Agents Of Erosion Research Articles

Erosion due to cultivation of calcareous clay soils on the hillsides of south west France. I. Effect of former farming practices

Between the principal river valleys of south west France, the tertiary molasse outcrops have produced a deeply undulating surface relief. Soil distribution in this upland landscape is highly disordered and the spatial organisation can only be understood from detailed examination of soil profiles. The considerable modifications to which the soil cover has been subjected may be explained by factors other than natural agents of erosion. Careful examination of former gullies and the hillside relief reveals the important erosive effect of the methods of cultivation used on these sloping soils. A simple model is proposed to test the effect of former contour ploughing in which soil was turned over towards the base of the slope. Simulation over a broad time scale gave the same results as those observed in the present landscape.

Geomorphic estimates of the stability of a uranium mill tailings containment cover: Nabarlek, Northern Territory, Australia

AbstractThe geomorphic stability of the cover (cap) over the pit of Nabarlek Uranium Mine in Arnhem Land, Northern Australia, is important because radon gas and other long‐lived radio‐nuclides arising from mill tailings must be contained for long periods. The primary agents of denudation in the region's seasonally wet tropical environment of low relief are rainwash, overland flow, rilling and gullying. Other agents of erosion are of less concern, although biogenic agents of erosion (e.g. termites and windthrow) may enhance fluvial activity.A combination of modelling, using the Universal Soil Loss Equation, and analogue estimates of denudation and thresholds of rilling and gullying from areas with similar geology, topography and climate are used to estimate the stability of the Nabarlek cover. Denudation rates are conservatively estimated at less than 100mm ky−1. It is suggested that with some minor design modifications the cover will retain its integrity for several thousand years.

Bioerosion rates on coral reefs: interactions between macroborers, microborers and grazers (Moorea, French Polynesia)

Abstract A two-year experimental study of bioerosion at Moorea Island, French Polynesia, clearly demonstrated the importance of microborers in the initial stages of the establishment of infaunal boring communities. Rates of erosion by micro- and macroborers and by grazers were estimated from measurements of carbonate removal from experimental substrates, using Image Analysis. The studied substrates have been exposed for 2, 6, 12 and 24 months. After 2 months of exposure, the only borers present in the substrates were cyanobacteria and one chlorophyte (Phaeophila sp.) and their bioerosion rate was estimated at 0.6 kg CaCO3 m−2 yr−1. In the course of the 2 years of exposure, recruitment of macroborers occurred and their estimated rates of erosion increased during this period from 2.15 to 90g CaCO3 m−2 yr−1. Carbonate removal by grazers was the dominant agent of erosion, responsible for 89% of the total bioerosion: 2.6 kg CaCO3 m−2 yr−1, as recorded in substrates exposed for 2 years. The measurable rates of bioerosion by microborers apparently decreased with the time of exposure from 0.6 to 0.2 kg m−2 yr−1, but these values are underestimations which need to be corrected by including the intensity of microboring in substrate layers removed by grazing. Bioerosion is dependent on numerous environmental factors such as depth, light availability, and nutrient supply. A good knowledge of bioerosional processes in modern environments could highlight bioerosion significance in the fossil record.

Pattern and Process in Alpine Vegetation and Landforms at Hill One, Southern Range, Tasmania

Hill One is a wind-exposed, alpine environment in southern Tasmania. The prevailing wind-stream is westerly. However, high intensity south-westerly winds associated with frost events appear to control the patterning of fjaeldmark. These winds cause necrosis of prostrate Richea scoparia and cushion plants on their south-western side and induce migration of individual plants in a north-easterly direction. Fjaeldmark is confined to the exposed mountain summit and terrace and step treads. Mosaic cushion heath occurs in more exposed and poorly drained areas than other heath communities. The horizontally bedded sediments of Hill One have been worked by erosional and depositional agents into a complex morphology. Large terraces and non-sorted steps are likely to have formed from altiplanation processes, that is, differential erosion of interbedded sediments, with accumulation of erosional debris at the foot of the risers. Depositional lobes and erosional washout features are actively forming in localised areas of concentrated drainage. The distribution of plant communities is closely associated with rockiness, wind exposure and drainage.

The importance of earthquake-induced landslides to long-term slope erosion and slope-failure hazards in seismically active regions

