Artistic portrayal of the Grand Canyon area today (east is up at the top) and what the area might have looked like when the Colorado River was just starting to erode into the sediments of the Grand Canyon. Art work by ASU student Alexis Ruiz, using Google Earth imagery and International Space Station image.

Lab Title Timescapes of the Grand Canyon

Lab SummaryThis multi-step lab tasks you with exploring the landscapes of the Grand Canyon from different time perspectives, including historic and working out the rates of change that would have been needed to produce this amazing wonder of the world – all within a geovisualization where you interact with the physical geography as an avatar in a video game.

Reason to select this lab

In addition to providing points in the multi-step lab category, this lab uses an innovative way to analyze landforms: a geovisualization that is like a video game. There is a cost, though, of $15. Also, you will need a laptop or a desktop Windows or Mac Computer that has at least 4 GB RAM (ideally 8 GB).

Interesting maps to download – not necessary to do the labs, but helpful to some students

National Park Service map of Grand Canyon National Park:https://www.nps.gov/carto/hfc/carto/media/GRCAmap1.jpg

NPS 3D map of the Grand Canyonhttps://www.nps.gov/carto/hfc/carto/media/GRCA3DMap.jpg

Interactive geologic map of the Grand Canyon:https://azgs.arizona.edu/interactive-geologic-map-grand-canyon

Topographic map of the Grand Canyon:https://www.loc.gov/resource/g4332g.np000100/

Shaded relief map of the Grand Canyon area:https://legacy.lib.utexas.edu/maps/national_parks/grand_canyon_map.jpg

Bright Angel Topographic Map:http://legacy.lib.utexas.edu/maps/topo/arizona/pclmaps-topo-az-bright_angel-1903.jpg

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Computer program used in this lab

You will be given instructions on how to purchase the geovisualization game environment in canvas on a page at the top of the multi-step modules. In the geovisualization, you are an avatar character able to investigate features to complete the lab. Since this lab is optional, you do not have to purchase the geovisualization for this course.

SQ general studies learner objectives

Students analyze geographical data using the scientific method, keeping in mind scientific uncertainty. Students also use mathematics in analyzing rates to change in the landscape. Students also work to enhance their understanding of fundamental principles of dynamics and mechanics governing the behavior of matter in physical systems.

Science & Society learner objectives

This lab meets three learner goals for this requirement in the context of how science and tourism interact. In studying the interplay between science and tourism, students analyze a case study on the reciprocal relationship between science and society in the context of The Grand Canyon. In doing so, they develop a critical understanding different ideas on tourism and science. Then, students formulate and communicate a view of this interaction.

Readings Associated with Science & Society Learner Objective

The readings below are links in Canvas or are hyperlinks:Hansen, Andrew. Challenges to arid public lands through the lens of the Grand Canyon; Pearson, Byron Some reflections about the Grand Canyon National Park CentennialNational Park Service. Tourism to Grand Canyon National Park Creates Economic Benefits: https://www.nps.gov/grca/learn/news/grand-canyon-economic-benefit.htm Visitor spending effects: interactive websitehttps://www.nps.gov/subjects/socialscience/vse.htm

Organization of the lab

Section 1. Preface: Timescapes of the Grand CanyonSection 2. Overview of the labSection 3. Extra background materials.Section 4. Geovisualization purchasing and playing

TABLE OF CONTENTS OF THIS DOCUMENT1. Preface: Timescapes of the Grand Canyon Page 32. Geovisualization: purchasing and playing 43. Overview of lab activities 54. Background information 65. Step-by-Step Guidance in answering questions for the laboratory. 18

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1. Preface: Understanding different timescales that produce the landscapes of the Grand Canyon

The depth of time involved in what you encounter at the Grand Canyon is mind boggling, at least to the lab developer (Professor Dorn).

Geological timescape: There are rocks deep down at the bottom of the canyon that formed over a billion years ago. Most of the geological strata you see exposed on the canyon walls formed in the Paleozoic era that ended about 250 million years ago. The geological timescale measures time by changes in evolution and the various preserved fossils in these layers.

Historical timescape: Then, there’s the opposite end of what has been happening in the period since Grand Canyon became a national park a century ago. Floods have roared down the canyon; landslides occasionally take place; and humans have modified the landscape in ways that range from tourism to managing flooding along the Colorado River through management of Glen Canyon Dam. Many of these changes have been documented through historical photography.

Geomorphic timescape: Between the geologic and historic timescales is the timescape of geomorphology where the Grand Canyon’s landscape evolved over the last 5 million years, the time during which the Grand Canyon landscape that you see today developed. Geomorphic erosion of the Grand Canyon is a mix of three different sets of processes. (1) The Colorado River has been doing two critical pieces of work: erosion downward (incising) into progressively older geological formations and also transporting all of the bits and pieces of rock material that landslide into the river, that are carried to the Colorado River by tributary streams, and also the rock material that the river itself has been eroding. The Colorado River also serves as the “base level” for all of the surrounding stream systems. As the Colorado River incises downward, it gives the side tributary streams more of a gradient to in turn erode downward. (2) Side tributary streams have been eroding downward in response to the dropping base level of the Colorado River. They have also been enlarging their drainage areas by spawning smaller tributary streams and building a network of small rivers. (3) The cliff faces have been retreating. Cliff retreat is the name for a lot of different mass wasting (landsliding) processes that go into having a cliff face move backwards away from the Colorado River.

This lab explores all three different timescales of change in the Grand Canyon.

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2. Video game geovisualization of the Grand Canyon for this lab: purchasing, downloading, and playing.

You do not have to do this lab! However, you decide to try this lab, you will need to purchase the geovisualization. You cannot do this lab without it.

All of the instructions you will need to purchase and download are found on Canvas page in the multistep module in Canvas.

There is also another page on hints about playing the game.

However, there are two items are often glossed over by students, but can solve a lot of frustrations.

Escape Key – hitting the escape key will enable you to move the rabbit, or alternatively access the features of the game

Mouse – by trial and error, you will learn to change the camera position so that you can cover your view well above the avatar to get a different perspective.

How to play and game and also use other programs

Mac WindowsWhile the game is already open

Holding down the apple command button, hit tab

Holding down the ALT key, hit tab

Before you open the game, access the Unity presets to make the game windowed and also lower the resolution

Hold down the OPTION key when you open the game. Then, click on windowed and any lower resolution will make the game be a window on your desktop.

Hold down the SHIFT key, when you double click on the application. Then, click on windowed and any lower resolution will make the game be a window on your desktop.

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3. Overview of multi-step lab activities

Lab Activities are divided into these very different timescales of influence on the Grand Canyon.

Part 1. Geological timescape: this is not a geology class. However, the nature of the earth materials is a critical aspect of how geomorphic (landform) processes created the landscape of the Grand Canyon. Thus, you start out by learning the basics of formations of the Grand Canyon.

Part 2. Geomorphic timescape: this is a physical geography class, focused on geomorphology and landform processes. Thus, this section has the goal of you coming to a deeper understanding of how the amazing landscape of the Grand Canyon was produced by a mixture of Colorado River downward incision, cliff retreat, and development of drainage basins of tributary streams. This lab does not get into the separate geomorphology issue of how the Colorado River made it across the Kaibab Upwarp geological structure. That the Grand Canyon is a transverse stream that crosses a geological mountain (upwarping of the earth) creates a problem in geomorphology. How did this river cross a mountain that is older, far older (tens of millions of years older) than the river itself that originated about 4.8 million years ago? There is another multi-step lab choice on this question.

Part 3. Historical timescape: A term is being debated by Earth Scientists called “The Anthropocene”. The Pleistocene is the period from about 2.5 million years ago to the end of the last ice age (about 15,000 years ago) when tens of ice ages came and went. The Holocene is the post-ice age period. Some earth scientists think that the impact of humans on Earth now deserves its own geological time period and have called this the Anthropocene. In part 3, you explore a mixture of natural and anthropogenic processes that have been modifying the Grand Canyon. This section includes readings and an essay that relates to The College of Liberal Arts & Science’s requirement of Science & Society.

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4. Background Information

4.1. Geological timescape:

The rocks and their time frame are illustrated in this diagram by Brian Gootee of the Arizona Geological Survey. The oldest rocks are the Vishnu Schist and Vishnu Gneiss—metamorphic rocks exposed in the inner gorge. Then, granitic rocks intruded plutons and dikes into the Vishnu Basement rocks. This includes granodiorite-diorite-and other similar rocks. Then, these rocks were eroded and the Grand Canyon Supergroup was deposited and then faulted. Then, the Great Unconformity occurred – where all of these Proterozoic Era rocks eroded. Then, sediments of the Paleozoic era deposited on top of this erosion surface.

Please notice that the very oldest rocks can be separated into two age groupings based on how the instrusive igneous rock bodies are moving into the basement metamorphic rocks. You will encounter Vishnu Schist and then granodiorite complex rocks in this lab deep down in the gorge of the Grand Canyon. Both are over a billion years old.

Then, also notice that there were two events that can also be seen in this diagram that follow. First, these Proterozoic rocks were eroded and put in a position where sediment could be deposited on top of them called the Grand Canyon Supergroup. Then, this sediment was faulted.

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Then, all of these rocks were eroded and an erosion surface created. Then, Paleozoic sediment (starting with the Tapeats sandstone) started to accumulate on top of this erosion surface that goes by the name of the Great Unconformity.

The Paleozoic Era was 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.

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You certainly do not need to memorize any of these formations, but you may be amused by this used in some geology courses for the formations above the inner gorge:•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 Sandstone

Most of what you will encounter in the geovisualization will be these Paleozoic rocks, starting with the light blue Kaibab Limestone in the game view below, and going all the way down to the goldish-colored Tapeats Sandstone at the bottom of the view.

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A basic concept that I hope is pretty obvious is that the sedimentary strata at the bottom of a deposition sequence must be deposited before the rocks on top.

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4.2. Geomorphic timescape:

When seen from space (courtesy of NASA), I hope you can see that the Colorado River goes through a mountain (called the Kaibab upwarp). The wetter and cooler higher elevations of this upwarp allow for pine and even spruce/fir trees to grow.

As you have seen in playing the geovisualization video game, the edge of the Grand Canyon is a plateau made up the Kaibab Limestone. When the Colorado River started flowing across this region, it was flowing at an elevation very close to that of the Kaibab Limestone you see today. It could have looked something like this, where the Kaibab Limestone once completely crossed the area now occupied by the Grand Canyon.

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When the canyon started to be incised by the Colorado River, this downward erosion exposes geological sedimentary in the reverse order that they were deposited: youngest is eroded first

Higher layers were exposed by the Colorado River as it incised (cut down) first, and then the lower strata were exposed only after the river eroded the higher layer. Thus, the order of incision is from the top towards the bottom.

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Key ingredient in geomorphic change: base level lowering impacts much more than the main Colorado River. Tributary streams are greatly impacted

This diagram, courtesy of the U.S. Geological Survey, show the basic idea that erosion by water (creeks, rivers, flash flooding) cannot go lower than the base level. Sometimes, the base level is a lake in the mountains. Sometimes, it can be a dam made by people. Ultimately, it’s the ocean.

A important aspect of base level is that if the landscape’s base level is MUCH LOWER than the high spots, erosion can be very fast. This is the case inside the Grand Canyon. The base level of all of the local tributary creeks is the Colorado River, and the Colorado has been eroding to reach the base level of the Pacific Ocean ever since it formed about 4.8 million years ago.

Now, think about a tributary stream that has the Colorado River as its base level. As the main river incises, the base level is lowered. This means the tributary stream has a steeper gradient and it too can erode down to reach the new base level. Also, as the tributary stream incises downward, it also extends headward and creates a longer stream. This concept is shown in the following diagram.

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In the videogame geovisualization, this is what the response of tributaries to base level lowering looks like. The camera angle is pulled far back and the avatar is tiny in the center of a tributary canyon. Notice how the tributaries are extending into the plateau in response to the lowered base level o the Colorado River.

Now, think about Bright Angel Creek, a major tributary creek and drainage in the Grand Canyon. Bright Angel Creek started to form when the Colorado River began to erode (incise) downward. Even when the Colorado River had no canyon except perhaps a few tens of feet deep – this small base level lowering made it possible for tributary streams to begin to develop. In the case of Bright Angel Creek, it had the advantage of using an ancient fault of crushed rock.

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When you transport yourself to Bright Angel in the geovisualization, this is where you end up (with a camera zoomed out view looking southeast.

Think about the development of these canyons. As the Colorado River kept incising (lowering), Bright Angel Creek kept eroding headward back up into the North Rim. Thus, the youngest parts of the eroding drainage have to be those near the top of the rim (where the video game camera is located). What layer of rock was the first to erode as this tributary developed? The top (Kaibab

Limestone) is the answer. Please look at the screen capture from the game above. Note how the smallest tributaries are just now starting to erode this top Kaibab Limestone layer. Then, as the tributary erodes further back, at any given location, deeper and deeper

layers are exposed. That is why way down by the Colorado River is where the deepest rocks are last exposed by erosion.

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A DIFFERENT GEOMORPHIC PROCESS IS HOW DO THE CLIFFS RETREAT BACK ROM THE CANYON?

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

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.

However, a very important way that the Grand Canyon walls erode by is by undermining of hard rock by weaker rocks. This is a diagram from geomorphic researchers in an article written by Duzsynki and colleagues that could very well apply to the Mauv Limestone and the Bright Angel shale in the Grand Canyon.

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The yellowish material would be the harder limestone layer, and the green would be the weak shale. Water moving through fractures in the limestone cliff leak out at the cliff face and help weaken the contact with the shale. Also, rain hitting the cliff wall runs down the cliff face and extends the cliff DOWNWARD into the shale (DIGRAM B). Then, the cliff collapses in multiple episodes leaving behind talus, that then decays and erodes (C and D), giving you a profile like A.

Next, turn to a helicopter view of the Grand Canyon on the next page and think about what made the steep shadowed cliff face erode backwards away from the Colorado River? The answer is that the rock underneath the cliff is weak, and when it eroded away the cliff face collapsed to erode back.

Next, think about which cliff face started to erode back first, the shadowed big cliff at the top of the scene or the cliff face near the river? The answer is the shadowed cliff face started to erode back from the river – right away. Even as the Colorado River was incising through it, it was starting to retreat (erode backwards away) from the river … just like the cliff face at the bottom is doing.

Lastly, what came first, the erosion of the narrow canyon at the bottom or the sand bars? Obviously, the narrow slow canyon had to erode out first, before the sand bars.

This sort of thinking logically about a sequence of events is what this section is about.

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5. Step-by-Step guidance in answering the questions in canvas.

The questions are sequenced in three parts, matching the information provided earlier in this PDF File: Part 1. Geological timescape questions: Part 2. Geomorphic timescape questions: Part 3. Historical timescape questions:

BEFORE YOU START ANSWERING QUESTIONS, UNDERSTAND THAT this lab does have some questions that depend on correct answers to previous questions. Its not the whole lab, but I wanted to be up front with you that several sets of questions are sequenced in this way. This causes some students anger, who think that this is unfair because if they get off track at one spot, they are forced to miss several questions. There are four answers to this perspective. First and most important to the learner objectives of a lab science class, this is the way that science works.  We do one problem at a time, and we build on solutions to develop a deeper understanding.  This is not a math class, where there are problem sets.  It is a science lab analyzing real data.  Second and most important to students, no incorrect answers will hurt your grade. You just earn points in another question. Third and also important to students, there are only a few of these situations where prior correct answers are needed for a follow up question. Its not the entire lab. Fourth and also important to students, if you read very carefully and think about the answers to subsequent questions – it is possible to self-correct earlier mistakes and use the second question in a sequence to return to the first question and figure out the correct answer.

Part 1. Geological timescape questions:

QUESTION 1: From oldest to youngest what are the geological formations that you see in these different views of the Grand Canyon? The purpose of this question is for you to familiarize yourself with most of the formations inside the Grand Canyon in a fun and interesting way. You are urged to go back to the background section 4.1 and look carefully at the geological cross-sections. Compare these cross-section in this PDF file to the Paleozoic key in the geovisualization game. Don’t stress. Just carefully move the rabbit up and down the different formations and don’t forget in that in a sedimentary sequence, the oldest has to be at the bottom!

