Landslides
Causing $1-2 billion in damages and more
than 25 deaths per year, landslides are
a major geologic hazard, caused by
earthquakes and floods. Although, landslides
are generally not as exciting or
costly as earthquakes, major floods, tropical
storms, and other natural
disasters, they occur in more expanded places and may
cause more property
damage than any other geologic hazards. A wide variety of
ground movements,
such as rock falls, slope failure, and shallow debris flows
can classify
landslides. When a portion of a hill slope cannot support its own
weight a
landslide will occur. When rainfall or some other water source
increases the
water content of the slope the weakness is irritated, reducing the
strength
of the materials. Although gravity acting upon an increased slope is
the main
reason for a landslide, there are other elements that contribute to
its
cause. Loud sounds that occur during an earthquake also cause
landslides.
Erosion caused by rivers, glaciers, or ocean waves create
oversteepened slopes.
Heavy rains and melting snow weaken rock and soil
slopes. Furthermore,
vibrations from machinery, traffic, and even thunder may
trigger failure of weak
slopes. Excess water can run through slope material
and can cause a debris flow
or mud flow. The rock and mud left over after a
landslide may pick up anything
in its path, such as trees, houses, and cars,
causing bridges and tributaries to
become blocked which causes flooding
throughout its path. Even though, the
natural cause of most landslides is
unable to be stopped, geologic
investigations, good engineering practices and
effective enforcement of land-use
management regulations can cut back
landslide danger. Landslides effect every
state in the United States
territory. The Appalachian Mountains, the Rocky
Mountains and the Pacific
Coastal Ranges and few parts of Alaska and Hawaii have
intense landslide
problems. USGS marine scientists have recently identified over
fifteen giant
landslides surrounding the Hawaiian Islands. These slides are some
of the
largest known on Earth, and most have taken place throughout the past
four
million years. The youngest landslide is estimated to have occurred only
one
hundred thousand years ago, and there is evidence today that large blocks
of
the island are starting to slide, causing enormous earthquakes. Each
landslide
that has happened over the bast four million years has ended with
huge land loss
and gigantic waves that move rocks and sediments up to 1000ft
above sea level.
The geologic hazards are important to learn about
because, they don't occur as
frequently as volcanoes or other disasters, they
have potential to destroy
lives, property, and natural resources (Giant
Landslides). It is possible that
any area made up of brittle and cracked
materials lying on a steep slope will be
subject to landslides. Scientists
continue to try their best to lower the risk
of landslides everywhere by
producing landslide susceptibility maps for areas in
the United States. Areas
that are generally accessible to landslide hazards
include: old landslides,
bases of slopes, at the base of minor drainage hollows,
at the base or top of
an old fill slope or steep cut slope, and developed
hillsides where leach
field septic systems are used. However, there are areas
that are safe from
landslide activity: on hard bedrock that has not moved in the
past, on flat
land away from rapid changes in slope angle, and at the top or
along the nose
of ridges, set back from the tops of slopes. In order to be
prepared for
landslides, pay attention to things that might occur before the
hazard. These
characteristics include wetness of ground that has not been wet
before, new
cracks or bulges in the ground, sidewalk, or street, cracks in
concrete
floors and foundations, leaning telephone poles, uneven fence lines,
rapid
increase of water level in creaks, and movement of soil away
from
foundations. Incase a landslide does occur, contact local fire, police
or public
works department, tell affected neighbors, and be sure to evacuate
the area.
Bibliography
"Giant Landslides Around the Hawaiian Islands".
http://walrus.wr.usgs.gov/docs/projects/haland.html
maintained by Molly Gowen
Groome last modified June 10, 1998, accessed 12/10/98.
This page updated:
16 November 1998 For suggestions and comments please send
e-mail to:
nlic@usgs.gov. Page URL:
http://landslides.usgs.gov/html_files/nlicsun.html
11/30/1998 The URL of
this page is
http://landslides.usgs.gov/html_files/nlic/new1ft.shtml
Contact:
Webmaster@gldage.cr.usgs.gov Updated: Monday November 16 1998
"Landslides."
http://germantown.k12.il.us/html/landslides.html