Understanding Earth Chapter 12: Mass Wasting Copyright © 2004 by W. H. Freeman & Company Frank Press, Raymond Siever, John Grotzinger, and Thomas H. Jordan Fourth Edition

Mass wasting is the downlsope movement of rock, soil, and mud under the influence of gravity. Nearby large slopes occur in Natchez and offshore at the continental shelf-slope break

Natchez (MS) Bluffs experience constant collapse

Offshore Louisiana the same occurs as large amounts of sediment are deposited rapidly. Moreover movement of underlying salt can destabilize the submarine slope. Billion-dollar oil platforms in deep water have to be carefully placed where there is no risk of submarine slides. A giant landslide broke 13 submarine cables that connected the US and Europe in That landslide was accompanied by a tsunami.

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Why does the sand castle not fall?

Internally, there are forces holding the sand grains together. These forces are surface tension between the grains and water wetting these grains. There is a net, inward surface-based attraction. (A little water is good) If there is too much water, the water begins to push the grains away from each other. The weiht of the water pushes outwardly (liquefaction). (Too much water is bad) What part of the beach do you run on? Why? Water and slope stability

What if the sand is dry??? Sand is an analog for unconsolidated materials (materials whose grains are not held together,… there is no internal “cement”) Mass wasting will take place more readily if the slope increases beyond some critical value and if the material is unconcolidated. The critical value is the natural angle of repose, or the maximum angle of stability before the material will flow, e.g. ice, snow, soil, sand have different slopes.

How can a slope be stabilized?? Having a harder rock Having a cover of soil

What can trigger Mass Wasting? Increase in the amount of water in the ground An earthquake

How do we classify types of Mass Movement? Based on SPEED and MATERIAL composition e.g., fast (>=5km/hour) e.g., rockslide e.g., ~1km/hr slow and soft sediment is creep e.g., moderately fast and soft -- debris flow In Louisiana we have slumps on the sides of ramps along I-10 and I-12 and along faults

Where should we NOT BUILD… on the side of a valley where the beds dip in the same direction as the valley wall where there are alternating clay layers with hard rock layers on a valley wall with lots of loose sediments. When rain can fall in bursts these loose materials can become debris and mud flows on avalanche deposits and debris flow deposits

Understanding Earth Chapter 12: Mass Wasting Copyright © 2004 by W. H. Freeman & Company Frank Press, Raymond Siever, John Grotzinger, and Thomas H. Jordan Fourth Edition