LANDSLIDE
LANDSLIDES
A
landslide is a mass movement of material, such as rock,
earth or debris, down the slope of a hill or cliff. They can
happen suddenly or move slowly over long periods of
time.
 Landslides
are classified by their type of movement. The
four main types of movement are falls, topples, rotational
slides, translational slides and flows. Landslides can be
classified as just one of these movements or, more
commonly, can be a mixture of several.
 At
the BGS we study the landslides that happen in the UK.
Large landslides occur around the world and also in the
sea.
WHY DO LANDSLIDES HAPPEN?
A
landslide may occur
because the strength of the
material is weakened. This
reduces the power of the
'glue' that cements the rock or
soil grains together. Located
on a slope, the rock is then no
longer strong enough to resist
the forces of gravity acting
upon it.
WHAT CAN INCREASE THE CHANCE
OF A LANDSLIDE?
Several factors can increase a slopes susceptibility to a landslide event:

water (rainfall or the movement of the sea) — this acts as a grease to the material increasing the
likelihood that it will slip and also adds extra weight to the rock

erosion processes — such as coastal erosion and river erosion

steepness of slope

type of 'rocks' — soft rock such as mudstone or hard rock such as limestone

shape of the rock 'grains'

jointing and orientation of bedding planes

arrangement of the rock layers

weathering processes — for example freeze-thaw reduces the stickiness (cohesion) between the rock
grains.

lack of vegetation which would help bind material together

flooding

volcanoes and earthquake activity nearby

man's activity — mining, traffic vibrations or urbanisation which changes surface water drainage
patterns
WHY STUDY LANDSLIDES?
 Landslides
are a serious geologic hazard common to
almost every State in the United States. It is estimated
that in the United States, they cause in excess of $1
billion in damages and from about 25 to 50 deaths
each year. Globally, landslides cause many billions in
damages and thousands of deaths each year.
THANK YOU FOR ATTENTION!