Part 3 Mass Movement

Chapter 5.3 : 

Chapter 5.3 Mass Movements

Stability of Soils : 

Stability of Soils Gravity and other forces are always at work on soil, changing its composition, shape, and position The transfer of rock and soil downslope due to gravity is called mass movement Mass movement can be very slow or very fast

Causes of Mass Movement : 

Causes of Mass Movement Gravity is the force behind mass movements Mass movements take place on slopes They are caused by Water Oversteepened slopes Removal of vegetation Earthquakes

Causes of Mass Movement : 

Causes of Mass Movement Water Saturated areas are susceptible to moving because pores in the soil fill with water allowing particles to slide past each other Clay becomes very slick when wet allowing sliding

Causes of Mass Movement : 

Causes of Mass Movement Oversteepened slopes Depending on the size of the particles, loose soil particles can maintain relatively stable slopes of 25 – 40 degrees Steeper slopes make mass movements more likely Oversteepened slopes can be a result of A stream undercutting a valley wall Waves pounding against the base of a cliff People (construction, etc)

Causes of Mass Movement : 

Causes of Mass Movement Removal of vegetation Plant root systems make slopes more stable When the plants are gone, the root system binding soil and regolith together is gone The soil is now much more susceptible to movement Causes of vegetation removal include Fires Human activity such as construction, logging, and farming

Causes of Mass Movement : 

Causes of Mass Movement Earthquakes One of the most dramatic causes Can move enormous amounts of rock and unconsolidated materials

Types of Mass Movement : 

Types of Mass Movement Geologists classify mass movements based on the kind of material that move, how it moves and the speed of the movement

Types of Mass Movement : 

Types of Mass Movement There are five main types of mass movement Rockfalls Slides Slumps Flows Creep

Types of Mass Movement : 

Types of Mass Movement A rockfall occurs when rocks or rock fragments fall freely through the air Common on slopes that are too steep for loose material to remain on the surface Many are a result of mechanical weathering such as frost wedging or plant roots

Types of Mass Movement : 

Types of Mass Movement Slides A block of material moves suddenly along a flat, inclined surface If the slide includes segments of bedrock, then it is called a rockslide Rockslides are among the fastest mass movements often reaching speeds of over 124 miles per hour Are usually caused by rain or melting snow Avalanches are a type of slide

Types of Mass Movement : 

Types of Mass Movement Rockslides http://www.youtube.com/watch?v=T7r39-OdR7c&NR=1 http://www.youtube.com/watch?v=CILRdjO6vwE

Types of Mass Movement : 

Types of Mass Movement Slump The downward movement of a block of material along a curved surface Do not move very far or very fast Upper surface sometimes tilts backward Leaves a crescent shaped cliff just above the slump Common where the slope is oversteepened and there is a lot of clay

Types of Mass Movement : 

Types of Mass Movement Flows Mass movements of material containing a large amount of water, which moves downslope as a thick fluid Two main types Mudflows Earthflows

Types of Mass Movements : 

Types of Mass Movements Mudflows Common in semiarid mountainous regions such as parts of southern California The mixture may have the consistency of wet concrete Follows the contour of the canyon taking boulders and trees along with it

Types of Mass Movements : 

Types of Mass Movements Mudflow http://www.youtube.com/watch?v=51C7vEAVbxk&feature=related http://www.youtube.com/watch?v=VMJiibdVYjE&feature=related

Types of Mass Movement : 

Types of Mass Movement

Types of Mass Movement : 

Types of Mass Movement Earthflows Flows that move relatively slowly, from about a millimeter per day to several meters per day Movement may continue for years Occurs on hillsides in wet regions Material breaks away forming a tongue shaped mass Can range in size from a few meters long to over 1000 meters long

Types of Mass Movement : 

Types of Mass Movement Creep The slowest type of mass movement (just a few millimeters or centimeters per year) Repeated expansion and contraction of the soil on a slope results in the gradual downhill movement of the soil Alternations between freezing and thawing of the soil can contribute to this