摘要:

ABSTRACTRillenkarren found in the Karkonosze granite massif in SW Poland are described, and their origin, age and significance are discussed. They are 35–350 cm long, 5–30 cm deep and 10–50 cm wide. The depth:width ratio varies from 1:1 to 1:5. Karren occur on slopes of bornhardts and on large tors, which are probably elements of pre-Pliocene relief. They have never been discovered on surfaces of Pleistocene age and therefore are regarded as forms initiated in a greater past. Surficial weathering controlled by local differences in moisture has been the main formative process. Climatic interpretation of karren is difficult; it may only be said that they presumably have not formed in moderately humid temperate or periglacial climates. Karren are persistent landforms, the persistence being related to diversified weathering between flutings and intervening ridges.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880424

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTCertain slope failures in tropical environments have been shown to be suction controlled where soils are highly weathered, deep and permeable. No research has yet considered whether this phenomenon occurs in humid temperate environments, despite numerous papers on characteristic angles of natural slopes. In this paper two models are employed to assess whether hillslopes in humid temperate environments may be suction controlled. The first model, the resistance envelope model, provides an initial indication of the general hydrological conditions under which failure occurs. The second model, a physically-based coupled slope hydrology-slope stability model allows closer inspection of the hydrological mechanisms which govern slope failure. In 1988 a series of storms produced several shallow planar slope failures, in freely-draining, permeable soils on slopes in the Glen Livet Estate, Scotland. These provide a unique opportunity to test whether slope stability in humid temperate environments can be suction controlled. The two models, when applied to these slope failures, indicate the possibility that slopes may fail under unsaturated conditions, and that their stability is thus controlled by the minimum suction which may develop at the shear surface during high-magnitude storms.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880425

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880426

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTLake Babati in Tanzania is a small lake that has flooded three times in recent years,i. e.in 1964, 1979 and 1990. The floods caused considerable damage to the nearby town of Babati, particularly in 1990. Both fluctuating amounts of rainfall and changes in the landscape have been proposed to be flood-eliciting factors. However, an analysis of rainfall trends in the region, a water-balance model simulating lake levels under both forested and deforested- degraded catchment conditions, and a series of interviews with senior citizens, all indicate that changes in the landscape,i.e.deforestation and land degradation, induced the floods. No rainfall trend have been found that can explain the flood events.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880427

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTA wide range of temporal scales of variability exists in suspended sediment and turbidity records from proglacial meltwater streams. These variations and their causes are illustrated in this paper using data from the stream draining the Haut Glacier d'Arolla, Valais, Switzerland. The data include hourly pump-sampler suspended sediment data from June to September 1990; a quasi-continuous 24 hour record of turbidity and velocity sampled at 5 second intervals in July 1992; and 3-minute series of turbidity and velocity at various heights in the boundary layer sampled at 10Hz, also obtained in July 1992. The high-frequency measurements made in 1992 employed an active head, infra-red suspended solids monitor deployed in close proximity to a twin-axis, discoidal electromagnetic current meter. Data were analysed using a combination of statistical and deterministic (‘event structure’) modelling. Particular emphasis is placed on the parallel variation of turbidity and velocity on time scales of less than 1 second. Variability at this scale has been relatively neglected, but must be understood before turbidity monitoring programmes can be designed that involve sampling from the continuous variation of turbidity by averaging over 1060 seconds every 30–120 minutes, logging the data automatically, and calibrating the record using pump or hand held samplers. Fluctuations in suspended sediment concentration and turbidity are accounted for in terms of glacial-hydrological, channel-marginal, and flow-related controls whose significance varies with timescale, from the seasonal through the diurnal to the instantaneous. The results have implications for research designs employing turbidity meters as indicators of suspended sediment variation. Representative turbidities, and comparisons between meters, must consider time-averages scaled with respect to turbulence characteristics at particular locations. The possibility of interaction between more or less discrete transport events results in turbidity variation which cannot, at present, be satisfactorily predicted.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880428

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTNorth East Scotland is an area characterised by selective glacial erosion. In this study a steady-state maximum ice sheet model is used to calculate basal ice sheet temperatures for the bed of a former Scottish ice sheet similar in dimensions to that of the late Weichselian in this area. A transect from the centre to the margin of the ice sheet measuring 140 by 20 kilometres is used and the model is adapted to take account of patterns of convergence and divergence of ice flow caused by an irregular bed topography. This model predicts the development of zones of basal melting and ice streams along topographic depressions such as large valleys and cold based ice over adjacent interfluves. Geomorphological mapping from aerial photography and field survey shows that these contrasts in basal thermal regime coincide with evidence of glacial erosion and glacial protection respectively. The conclusion is that the overall pattern of ice sheet erosion can be explained by the pattern of modelled basal ice temperatures at the ice sheet maximum if convergence and divergence are included in the calculations.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880429

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTA small bedrock ridge called Cuff Cape, protruding from an ice field in the inner part of Granite Harbour, Victoria Land, Antarctica, carries a system of moraine ridges. Cuff Cape was during deglaciation bounded to the south by a terrestrial, slow-retreat ice margin and towards the north and west by a faster-retreat, marine-based ice margin. Based on studies of contemporary processes along the present ice margin, sediment facies states of logged trenches and the morphology of the moraines, it can be concluded that moraines on low altitudes are composed of sediments deposited in fluvial troughs and meltwater ponds along a frontal glacier apron. The sediments were primarily deposited as debris flow diamictons, generated from melted-out sediments from basal debris bands and sorted sediments deposited as traction load and suspended load sediments in the marginal ponds. These sediments were in a frozen state later glaciotectonically thrust and stacked into moraine ridges during minor readvance stages. The largest moraine, covering a narrow retreat zone, was formed along the terrestrial ice margin by means of push and stacking of frontal apron diamictons. This moraine also carries superimposed minor ridges along its proximal slope, suggesting frequent readvance stages. Based on a survey of Cuff Cape, carried out by the English Terra Nova expedition in 1910–1913, it can be concluded that the youngest moraine has been formed since then. The absence of lichen growth on the moraines also suggests that they are of a very recent age.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880430

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTThe paper presents a brief review of contemporary knowledge concerning the development of cryoplanation terraces and their genetic equivalents—the cryoplanation summit flats. It is based mainly on results from Yakutia, where under present-day and Pleistocene permafrost conditions, these features are broadly distributed in upland and low mountain areas. The author shares the opinion of the majority of geomorphologists that, in the formation of cryoplanation terraces, processes of the parallel retreat of steeper slope segments were of main significance. The down-wearing of the surface appears to be an accompanying process. However, for better understanding of this serious problem long-term monitoring and measuring of the rate and the nature of slope processes on frost-riven cliffs and scarps as well as on the terrace treads in various physico-geographical and geological environments are necessary.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880431

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor