Stream_Landscapes_VL
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School
De Anza College *
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Course
010
Subject
Geology
Date
Apr 3, 2024
Type
Pages
7
Uploaded by CountTankPheasant43
© 2010 C. G. DiLeonardo
treams
(any channelized flow of water on the earth’s surface) are part of larger integrated systems drawing energy from the sun. It is through the evaporation on the surface of the oceans, lakes, and streams that the sun's energy lifts water to high elevations in the atmosphere. Water returns to the lands surface through precipitation. If the water reaches the land's surface above sea level the force of gravity will cause it to flow downhill. The energy of a stream is related to the difference in elevation between the head waters
(source of the stream) and base level
(quiet water that the stream flows into, normally sea level). This available energy will act to alter the stream system over time. S Grand Canyon of the Yellowstone The Grand Canyon of the Yellowstone and Yellowstone Falls in Yellowstone National Park, is a great example of landforms cut by a youthful stream. The canyon is V-
shaped, from channel down-
cutting and has no flood plain. The channel also has a number of cascading waterfalls typical of youthful streams cut by running water. Running water on the Earth’s surface is responsible for much of the shaping of the landscape that we see. Understanding how these dynamic systems evolve with time is important in understanding the earth system. Photo courtesy of the United States Geological Survey. Evolution of an Integrated Stream System Virtual Geology Laboratory Edition Christopher DiLeonardo, Ph.D. Earth & Space Sciences De Anza College
Introductory Geology Laboratory
Stream Evolution 2 Objectives
By completing this exercise you will be able to: • Recognize stream eroded canyons from topographic profiles. • Construct a long profile of a stream and relate slope to stream evolution. • Relate changes in the width, length, slope gradient, and depth of a stream canyon to stream evolution. Materials: U.S. Geological Survey topographic map of the Soda Canyon Quadrangle, Colorado, 1:62,500 and plastic raised relief model; pencil; color pencils; eraser; millimeter-scale ruler/straight edge. Valley Profiles You will find a vertical scale for constructing a topographic profile across the Mancos River (A – A’) and Johnson Canyon (B-B’) with map sections below. Each map section is zoomed to the same scale to make construction of a profile easy. Both profiles will constructed to the same scale. To construct your profile, use only index contours (the heavy contour lines). You can skip the other lines in plotting but remember they are still there and give us information about how the profile should look. Note: If you need a refresher on constructing profiles go back and watch the video tutorial again on the Canvas Virtual Lab Module page for this lab module. 450
500
550
600
500
550
450
650
600
500
550
450
650
600
400
Stream
X
Y
X
Y
500
550
450
650
600
400
Steps to constructing a topographic profile. Step 1: Identify every place a contour crosses the line of profile on the map. Step 2: Line up your vertical scale with the line of profile. Step 3: Transfer your elevation values from the line of profile to the vertical scale. Step 4 Complete the profile by connecting the points of elevation on the vertical scale with a single smooth continuous line. Make sure ends of your profile follow the slope to the of your graph. You have learned to construct topographic profiles in an earlier lab. If you need more help with them you should stop and review that lab before proceeding.
Introductory Geology Laboratory
Stream Evolution 3 6,500 ft
6,250 ft
6,000 ft
5,750 ft
5,500 ft
NW
SW
Zoom in of a portion of the Soda Canyon Quad Map from the U.S.G.S. Line of pro
fi
le from NW to SW
shown. Each index contour has been marked o
ff
for you. Note the last contour value is also shown.
Also note your plateau will extend above the 6,500 ft line on your vertical scale.
A
A’
6250
6250
5750
5750
6000
6000
6500
6500
6550
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Introductory Geology Laboratory
Stream Evolution 4 B
B’
6250
6250
5750
5750
6000
6000
6450
6400
6,500 ft
6,250 ft
6,000 ft
5,750 ft
5,500 ft
NW
SW
Zoom in of a portion of
the Soda Canyon Quad
Map from the U.S.G.S. Line of pro
fi
le from NW
to SW shown. Each index
contour has been marked
o
ff
for you. Note the last
contour value is also shown.
