Creep processes in landslides

Displacement of landslide blocks after initial slope failure can be very slow. In most cases movement of the blocks is attributed to sliding along a well-defined slip surface. It is discussed here whether, in addition to these so-called plastic movements, (continuous) creep processes are involved in the slow displacement. The study was carried out in the downstream part of the Bonne valley in the French Alps, where landslide complexes have developed in varved clay material. Displacements of landslide blocks were measured during a period of three years. Inclinometer measurements in flexible tubes showed that a creep zone developed above the slip surface in a zone about 1 m thick. These field observations on creep processes were supported by soil mechanical analysis. Threshold values for creep found in the laboratory nearly coincide with threshold values calculated from a field creep model developed by Ter-Stepanian. During the measuring period ±15 per cent of the displacement of the blocks possibly occurred via continuous creep.     

The behaviour of stones and stone implements,buried in consolidating and creeping Kalahari sands

This study reveals that the Quaternary mantle of reworked Kalahari Sands undergoes a post-sedimentary composite process at the archaeological site of Gombe (Kinshasa, Zaïre). There is a biological activity which consists of an upworking of soil particles, mainly by termites and worms. This causes a diminishing dry volume weight of the sediment. In response, the mantle reconsolidates. When the soil surface is horizontal, the particles which are not brought up will sink down in the soil profile as a result of the reconsolidation. When the soil surface is inclined, it is only the resettlement of the sediment which can give rise to creep, caused by wetting and drying. Creep of the dead mineralogical material alone seems to be very improbable once the structure and settlement of the sediment are in equilibrium with a given slope. Only a new phase of bioturbation can induce further creep movements. The experiments have shown that stone implements in reconsolidating Kalahari Sands do not exactly accompany the compaction movement of the sediment. Depending on their form, their size, their orientation and the water content of the sediment around them, stone implements can undergo differential movements during the reconsolidation process. This can result in a dispersion of the implements over levels of different ages. As creep is a phenomenon, going hand in hand with the resettlement of the sediment after biogenic upworking, partially analogous movements of stone implements can be expected in a creeping Kalahari Sands mantle. Partial or total reconcentration of the stone implements at the base of affective biogenic activity can be expected. This can lead to typical stone-line profiles which must be interpreted very carefully.     

A methodology to study rain splash and wash processes under natural rainfall

The complex interactions between rainfall‐driven erosion processes and rainfall characteristics, slope gradient, soil treatment and soil surface processes are not very well understood. A combination of experiments under natural rainfall and a consistent physical theory for their interpretation is needed to shed more light on the underlying processes. The present study demonstrates such a methodology. An experimental device employed earlier in laboratory studies was used to measure downslope rain splash and ‘splash‐creep’, lateral splash, upslope splash and rainfall‐driven runoff transport (wash) from a highly aggregated clay‐rich oxisol exposed to natural rainfall in West Java, Indonesia. Two series of measurements were made: the first with the soil surface at angles of 0°, 5°, 15° and 40°; and the second all at an angle of 5° but with different tillage and mulching treatments. A number of rainfall erosivity indices were calculated from rainfall intensity measurements and compared with measured transport components. Overall storm kinetic energy correlated reasonably well with sediment transport, but much better agreement was obtained when a threshold rainfall intensity (20 mm h^?1) was introduced. Rain splash transport measurements were interpreted using a recently developed theory relating detachment to sediment transport. Furthermore, a conceptually sound yet simple wash transport model is advanced that satisfactorily predicted observed washed sediment concentrations. The lack of replication precluded rigorous assessment of the effect of slope and soil treatment on erosion processes, but some general conclusions could still be drawn. The results stress the importance of experiments under conditions of natural rainfall. Copyright © 2002 John Wiley & Sons, Ltd.     

