Landslide studies can be organized into three phases
1) detection and classification of landslides
2) monitoring activity of existing landslides
3) analysis and prediction of slope failures in space
(spatial distribution) and time (temporal distribution).
Remote sensing techniques can be and are often used in
all three stages of a landslide investigation.
Examples of some remote sensing tools (not all of these
will be discussed in this page):
In order to study a landslide, you need to be able
to view the size and contrast of the landslide features and the morphological
expression of the topography within and around the landslide. Parameters
you might be interested in determining are the type of movement that has
occurred, the degree of present activity of the landslide, and the depth
to which movement has occurred.
The most common remote sensing tools used for the detection and classification of landslides are aerial photographs. Aerial photography has become a standard tool aiding in the study of landslides.
Other types of remote sensing techniques used in the detection and classification:
Remote sensing techniques:
Global Positioning System (GPS)
GPS is a useful tool for detecting first stage disaster
and further mitigation. It can detect movement of cm/yr, and aid
in determining the boundary of the landslide area. Monitors can be
placed anywhere you can access, and they are relatively easy to operate.
There are some significant disadvantages involved in using GPS, however.
Several of these disadvantages are precision is affected by the number
of observable satellites present, the obstruction of the observation point,
and the monitoring of installed GPS receivers which have been placed out
in the field.
Example:
Click
here for an example of using GPS to monitor unstable slopes along I-70
in Colorado
Satellite imagery/RADAR imagery
There are many types of visible band satellite imagery
that can help detect where slides have occurred or where they are about
to occur. Change detection images can be taken before and after movement
occurred. From these images you can often see surface disruption.
Radiometric and geometric calibration is required of the before and after
images to make images that have changed stand out from those that have
not.
Stereophotogrammetry
In the method of stereophotogrammetry, a satellite
acquires two images of the same ground scene within a relatively short
period of time, so that it can view surface features have not significantly
changed. These images can be processed to get topography from the
stereo pair of images. The series of stereo pairs offers a 3 dimensional
evolution of the landslide over time.
Another example…
Click
here for an example of using photogrammetry on the Slumgullion Landslide
in Hinsdale County, Colorado
This image
is one example of why it is so important to try to predict landslide occurrences
and slope failures. This is a picture of a debris flow from Rudd
Canyon into Farmington, Utah, in Spring of 1983. (Photo: S. Ellen, USGS).
Debris flow hazard map of a portion of the San
Francisco Bay Region
Click on the map for a larger image.
Landslide hazard analysis
Hazard – The probability of occurrence of a potential phenomenon within a specified period of time and within a given area (Varnes, 1984).
Zonation – The division of land into homogeneous areas or domains and their ranking according to degrees of actual/potential hazard caused by mass movements (Varnes, 1984).
Landslide hazard is typically depicted on maps which show spatial distribution of hazard classes, or “landslide hazard zonations.” The development of these zonations requires knowledge of the processes active in the area being analyzed, and factors (geologic and triggering) leading to the occurrence of landslides.
Landslide hazard map of the Conterminous U. S.
Click on the map for a larger image.
Landslide hazard maps typically aim to predict where failures are likely to occur without any clear indication of when they are likely to occur. They are useful for providing landslide hazard information needed for planning and protection purposes. An ideal map of slope instability hazard should reflect information concerning at least the following variables:
Temporal probability requires the analysis of potential
triggering factors (earthquakes, threshold precipitation, etc.) in relation
to the landslides and the application of complex prediction models.
Triggering factors, however, cannot be predicted. For this reason,
most landslide hazard models typically show spatial probability without
regard for temporal probability.
Input data required in physically-based prediction models often varies from location to location, which causes problems when trying to develop a model for a large area. Some alternatives to landslide hazard maps are listed below, but it is in no way a comprehensive list of the numerous methods available for predicting landslide occurrence.
Landslide Inventory Map
A typical landslide inventory map is based on aerial
photograph interpretation, ground survey, and/or a database of historical
movements within the area. The product of a landslide inventory map
is a spatial distribution of landslides as points or to scale. Landslide
inventory maps can and often are used as a basis for other landslide hazard
zonation techniques or an elementary form of a hazard map. These
maps, however, only provide information for a short period of time, and
they provide not insight into temporal changes in landslide distribution.
Landslide overview map of the Conterminous United States.
Click on the map for a larger image.
Landslide Activity Map
A landslide activity map is a refinement of the landslide
inventory map. It is based almost solely on multitemporal aerial
photograph interpretation.
Geomorphological Method Map
A Geomorphological method map is produced by mapping
movements in their geomorphological setting. This can be done from
aerial photos, satellite/RADAR images, etc. A degree of hazard is
allocated at each site in the terrain, but the rules of decision change
from place to place (and from person to person), which often leads to a
map which is very subjective.
Statistical Techniques
Statistical techniques aim at a higher degree of objectivity
and better reproducibility of hazard zonation. There are many statistical
methods used in this field.
GIS in analysis and prediction of landslides
A large database is necessary for the analysis and prediction
of slope failures. It needs to be able to store, manipulate, and
apply the data collected in first two stages (recognition and monitoring).
A Geographical Information System is ideal for this stage in a landslide
investigation because it is capable of handling large amounts of past,
present and future data and integrating this data with predictions.
It is capable of data storage and visualization, it is cheaper and easier
to use than a manual map production and overlay, it can have regional databases,
and therefor perform both local and regional modeling. There are
many types of GIS packages which differ in terms of hardware requirements,
potential of spatial functions, efficiency of the data-base, and internal
data structure.
Remote sensing techniques greatly aid in the investigations
of landslides, on both a local and regional scale. Although they
do not replace fieldwork, interdisciplinary research strategies, and testing
the reliability of landslide prediction models, remote sensing techniques
do offer an additional tool from which we can extract information about
landslide causes and occurrences. Most importantly, they greatly
aid in the prediction of future landslide occurrences, which is very important
to those who reside in areas surrounded by unstable slopes.
Landslide and Geomorphology
Links:
U.S.
Geological Survey Geologic Hazards Landslide Page
Landslide
Publications and Reports
The
Virtual Geomorphology
Landslide
Images
Landslide
Publications and Reports
San
Francisco Bay Area Landslide Maps
State
Information for Landslides in Your Area
Click
here for a bibliography related to this topic
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