy Fuels just 6 miles southeast of Tsuayan after a bitter court fight with environmental groups and the Havasupai tribe who worry that their water could be tainted. Mines are also proposed on the north rim outside of the national park.
4. Escalade. Driven by the political consultant, R. Lamar Whitmer, a group of developers from Scottsdale intend to construct the Escalade Tramway, a 1.5 mile long gondola extending from the rim, 3,200 feet, down to the confluence of the Little Colorado. A retail complex, food court, and amphitheater overlooking the Confluence is planned. The tramway would be capable of delivering 10,000 visitors a day to a spot that now rarely hosts more than a few dozen people on a typical summer day, and often none during the winter. Whitmer has persuaded a group of Navajo politicians that it would bring much needed revenue to the tribe.
The Hualapai’s wildly successful helicopter operation has drawn interest among the Navajo who believe this will be an anchor for a similar explosion of air tours along the eastern flanks of the canyon. Go to www.savetheconfluence.com to follow.
Each of these threats is capable of eroding a piece of the canyon’s majesty, and if implemented in full, will strip the landscape of its ability to do the thing that makes it unique, which is to instil humility by demonstrating the human beings are tiny in relation to the forces that have shaped this planet, and that we are not the centre of the world. The bigger threat is that Tusayan, the tramway, and Helicopter Alley have the potential to accelerate neighbouring development projects. If the Escalade goes ahead and if Tusayan’s development were to move forward, the impact would be enormous. You would have a mega-resort perched directly above the central portion of the canyon and bookended by a pair of massive air-tour operations, each anchored to its own new development. The entire sweep of the canyon would be transformed into something that looks less like a national park and more like an amusement park.
The canyon is emphatically not an amusement park. It is without handrails, a place where the dangers are real. But no less real are the rewards – among them the fact that when you move through an ancient wilderness that has not been compromised, you are reminded of our species’ humble place in it and the fragility of life. We all need places like that.
The Grand Canyon Trust is a conservation group that has spent 30 years battling an array of threats against the canyon.
Controlled flood experiments (the first was in 2004, the last in 2014) prove that high water flows move sand from river channel to sandbars. Huge expanses of sand formed after these “floods” were reminiscent of pre-Glen Canyon Dam beaches. To view before and after photos of 81 campsites for the 2013 controlled flood visit www.gcmrc.gov/gis/sandbartour2013/index.html.
WHAT IS DIFFERENT ABOUT THE GRAND CANYON?
1. 20 miles east of Grand Canyon Village, the Colorado turns 90° from south to west and cuts through the Kaibab plateau 3,000 feet higher than the Marble Platform to the east.
2. The river disregards the six major fault lines that cross its path. Rivers usually flow along fault lines as erosion is easier due to repeated earthquakes that create linear zones of shattered rock. But the Colorado crosses these faults at right angles through blocks of solid rock strata.
3. Evidence showed that the river once flowed in the opposite direction – to the northeast. Tributaries of the river in Marble Canyon (which now flows south), flowed to the north against present southerly flow. The Marble Platform also slopes to the northeast.
4. The river in Colorado state is 10-20 million years old but downstream in the Grand Canyon, is only 5-6 million years old.
5. Its severe depth in relation to the broad featureless plateau surrounding the canyon are likely because the plateau was formed at a different time under different erosional forces than the canyon.
FIVE INDEPENDENT CONDITIONS CONTRIBUTED TO THE GRAND CANYON
1. Presence of a thick stack of stratified rock
2. Vivid and varied color within these strata
3. Massive and widespread uplift of this strata so that it remains relatively flat lying
4. An arid climate
5. Presence of large rivers flowing through the region
HOW RIVERS CARVE CANYONS
FLOODS
The Grand Canyon was NOT carved by the slow and inexorable wearing away of the bedrock – the solid uneroded substrate below the river, or by the vast amounts of silt and sand that once traveled down the river and are now trapped behind the Glen Canyon Dam.
Bedrock is rarely exposed to muddy water flow as up to 75 feet of silt, sand, gravel and boulders deposited during floods rest on top of the bedrock, protecting it from erosion.
Rivers like the Colorado actually only deepen their channels during relatively rare, large-scale floods. When the volume of water during a flood is doubled, its ability to transport large size material is quadrupled. A 4 times increase results in a 16 times increase in size of the material moved. The huge amounts of rocky debris in motion – in huge floods the carrying capacity may be so large that the entire mantle on the bedrock is carried downstream – exposing the bedrock to car sized boulders rolling and forcefully pounding the bedrock and breaking off large chunks. The waning stage of each flood leaves a new mantle of sand and gravel. These catastrophic floods may have been frequent.
