摘要:

AbstractMore than 200 weathering sites, in southern and central Sweden, representing different rock types and environments have been investigated. Field studies were complemented by thin‐section examination and laboratory simulation experiments. Research results in a classification of weathering forms in crystalline rocks in cool temperate climates. Special attention is paid to Holocene microweathering, facilitated because glaciation removed most old weathered material. Only minor forms, including surface colorations, mineral weathering, pitting and flaking, have been produced entirely during the Holocene. Where recent breakdown is observed, the primary reason must be sought in the geological history of rock. Holocene microweathering a few cm in depth is caused by a complex interaction between different weathering processes. Salt crystallization, however, seems important in areas that have experienced seashore conditions. Often the forms produced are as much the result of rock properties as of actual weathering processe

ISSN:1045-6740    

DOI:10.1002/ppp.3430030403

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCavity development in ice‐rich permafrost at Pangnirtung followed a large rainstorm and runoff event in 1984. The cavities evolved along permeable zones in sediments containing segregated ice lenses. Cavities promoted subsurface flow and incremental collapse of the ground surface. Once formed, cavities remained relatively stable where they were free to drain, and where the enclosing ground remained frozen and rigid support was provided. Some cavities closed by infilling with sediment or freezing water, or by deformation of the surrounding frozen ground. Other cavities were enlarged by thermo‐erosional piping, a process involving both thermal and mechanical erosion of frozen ground together with sufficiently rapid throughflow to prevent refreezing.A classification of cavities in permafrost permits qualitative appraisal of their stability with respect to the depth of zero annual temperature change and the degree of natural arching support. Assessment based on elastic plate theory indicates that seasonal temperature changes are important factors in destabilizing near‐surface cav

ISSN:1045-6740    

DOI:10.1002/ppp.3430030404

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo data sets were used to examine the fractal geometry of constituent time series. Soil temperature and soil water ionic concentration observations were collected in August 1991 at proximal sites at the Caribou‐Poker Creeks Research Watershed near Fairbanks, Alaska. The second data set contains thermal records of the 1984 active layer freezeback from Toolik Lake. Following Fourier transformation, log (variance) was plotted as a function of log (wavelength) and three parameters were generated: the exponent (S) of the power law fit to the variance spectrum, the Hausdorff‐Besicovitch Dimension (Dhb) and the Coefficient of Determination (R2). This procedure measures both the degree of roughness of a time series (Dhb) and the degree to which the time series approaches a ‘pure’ fractal condition (R2= 1.0). The Caribou‐Poker Creeks data set demonstrates that time series from different microenvironments can be discriminated in (R2,S) space. The thermal records from Toolik Lake show that, during formation of the isothermal ‘zero curtain’ layer, heat transfer is accomplished primarily by non‐conductive processes. The zero‐curtain effect is characterized by a ‘pink noise’ spectrum with strong cyclic elements, an increase inDhband a corresponding decrease inR2. The methods were applied here to a single probe, but confirm previous analyses employing apparent thermal diffusivity calculations and spectral comparisons requiring data

ISSN:1045-6740    

DOI:10.1002/ppp.3430030405

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430030406

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe morphology of the Weichselian Late Pleniglacial land surface in the Groote Peel nature reserve (southern Netherlands) is characterized by numerous circular to oval depressions. The depressions are up to 90 m wide and 3 m deep. Some are surrounded by low (50–100 cm) ridges. Two depressions were selected for detailed study. One, of aeolian origin, is shallow (less than 1 m), the underlying sedimentary units are undisturbed and the ridge surrounding it consists of horizontally bedded aeolian sand. The second, formed by the melting of an ice core, is deeper (3 m) and dissects older units. The ice lens probably formed during the Weichselian Late Pleniglacial. Ice segregation was favoured by a low topographic gradient, impermeable beds in the subsoil and poor drainage. After partial decay of the ice core, a remnant survived during the cold, arid conditions of the Beuningen deflation phase. Final melting of the ice core occurred after deposition of Late Pleniglacial aeolian coversand, at the onset of the Late Glacial climatic amelioration. Palynological analysis indicates that infilling of the ice‐core depression started in the Late Glacial Older Dryas and possibly even during Oldest Dr

ISSN:1045-6740    

DOI:10.1002/ppp.3430030407

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractCryoturbations have always provoked discussions on their origin. However, the sedimentary structures which result from the deformations differ according to the mechanism involved. Diagnostic characterization by sedimentary structure is especially suited to distinguish between deformations caused by cryohydrostatic and cryostatic pressure on the one hand and by periglacial loading on the other.

ISSN:1045-6740    

DOI:10.1002/ppp.3430030408

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA variety of active periglacial microforms have been identified in the vicinity of Tlaeeng Pass (3275 m a.s.l.) in the Lesotho Highlands. These include thufa (both earth and stone‐cored varieties), terracettes, stone polygons and patterned ground. Ground ice within the saturated zone of soil profiles is clearly evident during the winter season, and pebbles perched on needle ice up to 5 cm in length are common. Although possible relict periglacial landforms (such as nivation hollows and protalus ramparts) have been recorded in the area, their identification and, hence, associated climatic inferences is problematic.The presence of active features clearly indicates present‐day periglacial activity, with the variety of forms resulting from diurnal or seasonal freeze‐thaw cycles. Considering a widely accepted global decrease in temperature during the Quaternary, a severity of temperatures greater than what is experienced under present marginal periglacial conditions can be projected for the Lesotho Highlands. However, past moisture regimes are more difficult to project from present‐day features, and this problem is exacerbated by the general paucity of clearly defined diagnostic relic

ISSN:1045-6740    

DOI:10.1002/ppp.3430030409

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractDuring the IGU/IPA Symposium entitled ‘Periglacial Environments in relation to Climate’ (3–6 May 1991) prominent aspects of modern periglacial research in the Netherlands were presented in a field excursion. This paper highlights the Dutch Pleistocene periglacial environments within the framework of palaeoclimatology, sedimentology and geomorph

ISSN:1045-6740    

DOI:10.1002/ppp.3430030410

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:1045-6740    

DOI:10.1002/ppp.3430030402

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY