GEOL 101 1nd Edition Lecture 13 Outline of Last Lecture I. Chemical WeatheringII. Rate of WeatheringIII. SoilIV. Slope StabilityOutline of Current Lecture I. Slope FailureII. Land FailureCurrent 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 undercuto Slides—occur when material moves down along a sloped surface Can be very fast and catastrophic Can also be very slowo 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 flowThese 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 surfacesslump/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 surfaceo 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 extractedo When this is happening and is close enough to the surface, a collapse or gradual subsidence can occuro Huge problem in the coal minesLand 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 lateron.-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
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