Lab 6 mass wasting - Google Docs

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University of Arkansas, Little Rock *

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Geography

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Oct 30, 2023

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Uploaded by BrigadierKouprey15497

Part 1: Basic Principles of Mass Wasting Questio n # Observe the diagrams in Figure 6.1 in the Lab 6 - Mass Wasting exercise file - then answer questions 1- 5. #1 Which component of gravity is greater on the slightly steep surface: the component acting perpendicular to slope or the gravity acting parallel to the slope ? a. The gravity acting parallel to the slope #2 Which component of gravity is greater on the very steep surface: the component acting perpendicular to slope or the gravity acting parallel to the slope ? a. Perpendicular #3 On a flat surface, with what are the parallel and perpendicular components of gravity aligned? A. It is aligned with the force of gravity #4 As the slope becomes steeper, what happens to the component of gravity that is parallel to the slope direction (gs)? #5 If you have two identically steep slopes, but earth materials are stable on one and not the other, what can you infer about the frictional forces on the two slopes? The gravitational weight is more than the forces on the stable slope Observe the diagrams in Figure 6.2 in the Lab 6 - Mass Wasting exercise file - then answer questions 6 - 8. #6 Based on the forces shown in the diagrams, explain what happens to the frictional forces when pore pressure increases between sediment grains and between planar surfaces.

They will decrease #7 What effect could a heavy or prolonged rainfall event have on pore pressure? It could increase pore pressure #8 What does the effect of question #7 mean for a mass wasting event? The friction is lessened giving the rocks the capability to slip Part 2 – Recurring Movement at La Conchita, California For questions #9 and #10, refer to Figure 6.3 in the Lab 6 - Mass Wasting exercise file. #9 Notice the dirt road (double dashed line) that traverses the hillside above the town. Explain how building this road would have made the slope less stable. It changes the structure of the ground. It would make it uneven. #10 Describe two ways in which heavy rains would cause the slope to become less stable. Way #1: The water easily moves around in the displaced soil Way #2: It adds weight to the displaced land For questions #11, #12, and #13, refer to the Lab 6 - La Conchita 1995 Google Drawing file

#11 Use a blue-colored line to outline the area on the photo in Lab 6 - La Conchita 1995 (Google Drawings) where the movement took place. [Open the file, click Insert → Line → Scribble] #12 The 1995 movement at La Conchita has been classified by the U.S. Geological Society (USGS) as a complex slump. List the physical characteristics you see in the photo that support the interpretation that this is a slump. It is a slump. Depression in the land and an axis parallel to the slope #13 Use a red-colored line to carefully trace the road as it comes down the hillside on the photo in Lab 6 - La Conchita 1995 (Google Drawing). Note that in the 1995 photo the road can still be found in the middle of the slump. For questions #14 and #15, refer to the Lab 6 - La Conchita 2005 Google Drawing file #14 The freshly exposed material visible on the photo in Lab 6 - La Conchita 2005 (Google Drawing) represents the area where renewed movement occurred in 2005. Use a pink-colored line to carefully outline the recent area of movement on the photo. #15 The USGS classified the 2005 event as a debris flow. As before, list the physical characteristics you see in the photo that indicates this is a debris flow. Sand and mud are moving. The crease in the land seems very fine For questions #16 and #17, refer to the both the 1995 and 2005 Google Drawing files #16 Based on what you see in the two sets of photos, which event--the 1995 or 2005 --was more deeply seated and which was shallower? Explain how you can tell. The one in 1995 was shallower. The one from 2005 went deeper in the ground. #17 From a hazard perspective, which event--the 1995 slump or 2005 debris flow --would have posed the greatest threat to people living at the base of the slope? Explain why.

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The event of 2005 was the bigger threat. The slide was much more dangerous and the movement was much faster and steeper. #18 Review Figures 6.4 and 6.5 in the Lab 6 - Mass Wasting exercise file. Based on the timing of the slides relative to the rainfall pattern, which event--the 1995 or 2005 --do you think the water would have infiltrated deeper into the subsurface? Why? The water in the 2005 event had more time to cycle through the earth. #19 Explain how this could account for the difference in volume of earth material that you outlined in questions #11 (1995) and #14 (2005). #20 List and describe 3 steps that could be taken that would help minimize the chance of mass wasting and loss of life at La Conchita. Step #1: Use barriers and retaining walls Step #2: They could cut back the slopes of the land Step #3: Rock bolts or cables that prevent the rocks from falling