GEY1111_Mod1_Lab3_BackgroundFiles
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Module 1 Lab 3 Intro to Topographic and
Geologic Maps: Background Information
and Instruction
Purpose In this lab, you will demonstrate an understanding of reading and working with both topographic and geologic maps. In Part A, you will draw contour lines on a base map with elevations, demonstrating that you understand the principles involved with contour mapping. In Part B, you will read a topographic map to answer questions. In Part C, you
will use a topographic map and construct a topographic profile. In Part D, you will read a
geologic map and cross sections to answer questions.
Time Requirements
This lab should take about 3 hours to complete.
Materials Needed Pencil and eraser, ruler, camera, and access to a printer.
CCCS Outcomes Addressed
N -
Locate and identify geologic features using topographic or geologic maps. GT Pathways Quantitative Literacy
(required for GT-SC1):
1.
Interpret Information a. Explain information presented in mathematical forms (for example, equations, graphs, diagrams, tables, and words).
2.
Represent Information a. Convert information into and between various mathematical forms (such as equations, graphs, diagrams, tables, and words).
Related Background information from other portions of this module
The readings and exploration introduced the concepts of maps will be addressed in this lab. This list is a brief reminder of what has been covered in this module regarding topographic and geologic maps. Page 1
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Required Readings
Fundamentals of Physical Geography (2nd ed.)
Chapter 2: Maps, Remote Sensing, and GIS
Physical Geology (2nd ed.)
Chapter 8: Measuring Geologic Time
Supplemental Reading:
VIVA Open Publishing:
Physical Geology Laboratory
: Interactive Diagrams and Questions (Chapters 10 to 53)
Exploration Topic
Topic 4:
Maps. There are several videos on maps in the Exploration for Module 1 on topics such as reading contours, constructing profiles, reading geologic maps. If you have not yet watched these videos, please do so before beginning this lab.
a.
How to Read a Topo Map
(3m 47s) (REI) b.
Visualizing Contour (Topographic) Maps In Google Earth
(8m 31s) (Geo Know) c.
How to construct a topographic profile. Not as hard as your teacher makes it sound!
(6m 49s) (Geo Know)
d.
THE GEOLOGICAL MAP "Drawing the Earth's skin"
(9m 47s) (Paleoceno)
Vocabulary and definitions related to maps and mapping
Topographic Map also called a topo or contour map:
A 2-dimensional representation of a 3-dimensional surface that uses lines of equal elevation to graphically display information including elevations and cultural features in a given area.
Contour Line
: An imaginary line of points of equal elevation on topo maps.
Index Contour Line
: Darker contour lines that are labeled with the elevation.
Contour Interval
:
The difference in elevation between 2 adjacent contour lines.
Relief
:
The difference in elevations between the highest and lowest points.
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Topographic Profile
: A representation of the elevation changes along a given line on a
topo map.
Geologic Map
: Shows ages and types of rocks present and structural features such as faults, usually overlain on a topographic map.
Geologic Cross Section
: A graphic representation of the rock formations in the subsurface along a vertical plane; usually has a topographic profile showing variations in elevation at the surface.
Strike
: The compass direction of a horizontal line in the bedding plane.
Dip
: The angle of the bedding plane relative to the horizon.
Background information for Parts A, B, and C on Topographic Maps and Profiles Topographic maps
show the 3-dimensional shape of the landscape by representing equal elevation with lines on a 2-dimensional map; they are in essence a type of contour map (also used in meteorology and oceanography). Although these can be mathematically derived, most geologists create them by measuring the elevation (and position) in the field (or from aerial photos), plotting elevation on a map and connecting lines of equal elevation (much like connect-the-dots, except that all the same numbers are connected, rather than in sequence). This module is designed to give you experience examining and reading topographic maps, understanding scale, calculating slope and drawing topographic profiles (Wenner & Baer, 2017).
Figure 1
. Sample Topographic Map (Wenner & Baer, 2017)
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Learning to Draw Contours
In Part A of Lab 3, you will be drawing contour lines on a base map that has points and the associated elevations. To be successful with this exercise, use the following rules for contouring.
Basic Rules for Contouring:
1.
A contour line never
crosses another contour line, nor do they divide into 2 lines.
2.
Contour intervals do not change on a map, but do differ from map to map.
3.
Index contour are darker lines that mark elevation along that line.
4.
Circles show highest point, circles with tick marks show lowest point.
5.
Closely spaced contour lines represent steep slopes, contours spaced far apart represent gentle slope.
6.
Contour lines trend up valleys, cross the stream, and return down the valley on the opposite side. They thus form a V which points upstream.
In Part B you will be reading a topographic map
and finding out some basic characteristics about the area it depicts such as the following types of information.
Finding the Contour Interval
We can determine a Contour Interval by reading the values on the darker index lines and find the difference between these, then count how many contour lines are between the index lines, and dividing the difference between index lines
by the number of contour lines.
Sample/Example Calculation
(from figure 20 in the instruction section below):
Index Lines 11 200 – 11 000 = 200 units (usually feet on US maps, may be meters)
There are five lines between 11 200 and 11 000, so 200 units divided by 5 = 40 units
Sample/Example Contour Interval
(CI) = 40 units
Finding the Relief of a given area
Relief is the difference in elevation between 2 points on a map. For example, in Figure 20: Topographic Map for Constructing a Cross Section
(see instruction section below), we can determine the relief across line A-A’. The highest point is 11 400’ at point A’; the lowest point is at A at about 10 600’, so: Sample/Example Relief
= 11 400 – 10 600 = 800’ Page 4
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Reading Features shown by contour lines
Streams and V contours:
If you look at the topographic maps in the instruction section below, you will find that streams are shown as blues line and if you observe the contour lines that cross a stream, you should see how the contours make a “V” shape pointing up stream. Flat or Steep terrane:
Since the distance between 2 contours is actually a vertical measurement in elevation, how close or far apart the lines are in a given area tell us if the area is fairly flat or steep. For example, closely spaced lines indicate a large change
in elevation like a steep mountain side, canyon, or cliff face. Lines that are spread far apart show that there is little change in elevation over a large distance—the land is relatively flat.
Background Information for Part C - making a Topographic Profile Directions for Constructing a Profile In Part C of Lab 3, you will be making a topographic profile. A profile is a 2-dimensional side view of a specific section of a topographic map which is drawn using a line on the map and projecting the information into a profile grid, like the example below:
Figure 2.
Topographic Map and Profile Construction (Wenner & Baer, 2017)
STEP 1. Draw or locate a line on your map and label both ends, for examples Line A-A’ on the Topographic Map below in Figure 3.
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Figure 3.
Topographic Map with line A-A’ drawn (Wenner & Baer, 2017)
STEP 2. Place the edge of a blank piece of paper along the line and mark the starting and ending points of the line (label them with A and A', or whatever the given line is labeled).
Note:
In Part C below, this type of paper is provided for you. Figure 4.
Example of placing the edge of paper along the line (Wenner & Baer, 2017)
STEP 3. Start at 1 end, make a tick mark on the line on the paper, at every point where a contour
line crosses the A-A’ profile line. As you make the marks, write down the elevation associated with each mark. Note:
For Part C in the Instruction section below, a graphic is provided for this that you may use or not if you choose instead to just mark your information on the profile grid that is provided.
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Figure 5.
Example of marking the points and elevations for the profile (Wenner & Baer, 2017)
STEP 4. Transfer the tick mark and elevation information to a profile grid and determine the scale
you will use on the y-axis (left side). Note:
For Part C below, you will need to add the elevations on the y or vertical axis on the left before plotting your points on the profile grid. Figure 6.
Example of plotting the appropriate location and elevation on a profile grid (Wenner & Baer, 2017)
STEP 5.
Connect the dots, but make sure to smooth out the lines so they look more natural and not disjointed.
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Figure 7.
Example profile created from a topographic map (Wenner & Baer, 2017)
Background Information for Part D: Geologic Maps and Cross Sections
How to Read Maps by RW Graymer
Note: The following information is from the USGS publication (1997) “How to Read Maps” that was originally developed by Russell W. Graymer, Western Region Mapping Team, U.S. Geological Survey, for the 1997 USGS Open house. This file is no longer listed on the USGS website.
Letter Symbols In addition to color, each geologic unit is assigned a set of letters to symbolize it on the map. Usually, the symbol is the combination of an initial capital letter followed by 1 or more small letters. The capital letter represents the age of the geologic unit. Geologists have divided the history of the Earth into eons (the largest division), eras, periods, and epochs, mostly based on the fossils found in rocks. The most common division of time used in letter symbols on geologic maps is the period. Rocks of the 4 most recent periods are found in the San Francisco Bay area shown on this map, so most letter symbols begin with a capital letter representing 1 of the four periods: J (Jurassic: 195 to 141 million years ago), K (Cretaceous: 141 to 65 million years ago), T (Tertiary: 65 to 2 million years ago), or Q (Quaternary: 2 million years ago until today).
