Cee 1030 1st Edition Lecture 15Current LectureMass Wasting  Mass wasting= movement of rock, regolith, and/or soil downslope, under the direct influence of gravity Landform development  Weathering= weakens and breaks rock apart  Mass wasting= transfers debris down slope via gravity  not talking about the part of the process that is weathering, strictly looking at things caused by gravity Stable and unstable slopes- when loose sediments (such as sand or gravel) are piled, particles will move downslope until the pile’s slope becomes stable- sediment piled too steeply is unstable, will collapse Angle of repose angle of repose- the steepest angle at which a pile of unconsolidated sediments remain stable  the angle of repose varies according to: -size and angularity of the sediments particles- how much water is mixed with the particles - the friction of the surface beneath the pile Role of particle size and shape - angle of repose is greater for sand than marble, because of particle size difference Role of water- dry particle, no water: angle of repose determined by friction of grain to grain contract- small amount of water: increases cohesion of particles, increases angle of repose- large amount of water: eliminates particle cohesion, decreases friction and adds weight, decreases angle of repose Role of underlying surface- angle of repose is affected by friction of particles against surface beneath sediment pile:These 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. low- friction surface= smaller angle of repose  high- friction surface= greater angle of reposeOversteepened slopes  oversteepened slope: landscape with slope greater than the material’s angle of reposeExamples: stream undercutting a valley wall, waves eroding base of a cliff oversteepened slopes are unstable: sooner or later the oversteepening will be eliminated by mass wasting and the slope restored to stability Effects of vegetation removal - deforestation increases rates of mass wasting by decreasing the angle of repose- root systems bind soil and regolith together- leaves on plants shield soil surface from erosional effects of rain Earthquakes as triggers- ground vibrations from earthquakes can cause liquefaction  liquefaction= when shake, water- saturated surface sediments can behave as a fluid and flow Landslides without triggers?- problem: not all mass wasting events are triggered by earthquakes, slope materials weaken over time and random events are unpredictable Submarine landslides- mass wasting is common and widespread on the ocean floor- landslides often occur along passive continental margins and flanks of submarine volcanoes- triggered by buildup of unstable sediments, or by forces such as storm waves or earthquakes - submarine landslides can trigger tsunamis Mass wasting processes - basis of classification: 1. type of material (rock, debris, earth, mud)2. type of motion (fall, slide, flow) 3. rate of movement ( rapid vs. slow) Material of mass wasting type of material involved:  rock: descending material began as bedrock  debris: descending material began as regolith, with more coarse particles than fines  earth: descending material began as regolith, with more fine particles than coarse Movement of mass wastingType of motion involvedfall: free-fall of sediment slide: sediment moves along a surfaceflow: material moves as a viscous fluid Velocity of mass wasting-fast mass wasting events tend to happen in geologically young areas, ten to wear down the peaks andfill in the valleys - slow mass wasting events as a landscape ages, less dramatic downslope movements occur Falls fall: rapid down-slope movement of rocks or regolith that have broken away from sloped outcrops-particles lose contact with surface as they free-fall through air, or bounce and roll downslope slide- slow to rapid downslope movement of a relatively intact rock or regolith that has detachedfrom a sloped outcrop moves along a well-defined rupture surface- translational slide- material moves downslope along a flat surface - rational slide (slump)- material moves downslope along a curved rupture surface, rotation as it moves and causing surface features to tilt Flows flow continues, downslope movement of water- saturated material (rock and regolith) that moves like a viscous liquid - different types of flows: differentiated by speed motion = slow, flow type= creep motion= fast, flow type= flow  motion= very fast, flow type= avalanche  debris avalanche: very rapid flow of water-saturated rock, regolith, vegetation, or even ice downslope Earth flows earth flow: moderate to rapid movement of water-saturated, clay rich (fine-grained) sediment downslope, commonly on hillsides in humid areas during heavy precipitation or snowmelt- earthflows typically from a tongue- or teardrop-shaped mass that moves slowly but persistently Debris flows (mud flows) debris flow- moderate to rapid movement of water-saturated, mostly coarse-grained regolith downslope Lahars lahar: a type of debris flow that occurs on volcano slopes when unstable layers of ash and other debris become water- saturated and move rapidly down slope Creep  creep: slow movement of water-saturated rock and/or regolith downslope; often driven by repeated expansion and contraction of surface sediments cause by repeated cycles of freeze-thaw or wet-dry  key indicators of creep: bent tree trunks, titled fences, breaks in retaining walls, tension cracks in roads Solifluction (soil creep)  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 infiltration to deeper