Topographic Maps Lab GE F23
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Iowa State University *
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100L
Subject
Geography
Date
Jan 9, 2024
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9
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Name: ______________________________________ Topographic Maps Lab Learning Goals ▪
Practice spatial thinking skills by translating information between 3-dimensional and 2-
dimensional representations of the Earth’s surface.
▪
Develop an understanding of how a 2-dimensional topographic map represents the 3-
dimensional surface of the Earth.
Introduction: Earth processes and the results of these processes occur in three dimensional (3D) space, but we often represent such information in two dimensions (2D) using maps. An important skill for scientists, therefore, is the ability to translate information back and forth between 2D and 3D. Topographic maps, or elevation maps, are a common way to represent Earth’s 3D surface in an information
-dense 2D format. Part 1: Interpreting topographic maps (2D → 3D)
The first part of this lab will involve learning how topographic features, such as mountains, ridges, and stream drainages, are represented on topographic maps. You will be asked to translate from a 2D map to a 3D surface that you sculpt in an Augmented Reality Sandbox (ARS). Only one team of 2-3 students can use the ARS at a time. Please spend no more than 15 minutes with the ARS to ensure that all teams have time to work with it. Part 2: Interpreting 3D terrains (3D → 2
D) Students will use digital landscapes in Google Earth to identify ridges and valleys and plan a hypothetical hike through the badlands of northern Wyoming.
Glossary and “Rules of Thumb” for Topographic Maps
A contour line connects points of equal elevation on a topographic map. Contour lines always separate points of higher elevation from points of lower elevation. For example, the 100 contour line separates the 104 point from the 96 point on the map to the right. One can determine which way is uphill or downhill on the map by checking adjacent areas with labeled contour lines. The contour interval is difference in elevation between any two contour lines. On the map to the right, the contour interval is 10 units. Some contour maps show heavier contour lines that are labeled with an elevation separated by finer contour lines that are not labeled. These lines are called index contours and minor contour lines, respectively. The closer the contour lines are on a map, the steeper the slope or gradient. In other words, steep slopes are represented by closely spaced contour lines. If the spacing between contour lines changes on a slope, then the steepness of the slope has changed. Contour lines never cross each other, but they may merge to represent vertical surfaces, like cliffs or walls. Valleys, and streams are represented on topographic maps with a V pattern in which the apex, or point, of the V points uphill. Closed, concentric rings of contour lines represent a hill or peak of a mountain. Closed, concentric rings of contour lines with hachure marks represent closed depression or pits.
Part 1: Interpreting topographic maps (2D → 3
D)
Each group must choose either the Mount St. Helens topographic map or the Island of Hawaii topographic map and complete the associated exercise and questions. Map 1: Mount St. Helens Elevation shown in meters. N
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Recreate the Mount St. Helens topographic map using the Augmented Reality Sandbox (ARS) and answer the following questions. Contour lines shown by the ARS do not need to perfectly match the contour lines shown on the map. Once you have finished: •
U
se the keyboard command “Function+PrtScn” to save a screen capture to the desktop; and •
Please include your section number and last names of your group members in the file name. Question 1: What is the highest elevation shown on the Mount St. Helens topographic map? Be sure to include units. Question 2: What is the lowest elevation shown on the Mount St. Helens topographic map? Be sure to include units. Question 3: What is the contour interval of the Mount St. Helens topographic map? Be sure to include units. Question 4: Locate three (3) valleys on the Mount St. Helens topographic map. Label the valleys on the map by drawing a stream (dashed or solid line) running through each valley and label the line “stream.”
What features on the topographic map did you use to locate the valleys? Question 5: In 1980, an earthquake within Mount St. Helens caused a side of the volcano to collapse, triggering an explosive eruption that sent a pyroclastic flow down into the surrounding area. Which side of Mount St. Helens collapsed due to the earthquake? Explain your reasoning by describing the shape of your ARS model. Question 6: Seconds after the first blast, an enormous vertical eruption occurred at Mount St. Helens which blew the top off of the mountain creating a nearly circular depression or caldera. Which has a steeper slope? The inside of the caldera or the flank of the volcano? Explain your reasoning.