Figure 8. Arrow 1 points to the map symbol Kjm (USGS; Graymer, 1997)
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Occasionally, the age of a rock unit will span more than 1 period if the period of many years required to create a body of rock happens to fall on both sides of a time boundary.
In that case, both capital letters are used. For example, QT would indicate that the rock unit began to form in Tertiary time and was completed in Quaternary time. The few geologic units formed an unknown amount of time ago have letter symbols with no capital letters. The small letters indicate either the name of the unit, if it has one, or the type of rock, if the unit has no name. So Kjm (arrow 1 on Figure 8 above) would be the symbol for the Joaquin Miller sandstone (formed in the Cretaceous Period), while Ks (arrow 2 on Figure 9 below) would be the symbol for an unnamed unit of shale formed in the same period, and gb (arrow 3 Figure 10 below) would be the symbol for gabbro (a dark-
colored igneous rock) of unknown age.
Figure 9. Arrow 2 points to the map symbol Ks (USGS; Graymer, 1997)
Figure 10. Arrow 3 points to the map symbol gb (USGS; Graymer, 1997)
Lines on the map - Contact Lines
The place where 2 different geologic units are found next to each other is called a contact, and that is represented by different kinds of lines on the geologic map. The 2 main types of contacts shown on most geologic maps are depositional contacts and faults.
All geologic units are formed over, under, or beside other geologic units. For example, lava from a volcano flows over the landscape, and when the lava hardens into rock, the place where the lava-rock rests on the rocks underneath is a depositional contact. Where the original depositional contact between geologic units is preserved, it is shown on the geologic map as a thin line (arrow 4 on Figure 11 below).
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Figure 11. Arrow 4 points to a depositional contact between geologic units (USGS; Graymer, 1997)
Faults
However, in geologically active areas like the San Francisco Bay area, geologic units tend to be broken up and moved along faults (it is fault movements that cause earthquakes). When different geologic units have been moved next to one another after they were formed, the contact is a fault contact, which is shown on the map by a thick line (arrow 5 on Figure 12 below). Faults can cut through a single geologic unit. These faults are shown with the same thick line on the map, but have the same geologic unit on both sides.
Figure 12. Arrow 5 points to a fault contact, which is shown on the map by a thick line (USGS; Graymer, 1997)
Remember, just because the map shows a fault doesn’t mean that fault is still active and is likely to cause an earthquake. Rocks can preserve records of faults that have been inactive for many millions of years. However, knowing where the faults are is the first step toward finding the ones that can move. Special geologic maps of the faults known to be still moving are constantly being upgraded here at the United States Geological Survey, as well as by state geological surveys and university researchers.
Other Lines - Folds
Another kind of line shown on most geologic maps is a fold axis. In addition to being moved by faults, geologic units can also be bent and warped by the same forces into rounded wavelike shapes called folds. A line that follows the crest or trough of the fold is
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called the fold axis. This is marked on a geologic map with a line a little thicker than a depositional contact, but thinner than a fault (arrow 6 on Figure 13 below).
Figure 13. Arrow 6 points to a fold axis line (USGS – Graymer, 1997)
Solid, dashed, or dotted lines
All thicknesses of lines are also modified by being solid, dashed, or dotted. Often contacts are obscured by soil, vegetation, or human construction. Those places where the line is precisely located it is shown as solid, but where it is uncertain it is dashed (arrow 7 on Figure 14 below). The shorter the dash, the more uncertain the location. A dotted line is the most uncertain of all, because it is covered by a geologic unit, so no amount of searching at the surface could ever locate it (arrow 8 Figure 15 below). The lines on the map may also be modified by other symbols on the line (triangles, small tic marks, arrows, and more) which give more information about the line. For example, faults with triangles on them (arrow 9 on Figure 16 below) show that the side with the triangles has been thrust up and over the side without the triangles (that kind of fault is called a reverse fault or a thrust fault). All the different symbols on the lines are explained in the map key (which is explained below).
Figure 14. Arrow 7 points to an uncertain contact shown with a dashed line (USGS; Graymer, 1997)
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Figure 15. Arrow 8 points to a dotted line indicating that the contact is uncertain, being overlain by another geologic unit (USGS; Graymer, 1997)
Figure 16. Arrow 9 points to a fault line with triangles, side with the triangles has been thrust up and over the side without the triangles (USGS; Graymer, 1997)
Map Key All geologic maps come with a table called a map key. In the map key, all the colors and
symbols are shown and explained. The map key usually starts with a list showing the color and letter symbol of every geologic unit, starting with the youngest or most recently formed units (in the example map those are the man-made deposits), along with the name of the unit (if it has 1) and a short description of the kinds of rocks in that unit and their age (in the key, the age is described by epochs, subdivisions of the periods shown in the letter symbol). After the list of geologic units, all the different types of lines on the map are explained, and then all the different strike and dip symbols. The map key will also include explanations of any other kinds of geologic symbols used on a
map (locations where fossils were found, locations of deposits of precious metals, location of faults known to be active, and any other geologic feature that might be important in the area shown by the geologic map). Because the geology in every area is
different, the map key is vital to understanding the geologic map.
