bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of deforestation on slope and channel evolution in the tectonically active Darjeeling Himalaya
Authors: Froehlich Wojciech , Starkel Leszek 
Published: February 2007

AbstractThe main indicators of Quaternary tectonic uplift are the young mountain slopes of the Darjeeling Himalaya, rising straight above the Ganga–Brahmaputra foredeep, fragments of uplifted river terraces and fresh fault scarps. Evidence for the continuation of the uplift includes downcutting of the Tista and other straight rivers in the bedrock, continuing aggradation in the plains and overriding of the metamorphic rocks on the alluvia. Owing to deforestation and extensive land use, the earlier natural tendency of a dominance of channel incision over slope degradation has changed to prevailing aggradation, even in steep valley reaches, caused by intensive slope mass movements and the overloading of the mountain creeks. Aggradation progresses upstream along the rivers dissecting the mountain front.
Tectonic causes of landslides
Authors: Alexander David , Formichi Renzo 
Published: February 2007

AbstractThe relationship between mass movements and tectonic lineaments is investigated in the Pliocene sand and clay terrains of Montepulciano (central Italy). Satellite images and aerial photographs show six families of lineament in southern Tuscany, all of which are present in the Montepulciano area. The orientation, location and density of these are related to corresponding attributes of morphological phenomena such as retrogressive slumps, drainage density and slope angle. Rose diagrams, stereographic plots and statistical analysis all reveal a close correspondence between slumping mass movements and the directions and spatial concentrations of fracture traces. Although slopes and valley trends respond more closely to Apennine (NW‐trending) and anti‐Apennine (NE‐trending) lineaments, the longitudinal axes of landslides are strongly orientated NNW to N, the direction of one of the most significant lineament groups in western central Italy and the local study area.
A note on the role of the lichen collema auriforma in solution basin development on a carboniferous limestone substrate
Authors: Moses C. A. , Smith B. J. 
Published: February 2007

AbstractA study carried out on Carboniferous limestone in the north and west of Ireland supports the idea that rock substrate is removed by the direct mechanical action of lichens. An experiment in which the lichen Collema auriforma was subjected to a number of wetting‐drying cycles, showed, using scanning electron microscopy, that contraction of the lichen thallus during the drying phase plucked rock fragments from the substrate surface. This process could contribute to the formation of karstic features including solution basins.
Role of porolithon algal‐ridge growth in the development of the windward coast of Tongatapu Island, Tonga, South Pacific
Authors: Nunn Patrick D. 
Published: February 2007

AbstractA description of the algal ridge fringing the windward coasts of the island of Tongatapu is given. Three coastal types can be distinguished according to the height of the algal ridge. Type A coasts have a low algal ridge and low wave energy. Surge channels are few and uncovered. Blowholes are poorly developed. The reef flat is wide and has numerous living corals. Many beaches occur except around promontories where a cliff‐foot notch is actively forming. Type B coasts have a medium‐height algal ridge and experience moderate wave energy. Surge channels are longer, more frequently covered and blowholes consequently better developed. The reef flat/shore platform has less coral living on its surface. Large beaches along type B coasts are the outcome of sediment becoming trapped on the shoreward side of the algal ridge following storms. Type C coasts have a high algal ridge and are characterized by a high‐energy regime. Surge channels are almost all covered, giving rise to spectacular blowholes, except where collapse has caused the algal ridge to assume a buttressed rather than linear form. The shore‐platform surface is devoid of living coral and lies above high‐tide level. The cliff‐foot notch is shielded by the algal ridge from direct wave attack. A notch is forming on the upper part of the outer slope of the shore platform: such notches were observed only along type C coasts.A model for Holocene coastline development is outlined. The reef established on the mid‐Holocene shore platform emerged abruptly by ˜ 2 m as the result of coseismic uplift around 4000 years ago. Sea level fell (around 3000 years ago): erosion concentrated on reducing emerged shore‐platform level. Sea level stabilized around 1000 years ago: the emerged shore platform continued to be lowered; around 600 years ago, algal‐ridge growth commenced thereon. Rates of vertical growth ranged from 0·5 to 2·1 mm a−1. The process regime along type C coasts changed around 362 years ago when the algal ridge reached a sufficient height to shield the shoreline from the processes which had fashioned it and a lower‐level notch began to be cut on the reef slope.
Quantitative sediment source ascription using magnetic measurements in a reservoir‐catchment system near Nijar, S.E. Spain
Authors: Yu Lizhong , Oldfield Frank 
Published: February 2007