IN THE GAME: Fast Travel to 36.1627 -111.8118 and then use the Helicopter Mode of travel to move to 36.1926 -111.7923 [Just type or paste in these coordinates and click on the helicopter).

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This allows you to see the geological formations in the game (with the key for guidance) to compare with a real helicopter video clip that stays close to the straight and vertical edge of the Desert Facade, then around a sharp corner to the gorge of the Little Colorado River in Grand Canyon. ASUMediaAmp Link – Plays fasterhttps://player.mediaamp.io/p/U8-EDC/qQivF4esrENw/embed/select/media/svJ95X_iDR8t?form=html

And the NPS Link, very big file:https://www.nps.gov/audiovideo/grca/C08E8681-155D-451F-67DB9F7FD8594406/grca-DesertFacadeandLCRGorge_480x270.mp4

QUESTION 2: From oldest to youngest what are the geological formations that you see in these different views of the Grand Canyon? This is the same question as before, but a different area of the Grand Canyon.

ADDITIONAL HINT: for the starting position in the inner gorge, you will have to click off the Paleozoic key in the game and click on the “Paleo” key (for Paleoproterozoic)

IN THE GAME: Fast Travel to 36.0651 -112.0142 and then use the Helicopter Mode of travel to move to 36.0919 - 111.9348 [Just type or paste in these coordinates and click on the helicopter).

This allows you to see the geological formations in the game (with the key for guidance) to compare with the real helicopter video clip that moves into a close up view of Vishnu Temple, as it rotates around for a full view of this landmark feature in Grand Canyon. ASUMediaAmpLink – Plays faster:https://player.mediaamp.io/p/U8-EDC/qQivF4esrENw/embed/select/media/AFHIClEGQdcc?form=html and the NPS Link, very big file:https://www.nps.gov/audiovideo/grca/BC0EE8C7-155D-451F-67B51E32D21BF188/grca-vishnugetclose_480x270.mp4

QUESTION 3. Study this diagram (same as in background information section) made by the Arizona Geological Survey to answer the following question: What was the sequence of geological events that you studied in the first and second questions?

You can either zoom in or look at the bigger diagram in the background info section.

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Part 2. Geomorphic timescape questions:

If you have not yet read the background information for geomorphic timescapes of the Grand Canyon, you will find it useful in answering these questions.

QUESTION 4: What is the name of the formation and the rock type that is responsible for the plateau (rim) of both sides of the Grand Canyon? HINT: this rock type is much ‘weaker’ in wetter areas, where it tends to make valleys because it tends to erode by dissolution in wet regions. However, in the semi-arid environment of the Colorado Plateau, it tends to be mechanically resistant to erosion.

IN THE GAME: Fast Travel to 36.0658 -111.8898 and then use the Helicopter Mode of travel to move to 36.0504 - 111.7968 [Just type or paste in these coordinates and click on the helicopter). This allows you to see the geological formations in the game (with the key for guidance) to compare with a real helicopter video clip that starts with details of the inner Grand Canyon, then zooms out slightly as the view extends to the rim country near Desert View and the Navajo Reservation beyond MediaAmpASUVideo – Play faster:https://player.mediaamp.io/p/U8-EDC/qQivF4esrENw/embed/select/media/5rxbU4CxAOlm?form=html and NPS link, very big file:https://www.nps.gov/audiovideo/grca/B6D01994-155D-451F-679C4406F71D1006/grca-desertviewrimcountrytiltup_480x270.mp4

QUESTION 5 Setup. Please rewatch the National Park Service video from Question 4, and freeze the frame just before the end. Look at the Desert View area and look at the small mesa in the background:

Then, in the geovisualization, go to the base of this mesa at 36.0430 -111.7649. Write down the elevation of the base. Use the Paleozoic key to determine the formations that are making up this mesa.

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QUESTION 5. What is the height of the mesa (at 36.0430 -111.7649) above the surrounding plateau and what formations do you see exposed in this mesa. Use the Paleozoic Key (hint: look at the very top of the key) to learn the names of the formations.

QUESTION 6. The basalt flow remnants on the mesa near Desert View on the South Rim of the Grand Canyon has a radioactive potassium amount where 99.512% is remaining. Using the equations above or one of the calculators, please calculate the approximate age of this lava flow, rounding off to 2 digits.

BACKGROUND YOU WILL NEED TO ANSWER QUESTION 6: What does not show in the geovisualization is the existence of the remnants of a basalt flow that once covered the formations you see in the geovisualization. This lava flow protected these formations from eroding. What is wonderful about basalt lava is that it is possible to date the lava using a technique called potassium-argon dating.

The idea of a radiometric method is illustrated by this graphic. It all depends on there being a radioactive element in enough abundance in a mineral to measure. In the case of volcanic rocks, potassium-40 (or 40K) exists in lots of different volcanic minerals. The radioactive 40K (parent) decays into a stable element Argon-39 (or 39Ar) over time. Every 1.277 billion years, half of the parent is turned into the daughter element. Then, in another 1.277 billion years, another half of the parent is turned into the daughter.

This is called potassium-argon (K-Ar) dating, and you’ll be making calculations in this activity using this method. However, K-Ar dating has been generally replaced by a more complicated approach to do the same thing called Argon-Argon dating. A nuclear

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reaction sends out neutron radiation and converts potassium into argon to make the measurement process more exact and able to use tiny samples.