Spillover Theory. Closed interior basins are on and adjacent to the Colorado Plateau. A lake may have existed along the course of the Little Colorado. When one basin overflowed, it could have catastrophically filled the next basin and so on downstream.
Ice Age Deepening – Ice Age tectonic events (the Toroweap and Hurricane faults occurred 30,000 to 4000,000 years ago) altered relative elevations of the western and eastern parts of the canyon. Ice did not cause or affect the rivers shape or profile (glaciers were never this far south). But the Colorado River’s headwaters extended north to glaciated mountains. Over at least 2 million years, mountain glaciers advanced and retreated numerous times alternately storing and freeing large amounts of water relatively quickly. Actually we are still in an ice Age as the last 10,000 years are interglacial.
Lava Dams. There were at least 13 lava dams formed in the Canyon between 850,000 and 100,000 years ago. All were eventually destroyed even though basalt lava is hard and dense but it was removed relatively quickly regardless of its resistance to erosion. Some dams were over 2,000 feet high and the one extending down from Lava Falls was 84 miles long, but all were removed before the next dam occurred. They start at Lava Falls at mile 179 and lava/basal formations are visible to mile 255.
These voluminous lava flows sometimes dammed the Colorado River creating large temporary reservoirs. Up to 13 dams were formed, some of which were hundreds to thousands of feet height. They were inherently unstable however, as they formed on top of loose river gravel, or because the lava shattered upon contact with river water. On at least five different occasions, these lava dams failed catastrophically in huge outburst flood events.
UPLIFT OF LAND
A mature plateau landscape dominated until the cycle of canyon cutting began 6 million years ago.
A grade is necessary to carve canyons. The North American plate drifts SW relative to the Pacific Plate causing crumpling and uplift and some of the vertical uplift. Heat generated with the earth causes the crust to rise. The Colorado Plateau delaminated from the mantle of the crust as it was lighter. The seas last left the area about 80 million years ago leaving less weight. The Colorado Plateau escaped the intense deformation in the Rocky Mountains.
There was significant uplift in the last 6 million years. Deposits laid down in the Gulf of California are now 1800 feet above sea level.
The western edge of the Colorado Plateau and the Grand Canyon are defined by the Grand Wash Cliffs.
FAULTS
Several faults cross the Colorado at right angles. All raise the land on the east upstream side. The margin of the uplift is called the kickpoint. It is attacked by flowing water and migrates upstream causing deepening of the canyon in that direction. For example, Niagra Falls, prior to being altered to produce electricity, migrated upstream almost 4 feet per year so that the downstream gorge is now 7 miles long and 160 feet deeper over the last 10,000 years.
The cumulative uplift of the Toroweap and Hurricane Faults in the western Grand Canyon in the last 3.5 million years equals about 1,900 feet. Therefore ⅗ of the depth of this part of the canyon was probably accomplished in this short time.
CLIMATE
This determines 1. The amount of runoff and thus the carrying capacity of water. 2. Freeze/thaw cycles break open rocks and chunks fall off cliffs. 3. Heavy rain causes landslides 4. Wind is of minor importance as grains are too small.
In tropical wet environments, the faster chemical breakdown of rocks causes everything to erode epically. The Colorado Plateau is arid, so erosion was slow away from the waters edge and a much deeper gorge resulted.
80 million years ago: sea retreated, climate humid sub-tropical.
55 m years ago: Broad plateau surfaces developed and the area was its hottest and most humid so that erosion was broad and planar. This removed large sheets of rock whose remnants still exist in Zion and Bryce National Parks.
15m years ago: aridity increased resulting in more localized erosion along river courses.
5-6m years ago: aridity increased and rivers began cutting their deep canyons.
HEADWARD EROSION & STREAM PIRACY
This results from uplift when the increased gradient of streams increase their erosive power. There was significant uplift of the Grand Canyon area in the last 6 million years.
For two rivers on opposite sides of a drainage, the steeper gradient stream lengthens its channel in the upstream direction, capturing terrain that previously belonged to the low gradient stream.
This steeper river moves more and bigger material and readily deepens its channel, eventually undercuts and steepens the headwall area near the drainage divide. This is called headward erosion. This may proceed until direction of runoff changes (drainage reversal).
