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Hanne H. Christiansen Ole Bennike Jens Bcher Bo Elberling Ole Humlum Bjarne H. Jakobsen 《第四纪科学杂志》2002,17(2):145-160
Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have provided the opportunity for an interdisciplinary approach to the investigation of Holocene glacial, periglacial, pedological, biological and archaeological conditions that existed during and after delta deposition. The raised Zackenberg delta accumulated mainly during the Holocene Climatic Optimum, starting slightly prior to 9500 cal. yr BP (30 m a.s.l.) and continued until at least 6300 cal. yr BP (0.5 m a.s.l.). Evidence of sea‐level change is based on conventional 14C dates of shells from the marine delta bottomsets, 14C AMS dating of macroscopic plant material from the foresets and of fluvial deposits. Arthropod and plant remains from 7960 cal. yr BP in the delta foresets include the oldest evidence of the arctic hare in Greenland and evidence of a rich herb flora slightly different from the modern flora. Empetrum nigrum and Salix herbacea remains indicate a summer temperature at least as high as today during delta deposition. Post‐depositional nivation activity, dated by luminescence, lichenometry and Schmidt Hammer measurements indicate mainly late Holocene activity, at least since 2900 yr BP, including Little Ice Age (LIA) avalanche activity. Pedological analyses of fossil podsols in the Zackenberg delta, including 14C AMS dating of selected organic rich B‐horizons, show continued podsol development during the Holocene Climatic Optimum and into the subsequent colder period of the late Holocene, until 3000–2400 yr BP. A Neo‐Eskimo house ruin found on the lower part of the delta, presently being eroded by the sea, is dated to AD 1800. It presumably was abandoned prior to AD 1869, and suggests that some of the last Eskimos that lived in northeast Greenland might have occupied the Zackenberg delta. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Determination of the rate and total amount of limestone pavement surface lowering is a critical issue in developing models of regional landscape change in limestone terrain. Erratic‐capped pedestals have frequently been used for this purpose but problems concerning definition and measurement of pedestal height, and the absence of a secure timeframe for erratic emplacement, have resulted in conflicting interpretations. We have used cosmogenic (36Cl) to establish the emplacement age of erratic boulders and the total amount of pavement surface lowering at sites in northwest England. Since erratic emplacement at 17.9 ka the limestone pavement has been lowered by 22–45 cm (average: 33 ± 10 cm), assuming lowering was continuous. Although indicating some spatial heterogeneity, the results contrast with earlier reported values based on the measurement of pedestal heights and inferred age for deglaciation. We consider that changes in climate and the character and duration of regolith covers to have been important influences in promoting surface lowering. It is argued that nivation (chemical and mechanical snow‐related processes) associated with several cool/cold periods is likely to have played an important role in surface lowering. Complicating factors associated with surface lowering (thickness and longevity of snow and regolith covers) are identified but as yet cannot be quantified. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Richard A. Shakesby John A. Matthews Mark S. Berrisford & Lindsey J. McEwen 《Geografiska Annaler: Series A, Physical Geography》1999,81(1):31-45
It is demonstrated that pronival (protalus) ramparts can be formed by a snow-push mechanism and need not accumulate in the conventional manner as a result of supranival processes. Ridges in pronival positions up to 1.2 m high and of unequivocal snow-push origin are described from two sites in Smørbotn cirque, Romsdalsalpane, southern Norway. The seven lines of evidence are: (1) parallel abrasion tracks on large boulders embedded in the substrate; (2) displaced surface and embedded clasts with proximal furrows; (3) corrugated (flute-like) substrate surfaces; (4) the sickle-shaped plan-form of the ridges; (5) generally asymmetrical ridge cross-profiles (shallow, concave proximal; steep, convex distal); (6) strong preferred orientations and dips of surface-embedded clasts on ridge proximal slopes; and (7) a subnival/pronival ridge comprising loosely packed diamicton forming along the contact zone between the snowbed and substrate. This evidence indicates ridge formation by snow sliding involving bulldozing of the substrate. Factors considered important in favouring snow push producing distinct pronival ramparts at the sites include: a maritime periglacial climate with heavy winter snowfall and rapid snow-firn conversion producing snow densities of up to 900 kg m–3 ; a deformable substrate with relatively small inputs of rockfall or avalanche debris; and a steep headwall susceptible to snow avalanching and hence enhanced snow supply. Consideration is given to the prospect that larger pronival ramparts can form incrementally by a snow-push mechanism. 相似文献
4.
