Soil and mass wasting
Most figures and tables contained here are from course text:
Understanding Earth Fourth Edition by Frank Press, Raymond Siever,
John Grotzinger, and Thomas H. Jordan
Soil
Soil is composed of:
•Regolith (rock debris)
•Air
•water
The layers of the soil are primarily developed by the process of
chemical weathering.
The type of soil that will develop in an area is therefore dependent
on the type of climate where the soil forms.
1
pedalfer
pedocal
New mine rals can be added to the soil from above by flood or wind
Top soil: organic rich layer
leached layer
chemical we athering removes vulnerable
minerals depending on climate
Zone of accumulation: minerals that are stable in the given will
precipitate here. Other unstable mine rals will still leach out.
Weathered parent rock: this materi al can decompose and float into
the soil. Burrowing animals or plant roots can further mix soil
layers.
Pedalfer
Soil will be tens of meters thick
Thick organic layer
Thick zone of accumulation
In this climate limestone
will be karsted (eroded
beneath the ground
2
Laterite
May be more than 100 meters
thick. Decay removes nearly all
organic material. The organic
layer may be gone. Only clay
will remain in the leeched layer.
All parent minerals are gone.
While forested the plants will
absorb nutrients faster than they
can be leeched away. Plant
roots also will also keep the soil
loose enough for moisture and
air to penetrate.
When converted to farm land by
burning away vegetation quickly
looses fertility and becomes clay
pan. This makes very poor farm
land.
Padocal
Thin layer of soil, may only be a
few meters thick. Thin or no
organic layer. This soil type is
richest in parent mate rial. Can be
made fe rtile with wat er. The zone
of accumulation will have caliche
Mass wasting
3
4
The angle of repose will depend on the grain shape
Surface tension will cause capillary w ater to adhere to grains
Capillary water c an increase cohesion of sand and improve its
internal strength. Complete saturation will cause the sand to loose
all internal strength due to loss of friction and buoyancy force
reducing the effective weight of the grains.
5
All flows and slides are caused when the down slope force exceeds
the strength or internal friction of the rock.
Flows in a flow there is a failure in the mate rial bulk internal
strength and the material will mix as it falls.
Slides are where the failure occurs in a layer (det achment zone)
and the material slides without mixing.
6
flow
flow
flow
7
slide
Creep occurs as a very slow flow of mate rial. This will affect more
areas than all other mass wasting.
fall
8
creep
Causes of slope failure
Addition of water
9
Removal of vegitation
Erosion or excavation can at the base of a slope will increase its
average slope and cause slope failure.
Construction or loading at the top of a slope also increases the
average slope which can cause slope failure.
Liquefaction
A loss of friction
triggered by an
earthquake.
Vibration will
cause water to
work its way
between grains
which will reduce
internal friction.
10
Lahar
A volcanic mud flow
11
slump
12
13
14