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Chp 5 weathering


Matthew Lewis

on 1 December 2010

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Transcript of Chp 5 weathering

Weathering, Soil
Mass Movements Weathering There are two categories of Weathering
Chemical Mechanical Weathering occurs when PHYSICAL forces
break down rock into smaller pieces Mechanical weathering can occur in
lots of different ways but it primarily
occurs through three physical processes. 1. Frost Wedging- When water works it's way into the cracks of rocks and freezes it expands and makes the crack even larger 2. Unloading -
a. Uplift or Erosion of Rock exposes underlying rock
b. The pressure on the underlying rock is reduced
c. Reduced pressure causes the rock to expand at different rates causing exfoliation (breaking of rock off in sheets) 3. Biological Activity - Living organisms break down rock by
a. Roots penetrating cracks in rocks
b. animals burrowing into rock Chemical Weathering occurs when compounds
dissolved in water chemically react with rocks
This typically produces some clays Rates of Weathering are affected by: Mechanical Weathering increases the speed of Chemical Weathering
- Mechanical increases the surface area of the rock Rock Characteristics can change the speed of weathering
Softer rocks weather faster
Brittle rocks weather faster
Rocks with a higher chemical reactivity weather faster Climate can affect the speed of weathering
Wetter climates have greater rates of chemical weathering
Temperate climates experience greater rates of mechanical weathering When Rock is broken down into smaller pieces Broken down pieces of rock are called:
Regolith Soil - is the part of regolith that supports
plant growth Soil has 4 main components:
1. broken down rock and mineral matter (majority of soil)
2. decaying organic matter (humus)
3. water
4. air Soil is classified by the % of sand,
clay and silt it contains Soil Forms at different rates
around the world due to specific factors 1. Parent material - the source of
rock and mineral matter for the soil 2. Time - The more time the soil is allowed
to develop the deeper and thicker it will be 3. Climate - Variations in temperature and
precipitation affect the depth and quality of soil 4. Organisms - Plants, animals and bacteria
contribute to different soil types around the world
plants contribute the bulk of the organic matter
animals mix soil due to burrowing and digging
bacteria convert compound into nutrients making more productive soils
i.e. the nitrogen cycle 5. Slope - Steeper slopes don't have well
developed soils due to higher rates of erosion
Slopes that face the sun have better developed soils Mass Movements - The transfer of rock or soil
downhill due to gravity Causes of Mass Movements include:
1. Water - increasing the water content of the ground
can trigger a mass movement 2. Over steepened Slopes - Increasing the angle
of a slope can trigger mass movements 3. Removal of Vegetation - Decreasing the amount
of roots and root systems can cause mass movements 4. Earthquakes - sudden movements of the
earth can disrupt the stability of the land Types of Mass Movements:
Mass Movements are classified by -
a. The type of material
b. The type of movement
c. The speed of movement 1. Rockfalls - any time rock or rock fragments
fall freely through the air
- often caused by ice wedging or root action 2. Slides- When a block of material moves
suddenly along a flat, inclined surface
-Slides can travel over 100 m.p.h.
- often caused by rain or melting snow 3. Slumps - a downward movement of a material
along a curved surface
- do not travel very fast or far
- common on over steepened slopes 4. Flows - movements of earth with a high water content
Classified into mudflows and earthflows
- mudflows move faster than earthflows 5. Creep- Slowest type of movement
caused by the freeze thaw cycle on soil.
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