摘要:

ABSTRACTHills eroded by floods of glacial meltwater in Swedish Lapland resemble streamlined erosional features on Mars. The morphology and materials indicate a similar origin for the features on both planets. The Båldakatj area can be considered a terrestrial analog for Martian landforms; this similarity suggest that other features in Lapland, including boulder deltas, may also occur on Mars.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880143

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTThis paper examines the distribution of annual and seasonal rainfall in the north-eastern Ghana during the 1975–1977 drought. Water budgets for the study area are estimated to assess the nature of water availability in the drought period.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880144

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTFlow of ice over a pair of streamlined bumps was studied in a laboratory apparatus. Experimental conditions were similar to those under a glacier about 100 m thick with a shear stress of 0.1 MPa. Temperatures in the ice and bed were monitored with thermistors. Cumulative deformation was determined with the use of threads frozen into the ice. The threads were initially vertical, but were deformed during the experiment.About 75 % of the accommodation of the bumps was by plastic deformation, and 25 % was by pressure melting. Much of the heat for melting came from the boundaries of the apparatus so the melt water formed did not refreeze in the lee of the bumps.The cumulative deformation in the ice is compared with a theoretical prediction of Lliboutry and Ritz (1978) for flow over hemispherical bumps. The principal difference between theory and experiment, aside from that in bump geometry, is that the theory assumes a frictionless boundary between the bed and the ice, whereas in the experiment small-scale roughness elements result in drag. Because the theory ignores this drag, it overestimates the velocity immediately above the bump. The experimental deformation profiles are consistent with those predicted for a non-linear rheology, but not with those predicted for a linear rheology.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880145

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTThe NE margin of the glacier Höfdabrekkujökull - a piedmont lobe extending from the SE part of the ice cap Myrdalsjökull—is currently advancing, and along the glacier terminus a dislocated push moraine as high as 5–10 m is being formed. In the period 1979–1982 the average frontal advance amounted to 10 m per year. During the following period 1982–1984 the average glacier advance increased to 32 m per year. During the advance, the glacier forefield is intersected by thrust planes dipping 18–25°upglacier. At the same time supraglacial debris roll and fall downslope the steep glacier front, and flow till is deposited in tongues at the foot of the push moraine. These features, which are formed and destroyed concurrently with the glacier advance, contribute to a very heterogeneous texture of the push moraine. Digging in the distal part of the push moraine showed glacio-tectonic disturbances by folding and thrusting. Floes were pushed as unfrozen slabs, 50–100 cm in thickness, forward in front of the advancing glacier to form an imbricate structure.It is concluded that the push moraine is formed by recurrent pro-glacial thrusting, folding, and stacking. During further advance the glacier and the upper part of the push moraine will override the lower part. Once the ice overrides the formed ridge, subglacial deformation by basal shearing may create a glacier bed of heavily disturbed deposits, which far back from the advancing ice margin may be overlain by basal till. If a glacier recession sets in, the push moraine under discussion will be transformed to a ridge about 3–5 m high. In accordance with this, the majority of older push-moraine ridges found in the forefield of Höfdabrekkujökull does not exceed 5 m in height.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880146

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTTill ridges at Eyjabakkajökull, Iceland, are considered to be 'crevasse-fill’ridges formed by the flow of sediments from the dilatant horizon of subglacial lodgement tills into open crevasses in response to local variations in overburden pressure. Crevasses are formed during the active phase of a surge cycle, and are filled with sediment during the early part of the quiescent phase as the stagnant glacier sinks into its bed. The resultant ridges form a network covering the whole of the area in which crevassing penetrated to the bottom of the glacier during the surge. Nowhere are they associated with till ridges formed at and parallel to the glacier margin. Since similar ridges have been observed at a number of other surging glaciers, it is suggested that lodgement till surfaces crossed by networks of‘crevasse-fill’ridges may be characteristic of surging glaciers.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880147

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTThe surficial movement of debris was studied in a high altitude talus of the Andean Páramo of Piedras Blancas, Venezuela, for a maximum period of 29 months. A total of 411 stones were marked with paint and placed along four transects at different altitudes of the talus. The record of movement showed a wide temporal and spatial variability, but stone displacement was found to be correlated with surficial talus texture and mean particle size. Markers placed on gravelly sand areas shifted downslope faster, at an average annual rate of 23.2 cm; markers on small-debris areas moved 15.9 cm, while those on large-stone stripes moved only 4.0 cm. Since coarse-debris areas were concentrated at the basal talus, there was a general trend of increased stability with lower slope position.The displacement of talus particles was also studied with burlap debris traps and other methods; clay columns inserted in the talus revealed that disturbance of the gravelly sand areas desed rapidly with depth, and that only a surficial layer of 5 to 7 cm moved swiftly downslope. The talus showed little or no subsidence or mass rotation. The processes thought to be presently operative in the talus include rockfalls, small dry slides and avalanches, debris flows, and creep. Creep was induced by needle ice growth, by surface runoff during intense rainfall or snow melting, and by the contraction and expansion of the talus clasts resulting from the wide daily temperature fluctuations of the High Andean Paramo.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880148

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTIce-cored mounds in a small area in northernmost Sweden are briefly described. The morphological features include hummocks, interpreted as pingos, more palsa-like mounds and fossil forms in the shape of circular ponds. Drilling in one hummock revealed a massive ice core covered by fine grained sediment and glacial till. The sediment is slightly organic and probably of interglacial age. A number of mounds appear to have subsided during the last two decades and no signs of growth have been observed during the same period. The subsidence is assumed to be climatically induced.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880149

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTWinter avalanches are of widespread occurrence in Scotland, and yet on many slopes where they are frequent they do not produce the distinctive landforms described by workers in other areas. This paper describes some small-scale features which do occur and which indicate the action of avalanches. These include perched boulders, lichen patches, boulder holes and scratch marks. The occurrence of these features in several locations suggest that they may be widespread indicators of avalanche activity. As such they may be more useful than other indications such as slope angle or sorting, which do not form unequivocal evidence in marginal areas.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880150

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTTunnel erosion has been noted in many areas, but few attempts have been made to measure development rates or to assess geomorphic or hydrologic significance. This paper reports measurements of two tunnel systems in the Dinosaur Badlands, Alberta, carried out as part of a major study of water and sediment budgets. These were instrumented and monitored through summer storm events and detailed water, sediment and solute discharge patterns were established. Tunnel hydrographs were similar to those for surface sheetwash and channel flow with short lag times and rapid recession. Total discharges were low compared with the main channels, but water yields per unit area drained were similar. Row rates indicated contributions to channel storm hydrographs. The results, together with an inventory of tunnel inlets and outlets, suggest that about 10 per cent of the total water flow in the catchment may be routed through tunnel systems. Suspended sediment concentrations were high, reaching 97.1 g 1-1in a moderate rainstorm, substantially above peak channel concentrations. Minimal estimates of total sediment yield during a single storm event ranged up to 0.42 kg m-2, equivalent to a denudation rate of about 0.3 mm. Solute concentrations were also higher than channel flow with peak electrical conductivities reaching 1200μS cm-1at 25°C. The solute load was dominated by sodium, reflecting high concentrations found in bordering lithologic units.A substantial portion of the catchment discharge passes through tunnels but a clear distinction cannot be made between surface and subsurface contributions in the storm hydrograph. Nevertheless solute and sediment yields indicate that tunnel erosion is a significant geomorphic process in this area.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880151

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTSoil loss was measured in Kiambu District during the long rainy season, 1982. From the data gathered during this period, the USLE was calibrated for the agro-ecologic conditions existing in the area. During 1983, soil loss measurements were collected in Murang'a District for the two growing seasons. Using the Kiambu calibrated USLE values, soil loss was estimated also for Murang'a. The significant correlation between the estimated and measured soil loss values indicates that the USLE, as calibrated for Kiambu, gives meaningful estimates in this area of Kenya. Nevertheless, the estimation of the erosivity values at the field level as well as the assessment of the conservation practices need further refinement.The measured soil loss values in both districts indicate that fields in annual crops, especially cotton and maize, result in the highest soil losses; perennial cash crops result in the lowest soil losses. It appears that approximately 25 % of the sampled fields are undergoing land degradation solely due to excessive soil losses. This is especially true in areas of recent agricultural expansion as they generally have higher soil losses than the established farming areas.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880152

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor