Grand Canyon Geomorphology: Why So Different? : GPH 112: Intro to Phys Geography Lab (2024 Spring)
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Arizona State University *
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112
Subject
Geology
Date
Apr 3, 2024
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Uploaded by DoctorProtonQuetzal26
Grand Canyon Geomorphology: Why So
Di
ff
erent? Due Apr 30 at 11:59pm
Points 7.5
Questions 8
Available after Mar 24 at 12am
Time Limit None
Instructions
In the previous lab, you learned of some hypotheses for the formation of the Grand Canyon.
Additionally then, we need to explain why the sides of the canyon (north and south of the river) differ
so much from each other.
Attempt History
Attempt
Time
Score
LATEST
Attempt 1
7 minutes
7.33 out of 7.5
Score for this quiz: 7.33 out of 7.5
Submitted Mar 24 at 6:33am
This attempt took 7 minutes.
This is an almost straight-down looking view (planimetric) of the heart of the Grand Canyon, between
the South Rim and the North Rim visitor centers. Clearly, one side (of the Colorado River) is not like
the other. Focus on the Colorado River and compare the south (lower) side to the north (upper) side. You should notice a difference in tributary stream lengths, drainage basin sides, and the presence or
absence of of temples (isolated mountains inside the canyon).
So the question is: WHY? Why does there exist such a dramatic asymmetry in the geomorphology of
these two sides? It is your task in this lab to figure out a reasonable and testable answer by
reviewing multiple hypotheses.
Question 1
1 / 1 pts
Now let's look at the major differences between the northern and southern side of the canyon, first by
looking at the presence of temples.
Temples are mountains inside the Grand Canyon. Photographers love to image them from all different
angles.
Isis Temple
Shiva Temple
Brahma & Zoroaster
Temples
Your task is straight forward. Take helicopter flights across the Grand Canyon to figure out where they
are found. Just look around for isolated mountains and determine if they are on the north side of the
Colorado River or the south side of the Colorado river. There really isn't another choice. Take two trips via helicopter and look for Temples and also the size of the drainage basins
(watersheds) draining the two sides). SOUTH SIDE FAST TRAVEL HELICOPTER TRIP
Start: 36.1158 -112.2798
End: 36.0184 -111.9420
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Correct!
Temples are found mostly on the north side of the Colorado River
Temples are found mostly on the south of the Colorado River
There are a few features that might be considered temples on the south side of the Colorado River,
but nothing is named. All of the famous Temples and 99% of the isolated mountains are found on the
northern side of the river.
Question 2
1 / 1 pts
NORTH SIDE FAST TRAVEL HELICPOPTER TRIP
Start: 36.2643 -112.2853
End: 36.0692. -111.9530
Drainage basins (tributary streams to the Colorado and all of their tiny tributaries) are found on both
sides of the Colorado River. Their size is vastly different on the north and south sides. Refer back to
the two helicopter trips you took in the previous question, and also refer to this International Space
Station image of the Grand Canyon that has been annotated to compare opposing watersheds on the
north and south sides of the river:
east
west
south
Correct!
north
The north side of the Colorado River has vastly larger drainage basins (watersheds).
Question 3
1 / 1 pts
QUESTION: What side of the Grand Canyon (between the North and South Rims) have the bigger
drainage basins? Hypothesis 1:
One of the first white explorers to keep a written record of their journeys to Grand Canyon region took
Yes. The rock types are completely different in their nature and sequence.
Correct!
No. The rock types (their sequence from top to bottom) are the same.
Yes. While there are similarities, the rock types are quick different in type and sequence.
The best answer is No. The rock types, both their sequence and their type, are virtually identical on
the rims and as you go down into the canyon. If you were a professional geologist, trained in field
mapping and the ability to evaluate thin sections via a petrographic microscope, you would find facies
changes. However, even the best geologists would never put down a different answer than NO! even
those that have studied these subtle facies changes.