Cryoplanation Terrace Orientation in Alaska 总被引：2，自引：0，他引：2
Frederick E. Nelson 《Geografiska Annaler: Series A, Physical Geography》1998,80(2):135-151
Exploratory analysis of the orientation of 303 cryoplanation terraces in interior and western Alaska lends tentative support to the hypothesis that these landforms develop through localized erosion related to spatial patterns of snow accumulation and ablation. Cryoplanation terraces exhibit orientation patterns similar to those of cirques in several regions of Alaska. In climatically continental east-central Alaska, cryoplanation terraces are developed preferentially on north-facing slopes and the frequency distribution of terrace orientation is similar to but less concentrated than that of glacial cirques. In south-central Alaska, both cirques and terraces have bimodal frequency distributions corresponding to generalized wind patterns that predominated during Pleistocene glaciations. In western Alaska, terraces and cirques have relatively diffuse patterns without preferred orientation. No clear relation is apparent between the orientation of cryoplanation terraces and their size or elevation, although this may be an artifact of the current inability to differentiate terraces by age. Data from the Eagle Summit/Mastodon Dome area in interior Alaska indicate a possible relation between snowline elevation and the concentration of terrace orientation. 相似文献
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长白山雪蚀地貌发育特征 总被引：1，自引：0，他引：1
在中国东北长白山广泛发育着雪蚀地貌，尤其以雪蚀洼和高夷高阶地最为多见。与世界其它地区相比，长白山发育的雪蚀地貌具有规模小，形成年代久，成因复杂等特点，此外，通过野外半定位观测发现，雪蚀洼地年下蚀作用存在着不均一性，本着重对上述方面进行论述。 相似文献
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Hanne Hvidtfeldt Christiansen 《地球表面变化过程与地形》1998,23(8):751-760
In the periglacial unconsolidated sediment landscape of Zackenberg in High Arctic NE Greenland, perennial and seasonal snowpatches dominate the geomorphological development in large areas and control the distribution of the vegetation. The existence and distribution of snowpatches and their associated landforms are mainly controlled by the dominating winter wind direction and the amount of snow precipitation, with aspect exerting much less influence. This makes them an important source of information on past environmental change, and knowledge of the combination of geomorphological processes and forms that result from their existence is thus essential. The main nivation processes are backwall failure, sliding and flow, niveo-aeolian sediment transport, supra- and ennival sediment flows, niveo-fluvial erosion, development of pronival stone pavements, accumulation of alluvial fans and basins, and pronival solifluction. The importance of failure, sliding and flow in the continuous retrogressive extension of nivation hollows and niches is emphasized under the term backwall failure. A morphological assemblage of landforms clearly demonstrates the direct nival sediment transfer link between the eroded nivation hollows, their associated meltwater eroded channels and the pronival alluvial fans or basins. All landform elements and their formative processes are integrated into a comprehensive model. © 1998 John Wiley & Sons, Ltd. 相似文献
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A Soil Chronosequence from Neoglacial Moraines in Western Norway 总被引：1，自引：0，他引：1
David J.A. Evans 《Geografiska Annaler: Series A, Physical Geography》1999,81(1):47-62
A soil chronosequence is presented based upon podzols developed on Holocene moraine crests in the Jardalen cirque complex, western Norway. Simple and inexpensive field and laboratory tests provide information on soil depth development, pH changes, silt/clay translocation and B-horizon reddening and thickness with age. Chronological control on historical moraine ages is provided by lichenometric dates, which support a 5 cm/100 year soil development rate for the first 700 years of pedogenesis. This initial rapid depth development tails off to a maximum rate of 0.06 cm/100 years between c . 1.5 ka and 10 ka BP based upon a Preboreal/Younger Dryas age for the oldest moraines and associated soils in the Jardalen cirque. 相似文献
8.
