摘要:

AbstractEstimates of suspended sediment yield over the past 800 years have been derived from a whole‐basin study of lake sediments in Llyn Geirionydd, North Wales. Magnetic and physical sediment properties were used to correlate a suite of cores to a master chronology based on210Pb and14C dates. The sources of sediment within the catchment were identified by comparing the magnetic and heavy metal properties of sediments, soils, and stream sediments. Mean suspended sediment yields range from 6 to 18 t km−2yr−1with high yields in the periods 1765‐1830 and 1903‐1985 corresponding to mining activities in the catchment. The impact of earlier deforestation, agricultural expansion, or climatic change on sediment yields is low, although there is evidence that agricultural activities increased levels of peak stream discharge. Afforestation in the 20th century does not appear to have significantly increased sediment yield. Sediment sources have remained fairly constant through time; they appear to be widespread and dominated by stream channel sides rather than point sources, except during the mining phases when spoil material has dominated the sediment load. Sediment loads to the lake today are still dominated by sediment derived from unvegetated sp

ISSN:0197-9337    

DOI:10.1002/esp.3290170102

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAlthough alluvial cutoffs record accurately the geometry, bedforms, and bed material of the channel when last active, few attempts have been made to use cutoffs in studies of channel changes. A detailed record of historical channel changes on the lower Hunter River in southeastern Australia has shown that this channel responds to naturally alternating periods of high and low flood activity, called flood‐ and drought‐dominated regimes respectively. Sinuosity decreased from 3·84 in 1870, to 2·66 in 1893 and to 1·38 in 1970 through the development of eight cutoffs. The channel also aggraded with medium sand burying the former bed material of mixed mud, coarse sand, and gravel. Channel straightening was a response to increased flood frequencies during the flood‐dominated regimes of the late 19th and 20th centuries, combined with localized river engineering works and increased sand load.Detailed stratigraphic studies were carried out on three neck cutoffs and one chute cutoff which were abandoned in 1890, 1950, 1952, and 1956. A comparison of former and present bed elevations and bed material size showed similar trends to those determined by the historical record, confirming the reliability of cutoffs as indicators of former channel conditions.The sedimentary infills of the cutoffs are not uniformly fine grained as recorded previously in the literature. Relatively thin, fine‐grained fills were deposited during the drought‐dominated regime of the first half of this century but thick, coarser‐grained fills were deposited after 1949 during the flood‐dominated regime. All fills fine upwards. Cutoff infills provide a record of changing flood activity an

ISSN:0197-9337    

DOI:10.1002/esp.3290170103

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe erosional morphology in the vicinity of the Main Divide of the Southern Alps, and Fiordland, New Zealand, appears to be a product of the interaction between Alpine Fault‐induced tectonic processes, rock mass strength of the uplifted and eroded bedrock, and the processes acting to denude the developing mountain landscape. The magnitude of the effects of glacial erosion on the landscape is directly controlled by the size and physical properties of the glaciers, whilst the form of the trough is a direct consequence of the rock mass strength (RMS) properties of the slope rock. Realistic models of development of the cross‐profile shape of glacial valleys must take into consideration the RMS properties of the eroded substr

ISSN:0197-9337    

DOI:10.1002/esp.3290170104

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe granite tors of Dartmoor are characterized by using the regional spatial patterns of 21 geomorphic, petrographic, and structural variables. The data were derived from topographic maps, field measurement, and laboratory analysis of rock samples collected in the field. Identification of spatial patterns and comparison of patterns between variables were made on contour maps generated from the data using ARC/INFO. Three tor types—summit tors, valleyside tors, and spur tors—are semiquantitatively characterized using these data and procedures.The three types of tors are distinguished with respect to variations in relative relief, joint spacing and joint type, rock texture, grain size, and composition. Summit tors have the highest relative relief (mean: 125·7 m), contain the most potassium feldspar (>30 per cent), and have the most widely‐spaced primary vertical (>300 cm) and secondary horizontal joints (>10 cm). The rocks are the most megacrystic (>15 per cent) and the coarsest grained. Plagioclase is also abundant in summit tors. Valleyside tors have the lowest relative relief (mean: 72·9 m) and the most widely‐spaced horizontal joints (primary, 60‐200 cm; secondary,>10 cm). Grain size, vertical joint spacing, and quartz and potassium feldspar abundances are intermediate. The shapes of valleyside tors are controlled by horizontal joints and the rocks are either very feebly magcrystic or equigranular in texture. Spur tors have intermediate relative relief (mean: 115·4 m), the narrowest joint spacing (vertical joints,<200 cm, 50‐75 cm; horizontal joints<60 cm,<10 cm) and the finest grain. In addition, the rocks are feeb

ISSN:0197-9337    

DOI:10.1002/esp.3290170105

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe seventy‐kilometre‐long Herbert Gorge of northeastern Australia preserves a record of past floods in slackwater deposits and palaeostage indicators. Step‐backwater modelling of water‐surface profiles indicates that discharges ranging from 11000 to 17000 m3s−1have occurred six times in the gorge during the last 900 years. These flood reconstructions provide insight into the role of extreme flows in shaping bedrock channel morphology. In particular, the hydraulics of extreme flows can be related to boulder transport, and to the location of large boulder bars.Large boulder bars occur throughout the Herbert Gorge, being best developed at loci of stream power minima along the inside of bends, at tributary junctions, and at obstructions in the channel caused by bedrock highs. Only the flows exceeding approximately 8000 m3s−1are competent to transport the boulders which constitute the bars. In the straight channel reaches, the boulder accumulations and bedrock highs have a fairly regular spacing which appears to be independent of lithologic or structural controls. The bars provide an efficient means of energy dissipation, and they are interpreted as a result of the inherent high turbulence of flow in a steep channel. The regular spacing of the bars, and their correspondence with the hydraulics of large flows, suggest that the bars and associated bedrock highs may represent a self‐regulating mechanism akin to the pool‐riffle sequence of alluvial channels. It may therefore be appropriate to view bedrock channels as deformable on the timescale of ext

ISSN:0197-9337    

DOI:10.1002/esp.3290170106

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA study of the erosion rate and the stability of sandy slopes was conducted on an eastern arm of a parabolic coastal sand dune, De Blink, central Netherlands. The contribution of rabbits to these processes was found to depend on two types of activity; the building of caves and sand mounds of up to 1·5 m2in area; and the digging of shallow burrows, whereby amounts of sand up to 1 kg per burrow were excavated. The burrowing activity was found over the whole dune, while cave holes were dug mainly on the northern slope. The total amount of sand actually transported on the dune due to this activity is not clear yet, but their influence on the development of stepped slopes is well established

ISSN:0197-9337    

DOI:10.1002/esp.3290170107

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper deals with the effects of wind on rockwall dynamics. On 5 and 6 January, 1988 very strong northwest winds (blizzard) were blowing onto the rockwall of Mount Saint‐Pierre (alt.: 424 m), Gaspésie, Québec (Canada). The most violent recorded squall reached 99·4 km h−1. During this event, the summit plateau received a large amount of aeolian sediments originating from the shale rockwall that forms the mountain's northwest side. In the 15 to 20 m wide by 75 m long belt located along the top of the rockwall, over a 1200 m2area, a continuous layer of debris completely covered the snow. This layer of debris had a mean thickness of 11·4 mm, which represents an accumulated volume in the order of 13 m3. Largely dominated by sand and granules (2–4 mm), the 28 samples collected for grain‐size analysis also contained numerous thin shale flakes, many of which were longer than 10 mm. The largest flake measured had a width of 134 mm and a weight of 164·3 g. Six available14C dates provide information concerning mean cliff‐top aeolian sedimentation rate for the last thousand years (

ISSN:0197-9337    

DOI:10.1002/esp.3290170108

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290170109

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290170101

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY