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1.
Arctic tundra surfaces are dominated by a variety of patterned ground forms. Whereas a large number of studies have described morphology, structure and processes of patterned ground, few have monitored detailed patterned ground dynamics and subsurface environments continuously. We applied electrical resistivity tomography (ERT) to understand near‐surface conditions of two types of patterned ground, ice‐wedge polygons and mudboils in Svalbard, where periglacial processes associated with permafrost are intensively monitored. Automated monitoring shows surface movement characterized by annual cycles of frost heave and thaw settlement, the amounts and rates of which are influenced by the intensity of ice segregation. A time series of ERT shows (1) a distinct resistivity boundary delimiting the active‐layer depth, (2) seasonal variation in resistivity controlled by thermo‐hydrological dynamics and (3) spatial variation in resistivity reflecting desiccation in summer and intensive ice segregation in winter. These results demonstrate ERT as a useful complementary technique for monitoring active‐layer depths and near‐surface hydrological conditions at periglacial patterned ground sites, where automated soil thermal and moisture measurements are limited.  相似文献   

2.
Soil‐forming processes and soil development rates are compared and contrasted on glacial deposits in two adjacent and coeval valleys of the Quartermain Mountains, which are important because they display Miocene glacial Stratigraphy and some of the oldest landforms in the McMurdo Dry Valleys. More than 100 soil profiles were examined on seven drift sheets ranging from 115 000 to greater than 11.3 million years in age in Beacon Valley and Arena Valley. Although the two valleys contain drifts of similar age, they differ markedly in ice content of the substrate. Whereas Arena Valley generally has ‘dry‐frozen’ permafrost in the upper 1 m and minimal patterned ground, Beacon Valley contains massive ice buried by glacial drift and ice cored rock glaciers and has ice‐cemented perma‐frost in the upper 1 m and considerable associated patterned ground. Arena Valley soils have twice the rate of profile salt accumulation than Beacon Valley soils, because of lower available soil water and minimal cryoturbation. The following soil properties increase with age in both valleys: weathering stage, morphogenetic salt stage, thickness of the salt pan, the quantity of profile salts, electrical conductivity of the horizon of maximum salt enrichment, and depth of staining. Whereas soils less than 200 000 years and older soils derived from sandstone‐rich ground moraine are Typic Anhyorthels and Anhyturbels, soils of early Quaternary and older age, particularly on dolerite‐rich drifts, are Petronitric Anhyorthels. Arena Valley has the highest pedodiversity recorded in the McMurdo Dry Valleys. The soils of the Quartermain Mountains are the only soils in the McMurdo Dry Valleys known to contain abundant nitrates.  相似文献   

3.
This paper interprets a stone‐banked lobe on the upper western face of Mt Rufus, at an altitude of 1380 m in western Tasmania, Australia. The morphology of the deposit resembles that of a solifluction lobe. Field observations show vertical and downslope movement of pebbles, cobbles and small boulders over a single winter season. The movement is largely related to frost pull (10–15 cm) and shallow freeze–thaw processes promoting the downslope (up to 50 cm yr–1) creep of material and the accumulation of coarse clasts at the lobe riser. The climate of Mt Rufus is strongly maritime and this is reflected in the limited duration and depth of penetration of frozen ground at this site during the 2013 winter. Despite the relatively mild climatic conditions, freeze–thaw processes are clearly the dominant geomorphic force operating at the site. These findings support observations of active stone‐banked lobes on sub‐Antarctic islands where intense freezing is absent. Both there and at Mt Rufus, movement is dominated by freeze–thaw processes operating in the upper c. 20 cm of the regolith. These are typical landforms of marginal freeze–thaw settings.  相似文献   

4.
The White Mountains, astride the California-Nevada stateline, are the highest and westernmost of the Great Basin ranges. This range was extensively glaciated during the Quaternary Period. Glacial landforms and scattered erratics were identified in the field using primarily morpho-and lithostratigraphic criteria, and mapped on aerial photographs and topographic maps. Topographic characteristics of the glacial deposits were analyzed using standard statistical procedures. A sequence of glacial deposits was identified in terms of six glacial stages, these glaciations named according to type site, and relative ages inferred. With the exception of perched Stage I (early) deposits along the range crest, reconstructed equilibrium-line altitudes and elevation of the glacier termini increase to the present, with glacier length and inferred size decreasing through time. Preliminary data suggest that weathering and pedogenesis are also progressive, though environmental gradients mask some of these distinctions between deposits. It is hypothesized that the White Mountains have a similar glacial chronology to the adjacent Sierra Nevada, but that with the intensification of the Sierran rainshadow during the Quaternary, the extent of glaciation in the White Mountains apparently decreased through time owing to regional tectonic uplift. This had led to the preservation of a more complete sequence of glacial deposits than in the Sierra Nevada, making the delineation of multiple mid-Quaternary events possible in many valleys. Further radiometric and chronometric dating of these deposits is in progress. [Key words: Glaciation, Quaternary, glacial geomorphology, White Mountains, California, Nevada.  相似文献   

5.
All periglacial and glacial landforms investigated in the Northern Foothills have a very thin active layer (0.1–0.3 m thickness) overlying a thin permafrost layer, characterised by electrical resistivities ranging between 13 and 50 kΩm and by different thicknesses. Below this surficial layer, different types of ground ice (with a resistivity range from 8000 to 0.1 kΩm) were detected. These different types of ground ice permitted ice-cored rock glaciers to be distinguished from ice-cemented rock glaciers, subsea permafrost to be identified in some raised beaches, and other interpretations to be suggested about a debris-covered glacier. These results have been obtained by vertical electrical soundings (VES) carried out in ice-free areas of the Northern Foothills, near Terra Nova Bay Station during the tenth national Italian expedition in Antarctica (1994–1995). In these areas on the basis of previous geomorphological research, some landforms such as rock glaciers, raised beaches with patterned ground and debris-covered glaciers were chosen to carry out the VES. The electrical prospection can be considered a good means for understanding the origins of landforms in ice-free areas of Antarctica and for making a contribution to the palaeoenvironmental reconstruction of this continent.  相似文献   

6.
Traditional methods of tracking soil movements may be unreliable in soils containing a large proportion of organic matter owing to the composition and mechanical properties of peat. A simple, inexpensive, and reusable “anchored” target can be used to monitor both vertical and horizontal components of soil movement in fibrous peat. The target is unlikely to be affected adversely by flooding, frost heave, or animal disturbance, and is applicable to a wide range of geomorphic problems in peatlands. [Key words: frost heave, peat, peat landforms, soil movement, survey targets.]  相似文献   

7.
Gurney, S.D. & Hayward, S. 2015. Earth hummocks in north-east Okstindan, northern Norway: Morphology, distribution and environmental constraints. Norsk Geografisk Tidsskrift–Norwegian Journal of Geography. ISSN 0029-1951.

Earth hummocks (also termed pounus or thúfur) are a common form of periglacial non-sorted patterned ground. The study objectives were to determine the morphology, distribution and development on slopes of earth hummocks in north-east Okstindan, Norway, an area with many hummocks but few documented accounts. The methodology involved detailed geomorphological mapping and precise measurement with a profileometer. The internal structure of the hummocks was investigated through excavations and sediment sample analyses. Fourteen sites with well-developed earth hummocks (accounting for over 650 individual hummock forms) were investigated. The sites have an average altitude of 750?m and occur on slopes with an average gradient of 7°. The hummock heights are in the range 0.11–0.52?m and their diameters 0.7–1.5?m, although coalescent forms are up to 5?m in length. The hummock morphology is characterised by a variable plan form, asymmetry with respect to upslope and downslope forms, downslope elongation, coalescence, and superimposed microtopography. The hummocks’ distribution appeared to have been controlled by the existence of a frost-susceptible ‘host’ sediment, but moisture availability and topographic position played a role. The authors conclude that differential frost heave and vegetation cover stability are critical for the hummocks’ longevity in the studied landscape.  相似文献   

8.
Block fields have developed on gently graded uplands of granite and gneiss on central and southern Melville Peninsula. The location of block fields is not controlled by elevation, but rather by areas covered by cold–based ice during the last glaciation. Block fields consist either of angular boulders, sorted circles 3–4 m across having blocky rims and central areas of weathered grus, concentrations of openwork boulders, or in the southeast, of immature bouldery till. The block fields are primarily relict features predating the last glaciation, produced by weakening of bedrock by weathering along joints, followed by frost heave, although some block fields have been modified by meltwater from regional glacier down–wasting. Frost processes are active in the modern environment but the extent of riven bedrock and the size of recent patterned ground forms on postglacial surfaces are insufficient to account for the forms in the block fields.  相似文献   

9.
Although snow is known to influence landform genesis and distribution, the spatial associations between snow and landforms within particular cold regions has received limited research attention. We present a case study from the high Drakensberg of southern Africa, comparing the contemporary spatial pattern of longest-lasting cold-season snow patches with the distribution patterns of active and relic cold region landforms. Two 30 m resolution sets of TM images dated 3 and 19 August 1990 and a DEM were used to demonstrate the geographic trends of snow patch depletion during late winter. Geomorphological phenomena with known coordinates were then incorporated into the GIS. The spatial distribution of several periglacial land-forms (earth hummocks, stone-/turf-banked lobes, block deposits, large sorted patterned ground) coincides with topographic positions that limit snow accumulation. However, the strong spatial association between longest-lasting snow patches and palaeo-moraines implies substantial snow accumulation at some high altitude south-facing sites during the last glacial cycle.  相似文献   

10.
Lunar landforms are the results of geological and geomorphic processes on the lunar surface. It is very important to identify the types of lunar landforms. Geomorphology is the scientific study of the origin and evolution of morphological landforms on planetary surfaces. Elevation and relief amplitude are the most commonly used geomorphic indices in geomorphological classification studies. Previous studies have determined the elevation classification criteria of the lunar surface. In this paper, we focus on the classification criteria of the topographic relief amplitude of the lunar surface. To estimate the optimal window for calculating the relief amplitude of the lunar surface, we use the mean change-point method based on LOLA (Lunar Orbiter Laser Altimeter) Digital Elevation Model (DEM) data and SLDEM2015 DEM data combining observations from LOLA and SELenological and Engineering Explorer Terrain Camera (SELENE TC). The classification criterion of the lunar surface relief amplitude is then determined according to the statistical analysis of basic lunar landforms. Taking the topographic relief amplitudes of 100 m, 200 m, 300 m, 700 m, 1500 m and 2500 m as thresholds, the lunar surface is divided into seven geomorphic types, including minor microrelief plains (< 100 m), minor microrelief platforms [100 m, 200 m), microrelief landforms [200 m, 300 m), small relief landforms [300 m, 700 m), medium relief landforms [700 m, 1500 m), large relief landforms [1500 m, 2500 m) and extremely large relief landforms (≥ 2500 m). The minor microrelief plains are mainly distributed in the maria and the basalt filled floors of craters and basins, while the minor microrelief platforms are mainly in the transition regions between the maria and highlands. The microrelief landforms are mainly located in regions with relatively high topography, such as wrinkle ridges and sinuous rilles in the mare. The small relief landforms are mainly scattered in the central peak and floor fractures of craters. The medium relief landforms are mainly distributed in the transition regions between crater floors and crater walls, between crater walls and crater rims, between basin floors and basin walls, and between basin walls and basin rims. Large and extremely large relief landforms are mainly found along crater walls and basin walls. The classification criteria determination for assessing lunar surface relief amplitude described in this paper can provide important references for the construction of digital lunar surface geomorphology classification schemes.  相似文献   

11.
月球地貌是月球表面发生的地质和地貌过程的结果,月球地貌单元的划分和等级分类体系的构建是月球地貌学研究的基础,也是月球地貌图制图的基础和关键科学问题。地貌学是研究形态和成因的科学,高程和起伏度是最基本的地貌指标。本文基于LOLA（Lunar Orbiter Laser Altimeter） DEM数据以及LOLA和SELENE TC（Terrain Camera）融合的DEM数据（SLDEM2015,文中简称SLDEM）,利用均值变点法确定月表起伏度计算的最佳窗口,并以起伏度100 m、200 m、300 m、700 m、1500 m及2500 m为阈值将月球表面分为微起伏平原（< 100 m）、微起伏台地[100 m, 200 m）、微小起伏丘陵[200 m, 300 m）、小起伏山地[300 m, 700 m）、中起伏山地[700 m, 1500 m）、大起伏山地[1500 m, 2500 m）及极大起伏山地（≥ 2500 m）地貌7个类型。划分结果显示：微起伏平原主要分布在月海平原区域、部分有玄武岩充填的撞击盆地的盆底区域以及撞击坑坑底区域;微起伏台地主要分布在月海和月陆区域的交界区域;微小起伏丘陵主要分布在月溪和皱脊等构造单元区域;小起伏山地主要分布在撞击坑中央峰及坑底断裂区域;中起伏山地主要分布在撞击坑坑底和坑壁过渡区域、撞击坑坑壁和坑缘过渡区域、撞击盆地盆底与盆壁过渡区域以及盆壁与盆缘过渡区域;大起伏和极大起伏山地主要分布在撞击坑坑壁区域及撞击盆地盆壁区域。本文确定的月表起伏度分级标准可以对月表数字地貌分类体系的构建和月球地貌图集的编研提供定量标准和重要参考。  相似文献   

12.
Miska Luoto  Jan Hjort 《Geomorphology》2006,80(3-4):282-294
Numerical studies of earth surface processes in relation to their environment are one of the central topics in physical geography. However, collinearity between explanatory variables and spatial autocorrelation can hinder the detection of key environmental correlates underlying response–explanatory variables' relationships identified by traditional regression methods. Moreover, conclusions about the potential importance of environmental variables have generally made on analysis conducted only at one spatial scale (resolution). In this study, a variation partitioning method provided a framework to obtain new insights into the relative roles of different factors determining patterned ground activity at multiple spatial resolutions. The variation in the distribution of the sorted and non sorted patterned ground was decomposed into independent and joint effects of relief, soil and spatial variables (geographical location) based on a multi resolution system of 1 ha, 25 ha and 100 ha cells covering in total 100 km2 of a subarctic landscape in northern Finland.The independent effects of relief and soil variables captured the largest fraction of the variation in the non-sorted patterned ground distribution, while relief had a major contribution for sorted patterned ground activity. The independent effect of spatial autocorrelation on sorted patterned ground was higher than that on non-sorted patterned ground. However, a considerable amount of variation in the distribution of both patterned ground types was accounted for by the joint effects of explanatory variables and may thus be causally related to two or all three groups of variables. Our analyses produced often contradicting results at different resolutions. Consequently, this has substantial implications for the study of geomorphological systems, since the choice of resolution can have a major effect on the inferences of analyses. Our results draw attention to the roles of resolution and spatial autocorrelation in the study of geomorphological systems.  相似文献   

13.
Tree uprooting plays an important role in hillslope evolution. The geomorphological impact of tree uprooting after a foehn wind occurrence, in December 2013 in the Tatra Mountains, was investigated. Geomorphological mapping was conducted in three watersheds. Additionally, in one of the watersheds, 459 windthrow pits were measured, in an area of 6.4 ha. The mean volume of a pit was 2.41 m3, and the mean surface area was 5.47 m2. 3.9% of the area was affected by windthrow pits, however locally the magnitude of changes was significantly higher, reaching up to 14.5% of the surface area. Slope inclination weakly influenced the effects of uprooting, and a decrease in the average depth of pits on steep slopes was observed. Individual windthrow pits (five cases) initiated the activity of geomorphological processes, and two cases of periodic springs were noted. Changes in the relief of small landforms caused by tree uprooting were documented. Windthrow creation facilitated the delivery of the soil material from the slopes into the channels.  相似文献   

14.
靳鹤龄  董光荣 《中国沙漠》2001,21(4):367-373
和田河是典型的干旱荒漠河流,也是塔里木盆地惟一南北向横贯塔克拉玛干沙漠的河流,流域的第四纪沉积以风成相与河流相冲洪物为主,其厚度达到250m以上,据其沉积特征推断时代为中更新世。18 ka MP以来麻扎塔格山下60km处河流向东摆动了3次,形成了三道古砂堤,造成河流摆动的原因是新构造运动、强烈的风沙活动和河流季节变化,河流及其摆动对沙漠及沙漠地貌影响主要表现在两方面：一是给沙漠及其风沙地貌发育提供丰富的碎屑物质;二是控制风沙地貌发育的活动性,并抑制了风沙地貌向高大复合沙山发育的速度。  相似文献   

15.
《自然地理学》2013,34(2):170-182
The enigmatic DeKalb mounds in north-central Illinois, United States, are oval, inactive hillocks of Wisconsinan age. They have heights up to 5 m, lengths up to 1 km, and are composed either of till and lacustrine sediment with a thin cap of loess, or entirely of outwash. They are underlain by one till member within a large depression that is flanked by higher, elevated, morainic till members. Different origins have been proposed for the DeKalb mound field but the only previous in-depth study identified them as pingo remnants, presumably due to the degradation of significant ground ice and permafrost. However, the investigators who reported this viewed their own hypothesis as problematical. These problems can be resolved by correlating the relict Illinois landforms to relict glacial landforms that show similar morphologies and field relationships in Saskatchewan, Canada, and North Dakota, United States. In this study, the DeKalb mounds are presumed to have developed from an intricate set of glacial dead-ice and mass movement processes. This reinterpretation reflects a range of either discontinuous permafrost or negative permafrost within the paleoenvironment.  相似文献   

16.
Jake E. Haugland   《Geomorphology》2004,61(3-4):287-301
Chronosequences of 250 to 130 years were established on two late Holocene glacier forelands in the Jotunheimen region of southern Norway. Patterned features occurring within chronologically established time units were studied. Young patterned features, forming 10–20 years after deglaciation, are frost active. Vegetation cover is minimal within the young patterned features, consisting of bryophytes/organic crusts. Soil development within patterned ground is also minimal/absent because frost action retards horizonization. With time and distance from the glaciated ice margin, frost activity declines within the patterned features, suggesting that a thin, active “periglacial zone” exists near the ice margin. Initially, frost activity decreases at the borders of the features with the centers stabilizing later in time. This results in fine-scale soil heterogeneity and variations of soil development. Fine-scale pedogenic development is first encountered at the borders of patterned ground that has developed on terrain exposed since the 1930s, yet soil development is predominantly absent at the centers of patterned ground. With time and distance from the ice margin, frost activity declines and allows patterned features to homogenize from border to center positions in regard to soil characteristics. Across the chronosequences, soils within patterned features pedogenically follow previous soil chronosequence studies, evolving from USDA classifications of Entisols into Inceptisols. Frost disturbance within patterned ground, however, produces a lag effect, that results in longer periods of time for pedogenesis to occur and thinner soils than that of the surrounding terrain.  相似文献   

17.
南极亚极地冰缘环境中分选环边缘砾石砾径与其斜度坡度呈正相关,可用y=-5.0606+1.42828x表示。若砾径小于15厘米时符合y=-6.15778+1.56273x方程,大于15厘米时则符合v=-17.1913+1.97643x,说明当分选环边缘砾石砾径大于15厘米时摩擦阻力和砾石间结合力迅速增大。分选环中心表面小砾石运动具有周期性,总的位移是向边缘。中心表层冻胀力比深层大,中心冻胀强,向四周逐渐减小。体积较大的物体受冻胀力影响大。  相似文献   

18.
《Geomorphology》2005,64(1-2):67-85
Snow cover reduces cosmogenic nuclide production rates in bedrock. Corrections for snow cover can be more than 10% in mountainous, mid-latitude regions where many glacial chronologies have been constructed using cosmogenic nuclide surface dating of landforms. Most published snow corrections use historic climate data of limited duration that are not likely to reflect adequately the full range of snow conditions over the time of exposure. We present a model for describing the impact of snow burial on long-term exposure histories of landforms. The model applies an energy balance approach to snowpack evolution and incorporates both historic and long-term climate proxy data. Attenuation of cosmogenic fast neutrons is modeled alternatively as a simple exponential decrease with increased shielding or as a thin surface layer with constant production followed by an exponential decrease with increasing depth. The choice of attenuation model has little effect on the modeled results for the Cairngorms but will have a more significant effect in regions characterized by thinner, less dense snowpacks. Spatial variability in snow cover is modeled as a function of elevation only, ignoring local variability in snow accumulation as a result of slope aspect, wind redistribution and local topography. Thus, model results reveal general spatial and temporal trends in snow shielding effects, rather than site-specific corrections.Applications to data from the Cairngorm Mountains of Scotland show that the constant-plus-exponential (CPE) production rate-depth profile reduces but does not eliminate snow-shielding effects. Under present-day conditions, snow at 900 m in the Cairngorm Mountains reduces average production rates by 6% using the CPE profile and 9% with the exponential profile (EP). Long-term climate simulations from 15.5 ka through today produce larger snow shielding effects, mainly because they predict an increased proportion of precipitation as snowfall during the Younger Dryas. At 900 m, this long-term simulation reduces average cosmogenic isotope production rates by 12% (CPE) and 14% (EP). These results indicate that snow-shielding corrections based on historic climate records may be a potential source of systematic error in midlatitude mountainous regions.  相似文献   

19.
In the mountain area of Swedish Lapland, landforms with semicircular or horse‐shoe ridges encircling hummocky ground occur. They are interpreted as landslide or avalanche deposits directly upon, from or adjacent to down‐wasting ice. Since they are restricted to the vicinity of fault scarps in the Pärvie fault system the releasing factor is suggested to be displacement of bedrock blocks or related seismic activity.  相似文献   

20.
One of the major goals of geomorphology is to understand the rate of landscape evolution and the constraints that erosion sets on the longevity of land surfaces. The latter has also turned out to be vital in modern applications of cosmogenic exposure dating and interpretation of lichenometric data from unconsolidated landforms. Because the effects of landform degradation have not been well documented, disagreements exist among researchers regarding the importance of degradation processes in the dating techniques applied to exposures. Here, we show that all existing qualitative data and quantitative markers of landform degradation collectively suggest considerable lowering of the surface of unconsolidated landforms over the typical life span of Quaternary moraines or fault scarps. Degradation is ubiquitous and considerable even on short time scales of hundreds of years on steeply sloping landforms. These conservative analyses are based entirely on field observations of decreasing slope angles of landforms over the typical range of ages in western North America and widely accepted modeling of landscape degradation. We found that the maximum depth of erosion on fault scarps and moraines is on average 34% of the initial height of the scarp and 25% of the final height of the moraine. Although our observations are limited to fault scarps and moraines, the results apply to any sloping unconsolidated landform in the western North America. These results invalidate the prevailing assumption of no or little surface lowering on sloping unconsolidated landforms over the Quaternary Period and affirm that accurate interpretations of lichen ages and cosmogenically dated boulder ages require keen understanding of the ever-present erosion. In our view, the most important results are twofold: 1) to show with a large data set that degradation affects universally all sloping unconsolidated landforms, and 2) to unambiguously show that even conservative estimates of the total lowering of the surface operate at time and depth scales that significantly interfere with cosmogenic exposure and lichen dating.  相似文献   

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