Spatial Distribution Of Landslides Research Articles

Scaling properties of landslides in the Rif mountains of Morocco

Landslides in the central Rif mountains (Morocco) were analyzed by multifractal analysis. Our results suggest that spatial distribution of landslides in the region is not a homogeneous fractal structure but a heterogeneous one with generalized dimensions D(1)=1.713> D(2)>…> D(12)=1.325. The value of D(12)= D(∞) is the fractal dimension of the most intensive clustering in the heterogeneous fractal set. It is worthwhile to note that we found D(0)< D(1). The analysis of areas affected by sliding from the geological map of Beni Ahmed at a scale 1:50 000 shows the power law size distribution: N( A> a)∝ a −1.57. This confirms the scale invariance of sliding and suggests that real landslides may exhibit a Self-Organized Criticality (SOC) behaviour.

Landslide disaster in the loess area of China

China is the country with most widely distributed loess area in the world, and its loess area accounts of 6.63% of total nation land area. The landslide disaster occurs frequently for complex natural condition and becomes major factors hindering the social and economic development of loess regions. Through different indexes, the authors divided the landslides into 9 principal types and analyzed the distribution characteristics of loess landslide in time and space, the affecting factors and mechanism of landslides. It is pointed out that time and spatial distributions of landslides are closely correlative to topographic and geomorphic conditions, earthquake and rainfall, and the key influencing factors include topography, geomorphology, new tectonic movements, earthquake activity, surface water, ground water and human activities. The authors emphasized that the loess landslide was an urgent task for sustainable development in the loess zone.

Frequency and spatial distribution of landslides in a mountainous drainage basin: Western Foothills, Taiwan

Maps from 1904 and 1915 and air photographs from 1963, 1980, 1985, 1993 and 1996 provide a record of landslide incidence in a 92.1-km 2 drainage basin, a headwater tributary of the Cho-Shui River in Taiwan. Interpretation of landslide patterns from the early maps indicate that in four sub-basins (36 km 2) structural geological factors control chronic landsliding regularly reactivated by intense rains. Within these four sub-basins, all later air photographs reveal a continuing high incidence of landslides (with landslide densities of 3–11 ha/km 2). Air photographs taken in 1963, following extensive logging, in 1985, following highway construction, and in 1996, following the very large typhoon Herb event demonstrate the short-term effects of disturbance in these structurally weak sub-basins. Air photographs from 1980 and 1993 demonstrate recovery of the land surface from logging and highway construction impacts, respectively. For the adjacent sub-basins (56 km 2), two modes of response to perturbations were identified: six sub-basins (48 km 2) showed direct response to logging, road construction and typhoon Herb and five sub-basins (8 km 2) were more buffered and showed some lagged responses. Even this last category of sub-basins is more active than the average for Taiwan, where the mean landslide density is 0.84 ha/km 2. It is proposed that, for the 92.1-km 2 Hoshe basin, the ‘formative event’ sensu Brunsden [Z. Geomorphol. Suppl. 79 (1990) 1] is one that produces approximately 200 ha of landslides, a value that has been equaled or exceeded in each of the periods of study (1963–1980, 1980–1985, 1985–1993 and 1993–1996). Logging activity, major road construction, and extreme typhoon and earthquake events produce short-term acceleration of landslide incidence. In principle, recovery rates of the land from pulsed perturbations of about 20 years for logging activity and about 8 years for major road construction may also be suggested.

GEOMORPHOLOGICAL CONTROLS ON LANDSLIDE ACTIVITY IN THE DU TOITS KLOOF, WESTERN CAPE MOUNTAINS, SOUTH AFRICA

ABSTRACT Landslide activity is known to be common in the Western Cape mountains and has been documented in a previous study for the Du Toit's Kloof. This study correlates the different geo- environmental factors with the occurrence of landslides in the Du Toit's Kloof. Various geomorphological parameters have been assessed in conjunction with geological and anthropological aspects to evaluate the occurrence of different types of landslides in the area. Eighty landslides were identified, mapped and classified by origin in the field. Each was studied in the context of lithology, slope angle, distance from major shear zones and the proximity to road cuts. The important causes for slope failure were found to be lithology and break in slope angle. The spatial distribution of landslides appears closely related to contact of sandstone and granite where the rock scarp meets the debris slope was a constant flux in the level of segregation.

A methodological approach for the analysis of the temporal occurrence and triggering factors of landslides

The temporal occurrence of landslides in an area of the Cantabrian Range during the last 120,000 years is analyzed. An initial relative chronology was established on the basis of aging degree and spatial relationships between landslides and glacial and fluvial features. Ten landslide classes were thus identified and their chronological limits defined on the basis of 19 14C age determinations on fluvial and glacial deposits (including eight new ones). The chronology was tested with 14C dates obtained on landslide deposits, 10 from previous work and nine new ones. The chronological classes identified were compared with existing climate models for the region; the type and spatial distribution of landslides in each class were also analyzed. The approach made it possible to identify periods during which landslides were triggered mainly by channel incision, seismic activity and rainfall increase. Human activity played a significant role after 5000 BP and especially in the last few centuries. Mobilization of materials by slope movements has increased in the region by a factor of 10, compared to pre-Neolithic rates.

