DeGraff, J.V., and Romesburg, H.C. "Regional Landslide-Susceptibility Assessment for Wildland Management: A Matrix Approach" in D.R. This will identify which combinations are associated with past landslides and which are not. Large-scale features such as secondary scarps, sag ponds, and ground-crack patterns may be represented on individual landslides. 0000001650 00000 n Landslide movement is perceptible and may take the form of falls, topples, slides, or flows. Tip: The point on the toe most distant from the top of the slide. Landslides and Landslide Susceptibility, 3. $E}k���yh�y�Rm��333��������:� }�=#�v����ʉe @���0Y�)L�:��X���dT)q%�a�S�(LF U�� �d�� -�h��DV ���`���Z��y�!�1���������ՠA���G��>0� ~-� Mora a, *, M. G .Lenzano b, C. K. Toth a, D .A. and Their Distribution, a. The process described above ensures that comparison of landslide hazard among different combinations takes place on an equal basis. THE W FUNCTION TO DEFINE FOUR LEVELS OF LANDSLIDE HAZARD. This yields the proportion of the unit area within the circle that is underlain by landslide deposits. Thus, the planner is determining acceptable risk. The interval between isopleths drawn to produce the map will depend on the proposed use. with Landslide Activity, a. 0000253538 00000 n To ensure that the points used to define the three groups are determined objectively, a non-hierarchical cluster analysis is used. This is not a decrease. This might take the form of permitting only warehouses and storage facilities in higher hazard areas, to reduce the vulnerability to the population should a landslide occur. Hillslope Stability and Land Use, Water Resources Monograph Series No. For convenience in establishing a data base, slope orientation is measured in degrees of azimuth from 0 to 360 degrees. For example, Bedrock B on slopes between 25 and 50 percent has 784 hectares of landslides. There are two basic approaches: first, to avoid landslide-susceptible areas, and second, to design measures to compensate for the inducement of landslides (see the box below). The former is the area where material once existed as the source of the landslide and appears as a scar. Figure 10-11 shows the extent to which each combination is present in the study area. An isopleth or any other analytic map can only serve as an initial assessment of landslide activity and not as a substitute for a landslide hazard map. Once the proportions are divided into three groups, bedrock, slope steepness, and hydrologic factor combinations representing different degrees of relative landslide hazard are identified. Mitigation strategies are then designed to reduce risk. Cotecchia, V. "Systematic Reconnaissance Mapping and Registration of Slope Movements" in Bulletin of the International Association of Engineering Geology, no. - Is landslide hazard assessment information available? The percent value is written on the gridded overlay next to the grid intersection. c. Slope Steepness or Discussions with local authorities responsible for public works, forestry, and agricultural activities can prove to be a valuable source of information since they may be familiar with past landslides in an area. Cluster Analysis for Applications (New York: Academic Press, 1973). Step Two: Now that the general points with regard to mapping the various land characteristics have been covered, the final section provides details on the techniques to do so in addition to presenting a step-by-step approach for preparing a landslide hazard map. Even with detailed investigation and monitoring, it is extremely difficult to predict landslide hazards in absolute terms. Interpreting the likelihood of future landslide occurrences requires an understanding of conditions and processes controlling past landslides in the area of interest. The objective of landslide information is to identify which relatively landslide-susceptible areas are best suited for what types of development activities. By overlaying the landslide inventory map on the maps of the type of bedrock, slope steepness, and indirect hydrologic measures, the association of past landslides with the factors controlling landslide occurrence can be recognized. Clearly, the amount of landslide hazard information needed is based on the level and type of anticipated development for an area. A significant amount of water may or may not be part of the mass. Existing standard geologic maps define units according to factors such as age, composition or lithology (rock type), and structure (faulting, folding, etc.). )ɩL^6 �g�,qm�"[�Z[Z��~Q����7%��"� Small-scale photography is less of a concern where bedrock and vegetation exist, since delineating areas with similar texture and appearance is easier than recognizing discrete features. The factor maps used to generate the landslide hazard map can be encoded to a geographic information system (GIS) and manipulated by a computer. - Vulnerability: the level of population, property, economic activity, including public services, etc., at risk in a given area resulting from the occurrence of a landslide of a given type. - Landslide Hazard: as represented by susceptibility, which is the likelihood of a potentially damaging landslide occurring within a given area. Materials can move up to 120mph or more, and slides can last a few seconds or a few minutes, or can be gradual, slower movements over several hours or days. These areas should be given priority for introducing some measure of mitigation. - Does the study area have a history of landslides and/or disasters caused by landslide events? Furthermore, once landslide susceptibility is identified, investment projects can be developed which avoid, prevent, or substantially mitigate the hazard. endstream endobj 53 0 obj<>/OCGs[54 0 R]>>/Type/Catalog>> endobj 54 0 obj<>>>/Name(Headers/Footers)/Type/OCG>> endobj 55 0 obj<>/Font<>/ProcSet[/PDF/Text]/ExtGState<>>>/Type/Page>> endobj 56 0 obj<>stream Refer to Figure 10-2 for the appropriate map scales. Carrara, A., and Merenda, L. "Landslide Inventory in Northern Calabria, Southern Italy" in Geological Society of America Bulletin, vol. DEFINITIONS - Landslide Hazard: as represented by susceptibility, which is the likelihood of a potentially damaging landslide occurring within a given area. Since all of these are permanent features, it is usually possible to map each factor. The number of grid squares in the circle through which landslide deposits are visible is counted. All of these factors are capable of being mapped. 