Mass movement
Mudflow
What is Mudflow?
• Mudflow is the movement of top-soil down
a gradient in the landscape and happens
both gradually and rapidly.
Description of Mudflow
Flows take place gradually, possibly faster at
one time in the year than another
Encouraged by wet winters mudflows
emerge from the base of a rotational slip
and slowly spread and pour over earlier,
lower slips and flows into the sea.
Mudflow can travel extremely fast at
more than 10ft/s.
How does it happen?
• It is often encouraged by heavy rain and
happens most often from October to
February when the wet conditions
lubricate the protective soil and wash
away bits of loose ground gradually. Flash
floods can often encourage rapid mudflow,
this is also known as a lanslide.
Conditions for mudflow
Materials involved:
• A mixture of mud and
water
•Soil and rock
Vegetation and human
factors:
•There are no human
factors
•Soil becomes saturated
Conditions needed:
•Heavy rainfall for long
period of time
•Both gravity and slope
angle play a part
•Slope angle must be
greater than 10°
Bowl-shaped hollow
marking start of flow
Easily
saturated top
soil
Input of
precipitation
increases
weight and
lubrication of
top soil
Downslope
movement of
saturated soil
lobe
Toe marks final
resting place
Angle of slope >10°
Landslides and Slumps
By James Morrison, Only James.
Type of Mass Movement – Landslides and Slumps
Concave
sliding
surface
Large sections of
rock and soil
break away and
move quickly
down-slope as a
unit
Key
Downward slumping of
heavy basalt rock
Earliest landslide
blocks are
hummocky
because of glacial
erosion and
deposition
Processes
A landslide is the movement of large
quantities of rock and/ or earth.
Landslides are a form of rotational sliding
which is when a mass of rock slumps
along a curved plane. This causes the
land to break away and move downhill as
a unit
This process is very fast.
Conditions
Material involved• Soft rock – Clay
• Hard rock – Sandstone
• Soft material such as clay overlies a harder
substance such as sandstone.
Weather conditions• Surface soil is saturated after prolonged heavy
rain which lubricates the rock
• Slopes are undercut because of river or sea
erosion
• Rock becomes weaker and unsupported.
Conditions Continued
Vegetation• Prevented by vegetation as the roots as
the roots bind the soil.
• Vegetation also protects the soil from
heavy rain
Movement• The movement is helped by gravity and
this process happens quickly
Slumping
This is defined as occasional,
rapid movements of large
quantities of soil and/or rock.
How much slope gives way?
Usually a whole section of a slope gives
way when a large amount of unsupported
solid rock and/or regolith begins to slip
plane.
Regolith – the general name given to the
end product of weathering
Movement
The Slump
block moves
downhill
slowly,
Gravity’s Role
• When the gravitational force acting on a slope exceeds
its resisting force, slope failure (mass wasting)
occurs. The resisting forces helping to maintain slope
stability include the slope material's strength and
cohesion, the amount of internal friction between grains,
and any external support of the slope. These factors
collectively define a slope's shear strength.
Gradient
•
Slope gradient is probably the major
cause of mass wasting. Generally
speaking, the steeper the slope, the less
stable it is. Therefore, steep slopes are
more likely to experience mass wasting
than gentle ones.
WE HAVE GRAFITIED YOUR
PRESENTATION!!!!!
LOL
PROCESS
• Definition
Soil creep is the result of repeated expansion
and contraction of particles of soil. Heavy rainfall
increases the volume of the soil, therefore,
weighs it down which makes the soil move
downhill under gravity!
Soil Creep is the slowest and least dramatic of
all down slope movements. Speed of less than
1mm/year.
Guide Planes!
Easily saturated
top soil!
CONDITIONS
• Materials involved:
Large sections of rock and soil.
• Weather Conditions
Rain helps lubrication of the rock.
CONDITIONS CONTINUED
• GRAVITY
The steeper the slope the higher the
gravitational force.
The steeper the slope the faster the
movement.
CONSEQUENCES
• Tilted trees, damaged walls, Cracked
roads
Rock fall
By Lorraine , Heather, Kirsten and
Kate
Processes
• Rock fall is the rapid, free-fall of rock
from a steep cliff face. Rock fragments
fall from the face of the cliff because of the
action due to gravity. This is made worse
by freeze-thaw action loosening the rock.
A scree slope of fallen rock is formed at
the bottom of the cliff.
Diagram
Free Face
Lines of
weakness
Rocks bounce
down rather than
roll
Scree
accumulates at
slope foot forming
heaps of sharp
debris
Conditions
• The ground is vertical and dry to help the
process of rock fall to take place. The material
that is involved is varying sizes of rock.
• Rock fall usually occurs in colder, wetter
climates due to freeze thaw action, one of the
main processes, works best at these climates
• Bare, hard rock is very vulnerable to rockfall water enters the joint, freezes and expands,
cracking the rock.
• It is common at high altitudes where there is
poor soil and less vegetation.
Mass movement
Rock fall
By Luke, Alexander, David and
Gary.
Bare rock, scree slopes and
freeze thaw weathering are the
three main factors in rock fall
mass movement.
The finer grained
scree (talus) fills
the small holes in
the rocks.
Freeze thaw weathering weakens joints and
bedding planes in the cliff. The rock that
falls off creates a scree slope. The scree
slope has an angle of repose which is
around 30 degrees.
Upper part
of scree
(talus) slope
Freeze thaw
Rockfall mass movement occurs in areas
where the temperature is low and
fluctuates around 0 degrees Celsius.
Gravity pulls
the rock off
the rock face
after it has
been
weakened
by freeze
thaw.
Some plants
holding the bottom
of the scree slope
together
After gravity has pulled the rock from the
rock face it falls down the scree slope, at
the bottom of the scree slope small plants
grow and hold the rocks together.