CEE 1030 1nd Edition Lecture 15: Mass WastingOutline of Last Lecture I. Mapping the ocean floorII. Types of continental marginIII. Types of plate boundariesIV. Isotasy and crustal thicknessV. Origin and evolution of continentsOutline of Current Lecture I. Mass wastinga. Role of particle size and shapeb. Role of waterc. Role of underlying surfaceII. Other factors of mass wastingIII. ReviewIV. Mass wasting processesCurrent LectureI. Mass wastinga. Mass wasting: the movement of rock, regolith, and/or soil downslope under direct influence of gravityi. Regolith: gathering of rocks on Earth’s surfaceb. Landform developmenti. Weathering: weakens and breaks rock apartii. Mass wasting transfers debris downslope via gravityc. Stable and unstable slopesi. When loose sediments are piled, particles move downslope until pile’s slope becomes stableii. Sediment piled too steeply: unstabled. Angle of repose: the steepest angle at which a pile of unconsolidated sediment remains stablei. Varies according to:1. Size and angularity of sediment particlesa. Larger particles have smaller angle of reposeb. Rounded particles have smaller angle of reposec. Think of marbles vs. sand, marbles vs. penniesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. How much water is mixed ina. Dry particles: angle of repose determined by friction of grain to grain contactb. Small amount of water: increases angle of reposec. Large amount of water: decreases angle of repose, eliminates particle cohesion3. Friction of surface beneath the pilea. Angle of repose is affected by the friction of particles against surface beneath the sediment pilei. Low friction surface: smaller angle of reposeii. High friction surface: greater angle of reposeb. Think of slippery snow vs. frozen dirtII. Other factors of mass wastinga. Oversteepened slope: landscape with slope greater than material’s angle of repose, unstableb. Effects of vegetation removali. Deforestation increases rate of mass wasting by decreasing angle of reposeii. Root systems bind soil and regolith togetherc. Stabilizing an unstable slopei. To stabilize, insert something that will increase the angle of reposeii. Add reinforced terracesiii. Establish native plants with deeper root systemsd. Earthquakes as triggersi. Ground vibrations from earthquakes can cause liquefaction: when shaken, water-saturated surface sediments can act as a fluid and flowe. Submarine landslidesi. Mass wasting is common and widespread on the ocean floorii. Landslides often occur along passive continental margins and flanks of submarine volcanoesIII. Reviewa. Primary force controlling mass wasting: gravityb. What would increase the angle of repose? Flatter particlesIV. Mass wasting processesa. Basis of classificationi. Type of material1. Rock, debris, earth (by decreasing size)ii. Movement1. Fall: free-fall of sediment2. Slide: sediment moves along surfaces3. Flow: material moves as viscous fluidiii. Velocity1. Most rapid events occur in areas of rugged, geologically young mountainsb. Types of slidesi. Translational slide: material moves down a slope along flat surfaceii. Rotational slide (slump): material moves downslope along a curved rupture surfacec. Types of flowsi. Creep: slow movementii. Flow: fast movementiii. Avalanche: very fast movementiv. Solifluction: a type of creep in which water-saturated soils flow slowly downhill, typically in areas where water cannot escape from the saturated surface layer by infiltrating to deeper
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