Cryoplanation terraces are elevated bedrock features resembling giant staircases, with alternating steep scarps and shallow sloping treads. These landscape-scale features have long been associated with periglacial environments, but the processes involved in their formation remain vaguely specified and contentious. The two leading hypotheses for the formation of cryoplanation terraces are centered on: (1) geologic structure; and (2) nivation-driven scarp retreat. The nivation-formation hypothesis invokes scarp retreat under erosion processes associated with late-lying snowbanks. To test whether cryoplanation terraces develop through scarp retreat, six relative weathering indices (fracture counts, Cailleux roundness, Cailleux flatness, Krumbein sphericity, rebound, and weathering rind thickness) were measured across well-developed terraces in unglaciated eastern Beringia (central and western Alaska) at Mt Fairplay, Eagle Summit, and Skookum Pass. Statistically significant differences in relative weathering indices detected through chi-square and multiple-comparison procedures indicate that material is less weathered closer to scarps, i.e. that these areas were more recently exposed than those distant from the scarp. Based on these findings, a refined model of time-transgressive cryoplanation terrace development through nivation-driven scarp retreat is proposed. This new qualitative model addresses the removal of weathered material from terrace treads down side slopes through piping and gravity-driven mass-wasting processes. © 2019 John Wiley & Sons, Ltd. 相似文献
9.
Kirsten Simonsen M. Sc. 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):26-35
Simonsen, Kirsten, 1973: Studies of household activity patterns and urban structure. Geografisk Tidsskrift 73: 26–35. København, juni 1, 1974. This Paper focuses upon the daily activity patterns of individuals and households. It gives a survey of the relevant literature and discusses the possible use of activity studies. Furthermore, it treats the interrelationship between activity patterns and environment and illustrates this by a case study from a Danish provincial town. 相似文献
10.
BY JULIO MUÑOZ JIMÉNEZ ARTURO GARCÍA ROMERO 《Geografiska Annaler: Series A, Physical Geography》2009,91(3):189-204
The purpose of this study was to determine plant distribution at a nivation hollow located in a Mediterranean high mountain area and to analyse the effects of snow cover, wind exposure, proximity to moisture and the characteristics of the substrate on the vegetation. We analyse these factors and interpret concurrent effects due to recent climate change.
The nivation hollow, called Ventisquero de la Condesa, is located at 2258 m a.s.l., 40°47'10"N and 3°58'35"W, in the Sierra de Guadarrama (Madrid, Spain). We established 579 small sample plots in the study area, and grouped them into 29 transects where snow duration, wind exposure, availability of meltwater, geomorphologic instability and surface rockiness were examined directly and indirectly. The types of plants and the number of individuals per species were registered for each plot to establish ecological affinities among the 28 distinguishable species. Six showed the highest level of chionophily while nine showed the lowest adaptation to snow cover duration. A statistical study incorporating other variables applied in the research revealed that wind exposure, moisture capture and the intensity of geomorphologic dynamics have a highly significant correlation with nivation, while surface rockiness is a virtually independent factor. Due to environmental changes caused by recent global warming, several plant species, especially adapted to survival in snow conditions, coexist in the hollow with saxicolous plants that have invaded the site from adjacent grass and shrublands. 相似文献
The nivation hollow, called Ventisquero de la Condesa, is located at 2258 m a.s.l., 40°47'10"N and 3°58'35"W, in the Sierra de Guadarrama (Madrid, Spain). We established 579 small sample plots in the study area, and grouped them into 29 transects where snow duration, wind exposure, availability of meltwater, geomorphologic instability and surface rockiness were examined directly and indirectly. The types of plants and the number of individuals per species were registered for each plot to establish ecological affinities among the 28 distinguishable species. Six showed the highest level of chionophily while nine showed the lowest adaptation to snow cover duration. A statistical study incorporating other variables applied in the research revealed that wind exposure, moisture capture and the intensity of geomorphologic dynamics have a highly significant correlation with nivation, while surface rockiness is a virtually independent factor. Due to environmental changes caused by recent global warming, several plant species, especially adapted to survival in snow conditions, coexist in the hollow with saxicolous plants that have invaded the site from adjacent grass and shrublands. 相似文献
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