EES 1030 1st Edition Lecture 15Mass Wasting:Mass wasting (slope failure): movement of rock, regolith, and soil downslope.Regolith: layer of rock and mineral fragments that covers nearly all earths land surface Examples of mass wasting- Landslides, mudflows, rock-falls, slumps.*combined effects of mass wasting and running water produce stream valleys such as the Grand Canyon Landform development: erosion weakens and breaks rocks apart, transfers debris down slope via gravity.Stable and Unstable Slopes: when loose sediments such as sand and gravel are piled, particles will move downslope until bottom. Sediment piled too steeply is unstable and will eventually collapse Angle of repose: the steepest angle where a pile of unconsolidated sediment can remainstable What cause the angle of repose to vary - Size and angularity of the sediment particles- How much water is mixed with the particles- The friction of the surface beneath the pileRole of Particle Size and Shape:- Large particles have a smaller angle of repose than smaller particles.- Rounded particles have a greater angle of repose than angular particlesEx) round marbles have a less angle of repose than sand, marbles have a greater angle of repose than penniesRole of water: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.- Dry particles, no water. Angle of Repose is determined by friction of grain to graincontact. - Small amount of water: increases cohesion of particles - Large amount of water: eliminates particle cohesion, decreases friction and adds weight.Role of the Underlying Surface: Angle of repose is affected by the friction of particles against the surface beneaththe pile. - Slippery with low friction- smaller angle of repose- Solid with high friction- greater angle of reposeThe force of gravity on a particle I divided between:- Resisting force and pulling force.- If resisting is greater than particles stay in place - If pulling is greater than particles move downslopeOver steepened slope: landscape with slope greater than the materials angle of repose.Ex) stream undercutting a valley wall, waves eroding a base of a cliff Eventually the over steepening will be eliminated by mass wasting and restored to stabilityEffects of Vegetation Removal: Root systems bind soil and regolith together, leaves shield the soil surface from erosionaleffects of rain. Removing it will make the max angle of repose less and the soil susceptible to erosion Earthquakes as TriggersGround vibrations from earthquakes can cause water saturated surfaces to behave as fluid and flow.Landslides without triggers: - Not all mass wasting events are caused. Slope materials weaken over time and random events can be unpredictable- Ex) sudden catastrophic landslide in 1967 along highway 50 outside Placerville California - Solution: us geological survey developed a real time landslide monitoring a system that detects early indications of landslides and activates a warning systemSubmarine landslides: landslides that occur along passive continental margins and flanksof submarine volcanoesTriggered by buildup of unstable sediments or by forces such as storm waves or earthquakes. Submarine landslides can trigger tsunamisMass wasting velocity – fast: most rapid events occur in areas of rugged geologically young mountains. Slow: as a landscape ages less dramatic downslope movement occurs.Types of mass wasting: rock fall, earth slide, debris flow.Fall: rapid-downslope movement of rocks or regolith that have broken away from sloped outcrops. They can free fall through the air or bounce and roll downslope.Slides: slow to rapids downslope movement of a relatively intact rock or regolith layer that has detached from a sloped outcrop. Translational: Materials move downslope along a flat surface Rotational: materials move downslope along a curved rupture surface, rotating as it moves and causing surface features to lift.Flow: continuous downslope movement of a solid material that moves like a fluid. Types of flows are differentiated by velocity of motion. Slurry flow : sediment flow that contains between 20-40% water. As the water content increasesabove 40% slurry flows grade into streams. Slurry flows have high velocity and are water saturated. Debris Flow(mud flow): highly fluid with high velocity, tend to travel along valley floors. Usually result from rain in areas with unconsolidated sediment. Ex) from high to low velocity: Mud flow, Debris flow, SolifluctionGranular flows: sediment flows with 0-20% water. Possible with little or no water. Fluid behaviorcomes from mixing with air. Low velocity, not water saturated. Ex) from high to low velocity: debris avalanche, grain flow, earth flow, creepDebris avalanche: high velocity flow of large volume mixtures of rock and regoliththat results from complete collapse of a mountains slope. Often triggered by earthquakes and volcanic eruptions.Earth Flows: usually triggered by heavy rain, low velocity and can remain active for long periods of time. Generally narrow tongue-like features that begin at a small cliffCreep: very low velocity, continuous movement of regolith down slope. Creep occurs on almost all slopes but the speeds vary. Indicators: bent tree trunks, tilted fences, breaks in retaining walls, and tension cracks in rocksLahars occur on volcano slopes when unstable layers of ash and debris become water saturated. High velocitySolifluction: (soil creep) water saturated soils flow slowly. Typically in areas where water can’t escape from the saturated surface layer by infiltrating the deeper layers *White Laurel North Carolina. September 2004 – hurricanes saturated western North Carolina resulting in a devastating debris flows. Houses were destroyed and condemned due to foundation cracks.*Geological date and tools can be used to predict and prevent natural hazards dueto mass