bree_hernandez_chapter_10

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Geography

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Dec 6, 2023

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Chapter 10 Mass Wasting Assignment 1. How does water affect mass-wasting processes? Water affects mass-wasting by speeding up ordinarily slow, mass wasting processes and greatly increases the chances that faster moving processes will occur. Water lubricates rock fragments so that they slide down slope more easily. Mass wasting occurs more readily in rainy seasons for this reason. 2. Describe the significance of the angle of repose. If a slope becomes any steeper than the angle of repose, then granular material will start moving downslope via mass wasting. For dry sand, the angle is about 34 degrees. Most accumulations of broken rock, such as talus, contain different sizes of fragments, some of which may be quite large; these often have slightly steeper, repose angles than dry sand. 3. How might a wildfire influence mass wasting? Wildfire destroys plants which anchor soils and loosen upper layers of soils, increasing mass movement events as the materials frequently move downslope. 4. What terms describe the way material moves during mass wasting? Define those terms. Fall, slide, and flow describe the way material moves during mass wasting. A fall is triggered by ice wedging or plant activities on steep slopes. A flow is triggered by large amounts of water and steep slopes. A slide is blocks of bedrock broken loose, which then slides downhill. 5. Both slump and rockslides move by sliding. How do these processes differ? Rockslides involve rapid slippage of fracture-bounded blocks along inclined, weak layers and fractures in bedrock. A slump denotes the slow, downhill movement of a block of soil or relatively weak rock along a curved, spoon-shaped, slip surface. As it moves downhill, the block often undergoes rotation, leaving its surface tilted back toward the hillslope. 6. What factors led to the massive rockslide at Gros Ventre, Wyoming? Water from melting snow and rain seeped into the soil and bedrock, saturating the ground above the shale and weakening the top of the supporting shale layer. The river had gradually downcut into the shale layer, depriving the inclined, sandstone slab of any lateral support on the downhill side. These conditions allowed a large, fractured slab of sandstone to break loose and rapidly slide downhill. The slide formed an

instant, natural dam and was moving fast enough to climb a short distance up the opposite side of the valley. Two years later the dam burst, causing a tremendous flood on the lower Gros Ventre and upper Snake Rivers. 7. Explain why building a home on an alluvial fan may not be a good idea. Building a home on an alluvial fan may not be a good idea because at any location on the fan surface, it may be highly active, where floods and debris flows can occur. 8. Describe the basic mechanisms that contribute to creep. The basic mechanisms that contribute to creep is the slow and subtle downhill movement of sediment triggered by repeated freezing and thawing of soils on gentle slopes. 9. During what season does solifluction occur? Explain why it occurs only during that season. Solifluction occurs during the summer season thaw when the water in the soil is trapped by frozen permafrost underneath it. This waterlogged alluvium moves down slope by gravity, supported along by freeze-and-defrost cycles that thrust the top of the soil outward from the slope. 10. Describe a type of mass wasting that might occur in your home area. Remember to consider characteristics such as climate, surface materials, and steepness of slopes. What would be the trigger? Landslides and rockfalls are potential types of mass wasting that might occur in Missouri. Bluffs that contain thick beds of sandstone or carbonate rock, buttressed by shale, are the most hazardous. Due to the changing seasons, water from melting snow and rain seeps into the soil and bedrock, saturating the ground above the shale and weakening the top of the supporting shale layer. Rocks that fall from bluffs will typically collect at their base. Steep slopes of loess, till, thick colluvium, alluvium and shale can be prone to land sliding. The problem is often exacerbated by seasonally high-water tables. In general, the higher and steeper the slope, the further and faster the slide will move.

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