摘要:

AbstractDuring the 1974 rainy season gullies of the order of 150–300 m long were active on the flanks of fixed Pleistocene dunes in the vicinity of Janjari, central Niger. The gullies terminate on small (0.5–1 × 104m2) alluvial fans, where sand deposition had occurred below the intersection point. Gully activity was probably the result of a particularly severe storm. Comparison between fixed dunes subject to differing climatic conditions suggests that gullying and alluvial fan formation may be characteristic of a restricted morphoclimatic

ISSN:0360-1269    

DOI:10.1002/esp.3290030202

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThis study reveals that the Quaternary mantle of reworked Kalahari Sands undergoes a post‐sedimentary composite process at the archaeological site of Gombe (Kinshasa, Zaïre). There is a biological activity which consists of an upworking of soil particles, mainly by termites and worms. This causes a diminishing dry volume weight of the sediment. In response, the mantle reconsolidates.When the soil surface is horizontal, the particles which are not brought up will sink down in the soil profile as a result of the reconsolidation. When the soil surface is inclined, it is only the resettlement of the sediment which can give rise to creep, caused by wetting and drying. Creep of the dead mineralogical material alone seems to be very improbable once the structure and settlement of the sediment are in equilibrium with a given slope. Only a new phase of bioturbation can induce further creep movements.The experiments have shown that stone implements in reconsolidating Kalahari Sands do not exactly accompany the compaction movement of the sediment. Depending on their form, their size, their orientation and the water content of the sediment around them, stone implements can undergo differential movements during the reconsolidation process. This can result in a dispersion of the implements over levels of different ages.As creep is a phenomenon, going hand in hand with the resettlement of the sediment after biogenic upworking, partially analogous movements of stone implements can be expected in a creeping Kalahari Sands mantle.Partial or total reconcentration of the stone implements at the base of affective biogenic activity can be expected. This can lead to typical stone‐line profiles which must be interpreted very caref

ISSN:0360-1269    

DOI:10.1002/esp.3290030203

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe Horton method of analyzing drainage network composition is reviewed, with the conclusion that it has not been very effective either in improving understanding or in developing useful methods of characterizing drainage basins. New methods which are based on the link rather than the Horton (or Strahler) stream are described. A number of detailed examples of the application of these new methods to the topologic and geometric properties of networks are provided. The results are compared with the predictions of the random model.Data used in the analysis were obtained from 1:24,000 U.S.G.S. topographic maps of eastern Kentucky. Thirty drainage basins were selected and their channel networks were outlined first by the contour‐crenulation (CC) method and then by another, more objective, method (SC) in which stream sources were identified by a quantitative slope criterion. The CC and SC samples comprise about 8,700 and 1,700 links, respectively.The three most important results of the analysis are: (1) the channel networks are slightly but significantly more elongated than predicted by the random model, (2) there are fewer second magnitude links than predicted, and (3) the length distribution for interior links depends upon the kind of link (interior or exterior) joined downstream. These features are found in both CC and SC network

ISSN:0360-1269    

DOI:10.1002/esp.3290030204

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe possibility of using metals from mining activity as tracers for identifying stream sediment sources is explored. Sampling of monthly bed sediment yield and of the spatial and temporal variation in Pb concentration was undertaken in a 1·02 km2catchment, and estimates of the sediment contribution from different stream reaches are calculated. The method has considerable limitations, for metal concentrations are notably dependent on sediment size, season, source availability, and the chemical mobility of the metal used. In most natural streams these must preclude the use of pollutants for simple sediment source identification

ISSN:0360-1269    

DOI:10.1002/esp.3290030205

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractMeltwaters were collected in Switzerland at the border of two alpine glaciers, the Tsanfleuron glacier resting on limestones and the Tsijiore Nouve glacier flowing over gneissic rocks. Waters were analysed by atomic absorption spectrophotometry for the four major cations.Cation exchange appears to be an essential mechanism in the explanation of the dissolved cationic content of meltwaters in the frontal zone of glaciers. This is indicated by a study of the rate and characteristics of water enrichment.The rate‐determining step in the process seems to be film diffusion. The influence of this diffusion is put forward in an analysis of the rates of change in concentration of the four major cations with discharge.Glacier grinding is considered as a factor favouring cation exchange in a proglacial environmen

ISSN:0360-1269    

DOI:10.1002/esp.3290030206

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractPeak rainfalls and peak runoff rates per unit area are comparable over a worldwide spectrum of climates. However, while the magnitude of the external contribution of energy or force in diverse regions is similar, the impact on the landscape varies markedly between regions. Absolute magnitudes of climatic events and absolute time intervals between such events do not provide satisfactory measures of the geomorphic effectiveness of events of different magnitudes and recurrence intervals. Although geomorphic processes are driven by complex sets of interrelated climatic, topographic, lithologic, and biologic factors, the work done by individual extreme events can be scaled as a ratio to mean annual erosion and the effectiveness of such events in forming landscape features can be related to the rate of recovery of channel form or mass wasting scars following alteration by the extreme event. Thus, a time scale for effectiveness may relate the recurrence interval of an event to the time required for a landform to recover the form existing prior to the event.River channels in temperate regions widened by floods of recurrence intervals from 50 to more than 200 years may regain their original width in matters of months or years. In semi‐arid regions, recovery of channel form depends not only upon flows but upon climatic determinants of the growth of bottomland vegetation resulting in variable rates of recovery, on the order of decades, depending upon coincidence of average flows and strengthened vegetation. In truly arid regions the absence of vegetation and flow precludes recovery and the width of channels increases in drainage areas up to 100 km2but remains relatively constant at larger drainage areas.Area as well as time controls the effectiveness of specific events inasmuch as the likelihood of simultaneous peak discharges or rainfalls and large areas is less, particularly in arid regions where events spanning areas of more than several thousand km2are extremely rare if experienced at all. To some extent a decrease in area in a humid region is comparable with a regional change from humid toward more arid climate reflected in the increase in importance of episodic as contrasted with more continuous processes. Exceedingly rare floods of extreme magnitudes, estimated recurrence intervals of 500 years or longer, may exceed thresholds of competence otherwise unattainable in the ‘normal’ record resulting in ‘irreparable’ transformations of valley landforms.Denudation of hillslopes by mass wasting during relatively rare events can also be related to mean rates of denudation and to recovery of hillslope surfaces after scarring by different kinds of landslides. Measured recovery times described in the literature vary from less than a decade for some tropical regions to decades or more in temperate regions. Recurrence intervals of high magnitude storms which trigger mass wasting range from 1 to 2 years in some tropical areas, to 3 or 4 per hundred years in some areas of seasonal rainfall and to 100 or more years in some temperate regions. The effectiveness of climatic events on both hillslopes and rivers is not separable from gradient, lithology or other variables which control both thresholds of activity and reco

ISSN:0360-1269    

DOI:10.1002/esp.3290030207

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290030208

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290030209

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290030210

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290030212

出版商:John Wiley&Sons, Ltd    

年代:1978

数据来源: WILEY