Pattern and rate of erosion inferred from Inca agricultural terraces in arid southern Peru

Earthworks of assumed age and their initial and current morphologies provide an ideal basis for developing and testing models for long-term landform erosion. Inca agricultural terraces abandoned at  1532 A.D in the drylands of southern Peru may be used to document morphological changes since the abandonment. The objective of this research is to determine the erosion pattern and process to estimate the erosion rate.The development of rills and channels on the Inca agricultural terraces is evidence for erosion by wash processes on slopes where the anchoring effect of vegetation is absent and loose material is available for removal. The pattern and amount of erosion from 1532–2005 A.D. is estimated by comparing elevation models of the observed morphology and reconstructed models of the original morphology of the Inca terraces. The results show that in areas of sediment accumulation surface elevation increased up to 0.5 m. Elevation lowering on the terrace treads was 0.7 m at maximum, and a temporally and spatially averaged lowering rate was 0.094 mm yr^− 1. This gives insights about how the rate of erosion occurs on currently disturbed lands in arid environments where soil resources are scarce and lands are prone to desertification.     

Lasting Legacies: Conservation and Communities at Huascaran National Park,Peru

This article uses a case-study approach to investigate the challenges of protected area (PA) management for Huascaran National Park in the Peruvian Andes. The park is analyzed by situating the timing of establishment of the park boundaries within the context of two historical Peruvian events: agrarian reform (1969) and an earthquake (1970). Interviews and narratives from community members and stakeholders associated with park delimitation and management were used for the study. Analysis of narratives revealed that the establishment of park boundaries, the legal definition used for the park, and land use restrictions contribute to diminished support for the park from surrounding communities. Community and national institutions negotiate the spatial boundary of conservation in Huascaran National Park while engaging with historical narratives that invoke environmental constraints and acts of resistance.     

Slope aspect, slope length and slope inclination controls of shallow soils vegetated by sclerophyllous heath—links to long-term landscape evolution

On upland Triassic sandstone slopes of the western Blue Mountains, nonswamp, sclerophyllous heath (shrub-dominated vegetation) on shallow soils is commonly found downslope and adjacent to sclerophyllous forest on deeper soils. Some consider heath—and thus shallow soils—as favouring west-facing slopes, which are expected to experience drier microclimates due to insolation, strong and desiccating winds, and severe summer fires. However, our analysis of extensive areas with heath on shallow soils, based on vegetation and topographic maps, and fieldwork of uplands with various degrees of dissection, suggests that aspect is a poor predictor of shallow soils. Rather, shallow soils and heath are found on short slopes and the lower segments of longer slopes with the latter significantly steeper than forested segments.The shallow–deep soil boundary, marked by contrasting modern vegetation structures, does not signify a catchment area threshold, and correspondingly, the vegetation patterns are not in balance with distributary catchment processes, as short slopes are mantled exclusively by shallow soils. Instead, the soil depth boundary represents the propagation of base-level lowering signals, which takes place not only by the headward retreat of knickpoints but also via increased lowering of slope segments adjacent to drainage lines. This leads to steep slopes immediately adjacent to canyons, narrow gorges, and small steep valleys, that are mantled by shallow, discontinuous soils undergoing rapid erosion. These steep slopes persist in the landscape for ≥ 10 My after upland stream rejuvenation until incision of more weatherable Permian sediments, underlying the Triassic cliff-forming sandstones, triggers rapid lateral expansion of gorges. Once shallowly mantled and steeper slopes adjacent to streams are consumed by gorge widening, slopes adjacent to wide gorge clifflines reflect former upland drainage patterns rather than the redirected flow to rapidly widening gorges. Hence, modern vegetation patterns reflect a significant phase of landform development, perhaps combined with enhanced erosion during the Last Glacial Period that is compounded by a humped soil production function on bedrock.     

Geomorphological characteristics of slope failures in northeast Viti Levu island,Fiji, triggered by Tropical Cyclone Winston in February 2016

The highways circumnavigating Viti Levu play a pivotal role in Fiji's socioeconomic development, and are a crucial link to transport aid during disasters. Slope failures triggered by heavy rainfall and tropical cyclones have led to considerable damage and fatalities along Viti Levu's main roads in the past. Knowledge of slope instability mechanisms is key for the successful identification and management of slope failure hazards, however, there is a paucity of such information for Fiji's main roads. Severe Tropical Cyclone (STC) Winston was the strongest cyclone on record to make landfall in Fiji and affected the Fiji Islands from the early hours of 20 February until 3 am, 21 February, 2016. We present a field reconnaissance examining the characteristics and mechanisms of slope failures induced by STC Winston along a 35 km stretch of the northern part of the Viti Levu's ring road, “Kings Road”. Approximately 61 distinct shallow, small‐scale slope failures were identified most of which were of a complex type and included earth and debris slides (planar and rotational) with a minor flow component. The trigger for the slope failures was the ~258 mm of rainfall in 24 hours after 30‐days of antecedent rainfall totalling 482 mm. This caused rapid increases in porewater pressures, especially at the contact of residual soils and the underlying weathered basement rock. Evidence of recurring slips along Kings Road indicates that contemporary slope instability is likely caused by elevated porewater pressure during high intensity rainfall events in clay‐dominated soils.     

Quaternary tectonics and large-scale gravitational deformations with evidence of rock-slide displacements in the Central Apennines (central Italy)

Eight cases of large-scale gravitational movements (with evidence of rock-slide type displacements) evolving close to Quaternary faults have been analysed in the Central Apennines. Geomorphological and structural surveys have defined the relationship between the gravitational displacements and the tectonically-controlled modifications of the landscape. The evolution of all the investigated cases has been conditioned by the presence of fault planes located along the mountain slopes. In most cases (Mt. Cefalone, Cima della Fossa, Villavallelonga, Casali d'Aschi, Gioia dei Marsi), the faults played or are playing a primary role in increasing the local relief and their activity represents the main geomorphic factor conditioning the gravitational movements. This kind of relationship has been observed along mountain slopes bordering depressions which have not been drained for most of their geomorphic history or have been characterised by an evolution of the hydrographic network that has been conditioned only by the local tectonic subsidence. In such cases, the gravitational movements develop in the footwalls of the faults. In other cases (Fiamignano, Pescasseroli) the faults have played a passive role, since they only bound the sliding masses and coincide with the surficial expressions of the sliding planes. Therefore, the gravitational displacements develop in the hangingwall of the faults. The evolution is conditioned by the incision of the hydrographic network in response to regional Quaternary uplift. The illustrated case studies provide a wide range of examples of the gravitational response of slopes to the modifications of the landscape due to linear and areal tectonics. The identification of the geomorphic traces of the large-scale gravitational movements along fault-controlled mountain fronts has implications for hazard, particularly for the evolution of the displacement. The quantitative analysis of the vertical displacements and data on the characteristics of the surface breaking during historical earthquakes demonstrate that along-fault offsets strongly increases where the unstable large-scale rock masses are located. Therefore, the large coseismic vertical offset may represent a major problem for the displacement of utilities and may represent a potential cause for the sudden and catastrophic evolution of the gravitational movement.     

Influence of structural framework on mountain slope deformation in the Maiella anticline (Central Apennines, Italy)

Relationships between tectonic framework and gravity-driven phenomena have been investigated in an area of the Central Apennines (Italy) characterised by high relief. The north–south, half-dome shaped Maiella anticline lies in the easternmost part of the Apennine fold-and-thrust belt. Its backlimb is bordered by the Caramanico Fault, a normal fault with a maximum downthrown of about 3.5 km that separates the western slope of the Maiella Massif from the Caramanico Valley. The southwestern Maiella area is affected by deep-seated gravitational slope deformation indicated by major double crest lines, down-hill and up-hill facing scarps, a pattern of crossing trenches, bulging at the base of slopes and the presence of different types of landslide and talus slope deposits.The onset and development of deep-seated gravitational slope deformations and the location of Quaternary, massive rockslope failures have been strongly influenced by the structural framework and tectonic pattern of the anticline. Deep-seated gravitational slope deformation at Mt. Macellaro–Mt. Amaro ridge has developed along the Maiella western, reverse slope in correspondence with the anticline axial culmination; it is bordered at the rear by a NNW–SSE oriented, dextral, strike-slip fault zone and has an E–W direction of rock mass deformation. Closer to the southern plunging area of the anticline, gravity-driven phenomena show instead a N–S and NW–SE direction, influenced by bedding attitude.3D topographic models illustrate the relationship between deep-seated gravitational slope deformation and massive rockslope failures. The Campo di Giove rock avalanche, a huge Quaternary failure event, was the result of an instantaneous collapse on a mountaine slope affected by a long-term gravity-driven deformation.     

Effects of environmental change on scree slope development throughout the postglacial period in the Chic-Choc Mountains in the northern Gaspé Peninsula, Québec

The combined study of present-day processes and stratigraphic data, has permitted the reconstruction of the dynamics of scree slopes of the northern Gaspé Peninsula throughout the postglacial period. In this region, liberated progressively from beneath an ice cover between 13,500 and 10,000 years BP, the scree slopes have to be seen as an integral part of a regional geosystem. Evolution of these slopes has been rapid, influenced by local paraglacial conditions (glacio-isostatic rebound, glacio-eustatic fluctuations, and re-equilibration of glacially over-steepened rockwalls) which operated against a backdrop of Late Glacial and Holocene climatic fluctuations. During the Younger Dryas and part of the Early Holocene period, as the foot slopes emerged from beneath the Goldthwait Sea, the basal part of several scree slopes advanced onto marine terraces as lobate rock glaciers, under the influence of a periglacial climate, characterised by permafrost. Many scree slopes continued to transfer debris downslope after regional establishment of a closed forest cover at ca. 7250 years BP. Forest colonisation in the early pre-emergent phase of the postglacial period was retarded, due to constant replenishment of the debris removed from the foot slopes by marine processes. In the later post-emergent phase, development of a complete forest cover has only been possible on slopes where the summit rockwall segment has been completely eliminated, a condition not yet fulfilled for many geomorphologically active scree slopes of the region. In fact, both of these paraglacial influences have been diachronous on a regional scale. Advance upslope of the forest front on the scree slopes appears to have been slow, difficult and subject to periodic regressions of possible climatic origin, as indicated by numerous buried soils in colluvial stratigraphic sequences, and for the past 150 years by dendro-ecological studies. Stratigraphic exposures, along with direct observation of slope events, have revealed the operation of a large variety of debris transfer processes, including niveo-aeolian sedimentation and frost-coated clast flows, the latter representing an important process first recognised on the scree slopes of Gaspésie.     

模糊坡位信息在精细土壤属性空间推测中的应用

坡位的空间渐变特征影响着小流域及坡面尺度上的土壤、水文、地貌等现象和过程,因此对精细尺度下的地理建模(如土壤空间信息推理)有重要作用。虽然目前已有多种模糊坡位信息定量提取方法,但所得到的模糊坡位信息还缺乏实际应用。本文以精细尺度下的土壤属性空间分布推测为例,对此展开探索。应用模型假设:(1)在小流域内,地形因素主导着土壤属性空间分布的变化;(2)典型坡位上对应分布着典型的土壤属性值,土壤属性与坡位之间存在协同变化关系。据此建立以模糊坡位信息对各类典型坡位上土壤样点属性值的加权平均模型,推测土壤属性的空间分布。模型应用于黑龙江省嫩江流域一个地形平缓的小区(面积约60 km²),通过一个以坡位典型位置作为原型的模糊坡位定量方法提取5类坡位(山脊、坡肩、背坡、坡脚、沟谷)的空间渐变信息,对土壤表层有机质含量的空间分布进行推测。推测结果通过研究区70个土壤采样点进行评价,以推测结果与评价样点集之间的相关系数、平均绝对误差、均方根误差作为定量评价指标,与使用常用地形属性的多元线性回归模型推测结果进行对比。评价结果表明,仅使用极少建模点的加权平均模型的推测结果优于多元线性回归模型的推测结果。     

Evolution stages of large deep-seated landslides at the front of a subalpine meridional chain (Maritime-Alps, France)

Studying long term-evolution of gravitational slope evolution is a key to understanding deep-seated landslide processes. This paper deals with three large Deep-Seated Landslides (DSLs) at a front of a subalpine meridional chain, on the “La Marbrière” slope near the town of Grasse (Alpes-Maritimes, France). The geological framework controlling the stability and morphology of the DSLs is associated with thick and tamped Triassic layers of mudstone with gypsum overlain by highly faulted Jurassic limestone. Gravitational deformation affects the entire slope, involving a movement of about 1.1 × 10⁸ m³ of rock material. It creates large disturbances in landscape morphology, such as scarps, counter-slope scarps, trenches and other typical gravitational morpho-structures. Geomorphological mapping coupled with deep electrical resistivity tomography (ERT) reveals a strong correlation between these morpho-structures and inherited brittle tectonic features. This observation relies on spatial and geometrical relations (on the surface and at the depth of more than 150 m, checked by ERT) between the most persistent fault and the gravitational morpho-structures. The specific distribution of the morpho-structures on the basis of their morphological typologies and variations in the stage of evolution of three DSLs provides an interpretation of their kinematics during the last 400 ka. It appears that soft substratums combined with inherited persistent anisotropies are key factors in the development of the DSLs. Indeed, outflow of mudstone due to the lithostatic pressure imposed by individual limestone compartments has led to general slope subsidence. Then, a progressive toppling of a rock mass may have led to the catastrophic rock collapse along bedding planes.The evolution of the DSLs can be divided into three distinct stages represented by three zones: a young collapse stage (zone 1), a pre-collapse stage (zone 2) and an old mature stage (> 400 ka, zone 3). As the DSLs occur on the same slope and in the same geological context, this area offers interesting perspectives for understanding factors controlling the long-term gravitational evolution of slopes.     

