GEOL 101 Mass Wasting
GEOL 101 Mass Wasting GEOL 101
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This 2 page Class Notes was uploaded by Victoria Williams on Thursday March 31, 2016. The Class Notes belongs to GEOL 101 at George Mason University taught by Mark Uhen in Fall 2016. Since its upload, it has received 21 views. For similar materials see Introductory Geology in Geology at George Mason University.
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Date Created: 03/31/16
Mass Wasting The largest landslide that occurred was in Mount Saint Helens. Mass wasting is the downslope movement due to the influence of gravity. The Grand Canyon is a great example of mass wasting over time. With flooding, landslides occur and the material is brought down to the river to be swept away. Controls of mass wasting o Dry soilhigh friction – no mass wasting o Saturated soil less friction – unstable and causes mass wasting Angle of repose is the slope at which unconsolidated particles assume a stable slope usually between 25 and 40 degrees, depends on the size and texture of the grains Vegetation removal also effects mass wasting. Foliation that burns in a wild fire, the roots dry up and crumble and don’t hold the soil together. This increases the probability of a mass wasting event. Earthquakes also can change the properties of materials by fracturing it or breaking apart the ‘cement’ holding it together. o Liquefaction – the earthquake vibrating saturated particles apart to make it act like a liquid Description of Mass Wasting o Type of material: rock, mud, ice o Type of motion: fall (through the air), slide (down a slope), flow (water) o Rate of motion: slow vs. fast A slump is another type of mass wasting which is motion along a curved surface/crack. The earth then flows a bit like water. The curved surface is caused by clay having conquoital fracture (circular fracturing). Rockslides occur when rocks move along a generally planar surface. A layer of rock break up and slide down, which can be caused by many things (floods, earthquake, etc.) Rock (mud, whatever) slide is similar to a normal landslide. In the Gros Ventre valley, a river weathered through a layer of clay holding a piece of sandstone up. The sandstone then slid and unfortunately killed a lot of people. Avalanches happen when snow moves along a planar surface. It’s just like other mass wasting events but it’s made out of ice/snow. Debris Flow consists of rock and soil mixed with a large amount of water so it acts like a liquid. Sometimes manmade objects can be swept up in this. They slow down when the debris spreads out. Lahar are associated with volcanic eruptions, they are a flow of volcanic ash and water. And usually the water is boiling hot as well. Earthflows happen when the soil is super saturated and it moves downhill in a tongue shaped mass. It’s similar to a slump but it doesn’t crack in a curved surface A creep is a slow, downslope movement of soil due to alternate expansion and contraction due to freezing and thawing. When water freezes, it expands and if it’s in a crack it pushes the crack apart. It moves in a kind of zigzag pattern, and each small cycle can take a year. Permafrost is permanently frozen ground. Like in the poles, there are spaces that never ever melt. Then in an outer ring around the permafrost zone there are places that thaw out a bit, but deep down there is always permafrost Solifluction happens when saturated soil moves slowly downslope in lobes impermeable (frozen) layers below. ONLY happens where there is permafrost.