Assignment+04+Histograms+%26+Measures+of+Spread
pdf
keyboard_arrow_up
School
San Diego State University *
*We aren’t endorsed by this school
Course
10092007
Subject
Geology
Date
Apr 3, 2024
Type
Pages
13
Uploaded by DukeThunderEchidna4
This lab is being used and was modified with permission from Gary Jacobson of Grossmont Community College. GEOL101 Dynamics of the Earth Name: Laboratory 1: Topographic Maps . . . There’s Ups and Downs Section: Learning Outcomes: ● Explain what contour lines are and why they are useful on flat maps ● Apply the concept of contour lines to visualize elevational patterns over a region ● Use map scales to estimate distances within a given region Introduction to Topography and Contours Most maps focus on the horizontal “lay of the land,” but topographic maps are also designed to communicate local variations in elevation of the land surface using contour lines
. Examine the three-
dimensional perspective drawing of a volcanic island in Figure 1A. While you can identify higher and lower areas based on the perspective, the exact elevations above sea are not shown and only about half of the island is visible. In Figure 1B, contours lines that connect locations of the same elevation have been added to this perspective drawing, but the view is still incomplete. If you were walking along a given contour line, you would not increase or decrease in elevation. Note that the contour lines are regularly spaced every 10 feet and do not cross one another. In Figure 1C, the view has been rotated such that you are looking directly down on the entire island . . . while you lose the three-dimensional perspective in the previous views, you can now see the entire island and how each contour line closes on itself. Also notice that only every fourth contour line is bolded and labeled (i.e., 0’, 50’, 100’); these are known as
index contours
. Figure 1: A. Three-dimensional view of a volcanic island. B. The same volcanic island with contour lines drawn every 10 vertical feet. Notice that the lowest contour or zero contour is at the base of the island where sea level would be. C. Topographic map of the volcanic island with index contours labeled. The contour interval
is the elevation difference between each contour line, and this difference is nearly always kept constant throughout an entire map. The contour interval in Figure 1C is 10 feet. Contour spacing visually conveys the relative steepness of an area: Widely spaced contours represent a shallow or gentle slope (Figure 2A and 2B, Box C), while closely spaced contours represent a steep slope (Figure 2A and 2B, Box D).
Figure 2: A. Topographic map of a cinder cone at Lassen Volcanic National Park in northern California. B. 3-D relief map with topographic overlay of the same locations as A. Notice that the contours in Box C are spaced farther apart than the contours in box D in both maps. A useful concept for interpreting contours is called the “the rule of V’s.”
When a contour crosses a valley, it has to turn to maintain its elevation and then return on the other side of the valley. On the map, this turn and return of the contour produces a “V” that points towards higher elevations (i.e., uphill or upstream). Figure 3A is a topographic map of mountainous terrain with a stream (yellow line) flowing from the top to the bottom of the map. Figure 3B is the same area shown in a 3-D relief map view. Notice that the contours “V” in the upstream or uphill direction in both views Figure 3: A. Topographic map with a stream in the middle in yellow. Lines 1 and 2 are ridges. B. 3-D relief map with contours draped over the terrain of the same location as A. Lines 1 and 2 are the same ridges as in A. Conversely, when a contour crosses a ridge, it will turn along the ridge to maintain the same elevation and then return on the other side of the ridge. On the map, the contour would also make a “V” but this time it would point downstream or downhill. Line 1 on Figure 3A is drawn along the apex of a ridge. This same line in Figure 3B shows the same ridge in 3D relief. Notice that the contours “V” or point down elevation. Line 2 in Figure 3A and B is also along a ridge. Understanding the difference between a ridge and a valley or stream is very important when reading a topographic map.