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Figure 17. Example of Geologic Map Key (USGS; Graymer, 1997)
SUMMARY Although the geology of every area is different, all geologic maps have several features in common: colored areas and letter symbols to represent the kind of rock unit at the surface in any given area, lines to show the type and location of contacts and faults, and
strike and dip symbols to show which way layers are tilted. The geology of an area has a profound effect on many things, from the likelihood of landslides, to the availability of groundwater in wells, from the amount of shaking suffered in an earthquake, to the presence of desirable minerals, from the way the landscape is shaped, to the kinds of plants that grow best there. Understanding the earth underneath is the first step in understanding the world around us. So, what’s the geology like in your neighborhood? If
you can read a geologic map, you can probably find out! (End of USGS article on reading maps by Graymer, 1997)
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Scoring Guide for Lab 3: Intro to topographic and geologic maps
Criteria
Expected information for each category
Points Possible
Title Information Name Date Lab Title Lab Partner Status 2, 1, ½, 0
Data and Observations Part A Topographic Contours:
1. Photo of finished contour map Part B Reading a topographic map: 2. CI, 3. Relief, 4a & b Stream flow directions, 5 a & b steep vs flat areas Part C: Topographic Profile:
6. Photo of finished topographic profile
Part C Geologic Maps:
prompts 7 - 12
9, 7, 3, 0
Lab Question Answers
1, 2, 3, 4
8, 5, 4, 2
Conclusions
1)
Summary of what you did in each part
2)
What you learned 3)
Questions you now have
4, 3, 1, 0
Sources or Citations
APA Most of APA Some of APA No citation
2, 1 ½, 1, 0
Instructions - Lab 3: Intro to topographic and geologic
maps Reminders: 1)
Use the Student Response Guide
file for recording your information, when finished with this lab submit the Student Response Guide to the appropriate assignment folder.
2)
All required photos must have your Student Information Card
with your printed name, signature, name of lab, and date.
3)
All graphs should be created using computer software such as Excel; no hand drawn graphs will be accepted.
Part A: Topographic Contours
Materials:
Access to a printer to print out required map materials, pencil and a good eraser, camera, and Student Information Card
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Directions In this section of the lab, you will be trying your hand at creating contours on a map based on the rules of contouring and the elevation values on the map below. 1.
Print out the map below:
2.
Helpful Hints
for completing this map: in addition to the basic rules for contouring
listed in the background section above (and the video) here are some additional suggestions:
(1)
Use a pencil and have a good eraser handy; you will probably have to draw and erase frequently until you like your final result.
(2)
Drawing contour lines is similar to making an advanced version of connect the dot picture. Since contour lines are lines where every point on the line is the same elevation and the contour interval on this map is 20 feet, then the lines will
only go through elevation points with a value of 20, 40, 60, 80, 100, 120, or 140. Make sure to label your contour lines with the appropriate elevation to help you keep track of your work.
(3)
You will have to estimate the distance from the contour lines for all elevations which are not one of these even numbers. For example, if the elevation is 50, then that point would be half way between the 40 and 60 contour interval.
(4)
Reminder, every point between two contour lines must be a greater value than the lower line and a smaller value then the line above. For example, elevations of 106, 104, 110, 118, and 118 are all located between the 100 and 120 contour lines.
(5)
When there is a stream or river, since the water erodes the surface under it, the contour lines tend to form a V shape pointing up river. The Wilde River on the map flows south, so the Vs should have their narrowest end where the contour line crosses the river toward the north relative to the rest of the line.
(6)
There is a hill in the upper left (north west) of this map with the highest point at 142. The lowest points on the map are toward the bottom (south). The area in the upper right (north east) is gradually increasing in elevation.
3.
Take a photo of your completed map with your Student Information Card and paste into the Student Response Guide.
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Figure 18. Map with Elevations for Learning to Draw Contour Lines
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Part B: Reading Topographic Maps
Materials:
No additional materials are needed for this section of the lab.
Instruction:
Here is an example of a topographic map for the Isis Temple on the Bright Angel quadrangle of the Grand Canyon, Arizona. You will be using this map to answer questions in the Lab Observations section on the Student Response Guide. This map is
not included in that file; you will have to access it here. (Note: You will return to this same area in Part D when you examine Figure 23 which is a geologic map of this area, and Figure 24 is the cross section for this part of the Grand Canyon.)