THE RELATIVE CONTRIBUTION OF SOIL TILLAGE AND OVERLAND FLOW EROSION TO SOIL REDISTRIBUTION ON AGRICULTURAL LAND

This study uses evidence for the long-term (35 years) pattern of soil redistribution within two agricultural fields in the UK to identify the relative importance of tillage and overland flow erosion. Spatially distributed long-term total soil redistribution data for the fields (Dalicott Farm and Rufford Forest Farm) were obtained using the caesium-137 (¹³⁷Cs) technique. These data were compared with predicted patterns of soil redistribution. Recent studies have demonstrated that the redistribution of soil by tillage may be described as a diffusive process. A two-component model was, therefore, developed which accounts for soil redistribution by both overland flow and diffusive processes. Comparison of the predicted patterns of overland flow erosion alone with the observed (¹³⁷Cs-derived) data indicated a poor agreement (r² = 0.17 and 0.11). In contrast, a good agreement exists between the predicted pattern of diffusive redistribution and the observed data (r² = 0.43 and 0.41). These results give a clear indication that diffusive processes are dominant in soil redistribution within these fields. Possible diffusive processes include splash erosion, soil creep and tillage. However, the magnitude of the diffusion coefficients for the optimum predicted pattern (c. 350–400 kg m⁻¹ a⁻¹) demonstrates that tillage is the only process capable of explaining the very significant soil redistribution which is indicated by the ¹³⁷Cs data. Consideration is given to the implications of these results for both soil erosion prediction and landscape interpretation.     

EFFECTS OF SOIL CRUSTING ON SOIL MOISTURE, RUNOFF AND EROSION: FIELD OBSERVATIONS

1 INTRODUCTION Soil crusting, or soil sealing, is one of the common phenomena in agricultural lands or semi-arid and arid soils. Due to the breakdown of soil aggregates by raindrops, soil surface develops a very thin, often less than a few millimeters, dense layer. Many studies indicated that such a thin layer significantly reduces infiltration capacity and increases surface runoff (i.e. McIntyre, 1958; Edward and Larson, 1969; Agassi et al., 1985; Bradford et al., 1986; Romkens et al.,…     

Hydrogeological indications of recent movements of the earth's crust

Hydrogeologic indications of recent movements of the Earth's crust in two regions of North Tian-Shan have been studied. Comparison of ground-water level changes and variations of recent vertical movements according to benchmarks located near a well demonstrates their good correlation. The ground-water level varies out of phase with the direction of vertical movements. A correlation between level variation and seismic regime has been observed up to a well, located in a near-fault zone. In the region of the Kochkorskaya Depression, well observations show that against a background of constant increasing of level, sharp decays are observed. The latter can be connected with creep displacements. Hydrogeologic observations, together with periodic levelling enable us to study recent movements of the Earth's crust in detail.     

THE DISTRIBUTION OF PREFERENTIAL PATHS AND ITS RELATION TO THE SOIL CHARACTERISTICS IN THE THREE GORGES AREA, CHINA

To study the characteristics of the distribution of the preferential paths and the affecting factors in the Three Gorges area, four soil profiles were dug to observe the distribution of preferential paths in the Quxi watershed in the Yangtze River basin. The Morisita exponential test method was used to examine the distribution type of preferential paths. The physical properties and infiltration characteristics of the soil were also measured to evaluate their relationship to preferential paths. The results showed that in this area, preferential paths clustered and mainly distributed in the 80-100 cm soil layer, and along the interface between the weathered layer and semi-weathered layer. There were more non-capillary pores in the 83-110 cm layer than in the other layers. It can be derived that most non-capillary pores in this layer were preferential paths caused by geological processes and rotten plant roots. The percentage of coarse soil particles increased with the depth of the soil layer. In the deeper soil layer, the coarse soil particles helped the formation of preferential paths. The fastest steady infiltration rate was observed in the of 83-110cm layer, which is inferred to be due to the greater number of preferential paths.     