Common Features of Topographic Maps Topographic maps typically include a variety of additional information within and outside of the map borders (See Figure 4). Inside the map, roads, buildings, and other human infrastructure may be shown if the map’s scale (discussed below) is fine enough. Outside the map borders, various descriptive information about the area and the nature of the map is provided along with magnetic declination and scale information, which are discussed in detail below. Magnetic declination
: Next to the data and projection information in the lower left corner, an arrow pointing toward the geographic North Pole indicates “True North.” Usually there is another arrow which points toward the Magnetic North Pole. These two arrows are drawn from a single point, and the angular difference between them in degrees is known as the magnetic declination
. Since the Magnetic North Pole moves slowly over time, the date of measurement of the declination is indicated beside the arrows. Magnetic declination is very important to know because 1° of latitude is equal to 69 miles on the Earth’s surface. Figure 4 is the USGS topographic map of La Mesa, CA. Notice in the enlargement that the magnetic declination is 11.5°. Ratio S
cale
: Of all the features of a map, scale is one of the most important and relates the distance on the map itself to the actual distance. This relationship is typically expressed as a ratio; for example, a 1:10,000 scale means that one unit of measurement on the map (say, 1 inch) is equal to 10,000 inches on the map (= 833 feet). One weakness of just showing the scale ratio by itself is that any reduction or enlargement of the map will introduce substantial errors in estimated distances; thus, most maps also include a bar scale with distance marks to minimize such problems. Bar scale
:
In this method a line or bar is drawn on the map. The actual length of the line or bar is the map distance. It is divided and calibrated according to the ground distance. On USGS maps more than one bar scale is usually shown, each one calibrated in different units-miles, feet, kilometers (Figure 4). To find the distance between two places, any piece of paper can be used, the map distance marked, and the ground distance read directly by placing the paper against the bar scale. This type of scale also has the advantage of remaining valid if the map should have to be enlarged or reduced for any reason, since the map distance and the length of the bar would both be changed equally.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Figure 4: USGS 7.5-minute quadrangle topographic map. Enlarged area showing magnetic declination, ratio scale, and bar scale.
Lab Activity Questions 1-7. Warm up – Match the contour map (1-6) to its corresponding mountain range (A – G) in the table provided. 1. 2. E 3. 4. 5. 6. A Choose your own adventure – See Map 1 at end of Handout You and a friend are hiking the Pacific Crest Trail (gray dashes) from Campo, California to Manning Park in British Columbia. You are hiking north and plan to go over Glen Pass (11,920’, blue star) tomorrow. You met a group of backpackers that just spent a couple days in Sixty Lake Basin (shaded purple) and highly recommend the detour. You are a day ahead of schedule and decide to take the recommendation. However, you would like to make it an adventure and do some off-trail hiking. Your goal for the day is to make it over Glenn Pass (blue star, lower left of map 1) and find a route into Sixty Lake Basin at the yellow star. Before you start route finding let’s get acquainted with the map. Use Map 1 (Mount Clarence King, CA) at the end of this handout to answer the questions below. Question 7. Complete the table below using Map 1 Contour interval (don’t forget the units) 80 feet Magnetic declination in degrees Direction of north on map Direction of south on map Direction of east on map Direction of west on map Highest elevation on map Lowest elevation on map
Question 8.
What is the distance between Glen Pass (lower left of map) at the blue star to Sixty Lake Basin at the yellow star as the crow flies? “As the crow flies” is a common way people talk about a distance that does not consider topography or necessary detours. You could think of it as measuring a distance along a flat straight line. To figure out the distance between the blue star and the yellow star use a piece of paper and place one corner of the paper on the blue star at Glen Pass and rotate the paper to the yellow star. With the paper lined up with the blue and yellow stars, use a pencil or pen to mark where the yellow star touches the paper, that is the map distance. Now line the paper up with the bar scale to read the land distance in feet and record this distance below. Then convert the distance in feet into distances in miles and kilometers (bottom bar scale). Question 9
. The distance you measured in Question 8 is meant to give you an estimate for how far you will need to hike from Glen Pass to Sixty Lake Basin. Is this measurement greater than or less than the actual distance you will need to hike? Why? Figure 5 shows a mountain range with passes, peaks, and ridges. A pass is the lowest point between two peaks and are the locations where most hikers aim to get from basin to basin. A ridge starts at a peak and extends down to a pass or the bottom of the basin or somewhere in between. A peak is the highest point on a mountain. Figure 5: Example of pass, peak and ridge. Question 10. Choose your own adventure. Below, outline the path you will take from Glenn Pass at the blue star to get into Sixty Lake Basin at the yellow star. Your path does not have to take the shortest or easiest path, you are welcome to add as much adventure to your detour as you’d like. However, you should take things like the steepness of slope into consideration, remember you are backpacking and wouldn’t have things like ropes and harnesses for rock climbing. Below is an example of what a route could sound like. (Don’t duplicate the example below) Starting at Glenn Pass we plan to head south back down the pass to just above the lake at ~ 11780’. We plan to follow this contour to the west north west along the gentle slope for about 600’ or until we are below the other 11,920’ pass in the bottom center of the map. Here we will start to climb ~240’ to the top of the pass. Based on the contour spacing on the north side of the pass it may be pretty steep. We plan to take our time and walk switch backs down to the gentler slopes around 11,600’. At that point it should be an easier walk down to the lake.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Sea level rise – See Maps 2 and 3 at the end of this handout Globally, sea level is on the rise due to two major factors. One is the thermal expansion of water: When water takes on heat the increase in molecular vibrations causes the water molecules to be farther apart, leading to an increase in volume taken up by a given amount of water. The second is the melting of land ice (glaciers and ice sheets), like those in Greenland and Antarctica, and the flow of the water into the global ocean. For the purposes of this lab, we are going to consider the effect of a 10’ (feet) rise in sea level in two coastal cities of the U.S. that have very different topographies. Starting in Miami Florida and Map 2 (Miami FL topo), note that this map only covers ~15 square miles of Miami’s 56 square miles. In other words, we are only looking at 26% of the city in this map. Before we get started, let’s get acquainted with the map. Question 11.
