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Easc lecture #8 & #9 Mass Wasting.docx

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Earth Sciences
EASC 104
Brent Ward

Mass wasting - One of the biggest driving forces is the slope steeper the slope, the more likely there will be a landslide o Depends on the types of materials on the slope and the climate Landslides - Many landslides happen especially in remote areas Slope (in) stability - when slopes are over steepened - slopes are debuttressed - for many landslides, it is the accumulation of water that creates water pressure which then can trigger the landslide Classification of landslides - regolith ( more common in USA)—intensely weathered bedrock - We also classify landslides by the amount of water content—whether it is dry or more wet Type of material - Something that is completely unconsolidated  sand o If completely loose and consolidated, it will not stand up steep - Great amount of water can decrease the cohesion - If there is clay, it will help hold the material together to stand up steeper Type of motion - Debris flow is what often blocks highways - Earth flow, it flows like a decries flow but doesn’t flow as rapidly Landslides: role of water - Adding more water to material increase pore water pressure - If in an area with clay minerals, the clay can absorb this water Rock slide and rock avalanches - Usually when material moves down slop and may break up but does not come fully mixed o More rapid types of rock failure: rock avalanches  the mixing then increases Creep (sackung) - Sakung caused because the rocks move slowly down; the slow movement then creates a catastrophic failure Toppling - Rapid movement that can trigger a large landslide Unconsolidated mass movement: creep - Pistol butted tree—thickening at the bottom of the tree that causes the tree to grow straight o Shows us that the slope is steep Unconsolidated mass movement: slump - The rotating surface causes the material to curve back into the slope - Also classified as a slump—quick clay Factors contributing to increased risk of landslides - Vegetation removal: rotting roots affects the cohesion of the slope  cohesion is the tendency for things to stick together - Undercutting slopes: rivers undercutting the slopes - Watering lawns or septic system o Water from swimming pools seeping in to the cracks of the creep which can cause a landslide - Cut and fill: e.g. road building -- when the original s
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