Arizona State University



Lab TitleWhat makes the Grand Canyon so grand?What is this lab all about? The Grand Canyon of the Colorado River is a “must see” for people who live all over Earth. Some save up for years to make the journey. Certainly, for anybody living in Arizona, it’s a point of pride as Arizona is “The Grand Canyon State”. So what’s the big deal? Here, you will explore the Grand Canyon from the perspective of physical geography.Lab WorthThe points you accumulate for correct answers count towards your grade. Incorrect answers do not hurt your puter program used in this labYou will be given instructions in a canvas module page on how to download virtual world of the Grand Canyon that shows the geology and the topography. In this program, you are a virtual character able to wander around the Grand Canyon’s landscape and rock types. WARNING: There are two different Grand Canyon geovisualizations – this one, and the other focusing on microclimate and vegetation. Interesting maps to download – not necessary to do the labs, but helpful to some studentsNational Park Service map of Grand Canyon National Park: 3D map of the Grand Canyon geologic map of the Grand Canyon: map of the Grand Canyon: relief map of the Grand Canyon area: Angel Topographic Map: SQ general studies criteriaStudents analyze geographical data using the scientific method, keeping in mind scientific uncertainty. Students also use mathematics in analyzing rates to change in the landscape. TABLE OF CONTENTS OF THIS DOCUMENT1. Preface: What makes the Grand Canyon so grand? Page 32. Overview of lab activitiesPage 5Stage A Basic Background: Written material for the basic background quiz that corresponds with the matching audiovisual presentation Page 8Stage B Exploration: Making some basic observations related to the landforms of the Grand Canyon Page 22Stage C more detailed analysis: Exploring connections between topography and rock types in the heart of the Grand Canyon Page 31Stage D synthesis: Short essay analysis of why the Grand Canyon is so grand (or perhaps not grand at all)? Page 59Photo: Courtesy of NASA1. Preface: What makes the Grand Canyon so grand? The Grand Canyon is deep, with an average depth of about a mile (1600 m) and a maximum depth of about 7800 feet (2377 m) if you are standing on the North Rim. Hells Canyon along the border of eastern Oregon and western Idaho, however, is deeper with a maximum depth of 7993 feet (2436 m). The Yarlung Tsangpo in the Himalayas is much deeper at 17,567 feet (5382 m). Some would argue that the Kali Gandaki Gorge (between the peaks of Dhaulgari and Annapurna) in the Himalayas is even deeper.The Grand Canyon is long, about 277 miles (446 km) by most starting and ending points. Again, the Yarlung Tsangpo’s “Grand Canyon” is longer at 308 miles (396 m). The Grand Canyon is not wide by international standards or even national standards. On average, its just 10 miles (16 km) wide as the helicopter flies, and its very narrow at Marble Canyon spanning only 1798 feet (548) meters. Hell’s Canyon, for comparison, is 10 miles wide (16 km). Perspective certainly matters in analyzing this lab’s question, and different sorts of people would probably answer the question differently. The historian Dr. Stephen Pyne wrote an entire book on “How the Canyon Became Grand.” The Hopi consider the Grand Canyon as the place of their creation and hence sacred. A geologist might argue that it’s the rocks on the canyon sides that make it so grand, exposing rocks as old as 1.75 billion years near the bottom and 230 million years near the top with abundant fossils and the ability to see clearly such things as unconformities. Other types of scientists would make claims to grandness as well, for example, biogeographers study a variety of plant and animal life that ranges from harsh desert at the bottom to spruce forests on the North Rim. The perspective of the writers of this laboratory admit to seeing the Grand Canyon as physical geographers. Also, our perspective was influenced heavily by taking geography students on field trips to the Grand Canyon and listening to their views. In the end, for a physical geographer, the grandness comes down to a combination of factors that could be summarized in this diagram showing the components of physical geography. All different aspects of physical geography would influence our answer.Image: Courtesy of Ron DornThis lab, thus, starts to answer the question of “Why is the Grand Canyon so grand” from the perspective of physical geography in general, and especially from the perspective of the geomorphology (landforms) part of physical geography. Because the landforms of the Grand Canyon depend heavily on the geology and the water/hydrology, these subjects are going to be part of this lab. Caveat about the lab: There is no doubt that an online lab about the grandness of the Grand Canyon is missing out on our five traditional sense of sight (and the changes in lighting), hearing of the wind whistling through the canyon, the taste of trail and camping food, the smell of plants, and touching of different rock textures. In the end, you will just have to experience these at the Grand Canyon for yourself. 2. Overview of lab activitiesThe purpose of this section is to provide you an overview of the activities you will complete. Before you dig into the lab, you are also welcome to learn extra background information about the geology and hydrology of the Grand Canyon in the third section. You certainly do not have to read the third section in detail to do this lab, but you will probably find that this enrichment material will help you get more out of “playing the video game” and the other lab activities.2.1 Parts of this lab: You should have already completed Stage 0 (begin). If you did not, please stop now. Go back to canvas. Find the Stage 0 for this lab, and do that first. Stage A gives you some basic background about the topography of the Grand Canyon and its link to the different geological formations. Stage A is followed up with a short quiz. It does not matter whether you read the background material or watch the audio-visual presentation. Its all the same material. In the exploration of this lab (Stage B), you will get a chance to enhance your grade by learning a bit about the Grand Canyon and the sorts of activities you will engage in if you decide to move onto Stage BC. In the detailed analysis part of the lab (Stage C), you will use the video game geovisualization to explore in greater detail the connection between the geomorphology and the rock types of the Grand Canyon. Then, Stage D of the lab encourages you to synthesize what you have learned in writing a short four-paragraph essay on why you think the Grand Canyon is grand. Most of this essay tasks you with covering what you learned in lab activities, but you are also encouraged to explain your own personal perspective on the lab question. 2.2. The study area The entirely of the Grand Canyon is far too big to analyze in this introductory laboratory. Thus, all of the laboratory activities will focus on what many consider to be the heart of the Grand Canyon, centered between the two National Park visitor centers on the North Rim and South Rim. The frame of the study area can be seen inside this map of northern Arizona, courtesy of the Arizona Geographic Alliance:A NASA space shuttle image from the winter of 2019 captures this study area as well, where up is to the East:This National Park Service map shows the study area and a bit of the surrounding area.STAGE A: BASIC BACKGROUND MATERIAL FOR THIS LABTHIS CLASS HAS NO PREREQUISITES. The assumption is that you’ve never heard of anything like this material before. Thus, this stage provides the basic background that you will find helpful in completing this lab.You can learn this basic material in different ways. You can read this section, or you can watch an audiovisual presentation that you can access through the Starting Page for the lab and also Canvas Stage A module page. When you access that audiovisual presentation you will be asked for a logon and a password. It is not your ASURite ID. It’s a general logon (gph111) and password (gaia). Background on Grand Canyon Geology This is not a class about geology. However, to understand the landscape of the Grand Canyon, it is very helpful to understand more about the rocks. Also, you will come to understand that geologists think differently about time than anybody else. They think in terms of eras (hundreds to tens of millions of years long) and periods (tens to millions of years long) distinguished by the nature of fossils found in the rocks. Not only that, the oldest rocks seem to excite geologists more than younger rocks. This excitement over old rocks comes out in the in the Grand Canyon with the two oldest eras exposed. Deep in the inner canyon are Proterozoic Era rocks that are most metamorphic and igneous with very steep slopes because these rocks are hard:[Note: most of the figures in this section are courtesy of National Park Service materials.]The second oldest geological era exposed in the Grand Canyon is the Paleozoic with lots of great fossils. Within the Paleozoic, Grand Canyon rocks include the Cambrian with fossils of crab-like animals and shells. Above (younger) than the Cambrian are Devonian and Mississippian periods (also known as early Carboniferous) with shells and coral fossils. Then comes the Permian era at the top with a mixture of sea fossils (shells, corals) and terrestrial fossils (e.g. insect wings, animal tracks). Quick check: What are the two geological eras exposed on the walls of the Grand Canyon? This is the sequence of Paleozoic layers (called formations by geologists) you will see in the game, but ‘painted’ on a photograph. You don’t have to