Mass Movement internet exercise 5
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Radford University *
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Geography
Date
Dec 6, 2023
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docx
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Mass Movement internet exercise
Dr. Anna Balog
Map of the USA showing the probabilities of mass movement.
https://pubs.usgs.gov/pp/p1183/figures/map.jpg
This figure 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.
At the website (under the map) you can click on the map and look at all of it in enlargement,
and read the legend.
1.
Please list the 3 major area where there is high susceptibility to landslides or mass
movement.
Appalachian Mountains, the Rocky Mountains, the Pacific Coastal Ranges, and some parts
of Alaska and Hawaii
.
Pacific Northwest (Washington and Oregon):
The Pacific Northwest is prone to landslides due to its steep terrain, heavy rainfall, and tectonic
activity.
The Cascadia Subduction Zone, a tectonic boundary off the coast, can generate powerful
earthquakes that trigger landslides
.
California:
California is another high-risk area for landslides, primarily in regions with hilly or mountainous
terrain
The combination of steep slopes and intense rainfall can lead to landslide activity, especially
during the rainy season.
Appalachian Mountains (especially in parts of West Virginia and Kentucky):
The Appalachian Mountains have steep slopes and are susceptible to landslides, primarily in
areas with weathered rock and poorly compacted soils.
2.
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.
T
he physical cause of many landslides cannot be removed, geologic investigations, quality
engineering practices, and effective enforcement of land-use management regulations can reduce
landslide hazards. USGS scientists continue to produce landslide susceptibility maps for many
areas in the United States. In every state, USGS scientists monitor streamflow, noting changes in
sediment load carried by rivers and streams that may result from landslides. Hydrologists with
expertise in debris and mudflows are studying these hazards in volcanic regions
.
There are many types of mass movement, but in all types, mass movement is characterized
by the downslope movement of materials under the influence of gravity. A landslide, caused
by gravity erosion, involves the movement of large quantities of material very quickly, and it
can be deadly. But whether it happens quickly or slowly, mass movement happens on all
slopes. The ultimate result is the movement of material from higher to lower elevation.
In the west coast states of California, Oregon, and Washington, there are many factors that
can lead to landslides. To begin, the location along the Pacific Ocean means that water has a
high probability of changing the angleof repose, undercutting cliff faces along the shore and
causing them to weaken and collapse. As well, the high probability of earthquakes in the
California area can trigger landslides by dislodging regolith. The presence of the Sierra
Nevada Mountains and the Cascades in Washington, also provide slopes that can see
landslides under heavy rain. Finally, the soft sheared rocks increases susceptibility to slides.
In the Rocky Mountain States, the severe elevation differences between the mountains and
the valleys create a steep angle that makes it easy for regolith to flow down. Thesnowmelt
that occurs every spring also creates a vast quantityof water that loosens regolith and causes
it to flow. The presence of soft shale within the mountains also makes it easy for mudflows
to occur. Frequent rock falls also trigger rockslides due to the weak nature of the underlying
geological structure. As rain storms are common in the Appalachia area, this provides a large
amount of water that can cause the soils and weakly established materials to flow and cause
disastrous mudslides
3.
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?
The potential for landslides in most of the counties in western Virginia is high.
As shown in
the map below, adapted from USGS Landslide Overview Map of the Conterminous United
States, at least half of the Commonwealth falls into zones of high potential.
4.
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.
a.
Describe the geological setting of La Conchita
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one of three small communities occupying a 25Km stretch of land along CA coastline
between Ventura and Carpinteria. Development along this coastline is limited. Few
patches between the mountains and the Pacific Ocean wide enough for development
b.
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.
Landslide occurred in La Conchita on January 10, 2005, destroyed 36 homes, and killed 10
people
-Triggered by heavy rainfall, reactivation along an older landslide surface (35,000 years ago,
6,000 years ago and 1995)
-Debris flow up to 45 km/h (30 mph)
c.
Where any mitagation measures taken between the two events to prevent further
disasters? If so, what measures were taken and how effective were they?
