摘要:

ABSTRACTA fundamental distinction exists between the initial glaciation of an upland landsurface, and all subsequent re-glaciations of the same uplands. Unfortunately, few areas of the world present an opportunity for the study of initial glaciation, since most glacial or periglacial regions have already undergone multiple glaciations throughout the Quaternary. Concepts of how glaciers are initiated and enlarge are inevitably influenced by the fact that models can only be derived from, and applied to, landscapes whose topography already demonstrates modification by glacier ice.Observations of snowpatch distribution in Southern Iceland allow us to examine this distinction between initial glaciation and re-glaciation. High resolution remotely sensed data were obtained showing the distribution of snowpatches at two topographically different sites, one previously glaciated and the other a young volcanic landscape that has remained unglaciated since the central caldera erupted, forming the basis of the present topography (Saemundson 1979). Both locations are only marginally unglaciated at present. Comparison of these distributions suggests that whilst the conventional“top-down”model of glacier growth may be appropriate for reglaciated uplands, a“bottom-up”model may be more applicable to steeply dissected upland terrain experiencing initial glacierisation. The importance of this distinction between initial glaciation and reglaciation in terms of erosion and deposition is also considered.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880467

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTThe formation of a moraine mound (hummocky moraine) complex at the Neoglacial limit of Pedersenbreen, Svalbard is discussed. The moraine mounds are composed for the most part of sheared basal diamicton with occasional units of fluvial gravel and laminated silts. In morphology the moraine mound complex resembles an imbricate stack of sediment units which dip towards the glacier margin. Observations of the debris structure within Pedersenbreen are used to explain the formation of the moraine mound complex. A model for the formation of such moraine mounds by englacial thrusting either as part of a glacier surge or due to flow compression at a polythermal ice margin is developed.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880468

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTBomb-derived fallout137Cs has been used as an environmental tracer to study rates of overbank sedimentation on river floodplains. The depth distributions of fallout137Cs in sediment cores collected from depositional sites on the floodplains of twelve lowland rivers in Britain have been employed to estimate mean annual overbank sediment deposition rates over the past 30–40 years, assuming a constant rate of sediment deposition and a correspondence between the shape of the observed137Cs profiles and the history of radiocaesium inputs. Values of sedimentation rate estimated for the twelve sites range from 0.11 g cm-2yr-1to 0.95 g cm-2yr-1. Variations in the levels of137Cs activity associated with surface sediment from the individual sites can be used to interpret the dominant sediment sources in the individual catchments.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880469

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTRadiocarbon-dated basal sediments of the highest lake in southern Finland, Sirkkajärvi (131.9 m a.s.l.), were studied for organic content, pollen and diatoms in order to follow early developmental phases of the lake, and by inference, Late Weichselian water level changes in the Baltic. The lake became isolated during the final drainage of the Baltic Ice Lake about 10,30014C years BP. Pollen and diatom analyses show typical developmental features from the earliest Holocene onwards, including rapid afforestation and progressive natural acidification. No traces of the hypothesised low water stage, g, were found in the sedimentary sequence studied, although the site and its surrounding should have been above the Baltic Ice Lake during this stage. This is in agreement with recent implications based on morphological evidence. Finally, the uncertainties associated with the approach are discussed.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880470

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

ABSTRACTThe use of the National Oceanic and Atmospheric Administration (NOAA) satellites, and the conventional Normalised Difference Vegetation Index (NDVI) model have shown promise as a large scale monitoring tool to understand the vegetation dynamics of the sparsely vegetated Sahelian grasslands. One of the assumptions of the NDVI model is that the soil background is spectrally homogeneous, which is not the case. Twelve sites, within twoSystème Probatoire d'Observation de Terre(SPOT) satellite imageries, corresponding to NOAA Advanced Very High Resolution Radiometer (AVHRR) Local Area Coverage (LAC) pixel resolution, were assigned representative soil NDVI values for both dry and wet conditions. These soil NDVI values, together with herbaceous above-ground biomass production estimates, were used in a multiple correlation and regression analysis to assess statistically the soil impact on integrated NDVI values, i.e. values supposed only to express the total amount of vegetation in the end of the rainy season. The analysis showed that soil influence varied significantly with different soil types and moisture content, and should therefore not be ignored in satellite based vegetation monitoring.

ISSN:0435-3676    

DOI:10.1080/04353676.1996.11880471

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor