Mass Wasting Chapter 9

1
Mass Wasting Chapter 9
2
Chapter 9 Objectives

• 1. Types of mass wasting and speed of movement
• 2. Effects of mass wasting
• 3. Potential causes and what triggers the
  release of debris

3
Mass Wasting

• Mass Wasting the downslope movement of rock,
  regolith, and soil under the direct influence of
  gravity.
• The Role of Mass Wasting
• Its the step that follows weathering.
• Weakens rock
• Mass wasting
• Stream transportation
• Ends up in the Sea
• Slopes change through time
• Earth is heading toward flat land. Thank
  goodness for Plate Tectonics.

4
Controls and Trigger

• Gravity is the controlling force of mass wasting.
• Its a series of processes that begin to weaken
  the rock.
• The pull of gravity
• Passes the threshold of stability
• TRIGGER last of the problem
• Saturation of material w/ water
• Oversteepening slopes
• Removal of vegetation
• earthquakes

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Triggers

• Role of Water
• Cohesion holds water
• Saturation - lets it slide(when saturated)lowers
  internal resistance
• Clay becomes slick
• Oversteepened Slopes - Angle of Repose 25 to 40
  degrees
• Streams undercutting a valley
• Waves action
• Removal of Vegetation
• Root system, cuts impact of raindrops
• Removed by fire, people(timber,development)
• Fireerosion, bake the ground(slows penetration)

6
More Triggers

• Earthquakes as Triggers movement
• Earthquakes and aftershock
• Liquification water saturated soils
• Landslides w/o Triggers
• Gradual weakening over time
• Other materials that fall on their own

7
Classification of Mass Wasting Processes

• Type of Material
• Rock, mud, regolith, other debris can all be
  part of the mass
• Type of Motion the way the material moves
• http//www.indiana.edu/geol116/week10/wk10.htm
• Fall
• Slide
• Slump
• Flow
• Rate of Movement
• Can move at high rates of speed (160 mph) and
  everything down to 1 centimeter/year
• Some can move fast enough to produce shock and
  wind waves

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Types of Mass Wasting

• Slump
• Downward movement as a unit along curved surface
• Usually in a thick cohesive material
• Water percolates downward
• Causes can be oversteepening
• Anchor material is removed at the base
• Too much weight at the top
• Undercut by a river
• Rockslide
• Large blocks of bedrock break loose
• Usually large amounts of unconsolidated
  debris(rock slide)
• Faster and most destructed
• Can be trigged by snow and rain (spring)

9
Types of Mass Wasting

• Debris Flow
• Involves soil and regolith w/ lots of water
• Mudflows characteristic of semiarid regions
• Lahars mostly volcanic material and water(like
  wet cement)
• Triggered by rapid snow melt or heavy rain
• Common on stratovolcanos
• Earthflow
• Common of hillsides in humid areas and heavy
  precip.
• Most materials are clay and silt and very
  viscous(slower)
• They can last for days to years and move as
  little as a few mm/yr

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Types of Mass Wasting

• Slow Movements cover a wider area than other
  mass wasting
• Creep gradual movement. Mainly due to freezing
  and thawing or wetting and drying gravity.
• Solification saturated soil(soggy)
• Can be promoted by layer of hardpan or permafrost
• Solification occurs in the active layer flows
  easily
• Submarine Landslides same as above ground
• Hawaii along continental slopes due to active
  volcanoes
• Many are larger than anything seen on land
• Biggest can be around Seamounts
• These landslides can have an impact on continents
  by growing the margins of the continents.

11
Ways to Avoid Disaster