Promoting sound land use planning based on known hazards.
Buying flood insurance to protect your belongings.
Relocating or elevating structures out of the floodplains.
Securing shelves and water heaters to nearby walls.
d.
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?
La Conchita, California, is unsuitable for permanent housing because of its high risk of
landslides
. The area has a long history of landslides, making it hazardous for residents
to live there permanently.
La Conchita is located on a coastal bluff with steep slopes that are prone to
erosion
and
instability. The region experiences heavy rainfall, which further weakens the slopes and
increases the likelihood of landslides.
The area's geology, characterized by unstable soils and layers of ancient landslide debris,
adds to the instability. Tragically, La Conchita has witnessed several devastating
landslides in the past, resulting in loss of life and property damage.
These events highlight the significant risks associated with living in the area. Given the
recurring nature of
landslides
and the potential danger they pose, it is considered unsafe
for permanent housing in La Conchita.
Residents face an ongoing threat to their safety and well-being, and efforts should be
focused on mitigation measures, such as slope stabilization and evacuation plans, rather
than encouraging permanent settlement.
In conclusion, La Conchita, California, is unsuitable for permanent housing due to the
high risk of landslides associated with the area's geology, steep slopes, and frequent
heavy
rainfall
. The safety and well-being of residents should be prioritized, and
alternative housing options should be considered to mitigate the risks posed by
landslides.
Case studies:
You can use the internet for further information at the different sites to
get your answers.
1.
Watch this video and answer the following question:
a.
How did this mass movement event happened?
the rock and soil materials on the cliff break off and fall to the base of the cliff. It
takes less energy for gravity to pull an object down a vertical or nearly vertical
surface than it does to move it along a flat or slightly inclined surface.
b.
What was the trigger at this site?
To show us that are multiple processes that can increase the risk of rockfalls along
highways, including frost wedging and root wedging that break up a slope, the slope
of the road, summer droughts, and spring rains. One process that can increase the
risk of rockfalls is frost wedging and root wedging that breaks up a slope.
c.
In your opinion heavy rain could have been a factor ?
2.
Oso, Washington state
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Before and after images show the true devastation to the area following the
colossal landslide in Oso, Washington state. Set side by side, the two images
show how the one mile stretch of land looked before the disaster this
weekend which has seen more than 175 people go missing and 14 confirmed
dead, and the bare cliff face that has been left in its wake.
a.
On the before pictures can you recognize anything which might have indicated the
possibility of a major landslide in the area?
b.
What was the trigger at this site?
A study of the
rainstorm
that triggered the landslide found that precipitation in the weeks
leading up to the event was only moderately intense, though unusual in its timing during the
normally drier early spring season.
c.
In your opinion heavy rain could have been a factor?
Disturbances in the natural stability of a slope cause landslides. Heavy rains can lead
to mudslides developing because when water rapidly accumulates in the ground, the
surge of water saturates rock and debris.
3.
Mudslide destroys home near Vinton; no
one injured
May 18, 2018.
a.
What was the trigger at this site?
torrential rains combined with excavation on the hillside behind the home
.
b.
What kind of geology we have in this area which helped for this to happen. Look at
the picture, what could be the composition of the slope?
Heavy rains overnight
helped trigger a mudslide that pushed a home off its foundation near
Vinton.
https://www.youtube.com/watch?v=ykECXnEIcZs
Please watch this video and answer the following questions:
a.
Where did this debree flow, mudflow, mudslide has happened?
In California
b.
How big is the affected area?
more than a dozen people missing after mudslides in Southern California destroyed an
estimated 100 houses, swept cars to the beach and left at least 17 victims dead
.
c.
What triggered the event: List the events
Relentless storms from a series of atmospheric rivers
d.
What is your opinion about living in this area? Based on the map in the
first part of this exercise.
In my opinion, this area is not safe to live in because it comes between
the Pacific Ocean and the Santa Mountains, and that is why there is a
high risk of natural disasters.
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