Question 4
1 / 1 pts
note of exactly what you observed in the first two questions - of the obvious asymmetry. They
hypothesized that the reason was the rock types were different on the north and south sides. You have the benefit of instant access to the geologic rock layers within the canyon. Within the
geovisualization of the Grand Canyon Topography and Rock types, you can quickly travel around and
examine the rock types. Observe the sequence of rock types from the rim down into the canyon. Do you think that the rock types are different on the north and south rims? Select the best answer. Hypothesis 2: Elevation
In the Grand Canyon microclimate and vegetation geovisualization, you developed a deep
understanding of the relationship between elevation, exposure, microclimate and the type of
vegetation (and its abundance). When you saw the title of this lab, you probably came up with the
immediate hypothesis that elevation might be a reason for the geomorphic asymmetry in drainage
basin size. If you need a refresher on the elevation of the north side of the Grand Canyon around the North Rim's
visitor center and the south side of the Grand Canyon around the South Rim's visitor center, then use
FAST TRAVEL in this geovisualization. SUGGESTION ON NORTH RIM HIKE: Start at Point Sublime (36.2388 and -112.2327) and just walk
or bounce the avatar along the rim to the east for awhile - keeping an eye on the elevation. SUGGESTION ON SOUTH RIM: Start and Desert View (36.0346 and -111.8288) and walk/bounce
towards the South Rim's Grand Canyon village (across from Bright Angel Canyon) and keep and eye
on elevation.
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They are about the same elevation.
Correct!
North Rim is about 300 meters higher
North Rim about 600 meters higher
North Rim about 1200 meters higher
The North Rim is about 2400 m in elevation, while the South Rim is about 2100 m.
Question 5
1 / 1 pts
Which side of the Grand Canyon (in this area) has a higher elevation and by about how
much? Hypothesis 3: Tilting
You have heard and read about the Kaibab Upwarp being a broad domed mountain, and the term
upwarp means the upwarping of rocks. You may remember this diagram showing a "cross-section" of
the geology across the central Grand Canyon (North Rim left and South Rim left)
You can probably see the tilting of the sediment. So a third hypothesis is that this tilting might be a
reason for the formation of the Temples (internal canyon mountains shown in this diagram) and bigger
drainage areas on the north side.
But in science, we try to test -- to falsify -- everything. Sure - this diagram looks interesting and it
looks like it is based on field mapping data. But please confirm it. You can do this in the
geovisualization by following "contacts".
The word "contact" means the touching of different geological features. So if you look at the bottom
of the Paleozoic layers -- it is the Great Unconformity. Below the Tapeats Sandstone is a mixture of
metamorphic and igneous rocks that are very old. In the game, they have all sorts of colors. But
above the Great Unconformity - the color sequence is the same. A dull Yellow Tapeats peaking out
from underneath an olive Bright Angel Shale.
You can test the tilting of sediment by "following" the contact between the Great Unconformity and the
Paleozoic sediment above -- and you do this by hiking your avatar up Bright Angel Creek (the very
straight drainage). Eventually, the ancient Proterozoic rocks underneath the Tapeats will disappear. But for the bottom part of Bright Angel Creek, you can examine the elevation of this contact.
If the elevation of this contact goes up steadily the further you go up the creek - this would be
consistent with (would not contradict) the tilting of the rocks. A good place to start is here: 36.1086
and -112.1006, where the avatar is standing at 1141 m on the Tapeats , which is directly on top of the
irregularly colored Proterozoic rocks beneath. When we travel up the canyon, we see that this contact
point rises to roughly 1380 meters!
The Kaibab-Toroweap formation contact on the North Rim is about 30 m higher at Cape Royale than at Shoshone
Point on the South Rim, and this also confirms the tilting. Correct!
The Kaibab-Toroweap formation contact on the North Rim is about 180 m higher at Cape Royale than at Shoshone
Point on the South Rim, and this also confirms the tilting. So to confirm this tilting of the layers within the canyon, we will try prove this tilt within another area of
the canyon, specifically we will look at the Kaibab-Toroweap formation contact point along the North
and South Rim. QUESTION
What is the elevation difference between the Kaibab-Toroweap contacts on the North Rim and
South Rim of the Grand Canyon? Does this confirm or disprove the existence of the tilting?
INSTRUCTIONS Fast Travel to Cape Royale on the North Rim and look at the elevation of the
contact between the lighter blue Kaibab Limestone (making up the plateau) and the darker blue
Toroweap formation underneath. If you walk along the rim, this contact is often right at the north rim
itself or just below it. Write down the elevation
Then, Fast Travel to Shoshone point on the South Rim, and look at the same thing - the elevation of
the contact between the Kaibab Limestone and the darker blue Toroweap formation. Write down the
elevation.
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The Kaibab-Toroweap formation contact on the North Rim is about 300 m higher at Cape Royale than at Shoshone
Point on the South Rim, and this also confirms the tilting. The Kaibab-Toroweap formation contact on the North Rim is about 580 m higher at Cape Royale than at Shoshone
Point on the South Rim, and this also confirms the tilting. The Kaibab-Toroweap formation contact on the North Rim is about 180 m higher at Cape Royale than
at Shoshone Point on the South Rim, and this also confirms the tilting.
Question 6
1 / 1 pts
Hypothesis 4: Ancient Lakes and Cliffs
Dr. John Douglass and colleagues
think that the position of the Colorado
River through the Grand Canyon was
established by the position of cliff faces
(often called escarpments). If you look
at image F in their 2020 paper -- look at
the Echo Cliffs and the Vermillion Cliffs.
Then, look at E, where the edge of the
brown shading would be the position of
those cliffs in the past. It's the normal
process of cliff retreat. So using typical
rates of cliff retreat, they
"reconstructed" the Echo cliffs
backward in time to when a giant lake
(Lake Hopi) overflowed (their
hypothesis for origin of the Colorado
River & the Grand Canyon). So when
the lake overflowed, the Colorado just
followed the lowest elevations, next to
the ancient Echo cliffs. The hypothesis here is that the bigger
drainage basins on the north rim were
set in motion by this original position of
the river, "downhill" from the big Kaibab
upwarp (Kaibab Plateau).
The lab that you submitted on the Rates of Change 2 for the Grand Canyon Geomorphology
geovisualization labs had you calculate the average rate of canyon widening (between the north and
south rims). That rate, when extrapolated to the nearest thousand meters was roughly 3000 meters
per million years.
Since 1000 meters is a kilometer, the rate in the example would be about 3 kilometers of widening per
million years to separate the north from the south rim.
Now let's see if the Dr. Douglass's hypothesis matches the measurements from the previous lab. According to this hypothesis, the average distance between the historic Vermillion Cliffs and the Echo
Cliffs at the middle point in Marble Canyon (look at figure F above) is about 17 kilometers. QUESTION: Determine the rate of canyon widening using the hypothesis from Dr. Douglass if
the canyon needed to expand 17 kilometers in 4.8 million years. What is the percentage
margin between the observations and this hypothesis (calculate the percentage difference). Then think about whether or not the percent difference is "close enough" to not contradict the
hypothesis of John Douglass and colleagues. There is no correct answer to this, we just wish for you
to think about whether or not the data you gathered in doing the Grand Canyon labs contradicts the
Correct!
3.5 km / mya - 15% difference
1.2 km / mya - 52 % difference
3 km / mya - 20% difference
2.6 km / mya - 15% difference
Question 7
1 / 1 pts
Correct!
Yes. More than one of the hypotheses could not be disproven.
No. All of the hypotheses could be disproven
What is missing is how the hypotheses might explain the larger drainage basins and the existence of
the temples. In other words, what processes would connect higher elevation and tilt to bigger
drainage basins and temples. Even if you think that the 15% difference disproves the idea of Dr. Douglass and colleagues, the
higher elevation and tilting of the rocks are both consistent with data you gathered (if you answered
the questions correctly). So yes is the best answer.
Question 8
0.33 / 0.5 pts
hypothesis proposed by Dr. Douglass and collaborators. In science, we often run into hypotheses that contradict each other. So that when you obtaining
confirming data for one, another is contradicted (falsified or disproven). But in many cases, it is
possible to have multiple hypotheses that have confirming data. This could be the case here. Based
on your observations/answers for the previous questions, are there multiple possible explanations for
the the larger drainage basins on the north side and the position of the temples on the north side of
the Grand Canyon?
So... what is the answer to the lab question? Why one side and not the other? What processes would
connect higher elevation, tilt, and possibly ancient river placement to bigger drainage basins and
temples?
The answer has to do with the connection between slope length and the development of a tiny
tributary creek (small drainage). There has to be a certain length of slope for there to be enough
runoff from rainfall (or snowmelt) to be able to begin to incise a channel and create a small creek.
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Answer 1:
Correct!
North Rim
South Rim
Answer 2:
Correct Answer
South Rim
You Answered
North Rim
Answer 3:
Correct!
taller
shorter
Quiz Score: 7.33 out of 7.5
Fill in the blanks that make sense within the reasoning provided. The length between the top of the [ Select ]
and the Colorado River is much
longer than the distance from the [ Select ]
to the Colorado River. Thus, a lot
more tiny creeks can exist on the Kaibab Plateau (north side of the river). Tiny creeks come together
to make bigger creeks, which come together to make even bigger creeks, and this is the way a
drainage basin develops. Drainage basins that grow larger and larger (as the tiny creeks extend headward) will eventually meet
in their headwaters. When they meet, they can create a Temple. The elevation difference of a
drainage basin is also important, and the bigger the elevation difference between top and bottom of a
drainage basin will result in taller temples.