However, for the purpose of this laboratory, you will calculate the K-Ar age of pieces of remnant basalt lava on top of this mesa

Below are shown three equivalent formulas describing exponential decay:

where    N0 is the initial quantity    Nt is the remaining quantity after time, t    t1/2 is the half-life

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    τ is the mean lifetime    λ is the decay constant

If you know the half-life (1.277 billion years), the initial quantity of the parent (100), and the measured amount of what remains, then its possible to calculate the age.

PLEASE TRY THIS EXAMPLE PROBLEM FIRST:

Example: Vulcan’s Throne where 99.935% of the original radioactive potassium remains. You are welcome to go through the calculations using the equation above, and you will come to 1.2 million years (rounded off to 2 digits). Or, you can use this calculatorhttps://www.calculator.net/half-life-calculator.html

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YOU ENTER: 100 for the initial quantityYOU ENTER: 99.935% radioactive potassium that remainsAnd the calculator produces an age that would be closest to a possible answer of about 1.2 million years old. You will pick the closest answer in the following question

Note: these calculators go off line (and please let me know). However, you can also use just about any other half-life calculator such as any of these:

https://miniwebtool.com/half-life-calculator/http://www.matrixlab-examples.com/half-life-calculator.htmlhttp://www.1728.org/halflife.htmhttps://rechneronline.de/chemie-rechner/half-life.php

QUESTION 6. The basalt flow remnants on the mesa near Desert View on the South Rim of the Grand Canyon has a radioactive potassium amount where 99.512% is remaining. Using the equations above or one of the calculators, please calculate the approximate age of this lava flow, rounding off to 2 digits.

QUESTION 7 SETUP: You now have all of the information you need to estimate the rate of erosion of material that once rested on top of the South Rim formation. There used to be the entire Mesozoic Era sediment (time of the dinosaurs) that rested on top of the Paleozoic formations. All of those Mesozoic Era sediments eroded away, except for little remnants like this mesa. Basalt flows provide geomorphologists the ability to obtain a tiny piece of information about the speed of the erosion of sediment on plateau’s like those on the South Rim of the Grand Canyon. There are more basalt flows than just the one you are studying. This is Red Butte that is relatively nearby, and it has a similar K-Ar age. The same formations as the mesa in question 4 are seen here, but I’ve removed their names.

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This photograph (with the redacted formations) hopefully allows you to see visually what you will be doing in estimating the rate of downward erosion of the rocks above the plateau. Rates of erosion are measured by a distance (in this case meters) and time (in this case millions of years). Thus, divide the answer you got for question 5 (height of the mesa above the surrounding plateau) by the answer you got for question 6 (K-Ar age for the basalt). You should get an answer of meters per million years. Meters per million years is actually the same rate as millimeters per thousand years. The reason is that there are 1000 mm in one meters, and 1000 thousand years in a million years. QUESTION 7: What is the rate of downward erosion of the sediments (exposed in the mesa) that used to cover up the plateau formation where the avatar is standing at at 36.0430 -111.7649? Please use the rate of meters per million years, and select the closest answer.

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SETUP TO QUESTION 8:

Now that you have an understanding of the general rate of erosion of sediments that once rested over the plateau surrounding the Grand Canyon, the next few questions have you figure out the rate at which the Colorado River has been incising downward (eroding downward) to expose progressively older Grand Canyon rocks.

Higher (younger) formations were exposed by the Colorado River as it incised (cut down) first, and then the lower strata were exposed only after the river eroded the higher layer. Thus, the order of incision is from the top towards the bottom. In other words, the RELATIVE ORDER of events is portrayed from 1-6 (deposition of formations) and then the progressive erosion of the Colorado River downward into those sediments in the opposite order (7-11).

To calculate the rate of downward erosion, you need:(1) when the Colorado River started to incise downward(2) the elevation at the top of the rim and(3) the elevation at the bottom of the rim.

You then figure out the elevation difference (subtraction) of the rim above the Colorado River, and divide by how long the Colorado River has been incising downward. It is a bit more complicated than this, but not much.

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MORE SETUP TO QUESTION 8: When did the Colorado River start to flow across the Kaibab Upwarp and begin the incise (erode) downward?

A key piece of information and the answer to this question comes from volcanic ash deposits in the tri-state area of where Nevada, Arizona and California now meet. Before there was a Colorado River, this area had a series of closed-basins that often contained lakes. The figure below from Dr. Jon Spencer of the Arizona Geological shows what the lakes would have looked like at their maximum extent – all before the Colorado River even existed.

Research by several Arizona Geological Survey scientists along with colleagues the U.S. Geological Survey and other institutions have located lots of different volcanic deposits. One bed of volcanic ash (called tephra) is particularly important. It was being deposited at the same time that waters from the Colorado River was first arriving into these ancient lake basins. Through a series of lake overflows over ancient paleodivides, a new river established itself in the lower Colorado River area. The age of this tephra is an important “clock” that established when the Colorado River first started flowing through the Grand Canyon area.

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So question 8 is very similar to question 6, where you calculate the K-Ar age of this ash that provides an estimate for the end of these closed basins and the beginning of the Colorado River:

QUESTION 8. The ash (tephra) deposited just about the time the Colorado River started flowing has a radioactive potassium content of 99.740%, after starting with a content of 100%. Using the equations above (see instructions to Question 6) or one of the calculators (see instructions to question 6), please calculate the approximate age of this lava flow, rounding off to 2 digits.