memorize these formations, but I guarantee you will come to know the Kaibab Formation (a limestone rock) as the top and youngest layer of the sequence! The Kaibab Limestone is what makes the plateaus on the South and North rims of the Grand Canyon. You will also get to know the Kaibab Limestone, the Coconino sandstone, and the Redwall Limestone because they make up the big cliff faces. In contrast, the Bright Angel Shale makes up the lower-angled slopes (ramps). So right away, you can see in the picture above that rock type can influence the landscape, where rocks that are harder to erode make cliff faces and rocks easier to erode make the lower slopes.Quick Check: What is the top (youngest) formation in the Paleozoic sequence of the Grand Canyon that also makes up the plateaus that surround the Grand Canyon?A founding “father” of geomorphology, G.K. Gilbert interpreted slope steepness as a function of a rock’s resistance to rock decay (weathering) and erosion. Gilbert went to the Grand Canyon and felt that the rocks of the inner gorge have very steep slopes because they are so resistant. Rocks that are very weak do not need steep slopes to erode them. However, very strong rocks (resistant to decay and erosion) will just get steeper and steeper slopes until they do start to erode. Gilbert, thus, discovered that slopes adjust their angle to be able to transport rock material (or soil if there is a vegetation cover). Thus, the inner gorge slopes are so steep because they are highly resistant to both decay and erosion. Grand Canyon Unconformities: These are not really a part of this lab, but they should be mentioned here because geologists get very excited when they see an unconformity, especially when it is so well exposed and so dramatic as in the Grand Canyon; in the Grand Canyon, it is called the “Great Unconformity”. What’s the big deal? A very long amount of time and a lot of geological events are between what’s underneath and what’s above this unconformity. Geologists also stress that because the top of the Great Unconformity is pretty flat, it represents a long time for erosion to erode the land surface to low relief.Underneath the Great Unconformity are rocks of the “Grand Canyon Supergroup” that represent a lot of geological events including deposition of Proterozoic Era rocks, faulting, and then erosion of these rocks.All of the rocks above the Great Unconformity are from the Paleozoic Era, a time when organisms like marine shelled life, fish, amphibians, reptiles, and land plants first appeared. [Sorry if you like dinosaurs, birds and flowering plans; you will have to travel north of the Grand Canyon to see Mesozoic rocks with those types of fossils.] All of the rocks underneath the Great Unconformity are much older from the Proterozoic Era. Quick Check: Geologists make such a big deal of unconformities, especially the Great Unconformity in the Grand Canyon. What is an unconformity? You may be amused by this cute way to learn the Paleozoic layers in the Grand Canyon in order from YOUNGEST (top of the sequence) to OLDEST (bottom of the sequence). No reason to memorize these. You will learn them in playing the game and doing the lab. ?Know - Kaibab Limestone?The - Toroweap Formation?Canyon’s -Coconino Sandstone?History: -Hermit Shale?Study - Supai Formation?Rocks - Redwall Formation?Made -Muav Limestone?By -Bright Angel Shale?Time -Tapeats SandstoneIn addition to the rock layers, ancient faults (no longer active) will influence the topography seen in the lab. In particular, there is a very straight feature called Bright Angel Canyon. The rocks were faulted (broken) in the Proterozoic Era and then again in the time frame of 50-80 million years ago (long after the Paleozoic rocks were deposited) in a time geologists call the “Laramide Revolution” when the Grand Canyon area was uplifted (along with the Rocky Mountains). The fault itself certainly did not make the Grand Canyon, but crushing the rocks made them easier to erode – making them the location of Bright Angel Creek. The reason why Bright Angel Creek is a canyon is that the main river – the Colorado River, eroded down to a lower elevation. Each time the Colorado River eroded down just a bit, Bright Angel Creek could also erode down some more. Also, as Bright Angel Creek eroded down to lower-and-lower elevations, it also extended the canyon further by eroding headward (in an uphill direction). Geomorphologists call this “headward erosion”. Quick Check: Why are some of the side canyons (e.g. Bright Angel) of the Grand Canyon so straight? If you want to learn some more and really nerd out about the rock types of the Grand Canyon, for enrichment, you are welcome to watch a presentation made by Professor Larson of Mankato State University when he was a Ph.D. student at ASU. It’s a tour of what you would see walking down to the bottom of the Grand Cayon from the South Rim:You will need a special logon (landforms) and password (rock) on some aspects of Grand Canyon geomorphology This section provides some insight into the following questions:? how did the Colorado River start (come into existence in the Grand Canyon area and start to erode downward? ? when did the Colorado River come into existence in the Grand Canyon area and start to erode downward?? are canyon deepening and canyon widening processes different? ? how did the Colorado River deepen the canyon?? how do the slopes on the side of the Grand Canyon erode back from the river?? why do you see so much bare rock in the Grand Canyon?? how did all of the small drainages (watersheds) develop on the side of the Grand Canyon? How did the Colorado River start (come into existence in the Grand Canyon area and start to erode downward? The answer to this question has to explain how the Colorado River was able to cut through a mountain. The image below from the International Space Station shows a forested region of higher elevation topography that the Grand Canyon splits into two parts. The darker green forest identifies the location of a geological feature that formed about 50 to 80 million years ago in the “Laramide Revolution” when the entire Colorado Plateau was uplifted. This “Kaibab Upwarp” is a very large mountain, and the Colorado River cuts right through this mountain in the core of the Grand Canyon between the North Rim and the South Rim. Image: Courtesy of NASA, International Space Station Photo Quick check: what is the name of geological upwarp structure (mountain) that the Colorado River crosses (and is the location of the heart of the Grand Canyon)? There are only four ways that rivers can cross geological uplifts (mountains) like the Kaibab Upwarp. Dr. John Douglass is the world’s foremost expert on the formation of the Grand Canyon, and he created a diagram to show the four ways: John Wesley Powell thought that Colorado River was antecedent, in that it predated the uplift that took place between 50 and 80 million years ago (Laramide Revolution). As you will learn in the next section, the age of the river itself is much younger – even though some geologists think there could have been a super ancient canyon in this location (a view that the developers of this lab do not hold). All of the other three processes have their advocates. Arthur Strahler suggested that some aspects of superimposition could apply in the Grand Canyon, although not getting across the Kaibab Upwarp. Newberry, Blackwelder, and then John Douglass and Norman Meek all think lake overflow caused the Colorado River to be born. Many different investigators favor piracy by different processes such as headward incision and groundwater sapping. You will not learn here what the developers of this lab think. If you want to dig deeper into this topic, take GPH 211 (the landform processes class) that has the formation of the Grand Canyon as an assignment. What’s important is that the origin of the Grand Canyon does not matter to you finishing this lab. Its just a question that everybody asks. The next question of when is important to you doing this lab. When did the Colorado River come into existence in the Grand Canyon area and start to erode downward?About 4.8 million years ago is the answer. Recent research conducted by the Arizona Geological Survey and colleagues have done award-winning research in establishing when the Colorado River came into existence. I encourage you to read the article in the footnote. In brief, before the Colorado River came into existence, there were a series of closed depressions between present-day Arizona and Nevada-California sometimes forming lakes with deposits at the bottom. The first influx of river water into these lakes started about 4.8 million years ago. As Dr. Jon Spencer concludes in this article: “Rapid incision of the Grand Canyon began at this time.” The Colorado River then eroded downward through the Paleozoic rocks down to close to its current level by 1.2 million years ago, as explained below. Quick question: how long ago did the Colorado River start to incise into the rocks of the Grand Canyon? And when did this incision (down cutting) of the Colorado River each its present-day elevation (level)? Are canyon deepening and canyon widening processes different? Yes! Although many people think that the Grand Canyon was created by the Colorado River, this thinking is incorrect. How did the Colorado River deepen the canyon?Rivers incise (cut down into) bedrock when the gradient (steepness) of the river increases. Sometimes, the river’s longitudinal profile (elevation profile along its length) steepens because mountains are uplifted, but this is not the case here. The Rocky Mountains (and the Kaibab Upwarp) lifted 50 to 80 million years ago and have been slowly eroding ever since.In this case, the river’s gradient became steep when it