Strong motion displacement waveforms using 10‐Hz precise point positioning GPS: an assessment based on free oscillation experiments

The recently developed precise point positioning (PPP) technique permits to compute instantaneous coordinates of a GPS station relatively to distant reference stations and waveforms of ground displacements during strong motions at the 1 Hz level. This is another application of GPS, different from the computation of static coseismic movements or of accurate monitoring of dynamic displacements of structures using a static receiver and a nearby moving receiver (DGPS). Recently, earthquake ground displacement waveforms using 10‐Hz GPS data have also been calculated, but no independent evidence to assess their quality exists. To overcome this problem, we evaluated the output of 10‐Hz PPP results on the basis of supervised learning experiments. Semistatic and dynamic displacements (damped harmonic oscillations) of known characteristics of the order of a few centimeter were produced and were recorded by GPS, an accelerometer, and a robotic total station. Time series of instantaneous displacements were analyzed using different PPP techniques and were compared with reference (true) values derived from DGPS and the other sensors. Our analysis revealed that the PPP‐derived coordinates are contaminated by long‐period noise but they can display the details of semistatic displacements, while their short‐period component describes well the pattern of waveforms and spectra (at least up to 4 Hz) of dynamic displacements, with up to 20 mm accuracy for isolated points. These results indicate that 10‐Hz PPP‐GPS is useful for earthquake engineering and can safely be used to reconstruct waveforms of deflections of the ground and of various points on structures during strong motions. Copyright © 2014 John Wiley & Sons, Ltd.     

Temporal and spatial variation of infilling processes in a landslide scar in a steep mountainous region,Japan

The duration of the soil‐depth recovery needed for reoccurrence of shallow colluvial landslides at a given site in humid regions is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the rate of change in soil depth in landslide scars is therefore necessary to evaluate return intervals of landslides. Spatial variation in sediment transport at the Kumanodaira landslide scar in central Japan was investigated by field observations. Spatial distribution of the rate of change in soil depth was estimated using sediment transport data and geographic information system (GIS) analysis. Observations revealed that the timing of sediment transport differed for shallow and deep soil layers. Near‐surface sediment transport (mostly dry ravel and some shallow soil creep at depths ≤0·05 m) measured in sediment traps was active in winter and early spring and was affected by freezing–thawing; soil creep of subsoil (i.e. >0·05 m), monitored by strain probes, was active in summer and autumn when precipitation was abundant. Near‐surface sediment flux was estimated by a power law function of slope gradient. Deeper soil creep was more affected by relative location to the landslide scar, which influences soil depth, than by slope gradient. Our study indicated that the rate of soil‐depth recovery is high just below the head scarp of the landslide. Abrupt changes in the longitudinal slope topography immediately above, within and just below the head scarp became smoother with time due to degradation proximate to the landslide head scarp and flanks, as well as aggradation just below the head scarp. Copyright © 2014 John Wiley & Sons, Ltd.     

The characteristics of soil water cycle and water balance on steep grassland under natural and simulated rainfall conditions in the Loess Plateau of China

Large-scale vegetation restoration has been helpful to prevent serious soil erosion, but also has aggravated water scarcity and resulted in soil desiccation below a depth of 200 cm in the Loess Plateau of China. To understand the dynamic mechanism of soil desiccation formation is very important for sustainable development of agriculture in the Loess Plateau. Based on natural and simulated rainfall, the characteristics of soil water cycle and water balance in the 0–400 cm soil layer on a steep grassland hillslope in Changwu County of Shaanxi Loess Plateau were investigated from June to November in 2002, a drought year with annual rainfall of 460 mm. It was similarly considered to represent a rainy year with annual rainfall of 850 mm under simulated rainfall conditions. The results showed that the temporal variability of water contents would decrease in the upper 0–200 cm soil layer with the increase in rainfall. The depth of soil affected by rainfall infiltration was 0–200 cm in the drought year and 0–300 cm in the rainy year. During the period of water consumption under natural conditions, the deepest layer of soil influenced by evapotranspiration (ET) rapidly reached a depth of 200 cm on July 21, 2002, and soil water storage decreased by 48 mm from the whole 0–200 cm soil layer. However, during the same investigation period under simulated rainfall conditions, soil water storage in the 0–400 cm soil layer increased by only 71 mm, although the corresponding rainfall was about 640 mm. The extra-simulated rainfall of 458 mm from May 29 to August 10 did not result in the disappearance of soil desiccation in the 200–400 cm deep soil layer. Most infiltrated rainwater retained in the top 0–200 cm soil layer, and it was subsequently depleted by ET in the rainy season. Because very little water moved below the 200 cm depth, there was desiccation in the deep soil layer in drought and normal rainfall years.     

