摘要:

ABSTRACTGlacial erosion by plucking and abrasion is relatively well understood at the small scale of individual bed-forms several metres in dimension. Erosion at this scale is controlled by basal ice pressure, ice regelation and freeze/ thaw. Explanations are lacking for the formation of medium scale landforms of glacial erosion several hundred metres in dimension, where processes such as regelation and cavitation are less well understood.Study of a medium scale glacial erosional feature in South Greenland shows that the distribution of abraded and plucked surfaces is similar to that found on small scale features of glacial erosion. Polished surfaces are found on the stoss side of the larger feature, with plucked surfaces restricted to the lee side. Lateral cliffs have developed parallel to the ice movement direction, possibly related to the constricted flow of flanking ice.It is suggested that the distribution of these landforms of glacial erosion is related to the pressure fluctuations in basal ice developed over large bedrock obstacles. The processes important in the formation of medium scale features of glacial erosion are essentially small scale, but their relative dominance is controlled by meso - scale basal ice conditions.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880317

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTThe methods used to extract ice flow directions from striae data are discussed. Four types of change regarding the subglacial environment are recognized as important for the preservation of coherent striae patterns in formerly glaciated areas. These are: 1/ Deglaciation, 2/ Change to frozen-bed conditions 3/ Burial of bedrock surface beneath till, and 4/ Location near an ice divide. The general concept of a migrating“preservation borderline”is introduced in a discussion about the spatial striae patterns expected to be related to areal expansion of frozen-bed zones. The types of large-scale spatial patterns to be expected from the four described preservation scenarios are discussed, as well as the difficulties in obtaining flowline information from metachronous patterns. A stepwise procedure for deciphering of palimpsest-type striae patterns in core areas of the last ice sheets is outlined and applied on two areas placed centrally under the last Scandinavian ice sheet. From the southern study area it is concluded that there is no geological evidence for the ice flow from the east over central Sweden during the Late Weichselian maximum, modelled by Denton and Hughes (1981) and Boultonet al.(1985). If a Bothnian Gulf monodome configuration existed, it must have been cold-based under large central areas. A two-domed configuration provides a better fit to the geological evidence.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880318

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTA large talus-foot debris accumulation on Muckish Mountain is interpreted as a fossil rock glacier rather than a glacial moraine as previously suggested. Sedimentological characteristics indicate that the debris accumulated initially as talus. Rock glacier flow probably occurred due to the deformation of interstitial ice and ice lenses. A bedrock ridge at the talus-foot was almost totally buried by rock glacier flow and now exaggerates the height and thickness of the fossil rock glacier. The major stages in the development of the fossil rock glacier are outlined in a simple model. Debris accumulation is believed to have occurred during the Lateglacial period with rock glacier movement taking place in the Nahanagan Stadial.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880319

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTIn Quaternary sandy glacial outwash sediments situated in the Inn Valley NE of Innsbruck (Austria) occur redeposited diamicton blocks containing flatiron-shaped and ice-striated pebbles. Associated with these blocks are small, graben-like structures offset by small highangle faults (“ice-melt graben structures”) interpreted to have been caused by the melting of underlying ice-rich blocks. The diamicton blocks most likely originated from frozen glacial sediments, probably tills from the advancing Inn Glacier by fluvial erosion and are believed to be a prominent indicator for periglacial environments.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880320

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTThe evolution of the Grande del Nevado Glacier surge was documented through analysis of Landsat data, using image and computer-compatible tape formats, for 22 different dates between 1976 and 1986. Through time-lapse analysis of the sequential satellite images, it was determined that the glacier had a surge or rapid advance in 1984. The glacier front was in progress sometime between 16 February 1984 and 4 April 1984. Following an advance of 2.7 km, it dammed the Río Plomo in November 1984, creating a lake which, by January 1985, was 2.8 km long and 1.1 km wide. Fortunately, in March 1985, the lake began slowly draining through a natural subglacial tunnel, and continued outflowing until the end of this month, when the lake was no longer observable on satellite images.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880321

