A landslide occurs when the stability of a slope changes, making it unstable. This can be caused by natural factors like heavy rain, earthquakes, or erosion, as well as human activities like construction, deforestation, and blasting. Sand boils occur when water under pressure wells up through sand, looking like it is boiling. They can contribute to levee or dike failure during floods by creating pipes through the embankment that remove soil particles and weaken the structure. The most effective way to stop a sand boil is by creating a body of water above it using sandbags to balance the water pressure.
8. Landslides occur when the
stability of a slope changes from a
stable to an unstable condition. A
change in the stability of a slope
can be caused by a number of
factors, acting together or alone.
Natural causes of landslides
include:
9. groundwater pressure acting to destabilize the
slope.
Loss or absence of vertical vegetative
structure, soil nutrients, and soil structure (e.g.
after a wildfire).
erosion of the toe of a slope by rivers or
ocean waves.
weakening of a slope through saturation by
snowmelt, glaciers melting, or heavy rains.
earthquakes adding loads to barely stable slope.
Earthquake-
caused liquefaction destabilizing slopes.
volcanic eruptions.
12. deforestation, cultivation and construction, which
destabilize the already fragile slopes.
vibrations from machinery or traffic.
Blasting.
earthwork which alters the shape of a slope, or
which imposes new loads on an existing slope
in shallow soils, the removal of deep-
rooted vegetation that
binds colluvium to bedrock.
Construction, agricultural or forestry activities
(logging) which change the amount of water
which infiltrates the soil.
13.
14.
15.
16. - Sand boils or Sand
Volcanoes occur when water under
pressure wells up through a bed of
sand. The water looks like it is
"boiling" up from the bed of sand
17.
18. Sand boils can be a mechanism contributing
to levee failure during floods. This effect is
caused by a difference in pressure on two
sides of a levee or dike, most likely during
a flood. This process can result
in piping, whereby the removal of soil
particles results in a pipe through the
embankment. The creation of the pipe will
quickly pick up pace and will eventually
result in failure of the embankment.
19.
20. A sand boil is difficult to stop. The
most effective method is by creating a
body of water above the boil to create
enough pressure to slow the flow of
water. A slower flow will not be able to
move soil particles. The body of water
is often created
with sandbags forming a ring around
the boil
