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Unformatted text preview: EAS 111 General Announcements 11/17/10 Today: Unstable Ground : Ground Collapse and Slope Failure Coastlines and Coastal Processes on Monday Schedule Issues looking ahead Monday = last new content for Lecture Exam 3 Study guide posted tonight NO LABS Next Week Thanksgiving Break Mon (11/29) = Review; Weds. (12/1) = LECTURE Exam 3 The week after that (12/7-10) = Dead Week = LAB Exam 3 AND our last wrap-up lecture & review Earth and Atmospheric Sciences 111
Fall 2010 Flowing Ground: Ground Collapse and Slope Failure
-Why does the ground collapse? -Why do slopes fail?
-Lecture 20 Ground Collapse Subsidence Sinkholes Ground Collapse Subsidence Sinkholes Effects of Pumping Groundwater
Before pumping B A 17.08.a After pumping: cone of depression Subsidence from Fluid Withdrawal
Water table drops, aquifer compacts, land subsidence Earth fissures How would one best prevent this type of problem? Subsidence from Fluid Withdrawal A.do not withdraw any water, ever, from an aquifer B. make sure the withdrawal rate is less than the recharge rate Water table drops, aquifer C. make sure the withdrawal rate is greater than the Earth fissures compacts, land subsidence recharge rate D. you can't prevent this, it is inevitable Ground Collapse Subsidence Sinkholes How Do Caves Form?
Most in limestone (soluble) Groundwater dissolves material Above water table cave may be dry Features widen to cavities and caves
17.06.a1 Below water table water further dissolves material What Features Accompany Caves?
Roof collapse can form sinkhole on surface Dripping water evaporates, precipitates calcite Cave formations on roof, floor, and walls Surface with sinkholes, limestone pillars, disappearing streams = karst topography 17.06.c1 17.06.a2 17.06.b1 Slope Failure Gravity Failure types & anatomy Hazards Role of Gravity in Slope Stability
Gravity acts vertically so block will not move on a flat surface Gravity pulls block at an angle so block can move on an angled slope Normal component pushes the block against the slope
15.07.a1 Shear component pushes block down slope Consider how steep a slope can be and remain stable Sand dune Angle of repose for dry sand 15.07.b Some parts of slope steeper than angle of repose Scoria cone Talus slope Coarse material can have a steeper angle of repose Observe what factors control slope stability Amount of water Angle of repose for material Discontinuities: fractures, cleavage and bedding
15.07.c Observe some ways that slopes fail Earthquake activity Undercut cliff 15.08.a1 Too steep a slope Landslide Undercut slope Observe some events that could trigger slope failure Precipitation Volcanic eruptions Sudden shock, as from an earthquake Changes in land use Overloading slope Undercutting slope 15.07.d1 Classification of Slope Failures
Mechanism of Movement Fall Type of Material Solid rock Unconsolidated Flow Rate of Movement Fast Slow
15.08.b1 15.08.b Observe what happens when rocks fall or slide Rock fall and debris fall Rock slide Rotational slide (Slump)
15.09.a1 Observe the types of slope failure that involve flow: Part 1 Creep Debris slide Earth flow 15.10.a Observe the types of slope failure that involve flow: Part 2 Debris flow Rock or debris avalanche 15.10.a Observe the potential for landslides in the U.S. Northern Indiana doesn't show a widespread risk of landslides at this scale on this map. Does this mean we can completely forget about it? A.Sure! There is no slope failure risk here because we have no slopes B. Sure! The ground surface in Northern Indiana is so tough it will never fail regardless how steep the slope. C. No! Our problems are more local in scale and don't show up on a national map Red = high potential Yellow/green = intermediate Unshaded = low or unknown 15.11.b1 Assessing Potential for Slope Failure 15.12.c Past failures Known problems Steep slopes Changes in slope Conditions of material Potential triggers EAS 111: Assignment for Monday 11/22/10 Readings from Exploring Geology
Coastal Processes & Shorelines 14.1, 14.3, 14.4, 14.5, 14.6, 14.8 ...
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- Spring '10