0000252099 00000 n Slope orientation or aspect is described in terms of the eight cardinal directions, i.e., north, northeast, etc. For example, soils (in the engineering rather than agricultural sense of the term) derived from schists or shales will contain high percentages of clay. The method described in this chapter can be readily adapted to computer-generated mapping (Brabb, 1984). The slope steepness map displays the steepness values associated with the majority of existing landslides and is derived from an existing topographic map. U(f`��� v��� ,%�L�0E��`�t trailer Pomeroy, J.S. Landslide Maps Showing Field Classifications, Point Dume Quadrangle, California, U.S. Geological Survey Field Studies Map MF-1167 (Reston, Virginia: U.S. Geological Survey, 1980). Goals and Tasks of the Landslide Part of a Ground-Failure Hazards Reduction Program, U.S. Geological Survey Circular 880 (Reston, Virginia: U.S. Geological Survey, 1982). Landslide hazard has been determined with a high degree of reliability for only a few locations. ), More information can be provided by producing an intermediate inventory. Wright, R.H., Campbell, R.H., and Nilson, T.H. As the name suggests, this map divides the entire study area into sub-areas based on the degree of a potential hazard from landslides. - "Quantitative Approach to Assessing Landslide Hazard to Transportation Corridors on a National Forest" in Transportation Research Record 892 (1982), pp. Computer-Generated Mapping. Permanent factors are characteristics of the landscape which remain unchanged or vary little from a human perspective. In general, however, specifying a time frame for the occurrence of a landslide is difficult to determine even under ideal conditions. At worst, some areas may not be detected at all. Due to the lack of long-term records relating landslide activity to historic earthquakes, storms, or other initiating factors, permanent factors are usually used to estimate landslide hazard. Step 3: The boundary is shifted to the right to seek the desired decrease in W function: W = W1 + W2 + W3 =.1479 + 0 +.0365 =.18435. Overlay of Landslide Inventory, c. Deforestation, clearance or clearing is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use. Second, the landslide hazard map should be at a scale not markedly different from the data maps used to produce it. the Physical Factors Associated with Landslides, a. Mapping Figure 10-13 STEPS TO PREPARATION OF AN ISOPLETH MAP. Integrating Landslide Hazard Zonation Maps into the Development Planning Process, c. The landslide inventory table prepared in Step 2 shows only the area of past landslides present for each combination. Hutchinson, J.N., and Kogan, E. 'The Mayunmarca Landslide of 25 April 1974" in UNESCO Serial No. x�b```��l��B c�r�8410t|~��aj��9!� lɍ���$"r[�1��l2M^:��lY�:���6Hfng�����pD��Sc3��A/���2��ewD�?h5e��`��=>�I��E7�!��f�)� lW��(0 h�\G0��+� 0000260514 00000 n - Slides: a mass displaces on one or more recognizable surfaces, which may be curved or planar. The method described here requires a minimum of three factors mentioned earlier: distribution of past landslides, type of bedrock, and slope steepness, and a fourth, hydrologic factor may be added to reflect the important role which groundwater often plays in landslide occurrences (Varnes, 1985, and USGS, 1982). Landslides and Related Phenomena (New York: Columbia University Press, 1938). Step 4: The left-most boundary is moved to the left by one value. Similar conditions found outside the assessed area may not produce the same degree of hazard because of some seemingly minor difference in one of the factors. 0000069182 00000 n This is a way to check that all combinations are included in the analysis. Large failures of four or more square kilometers are extremely difficult to detect on aerial photography smaller than 1:40,000. Past Landslides For example, make location decisions so as to avoid building in certain areas, such as placing dwellings and critical infrastructure outside areas with a high likelihood of natural landslide activity. For example, an interval of 10 percent has been used with some isopleth maps applied to land-use planning (Campbell, 1980, and Pomeroy, 1978). For example, converting a forested area to grassland or one where crops are cultivated can increase the moisture in the soil enough to cause landslide problems (DeGraff, 1979). Steepness for landslide hazard assessments is commonly expressed as a percentage rather than in degrees. 2 Landslide and other ground failures posting substantial damage and loss of life In U.S., average 25–50 deaths; damage more than $3.5 billion For convenience, definition of landslide includes all forms of mass-wasting movements Landslide and subsidence: naturally occurred Toe of Surface of Rupture: The intersection (sometimes buried) between the lower part of the surface of rupture and the original ground surface.