Reminder: the background information above includes information for:
Calculating contour interval
Calculating relief
Reading the features from contour maps such as Vs near streams and flat or steep terranes.
See the Student Response Guide Lab Observations Part B for the prompts related to this map.
Topographic Map of Isis Temple, Grand Canyon National Park, Arizona
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Figure 19. Topographic Map of Isis Temple
, Bright Angel quadrangle, Grand Canyon National Park, Arizona (USGS, 1961) Note:
North is at the top of the page.
Part C: Making a Topographic Profile
Materials:
Access to a printer to print out required map materials; pencil, ruler, and eraser; camera; and Student Information Card
Directions See the information in the Background section above to help you complete this activity, both the step-by-step instructions and figures and the video: GeoKnow (November 10, 2016) How to construct a topographic profile.
On the map (figure 20), note that the highest elevations are to the right (east) and the lowest to the left and bottom (southwest) where the stream that crosses A-A’ joins another stream. There is a good amount of relief—climbing up and down 800’ would be like going up and down the stairs in a 35-story building—so we can interpret this as a steep, mountainous area with streams cutting valleys through the mountains. This map is from near Leadville, Colorado, so that would be the type of topography we would expect for this area.
You will need to print out the map (figure 20) with the cross-section line A-A’ and the graph like the profile grid on which you will plot your profile. There is an additional strip (Figure 21) from the map that you may find helpful for transferring the elevations from the map to the profile grid or you may ignore this strip and directly transfer your data onto the grid below (Figure 22).
On the provided grid (Figure 22), you will need to add the elevation values on the left hand vertical or y-axis. Notice that the dark contours (index contours) vary by 200 feet from the adjacent index contours (the dark ones) with 4 lighter lines subdividing this larger interval 5 five contour
intervals between each of the index lines, which indicates that the contour interval is 40 feet. (200/5 = 40 feet).
The highest index contour line across the profile A-A’ is at 11,400 just to the right of A’. This should be your highest elevation at the top of your vertical axis. The lowest index contour is on the left, near A at 10,600, although there are 2 more contour lines below this index—these will be your lowest elevations at the bottom of your vertical axis.
Note that the index grid has been shaded alternating between gray and white. This shading correlates to elevations between the index contours.
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Figure 20:
Topographic Map for Constructing a Cross Section (USGS, 1994 Leadville North 7.5’ quadrangle, Eagle and Lake Counties, Colorado)
Optional Line: you may choose to use this line for marking the points where the contours cross the line and add in elevations
Determine the location and elevation of where the contour lines cross the profile line A-A’. Write the elevation for each line in the area below the figure, you may wish to write
in a vertical method.
Figure 21:
Optional line for transferring data
Transfer the elevation information to the appropriate elevation line on the profile grid chart below by sliding the paper you use to record the elevations up and down the profile grid chart as needed. You may use the profile chart below or make your own. Note the spaces are the contour intervals.
Complete the profile—follow the steps—start with adding the vertical elevations on the left side.
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Figure 22: Profile Grid for Constructing a Topographic Profile
Take a photo of your completed profile and paste it into the appropriate space under Part C: Lab Observations. Remember to include your Student Information Card visible next to your profile in your photo.
Part D: Geologic Maps
Materials:
No additional materials are needed for this section of the lab.
Instruction:
You will be using the following figures to answer question prompts on the Student Response Guide. Note that Figures 23 and 24 are the same area as shown in the topographic map that you worked with in Part B. These figures are not included in the Student Response Guide, so you will have to access this Background Information and Instruction file to answer the questions.
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Geologic Map of Isis Temple, Grand Canyon National Park, Arizona
Figure 23. Portion of the Bright Angel quadrangle Geologic Map showing the Isis Temple, Grand Canyon National Park, Arizona (USGS, 1961)
Cross Section of a Portion of Area near Isis Temple, Grand Canyon National Park
Figure 24. Cross Section from of the Bright Angel quadrangle Geologic Map Grand Canyon National Park, Arizona (USGS, 1961)
See Student Response Guide for Lab Questions and so on
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Sources Used for Lab 3 Images:
National Geologic Map Database (NGMDB) Product Description Page
Geological Map of the Bright Angle Quadrangle Grand Canyon National Park, Arizona
How To Read A Geologic Map
Geological Survey Map of Leadville North 7.5’ Quadrangle, Eagle and Lake Counties, Colorado
The Math You Need, When You Need It
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