Use the map to answer the question.                         Louisiana has lost and gained land on its coast over the years. The red color on the map shows the land gained in Atchafalaya Bay between the years 1932 and 2000. What caused the new land to form? A.sediments moved by waves B.tectonic uplift C.sediments carried by rivers D.dropping sea levels

Mass Movements at Earth’s Surface Pg. 75

Mass movements The downslope movement of loose sediments and weathered rock resulting from gravity Weathering  erosion  mass movements Climate controlled All occur on slopes

Influencing variables Material’s weight Resistance to sliding or flowing A trigger event (ex. Earthquake) Erosion at the foot of a slope water

Water and mass movements Too little prevents sediments from holding together, increasing potential for movement Too much water increases the weight of the soils; can also act as a lubricant Not involved as transport agent

Types of mass movements Classified as: Creeps Flows Slides Falls Slumps Avalanches

Creeps Slow, steady downhill flow of soils Noticeable over long periods Observe structures to identify creeps Solifluction occurs when layer above permafrost slides downhill

Flows Flow as if the mass was a thick liquid Can move fast or slow Mudflows-swiftly moving mixtures of mud and water Common in volcanic regions Also common in semi-arid regions that experience intense short rainstorms (So Cal)

Slides Rapid, downslope movement of earth’s materials Happens when a thin block of loose soil, rock, and debris separate from the bedrock (landslide) Can cause flooding Common on slopes that are water saturated Rock slides are triggered by earthquakes

Slumps When material in a landslide rotates and slides along a curved surface Occur in areas with thick soils and steep to moderate slopes Common after rains Leave crescent shaped scars

Avalanches Landslides that occur in mountainous areas with snow Usually occur on slopes of at least 35 degrees 10000 avalanches occur every year in west US alone Sun melts surface snow  refreezes over night loose snow accumulates  becomes heavy and slips off Snow refreezes into crystals  vibrations send the layer down slope

Rock Falls Occur at high elevations, in steep road cuts, and rocky shorelines Rock breaks and falls downward Produces a cone shaped pile of debris called talus Less likely to occur in humid regions

Mass movements and people Constructing heavy buildings and roads and poor maintenance of sewer systems can result in mass movements Venezuela 1999 experienced heavy rains which resulted in severe mudflows killing tens of thousands of people Can be avoided by not building structures on steep slopes Trenches can be dug to divert water