Complete the table below using Map 2 Contour interval (don’t forget the units) Magnetic declination in degrees Direction of north on map Direction of south on map Direction of east on map Direction of west on map Highest elevation on map Lowest elevation on map Question 12. Based on your observations of the contour spacing of this section of Miami how would you describe the topography? Flat, hilly, mountainous, or another term? Question 13. Are there any waterways on the map (rivers, lakes, streams, lagoon)? If so, please name them. Question 14.
At what elevation or contour does the water way lie (i.e., 10’, 20’, sea level or 0’)? Question 15.
Hypothesize how the waterway affects sea level rise. Does the waterway allow water to move farther inland or prevent water from moving inland?
Question 16.
With a 10’ sea level rise what contour on map 2 will be the new shoreline? Question 17. Use the method above to measure the land distance that the shoreline retreated (or moved inland) during the rise in sea level along Line A-B. Give this distance in both miles and kilometers. Question 18. Now measure the distance along Line C-D that is perpendicular to the Miami River, which measures the distance to the new shoreline or width of the river. What is the distance between the points E and F (old shoreline, or old width)? Give this distance in both miles and kilometers. Question 19.
By how much or by what percentage did the river grow? Use the formula below to help you (show your work). % growth = (new width/old width) x 100 Question 20.
According to the United States Census Bureau, the population of Miami city as of 2018 was 470,914 people. If we assume that the population in Miami is evenly spread, then we can assume 26% of the 470,914 people that live in the city live in this map. How many people live on this map? (show your work) Question 21. Based on the number of people you estimate live in this mapped area (Question 20) how many of these people do you estimate will be displaced by a sea level rise of 10’? For this question, only think about sea level rise, not tides, potential storm surges, infrastructure, or any of the other, many potential issues. Let’s now travel to the west coast and look at the San Luis Rey Map 3 (Carlsbad, CA topo). This map covers ~5 square miles of Carlsbad’s 39 square miles. In other words, we are only looking at ~13% of the city in this map. Before we get started, let’s get acquainted with the map.
Question 22. Complete the table below using Map 3 Contour interval (don’t forget the units) Magnetic declination in degrees Direction of north on map Direction of south on map Direction of east on map Direction of west on map Highest elevation on map Lowest elevation on map Question 23.
Based on your observations of the contour spacing of this section of Carlsbad, how would you describe the topography? Flat, steep, hilly, mountainous, or another term? Question 24. Are there any waterways on the map (rivers, lakes, streams, lagoon)? If so, please name them. Question 25
. At what elevation or contour does the water way lie (i.e., 10’, 20’, sea level or 0’)? Question 26.
Hypothesize how the waterway affects sea level rise. Does the waterway allow water to move farther inland or prevent water from moving inland? Question 27.
With a 10’ sea level rise what contour on Map 3 will be the new shoreline? (Is there even a 10’ contour on this map? If not, where would the shore be?) Question 28.
What part of Carlsbad will be hardest hit with a 10’ sea level rise? Do you think many people live there?
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Question 29. After looking at the topo maps of two cities with differing topographies in a few sentences explain how topography plays a role in the potential effects of sea level rise. Question 30
. In both maps you looked at there was some kind of waterway. In the Miami map there was the Miami River and in the Carlsbad map there was Agua Hedionda lagoon. Discuss below the effects of the waterway in each map and how or if these effects were dependent on topography.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help