Massmovement
(Internet exercise from
Prof.
Stephen A. Nelson Tulane University)
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The web site at
http://landslides.usgs.gov/learning/nationalmap/
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shows the National Landslide Hazards Map, published by the
U.S. Geological Survey. This is a map of the lower 48
states showing areas where there have been a high incidence
of landslides, and areas that have a high susceptibility to
landslides. Notice that you can click on various dots on
the map and map legend to get an enlargement of various
areas or the legend of the map. On the large map, the areas
colored in red are areas where there is a high incidence of
landslides (covering greater than 15% of the area). There
are three major zones where high incidence of landslides
occur. (1) near the west coast in the states of California,
Oregon, and Washington, (2) in the Rocky Mountain states of
Colorado, Utah, and Wyoming, and (3) in the Appalachian
mountain states of Ohio, Pennsylvania, Virginia, West
Virginia, Kentucky, Tennessee, and Georgia. Surrounding
these areas are areas of high to moderate susceptibility to
landslides.
a.
For each of these three areas that have
high incidence or susceptibility to landslides, what geologic
features are present that contribute to the high incidence or
susceptibility to landslides? In answering this question, think
about the major factors involved in landslides (the role of
gravity, especially slope angle, the role of water, the
role of different geological materials like soil and rock, and
the presence of processes that trigger landslides.
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Click on the yellow dot just north of Louisiana to get
an enlarged view of the southeastern United States.
Notice that there are zones running roughly north-south
near the left-hand side of the map that show moderate
and high susceptibility to landslides (buff and pink
colored zones). Notice that this band runs through the
city of Memphis, Tennessee. For a view of what Memphis
looks like (before they built all of the buildings and
planted trees)
http://www.history.navy.mil/photos/images/h59000/h59055.jpg.
and for a more modern view click
HERE
What reasons can you give that these areas are
moderately to highly susceptible to landslides? (use the
same criteria you used in part a, above)
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Find as near as possible the area where you live. What
zone do you live in (answer by first stating exactly
where you live, then by indicating the color zone on the
map and the meaning of the color zone from the map
legend)? If it is a zone with a moderate to high
incidence of landslides or a zone with a moderate to
high susceptibility to landslides, what features in the
area do you think are responsible for the incidence or
susceptibility rating? If it is zone with a low
incidence or low susceptibility of landslides, what
features or lack of features are responsible for the
incidence or susceptibility rating?
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Since you decided not to take the job in Tacoma and accept
the house in Orting, Washington, you are back in your house
near San Francisco and comfortably settled into your job as
an executive with Denyallclaims Insurance Company. One of
your friends is a developer who is planning a resort hotel
project in southern California and wants to get a good deal
on insurance coverage from Denyallclaims. His project is
located just to the northwest of a town called La Conchita,
on the coast in Ventura County, California. Before agreeing
to insure this project, you vaguely recall having heard
something about La Conchita in the news within the last
couple of years. Because you know that your company will
probably take away your job (and house) if they have to pay
large claims, you decide to fly down to La Conchita to check
it out. But, since your company does not like to pay travel
expenses either, you decide that a better approach would be
to use the internet (particularly a U.S. Geological Survey
site) to check out this property. By doing so, you quickly
learn that there have been two events in the last 12 years
that have affected the community.
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Describe the geological setting of La Conchita
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Discuss any disastrous events that have occurred in La
Conchita within the last 12 years, including a
description of events, any damage that has occurred, and
any serious injuries or deaths that have resulted from
these events. Be pretty detailed! This is one of
the pictures of this site.
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Where any mitagation measures taken between the two
events to prevent further disasters? If so, what
measures were taken and how effective were they?
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You should be able to find plenty of photos of the area
that includes the area just to the northwest of La
Conchita. From those photos, what is your evaluation of
the risk involved in building a resort hotel just to the
northwest of La Conchita?
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Whether or not you currently live in an area prone to
landslides, you may in the future. It would be a good idea
to know something about some of the features to look for
that might indicate a landslide may occur in the near
future, especially if there is any sloping ground around the
area. Find an internet site (hint, the U.S. Geological
Survey has a good one) that tells you what features to look
for.
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Give at least 10 such features that might be noticed
before landslides occur.
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List 4 things you should do if you suspect immediate
landslide danger
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For each of the following drawings, determine (i) What
potential mass-wasting hazards exist, (ii) why these hazards
exist, and (iii) what might be done to mitigate the hazard
or remove the danger. Be sure to consider all information
available, such as direction of fractures, type of rock or
soil, slope angle, and any other features shown on the
drawings.
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a.
b.
c.
d.
For this one also state which site (X, Y, or Z) would be the
best site on which to build your house. |
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