2Mass MovementsMass Movement - The transfer of rock and soil downslope due to gravity
3Triggers of Mass Movements Gravity is the force behind mass movements.Several factors make slopes more susceptible to the pull of gravity.
4Factors that Trigger Mass Movements Saturation of surface materials with waterOver steepening of slopesRemoval of vegetationEarthquakes
5Water as a Trigger for Mass Movement Heavy rains and rapid snowmelt can saturate surface materials and trigger a mass movement.Example – 1998 Hurricane Mitch produced torrential rains, causing devastating mudflows.
7Water as a Trigger for Mass Movement When pores in sediment become filled with water, the particles slide past each other more easily.
8Water as a Trigger for Mass Movement When sand grains are slightly moist they will stick together, even on a relatively steep slope.If you add enough water however, the pores between the grains will fill with water and the sand-water-mixture will ooze downhill
9Over-steepened Slopes Loose soil particles can maintain a relatively stable slope up to a certain angle.The slope angle ranges between 25 and 40 degrees, depending on the size and shape of the particles.
10Over-steepened Slopes An over-steepened slope is a slope which exceeds the stable angle for the type of material in the location.
11Over-steepened Slopes An over-steepened slope can result when a stream undercuts a valley wall or waves pound against the base of a cliff.People can create over-steepened slopes during excavation for roads or other structures
12Removal of VegetationPlants make slopes more stable because their root systems bind soil and regolith together.When plants are removed by forest fires or human activities such as logging or farming, the likelihood of mass movement increases.
13Removal of VegetationIn Menton France, farmers replaced olive trees, which have deep roots, with carnations, a more profitable but shallow rooted crop.Planting the carnations made the slopes less stable.A landslide on one of the slopes killed 11 people
14EarthquakesEarthquakes are one of the most dramatic triggers of mass movements.An earthquake and its aftershocks can dislodge enormous amounts of rock and soil.The landslide in thepicture was triggered byan earthquake
15Types of Mass Movements Geologists classify mass movements based on the kind of material that moves, how it moves, and the speed of the movement.There are 5 main types of mass movementRockfalls, slides, slumps, flows, and creep
16RockfallsA rockfall occurs when rocks or rock fragments fall freely through the air.This type of mass movement is common on slopes that are too steep for loose material to remain on the surface.
17RockfallsMany rockfalls result from the mechanical weathering of rock caused by freeze-thaw cycles or plant roots.Rockfalls sometimes trigger other mass movements.
18SlidesIn a slide, a block of material moves suddenly along a flat, inclined surface.Slides that include segments of bedrock are called rockslides.
19Click for Rockslide Video RockslidesRockslides are among the fastest mass movements, reaching speeds of over 200 km per hour.Click for Rockslide Video
20SlumpsA slump is the downward movement of a block of material along a curved surface.The material in a slump usually does not travel very fast or very far.As the block moves, its upper surface sometimes tilts backward.
21SlumpsSlumps leave a crescent-shaped cliff just above the slump, which you can see in the picture.They are common on oversteepened slopes where the soil contains thick accumulations of clay.
22FlowsFlows are mass movements of material containing a large amount of water, which move downslope as a thick fluid.Flows that move quickly, called mudflows, are common in semiarid mountainous regions, such as parts of southern California.
23MudflowsIn these regions, protective vegetation is sparse. A heavy downpour or rapid snowmelt can flood canyons with a mixture of soil, rock, and water.The mixture may have the consistency of wet concrete.
24MudflowsIt follows the contours of the canyon, taking large boulders and trees along with it.As you see in the photo, mudflows in populated areas are very dangerous and destructive.Click photo for mudflow video
25EarthflowsEarthflows are flows that move relatively slowly—from about a millimeter per day to several meters per day.Their movement may continue for years.Earthflows occur most often on hillsides in wet regions.
26EarthflowsWhen water saturates the soil on a hillside, the material breaks away, forming a tongue-shaped mass like the one shown
27CreepThe slowest type of mass movement is creep, which usually only travels a few millimeters or centimeters per year.One factor that contributes to creep is alternating between freezing and thawing
28Creep Because creep is so slow, you cannot observe it directly. You can recognize the effects of creep easily however – creep causes structures that were once vertical to tilt downhill.
33*Creep *Mudflow *Earthflow *Rockslide Earth & Space ScienceToday’s ScheduleSeptember 16, 2014HomeworkThe Ever-Changing Surface of the Earth - Part 1: Erosion WKS5 min-Bell ringer30 min- Mass Wasting Notes and Videos25 min Erosion & Deposition definitions (cause & effect), examples matching review10 Exit – HASHTAG VOTESEssential QuestionWhat are different types of deposition?Vocabulary*Creep *Mudflow *Earthflow *Rockslide*LandslideToday we will…….ES Demonstrate the possible effects of atmospheric changes brought on by things such as acid rain,ES.1.26ES Differentiate among the processes of weathering, erosion, transportation of materials, deposition, and soil formation.ES.1.27ES Illustrate the various processes that are involved in the rock cycle and discuss how the total amount of material stays the same through formation, weathering, sedimentation, and reformation.