Introductory Geology Laboratory
Stream Evolution 5 Slope Gradient and the Long Profile of a Stream System Long Profile The profiles constructed above are sometimes referred to as "cross-profiles" because they extend across a stream valley. These are useful in considering the shape of a stream canyon. To consider the slope of the stream along its length it is necessary to construct a long profile (a graphical representation of slope of the stream). A number of elevation stations have been established along the Johnson Canyon ending at its confluence with the Mancos River. The data in Table 1 can be used to construct a long profile showing the slope along the stream starting at Station A at the headwaters of the tributary to Station F on the Mancos River. Construct this long profile using the vertical scale below. Constructing the long profile of a stream is a simple X – Y plot of data. To construct the long profile plot the points A through F on the graph below. Plot and label each point (A has been done for you. Use 1 mile = 2 cm for your horizontal scale for the long profile. So, 0.1 mile = 2 mm when plotting. Point A has already been plotted for you. Complete the long profile by connecting the points with a curved smooth continuous-line. Table 1 Elevation Data from the Mancos River and Adjoining Streams Station Elevation Distance from Cumulative Previous Station Distance Headwaters
A 6,500 ft. 0.0 miles 0.0 miles
B 6,250 ft. .4 miles .4 miles
C 5,900 ft. 1.8 miles 2.2 miles
D
5,750 ft. 2.0 miles 4.2 miles
E
5,700 ft. .6 miles 4.8 miles
Confluence F
5,665 ft. .7 miles 5.5 miles
Slope Gradient The
Slope Gradient is the change in elevation along a path compared to its change in distance.
To calculate slope gradient, divide the elevation change by the total distance. Slope Gradient = (Elevation A – Elevation F) ft/ (5.5 miles Total Distance
) = _____________ ft/mile. 6,500 ft
6,250 ft
6,000 ft
5,750 ft
5,500 ft
A
o
f
152
6,50
5661
85
51.8
Introductory Geology Laboratory
Stream Evolution 6 Evolution of the Stream System The Mancos River and its tributaries represent an integrated stream system. All stream systems evolve with time. To consider this evolution use the large format .pdf map of the Soda Canyon Quadrangle. This is a “historic” archival map from the US Geological Survey. You can view the map in the Virtual Geology Lab page for this week to answer the questions below. 1. Consider the drainage network formed by the Mancos River and its tributaries. How would you describe this network (i.e. dendritic, radial, trellis)? 2. What does the drainage network tell you about the underlying geologic control on the development of this integrated stream system? Why would such a stream system be an important choice in selecting an area to study stream evolution over time? Hint: Think about 3. Study topographic profiles A-A' and B-B' that you constructed below. Do tributary valleys become deeper or more shallow than the valleys into which they flow? Circle One: Tributaries are Deeper Tributaries are More Shallow 4. Are the tributary valleys wider or more narrow than the valleys into which they flow? Circle One: Tributaries are Wider Tributaries are More Narrow 5. Examine the long profile you constructed. How does slope change as you trace the flow of the stream down hill from Station A through Station F? Circle One: Slope Becomes Steeper Slope Becomes More Gentle
6. If the energy of the stream is related in part to the slope gradient, would you consider the energy of the stream to be evenly distributed over the length of the long profile you constructed? If it is uneven which parts of the profile has a greater concentration of energy? 8
The network formed by Marcos River and its tributaries are dendritic, meaning the small streams converge into larger ones. The energy of the stream is not evenly distributed, the energy upstream is concentrated where the current is greater. Related to the slope gradient, there is more rapid flow upstream. The drainage network shows that the water flows turbulently because of the steep slopes. This stream system is an important choice in selecting an area to study stream evolution because it di
ff
ers from radial and trellis.
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Introductory Geology Laboratory
Stream Evolution 7 Examine your answers for questions 1 through 6 and complete the matrix below. Use descriptive terms i.e. "wider," vs. "narrower," etc., to compare the Mancos River to Johnson Canyon and to an unnamed tributary of Johnson Canyon. For slope gradient use descriptive terms as well, steep, gentle, intermediate (you don’t have calculations for all three streams). Also add the relative age of these three streams to each other. Which one is older, that is which one has been around the longest? Table 2 Evolutionary Trends in an Integrated Stream System STREAM Size Width Slope AGE
Gradient Mancos R. ____________ ____________ ____________ ____________ Johnson C. ____________ ____________ ____________ ____________ Tributary ____________ ____________ ____________ ____________ Generally, streams are evolving dynamic systems. The evidence of this rests in the observations and conclusions listed above. 8. How did you determine the relative ages for these three streams?
Acknowledgements The Soda Canyon Quadrangle map used for this activity was provided courtesy of the United States Geological Survey. About the Earth Discovery Project The Earth Discovery Project is a collaborative effort to integrate hands-on discovery-based learning with modern research tools in undergraduate geoscience education. The approach is to develop and disseminate a comprehensive set of learning resources and experiences supporting systemic educational reform. The logo of the Earth Discovery Project portrays the earth as a three-dimensional puzzle. The globe used in the logo is from NASA’s Blue Marble Project
. The Blue Marble
is a unique view of the earth, which integrates numerous data sets to construct a “true-color” three-
dimensional globe.
Longer
Widest
Intermediate
Oldest
Long
Wide
Gentle
Younger
Short
Narrow
Steep
Older
Young streams are faster and erode. Middle aged streams are slower and are v-
shaped. Older rivers are much slower, wider and level.