AbstractThe magnetic properties of sediments from a dried‐out reservoir and its inflowing streams were measured to provide a basis for sediment source determination. Quantitative estimates of source component proportions in the reservoir sediments were made using linear programming procedures. The study confirms that this type of research must be based on a detailed knowledge of the relationship between magnetic properties and particle size in both the sediments and the potential sources. In the case of the site studied, the Isabel II reservoir, near Nijar, S.E. Spain, the sediments generated by contemporary surface processes within the reservoir catchment fail to reflect fully the 19th century material largely responsible for the rapid infill of the reservoir. An additional source type, namely unweathered schist‐derived material not represented in the fine sediments sampled within channels upstream from the reservoir, has to be included in the model before calculations of source component contributions can be made. It is inferred that one or more high magnitude, low frequency event outside the amplitude of the most recently operating processes was largely responsible for the infilling of the reservoir.
Effects on bedload transport of experimental removal of woody debris from a forest gravel‐bed stream
Authors: Smith R. D. , Sidle R. C. , Porter P. E. 
Published: February 2007

AbstractExperimental removal of woody debris from a small, gravel‐bed stream in a forested area resulted in a four‐fold increase in bedload transport at bankfull discharge. This was caused by increased transportability of sediment previously stored upslope of debris buttresses or in low‐energy hydraulic environments related to debris. Bank erosion delivered additional sediment to the channel, and transport energy was increased by an inferred increase in the component of total boundary shear stress affecting grains on the bed. Increased transport following debris removal in May 1987 continued throughout the entire autumn storm season through late November 1987, indicating persistent adjustment of the stream bed and banks despite marked response to earlier flows as large as bankfull. Stream bed adjustments included development of a semi‐regular sequence of alternate bars and pools, many of which were spaced independently of former pool locations.
Soil hydrophobicity effects on rainsplash: Simulated rainfall and photographic evidence
Authors: Terry James P. , Shakesby Richard A. 
Published: February 2007

AbstractLaboratory rainfall simulation experiments indicate greater splash losses for hydrophobic (water repellent) than for wettable sandy loam soils at different rainfall intensities, durations and soil surface inclinations. Using synchronized video cameras with different shutter speeds and stroboscopically illuminated 35 mm still photography, differences in splash droplets and ejection trajectory characteristics are examined. For hydrophobic soil, raindrop impact gives rise to fewer, larger, slower‐moving daughter ejection droplets which carry more sediment and hence follow shorter range trajectories compared with wettable soil. Implications for erosion of hydrophobic soils are discussed.
Modelling late‐holocene snow‐avalanche activity: Incorporating a new approach to lichenometry
Authors: McCarroll Danny 
Published: February 2007

AbstractWhere snow avalanches descend steeply into large rivers, displacing bedload, avalanche boulder‐ramparts may accumulate, retaining a record of late‐Holocene snow‐avalanche frequency. The age frequency of surface boulders on 12 such features in upper Jostedalen, southern Norway, was investigated using the size‐frequency distribution of lichens. A model was constructed to simulate the influence of variations in avalanche frequency sinceAD1325 on lichen‐size‐frequency distributions.Using this modelling approach it is not possible to define a unique pattern of avalanche activity to account for the observed lichen‐size‐frequency distributions, but it is possible to place strict limits on the range of scenarios that are acceptable. The results suggest that maximum avalanche activity occurred during the 19th century, after the peak of the Little Ice Age. This conflicts with historical records of avalanche damage to property at lower altitude in nearby valleys, which may reflect avalanche activity only during a short period of extreme climatic conditions. Close agreement between the records of snow avalanches and debris flows suggests that both reflect periods of high winter snowfall and rapid spring melting rather than low temperature. Future ‘greenhouse warming’ may therefore result in increased avalanche activity in southern Norway.
River response to channel regulation: Case study of the Raba river, Carpathians, Poland
Authors: Wyzga Bartłomiej 
Published: February 2007

AbstractProcesses induced by the channelization of the Raba River in the present century are examined to illustrate the response of a gravel‐bed stream following narrowing and straightening of its channel. Up to 3 m of incision has occurred. The change from a slow and relatively steady degradation in the lower reaches to separate degradation events in the higher reaches is attributed to the differential rate of headcut retreat and to the control exerted by mid‐channel bars upon the rate of river‐energy dissipation. Progressive outwashing of finer grains from bed material has followed the diminishing sediment yield of the basin and the increase in stream power. The ensuing growth in mean grain size and changes in sediment fabric have increased boundary resistance to flow and reduced particle susceptibility to entrainment. Downstream magnification of peak discharges has become increasingly pronounced with the advancing incision. The decrease in flood‐plain storage and self‐acceleration of flows passing the relatively deep and straight channel has caused flood waves to become progressively more flashy in nature.An increase in channel depth and reduction in gradient caused by downward and backward erosion, as well as bed material coarsening has promoted the re‐establishment of an equilibrium. Conversely, flow velocity increases due to flow concentration in the deepened channel. Reduction in grain mobility allows the river to attain a new equilibrium at flow‐velocity and stream‐power levels higher than before the channelization.Numerous disadvantages of the applied regulation scheme and its failure to reduce flood hazard raise the question of its maintenance. To be successful, any regulation design must take into account changes in sediment supply and flood hydrographs resulting from the simultaneous alterations in basin management.
Geometry, bed topography and drainage system structure of the haut glacier d'Arolla, Switzerland
Authors: Sharp Martin , Richards Keith , Willis Ian , Arnold Neil , Nienow Peter , Lawson Wendy , Tison Jean‐Louis 
Published: February 2007

