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In April, 2014, 20 ISU Geology students and faculty set off for the north rim of the grand Canyon. We stayed at Tuweep, from which we could investigate faults, volcanoes, bedrock channels, and (limited) stratigraphy). Student groups, led by grad students and Seniors, each took a separate topic to focus on and share with the rest of the class. The following are topic summaries, prepared by undergraduates from the Freshman through Junior levels:
Formation of the Grand Canyon: Competing Ideas
The “Young Camp”
Rebecca Flower’s 2012 paper turned our understanding of the Grand Canyon on its head. Prior to her paper it was accepted by many that the Grand Canyon had been cut by the Colorado River within the past 5-6 million years. Estimated incision rates for the past 100 thousand years are in line with the 5-6 million year old Grand Canyon hypothesis. Even still the “young” hypothesis had to be adapted to Flowers’ new data, which can be recreated (and has been in Karlstrom’s most recent paper, 2014). As a result the most recent “young” hypothesis presented by Karlstrom argues that portions of the Grand Canyon were incised as separated paleocanyons at 70-55 million years ago by northeast flowing rivers. These canyons were not connected at this time, in fact they did not become connected until the current Colorado River flowed through, starting 5-6 million years ago, and joined the canyons. I believe this is the most reasonable hypothesis, as recent Apetite-He results appear to fit this narrative the best.
Works cited
Flowers, R.M., and Farley, K.A., 2012, Apatite 4He/3He and (U-Th)/He evidence for an ancient Grand Canyon.: Science (New York, N.Y.), v. 338, p. 1616–9, doi: 10.1126/science.1229390.
Karlstrom, K.E., Lee, J., Kelley, S.A., Crow*, R., Young, R.A., Lucchitta, I., Beard, L.S., Dorsey. R., Ricketts*, J.W., Dickinson, W.R., and Crossey, L.C., 2013, Arguments for a young Grand Canyon: Technical Comment on: R. M. Flowers & K. A. Farley, Apatite 4He/3He and (U-Th)/He Evidence for an Ancient Grand Canyon: Science, Nov. 2012, 10.1126/science.1229390
Karlstrom, K. E., Lee, J. P., Kelley, S. A., Crow, R. S., Crossey, L. J., Young, R. A., ... & Shuster, D. L. ,2014, Formation of the Grand Canyon 5 to 6 million years ago through integration of older palaeocanyons. Nature Geoscience.
Sears, J.W., 2013, Late Oligocene – early Miocene Grand Canyon : A Canadian connection ?: , p. 4–10, doi: 10.1130/GSATG178A.1.4.
--Michael Ward
The “Old Camp”
Despite everyone agreeing on the grand nature and beauty of the Grand Canyon, not everyone agrees on its origin. Karl Karlstrom believes that the formation of the modern Grand Canyon occurred around 5-6 million years. I do not agree with this, I believe based on my observations of the cutting of the sandstones and limestones that incision rates would not be nearly high enough to carve the Grand Canyon to the depth that it is. Research by Victor Polyak “(Polyak et al, 2008) used features found in caves in the canyon's walls to try to put a date on the natural wonder. The researchers studied structures known as mammillaries or "cave clouds" — deposits that form at or near the water table level, and dated the features using uranium-lead isotope dating techniques.” This research put the date of these features at least 17 million years ago in some features. To the same effect, Rebecca Flowers and Kenneth Farley, of University of Colorado, Boulder and California Institute of technology, respectively, have found exhumation ages of 55-70 million years ago in various portions of the Grand Canyon (Flowers, 2012). I believe that both of these points of evidence are sufficient to conclude the age of the Grand Canyon is older than 5-6 million years. I believe future research needs to locate sediments sourced from the, Supai Sandstone and Hermit Shale groups (which are located near the top of the canyon) so that the timing of incision through these formations can better be constrained.
Work Cited:
Flowers, R.M., and Farley, K.A., 2012, Apatite 4He/3He and (U-Th)/He evidence for an ancient Grand Canyon.: Science (New York, N.Y.), v. 338, p. 1616–9, doi: 10.1126/science.1229390.
