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?1.A.sediments moved by waves2.B.tectonic uplift3.C.sediments carried by rivers4.D.dropping sea levels

Mass Movements at Earth’s Surface

Pg. 75

The downslope movement of loose sediments and weathered rock resulting from gravity

Weathering erosion mass movements Climate controlled All occur on slopes

Mass movements

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

Influencing variables

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

Water and mass movements

Classified as:◦ Creeps◦ Flows◦ Slides◦ Falls◦ Slumps◦ Avalanches

Types of mass movements

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

permafrost slides downhill

Creeps

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)

Flows

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

Slides

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

Slumps

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

Avalanches

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

Rock Falls

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

Mass movements and people