Post‐deforestation soil loss from steepland hillslopes in Taranaki, New Zealand

AbstractSoil erosion on steepland hillslopes in Taranaki, New Zealand, where landsliding is the dominant erosion form, was investigated by comparing mean regolith depths between first‐order basins that have had their forest cover removed for different periods of time. Regolith depth and slope angle data were collected along 19 profile lines and 30 profile lines from steepland basins that had been deforested for 10 and 85 years, respectively. These profile lines were subdivided into a total of 236 profile segments of relatively linear slope angle and uniform regolith depth, that averaged 17·5 m in length.The depth of pre‐existing regolith on post‐deforestation landslide sites is estimated from a regression of regolith depth on slope angle for undisturbed (non‐landslide) profile segments. Regolith depletion on landslide sites is in turn estimated by subtracting the depth of regolith on landslide sites from the estimate of pre‐existing regolith depth. Regolith depletion by post‐deforestation landslides, averaged over the entire length of profile lines, gives an estimate of average surface lowering. For the area deforested for 85 years, average surface lowering by post‐deforestation landslides is 0·15 ± 0·04 m, and is the same as the difference in mean depth of 0·15 ± 0·11 m between this area and the area deforested for 10 years. Erosion of regolith from hillslopes by processes other than landsliding appears to be minimal. The 0·15 m average surface lowering represents a regolith depletion rate of 1·8 ± 0±5 mm yr−1. For hillslopes steeper than 28°, where all post‐deforestation landslides occur, average surface lowering is 0·20 ± 0·05 m, and the regolith depletion rate is 2±4 · 0±6 mm yr−1. Average surface lowering is greatest at 0·23 ± 0·07 m on hillslopes steeper than 32° where most post‐deforestation landslides occur. Here, the regolith depletion rate is 2·7 ± 0·8 mm yr−1.A large‐magnitude, low‐frequency storm in March 1990, produced an average surface lowering of 0·041 m. There were proportionately more landslides in the area deforested for 10 years, illustrating the importance of previous erosion history of hillslopes on the spatial distribution of landslides. There were also comparatively few landslides on steeper hillslopes because previous lower magnitude storms had already removed much of the deeper regolith.

Trapped bedfellows: A comment on windle and neigher

Large-scale landslides in the Himalaya are defined as huge, deep-seated landslide masses that occurred in the geological past. They are widely distributed in the Nepal Himalaya. The steep topography and high local relief provide high potential for such failures, whereas the dynamic geology and adverse climatic conditions play a key role in the occurrence and reactivation of such landslides. The major geoscientific problems related with such large-scale landslides are 1) difficulties in their identification and delineation, 2) sources of small-scale failures, and 3) reactivation. Only a few scientific publications have been published concerning large-scale landslides in Nepal. In this context, the identification and quantification of large-scale landslides and their potential distribution are crucial. Therefore, this study explores the distribution of large-scale landslides in the Lesser Himalaya. It provides simple guidelines to identify large-scale landslides based on their typical characteristics and using a 3D schematic diagram. Based on the spatial distribution of landslides, geomorphological/geological parameters and logistic regression, an equation of large-scale landslide distribution is also derived. The equation is validated by applying it to another area. For the new area, the area under the receiver operating curve of the landslide distribution probability in the new area is 0.699, and a distribution probability value could explain > 65% of existing landslides. Therefore, the regression equation can be applied to areas of the Lesser Himalaya of central Nepal with similar geological and geomorphological conditions.

A new odontograph

Coseismic landslides are important effects of strong earthquakes and one of the most poorly understood. Such landslides are driven by inertial forces acting on slopes and can vary in size from individual rock blocks of a few m3 in volume to catastrophic rock avalanches of many Mm3, which can claim many thousands of lives. The capability of an earthquake to trigger a landslide is a function of energy arriving at the site, which is itself related to earthquake magnitude and epicentral distance. However, as much as these two parameters can be shown to exert a limit on the ability of the earthquake to cause landslides, it is clear from the spatial distribution of landslides caused by earthquakes that these are not the controlling factors. A detailed consideration of ground accelerations recorded during earthquakes indicates that threshold or yield accelerations are required to initiate movement on slopes. These yield accelerations are strongly dependent on the degree of stability of the slope under ambient stress conditions, development of pore-water pressures during shaking, and degradation of strength and stiffness under cyclic loading. Traditional engineering analyses have tended to focus on horizontal accelerations; however, a growing body of evidence points to the importance of vertical accelerations in seismic slope stability. In addition to the polarity of ground motions, there is an important influence from topographic amplification of shaking. This can give rise to ground motions that are 5–10 times higher than free-field accelerations, meaning that ground shaking at slope crests and ridges can be considerably higher than the vibration at the foot, or behind the crest, of the slope. This variation in ground motions means that shaking recorded on free-field instruments is unlikely to be representative of ground motions driving slope instability. Therefore, several significant unknowns severely limit understandings of this group of dynamic slope processes.