12. landforms of mass wasting

Geomorphology 12. Landforms of Mass Wasting

K.A. Lemke – UWSP 97

12. LANDFORMS OF MASS WASTING

40 Points

The objective of this lab exercise is to learn how to identify landslides and earth flows using stereo-aerial photos in conjunction with topographic maps, and to improve your ability to use topographic maps for measuring and analyzing the landscape.

YOU SHOULD BE ABLE TO:

• Identify and correlate landforms of mass wasting and on stereo air photos and on topographic maps; • List some of the signs evident on topographic maps and air photos that allow mass wasting landforms to be

distinguished from other landforms, or from mass wasting landforms of a different age; • State some of the limitations of using just air photos and/or topographic maps to identify landforms of mass wasting

and other characteristics of mass wasting events; • Calculate the area of features on topographic maps; and • Describe examples of how mass wasting events may affect rivers and river flow.

KING HILL, IDAHO

1. The relatively flat area in the northeastern portion of the topographic map and the air photo is a basalt-capped mesa. On the map it appears as a relatively flat area and on the photo it is relatively consistent shade of light gray. Outline the edges of this mea on the topographic map and on the air photo. [1]

2. The southwestern slope of the mesa failed. At the top of the failed area, three well-defined slump blocks are clearly visible on the air photo. The back side of each slump block is defined by a scarp. Highlight these slump blocks on the air photo. [2]

Figure 12.1. Scarps at the head of slump blocks

3. On the air photos, how do the topography, tone, and coloring of the slump blocks allow them to be easily identified? [2]

scarps

12. Landforms of Mass Wasting Geomorphology

98 K.A. Lemke – UWSP

4. The three slump blocks are just the upper part of the failure. Identify the rest of the failure and outline the entire failed region on the air photo. Use variations in topography, visible through the stereoscope, to help define the boundary of the failure. [3]

5. On the topographic map, outline the entire failed area. Use variations in topography and reference points such as the rivers, the ditch, and roads, to match the topographic map to the air photo and to determine the location of the failure boundary. [4]

6. On the topographic map, what aspects of the contour line patterns (e.g. shape, spacing) helped distinguish the failure from the surrounding areas? [2]

7. If you didn’t have the air photo, could you identify the individual slump blocks on the topographic map? Why or why not? [1]

8. The topographic map has a scale of 1:24,000. Estimate the approximate area of the entire failure in square miles. Remember, the entire map scale must be squared when you’re working with area; don’t just square the units, square the numbers that go with them as well. Show your work. [2]



King Hill, Idaho 1:24,000

Contour Interval = 20 ft



SLUMGULLION, COLORADO

9. On the air photo, locate the Slumgullion slide and outline it. Use variations in topography, visible through the stereoscope, to help define the boundary of the failure. [2]

10. On the topographic map, outline the portion of the Slumgullion slide that’s visible on the air photos. Use variations in topography and reference points such as roads to determine where the failure boundary is. [2]

11. What aspect of the slide topography visible on the air photos was most helpful for delineating the slide on the topographic maps? [1]

12. On the topographic map, extend the boundary of the slide all the way back to the very head of the slide. The upper portion of the slide is more difficult to define than the lower portion because we have no air photo to accompany the map. Use a dashed line for any uncertain boundaries. [2]

13. How did the shape of the contour lines help you identify the edges of the slide in the area not covered by the air photo? What did you look for with regards to contour line shape and elevation to determine where the edges of the slide might be located? [2]

14. There is a small triangular wedge-shaped feature at the southern end of the slide on the northeastern edge of Lake San Cristobal, where Slumgullion Creek flows into Lake San Cristobal.

a. On the air photo, compare and contrast the appearance of this feature to the appearance of the main part of the failure. What similarities and/or differences exist between this feature and the main part of the failure? [2]

b. Based on similarities and differences in appearance, do you think this feature is part of the original slide, a feature associated with mass wasting activity subsequent to the main failure, or a result of some other process? Explain. [2]



15. The Lake Fork of the Gunnison River flows northward into Lake San Cristobal, and eventually flows out of the lake over Argenta Falls. Use the stereoscope to locate Argenta Falls on the air photo and mark this location. [1]

16. Explain how the Lake Fork of the Gunnison River, Lake San Cristobal, the Slumgullion Slide and Argenta Falls are related to one another. [3]

12. landforms of mass wasting

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