AbstractAs part of an integrated study of the hydrology, meltwater quality and dynamics of the Haut Glacier d'Arolla, Switzerland, the glacier's drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier. This structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by (a) the subglacial hydraulic potential surface, and (b) the subglacial bedrock surface. These reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio‐echo sounding techniques. The two reconstructions simulate the drainage system structures expected for (a) closed channels, in which water is pressurized by the overlying ice, and (b) gravity‐driven, open‐channel flow. The closed‐channel model provides the best fit to the observed structure, even though theoretical calculations suggest that, under summer discharge conditions, open‐channel flow may be widespread beneath the glacier. Possible reasons for this apparent discrepancy are discussed.
The role of wind direction in eolian transport on a narrow sandy beach
Authors: Nordstrom Karl F. , Jackson Nancy L. 
Published: February 2007

AbstractComparison of eolian transport during five high‐velocity wind events over a 29 day period on a narrow estuarine beach in Delaware Bay, New Jersey, USA, reveals the temporal variability of transport, due to changes in direction of wind approach. Mean wind speed measured 6 m above the dune crest for the five events ranged from 8·5 to 15·9 ms−1. Mean wind direction was oblique to the shoreline (63° from shore‐normal) during one event but was within 14° of shore‐normal during the other events.Eolian transport is greatest during low tide and rising tide, when the beach source area is widest and when drying of surface sediments occurs. The quantity of sediment caught in a vertical trap for the five events varied from a total of 0·07 to 113·73 kgm−1. Differences in temperature, relative humidity and moisture and salt content of surficial sediments were slight. Mean grain sizes ranged from 0·33 to 0·58 mm, causing slight differences in threshold shear velocity, but shear velocities exceeded the threshold required for transport during all events.Beach width, measured normal to the shoreline, varied from 15·5 to 18·0 m; beach slope differed by 0·5°. The oblique wind during one event created a source width nearly double the width during other days. Beach slope, measured in the direction of the wind, was less than half as steep as the slope measured normal to the shoreline. The amount of sand trapped during the oblique wind was over 20 times greater than any other event, even those with higher shear velocities. The ability of the beach surface to supply grains to the air stream is limited on narrow beaches, but increased source width, due to oblique wind approach, can partially overcome limitations of surface conditions on the beach.
Meanders caused by hyperconcentrated water flow: An example from the loess plateau, China
Authors: Jiongxin Xu 
Published: February 2007

AbstractThis paper describes meandering alluvial rivers with mean annual suspended‐sediment concentrations of more than 100 kgm−3 on the Loess Plateau, China, and explains their formation as caused by the effect of hyperconcentrated water flow. When the river is dominated by hyperconcentrated flow, the rate of energy expenditure required for sediment transport declines significantly. Accordingly, the river channel adjusts itself to a lower channel gradient by increasing the river length, resulting in a meandering channel. Since the stable transportation of sediment by hyperconcentrated flow is dependent on river channel boundary conditions, the latter play an important role in the formation of meanders of this kind. The paper also discusses the conditions for the discrimination of meandering and braided rivers in this area.
The significance of rainstorm variations to shallow translational hillslope failure
Authors: Brooks S. M. , Richards K. S. 
Published: February 2007

AbstractLandsliding in eastern Scotland results from high‐magnitude rainstorms generated under either cyclonic or anticyclonic conditions, particularly during the summer. Data from Aviemore indicated that cyclonic storms produce higher rainfall totals than anticyclonic storms, as well as being of longer duration and lower intensity. The distribution of rain during individual storms also varies with the synoptic conditions under which the storms are produced. These different rainfall characteristics produce different geomorphic responses, which can be investigated in detail using physical based modelling. In this paper, a physically based coupled hydrology–stability model is used to assess the significance of these rainfall characteristics to soil moisture response and slope instability for mature podsols. The results provide evidence that rainstorms of different synoptic origin produce varying hydrological response, involving both the extent and the timing of moisture content change. This affects the depth and timing of slope failure, with anticyclonic storms promoting a large, rapid response in the factor of safety at shallow depths within the soil. Cyclonic storms produce a more gradual response, with the region of probable failure being deeper. Futhermore, each of these storm types is associated with different rainfall distributions, and this is also shown to have a significant effect on the timing and depth of slope instability.
On being a ‘real’ geomorphologist
Authors: Rhoads Bruce L. 
Published: February 2007

AbstractIn a recent editorial Richards (1990) advocated a realist perspective for geomorphology. Scientific realism, defined broadly, is the doctrine that science attempts to generate true knowledge of the observable and unobservable (i.e. non‐empirical) aspects of an objective world. Various brands of realism exist; the particular version cited by Richards (1990) has not strongly influenced mainstream philosophy of science. Also, critical rationalism, which Richards (1990) contrasts with realism, fully adopts a realist perspective. In its broadest sense, realism encompasses the entire spectrum of geomorpho‐logic research, thus providing a unifying philosophical framework for geomorphology.
Channel and floodplain response to recent abrupt climate change: The tyne basin, Northern England
Authors: Rumsby Barbara T. , Macklin Mark G. 
Published: February 2007

AbstractThis paper examines the timing, nature and magnitude of river response in upland, piedmont and lowland reaches of the Tyne basin, northern England, to high‐frequency (20–30 year) changes in climate and flood regime since 1700 AD. Over this period fluvial activity has been characterized by alternating phases of river‐bed incision and stability coinciding with non‐random, decadal‐scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large‐scale upper atmospheric circulation patterns. Episodes of widespread channel bed incision (1760–1799, 1875–1894, 1955–1969) result from a higher frequency of large floods (> 20 year return period) and cool, wet climate under meridional circulation regimes. Phases of more moderate floods (5–20 year return period), corresponding to zonal circulation types (1820–1874, 1920–1954), are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment, and channel narrowing and infilling downstream. Rates of fluvial activity are reduced in intermediate periods (1800–1819, 1895–1919) with no dominant circulation regime associated with lower flood frequency and magnitude. The results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change.
Criteria for recognition of constructional silicic lava flow surfaces
Authors: Anderson Steven W. , Krinsley David H. , Fink Jonathan H. 
Published: February 2007

AbstractSurface‐exposure dating (SED) methods typically rely on the measurement of a geochemical parameter that systematically changes with time. A pivotal task in the calibration of many of these techniques is to demonstrate that lava flow surfaces sampled for dating have not experienced erosion. Although criteria for identification of constructional basaltic lava flow surfaces have been published, no such criteria presently exist for the recognition of constructional silicic flows. Here we present several criteria for identifying constructional silicic lava flow features in the field. First, crease structures are fractures with easily identified, curved, striated walls that are commonly observed on recent and active silicic lava flows. Crease structures form during extrusion, and are resistant to mechanical disintegration because they expose dense material from the flow interior. Second, some crease structures break apart during formation, leaving a deposit of striated blocks on the flow surface. Crease structure blocks are striated on only one side, whereas blocks from internal columnar joints exposed through erosion are striated on two or more sides. Only the striated side of the crease structure block is definitively constructional. Finally, many silicic flow surfaces exhibit expanded or breadcrusted textures. These features consist of a dense, fractured rind, 1 –2cm thick, enclosing highly vesicular material. Breadcrust flow textures appear similar to breadcrust bombs produced during volcanic explosions, so it is imperative to demonstrate that they are part of the lava flow surface. These criteria should enable investigators to positively identify constructional silicic lava flow surfaces when calibrating an SED method.
Subglacial observations from øksfjordjøkelen, North Norway
Authors: Rea Brice R. , Brian Whalley W. 
Published: February 2007

AbstractStepped bedrock topography at the snout of a small outlet glacier from Øksfjordjøkelen, North Norway, produces an extensive subglacial cavity system which stretches some 70m across and 100m up‐glacier, giving access beneath ice ≤50 m thick. Inside the cavity, regelation ice, clean glacier ice and deforming basal ice have been observed. Samples were taken and basal debris concentrations at the glacier sole were found to vary between 0.005 and 15.38 per cent by volume. The basal ice velocity has been determined using a linear variable differential transformer attached to an analogue recorder, and also by means of measured displacements of ice crews and clasts embedded in the basal ice. Velocities were found to differ both spatially and temporally from a maximum of 2.55 mm h1 to a minimum of 0.3 mm h−1. The measurements and observations, which have been related to present theory, show how spatially averaged values for a number of variables could lead to inaccuracies in predicted erosion values, certainly at a local scale. On the exposed foreland, jointcontrolled lee‐side faces provide evidence for extensive subglacial plucking (here taken to mean the removal of preloosened bed material and/or material resulting from bed failure). Indeed, in the cavity the early stages of removal of joint‐controlled blocks by ice deformation along joints have been observed. The importance of debris‐rich basal ice is shown in the formation of large striations (up to 500cm × 16cm × 2cm) present on the foreland.