Relation of surface movements in West Bohemia to earthquake swarms

GPS observations in the Western Bohemia/Vogtland earthquake swarm region revealed indications of horizontal displacements of low amplitude, and no clear long-term trend in 1993–2007. On the other hand, in 1998–2001 there was relatively significant active movement along NNE-SSW oriented line that we called the “Cheb-Kraslice GPS Boundary” (ChKB), identical with an important limitation of earthquake activity. The most impressive were dextral (right-lateral) movements in the 1998–1999 period followed by reverse sinistral (left-lateral) movements in 1999–2000 that correlate with prevailing motion defined by fault plane solutions of the Autumn 2000 earthquake swarm. Before the February 2004 micro-swarm, two points located on opposite sides of the Mariánské Lázně fault showed extension in the order of about 7 mm in the same NNE-SSW direction of ChKB. The new NOKO permanent GPS station in Novy Kostel showed the peak-to-peak vertical changes up to 10 mm before and during the February 2007 micro-swarm. Annual precise levelling campaigns in the local network around Novy Kostel revealed regular vertical displacements during the 1994, 1997 and 2000 earthquake swarms. The points around the Novy Kostel seismological station showed uplift during the active periods, including the micro-swarm February 2004. However, no such indication was observed on levelling points in the period of the February 2007 swarm. Long-term vertical displacements depend on the same direction NNE-SSW (ChKB) as the GPS displacements. Both geodetic techniques have revealed oscillating displacements, GPS horizontal, and levelling vertical, rather than any long-term trends in the study period 1993–2007. The displacements exhibited significant spatial and temporal relation to tectonic activity (earthquake swarms) including their coincidence with the seismologically determined sense of motion along the fault plane during earthquakes.     

海河隐伏活断层探测中土壤气氡和气汞测量及其结果

在海河隐伏断裂的探测中,利用FD-3017RaA测氡仪和XG-4型测汞仪开展了土壤气氡和土壤气汞的测量工作。根据12条断层气测线的测量结果,结合人工地震探测资料,对断层气异常位置与断层位置的关系进行了分析;运用断层气异常强度与断层活动性的关系对海河断裂的活动性进行了研究,给出了海河断裂天津段的位置和活动性分段。研究结果表明,断层气方法不仅能给出断层的初步位置,而且能够用于断层的活动性初步分段,但断层气方法所给出的断层位置应是一个条带。经与人工地震探测结果对比分析,断裂位于这个条带内;根据土壤气氡测量结果,可将海河断裂分为东、西两段,且东段的活动性要强于西段。这种强、弱之分仅是一种相对结果,在判定断层是否为活断层方面还存在一定困难     

Modeling soil erosion using a spatially distributed model in a karst catchment of northwest Guangxi,China

Reliable assessment of the spatial distribution of soil erosion is important for making land management decisions, but it has not been thoroughly evaluated in karst geo‐environments. The objective of this study was to modify a physically based, spatially distributed erosion model, the revised Morgan, Morgan and Finney (RMMF) model, to estimate the superficial (as opposed to subsurface creep) soil erosion rates and their spatial patterns in a 1022 ha karst catchment in northwest Guangxi, China. Model parameters were calculated using local data in a raster geographic information system (GIS) framework. The cumulative runoff on each grid cell, as an input to the RMMF model for erosion computations, was computed using a combined flow algorithm that allowed for flow into multiple cells with a transfer grid considering infiltration and runoff seepage to the subsurface. The predicted spatial distributions of soil erosion rates were analyzed relative to land uses and slope zones. Results showed that the simulated effective runoff and annual soil erosion rates of hillslopes agreed well with the field observations and previous quantified redistribution rates with caesium‐137 (¹³⁷Cs). The estimated average effective runoff and annual erosion rate on hillslopes of the study catchment were 18 mm and 0.27 Mg ha^?1 yr^?1 during 2006–2007. Human disturbances played an important role in accelerating soil erosion rates with the average values ranged from 0.1 to 3.02 Mg ha^?1 yr^?1 for different land uses. The study indicated that the modified model was effective to predict superficial soil erosion rates in karst regions and the spatial distribution results could provide useful information for developing local soil and water conservation plans. Copyright © 2014 John Wiley & Sons, Ltd.     