SET UP TO QUESTION 9: NOW – you have almost all the information needed. You know when the Colorado River started to flow (answer to question 8). You know when the Colorado River reached its current level (about 1.2 million years ago). So you know how long the river took to incise into the Kaibab Upwarp (answer to question 8 minus 1.2 million years ago). So to finish estimating the rate of downward erosion, you just need the elevation at the top of the rim and the elevation at Colorado River beneath the rim location.

QUESTION 9: What was the rate that the Colorado River eroded downward in the area of the South Rim’s visitor center (36.0580, -112.1290)  answered in millimeters per year?

GUIDANCE: You need to know that Colorado River started eroding 4.8 million years ago, and the 1.2 million age of reaching its current elevation was established using the lava flow at Vulcan’s Throne that you learned about earlier in this lab. Thus, it took 3.6 million years for the Colorado River to incide downward through the rocks. Alexis (an ASU student and artist) used Google Earth imagery to simulate what the area might have looked like 4.8 Ma (on the right), when the Colorado River started to flow through the region. You can see all the erosion that has occurred since on the left, courtesy of a International Space Station image.

You can see that there’s two basic types of erosion going on to make the Grand Canyon. The Colorado River is incising downward, and also the formations are retreating

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(eroding backwars) from the River. The focus of this question is ONLY the rate of downward erosion of the Colorado River at the location the South Rim’s visitor center. You will use a time frame of 3.6 million years. This is because the Colorado River incised between 4.8 and about 1.2 million years ago (or over 3,600,000 years). To calculate the rate of downward erosion (incision), you need the millimeters in elevation loss between the South Rim’s visitor center and the Colorado River.

You will be using the fast travel part of the video game, and when you copy and paste (or write down and type in) the latitude and longitude and travel, you will see the elevation next to the compass and the latitude and longitude.

Look at the arrow in this screenshot. The avatar is in the lower right corner, and when the avatar moves, the elevation reading will change.

NOTE: you can copy and paste the elevation information or you can write it down

Visitors Center: 36.060068, -112.110343 Colorado River beneath: 36.097564, -112.117690

By Fast traveling between these locations, you can see the elevation difference and divide that by the time of erosion.

QUESTION 9: What was the rate that the Colorado River eroded downward in the area of the South Rim’s visitor center (36.0580, -112.1290)  answered in millimeters per thousand years? (remember that mm/ka is the same as m/Ma)

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SETUP TO QUESTIONS 10, 11 and 12:

When seen from space (courtesy of NASA), I hope you can see that the Colorado River goes through a mountain (called the Kaibab upwarp). The wetter and cooler higher elevations of this upwarp allow for pine and even spruce/fir trees to grow.

As you have seen in playing the geovisualization video game, the edge of the Grand Canyon is a plateau made up the Kaibab Limestone. You know from studying the K-Ar age of lava flows near the Grand Canyon that only a few tens of meters of rock layers that USED to be on top have eroded away in the last 9 million years.

When the Colorado River started flowing across this region, it was flowing at an elevation very close to that of the Kaibab Limestone you see today. From earlier questions, you know that there was probably a few hundred meters of Mesozoic dsediment on top. However, for the purposes of this lab, you can consider the edge of the plateau next to the Grand Canyon to be the “starting elevation” of the Colorado River about 4.8 million years ago.

In doing this lab, you learned that the Colorado River incised (eroded downward) over a 3.6 million year period, reaching a position close to today’s elevation about 1.2 million years ago.

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This activity asks you to figure out how fast the Colorado River incised (eroded downward) into the Grand Canyon. There are three areas where you will make your measurement and calculations in the next 3 questions

Heart of the Grand CanyonEastern end of the Grand CanyonWestern end of the Grand Canyon

You could find some big differences from place to place.

There are pools of questions inside canvas or these questions, and so I will give you examples of the sorts of questions that you will receive in canvas. You will need to pause the lab once you receive your particular question and work out the answer.

Example Question: what is the approximate rate of Colorado River downcutting (incision) at this location (Latitude: 36.3232 Longitude: -111.8465) in meters per million years?

Step 1: Fast Travel to these coordinatesLatitude: 36.3232Longitude: -111.8465

Step 2: Write down the elevation that is on the rim of the Grand Canyon: 1891 m

Step 3: Jump down to the bottom of the Grand Canyon. You can see the avatarway below hanging out in this screenshot, and look at the elevation of the Colorado River: 901 m

Step 4: Determine how deep the Grand Canyon is at this spot? 1891-901 = 990 m

Step 5: Divide the Depth (990 m) by the amount of time it took the Colorado River to reach its current position (4,800,000 – 1,200,000 or 3.6 million years. The unit of the

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answer should be in meters per million years (m/Ma). The answer would thus be 275 m/Ma.

WHAT DOES THIS MEAN? By itself, its just a number telling you the timescale of downcutting of the Colorado River. Another way of thinking about this is that this rate is the same as 275 mm per thousand years (1/4th of a meter), and it’s the same as 1/4th of a millimeter per year. The Grand Canyon is a spectacular place, and the Colorado River had a lot more work to do than just incise. It also had to transport all of the sediment moved into the river by the side canyon tributary downcutting and also the landsliding of cliff-faced rock that fell into the river. Still, I hope it makes you pause and think about the timescale of canyon cutting.

Example Question: what is the approximate rate of Colorado River downcutting (incision) at this location (Latitude: : 36.0135 Longitude: -111.911) in meters per million years?

Step 1: Fast Travel to these coordinatesLatitude: 36.0135Longitude: -111.911

Step 2: Write down the elevation that is on the rim of the Grand Canyon: 2181 m

Step 3: Jump down to the bottom of the Grand Canyon. You can see the avatarway below hanging out in this screenshot, and look at the elevation of the Colorado River: 780 m

Step 4: Determine how deep the Grand Canyon is at this spot? 2181-780 = 1401 m

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NOTE: DO NOT WORRY ABOUT EXACTLY WHERE IS “THE RIGHT” SPOT TO MEASURE THE ELEVATION. THE CHOICES WILL BE FAR ENOUGH APART SUCH THAT WHERE YOU DECIDE TO HOP THE AVATAR DOWN TO THE BOTTOM WILL NOT MAKE A DIFFERENCE.

Step 5: Divide the Depth (1401 m) by the amount of time it took the Colorado River to reach its current position (4,800,000 – 1,200,000 or 3.6 million years. The unit of the answer should be in meters per million years (m/Ma). The answer would thus be 389 m/Ma.

NOTE: THE INCORRECT CHOICES WOULD BE FAR ENOUGH AWAY SUCH THAT THE EXACT ELEVATION OF THE AVATAR WILL NOT MATTER. CLOSE IS GOOD ENOUGH. JUST WALK DOWN BELOW THE STARTING POINT TO THE BOTTOM OF THE RIVER.

WHAT DOES THIS MEAN? You probably noticed that the rate of incision is a lot higher here in the heart of the Grand Canyon. The reason is that the elevation of the top edge is a lot higher. Thus, the river had to incise into a lot more rock material.

NOTE 1 The questions you will receive from canvas will not be all of the same. They will be randomly delivered to you from three “pools” of questions from the eastern end of the Grand Canyon, Heart of the Grand Canyon, and western end of the game study area.

NOTE 2: The answers are far apart numerically. Thus, even if you find that your answer is a bit different, please pick the CLOSEST to what you calculate.

Note 3: The wording of the question will be the same for all questions, where the X and Y are replaced by pool questions. You will get three questions, one from the eastern, one from the heart, and one from the western end of the Grand Canyon.

What is the approximate rate of Colorado River downcutting (incision) at this location (Latitude: X Longitude: -y ) in meters per million years?

This site is in the eastern part of the Grand Canyon before the Colorado River encounters the Kaibab Upwarp.OrThis site is in the heart of the Grand Canyon where the Colorado River goes through the middle of the Kaibab Upwarp. OrThis site is in the western part of the Grand Canyon after the Colorado River is past the Kaibab Upwarp.

The feedback you will receive after these questions are graded will be as follows: The key to getting these questions correct is to follow the examples provided in the PDF file of instructions. By going slowly through this PDF file, you will have the best

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guidance in how to make these calculations. If you did not understand the PDF file’s instructions, then you need to have contacted your instructor before you took this quiz to obtain extra help. The elevation at the top of the Grand Canyon at this location is ____ m, and at the bottom is _____ m. Thus, the depth of incision is ____ m. When the depth of incision is divided by 3.6 (million years), the answer is ____ m/Ma.

SETUP TO QUESTION 13 on Comparison of Incision Rates Across the Kaibab Upwapp

The Kaibab Upwarp occurred between 70 and 40 million years as a part of a great geological mountain building event called the Laramide Orogency. The river started long after this upwarp. Thus, a mountain stood in the way of the river. How the river gets across this mountain is the subject of a different multi-step lab. In this question, you just rank the implications of this upwarp for rates of river incision that you just measured.

QUESTION 13: Order the rate of incision from highest to lowest of these sections.  Select the best answer.       I realize that this is a compound question, in that you need to have gotten the answers correct for the first part to get this answer correct. This is the way science works. Knowledge is built on knowledge. However, please keep in mind that your grade is based on accumulation of points and you are not penalized for incorrect answers. HINT: The higher the mountain (or rim elevation), the greater the rate of incision. So just look at the space station image on the left and remember the game to think about the relative order from highest incision rate to lowest rate.

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SETUP TO QUESTIONS 14 and 15 ON RATE OF WIDENING OF THE GRAND CANYON:

In answering the previous questions about rates of downward incision of the Colorado River, you now understand the variability of rates in different parts of the Grand Canyon. Rates of incision are highest where the river cuts through the Kaibab Upwarp. They are lowest on the eastern side around Marble Canyon. The same is true for rates of widening of the Grand Canyon. Just look at this cross-section of the Grand Canyon. The Coconino Plateau (South Rim) is much closer to the Colorado River than the Kaibab Plateau (North Rim). This means that the rate of retreat of the rim is much faster on the north side of the canyon than the south side. Widening started 4.8 million years ago, and so the greater distance on the north side means that the rate of retreat was much faster.

Questions 14 has you calculating the rate of widening AND incision at the same spots. Calculating widening is similar to what you did for calculating rates of incision. You just need a distance and the amount of time. The amount of time is when the Colorado River started to incise, which is 4.8 Ma (million years) ago. With each bit of river incision, the formation starts to retreat and the side tributary streams start to erode downward.

Please visit these locations in the geovisualization and write down the elevations you see on the South Rim, Colorado River, and North Rim

South Rim Location: 36.0421° -111.8261° Horizontal distance between: 4500 mColorado River Location: 36.0945° -111.8489° Horizontal distance between: 7000 mNorth Rim Location: 36.1438° -111.9138°

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QUESTION 14. This is a 2 part question. Using the following informationSouth Rim Location: 36.0421° -111.8261° Horizontal distance between: 4500 mColorado River Location: 36.0945° -111.8489° Horizontal distance between: 7000 mNorth Rim Location: 36.1438° -111.9138°

Part 1. Calculate the rate of incision (using the time of 3.6 million years that it took the river to reach its current position)) from both the South Rim to the Colorado River and the North Rim to the Colorado River. Part 2. Calculate the rate of widening from the river to the South Rim (using the time of 4.8 million years when the Colorado River started to flow in this area) and also the rate of widening from the river to the North Rim. QUESTION 15. How to these rates compare? Looking at the data you gathered in question 13, what description would be the best generalization for how rates of deepening and widening compare at this particular cross-section of the Grand Canyon (that is pretty representative of the whole)?

