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These slide-shows are all on the blog if you wish
to copy any notes from them we will not be
stopping in class for you to do this
Mass movements is the term used to define the
different ways that weathered material can alter
the scenery.
The two forces acting on the material are-
Friction, which stops them sliding downhill too
fast.
Gravity, which pulls the particles down.
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Four main factors that influence mass movements-

1. How much water is involved in the action.
2. How much of an angle is needed on the slope.
3. How quickly the movement happens.
4. The amount of vegetation cover is also important
   in some types of movement.

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ROCKFALLS- read pages 1-4 and answer the
questions on page 4 Then read higher notes on
pages 78-86 Answer questions 1, 2bcd,3,5,6, on
page 139-140 use pages 72-86 to help you
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1. What angles are rockfalls most likely to
happen at?
2. Which of the two forces is the dominant one?
3. Which secondary processes are very important
too?
4. So what condition ought the rock face to be in
if a rockfall is to happen?
Four more questions after the answers to these!
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2. Gravity is more effective here than friction.
1. The best angle is between 70 and 90 degrees
from horizontal.
3. Freeze-thaw and frost-shattering are important
processes.
4. The face should be well- jointed or cracked
for rockfalls to happen.
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5. What angle does scree usually initially settle
at?
6. Explain what is meant by size- sorting and
why it happens.
8. What is the usual angle of an inactive scree
slope?
7. Why will weathering of the rock face cease in
time?
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6. Particles travel down the slope depending on
their weight and density. Lighter ones finish
nearer to the face, heavier ones travel further,
often moved by rolling over smaller ones.
5. Scree settles between 34 and 40 degrees,
usually.
8. The inactive slope consolidates at 37 degrees
where it usually grasses over.
7. If scree covers the rock face, freeze-thaw
cannot act and weathering stops.
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Climbers call these types of screes stone
chutes.
Their technical name is talus slope.
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A rockfall and talus slope in Arizona
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1.What two roles does heavy rainfall play?
2. Where can the slip plane/ a.k.a. glide plane
be found?
3.How does the result of this movement look
different to a rockfall?
4.Slumps- special kinds of slides- have a
different kind of slip plane- in what way?
5. What is the difference in the motion of the
material in slumps?
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1. It lubricates the slip plane and makes the
material heavier and likely to move.
2. The slip plane is below the surface.
3. There are bald spots visible on the slip
plane and there is no sorting. Material moves as
a oner.
4. A shear is curved, steeper at the top than the
bottom.
5. Slumped ground has rotated whereas slides
travel down in a straight line.
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The Quiraing in Skye shows spectacular rotational
slumping.
Spot the tourists?
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1. How gentle a slope can mudflows start on?
2.What angles are more likely?
3. What shape does the material stop in?
5.How do you describe the speed of a mudflow?
4. Describe the two factors that help create
mudflows.
6. What condition does the surface below the flow
have to have?
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1. They can start on a slope as gentle as 5 or 6
degrees.
3. The material stops in a lobe/fan shape.
2. Angles over 10 degrees are more common.
5. Mudflows happen very quickly indeed!
4. They need high rainfall and little vegetation
cover.
6. The lower layers need to be impermeable to
water.
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This mudflow happened several years before the
photo was taken- the scars are still very visible!
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A mudflow in Central America, October 2005
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1.What angle of slope does this require?
3.Why do particles not travel back at the same
angle as they heave?
2. Define the term heave.
4.Describe how biological activity may enhance
the activity.
5. Describe what terracettes look like.
6.Describe four results of soil creep.
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1. Angles over as little as 5o but gt6 degrees are
most susceptable.
3. Gravity (and the effects of contraction) are
the dominant forces here.
2. Heave is the upward motion of particles.
4. Plant roots and burrowing animals help the
soil to move.
5. Terracettes are small-scale ridges parallel to
the slope.
6. See the next slide for the answer.
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6. a). Fence and telegraph posts lean down-slope
as their supports are undermined by the creep. (
note these are the same effect) b). Soil piles up
behind walls, creating deeper pockets, pushing
walls over in time. ( note there are two effects
here!) c). Roads may crack open parallel to the
slope angle, and will need frequent repair. d).
Terracettes spoil the smooth surface of fields,
and affect land use.
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Terracettes can be seen to the right of the river
valley.