Observations of urban snow properties in Calgary,Canada

Urban winter hydrology has garnered very little attention owing to the general notion that high‐intensity rainfalls are the major flood‐generating events in urban areas. As a result, few efforts have been made to research urban snow and its melt characteristics. This study investigates the characteristics of urban snow that differentiate it from rural snow, and makes recommendations for incorporating these characteristics into an urban snowmelt model. A field study was conducted from the fall of 2001 to the spring of 2002 in the city of Calgary, Canada. Snow depths and densities, soil moisture, soil temperature, snow albedo, net radiation, snow evaporation, and surface temperature were measured at several locations throughout the winter period. The combination of urban snow removal practices and the physical elements that exist in urban areas were found to influence the energy balance of the snowpack profoundly. Shortwave radiation was found to be the main source of energy for urban snow; as a consequence, the albedo of urban snow is a very important factor in urban snowmelt modelling. General observations lead to the classification of snow as one of four types: snow piles, snow on road shoulders, snow on sidewalk edges, and snow in open areas. This resulted in the development of four separate functions for the changing snow albedo values. A study of the frozen ground conditions revealed that antecedent soil moisture conditions had very little impact on frozen ground, and thus frozen ground very nearly always acts as a near impervious area. Improved flood forecasting for urban catchments in cold regions can only be achieved with accurate modelling of urban winter runoff that involves the energy balance method, incorporating snow redistribution and urban snow‐cover characteristics, and using small time steps. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of frozen soil and snow cover on cold‐season soil water dynamics in Tokachi,Japan

Despite the potential impact of winter soil water movements in cold regions, relatively few field studies have investigated cold‐season hydrological processes that occur before spring‐onset of snowmelt infiltration. The contribution of soil water fluxes in winter to the annual water balance was evaluated over 5 years of field observations at an agricultural field in Tokachi, Hokkaido, Japan. In two of the winters, soil frost reached a maximum depth of 0·2 m (‘frozen’ winters), whereas soil frost was mostly absent during the remaining three winters (‘unfrozen’ winters). Significant infiltration of winter snowmelt water, to a depth exceeding 1·0 m, occurred during both frozen and unfrozen winters. Such infiltration ranged between 126 and 255 mm, representing 28–51% of total annual soil water fluxes. During frozen winters, a substantial quantity of water (ca 40 mm) was drawn from deeper layers into the 0–0·2 m topsoil layer when this froze. Under such conditions, the progression and regression of the freezing front, regulated by the thickness of snow cover, controlled the quantity of soil water flux below the frozen layer. During unfrozen winters, 13–62 mm of water infiltrated to a depth of 0·2 m, before the spring snowmelt. These results indicate the importance of correctly evaluating winter soil water movement in cold regions. Copyright © 2010 John Wiley & Sons, Ltd.     

Relating aerial erosion,soil erosion and sub‐soil erosion to the evolution of Lunan Stone Forest,China

Stone forest (‘Shilin’ in Chinese) is a unique karst landform with a complex evolution process. Based mainly on the characteristics and interrelationships of sub‐soil, soil and sub‐aerial erosion in Lunan karst area, the authors develop a triplex erosion model to describe the evolution of stone forest, and apply it to examine the current development stage and the prospect of the Lunan Stone Forest. The study shows that sub‐soil corrosion, a basic driving force for the vertical scope of a stone forest, usually occurs within 10 m below ground surface but is observed to be most active within the top 2 m, which constitutes the best development zone for stone forest. Under modern climatic conditions, the tip of the stone pillars in Lunan karst area is lowering at a rate of 10·4 mm ka^?1, whereas the base of the stone pillars is deepening at 26·17 mm ka^?1. Therefore, the height of stone pillars is increasing at a rate of 15·77 mm ka^?1. Considering that soil erosion in the study area is as high as 650 mm ka^?1, the visible height of the stone forest is actually increasing at a rate of 639·6 mm ka^?1. However, the best evolution time for Lunan Stone Forest has already passed despite the fact that it is still growing taller at the present time. This is because the soil layer, which plays an extremely significant role in the heightening of stone pillars, is rapidly thinning at a rate of 623·83 mm ka^?1. Copyright © 2006 John Wiley & Sons, Ltd.     

