MASS WASTING

SURFICIAL PROCESSES Erosion, Transportation, Deposition on the Earth’s Surface Landscapes created and destroyed Involves atmosphere, water, gravity Agents: –Mass wasting (gravity), Running water (streams), glaciers (ice), wind, water waves, ground water

MASS WASTING Masses of debris (mud, sand, gravel) or bedrock moving downhill Landslides and slower movements Driven by GRAVITY

Classification of Mass Wasting RATE of MOVEMENT –Extremely slow (~1mm/year) to very rapid (>100 km/hour) MATERIAL –Bedrock –Debris- (“soil”, sediment)

Classification of Mass Wasting TYPE OF MOVEMENT –Flow –Slide Translational slide Rotational slide (Slump) –Fall

Controlling Factors Slope angle- gentle vs steep Local relief- low vs high Thickness of debris over bedrock- slight vs great Planes of weakness ( in bedrock) –bedding planes; foliation; joints –planes at right angle to slope vs parallel to slope most dangerous

ANGLE OF REPOSE

Controlling Factors Climatic controls –Ice- above freezing vs freeze & thaw –Water in soil- film around grain vs saturation –Precipitation- frequent but light vs periods of drought and heavy rainfall –Vegetation- heavily vegetated vs light or no vegetation Gravity –Shear force- parallel to slope, block’s ability to move –Normal force- perpendicular to slope, block’s ability to stay in place due to friction –Shear strength- resistance to movement or deformation of debris

The Effect of Slope & Gravity G=gravity S=shear F=friction N=normal S GN F

Controlling Factors Water –adds weight –increased pore pressure in saturated debris decreases shear strength –surface tension in unsaturated debris increases shear strength Triggering Mechanisms –Overloading –Undercutting –Earthquakes

Common types of mass wasting CREEP –gentle slopes –vegetation slows movement –very slow flow (< 1 cm/year) facilitated by water in soil or by freeze-thaw in colder climates –Indicators of creep ‘pistol butt’ trees leaning tombstones, walls, posts

Solifluction & Permafrost Solifluction: –Flow of water saturated debris over impermeable material Permafrost: –Ground that remains frozen for many years

Common types of mass wasting DEBRIS FLOW –Motion taking place throughout moving mass –Includes Earthflow Mudflow Debris Avalanche

Earthflow –Primarily flow of debris –may involve rotational sliding –Scarp above –Hummocky surface in lower part –May be slow or fast –Solifluction role of Permafrost in cold climates

Mudflow –Flow of watery debris –Occurs where lack of vegetation: Dry climates Volcanoes After forest fires

Debris Avalanche Very rapid, turbulent flow of debris –mud-boulders >150 km/hr Triggered by –volcanic eruptions- Mt. St. Helens 1980; Nevado del Ruiz 1985 –intense rainstorms- Venezuela 1999 –earthquakes- Japan 2000

Rockfalls and Rockslides Rockfall –Bedrock breaking loose on cliffs –Talus at base of cliffs Rockslide –Bedrock involved –Sliding along planes of weakness parallel to slope Bedding planes; foliation planes; fractures in rock (joints)

Debris Slides and Debris Falls Debris fall –Free-falling mass of debris Debris slide –Debris moving along a well-defined surface

Preventing Landslides Preventing mass wasting of debris Preventing rockfalls and rockslides on highways