KARST COLLAPSE
This entails an intial subsurface integration by groundwater flow throygh confined caves that ultimately collapse and create a surface connection. This is a subterranean-to-surface process. This may explain how the Kaibab Plateau was cut into from the lower Marble Platform via caves in the Redwall Limestone.
EROSIONAL PROCESSES
Although there would be no Grand Canyon without the Colorado River, the river itself has done very little of the cutting. Other forces of erosion such as gravity, freeze and thaw cycles, and side canyon dissection have made the canyon much wider than the river.
OTHER FACTORS
Why do dry tributary streams enter the main river at grade? As many are dry 95% of the time, one would expect them to enter high above the river grade. But these side canyons carve their depth only during flood events. Their steeper gradients carry much larger material.
Width of River. The river has probably always been about as wide as it is now – about 300 feet on average. The canyon’s width is the result of tributaries undercutting the rim and causing retreat backwards.
Width of Canyon. Freezing, thawing, undercutting and gravity cause the layers at the top exposed to erosion for the lonest time to erode faster. Possibly more important is the faster erosion of soft shales undercutting and collapsing the harder overlying layers. This is likely why the canyon is wider at the top – differential erosion of the variable strata.
The river cut the Grand Canyon not on the crest of the vast continuous plateau, but on its south flank. The rock strata dip to the south at 1-2 degrees so that the North Rim at 8200 feet is 1200 feet higher than the South Rim. This causes more runoff to enter the canyon from the north side and thus more erosion. So the north rim is eroded back away from the river about twice as far as the south rim.
Rock Type. This has a significant role in determining the overall width and profile of the canyon walls.
But has virtually no effect on limiting the rate of down cutting of the river. The Colorado River has cut through approximately 19 different sedimentary formations and 2 crystalline rocks at the very bottom – each with its own resistance to erosion based on rock type and hardness or density. But this was meaningless as canyon cutting occurred in discrete periods of time that involved the large and more important active uplift, climate change and increased runoff. It doesn’t matter – the channel will deepen as quickly.
Punctuated Equilibrium. Most of the canyon’s history involves periods of stability with no deepening or widening to be disrupted episodically by periods of great change due to increased uplift, climate change or runoff amounts. This all impacts the ability to say “How old?”
Over 800 cubic miles of material have been removed in the Grand Canyon. Most of this dirt is in the Imperial Valley.
GEOLOGY & TIME LINE
This is difficult to understand. Over the last 2 billion years, tremendous amounts of sediment were constantly being eroded, washed down from mountainous areas and deposited in ancient seas. They were preserved in this area as stratified rock layers as the earth’s crust here was actively subsiding (ie lowering) along the shoreline of the continent. Plate tectonics was forming and reforming the supercontinents of Pangea and Godwana. This subsidence created the vertical space for more and more sediment to accumulate. This time involved the longest span of geologic time when the Grand Canyon region was near sea level. Then there was a much shorter interval when the rocks were uplifted, erosion removed and destroyed them and more strata up to 2 ½ miles thick were deposited. This again eroded away in most places all the while being folded into the earth’s crust. Ancient environments included wave-washed beaches (Tapeats Sandstone), tropical seas teeming with sea life (Redwall Limestone) and vast Sahara-like deserts (Coconino Sandstone). Gaps called unconformities represent missing chapters in the geologic record when erosion removes layers of rock and new layers are deposited on top, creating a time gap.
Only in the last 6 million years was the actual Grand Canyon formed by the Colorado river.
Three different rock strata sequences are shown in the geologic record: flat-lying strata that make up the bulk of the canyon walls; an inclined set of strata below these representing the Grand Canyon Supergroup, and father below, a completely different package of metamorphic rock of igneous origin. Each rock unit or formation records the multiple environments that once existed there, while the gaps (unconformities) between the three packages record the specific mountain building or erosional events that separate them.
Do you understand now?
2 – 1.8 billion years ago.
Sand, mud and lava accumulate to a great thickness as volcanic islands collide with the southern edge of ancient North America.
1.8 – 1.2 billion years ago.
The oldest rocks in the Grand Canyon are between 1.84 and 1.65 billion years old and are considered the basement of the North American continent. They originated as the above layers of sandstone, shale, or volcanic rock that ultimately became buried, deformed and altered in a great collision between ancient North America and other pieces of the earth’s crust.