This paper describes a general method for determining the amount of earthquake-induced landsliding that occurs in a seismically active region over time; this determination can be used as a quantitative measure of the long-term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope-erosion rates and landscape evolution. The method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude, M , and seismic moment, M 0, of the earthquake. From worldwide data, a linear-regression relation between landslide volume, V, and M 0 is determined as: V = M 0/10 18.9(± 0.13), where V is measured in m 3 and M 0 is in dyn-cm. To determine the amount of earthquake-generated landsliding over time, this relation is combined with data on seismic-moment release for a particular region, which may be derived from either earthquake-history or fault-slip data. The form of the M 0− V relation allows the rate of production of earthquake-induced landslides over time to be determined from total rate of seismic-moment release without regard to the distribution of individual events, thus simplifying and generalizing the determination. Application of the method to twelve seismically active regions, with areas ranging from 13,275 to 2,308,000 km 2, shows that erosion rates from earthquake-induced landslides vary significantly from region to region. Of the regions studied, the highest rates were determined for the island of Hawaii, New Zealand, western New Guinea, and the San Francisco Bay region of California. Significantly lower rates were determined for Iran, Tibet, the Sierra Nevada-Great Basin region of California, and central Japan (for the time period from 715 AD to the present). Intermediate rates were determined for Peru, southern California, onshore California, Turkey, and central Japan (for the time period from 1586 AD to the present). To determine the relative, long-term importance of seismically triggered landslides, these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge. Comparisons with other slope processes indicate that earthquake-induced landslides are the predominant agents of slope erosion on the island of Hawaii, in the San Francisco Bay region, and in western New Guinea. For Hawaii, the San Francisco Bay region, and Sierra Nevada-Great Basin region of California, the erosion rates calculated for earthquake-induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge.

Subglacial meltwater origin and subaerial meltwater modifications of drumlins near Morley, Alberta, Canada

Drumlins in the Bow valley west of Calgary, Alberta, are interpreted as the product of subglacial and subaerial meltwater erosion. On the sides of the Bow valley highly elongated, streamlined, first-generation drumlins are aligned in an en-echelon fashion and are not significantly modified by post-glacial processes. In the valley bottom, scalloped, stubby, irregularly spaced second-generation drumlins are found in close association with valley fill. The drumlins are composed of bedrock and diamicton, and some are overlain by a thin gravel veneer. Stratified gravel is found on the leeward flanks of some second-generation drumlins. Meltwater erosional forms (s-forms) found on the limestone bedrock up-flow of the drumlins, and crescentic furrows around their proximal ends, indicate that subglacial meltwater beneath the Bow valley ice was probably the main erosive agent responsible for the shaping of the drumlins. The second-generation drumlins are believed to be the remnants of the first-generation drumlins that were dissected and reworked by postglacial, subaerial meltwater flow(s). Meltwater drainage from ice-dammed glacial Lake Kananaskis and possibly other glacially dammed tributary valley lakes, resulted in the deposition of megaripples (3.5 m high, 40 m wavelength) 8 km down-flow from the drumlins and reverse eddy deposits on the flanks of the drumlins. Post-glacial Bow River incision and terrace development has continued to further sculpt these forms.

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Braided rivers are of considerable importance to the geologist, geomorphologist and engineer and an understanding of their dynamics and deposits holds many key economic applications. This book presents the first interdisciplinary approach to the study of braided rivers, with comprehensive views on their dynamics, sedimentation and economic applications with examples drawn from modern and ancient braided rivers. Braided rivers form some of the world's largest lowland rivers and are common in upland and proglacial settings. They are the agents of substantial erosion, deposition and landscape evolution. For the geomorphologist and engineer, braided rivers often pose considerable problems through their high rates of sediment transport, rapid bank erosion, substantial bed scour and frequent channel shifting. Braidplain behaviour may therefore dictate the design of within-channel structures, such as bridges, as well as those on the floodplain such as roads and flood embankments. Braidplain management becomes especially important in parts of the world where these rivers dominate regions of high population density. Geologically, braided river deposits form some of the largest and most valuable aquifers, hydrocarbon reservoirs, placers and aggregate deposits. An understanding of their facies architecture, heterogeneity and the controls upon deposition is essential for the effective exploitation of resources as well as in the interpretation and reconstruction of ancient sedimentary environments.

The grizzly bear as an erosional agent in mountainous terrain

The grizzly bear as an erosional agent in mountainous terrain

Effects of fire and of clearing in a Mediterranean Quercus ilex woodland: An experimental approach

The object of the study is to compare the importance of soil and nutrient losses from plots in an ever green oak ( Quercus ilex) woodland under different environmental conditions; namely under undisturbed forest and at sites that had been clear felled and burnt under controlled conditions. At each site, the plots were instrumented with 10 Gerlach troughs located at the footslope of each plot, and with 12 troughs in the upper part of the burned plot inserted at regular intervals from the water divide. Raingauges were subsequently added and data on rainfall intensity collected at a nearby station. Results indicate that burning has a significant effect with respect to runoff and nutrient and sediment losses. The impact of clear-felling is much less. Sediment transport on the slope is not only caused by surface runoff but by other agents of erosion as well.