Map 2: The Island of Hawaii Elevation shown in feet. N X
Recreate the Island of Hawaii topographic map using the Augmented Reality Sandbox (ARS) and answer the following questions. Contour lines shown by the ARS do not need to perfectly match the contour lines shown on the map. Once you have finished: •
U
se the keyboard command “Function+PrtScn” to save a screen capture to the desktop; and •
Please include your section number and last names of your group members in the file name. Question 1: What is the highest elevation shown on the Hawaii topographic map? Be sure to include units. Question 2: What is the lowest elevation shown on the Hawaii topographic map? Be sure to include units. Question 3: What is the contour interval of the Hawaii topographic map? Be sure to include units. Question 4: Locate two circles on the map: a gray circle and a circle with an “x.” The circle with the “x” represents the location of the city of Hilo whereas the gray circle represents the Mauna Loa Observatory, a facility used to monitor atmospheric conditions since 1957. Assume your group is in charge of designing and building a road between Hilo and the observatory. Ideally, the road should cover: 1) the least amount of horizontal distance; 2) the least amount of elevation change (i.e., does not go over multiple hills and valleys); and 3) the shallowest topographic gradients or slopes. Using the map and your ARS model, choose the path of your road that fulfills the three criteria above and draw and label the path on the topographic map. Question 5: The Mauna Loa Observatory (gray circle) is positioned, strangely enough, near the summit of the Mauna Loa volcano. The summit of the volcano is an ideal place for an observatory, because its elevation is high enough that measurements represent a good average of the entire Pacific region and are not affected by local events on the island. What is the approximate elevation of the Mauna Loa Observatory? Find another location on the island (not on Mauna Loa) that would be a good site for a similar observatory. Mark and label this location on the topographic map.
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Part 2: Interpreting 3D terrains (3D → 2
D) Each student will be provided with a Google Earth file of Alkali Anticline in northwestern Wyoming. Please use a personal device or one of the provided tablets to explore the landscape. Ask your instructor for help in using the on-screen tools to navigate in Google Earth. Alternatively you can use the keyboard shortcuts listed on the last page of the lab. Task 1:
Note the red lines marking the tops of some ridges and blue pins marking low elevation areas (depressions, valleys, etc.). Find these ridges and areas of low elevation on the topographic map on the next page and mark them on the map using colored pencils.
Points will be awarded based on accuracy. Task 2: Imagine that a friend and you have parked a vehicle at the spot marked “P” on the topo map. Your goal is to hike to a point of high elevation in the area to take a panoramic photograph of the landscape. •
Find a point of high elevation on the map and 3D print that is relatively close to your parking spot and provides an unobstructed view of the landscape. Mark the high point with an “H” on your copy of the topo map.
•
Choose a path from your parking spot to the high point that minimizes (1) the amount of horizontal distance traveled and (2) the number of steep slopes you would need to hike. Mark this path on your topo map with a colored pencil (a color besides red or blue, please). •
Use your 3D model and topo map to find the steepest slope
you would have to hike on your chosen path. Estimate the steepness of the slope by calculating the grade of the slope. Slope grade is often represented by a percentage, such that a 5% grade means that slope changes by 5 feet vertically for every 100 feet horizontally (5 vertical/100 horizontal x 100 = 5%). Step 1: Using the contour lines on the map, estimate the vertical distance by subtracting the elevation at the bottom of the slope from the elevation at the top: Step 2: Using the scale at the bottom of the map (0.5 inches = 1000 feet), estimate the horizontal distance between the top and bottom of the slope: Step 3: Calculate the grade: (vertical distance/horizontal distance) x 100) •
A class 2 hiking trail, a difficult trail that does not require climbing with your hands, usually includes grades that vary from 0-18%. Based on the grade you calculated above, would your chosen path be more difficult than a class 2 trail?
P
Keyboard Shortcuts for Google Earth
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