RUNOFF GENERATION AND SOIL EROSION IN SMALL AGRICULTURAL CATCHMENTS WITH LOESS-DERIVED SOILS

Over a two-year period, rainfall, runoff and sediment output were measured in six small agricultural catchments (3–10 ha) in south Limburg (The Netherlands). These measurements were needed for validation of an erosion model for South Limburg (LISEM). In this paper, results of the measurements are presented and processes that determine surface runoff and sediment yield during winter and summer rainfall are identified. Before the start of the measurement programme, surface slaking and crust formation on the erodible loess soils were thought to be the main cause of overland flow and soil erosion in South Limburg. This was the starting point for soil conservation measures in the area. The measurement results discussed in this paper show that in some catchments much runoff occurred in winter and that soil moisture storage capacity may be just as important for runoff generation as infiltration capacity. Therefore, when modelling soil erosion and optimizing erosion control measures for South Limburg, runoff generation through Hortonian as well as through saturation overland flow must be considered.     

Temporal and spatial variations in periglacial soil movements on alpine crest slopes

This paper describes up to ten years of continuous monitoring of frost heave, creep and associated parameters on high mountain crest slopes in the Japanese and Swiss Alps, aiming to evaluate spatial and interannual variations in the rates and controls of soil movement. Shallow frost creep re?ecting diurnal frost heave activity dominates the crest slopes that lack a vegetation mat and have a thin debris mantle with good drainage. Seasonal frost heave activity can induce slightly deeper movement where ?ne soil exists below the depth reached by diurnal freeze–thaw penetration, although the shallow bedrock impedes movements below 20 cm depth. As a result, downslope velocity pro?les display strong concavity with surface velocities of 2–50 cm a^?1. The frost creep rates vary spatially, depending on the soil texture, slope gradient, frequency of temperature cycling across 0 °C and moisture availability during freeze–thaw periods. Soil movements recur in every freeze–thaw period, although with some interannual variations affected by the length of seasonal snow cover and the occurrence of precipitation during freeze–thaw periods. The Swiss Alps encounter more signi?cant interannual variations than the Japanese Alps, re?ecting the large variability of the annual snow regime. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of horizontal ground displacements in Avonside area,Christchurch from air photo,LiDAR and satellite measurements regarding pipeline damage assessment

Recent earthquakes show that pipeline damage is severe in the areas where permanent ground deformations (e.g., liquefaction zones) occur. Ground movement hazard to pipeline systems can be assessed by using ground displacement measurements around the location of pipelines. There are many different ways of measuring ground displacements after an earthquake occur. This paper compares displacements measured in Avonside area, Christchurch, NZ, by using four different ways with respect to their effects on pipeline damage assessments. They are air photo, satellite, high resolution light detection and ranging (LiDAR) surveys data presented at 4- and 56-m grids acquired before and after the M_w6.2 22 February 2011 earthquake. Avonside area was in the liquefaction zones of the 22 February 2011 earthquake. Where possible, benchmark measurements were also included in the comparisons. In this study, the focus was on asbestos cement and cast iron water pipelines as the length of the pipelines and the number of damages in the study area was much higher compared to other pipe materials, providing sufficient repair rate data passing the screening criteria to develop linear regressions. The correlations between pipeline damage and lateral ground strains were developed by calculating the horizontal strains from these four different type displacements. The comparisons show that satellite imagery is good for estimating total movements but not so good for estimating lateral strains and conversely LiDAR surveys are not so good for estimating total movements, but much better for estimating lateral strains. Hence, pipeline damage correlations with LiDAR calculated strains provide higher determination coefficient (r²) value. The results of comparisons are presented and discussed.