Polyak, V.J., Hill, C., Asmerom, Y., 2008 Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table-Type Speleothems: Vol. 319 no. 5868 pp. 1377-1380, geomorphology.sese.asu.edu/Papers/Polyak_etal_Sci_08.pdf
--Justin Huse
The life of John Wesley Powell and the events leading to the 1869 Grand Canyon expedition
The life of John Wesley Powell and the events leading to the 1869 Grand Canyon expedition
Powell was born in 1834, the son of Joseph and Mary Powell, emigrated to the U.S. from Shrewsbury, England. He grew up on a farm in Wisconsin where he was home schooled and grew strong interest for the outdoors and natural sciences. In the 1850s, he spent 4 months walking across Wisconsin and rowed the Mississippi and the Illinois rivers. Powell was elected to the Natural History Society in 1859, at age 25. Loyal to the union, he enlisted in 1861 where he became major and lieutenant colonel but was always referred to as “Major Powell”. He kept his strong interest for natural sciences throughout the war, often witnessed looking for rocks and fossils in the trenches. At the end of the war, he taught geology at Illinois Wesleyan University. He became the first college professor to combine field teaching with Western exploration by leading a series of expeditions to the Rocky Mountains and around the Green and Colorado rivers. Powell decided later to explore the Green and Colorado rivers by boat in order to map this region which was until then a blank spot on the map. This expedition is known as the 1869 Grand Canyon Expedition.
-Geoffroy Prigent
Powell, the Grand Canyon Expedition of 1869 and Naming Along the Colorado River
Major John Wesley Powell’s 1869 Grand Canyon expedition, the first of its kind, was an immensely important journey for scientific, cultural, and historic reasons. Powell and 9 other men traveled over 1000 miles of uncharted territory in just over 3 months from May 26 to August 29. They mapped the landscape, collected samples, lost boats and provisions, camped through storms, rode the rapids, and exited the canyon near present-day Lake Mead. One man left the expedition after a month on the river; three other men hiked out of the canyon just 3 days before the expedition ended only to be killed by Indians.
This being the first explorative expedition of the Grand Canyon by river, Major Powell named and described several of the canyons and rapids that still bear those names today. Some of those include:
“Flaming Gorge,” named May 26 for its vibrant colors
“Canyon of Lodore" and “Disaster Falls,” named June 9-12; the party also lost their first boat, No Name, and 1/3 of their provisions to these rapids
“Hell’s Half-Mile,” named June 15-16 for a treacherous section of the river that drops 100 ft in a half-mile
“Antelope Valley,” named June 27-28 for a calm section of river with meadows on either side where Powell and the crew saw antelope grazing
“Desolation Canyon,” named July 7-9 for a dangerous section of river with steep cliffs forcing the crew to ride the rapids; they flipped one boat, broke rowing oars, lost two guns and barometers, and blankets
“Gray Canyon,” named July 13 for the gray sandstone in the cliffs
“Labyrinth Canyon,” named July 15-16 for its towering canyon walls
“Lava Falls,” named August 25 for the remnants of cascading lava that flowed into the Grand Canyon from Vulcan’s Throne, a cinder cone volcano perched on the north rim
“Separation Rapids,” named in 1939 for the place where, 2 days before reaching the end of the expedition, Seneca and O.G. Howland and William Dunn, fed up with Powell and the expedition and fearing their lives, chose to leave the group and hike out of the canyon; they were never seen or heard from again.
On August 29th, starving and weary, Powell and the remaining 5 other men exited the canyon and reached Grand Wash. Despite the loss of food, materials, samples, instruments, and life, the trip was a success. Powell, the first explorer through the Grand Canyon, now knew the river was passable (albeit treacherous in places), and immediately began planning for a second expedition that he lead in 1872.