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTA detailed field study of sediment transfer processes, sediment yield and channel change was undertaken in the proglacial zone of the Bas Glacier d'Arolla, Val d'Hérens, southern Switzerland, during the 1987 ablation season. Sediment yield estimates were derived from continuous discharge and suspended sediment concentration series combined with bedload transport estimates from sediment traps.Valley sandur sediment transport dominated proglacial sediment transfers. Tributary streams and hillslopes contributed minor amounts of sediment. Channel change was episodic and channel pattern switched from single-thread to multi-thread to single-thread over the ablation season. Meltwater floods were responsible for catastrophic changes in channel form.Intensive field measurements (25 May - 30 July) define a proglacial sediment budget which indicated that proglacial sediment sources contributed 23% to the total basin sediment yield. The overwhelming proportion of the proglacial sediment (95%) was eroded from the valley sandur during the brief period of meltwater flooding July 15–18. Expressed in terms of work, the budget suggests that four basic process subsets can be distinguished: (1) channel processes; (2) valley sandur (channel margin) processes; (3) hillslope processes, and (4) slopewash. Large magnitude, infrequent flood events are the dominant control on the release of sediment from proglacial storage.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880322

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTSoil erosion, sediment transport and deposition in river systems in Sweden are discussed. The database consists of observations from a research project and from the Swedish network for the measurement of sediment transport. Examples are given from measurements in small plots, and from river basins of different sizes and characteristics. Effects of hydrological regime, of deposition in lakes, and of geology and human impact are illustrated. It was found that observations of erosion losses in index plots cannot easily be extrapolated to large areas, and that trends of transport most likely reflect trends in runoff.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880323

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTThis study focuses on the relationship between water discharge and suspended sediment concentration in the River Malewa, Kenya. The period investigated covers the interval from 1931 to 1959. The river is located in a semi-arid part of Rift Valley Province, Kenya. The River Malewa catchment covers an area of approximately 1 550 km2. Average annual rainfall within the catchment varies between 650 mm in the lower southeastern parts, and 1 100 mm on the slopes of Nyandarua Range. During the period investigated the measured daily discharge ranged between 1–138 m3/s. The data indicate a maximum daily transport of suspended sediment load of approximately 10 000 tonnes. This is equivalent to a suspended sediment yield of approximately 6 tonnes/km2. Based on the measurements of suspended sediment concentration and water discharge, different regression models are used to establish the best relationship in sediment rating curves. Comparison is made between the amount of load measured and the calculated figures of total suspended sediment load, derived from regression analysis. From the established relationships between water discharge and suspended sediment concentration, the calculated minimum average soil loss within the Malewa basin (1931–1959) amounts to 9 tonnes/km2and year.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880324

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTIn 1980, the glacial sculpture, shore displacement and lake sediments were studied on Prins Oscars Land, Nordaustlandet, Svalbard. The results indicate that there was a thin ice cover over the area in the Late Weichselian. An advance of Austfonna reached the southern part of the peninsula, whereas a mainly cold-based ice cap was built-up in the north. The maximal glaciation occurred earlier in the Weichselian. The evidence of a relatively insignificant glacial expansion in the Late Weichselian agrees with indications of large ice-free areas in other northern areas of Svalbard at this time.The ice retreated from the coast areas of Prins Oscars Land 11 000 to 10 000 years B.P. In the north there are indications of a considerably longer ice-free period in areas below the Postglacial marine limit. Since the deglaciation, shore displacement has been almost 45 m in the northern part of the peninsula and over 55 m in the south. A distinct terrace at about 15 m in the north and 20 m in the south was formed 8000 to 6500 years ago. Pumice is frequently associated with the terrace.The altitude of the terrace does not agree with the elevation of the marine limit or with other evidence of a relatively modest thickness of the ice cover. The explanation may be that the crustal uplift has been influenced by other factors in addition to the glacio-isostatic rebound. Hence, the value of the pumice levels as indicators of the Late Weichselian glacial conditions is also discussed.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880325

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

ABSTRACTThe Schmidt Test-hammer has for some years been used to measure the hardness of different rock-surfaces, and to date boulders in moraine deposits relative to each other. In this paper applications on isostatically raised boulder-beaches and rocky shores are described. The research area is the northern Swedish Bothnian coast where present isostatic uplift is between 0.8 - 1.0 cm/year. Elevations above sea-level can thus be converted to a time scale. Rebound-values (R) of the Schmidt-hammer are correlated with the altitude, and rock-weathering rates can be estimated for each site.A raised boulder-field in the Nordingråregion has been studied using the method to construct a weathering regression line and to find out if some of the higher ramparts could represent transgression-zones. Lichenometric studies, including the construction of a thallus growth curve forRhizocarpon geographicumhave also been carried out. The lichenometric results were used to try to confirm the results of the Schmidt hammer measurements.This method has applications in both geomorphology and archaeology. For example, the catchment areas for some large ancient grave-cairns on the boulder-beach have been discovered.

ISSN:0435-3676    

DOI:10.1080/04353676.1990.11880326

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor