Lab Exercise 7_stream processes_FA21
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Laboratory Exercise 7: Stream Processes and Landforms
Introduction to Geology II: Earth’s Surface Processes
Name____________________
Score _____/25
INTRODUCTION In this exercise, we will review some different stream processes and the landforms they create by using topographic maps and Google Earth. For a review of topographic map concepts, see the Week 5 lab and its tutorials
. For a review of how to use Google Earth, see the Week 3 lab and its tutorials
. Having your textbook
handy will be helpful for reviewing the names of different concepts and landforms, as well as using the diagrams and links in the Short Lesson page in this week’s module.
Part A: Evaluating streams on the Promontory Butte, AZ map
On the next page, you will find a portion of a topographic map. The original map is a 7.5-minute quadrangle titled the Promontory Butte Quadrangle, Arizona. This location is in the high desert, just south of Flagstaff, AZ and the Grand Canyon. Examine the map clip and note the scale below it. (Note: If you have trouble reading the numbers on
the map, or seeing the contour lines, please download and look at the entire quadrangle, which can be found in the Week 7 Module materials. This is a quality pdf file and you can zoom in to see more clearly.)
Task A1. Stream Gradients (2 points)
Find the Mogollon Rim on the clip. This is a steep feature that runs across the map. If you want to know what it looks like in real life, do an internet search to find an image. Of course, you already knew this would be steep from the topographic map, as the contour lines are very close together! Let’s look at the streams on the map. They are blue lines. The ones on the north side of the rim flow from the rim downhill, to the north. On the south side of the rim, the flow from the rim downhill is towards the south. How do I know this? I looked at the contour lines and found the elevations along a river. Find Beaver Canyon on the north side of the Rim. At its headwaters, very close to the rim, I see where the blue line starts, and look for the brown contour line nearby. There is a bold brown line, called an index contour, that is labeled 7750, meaning the elevation is 7750 feet along that line. There is another brown line downhill from that, closer to the stream. Because the contour interval is 50 feet on this map, I know that this contour line represents 7700 feet in 1
©Michelle Stoklosa 2021
elevation. So…Beaver Canyon starts at about 7700 feet in elevation, right? If you follow that blue line further to the top, or north, on the map, and check in with the brown contour lines nearby, you will see that they are lower and lower in elevation, so the stream is flowing in that direction. You can also just look at the contour line shape as the cross a stream. They are V-shaped, and the V points in the upstream direction. Now that you are familiar with the appearance of streams on a topographic map, let’s calculate some gradients (also called the slope of stream). More specifically, let’s calculate the gradient of a 2-mile stretch of Beaver Canyon on the north side of the Mogollon Rim and a 2-mile stretch of Horton Creek to the south. To do this, print out the map on the next page, then use a string (or piece of paper) to measure out 2 miles (you must use the 2 mile line at the bottom of the map clip),
then placing this on the
map along the stream. Start as close to the headwaters as you can, and note the elevations at each end of the string. Input these values into the blanks below then divide the difference in elevation by 2 to get a gradient in feet/mile. Note that we have already determined the elevation of the headwaters for Beaver Canyon, so that elevation is already done
. (Don’t have a printer? Do the best you can on your computer screen by manipulating the blue line, as that represents 2 miles on that map.)
Gradient of Beaver Canyon=
(7700 ft - ________ft)/ 2 mi = __________ft/mi
Gradient of Horton Creek = (______ft - ________ft)/2 mi = __________ft/mi
Questions: 1.
(1 point) Which of these two streams has the steeper gradient? Explain your answer below by:
a.
First, using the values you calculated above
b.
Then, checking your numerical answers to see if they agree with the closeness of the contours on the map.
2.
Which type of stream are both Beaver Creek and Horton Creek most like, straight, braided or meandering? (
Choose just one type, and be sure to look at your textbook for ideas
.) (1 point)
3.
Which letter of the alphabet might resemble the shape of the cross-section (or side-view)
of these creek beds, a narrow V or a wide U? (1/2 point)
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©Michelle Stoklosa 2021
Portion of Promontory Butte Quadrangle, Arizona (United States Geological Survey, 1952)
Map scale 1:62,500 Length of line below = 2 miles
Contour Interval = 50 feet
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©Michelle Stoklosa 2021
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Task A2: Creating a topographic profile across the Mogollon Rim (3 points)
Now let’s get an idea of how steep that Mogollon Rim really is using the contour lines. Using the graph below
, create a topographic profile across the Mogollon Rim, from South to North. To do this, find the red double-headed arrow running north and south on the map clip on the previous page. Create a profile starting at the head of the double-headed red arrow on the south and ending at the head of this arrow at the North.
To review how to make a topographic profile, review the videos and your lab from the Week 5 lab on topographic maps. I would suggest filling in the elevations for each line on the y-axis to make it easier to plot. Whether you are printing the lab and completing it by hand or completing the lab electronically, the easiest way to complete the profile is using the “Map and Grid for Week 7 Profile.jpg” file located in the week 7 module. Also, because this is a steep area, with many contour lines, you can use just the index contours (the bold brown ones) to create this profile, if you’d like. South
North
Questions: (1 point)
1.
Use the two different gradients you calculated in Task A1 to determine which direction the steep ridge of the Mogollon Rim will most likely migrate over time (North or South; choose just one). Remember that streams erode in a headward (upstream) direction! Explain your answer.
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©Michelle Stoklosa 2021
8000 ft
7000 ft
6000 ft
Part B: Evaluating the Missouri River near Leavenworth, KS
On the next page you will find a portion of the Leavenworth, KS 7.5-minute quadrangle. This is a location in the Great Plains of the U.S. Examine the map clip and note the scale and contour interval information below it. (Note: If you would like to see the entire quadrangle, you can download the file from the Week 7 module in Canvas).
Task B1: Floodplain of the Missouri River (3 points)
1)
Measure the width of the Missouri River floodplain
(not just the part of the river that has water in it) in two different places on this map clip, and note these measurements in the spaces below. I have measured one width for you…yours should not be way off from this.
Width 1: ___2.6__map inches
Width 2: _________map inches
Width 3: _________map inches
Note: Be sure to measure the width perpendicular to the river and floodplain, not just horizontally. How will you measure the width of the floodplain? You can print out the page and use a ruler. You can also show the ruler for your document on your screen(View > Ruler), then use a piece of paper to measure the width of the floodplain on the screen, then hold it up to the ruler. See my example (double-headed red arrow across the river and flood plain) of one place to measure. I used a piece of paper to mark the ends of each arrow on my sheet, then rotated my sheet a bit and held it up to the ruler shown in the Word document, and it measured at 2 and 5/8”, or 2.625”. I rounded to one decimal, and put 2.6 inches for Width 1 above. Now do this for 2 more places.
2)
Now let’s get an average width:
Average width = Add all three widths above, then divide by 3 = ______ map inches
3)
Now use the
fractional scale,
given at the bottom of the map clip, to calculate this width in miles. Show your work by following each of the steps below:
a.
First, convert map inches (found above) to real world inches by multiplying the average width you found above, in inches, times 62,500 = ___________real world inches
b.
Now convert these real-world inches to miles: ____________real-world inches/12 inches = ___________real-world feet
___________real-world feet/5280 feet = _____________real-world miles
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©Michelle Stoklosa 2021
Portion of Leavenworth, Kansas Quadrangle (United States Geological Survey, 1951)
Scale 1:62,500
Contour Interval = 20 feet
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©Michelle Stoklosa 2021
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Task B2: Calculating gradient (1 point)
Now calculate the gradient of the river in this location using the following information:
The 760-foot brown contour line crosses the river at about Weston Bend on this map clip. The next contour
line that crosses the river upstream
is 12 river miles away (and off this map clip). Hint: You do not actually need to look at the map to figure out the gradient…all necessary information is given in the statements above.
Show your work below, and express the gradient in feet/mile:
Questions:
Use the work you did in Tasks B1 and B2, and look at the entire map (called the Leavenworth Quadrangle, which can be found in the lab files of Week 7 in Canvas) to address the following questions:
1. Which type of stream is the Missouri River most like, straight, braided or meandering? Choose just one type and don’t forget to consult your textbook for help. (1/2 point) 2. Which stream landform are both Mud Lake and Horseshoe Lake? (You need to look at the entire map posted in Canvas to find these, not just the clip on the page before.) (1
point)
3. Which letter of the alphabet might resemble the shape of the cross-section
of this river bed, a V or wide U? (1/2 point)
4. Now summarize, in a sentence or two
below, how the Missouri River is different
than the streams on the Promontory Butte map. Include aspects of gradient, cross-
sectional shape of stream channel, landforms,
and anything else. (1 point)
5. Now consider the sediment
that you would find associated with the Missouri River (part B) and the streams in part A. More specifically, contrast the clast size, shape and 7
©Michelle Stoklosa 2021
sorting of the
sediment
you
would expect to
find in the
floodplain of the
Missouri River
with that in the
floodplain of
Beaver Canyon,
and do this in a
sentence or two.
(
Hint: review
section 14.3 in
your textbook,
especially “How
do streams
transport?” and
“Depositional
Processes” AND
look at the figures
from Chapter 6
that I posed in our
Short Lesson
in
this week’s
module) (1 point)
Part C. Using
Google Earth to
examine stream
processes and
landforms
To get started on this part of the exercise, open your good friend, Google Earth Pro, on your computer. Task C1. Goosenecks of the San Juan River
Type in “Goosenecks State Park, UT” into the Search window in Google Earth (top, left) and hit enter or Search. You will fly to the edge of the San Juan River in Utah, at a portion referred to as the Goosenecks. Zoom out and have a look around.
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©Michelle Stoklosa 2021
Questions
1.
What are these “gooseneck” stream features also called? (Hint: A photo of this area can be found on page 484 of your textbook, in the section on Stream Rejuvenation.)
(1/2 point)
2.
This area experienced stream rejuvenation
, which means that something caused the San Juan River to cut down dramatically into the landscape later in its
life, and thus it has deep sides. What most likely caused this river to “rejuvenate”? (1 point)
3.
Now zoom way out (so that your eye altitude is over 30 km) and look around at the drainage pattern
in the area. Which drainage pattern does the San Juan River dominantly show (use Figure 14.4 Different Types of Drainage Networks, on page 471 of your textbook, to help you decide)? (1 point)
Task C2. Determining drainage patterns
Go to the locations below by copying and pasting the decimal degrees coordinates
below into the Search window in Google Earth, then clicking Search. Look around (you will need to zoom out to get a view of the drainage patterns), then determine which drainage pattern is shown at each location. Use Figure 14.4 in your textbook to help you decide. (3 points)
Location Name
Decimal Degrees
Best eye altitude to see pattern
Choose a drainage pattern type
Mt. Rainier
46.852415, -121.759712
~30 km
Radial or Dendritic?
Susquehanna River near Harrisburg, PA
40.270064, -76.899665
~30 km
Parallel or Trellis?
Grand Canyon Village
36.054630, -112.140171
~60 + km
Rectangular or Dendritic?
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©Michelle Stoklosa 2021
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Task C3. Finding stream landforms
For this task, you will need to browse around the Earth using Google Earth Pro and looking for examples of the stream features listed below. You might start by typing in the name of a river you know into the Search window, then browsing around looking for these features. Once you find the feature, make note of the name of the stream in the table below, and write down the latitude and longitude coordinates of where this feature can be seen, in decimal degrees.
(To change the coordinates to this format go to Preferences under the Google Earth menu (Mac) or Tools then Options (PC), then
select Decimal Degrees and save. Write down the coordinates when the hand tool is right in the middle of the feature. See my example below. Note that by copying my coordinates and pasting them into the Search window in Google Earth, you will fly right to the center of the delta. To see the delta more clearly, you will need to zoom out to an eye altitude of about 80 kilometers. Please help me see your features by adding eye altitude as well. (3 points)
Stream Landform
Name of stream
Latitude, Longitude (in decimal degrees)
Best eye altitude to see
this feature
Delta
Mississippi River
29.236656, -89.350657
80 km
Braided stream
Alluvial fan
Point bar
References:
United States Department of the Interior Geological Survey. (1951). Leavenworth Quadrangle, Missouri-Kansas [topographic map]. 1:62,500. Denver, CO or Washington,
D.C.: U.S. Geological Survey.
United States Department of the Interior Geological Survey. (1952). Promontory Butte Quadrangle, Arizona [topographic map]. 1:62,500. Denver, CO or Washington, D.C.: U.S. Geological Survey.
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©Michelle Stoklosa 2021