Science Starter • What is the difference between a PEDOCAL SOIL and a

PEDALFER SOIL? •  Pedocal soils form in drier areas that have grasses and brush

vegetation. Have a lot of calcite or calcium carbonate and are light gray-brown.

•  Pedalfer soils form in temperate areas with at least 63cm of rain a year. Large amounts of iron oxide and clays. Brown to red color.

MASS MOVEMENTS Chapter 5, Section 5.3

Looking  Back  

• Mechanical  and  Physical  Weathering  

• Soil  • Soil  Profiles/Types  

Looking  Ahead  

•  Tomorrow  we  will  start  Chapter  6  •  TURN  IN  YOUR  WORK  

Report  Cards  October  15  Test  Chapter  5  &  6  on  10/21  

This  means  that  we  will  NOT  have  review  but  there  will  be  chances  for  points  

Vocabulary  Quiz  Ch.  6    10/14  Notebook  Check  (TEST  GRADE)  10/8  STUDY  STUDY  STUDY  STUDY  

Today’s Plan

• Finish 5.2 Soil •  You should have your handwritten notes from my

absence, but feel free to add more (HINT HINT)

• Start 5.3, Mass Movements

Let’s Review •  List the four major components of soil:

•  Mineral Matter, organic matter (humus), water, and air.

• What climates are associated with pedalfers? •  Temperate climates with 63+ inches of rain a year.

• What climates are associated with pedocals? •  Drier, arid climates with less than 63 inches of rain a year.

• What climates are associated with laterites? •  Wet, humid, tropical climates.

• How can road construction affect the rate of soil erosion? •  Increases road runoff that increases sheet erosion, removes

vegetation that roots soil in place.

Introduction •  Earth’s surface consists of

slopes •  Some are steep, some are

gradual •  Slopes may appear stable,

but they are always changing.

•  Force of Gravity causes material to move downslope.

•  The transfer of rock and soil downslope due to gravity is called mass movement. •  Some so slow you can’t see

them •  Some are very sudden

Mass Movements Slow vs. Fast

Introduction • Combined actions of weathering and mass movement produce landforms!

• Once weathering weakens and breaks rock apart, mass movement moves the debris downslope. A stream then carries it away. •  Stream valleys like this are

the most common of Earth’s landforms.

Triggers of Mass Movements • Gravity is the force behind mass movements.

• Factors that commonly trigger mass movements: •  Saturation of surface

materials with water •  Over-steepening of slopes •  Removal of Vegetation •  Earthquakes

Water • Heavy rains and fast snowmelt can trigger mass movements. •  Hurricane Mitch caused

devastating mudflows. • Pores in sediment are filled with water, and the particles slide past one another more easily. •  Add enough water to have

sand STICK but too much and the sand oozes.

•  Clay becomes slick when wet

Oversteepened Slopes •  Loose soil particles can

maintain a relatively stable slope up to a certain angle. •  25-40 degrees depending on

size and shape •  Called Angle of Repose

•  If steepness of slope exceeds this, the slope is said to be oversteepened. •  Mass Movements more likely •  Stream undercuts valley wall,

waves on a cliff base, building roads and buildings on a slope.

Angle of Repose

Oversteepening

Removal of Vegetation • Plants make slopes more

stable because their roots hold soil and regolith together and in place.

• Plants are removed •  Fires •  Logging (Human Activities)

•  Loss of stabilization results in mass movements

• Menton, France •  Replaced olive trees (deep

roots) with trees with shallow roots. Landslide killed 11 people.

Earthquakes • Most dramatic trigger of mass movements.

• Earthquake and its aftershocks can dislodge big amounts of rock and unconsolidated material. • Mass movements do

more damage than earthquakes do in these cases

TYPES OF MASS MOVEMENTS

Introduction • Geologists classify mass movements based on:

•  Kind of material that moves •  How the material moves •  Speed of movement

•  Five basic types: •  Rockfalls •  Slides •  Slumps •  Flows •  Creep

Rockfall • Rock or rock fragments fall freely through the air.

• Common on slopes too steep for loose material to stay on surface.

• Result from mechanical weathering of rock caused by freeze-thaw cycles or plant roots

• Sometimes trigger other mass movements.

Rockfall

Slides •  In a slide, a block of material moves suddenly along a flat, inclined surface. •  If includes segments of

bedrock: Rockslide •  Occur in high mountain

areas •  Among fastest mass

movements •  Speeds of over 200km/hr

• Can be triggered by rain or melting snow.

Slides

Slumps • A slump is the downward

movement of a block of material along a CURVED SURFACE.

• Material does not travel fast or far.

• Upper surface tilts backwards sometimes.

•  Leaves crescent-shaped cliff just above the slump.

• Common on oversteepened slopes where there is a lot of clay.

Slumps

Flows •  Mass movements of material

containing large amounts of water. •  Moves downslope as a thick

fluid. •  Mudflows: Move quickly

•  Common in semi-arid regions •  Not a lot of plants, floods

canyons •  Moves large boulders and trees

with it, consistency of wet concrete

•  Earthflows •  Move slowly (1mm-several m a

day) •  Continues for years •  Occur on hillsides in wet regions

Creep • Slowest type of mass

movement. •  Travels a few mm or cm a

year • Alternating between

freezing and thawing •  Freezing expands water, so

the soil lifts at right angles and then deposits lower when they thaw.

• Cannot observe creep happening because it is so slow. •  Can see effects of it though.

Creep Examples

MASS MOVEMENT CHART Rock (Large) Debris (Middle) Earth (Fine)

Fall Rockfall Debrisfall N/A Slide Rockslide Debris Slide Earth Slide Slump Rock Slump Debris Slump Earth Slump Flow N/A Debris Flow Earthflow/Mudflow Creep - - - Avalanche Rock Avalanche Debris Avalanche N/A

Avalanche: Large amount of Rock, Earth, or Snow that falls on a CUSHION OF AIR. *Creep is generally called ‘creep’ regardless of material size.

VIDEOS

Videos

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Let’s Review • What are mass movements classified by?

•  Kind of material that moves, how fast it moves, and how fast it moves.

• What are the main reasons mass movements happen? •  Oversteepening of slopes, removal of vegetation, saturation of soil,

Earthquakes.

• What is the main influence on mass movements? •  Gravity

• What is the slowest mass movement? The fastest? •  Creep = Slowest, Slides = Fastest