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Slope Movement
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  • 1. SLOPE CURRENTLY ACTIVE LANDSLIDE IN PAKISTAN
    • Lots of angular rock fragments
    • lying at foot of slope-talus.
    EVIDENCES: (2) Bare rock exposed to weathering. (3) Absence of vegetation.
  • 2. WHY ARE SLOPES IMPORTANT? Wyllie Vineyard, California Rock Climbing skiing Hang gliding Mountain Biking Rice terrace in Philippines
  • 3. MAJOR SLOPE PROCESSES (I) ROCK FALLS:
    • Rapid movement occurs on steep slopes.
    • Rock fragments/slabs of rock suddenly detached and fall at base of slope.
    • This is due to gradual processes such as freeze-thaw/earthquakes.
    • The angular debris collects at base of slope to form scree / talus.
  • 4. MAJOR SLOPE PROCESSES (II) LANDSLIDE :
    • Movement takes place along a flat/planar slide plane.
    • It commonly occur along bedding planes when underlying bed is impermeable,lead to a high moisture content that lubricate the slide surface.
    • Landslides are very rapid and cause damage & loss of life.
  • 5.
    • (III) ROTATIONAL SLIP/LANDSLIP.
    • It differs from landslide in that the slide
    • plane is concave in shape.
    • It causes rotational movement.
    • Common in weak rock such as clay.
    • Most common in UK.
    MAJOR SLOPE PROCESSES head scarp Curved Slide plane foot toe
  • 6.
    • (IV) MUDFLOW
    • When soil/weak rock such as clay or volcanic ash become saturated, it begin to flow downhill.
    • This flow can be slow but mostly rapid depend on water content.
    • Mudflows from volcanic summits combine with ash to form deadly flows called lahar.
    • Lahar caused loss of life & damage property e.g. eruptions of Mt. Pinatubo, Philippines (1991).
    MAJOR SLOPE PROCESSES
  • 7.
    • Solifuction is the slow downhill flow of saturated soil.
    • Common process in periglacial environments.
    • Seasonal thawing of uppermost layer provide enough water to enable flow to occur.
    • Gelifluction refers to solifuction takes place on top of frozen ground.
    MAJOR SLOPE PROCESSES (V) SOLIFUCTION
  • 8.
    • (VI) SOIL CREEP
    • It involves a heavy process where individual particles rise & fall respond to expansion & contraction.
    • This is due to wetting & drying /freeze thaw action.
    • 3. A very slow process, particularly on clay slope.
    • 4. Terracettes on grassy slopes result from soil creep.
    MAJOR SLOPE PROCESSES
  • 9. FACTORS AFFECT SLOPE PROCESSES
    • Physical
    • (i) Rock type : Tougher rock such as igneous & metamorphic rocks
    • (steep) while sand and gravel (gentle slope).
    • (ii) Geological structure : Rock slabs detached along joints and bedding
    • planes promote rockfalls & landslides.
    • (iii) Permeable & porosity : An impermeable rock will be liable to surface water flow, deep
    • gullies may be form.
    • (iv) Climate : affect weathering type; physical weathering such as frost shattering
    • produce angular, bare rock surface and chemical weathering tend to disolve
    • and produce fine clay producing more rounded slopes.
    • (v) Tectonic activity: Earthquakes may also trigger slope failure.
  • 10.
    • ( B) Human factors:
    • Vegetation : If a slope is forested/covered with bushes & grass it is likely to be active. Vegetation help to protect slope from direct effects of rainfall & help bind rock and soil particles.
    • (ii) Basal excavation : it takes place in the form of river undercutting of a slope/sea cutting a notch in a cliffline. Human activity such as road construction have same effect. This lead to a steep slope, make it unstable.
    • (iii) Human activities : people alter slopes by mining & quarrying, road construction, housing estates and terracing land for farming. Deforestation can cause soil erosion.
    FACTORS AFFECT SLOPE PROCESSES
  • 11.
    • Several ways to make a slope more stable:
    • Plant vegetation to bind soil together & intercept rainfall.
    • Improve drainage to prevent slope saturated & to stop lines of weakness for e.g. bedding panes becoming lubricated.
    • Use wire nets & metal stakes to hold a slope together
    • Reduce gradient by adding material to the base of a slope.
    Stable slopes.