GEOL 101 1nd Edition Lecture 13 Outline of Last Lecture I Chemical Weathering II Rate of Weathering III Soil IV Slope Stability Outline of Current Lecture I Slope Failure II Land Failure Current Lecture Slope Failure Landslide is a general term for mass wasting Categorize mass movements by Speed can be very fast or very very slow Material soil rock mixture of both and vegetation Movement o Falls are the fastest form or mass wasting Materials free falls or rolls down a steep slope or clif Are common in the spring and fall when freeze thaw cycles break apart rocks Many clif along mountain highways are undercut o Slides occur when material moves down along a sloped surface Can be very fast and catastrophic Can also be very slow o Flows occur when unconsolidated slope material becomes water saturated Can include soil vegetation or rock sediments These are triggered by intense rain or snowmelt Debris flow 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 Lahars Earthflows mud slides o Creeps is a very slow type of Earth flow moving as slow as 1 mm per year Can be triggered by freeze thaw water freezes and expands and creep their way downslope Evidence for creep is often seen in curved trees and fence posts or utility poles Slides can occur along a single planar surface of failure translational slide Or they can occur multiple curved slip surfaces slump rotational slide Subsidence the gradual settling of sudden collapse of leveled land Can be natural o Regional subsidence happens in broad geographic region It is caused by the compaction of underlying rocks Common in deltas as sediments pile up and squeeze the underlying rocks New Orleans Venice It may be caused when humans draw out water from aquifers or petroleum from rock layers below the surface o Karst Terrain limestone develops where bedrock is composed of limestone Limestone is easily dissolved in mild acidic water Caves that form close to the surface may collapse in on themselves leaving a sinkhole at the surface Without cave mapping it is hard to tell where a sinkhole is forming Or human induced mining related subsidence Both can be hazardous to people Underground mining creates vids in the subsurface as the material is extracted o When this is happening and is close enough to the surface a collapse or gradual subsidence can occur o Huge problem in the coal mines Land Failure Weather Heavy precipitation or snowmelt can trigger mudflows debris flows and lahars Earthquakes Can shake loose otherwise stable land Wildfires Consume vegetation leaving slopes more exposed to heavy precipitation and failure later on Slope Steeping This may be natural by rivers or ocean waves eroding the adjacent land Can occur when roads are constructed in mountainous areas Permafrost Subsidence Permafrost is permanently frozen ground in high altitudes and polar regions As grounds contracts is subsides damaging surface Constructing homes roads and other structures on permafrost soil can lead to structural damage over time Heat from buildings leaks into subsurface can melt frozen ground water Withdrawing groundwater Houston s use of groundwater has caused parts of Galveston TX to sink below sea level
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