During collision, the rocks were folded deep into the crust where they were altered by heat and pressure (metamorphosed) forming a crystalline rock called the Vishnu Shist. Deeper still, other rocks melted completely forming magma, which rose upward and intruded into the shist, creating a pink-coloured igneous rock called Zoraster Granite. It is believed this metamorphism occurred some 13 miles below the surface and that ancient mountains most likely capped the Grand Canyon region at this time.
These basement layers are seen today in the deep recesses of the Upper, Middle, and Lower Granite gorges, and are first encountered below Hance Rapid at river mile 78.
During the next 400 plus million years, erosion attacked and buried these ancient mountains. The confining weight that was removed by erosion allowed the rocks below to progressively rise. In this way, the Vishnu Shist was eventually brought up to the Earth’s surface. Erosion smoothed the topography into an undulating plain across the landscape.
1.2 billion – 740 million years ago.
On this subsided surface of eroded mountains, a sequence of strata 2 ½ miles thick was deposited during shallow marine, coastal dune, sluggish river, and volcanic environments. These layers are called the Grand Canyon Supergroup, creating the Greatest Angular Unconformity.
They were later subjected to faulting that disrupted and tilted the strata.
740-525 million years ago.
Stretching of the earth’s crust creates faults and tilts the Supergroup rocks down to the northeast. Some blocks were faulted down and buried, thus escaping the 200 plus million years of erosion that followed. Most was removed and only wedge-shaped, tilted-up remnants remain today and why the Supergroup rocks are found today in only a few localities in Grand Canyon.
These exquisitely coloured and tilted rocks are a nice diversion in a canyon known for it flat-lying strata; the best exposures are seen at river level between river miles 63-78, and 131-139.
525 million years ago.
An ancient sea slowly inundates the eroded surface and creates the Great Unconformity. The Tapeats Sandstone rests immediately above this gap in the rock record.
525-270 million years ago.
Throughout most of the Paleozoic Era (some 255 million years of time), many different layers of sediment accumulated and hardened into the strata that enclose the Grand Canyon.
240-70 million years ago.
Mesozoic-age deposits cover the Grand Canyon region with up to 10,000 feet of additional rock strata. These deposits are mostly eroded now except for remnants at the Vermillion and Echo cliffs near Lee’s Ferry.
80-70 million years ago. The last sea withdrew from the Grand Canyon region leaving the low-lying landscape a blank canvas with an initial river system.
70m-40m years ago. The Grand Canyon region began its rise above sea level. Uplift of the Rocky Mountains and the Colorado Plateau placed all of these rock units into a position where they were subject to erosion. Until 30m years ago, the early river system flowed to the northeast, opposite its direction today.
30m years ago. Source area for the NE flowing streams subsided through faulting and erosion
30m-16m years ago. There is no evidence of any rivers as the Colorado Plateau was eroding and the rivers too small to leave sediment because of aridity with only intermittent streams into interior basins.
16m years ago. Interior drainage basins existed and drainage basin reversal occurred. The old Mogollon Highlands, a range of mountains that existed south and west of the Colorado Plateau were destroyed by the faulting of the Basin and Range Disturbance. Therefore, any precursor of the Colorado River could not have existed before this. Subsidence of the Basin and Range caused a tremendous difference between it and the Colorado Plateau.
6m years ago. The San Andreas Fault created the Gulf of California and drainage was directed of the southwestern edge of the plateau. The young Colorado was relatively short and of moderate volume fed from the north by the ancestral Virgin, Kanab and Paria Rivers and from the south by the Little Colorado. These multiple river systems were integrated by headward erosion and stream capture as the young Colorado was able to capture drainage area from other nearby rivers because of its steeper gradient and its shorter course to the Gulf of California. Combined with catastrophic flood events, such as spillover of lakes, lava dam releases, and Ice Age Deepening, the Colorado River we see today was created.
3.5m years ago. The Grand Canyon significantly deepened. This was accomplished by the difference between the plateau edge and the Basin and Range, upstream deepening of the canyon after movement of faults and increased runoff in the Ice Age.
830,000 to 100,000 years ago. Spectacular lava flows cascading into the Grand Canyon created lava dams and perhaps reservoirs behind them that eventually loosened huge outburst floods when the lava dams failed catastrophically.
Over 6 million years, erosion carved through an additional one-mile thickness of rock to create the Grand Canyon. Today farmers in southern California grow crops in eroded material from the Grand Canyon and the Rocky Mountains.