-Angie Young
Bedrock River Processes
The Grand Canyon is influenced by many processes. One of the most notable being bedrock river processes. The Grand Canyon is classified as a bedrock river because it has a long term capacity to transport bedload, and is actively incising through in-place rock in the long-term. There are three major controls on bedrock channels: discharge, lithology (dip of the bedding), and rock uplift rates. These three together control the channel. Sediment is transported in three ways in the river, dissolved load, suspended load, and bed load. Dissolved load is ions dissolving in the water and being carried. Suspended load consists of fine grained material such as sand or silt which gets carried in the water column downstream. Bed load is the most difficult to move due to its size and mass, and generally skips along the bottom of the river. These types of sediment transport can cause erosion and incision which breaks up the bedrock. Sediment hitting rock acts like sandpaper wearing down rock surfaces, and this is called abrasion. Cavitation is when air bubbles in the water implode when they experience areas of higher pressure, this implosion creates a jet of water which damages rock. Plucking involves loose blocks of bedrock which can be entrained in the flow. The amount of sediment available to the river influences the amount of erosion occurring. With an increasing amount of sediment, erosion increases to a point because the river has more tools to erode bedrock with. After that point there is too much sediment in the water which armors the bed and protects it from erosion.
-Ryan Goldsby and Justin Foster
Dam It. Glen Canyon Dam's Impact on the Colorado River
When construction ended on the Glen Canyon Dam in 1966 there were many consequences on the downstream hydrology and ecology. Prior to completion of the dam, the Colorado River was prone to annual cycles of flooding. These cycles ranged from summer lows of 1000 cubic feet per second (CFS) to as high as 100,000 CFS during spring runoff. Water temperature also changed seasonally, ranging from 32 degrees to 80 degrees Fahrenheit. The water in the river now flows at 5,000 to 25,000 CFS year round and remains a chilly and stable 48 degrees.
The Glen Canyon Dam now traps 90% of the sediment that once flowed freely through the Grand Canyon. The Colorado River’s previous flooding cycle brought with it a turbid, muddy flow loaded with nutrient packed sediments, which have since given way to clearer and colder waters. Introduced trout species thrive in the river’s new conditions, while native species, such as the Humpback Chub, who spawns in backwater areas behind sandbars, are struggling as sediment levels recede and sandbars disappear.
Pre-dam, the Colorado River was able to maintain its sandbars very well. The amount of sandbar erosion was near equal to the amount of sandbar replenishment. Maintaining geomorphic features outside of their original depositional environments is nearly impossible; therefore, since the dam was built, and sediment deposition dropped significantly, sandbar maintenance has become very difficult. Along with fish, disappearing sandbars also affect plant life and tourism. Willow trees that are able to grow in rocky conditions are slowly choking out those plants that thrived in the more variable environment below the high-water level of the pre-dam Colorado River. River goers, be they rafters or hikers, are finding fewer and fewer places to camp at the river level and recreation in the area could possibly see a significant decline over the coming years.
Even though the Glen Canyon dam creates power, revenue, and recreation on its reservoir side, some negative effects of it are becoming apparent and arguably problematic. We are left to decide for ourselves if the consequences, foreseeable or not, were worth damming, or damning, the mighty Colorado.
References
1.http://www.usbr.gov/projets/Facility.jsp?fac_Name=Glen+Canyo+Dam&groupName=Overview
3.http://www.hcn.org/issues/230/11324
4.Infalt, Susan B. (2005-03-10)"Colorado River Native Riparian Vegetation in Grand Canyon: How Has Glen Canyon Dam Impacted These Communities?". Department of Geology. University of California Davis. Retrieved 2011-05-27.
