摘要:

ABSTRACTA study of long-term temperature data (1881–1970) from 13 stations in Canada, east of the Rockies, shows that the mean length of the annual frost-free season decreases zonally from east to west. Meridional distinction among the stations though present is muted. Three regions are identified—a prairie region, a southern Ontario-South Atlantic axis and a Quebec-Maritime region. The spatial correlation in the length of the season is strong to moderate within regions, but declines rapidly between regions. A strong internal consistency in the length of the season at each location is observed. However, most stations show a marked change in the nature of the season after 1940 which resulted in a significant shift in the probable dates of the first and the last frost of the season.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880125

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTDrumlins in central Ulster, Northern Ireland show complex variation in composition and internal structure. These can be resolved by facies modelling into four major till facies associations, reflecting either a particular depositional process or environment. They show that drumlin formation resulted from the interplay of a number of processes. Subglacial erosion, localised till lodgement, widespread subglacial till melt- out subglacial fluvial-lacustrine sedimentation, subglacial cavity sedimentation, superglacial till superimposition and resedimentation all contributed to drumlin formation in this area. The associations reveal contributed to drumlin formation in this area. The associations reveal spatial and temporal changes in processes and patterns of subglacial sedimentation, prior to, during and following drumlinisation. One of the most important changes identified in this study was the infilling and blockage of subglacial drainage networks prior to drumlinisation. This caused a reduction in hydraulic transmissibility at the ice-substrate interface and may have initiated widespread subglacial till melt-out. During and following drumlinisation, large quantities of meltwater were stored at the ice-substrate interface, contributing to ice sheet instability. Drumlinisation in central Ulster may have occurred under surging conditions. Associated with periods of high subglacial meltwater expulsion. This study suggests that subglacial hydraulic processes may have played an important role in drumlinisation and at least some types of drumlins could form as features of subglacial meltwater erosion.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880126

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTThe volumes of over 900 debris-flow deposits are compared. There is no definite relationship between magnitude and frequency, although small-scale flows occur more frequently than large-scale ones. The proportion of work done by relatively rare events varies from site to site. There are major differences in the volumes of debris flows in Scotland and Norway, Norwegian flows being an order of magnitude larger. The debris flows described here are most appropriately termed‘infrequent events’, the existing magnitude-frequency terminology being inadequate.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880127

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTSedimentary processes and recent sediments are described from the lower course of the Sachs River, Banks Island and from adjacent sandflats. The river is characterised by a short period, annual spring flood which deposits a hierarchy of superimposed bedforms in the high-stage river channel. In the early part of the melt season ephemeral stream action also occurs on the sandflats adjacent to the river. The fluvial deposits of the ephemeral streams and the channel are subject to aeolian modification during the subsequent arid summer months such that interbedded fluvio-aeolian sediments accumulate.The presence of permafrost restricts the depth of aeolian reworking so that ripples and climbing adhesion structures are the typical aeolian bedforms whilst laterally persistent, planar deflation surfaces are ubiquitous in sections through the sandflats.These observations have been integrated to produce a local model of fluvio-aeolian sedimentation which is characterised by channel fills and sediments deposited as aeolian sandsheets which are truncated by deflation surfaces.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880128

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTSand dunes that are subjected to different wind directions attain different steady state profiles. Two fundamental types of profile are known: the convex asymmetric one, characterizing barchans and transverse dunes, and the symmetric triangular one of seif dune. The distribution of wind velocity along these two fundamental profiles indicates that the convex profile of barchan and transverse dunes are in a steady state to uni-directional winds. A steady state profile having a separate crest and brink ensues a higher advance of slip-face relative to the windward slope.A triangular sharp-edged profile of seif dunes is not in a steady state under long-term perpendicular uni-directional wind. Steady state can be attained, however, by bi-directional winds of oblique approach to the dune. In this case seif dunes are in a steady state with respect to profile oblique to dune axis and parallel to wind direction. A sharp-edged profile causes a substantial separation of perpendicular flow over the lee slope. The separation vortex reduces the wind-velocity's rate of increase near the crest line which keep its sharp profile during a short period of perpendicular wind. In the case of the wind shifting to a perpendicular direction for a longer period, the triangular shape will turn into a convex asymmetric one.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880129

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTA comparison of detransformed logarithmic regressions and power function regressions is illustrated with regressions of sediment concentration in a Swedish river. Quite different parameters were obtained when power function equations were developed from log-transformed data compared with development from the original data. This is a consequence of different model assumptions. Power function regressions are calculated from an additive model. While detransformed logarithmic regressions represent a multiplicative model. Detransformed logarithmic regression equations are biased with respect to the original data. Some of the bias can be reduced by a correction factor.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880130

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTHourly observations of stream discharge and suspended sediment concentration obtained during parts of 1978 and 1981 from the proglacial stream of the glacier de Tsidjiore Nouve, Valais, Switzerland, are used to investigate the usefulness of suspended sediment rating curves. Residuals from standard ordinary least squares (OLS) rating models fitted to the data from both ablation seasons are highly serially correlated. Discriminant ratings produced by fitting standard OLS models to data from partial periods, and to data filtered according to diurnal and seasonal fluctuations in stage, climatic conditions and process lag are similarly autocorrelated. Estimates of suspended sediment concentration provided by the rating models are therefore likely to be unreliable. Forecasts from the 1981 rating models considerably underestimated observed suspended sediment concentrations, and provided only a 79% prediction of observed load in the eight days following the calibration period. Forecasts for this period from the 1978 rating models were almost as good as those from the 1981 models. In general, considerable inaccuracies occur in forecasting from rating models. In certain circumstances, however, it may be‘acceptable’to use a general rating model to forecast suspended sediment concentrations and loads for any given period. Some pragmatic ground rales for the use of rating curves are outlined.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880131

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTA detailed sediment budget study was undertaken for a relatively shallow glacial lake in the Purcell Mountains of British Columbia. The lake, with it's relatively large water and sediment input levels and short water residency time, may be characterized as a high energy lacustrine environment. Using detailed measurements of the major aspects of the entire climatic-hydrologic-sedimentological system, involving some 100 channels of data in conjunction with a systematic coring program, a careful analysis was made of the components of the budget and resulting deposits in this environment. The results indicate that the major inputs consisted of: 1) low sediment concentration level inputs which result in either suspension settling of material to the lake floor, or the transport of material by relatively low overall density lake surface currents (termed overflows) through the system and out the outlet stream with essentially little material being deposited in the lake; 2) higher level sediment concentrations which result in the material being deposited on the lake floor by turbidity currents; 3) extreme discharge events which bring in large amounts of material as bedload to be deposited in the delta; and 4) snow avalanches which deliver large amounts of material to the lake ice surface with the possibility of subsequent rafting.These findings differ somewhat from the findings of other studies. Of particular note they point to: 1) the capacity of overflows to transport material through such lakes with little deposition (thereby significantly affecting the budget); 2) the significance of snow avalanche delivered material as a major component of the budget in such environments. The results of the study also indicate the need for careful monitoring of all input and output operations if a better understanding of glacial lake sediment deposition processes are to be achieved.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880132

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTA review of the deglaciation history of one of the large lake basins in Sweden, the Lake Siljan basin is given. A quantitative approach to the deglaciation of the area is applied with respect to the discharged amounts of water. To establish the palaeodischarges a formula based on the process of sedimentation and sorting of fluvially transported suspended matter is applied. The sediments for which the formula is used are annually varved silty sediments deposited as very distal delta sediments during the deglaciation of the southern part of the Lake Siljan basin. Connection to an absolute time scale and correlation of the new varve diagrammes is performed with a computer-based programme in order to eliminate subjectivity. Computations of palaeodischarges indicate that the water discharges during the melting season at the time of deglaciation were approx. 10 times greater than the present day mean annual discharges in the RiverÖsterdalälven that now drains the basin.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880133

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

ABSTRACTThe paper describes experimental rock weathering in a climatic chamber of about 90 different Swedish rocks. The specimens were when possible sawed into cubes with a side of about 7.5 cm. The amount of material released from Precambrian crystalline rocks after 324 freeze-thaw cycles is extremely low. Often the debris is less than 0.001% of the original weight. In spite of the low weathering rate a clear distinction can be seen between different rock types. The soft sedimentary rocks included in the experiment have produced between 400 and 5000 times more material of grain sizes smaller than 0.25 mm than the mean for granites. The amount of material produced after 252 wetting-drying cycles is on an average 10 times lower than in the freeze-thaw experiments.

ISSN:0435-3676    

DOI:10.1080/04353676.1985.11880134

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor