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Soil and mass movements

Soil and mass movements. By Sturdivant. SOIL. We learned about the two types of weathering on rocks – mechanical and chemical After rocks are weathered and broken down, they leave behind finer grained materials

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Soil and mass movements

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  1. Soil and mass movements By Sturdivant

  2. SOIL • We learned about the two types of weathering on rocks – mechanical and chemical • After rocks are weathered and broken down, they leave behind finer grained materials • This layer of broken up rocks and minerals that covers almost all of Earth’s surface is the REGOLITH • The part of the REGOLITH where plants can grow is SOIL

  3. LOOK AT THAT THERE FIIIIIIIIIIINE SOIL

  4. Composition of soil • Soil has 4 major components • BROKEN DOWN MINERALS (OR ROCK) • ORGANIC MATTER (called HUMUS) • WATER • AIR

  5. soilS of the world • Depending on your location, soils vary greatly by composition • In bog areas – almost all organic matter, very acidic • In deserts – very little organic matter, mostly minerals and air

  6. SOIL and plant growth • Soil can contain every necessary component for plant growth • Minerals/rocks give a surface to attach to • Organic matter provides nutrients for photosynthesis • Water and air within the pore spaces of soil is essential for photosynthesis

  7. Identifying soils by particle size • When studying rocks, we looked at grain sizes (especially with sedimentary rocks) • We found grain sizes range from large (sand/gravel) down to smaller (silts) down to too small to see (clays) • Soils rich in clay don’t allow water to flow, whereas soils too rich in sand (the desert) allow water to flow right through • For ideal plant growth – we want a combination of soil textures, called LOAM

  8. Soil texture diagram • We analyze soils based on percentages of each different texture (sand, silt, and clay)

  9. Soil formation • What type of soil develops in an area depends on parent material, time, climate, organisms, and slope • Parent material – determines mineral/rock make-up of soil • Time – soil thickens over time • Climate – greatest factor, determines whether soil is mechanically or chemically weathered • Organisms – the vegetation and animal life in an area determine the organic qualities of soil • Slope – slope affects how much water/sunlight/erosion the soil gets

  10. Soil erosion • Erosion is the movement of soil from one place to another • Water – strongest erosive force, picks up soil and takes it somewhere else • Streams transport soil (which we’ve called sediment so far) and deposits it when the water slows • Wind and other agents also contribute to soil erosion

  11. Erosion rates • Past erosion rates were slower than modern erosion rates – this is because humans have removed much of the planet’s natural vegetation, which held the soil in place • By looking at how much sediment is flowing in a river, we get an idea of how much erosion is taking place in some region • Areas with no vegetation erode easily • QUESTION – Why would a steep hill erode more easily than a flat surface?

  12. Sediment deposition • When water loses velocity, it may no longer have the power to move sediment, and the sediment drops. We call this DEPOSITION • We notice excessive deposition as a problem with HYDROELECTRIC POWER

  13. Mass movements • Mass Movement – transfer of rock/soil downhill due to gravity • Weathering breaks rock apart, mass movements moves the debris downhill • This process forms most landforms

  14. Causes of mass movements • All mass movements occur because of gravity • Some factors can trigger mass movements – saturation with water, oversteepening of slopes, removal of vegetation, and earthquakes

  15. 4 Triggers of mass movements • Saturation – when soil begins to fill its air content with water, the grains can slip over each other. This allows it to slide downhill (mudflows) • Oversteepened Slopes – angles steeper than about 40 degrees cannot hold soil in place. This occurs in steep stream valleys, excavating • Removal of Vegetation – Plants hold soil in place, stabilize slopes. When plants are clear cut, due to fire/insects/etc, the slopes destabilize • Earthquakes – the force of an earthquake can dislodge rock and trigger dramatic mass movements

  16. Types of mass movements • Mass movements differ by type of material that moves, howthe material moves, and speed of movement • We will look at rockfalls, rockslides, slumps, mudflows, earthflows, and creeps (not that kind)

  17. Rockfalls • Rocks or fragments of rocks freefall

  18. Rockslides • One of the fastest mass movements, up to 200 km/hr

  19. slump • Slow sliding of oversteepened slope

  20. mudflow • Usually caused by floods in semiarid regions

  21. Earthflow and creeps • Earthflows and creeps are the slowest mass movements, so there aren’t good videos • Earthflows move a few inches to several feet a day • These slow slides occur on hills of wet regions • Creep occurs in regions with alternating freezing and thawing of soil • This process creeps soil along downhill, sometimes only a few millimeters a year

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