6.Beus, S. and C. Avery 1993. The influence of variable discharge regimes on Colorado River sand bars below Glen Canyon Dam. Glen Canyon Environmental Studies, Report PHY0101, Chapters I through 7. Northern Arizona University, Flagstaff, AZ
7.http://pubs.usgs.gov/fs/2011/3012/fs2011-3012.pdf
--Chris Borg and Justin Mckoon
Magmatic guts: structural/tectonic controls and magmatism in Uinkaret Volcanic Field
Structural and Tectonic Controls of the Western Grand Canyon Volcanic Field
The Grand Canyon is my most notably recognized for its spectacular geologic exposures. The Western Grand Canyon is likewise known for its structurally and tectonically influenced volcanic field comprised of basalt flows, scoria cones, dikes, and sills that express an overall linear northeasterly trend as the North American plate migrated in a southwesterly fashion. Perhaps the greatest influence on the migration of this volcanism owes to north-south striking westerly dipping normal faults resulting from westerly directed basin and range extension and the consequential crustal thinning. The three most influential structural controls of the Uinkaret Plateau are the Grand Wash Fault, the Hurricane Fault, and the Toroweap Fault. The boundary between the Colorado Plateau and the Basin and Range province is marked by the Grand Wash Fault that extends from southwest Utah into west central Arizona. The greatest volume of volcanism on the Uinkaret Plateau is bound between the Hurricane and Toroweap faults. Changes in tectonic plate motion and reorganization further impacted the area to result in magma generation. Loss of the subducting shallow-angle, lithospherically hydrating Farallon plate beneath the Basin and Range extensional provinces during Laramide time resulted in intense magma production that is thought to have migrated along the linear conduits of the region.
Pictured above is a remarkable view of the Toroweap fault displaying the offset strata of Pennsylvanian, Supai Group. The flat floors of Prospect Valley (near middle) are the result of lava flows that followed the drainages of the archaic steep-sided Prospect Canyon and gradually filled it up to the level of the Esplanade Platform. What we see on the south side of the canyon is the results of erosive processes incising into the Esplanade Platform continually re-excavating the Prospect Canyon. We can also see that Vulcan’s throne (where the picture is taken) is cut by the Toroweap Fault. Due to poor preservation as the result of hill slope diffusion the structure was not found here; however, consensus among students placed the most probable location off-centered from the Saddle.
-Samantha Kofoed
Volcanism and Lava Dams in the Grand Canyon
Figure 1 Vulcan’s Throne, looking south. Image by Bryan Nicholson
There are four main types of volcanoes: strato, shield, dome, and cinder cone. Vulcan’s Throne is a cinder cone that formed approximately 73,000 years ago as determined from cosmogenic nuclide dating. The last known eruption dates to about 1,000 years ago, which was constrained by pottery shards found in lava flows south of Mt. Trumball (GVP, 2013). Vulcan’s Throne is approximately 1 km wide.
Thirteen lava dams formed from multiple lava flows in the Grand Canyon over the last 1.5 million years. Each lava dam was subsequently eroded by the Colorado River over the course of a few thousand years. Each time these dams blocked the Colorado River a temporary lake formed upstream. Shorelines of the deeper lakes can be found near the base of the Redwall Limestone in the area of the park headquarters. Additionally, shoreline evidence suggest that some lakes extended upstream beyond the present shore of Lake Powell (Dalrymple and Hamblin, 1998).
The majority of lava flows can be classified as either pahoehoe or A’a. During one of the latest eruptions, within the last 10,000 years, a lava flow erupted from the side of Vulcan’s Throne instead of the vent; which makes sense given the unconsolidated nature of scoria and, in particular, Vulcan’s Throne. The lava flow started out as pahoehoe on the esplanade plateau, but it transitioned to A’a as it began to cascade into the canyon. This is because the increase in slope decreased the critical thickness, allowing for a faster flow and greater shearing of the lava.
References:
Global Volcanism Program (GVP), 2013. Uinkaret Field. http://www.volcano.si.edu/volcano.cfm?vn=329010
Dalrymple, B. and Hamblin, K., 1998. K-Ar ages of Pleistocene lava dams in the Grand Canyon in Arizona. Proceedings of the National Academy of Sciences of the United States of America (PNAS). Vol 95, No. 17. 9744-9749, doi: 10.1073/pnas.95.17.9744
-- Lauren Gepner and Gail Martin
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