Geology 210 – Lab #1 – Spring, 2005
Structural Landforms, an Introduction to Images, Maps and Data Contouring
Introduction: This lab is designed to introduce basic concepts regarding structural landforms and use of topography and aerial photo image files. Hopefully this will be review for most of you.
The lab includes a short exercise on digitizing and contouring of spatial data to introduce you to Surfer, a software package that we will be using throughout the course.
As you work your way through the lab, pay attention to the file types and file sizes that you are working with. Note that these are all raster (image) files of various sorts.
Readings: The following articles will be available for background reading (these are available as .pdf files in the lab folder on the network – you will need to read these to be able to answer the questions in the first part of the lab):
Weimer, R. J. and Le Roy, L. W. (1987) Paleozoic-Mesozoic section: Red Rocks Park, I-70 road cut and Rooney Road, Morrison area, Jefferson County, Colorado; Geological Society of America Centennial Field Guide-Rocky Mountain Section, p. 315-319
Baars, D.L. and Doelling, H.H. (1987) Moab salt-intruded anticline, east-central Utah; Geological Society of America Centennial Field Guide – Rocky Mountain Section, p. 275-280
Topographic Maps: After you have had a look at the lab materials, you may want to visit
http://mac.usgs.gov/mac/isb/pubs/booklets/usgsmaps/usgsmaps.html#Topographic Maps
This site presents basic information about the U.S. Geological Survey’s mapping program and describes the various types and scales of maps that are available. Whenever you are involved in a project that requires base maps, the USGS is the first place you should look.
1. Morrison, Colorado:
a. Examine the topographic map paper copy and the digital image included in the lab folder on the network.
b. Note the north-south linear ridges (Dinosaur Ridge, etc). Briefly explain the origin of these ridges and the intervening linear valleys.
c. Sketch an east-west cross section which illustrates your understanding of the relationship between the landform and underlying geologic structure.
d. Briefly describe the relationship between topography and urbanization in this area.
2. Moab, Utah:
a. Does the Colorado River run from NE to SW or SW to NE through this area? What is the evidence for this on the map?
b. How can you explain the fact that the Colorado River course pays no heed to the NW-SE Moab Valley? (This observation by early explorers in the area caused the structural extension of the Moab Valley to be called the “Paradox Basin”.)
c. What is the origin of the Moab Valley, if it was not carved by the river?
Aerial Photo Files:
1. Morrison, Colorado or Moab, Utah:
a. Use the topographic base map to calculate the approximate scale of the digital images (note which image file you used). For digital image files, we present the scale as meters/pixel).
b. Are these images ortho-corrected? Explain how you know.
Digitizing and contouring of water table data:
The data for this next section of the lab is drawn from the Moab area. Examine the attached map, noting the location of the levee impoundment, uranium tailings pile and the Colorado River. The websites listed below will provide background on the area and the nature of the problem. The uranium processing waste (tailings) on the site is the subject of continuing controversy in the area, and numerous agencies and environmental groups are engaged in litigation with Atlas Steel Corporation to try to bring about the next phase of remediation of the site. At present, the old mill has been removed, and a large pond built as shown on the map. The goal of building the impoundment pond was to prevent downward infiltration of rainwater (the pond is lined with very low conductivity clay) through the tailings, and thus reduce the flow of groundwater from beneath the pond toward the Colorado. Since Moab is a hot, dry place, the water that runs into the pond evaporates instead of infiltrating, in theory.
This map is also available as an image file on the Colgate Network in Fileshr01/labsandclasses/geology210/LabsSpring2003/Lab1/basemaplab1.
a. Hand contouring: Examine the range of elevations, and chose an appropriate contour interval. Note that the elevation of the river is 3954 feet at average low water and 3959 feet at average high water where the river enters the map. The elevation of the river is about 3 feet lower where it exits the map. The river level will form the top of the water table at the river’s edge.
Use the paper copy of the map to hand-draw contours (use a pencil). You may need to try a couple of times to develop an internally consistent contour pattern. You will find it useful to make a map for both high flow and low flow river levels. Extra copies of the base map will be available in lab. Note that groundwater at the top of the saturated zone will flow perpendicular to the water table contours in the down-gradient direction.
b. Digitizing: Using the procedures outlined in lab, load the map file as a base map into Surfer. Note that the map will have an arbitrary grid system attached to it when it is imported. If you used the Import command, there will be no grid system. Note that you could reassign the actual UTM or lat/long co-ordinates to the corners of the map, if you wished. However, for the purposes of this exercise we can use the arbitrary co-ordinates which are assigned from the pixel dimensions of the image file.
Using the Digitize command under the Map menu, assign the appropriate elevation to each point by entering the data in the pop-up window. Note that the base map must be selected (black squares around the corners) before the digitize command will be enabled. You may wish to assign values for the water table elevation along the stream bank. When you are finished, use the File-Save As command within the pop-up window to save the file to your Zip disc with a .dat extension.
c. Gridding: The Grid-Data command will allow you to navigate to the file with the .dat extension you just built. The grid operation uses algorithms to calculate data values that appear at regularly spaced grid intersections from randomly-arranged data. The Grid-Data command will produce a .grd file.
d. Contouring using Surfer: Select the Map-Contour Map command to produce a contour map of the .grd file data. You may also wish to try the Map-Vector Map command. When you have a suitable contour map, double-clicking on the map will allow you to change options as needed. The contour map can be superimposed on the base map using the Map-Overlay Maps command.
e. Atlas Steel contends that since the water table in the area of the impoundment pond and tailings area is “……below average river level of 3956.5 feet above sea level, thus contaminated groundwater cannot flow into the river. In addition, the impoundment pond traps rainfall which might infiltrate the tailings and then flow toward the river.” What do your maps show?
f. How do your hand-drawn maps compare with the maps generated using Surfer? What might account for the difference? Which maps better depict the actual groundwater flow system, in your opinion?
http://www.pogo.org/nuclear/moabrep.htm#Problem
http://detnews.com/1998/nation/9811/29/11290068.htm
Note that Surfer is available on the Windows workstations in Lathrop 305 and Lathrop 401. Please print maps on the black-and-white laser printers for this lab.