MASS WASTING: The removal of weathered rock and soil. More than 100x more destructive in U.S. than earthquakes and volcanoes combined!!!
Major Influences * Water - too much vs. too little * removal of vegetation (human-causes, forest fires, drought) * stream undercutting (changes the slope) * alternating freezing and thawing * earthquake vibrations * type of bedrock, direction of bedding or jointing
1st Rule of Geology: Rocks Fall Downhill
Rockfall
Demonstration of “Angle of Repose” – Usually about 30
Landslide Ex/ Gros Ventre River, Wyoming, was dammed by landslide in 1925. The dam burst 2 years later, wiping out the town of Kelly, Wyoming.
Landslide
Slump (Listric fault) Often initiated by over-saturation.
Slump
Slumping on Mars
Slump Major hazard along many coastlines
Mudflow Often about 30% water Can occur on slopes less than 5 Can be >100 m thick, and >100 km long
Mudflow (lahar) (Pinatubo, 1991)
Creep Typically 1-2 mm/yr, but can be as great as 10 cm/yr in cold or semi-arid regions
Creep
Creep
Underwater flows Can cover 100,000’s of square kilometers. Can flow over slopes of less than 1 at speeds of more than 100 km/hr. Ex/ Cable breaks at Grand Banks, Newfoundland, 1929.
Massive landslides in places like the Canary Islands could cause enormous tsunamis
Ex/ Puerto Rico Trench
Weathering/Mass Wasting – Responsible for the appearance of the land surface.
Stream Tributaries
Fractal nature of tributaries
Major Streams of the world
Major drainage basins of the world
Components of a Stream: Discharge Slope Velocity Sediment Load
Effect of urbanization on stream run-off
Stream Gradient
Stream Gradient Mostly erosion Erosion and deposition Mostly deposition
Dams: Many positive and negative aspects
Stream down-cutting works together with mass wasting
Differential erosion
Stream velocities fastest at the outside of a turn
Development of stream meanders and oxbow lakes
Floodplain features
Incised meander: San Juan River, Utah
Flooding – can carry MOST of the sediment of a stream Mississippi River, 1993