Character,Age, and Ecological Significance of Pleistocene Periglacial Slope Deposits in Germany

Periglacial slope deposits (PSD) of Pleistocene age are one of the most widely distributed sediment types in nonglaciated mid-latitude regions. As diamictons of different genesis (geli-solifluction, cryoturbation, eolian transportation) they have a wide range of physical, chemical and mineralogical characteristics which are mainly controlled by bedrock geology, including saprolite. This paper reviews concepts used in Germany to study PSD stratigraphy and describes the different PSD units encountered (Upper Head, Middle Head, Lower Head). The paper is relevant to the understanding of PSDs in other mid-latitude regions. Classical and new results concerning the age of PSDs show differences in the interpretation of Upper Head genesis. In terms of their ecological significance, case studies from eastern Bavaria illustrate the influence of PSDs on the character and intensity of slope hydrological processes as well as on the formation and distribution of soils. Presently important research questions include (1) the establishment of a genetically based classification of PSDs, (2) the intensification of dating studies on PSDs, and (3) the clarification of hydrological processes in PSDs.     

Numerical modelling of the gravity-induced destabilization of a slope: The example of the La Clapière landslide, southern France

A finite difference two-dimensional model with Hooke–Mohr–Coulomb properties and topography derived from the DEM are used to reproduce the La Clapière landslide. The principal factor defining the gravity-driven destabilization of the model is a gradual reduction in the cohesion. This reduction simulates a degradation of the material properties with time because of weathering/alteration processes. The inelastic deformation, fracturing, and faulting first occur at mountain scale and results in normal fault formation causing crest sagging. Later, the failure process is concentrated in the lower part of the slope and leads to the formation of a localized fault subparallel to the slope surface at a depth of ca. 100 m. This corresponds to the initiation of the La Clapière landslide and its propagation upslope. A slow crest sagging continues during the whole model evolution.     

三峡水库蓄水后荆江洲滩变化特征

目前对三峡水库蓄水后荆江河段的洲滩演变还缺乏完整认识。基于三峡水库蓄水前后枯水期遥感影像,分析了荆江洲滩的冲淤变化与分布及形态演变。结果表明,蓄水后荆江洲滩总面积持续冲刷减小,累计冲刷4.56 km²,大部分发生在蓄水后前6年（冲刷速率0.55 km²/a）。上、下荆江洲滩的冲淤演变存在差异性。上荆江洲滩总面积一直处于冲刷萎缩中,且其强度明显大于下荆江,累计冲刷6.46 km²;下荆江前期（2002-2009年）冲刷、后期（2009-2015年）淤增,累计淤1.90 km²。在冲淤分布上,上荆江凸岸滩持续冲刷萎缩,凹岸滩前期冲刷、后期略有淤增,心滩（洲）前期淤积增长而后期冲刷萎缩;下荆江主要是凸岸滩冲刷,凹岸滩和心滩（洲）有所发展。根据滩体位置活动和冲淤动态性,荆江心滩（洲）演变被划分为8种典型类型。在形态演变上,上荆江以凸岸突出滩体和边滩发育的凹岸滩冲刷显著,形态变化不大。下荆江凸岸滩上游弯侧冲蚀后退、湾顶退缩、下游弯侧淤积伸长,形态趋向低弯扁平化,在高弯曲特定河湾平面形态格局下凸岸冲刷—淤积过程延伸到相邻河湾凹岸,成为下荆江凹岸滩和心滩淤积发展的重要因素,但淤积一般不越过凹岸湾顶。     

基于旅游发展潜力的县域单元旅游空间功能区划探讨——以江苏省常熟市为例

区划是地理学的重要研究内容。从旅游发展潜力出发, 以江苏省常熟市为例, 探讨县域单元旅游空间功能区划方法。综合分析各个已有的区划, 并对其进行叠置和合并分析, 确定功能区的基本单元。从城镇影响、社会经济、交通可达、资源影响四个方面构建旅游经济发展潜力评价指标体系, 评价县域单元的旅游发展潜力, 发现常熟市旅游发展潜力呈现出以县城为中心的圈层空间结构, 并向南部突出。在此基础上, 评价各个基本单元的旅游发展潜力, 将其划分为重点发展区、引导发展区、限制发展区、不宜发展区四类功能区, 重点发展区和引导发展区依托县城优越的基础设施服务, 呈现出集中分布的特征。限制发展区和不宜发展区数量最多, 覆盖区域最大, 多分布在县域单元的外部, 距离县城相对较远, 旅游发展难度相对较大。