SET UP TO QUESTION 16: THE WEAK LINK IN THE CHAIN There is a relatively thick formation in the Grand Canyon that is extremely weak, meaning it decays faster (breaks apart into pieces) and it also erodes faster (by rainsplash and overland flow) than the other formations above it and below it. Because this unit erodes faster, it undermines the harder rocks above it, and they will collapse suddenly as rock falls and landslides – producing cliff faces above this weak formation. Also, because this unit erodes faster than the rock underneath it, it will erode away, leaving behind a platform of hard rock – called the Tonto Platform and giving a bench appearance.

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IN THE GAME: Fast Travel to 36.1017 -112.2265 and then use the Helicopter Mode of travel to move to 36.0953 - 111.1779 [Just type or paste in these coordinates and click on the helicopter). This allows you to see the geological formations in the game (with the key for guidance) to compare with a real helicopter video clip that shows a view into the heart of the Grand Canyon, going up canyon along the Tonto Platform in the Hermit/Monument creeks. MediaAmpASUVideo – Play faster:https://player.mediaamp.io/p/U8-EDC/qQivF4esrENw/embed/select/media/Cxl456tU3K1t?form=html

NPS link very big file:https://www.nps.gov/audiovideo/grca/C17AE4EE-155D-451F-677D32C4234C2F0E/grca-hermitbasinaroundpimapt_480x270.mp4

Question 16: What rock type and formation is responsible for being the weak link in the chain and allowing the rate of canyon widening to be as fast as it is? To have a better view and understanding of this weak material, and also to figure out the name of this formation and rock type. BE SURE TO LOOK AT THE PALEOZOIC KEY IN THE GEOVISUALIZATION TO FIGURE OUT THE NAME OF THIS FORMATION AND ROCK TYPE.

Part 3. Historical timescape questions:

Questions 16, 17, 18, 19 – using historical photos to understand the pace of change in the Grand Canyon

The questions in this section will be true/false. I rarely use these sorts of questions. However, I think the true/false format will be a bit less stressful and facilitate your thinking about a variety of geomorphic processes that can be observed directly through film or (if you are lucky) in person.

EXAMPLE QUESTION

View in 1890 of Crystal Rapid in the Grand Canyon, where the flow is left to right. The rocks in this rapid come from a side canyon the sometimes sends down flash flooding debris. The photo comes from Robert B. Stanton’s 1890 expedition.

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Then, the next image came from 100 years later …

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Here’s both images, focusing on the rapid:

True or False Question: Crystal Rapid changed from a relatively small obstacle (rapid) for boaters in 1890 into a rapid with lots of large boulders by 1990.

Answer: True. In the 1890 view, the river surface looks to be fairly quiet with a few boulders sticking out above the flow. In the 1990 view, the channel of the Colorado River looks to be choked with boulders resulting in a major rapid. Two major floods in the side canyon, in 1966 and again in 1983, provided the boulders. Eventually, without major flash floods, the Colorado River will be able to erode the boulders and Crystal Rapid will return to its 1890 “more quiet water” appearance. Alternatively, more floods will continue to deposit large boulders and keep the rapid dangerous.

The questions that you will encounter in Activity 1 in this lab via canvas will involve repeat photography in the Grand Canyon, where you will have to observe changes over decades.

You will have 4 questions like this one delivered by Canvas. Just relax and interpret.

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Questions 20 – an essay question that asks you to think about the connection between tourism at the Grand Canyon and science.

It is important that you understand the context of this question. This lab meets three learner goals for the Science & Society requirement in the context of how science and tourism interact. In thinking about the interplay between science and tourism, you are tasked with thinking about reciprocal relationship between science and society in the context of The Grand Canyon.

The Grand Canyon is a “hot topic” for scientific research. It is a mecca for environmental historians, for biogeographers and ecologists who want to study extreme changes in environment over short distances, for wildlife biologists who study endangered species, for geomorphologists who study everything from the timescale of river processes and beach erosion in the canyon to how the Colorado River established itself across a mountain.

There is no question that one of the reasons why so many scientists love to study the Grand Canyon is because its an amazing place – really, the same reason why so many tourists visit the Grand Canyon each year.

There are four readings linked in the canvas instructions to this multistep lab that relate to both tourism and the environmental history of the Grand Canyon. You are expected to refer to these readings, and you are welcome to also cite (citation style should be APA if you refer to outside readings) other sources of information.

How is your essay graded? One third of the points are based on your evidence and reasoning on the topic of all aspects of tourism at the Grand Canyon – from its history to its economic and environmental impacts. One third of the points are based on your evidence and reasoning on the topic of how people have impacted the Grand Canyon – all types of people from scientists impacting the knowledge about the Grand Canyon to your own personal observations if you have ever visited. A third of the points are based on your thoughts about the interplay between science and society through the lens of the Grand Canyon. I hope you can tell that there is no correct answer. We are just looking to read a well-informed and well-reasoned students’ thoughts on the general interplay of science and society at this tourist mecca.

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