Science Starter · • The transfer of rock and soil downslope due to gravity is ... • Combined...
Transcript of Science Starter · • The transfer of rock and soil downslope due to gravity is ... • Combined...
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.
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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