started flowing over the western edge of the Colorado Plateau down into the lowlands in the modern-day Lake Mead area. The giant drop in elevation from the starting elevation of the Colorado River in the Grand Canyon area down to the Basin and Range was about 6000 feet. This big drop gave the river enough steepness to have its flow be very turbulent. Professor Mark Schmeeckle at ASU is a world leader in understanding the importance of turbulence and how this allows rivers to transport sediment and hence incise downward. Thus, the steep river profile allowed a high enough velocity of flow with a lot of turbulence to cut downward (incise). If there is only river incision going on, the canyon would be only as wide as the river. The form would be a slot canyon much more massive than Antelope Canyon. The Grand Canyon widened from two categories of processes: slope retreat and development of drainages. How do the slopes on the side of the Grand Canyon retreat (erode back) from the Colorado River? Clarence Dutton’s study of the region in the 19th century included tremendous artwork that included this view exemplifying a series of steep cliffs, gentle slopes, and steep slopes. The processes operating on these slopes lead to their retreat from the river. The Tonto Platform (fairly low relief surface INSIDE the canyon) was made by retreat of the cliffs above. The cliff faces erode by mostly mass wasting (landsliding). The rocks decay and weaken to the point where they detach and produce rock falls and larger events called rock slides. This is a screenshot video showing a rock slide in the Grand Canyon and the aftermath of another: A completely different way that the Grand Canyon sides retreat (erode back) involves water moving through drainages. No matter whether the drainages are ephemeral small creeks or larger creeks, flash flooding occurs and the turbulence of the flood waters erodes both hard rock and soft rock. When the drainages encounter a hard layer of rock, the flow becomes a waterfall. This all results in the erosion of rock material and the deepening of these drainages as seen in a NPS Video, a video screenshot and a still photo. Clicking on this link brings you to an enrichment video (Deer Creek falls) In general, when layered sedimentary rock erodes back (retreats), in this case back from the Colorado River, you will see the weakness or hardness of the rock through the slope steepness. Often, there are big differences in weakness that produce cliff faces (caprock) made up of strong rock and the footslope made up of weak rock. Erosion of the weak rock undermines the harder rock above, leading to collapse and rock falls (and rock slides). There is another way that steep cliff faces can be produced through collapse and rock fall, and this is spring sapping. Ground water can leak out of cliff faces if the cliff stores water and the rock underneath (e.g. shale) cannot, creating springs. The slow water leak decays the rock, which erodes away and produces cavernous alcoves. Eventually, the roof of the caverns collapse and a new cliff face is born. Image courtesy of TM Oberlander. Image courtesy of TM Oberlander. Quick check: How do the cliff faces on the side of the Grand Canyon retreat (erode back) from the Colorado River??Sedimentary layers in the Grand Canyon are tilted. This occurred when the Colorado Plateau was uplifted during the Laramide Revolution (50 to 80 million years ago). A cross-section of the rocks in the Grand Canyon you see below is oriented North Rim (Kaibab Plateau) on the left and South (Coconino Plateau) on the right. You can probably perceive that the tilt (what geologists call dip) of the rocks are mostly north-to-south. The dip of the sedimentary rock is important in explaining the different widths of the canyon on the north and south sides between the North Rim and the South Rim. Higher elevations are on the north side, giving more opportunity to develop canyon systems (drainages). Also, the tilt towards the south on the north side tends to favor more springs.Rim Why do you see so much bare rock in the Grand Canyon? Part of the reason why physical geographers consider the Grand Canyon so grand is the exposure of bare rock. While trees and soil can cover slopes near the very top on the North Rim, the view everywhere is of exposed rock. This allows dramatic views. An obvious answer is that you see bare rock because the climate is so dry. Once you drop below the rims, the amount of precipitation decreases to the point where trees cannot grow and shrubs are scattered. Since plants tend to hold soil in place, a lack of plants means that loose soil can be eroded. A not so obvious answer to this question has to do with the balance between rock decay (weathering) and erosion (transport of loosened rock material). All of widening of the Grand Canyon starts with the decay of rock (called weathering). The rock must be decayed to the point where it detaches from the hard rock, creating loose material. G.K. Gilbert discovered that slopes that expose lots of bare rock have rates of weathering much slower than rates of transport of rock. He called these slopes “weathering limited”. You have to think about this slowly and in this sequence … If rock decay was faster than transport, then lots of loose rock would accumulate and you would see lots of soil. This is not the case in the Grand Canyon. You see lots of bare rock, because as fast as the rock decays – it is then transported (by water flowing over the surface, by rills, by gullies, by rock fall, by rock slides). This is called a “weathering-limited landscape”.Quick check: Why do you see so much bare rock in the Grand Canyon?How did all of the small drainages (watersheds) develop on the side of the Grand Canyon? A view of the Grand Canyon from the Space Station below shows a lot of side canyons on both sides. These tributaries of the Colorado are all cutting down (incising) for the same reason as the main Colorado River: there is a steep gradient (slope) from the Colorado River up to the rims on both sides. This steepness gives the water flowing in the creeks (typically only after an intense rain) more velocity and turbulence to transport rock and erode their beds. You will probably notice that these canyons are much bigger on the north side than the south side. The Kaibab Plateau on the north side is a much higher elevation. The higher elevation means that there’s more precipitation falling and there’s more topography to erode into as a canyon system (drainage basin) develops. Also, notice the plateau (flat surface) that surrounds the Grand Canyon. It is the plateau topography that contrasts so greatly with the canyon itself. Quick question: what allows the tributary streams (side streams) of the Grand Canyon to erode down to the level of the main Colorado River? How can you connect all of the different pieces in this section? One way to put this all together is to look the two views of the Grand Canyon separated by 140 years: Space Station and Clarence Dutton’s artwork that emphasizes the stair-stepped nature of the topography in the Grand Canyon.About 4.8 million years ago, a newly formed Colorado River started incising down into the Colorado Plateau’s rocks. Rock layers started retreating backwards in response. As the width of the canyon grew, so did its depth. Long enough slopes allowed tributary canyons to develop, and the rock-face retreat processes supplied loose rock to these tributaries, that transported the rock to the Colorado River. However, all of this canyon widening did not overwhelm the transport-capacity of the tributaries or the main river, because both depth incising down. Rock decay, rock detachment, rock fall down into creeks caused the layers to retreat back and allowed the tributary canyon systems to grow. This all continues today, as the canyon is still widening and the rivers are still transporting the rock material supplied from the canyon side walls. An interesting way to think about all this comes from Dr. Jon Spencer, retired head of the Arizona Geological Survey. The drainage basin of the Colorado River did not exist prior to the start of the Grand Canyon. When the Colorado River formed and the Grand Canyon started to deepen and widen, the continental divide hifted from western Arizona and western Utah back up into Colorado and New Mexico. The continental divide is where precipitation on one side could make its way to the Pacific Ocean and the other side to the Atlantic Ocean. The implication of Grand Canyon’s formation include this massive shift in North American’s drainage divide. Stage B Exploration: Making some basic observations related to the landforms of the Grand CanyonThe idea of Stage A is for you to explore the relationship between topography and rock type in and around the Grand Canyon using the geovisualization game. You get familiar with the game, and also make your own hypotheses about the Grand Canyon’s basic geomorphology. Question B1: What is the formation and rock type that makes up the plateau (relatively flat) surface that surrounds the Grand Canyon on both the North Rim and the South Rim? Your choices are:Hermit Formation – Shale Coconino Formation - SandstoneKaibab Formation - LimestoneRedwall Formation - LimestoneBackground setup for Question B1: There are lots of sedimentary layers of Mesozoic age that used to be on top of this material. You can see these strata by visiting areas north of the Grand Canyon, such as Bryce and Zion National Parks, as illustrated in the diagram below on the next pageThe only Mesozoic strata you will see in the Grand Canyon lab has been protected by a lava flow. On the right is a screenshot of this rare setting. The green Moenkopi Formation is Mesozoic in age, and the Kaibab Limestone underneath is Paleozoic.You can visit this place via Fast Travel in the game at these coordinates:36.0510 -111.7715MESOZOIC ROCKS FOUND AT BRYCE AND ZIONThis is a photograph of a similar lava flow not visible in the game: Red Butte Mountain (photo courtesy of the U.S. Forest Service). However, all of these Mesozoic strata have been eroded away — leaving behind the plateau-making material that is highly resistant to erosion in a dry arid climate. The photo above, by the way, was taken on the same rock type that makes up the rim of the Grand Canyon. These videos show the rim and plateau surface surrounding the Grand Canyon: & B1: What is the formation and rock type that makes up the plateau (relatively flat) surface that surrounds the Grand Canyon on both the North Rim and the South Rim? Your choices are:Kaibab Formation - LimestoneCoconino Formation - SandstoneHermit Formation - ShaleRedwall Formation - LimestoneSee the tutorial on the next page on how to use the geology key.TUTORIAL ON HOW TO USE THE GEOLOGY KEY TO FIGURE OUT ROCK TYPE – Example of Question B1Step 1. Enable Geology key (this should be a default when the game starts up). If the key is not showing, or if you are not seeing the choices in question B1 (Kaibab, Hermit, Coconino, Redwall formations), then access the menu and the map part of the menu. Click the buttons until you see the key.Step 2. Go to the edge of the Grand Canyon. Any edge of the plateau would work in the game. Just hop off the edge and look at the layers. Focus on the rock formation that makes up the flat plateau surrounding the Grand Canyon. A view like this one would work well … and then do your best to slide the bars in the geology key to match layers, like this fairly typical view just off the plateau. The correct answer is the rock formation that is found on the plateau surface. Question B2: There is a ‘platform’ in the Grand Canyon, a relatively flat surface compared to everything surrounding it. The platform is composed of a resistant layer of rock. However, a layer used to be on top of the platform-forming rock. It is much weaker, and it eroded away fairly fast. What is the material that was eroded away (that used to be on top of the platform rock type)? Your choices are:Muav Formation - LimestoneTapeats Formation - SandstoneBright Angel Formation – Shale Redwall Formation - LimestoneBrief Setup for Question B2: This is Clarence Dutton’s famous artwork of the view from Torroweap, showing the Tonto platform — a relatively flat surface inside the Grand Canyon. For enrichment, this is a video that shows the Tonto Platform: & a geological cross-section (courtesy of the National Park Service)TUTORIAL ON HOW TO USE THE GEOLOGY KEY TO FIGURE OUT ROCK TYPES – Example of Question B2Step 1. Enable Geology key (this should be a default when the game starts up). If the key is not showing, or if you are not seeing the choices in question B1? Tapeats, Muav, Bright Angel, Redwall), then access the menu and the map key. Step 2. Fast Travel to Granite Gorge. You can click on the location in the Fast Travel menu, or you can type in (or copy and paste) the coordinates:36.1035 -112.0723Remember to click the fast travel button Turn around, pull the camera angle back and above (experiment with thescrolling on your mouse) and you should have a view like this, where I scrolled the geologic key menu to show the relevant formations. I hope you can see that the rock formation of the platform is the Tapeats Sandstone, a fairly hard layer of rock. Step 3. Walk around the edges of the Tonto Platform. Look at how the layer above the Tapeats is behaving in the landscape. Bits an pieces of this layer can be seen on top of the Tapeats Sandstone, but its in the process of eroding away by rainsplash and little gullies. It is a very weak layer of rock. The name of the formation is one thing. The type of rock is another issue. You can find both the formation name and the rock type name as you scroll the key. Please stay focused on this rock type. It is the subject of the next question. Question B3: The Grand Canyon is a stair-stepped landscape. What type of rock material that is found in the Grand Canyon tends to produce the lowest slopes (e.g. the weakest rock type) ? Setup for Question B3:This is Clarence Dutton’s famous artwork of the Grand Canyon from Point Sublime shows the canyon’s stair-stepped topography. The stair-stepped appearance of the Grand Canyon is obviously connected to rock type. Strata (sedimentary layers) that are resistant to decay and hence erosion make up cliff faces. These cliff faces are undermined by the erosion of weaker strata that also produce ramps (slopes with lower angles) instead of cliffs.This is a video that shows the stair-stepped nature of the Grand Canyon: Suggestion: Fast Travel to Shoshone Point. Hop down from the point to the base of the cliffs. Then, walk a bit towards the Colorado River, and the screenshot to the right is where you will be… standing on the boundary between the Bright Angel Shape and the Mauv Limestone. I suggest you walk around the base of the cliff and hop up and down the cliff above you. Decide the rock type with the lowest slope angle. Question B4: How much faster is the Grand Canyon widening than downcutting (incision) at the location of Grandview Point? The Grand View Watchtower location is one of the most famous in the Grand Canyon. Those who enter the national park from the East get their first view at this location, and those to exist to the East get their last view. Your choices are:The rates of widening and downcutting are about the same, and thus when you divide the same number by itself, the best answer is “about 1”. About 2 timesAbout 4 timesAbout 8 times Setup for Question B4:Research by a team of scholars from the Arizona Geological Survey and colleagues elsewhere have determined that the Colorado River started eroding the Grand Canyon about 4.8 million years ago. Thus, you will be able to estimate the rate of Grand Canyon widening and deepening. Take a look at this image taken from the International Space Station in the winter of 2019, courtesy of NASA. The Colorado River starting eroding downward 4.8 million years ago pretty much at its present position. At the same time, the cliffs started eroding back (retreating), with the north side eroding away much faster than the south side. Enrichment Video: Sunset at Grandview Point Step 1: In the Geovisualization Fast Travel to Grand View: 35.998424, -111.987628Step 2: Write down the elevation that you see in the compass information. Its next to the Latitude and Longitude displayStep 3. With your avatar, jump down to the bottom of the Grand Canyon and find the elevation in the game of the Colorado River. Step 4. Determine the rate of Colorado River downcutting (incision) in units of meters per million years (m/Ma), assuming that the Colorado River’s elevation was reached 1.2 million years ago, and that the Colorado River started cutting (incising) into the ground canyon 4.8 million years ago. Simply divide the difference in elevation by the amount of time the river was downcutting. Step 5: What is the rate of widening of the Grand Canyon at this location (in m/Ma). The Grand Canyon is 14 km wide from South Rim to North Rim at this place. You will be making these sorts of measurements in Stage B, but for now just convert 14 km to meters. The amount of time that widening has been going on is a bit different. We know the river reached its current elevation about 1.2 Ma from the age of a lava flow that reached the current Colorado River, so incision occurred from 4.8 to 1.2 Ma. However, the widening of the Grand Canyon did not stop at 1.2 Ma. It has been going on for the last 4.8 Ma. Thus, divide the width (in meters) by the time (in millions of years. This will give you a rate of widening in m/Ma.Step 6. Take the ride of widening and divide that by the rate of incision. You now have your answer. HINT: Do not obsess about precision and exactness. The potential answers are very different. You just have to get close with your estimates. The idea is for you to pause and think about the processes that are going on to make the amazing scenery. You’ve learned that one set of processes is quite a bit faster than the other. STAGE C more detailed analysis: Exploring connections between topography and rock types in the heart of the Grand CanyonThe developers of this lab hope that this stage opens the door to your personal exploration of the Grand Canyon, that by “running around” this visualization of the heart of the Grand Canyon, your interest will be lead to life-long exploration of this special place. The basic research question asked in this stage is: how does the geology (e.g. different rock types, faults, different tilt in the sedimentary layers) and development of tributary river canyons (hydrology/water) influence the topography of the Grand Canyon? The video game environment is certainly not at a spatial resolution that allows you to explore relations at the meter to millimeter scale. For that, you will have to visit in person. However, the unique geovisualization allows you to explore relations at the scale of tens to hundreds of meters in a way that does not risk your life or take months of time trying to map the canyon . In designing the laboratory activities to match this geovisualization, we had to articulate to the general studies criteria of the sorts of learning objectives involved in an SQ science class. There’s no reason to bore you with the details of these, because they boil down to thinking like a scientist who asks questions (or are asked by others). Then, data are collected, analyzed, and then a possible answer(s) comes to mind (hypothesis). Accordingly, Section B has four sorts of tasks:BEFORE YOU GO ANY FURTHER: DEALING WITH STUDENT WORRY ABOUT PRECISION AND ACCURACYBefore you open the video game and start making measurements about the Grand Canyon, it is important that you not worry about being too precise or too accurate in your measurements. The reason is that the original data are not very precise or accurate.A common question from students involves worrying over differences between what they measure and the key for a question. For example, if students measure 8310 m for a distance, and the choices in the answer to a question are 1500 m, 4500 m, 8100 m, and 9850 m — many students work that what they measured (or calculated) means that they did something wrong. Don’t worry! Pick 8100 m, because it is the closest answer. One of the key objectives of lab science courses rests in having students realize that uncertainty is scientific measurement is a fact of doing science. This is especially true when dealing with measurements related to topography (of horizontal distance and vertical elevation change). The reality is that we do not have very precise or accurate data on the topography of most of our planet. Questions C1 through C4: Compare rates of incision (downcutting) and widening of the Grand Canyon.If you did Stage A, you have already made the incision rate calculation and the widening calculation for the whole canyon at Grandview. So why bother with this again? The reason is to compare the North Rim to the South Rim. If you look at the image below, it looks obvious that the North Rim has to be widening much faster than the South Rim, because its further away from the Colorado River. Likewise, the North Rim is much higher, and so if you use the elevation of the north rim, the river downcutting (incision) rate has to be higher also. See how this all works out in questions C1-C4. C1. How fast is the Grand Canyon widening? (or, put another way, what is the rate of cliff retreat?) Answering this question can be done in several steps. Please go through these steps for the example of Tiyo Point and Hopi Point. Even if you are not given this example via the random question select by canvas ( you might get another two points), this example will be used in question B1. So its worth your time to go through this example. Step 1 is to understand what slope retreat means. Slope retreat in this case means that the sides of the Grand Canyon are eroding away from the location of the Colorado River. The position of the Colorado River has not changed since it started eroding down through the Grand Canyon. However, the canyon itself has also widened as the Colorado River incised. In the image below, you can see North Rim has moved much further from the river than the South Rim. Each side started eroding back at the same time, when the Colorado River started flowing through the Grand Canyon, so north side must be widening (retreating) faster than the south side at this spot.Image taken from the International Space Station in the winter of 2019 is courtesy of NASA. Step 2 is to understand why the North Rim has faster slope retreat. The reason has to do with the way the geological layers (strata) are tilted (dip) and the higher elevations on the North Rim. Courtesy of the National Park Service, the geological cross-section below is oriented north (to the left) to south (to the right). Notice that the layers are tilted towards the south. Perhaps you can see the north side is also several thousand feet higher than the south side. Both factors speed up the rate of cliff retreat.Step 3 is to learn when the Colorado River started eroding down into the rocks of the Grand Canyon. The answer to this question comes from recent research conducted by the Arizona Geological Survey and colleagues. While I encourage you to read this short article in full linked in the footnote, the answer is about 4.8 million years ago. Prior to 4.8 million years ago, the Colorado River did not exist as we know it today.Step 4 is where you start your activity. Measure the distance between the Colorado River and the edge of the Grand Canyon. This distance is a horizontal measurement, because the units of measurement will be in a rate of meters per million years (m/Ma). Then, you will then convert that to meters per thousand years. Step 4A is to decide where to make these distance measurements, because the answer will vary from spot to spot. Obviously, canyon edges far from the river must retreat back much faster than canyon edges right next to the river. For the purpose of this laboratory, in this stage, this example has you measuring the distances and calculating rates of retreat between You might get this example as question B1 in Canvas, or you might get another set of coordinates. There is a pool of questions. So please use this as a step-by-step example. Tiyo Point on the North Rim: 36.1806, -112.1278AndColorado River between: 36.1055, -112.1562AndHopi Point on the South Rim: 36.0733, -112.1551For enrichment, this video will also give you a feel for Hopi Point: ON MEASURING MAP DISTANCES IN THIS LAB:You will use the Pythagorean Theorem to figure out horizontal (map) distances in this lab. Why? Because the apps that measure such distances use this theorem. Part of a science class is to understand how such things work. What follows is an example of how to do this from the far southwest corner of the game and Hopi Point. Then, you can do this between Hopi Point and the Colorado River, and then then to the north rim. The game board starts in the far southwest corner. The far southwest corner is 0 (x) and 0 (y). Hopi point’s X,Y coordinates are 17674, 17051. So how far is it between the southwest corner and Hopi Point? Just use the Pythagorean Theorem. You can even use a calculator: following is a screenshot from the coordinates entered into the Google calculator, and the map distance from the southwest corner of the game to Hopi point is 24, 558 meters, rounded to the nearest 0.1 km or 24.6 km.How would you now calculate the map distance between Hopi Point and the Colorado River (displayed below)?Remember, Hopi point’s X,Y coordinates are 17674, 17051. You can see that the Colorado River’s X,Y coordinates are 17555, 20529. I hope you can look at the numbers and see that the X (west-east) is not that much … 17674-17555 (119). The Y (north-south) is a lot more … 20529-17051 (3478). Do the subtraction and you’ll have your X and Y (or a and b) to use with the Pythagorean Theorem. Please crunch the numbers now and see the answer just below. How would you now calculate the map distance between the Colorado River and Yaki Point? Travel to Tiyo Point and look at the X-Y coordinates and do the same subtraction. This is a screenshot of Tiyo Point on the North Rim. PARTIAL ANSWER: The distance between Hopi Point and the Colorado River would be about 3480 m. Then, the distance between the Colorado River and Tiyo Point on the North Rim would be about 8677 m. Step 4C: Divide the distance from Tiyo Point to the Colorado River and also the distance between Hopi Point and the Colorado River by 4.8 million years (the length of time the Grand Canyon has been in existence). When you divide a distance in meters by the 4.8 (million years) age of the Grand Canyon, this will give you the rate of canyon widening between these locations in meters per million years (m/Ma). Step 4D. The number you get can be hard to understand, because a million years is not really comprehensible to most people. Meters of widening per century is something that humans can grasp better, because most hope to live to be a hundred. To convert meters per million years (m/Ma) into centimeters per century, you have to move the decimal place 2 over (divide by 100). So, for example, 1000 m/Ma would be 10 cm/century. [If you wanted millimeters, you would need to move the decimal 3 places.)Step 4E: Remember to do this calculation for the north side and also the south side. Question C1. How fast is the Grand Canyon widening? (or, what is the rate of cliff retreat?) Please use these places in the geovisualization. Remember, you will be measuring distances between the North Rim and the Colorado River, and then the South Rim and the Colorado River to be able to calculate rates. Please calculate your answer in centimeters per thousand years (cm/ka).Tiyo Point on the North Rim: 36.1806, -112.1278AndColorado River between: 36.1055, -112.1562AndHopi Point on the South Rim: 36.0733, -112.1551 You might get this example as question B1 in Canvas, or you might get another set of coordinates for places like Point Sublime or Cape Royal. There exists a pool of questions, so please use this as a step-by-step example. LEAD UP TO QUESTION C2: First, it is assumed that you worked through the example in C1, because you will use the answer from the example in C1 in question C2. Physical geography students who visit the Grand Canyon on field trips comment that its grandness relates to its width. Canyons that are wider make it hard to see the other side, while canyons that are much narrower just don’t impress as much. The current width allows a person to see a mix of lots of dramatic scenery inside the canyon, while also seeing clearly the other side. Thus, the students think that the rate of widening is just about right to produce a grand scene.This led one student to ask what would things look like if the Colorado River was 10 million years older (arriving 14.8 million years ago, instead of 4.8 million years ago). Question 2: How wide would the Grand Canyon be (between some future Tiyo and Hopi Points) 10 million years from now, using the rate you established in the example in the PDF file for question 1? The correct answer will be in miles, since most people understand miles at an intuitive level.Guidance on how to answer this question:Step 1 would be to add together the current distances from Tiyo Point and the Colorado River and Hopi Point and the Colorado River. Keep that sum handy.Step 2: Use the rate of retreat (meters per million years) for the south side and multiple that rate by 10. Add this distance to the sum in Step 1.Step 3. Use the rate of retreat (meters per million years) for the north side and multiple that rate by 10. Add this distance to the sum in Step 2. You know have the width in meters. Just convert meters to kilometers (divide by 1000).Step 4. Convert kilometers to miles …. and you have your answer. THINKING NOTE FOR THE ESSAY (Stage D) AND A HINT: When you calculate the width of the Grand Canyon 10 million years from now, you are really just figuring out what would the canyon look like if the Colorado River started 15 million years ago instead of 4.8 million years ago. You will find that the width is about 3 times what it is today. This is the hint. The thinking note is for you to wonder if the Grand Canyon would really be so grand if it was 3 times wider. The other side would not be “in your face” like it is today. It would be much further away. LEAD UP TO QUESTION C3: Many visitors to the Grand Canyon incorrectly think that the Colorado River created it. You understand that the Colorado River certainly enabled its erosion, by first incising downward, and now being a “conveyor belt” for all of the rock material that is being moved by mass wasting and tributary streams from the side down to the Colorado River. Certainly, without the downward incision, there would be no Grand Canyon. Certainly, without sediment transport, the Grand Canyon would be clogged with rock and sediment. Thus, the third question tasks you with figuring out the rate of downward incision. NOTE: This topic is explored in much greater detail in the “Telling Time” lab, where you look at differences in Colorado River incision (synonyms would be downcutting and downward erosion) as it crosses the Kaibab Upwarp that makes the heart of the Grand Canyon. However, for this lab, you just make one of these measurements.Question C3: How fast did the Colorado River incise down into the Grand Canyon between 4.8 and 1.2 million years ago (or over a 3.6 million year period)? The correct answer will be in centimeters per century.Step 1. The Colorado River incised (eroded downward) into the Grand Canyon in about 3.6 million years. How do we know that? Recent research conducted by the Arizona Geological Survey and colleagues have done award-winning work in establishing when the Colorado River came into existence. The first influx of river water into these lakes started about 4.8 million years ago. As Dr. Jon Spencer concludes in this article: “Rapid incision of the Grand Canyon began at this time.” The Colorado River then eroded downward through the Paleozoic rocks down to close to its current level by 1.2 million years ago, as explained below. Thus, we know that almost all of the canyon incision occurred in the time from 4.8 to 1.2 million years ago, or a period of about 3.6 million years.Step 2. Determine the elevations of the points you are assigned by the canvas question (there are a pool of questions).BY WAY OF EXAMPLE … Determine the elevations of Tiyo Point, Hopi Point, and the Colorado River between Tiyo and Hopi Point. Use Fast Travel in the video game to jump to these locations and look at their elevations in the compass view. Tiyo Point on the North Rim: 36.1806, -112.1278AndColorado River between: 36.1055, -112.1562AndHopi Point on the South Rim: 36.0733, -112.1551For example, Tiyo Point has an elevation of 2371 m in the screenshot belowStep 3. Calculate rate of incision between Tiyo Point and the Colorado River, and also between Hopi Point and the Colorado River. Step 3a. Subtract the Colorado River’s elevation from Tiyo Point. Step 3b. Subtract the Colorado River’s elevation from Hopi Point.Step 3c. Divide the elevation difference by 3.6. This will give you two incision rates of meters per million years – one for Hopi Point and one for Tiyo Point.Step 3d. Divide the meters per million years (m/Ma) incision rate by 100 and this will give you the rate in centimeters per century. EXAMPLE USING ELEVATION VALUES THAT ARE WRONG: Pretend the north-rim point is 3000 m in elevation and the Colorado River is at 1000 m. That’s 2000 meters of incision that you divide by 3.6 to give 555.55 or rounded to 556 m/Ma. Then, when you divide this by 100, it would be rate of 5.6 cm/century. You would do this sort of calculation for the north rim and then also for the south rim for the locations given to you in canvas, and these rates would give you a “ballpark” or order-of-magnitude understanding of how fast the Colorado River incised downwards. Question C3: How fast did the Colorado River incise down into the Grand Canyon between 4.8 and 1.2 million years ago (or over a 3.6 million year period)? The answer should be in centimeters per century and be calculated for both Tiyo Point on the North Rim and Hopi Point on the South Rim. Your choices are:From the north rim’s higher Tiyo Point, the incision rate was approximately 0.88 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 0.74 cm/century. From the north rim’s higher Tiyo Point, the incision rate was approximately 0.38 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 0.25 cm/century. From the north rim’s higher Tiyo Point, the incision rate was approximately 50 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 30 cm/century. From the north rim’s higher Tiyo Point, the incision rate was approximately 5 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 4 cm/century. CORRECT: From the north rim’s higher Tiyo Point, the incision rate was approximately 5 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 4 cm/century. INCORRECT1: From the north rim’s higher Tiyo Point, the incision rate was approximately 0.88 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 0.74 cm/century. INCORRECT 2: From the north rim’s higher Tiyo Point, the incision rate was approximately 0.38 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 0.25 cm/century. INCORRECT 3: From the north rim’s higher Tiyo Point, the incision rate was approximately 50 cm/century, and the lower south rim’s Hopi Point, the incision rate was approximately 30 cm/century. FEEDBACK:The elevation of Hopi Point is 2131 m, while the Colorado River underneath Hopi and Tiyo Point is about 721 m. The difference is 1410 meters, and 391 m/Ma is the rate when you divide by 3.6. When you convert this rate to cm/century, you will get 3.9 or rounded to 4 cm/century. The elevation of Tiyo Point is about 2371 m, and that’s about 1650 m above the Colorado River. When you divide by 3.6, the rate of incision would be 458 m/Ma and that would be approximately 4.6 cm/century that is rounded off to 5 cm/century.LEAD UP TO QUESTION C4: Think about what proportion of depth to width provides the most “grand” looking canyon. Is it the Grand Canyon’s proportion? Do you like narrower canyons? This question explores the balance of widening versus deepening at the Grand Canyon.Question C4: How do the rates of widening compare to the rates of incision in the area between the north and the south points that you measured?Instructions: Look at the rates of widening that you measured, between the two points on the north and south sides and the Colorado River. Then, look at the rates of incision that you measured. The rates are in centimeters per century. You are not asked for a precise measurement or ratio, but to select the closest answer.EXAMPLE WITH INCORRECT FIGURES … The rates that I am about to give you are not close to what you were measuring. However, they will help you think about what is being asked. Let’s say that the rate of Grand Canyon widening is 15 and 12 meters per thousand years (it is NOT) for the north and south sides. Then, pretend the rate of Coloado River incision is about 3 and 2 meters per thousand years (it is NOT) for the north and south sides. The best answer to this question would be as follows: The rate of Grand Canyon is widening has been five to six times faster than the rate of canyon incision. This “best answer” was determined by dividing 15/3 and then 12/2. LEAD UP TO QUESTION C5: When sedimentary strata (the name that geologists give strata like you see in the Grand Canyon) erode backwards, they tend to produce two basic sorts of forms: slickrock or cuesta landforms. The cuesta landscapes of the Colorado Plateau, including the Grand Canyon, require that hard rocks alternate with weaker rocks. The weak rock is typically shale (or compressed mud). The shale erodes away pretty fast, and it undermines the overlying hard rock. Eventually, the caprock collapses in a rock fall. Slickrock is the opposite. When a rock type (like sandstone) does NOT have a weak layer of rock exposed underneath it, it rounds. The rounding is from the slow detachment of sand grains by water flowing over the surface. Image courtesy of TM Oberlander. The Grand Canyon does have bits and pieces of slickrock, but they are few and far between. Almost everywhere you look, you see cliff faces with a weaker layer of rock underneath. There is one particularly very weak rock layer in the central Grand Canyon. It is, of course, shale (compressed mud). It is so weak that the cliff on top of it eroded back faster than any other layer. The cliff face on top keeps collapsing, because the weak layer erodes out from underneath it.This layer of rock is something you can see very clearly – if you know what to look for. The widest “platform” or relatively flat surface inside the canyon was produced because this layer is truly “the weak link in the chain”. This weak layer has strong rock underneath it, so where it has completely eroded away, you an see the strong rock (a sandstone) and this strong rock is where you will find bits and pieces of slickrock.Question C5: What is the color of the weakest rock in the Grand Canyon (called Bright Angel Shale) as displayed in the geovisualization video game? Also, what are the colors of the rock layer above it (a limestone, the Muav Limestone) and below it (Tapeats sandstone)? INSTRUCTIONS: Jump, hop, or run virtually around the Grand Canyon. Look for this platform (called the Tonto Platform). You will see one particular layer where the slope is less steep than all other layers. You will find the Tonto Platform above the very steep inner gorge. The hope is that this is a particularly simple task, but really, the idea is for you to have fun exploring the Grand Canyon and the connection between the rock type and the topography. That is what Section B in this lab is all about.HINT #1: There is geology key, where you can see the color of the Bright Angel Shale.HINT #2: If you Fast Travel in the videogame to Granite Gorge, the avatar is standing on the Tapeats Sandstone, but is very close to the Bright Angel Shale that is the next highest layer. If you walk a bit closer to the Colorado River, you will be fully on to Tapeats Sandstone, and if you walk away from the Colorado River, you will be on the Bright Angel Shale (and if you don’t jump, the avatar will just come to a stop). QUESTIONS ABOUT THE GEOMORPHOLOGY OF THE REDWALL LIMESTONEQuestions C6 through C9 start with basic observations about what influences the position of the Redwall Limestone cliff. [Even though the cliff also includes the Temple Butte Limestone and the Muav Limestone underneath, you can think of all three as the Redwall cliff of the Grand Canyon, because all three layers are strong and make up a cliff that is underlain by a weak rock:This enrichment video gives you a sense of the dramatic nature of the Redwall Limestone cliff as it comes into full view halfway through the video: You start with basic observations about why the Redwall cliff moves away and towards a river, and the hope is that the question sequence explains a lot about the landforms you see in the Grand Canyon. Question B6. In the geovisualization video game, Fast Travel to the canyon of the Little Colorado River. Hop down to the junction with main Colorado River. Your avatar should be standing next to the Redwall Limestone (Purple Color)Verify that you are next to the Redwall and Temple Butte limestones (you can use the geology key), and then move up and down the canyon. Pay attention to the straightness of the cliff faces of the Redwall Limestone. Pay attention to where the cliff faces does bend away and towards the river a little bit and what might be a cause of this bending. C6 Question: Based on your observations along the canyon of the Little Colorado River, what topographic feature occurs most commonly where the Redwall cliff faces bends towards and away from the Little Colorado River?Enrichment Video showing the cliff face (that includes the Redwall Limestone) of the Grand Canyon and moving into the Little Colorado River’s canyon: Your choices in canvas will be:The Redwall Limestone cliff faces are straight where they are directly underneath the Kaibab Limestone, but bend where they are not.The Redwall Limestone cliff faces are straight where there are no river valleys, but bend where they cross a river drainage.The Redwall Limestone cliff faces are straight where they are on top of the Supergroup, but bend where they area not. All of the other answers are correct and thus this is the best answer.Set up for Question C7. Fast travel to Shoshone Point. Hop down to the base of the cliffs. The idea is for you to change the camera and look at a bigger area. Just pull back to see how the cliff moves towards and away from the Colorado River.Zoom out with the camera (as though the camera was a helicopter far away) and then spin around the camera to look at how the Redwall Limestone (purple layer) moves away and towards the Colorado River. For example in the screenshot of the game below, the arrow is aimed at your avatar with the other end starting at the Colorado River. Notice how there are places where the Redwall cliff sticks out as a point and places where it recedes back. Try rotating the camera to get different views and perspectives and then answer the question C7 question: What appears control the location of Redwall Limestone cliff in the area below Shoshone Point? Select the best answer, but realize that this question is very similar to the previous one. You are just observing the phenomenon in a different location. These are your choices:The Redwall cliff appears straight and this might be due to faulting. The Redwall cliff meanders back and forth randomly and hence there is no clear control over its position. Everytime the Redwall cliff crosses a drainage, even a small-looking ravine, it moves back away from the Colorado River. All of the other answers are correct and hence this is the best answer. Setup for Question C8. Use Fast Travel to get to an overlook of Bright Angel Canyon. The camera angle is pulled back and your avatar is standing on the point on top of the Kaibab Limestone, perhaps something like this view.Please walk down to the canyon and travel around to observe what happens to the Redwall Limestone cliff as it passes tributary drainages to Bright Angel Creek. The controls in the video game allow you to “zoom out” and see the smaller scale (bigger area) view. By now, you have figured out that crossing a drainage influences the position of a cliff-forming layer in the Grand Canyon. Please think about why and select the best answer. By the way, the hope of this sequence of questions is that you are now thinking a bit more like a physical geographer. These will be your choices:There are many different ways that the Redwall Limestone formation can undergo erosion. The most common way in the Grand Canyon is where the Bright Angel Shale has undercut the big cliff face (that actually combines the Redwall, Temple Butte and Mauv limestones). This undercutting occurs because the shale is a weak rock and erodes with rainstorms. The undercutting eventually leads to the collapse of the cliff face (by rock falls and rock slides). There are many different ways that the Redwall Limestone formation can undergo erosion. The second most common way is when a drainage (whether it is gully, a small creek, or large creek) flows over the Redwall Limestone. Floods carry rock material as bedload (cobbles and sometimes boulders) that abrade the Redwall. This process of erosion is made more effective by the steep cataracts and waterfalls associated with this formation being on top of the Bright Angel Shale. Essentially, the rapid erosion of the weak shale creates this knickpoint (cataract and waterfall) condition. Even though rock falls and rock slides are fairly common in the Grand Canyon, intense rainstorms that produce flooding in drainages are more frequent. Thus, the rate of erosion of the creek beds cutting down into the Redwall Limestone (and underlying Temple Butte and Mauv limestones) is faster than the rate of cliff retreat by undercutting. This means that the Redwall cliff is eroding away from the Colorado River faster and hence bends away from the river more where it crosses drainages. All of the other answers are correct, and thus this is the best answer.SETUP FOR QUESTION C9: Please look again at this NASA space shuttle image from the winter of 2019 captures this study area. North is to the left. South is to the right. East is top and west as bottom. Please think about the previous section where you measured rates of Grand Canyon widening for the north side and south side of the Grand Canyon. Even from the picture above, you can see that the amount of widening is much more extensive on the north side of the Colorado River. Thus, the rate of widening is considerably faster on the north side of the Colorado River. So if you have different answers in canvas, STOP AND GO BACK!! Now, please look at a geological cross-section that runs from the north rim on the left to the south rim on the right. Can you see that the elevation of the north rim is higher? The reason is that the big geological structure in the area is called the Kaibab Upwarp. All of the formations are warped up (folded up) to make a mountain range that the Grand Canyon has to cut across. Question C9. Given what you read in the previous question and what you read in the PDF file information about this question (and please reread all of the answers before you answer this question) why is the north side of the Grand Canyon widening much faster than the south side?Your choices are:The higher elevation of the northern side results in greater amounts of precipitation (both rainfall and snow that melts) that flows into drainages. Hence, there are a lot more drainages flowing down from the north rim than from the south rim. The two major ways that rock formations erode in the Grand Canyon are erosion from floods in drainages (ravines, small creeks, large creeks) and the collapse of cliffs due to undermining of the weaker rock underneath (e.g. shale under limestone or shale under sandstone). The rate of erosion from floods in drainages is faster than the rate of erosion from rockfalls/rockslides due to undermining of cliff faces. The greater number of drainages and also the greater number of larger drainages on the north side of the Colorado River, thus, means that the north rim is eroding back faster than the south rim. In other words, the south rim’s retreat tends to be more influenced by cliff retreat where as the north rim’s retreat is more influenced by erosion along drainages. All of the other answers are correct, and hence this is the best answer. QUESTIONS ABOUT TEMPLES IN THE GRAND CANYON – The last set of questions relate to Grand Canyon temples. The Temples of the Grand Canyon are separate mountains all within the Grand Canyon. To understand what they look like and their dramatic appearance, you are welcome to watch one or all of these enrichment videos: Vishnu Temple: This flight goes through the drainage that separates the Towers of Ra and Set: Zoroaster and Brahma Temples Confucius and Mencius Temples: Setup to Questions C10 and C11: Isis Temple is one of the most photographed mountains on Earth. Every visitor to the South Rim who takes a photograph of the Grand Canyon inevitably takes its picture. This mountain is bordered on its south by the Colorado River. It is bordered on the east by Phantom Creek, while Trinity Creek bound its west side. It is separated from Shiva Temple to its north by a tributary of Trinity Creek.Question C10 INSTRUCTIONS: Fast Travel to the Isis Temple in the geovisualization. This is one of the selections. Move off the top and then move around the temple and get a feel for the size of the mountain. Focus on the feature(s) that separates a temple from the rest of the Grand Canyon. Also, focus on the rock type that makes the uppermost hard rock at the top that is protecting the weaker layer of rock (a shale) directly underneath. Just use the Geology Key.:Question C10. What rock layer occurs at the top of Isis Temple that protects the weaker layer underneath, and what landform feature separates Isis Temple from the rest of the Grand Canyon?Your choices are:Temples are pieces of the plateau that have broken loose from the plateau itself. Since the Kaibab limestone is the resistant rock formation that makes up the plateau (and edge) surrounding the Grand Canyon, it is this layer of rock that forms the top of Isis Temple. Isis Temple itself is a giant block that separated from the north rim due to a giant landslide, and features of the landslide compose its border. Hermit Shale makes a protective summit of Isis Temple, while narrow ridges that are eroding by rock fall separate Isis from the rest of the Grand Canyon.Coconino Sandstone makes a protective summit of Isis Temple, while creeks (drainages) separate Isis from the rest of the Grand Canyon.Hermit Shale makes a protective summit of Isis Temple, while creeks (drainages) separate Isis from the rest of the Grand Canyon.Question C11 INSTRUCTIONS: Fast Travel yourself to the pre-selected location for Granite Gorge in the Grand Canyon in the geovisualization. Move off the top and then start traversing the south side of the Colorado River looking for any Temples, or any fully isolated mountains within the Grand Canyon itself. I suggest you wander in a westward direction and look around for a couple of minutesQuestion C11. Have you identified any temples on the south side of the Grand Canyon? If so, where. If you could not find any temples, what would be the most best explanation for their lack – given what you have observed in section B of this lab?Your choices are:There are no clear examples of temples on the south side. There are lots of narrow ridges, but these all extend back to the edge of the south rim. The best explanation for the lack of temples on the south side is the lack of faulting. Faults break apart the rock formations of the Grand Canyon, and the fault breaks are the reason for the existence of temples. In contrast, the north side of the Grand Canyon has an extensive network of faults that separate temples from the plateau of the North Rim. There are no clear examples of temples on the south side. There are lots of narrow ridges, but these all extend back to the edge of the south rim. The best explanation for their lack on the south side and their presence on the north side would be the amount of drainage development. The south drainages are short and connect directly up to the south rim, while the north-side drainages are longer and much more extensive with tributary development that can separate temples. There are no clear examples of temples on the south side. There are lots of narrow ridges, but these all extend back to the edge of the south rim. The best explanation for the lack of temples on the south side is the lack of big landslides on the south side of the Colorado Rive. The North Rim is both higher and wetter than the South Rim. The elevation and moisture have resulted in large landslide blocks that break loose from the North Rim. They slide slowly towards the low spot of the Colorado River. As they slide, they separate from other rock formations and end up as isolated Temples. The south side of the Colorado River does have temples. They are found right next to the Colorado that they tower over. The Redwall Limestone is the formation that typically makes up the summits of these temples. There are too many south side temples to name, but nice ones can be found underneath Hopi Point and Shoshone Point.THE NEXT TWO QUESTIONS: relate to how the Temples formed and hopefully get you to think differently about its amazing topography Question C12 asks you to explore if faults could be involved in the formation of temples. Are there any locations where the Temples of the Grand Canyon are bounded by these faults? Select the best answer.SETUP FOR QUESTION C12: There are faults in the Grand Canyon, but geologists think that most of these faults are extremely old and fractured the deep basement rock, and then were re-activated between 40 and 70 million years ago when the region was uplifted during the “Laramide Orogeny” mountain building time. Here is a map that shows faults in the study area, and you will focus on the Bright Angel and Butte faults. You probably noticed the very straight nature of the Bright Angle Creek when you were tasked with exploring that canyon in an earlier question. The Bright Angel Creek canyon started when Colorado River started cutting down. Then, a tributary used the weakness of the rock crushed by faulting to erode itself back up to the north rim in a fairly straight line. There is also matching straight tributary on the south rim. You are welcome to jump back to the Bright Angel Canyon in the geovisualization and look around again at how this canyon is extending into the North Rim using the fault weakness. You might enjoy this enrichment video of Bright Angel Creek and the image on the next page. Then, look around the canyon aligned with the Butte Fault. The map view below shows the Little Colorado entering right next to the middle of the Butte Fault. FAST TRAVEL COORDINATES: 36.2517, -111.8595Question C12. Are there any locations where the Temples of the Grand Canyon are bounded by these faults? Select the best answer.Setup for Question C13: This is a screenshot from, where the avatar is on the North Rim, looking across a gap at Shiva Temple. The caprock for both points of high topography is the Kaibab Limestone, as indicated by the key. The issue here is when Shiva Tempe separated from the North Rim? Was it at the inception of the Grand Canyon, or this an evolving process where new future Temples are in the process of separating? For these future Temples, how long will it take for this sort of a gap to develop? B13 Question: Estimate how long ago _________ Temple (coordinates given in canvas) was connected to a nearby piece of topography (coordinates given in canvas). Select the best answer in units of years ago. Then, think about this length of time from the perspective of when the Colorado River started to flow. This thinking will be useful in the stage C essay. Instructions: In the geovisualization, obtain the X and Y coordinates of the two different pieces of high topography (Temple and nearby matching topography) that you are given in canvas. Use the Pythagorean Theorem (as you did earlier) to measure the planimetric distance between these two highpoints in meters. Use a rate of separation of 1000 meter per Ma (million years) For example, if you used the Pythagorean Theorem to measure a gap of 300 meters,You would do this calculation: 300 meters 1000 m/ MaIn this sort of a fraction, meters would “cross out” leaving you with 0.3 million years, which is 300,000 years. STAGE D: Your analysis of why the Grand Canyon is so grand (or not grand at all)?This is your chance to combine observations made doing this lab with your own experience (including outside readings and your own travels). Keep in mind that the grading of this essay is based on the evidence and reasoning that you present. Answers that do not refer to specific evidence from this lab (and outside material) will be given little credibility and will not receive full points. In other words, if we do not see clear evidence from this lab (and outside material), do not expect more than a point. We do not have any particular answer in mind. We want to know your opinion, but backed up by evidence and reasoning (beefy paragraphs).You do not have to do this essay. It simply provides you an opportunity to synthesize the lab and let us know your thinking on the basic question of the lab.Paragraph 1. State your view of whether the Grand Canyon is grand or not. Write a synopsis of your thinking detailed in the next paragraphs. Paragraphs 2 through 4. We are looking for three well thought out reasons to back up your position. Each paragraph details the evidence in support of each one. Each paragraph details your reasoning. Please don’t ask what we are looking for in an answers. We will simply refer you to the text material in this laboratory PDF file for ideas if you are drawing a blank. However, we really are most interested in your thoughts on the question. Each paragraph could has a maximum point value of 0.5 points or 2 points total. The assigning of points is based on the level of detail you provide in writing teach paragraph. ................
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