Sorbed Chemical Transport in Overland Flow: II. Enrichment Ratio Variation with Erosion Processes

AbstractBreakdown of soil aggregates by rainfall, loss of sediment, and the enrichment of fine particles, organic matter, and N in eroded sediment were measured in flume experiments with a constant rainfall rate of 100 mm h−1. Experiments covering two soil types with different soil surface configurations and slopes were designed to ensure beth exclusion of runoff entrainment as a major erosion factor, and that throughout exposure to rainfall the soil surface was unprotected by any significant depth of water. Sediment concentration differed initially for different experimental configurations, but all approached a single value after equilibrium was attained. Slope length did not have any effect on sediment concentration when rainfall was the only erosive agent at work and no surface rilling occurred. A rainfall‐induced mechanism of transient microrilling has been proposed for sediment transport when there is no significant depth of water or rills under rainfall. Aggregate size distribution of the eroded sediment was drastically different to that of the original soil. The percentage of fine particles in the eroded sediment was more than 50% of the total, while this size fraction constituted less than 5% of the original soil. The proportion of large aggregates in the eroded sediment was less than in the original soil, and the intermediate size fractions remained unchanged. This dramatic production of fine particles is due to direct raindrop impact on the exposed surfaces of soil aggregates. The resulting loss of fine sediment from large aggregates has been termed raindrop stripping, a process that can lead to significant enrichment of any sorbed chemical concentrated in the outer layers of soil aggregates. The peeling action of raindrops was shown to be responsible for the formation of the bulk of fine particles found in eroded sediment. This mechanism, together with the differential concentration of sorbed chemicals within the aggregates, were found to be the main cause of the enrichment of sorbed chemicals in the eroded sediment. The enrichment ratio of organic C and N beth decreased with cumulative soil loss and duration of the erosion event.

Effects of fluctuating levels of lake superior on morphological adjustments in the neebing‐mcintyre floodway, thunder bay, Ontario Canada

AbstractThe Neebing‐McIntyre Floodway, a relatively straight, trapezidal flood‐control channel, was constructed in 1983 to dispose of the combined flows of the Neebing and the McIntyre rivers into Lake Superior. Because of its location in a transitional fluvial/lacustrine environment, related processes had direct and indirect impacts on its morphological readjustments. During the post‐construction period (1983‐88) the combined peak flows of the Neebing and the McIntyre rivers never exceeded the two‐year design floods for the floodway, resulting in relatively low stream power and sediment transport rates. The average rate of sedimentation in the new channel (1100 m3 y−1) was thus much lower than the designers' estimated volume (11 800 m3 y−1). These low‐flow events coincided with high water levels in Lake Superior in 1985‐86, reinforcing the normal backwater effect in the floodway and further dampening its stream power. During this event the floodway behaved hydraulically almost like a reservoir, with fluctuating water levels and wind‐generated waves as the principal geomorphological agents of bank erosion. Estimates based on volumetric surveys indicate annual rates of bank erosion ranging from 0.03 to 0.16 m3 m−1 of bank length, with an average annual rate of 0.1 m3 m−1. The bank materials are composed of highly erodible sandy loam and loamy sand, which have a tendency to disperse and liquefy relatively easily. There are no significant spatial variations in erosion rates along a given bank but contrasts in the magnitude of erosion between the north and the south banks can be related to the relative exposure of a bank to average wind velocities, total duration of winds and the effective wind‐wave fetches.

A semiquantitative method of recording experimental tooth erosion and estimating occlusal wear in the rat

As the erosive agent, a sport-drink mixture with pH 3.2 was given to Osborne-Mendel rats for 6 weeks. Lingual surfaces of the right first mandibular molar crowns were chosen for the recording. With the aid of a drawing tube mounted on a stereomicroscope, enlarged drawings of the surfaces were made encircling the intact and eroded areas. A computer-coupled analyser was used to measure the areas of the total surface, intact surface, eroded enamel and exposed dentine in square millimetres. The data was evaluated statistically and used to calculate erosion changes and to estimate occlusal wear.

Studies on Soils and Potential for Soil Erosion in the Sheep Farming Area of South Greenland

Field data are lacking in studies of soil erosion in South Greenland and its relationship to soil processes and soil-forming factors. The main soil-controlling factors are climate, vegetation and other organisms, parent material, relief, time, and the influence of man. The potential for soil erosion is primarily expressed through the balance between the factor vegetation and the other soil-forming factors. The local conditions point to climatic or topographic gradients as the controlling agents of soil erosion when and if the vegetation cover collapses. The rate of soil erosion is dependent upon the existing soil, the parent material, temperature (length of growing season), and soil moisture. The latter two factors are especially decisive for controlling the vegetation cover. The soil profile is a snapshot of the effect of soil forming processes since the retreat of the ice about 9000 yr ago.The studies to date have shown that a two-sequence profile is found in most places. The top of the first sequence c...

Morphology and Evolution of Shale-Filled Paleochannel in Wilcox Group (Paleocene-Eocene), Southeast Texas: ABSTRACT

ABSTRACT Local extensive paleo-channels exist with the upper to lower Wilcox Group (Paleocene-Eocene) of the Gulf Coast of North America. Recent reports document paleo-channels of the Wilcox Group: Bejuco-La Laja, Chicontepec, DeSoto, Nautla, Ovejas, St. Landry, and Yoakum. An eighth channel, the Tyler (Hardin) channel suggests that passive submarine erosional forces shaped the channels prior to any active erosional forces such as those related to turbidity currents. The north-south trending Tyler (Hardin) channel is 24 mi (40 km) long and 12 mi (20 km) wide and displays over 1000 ft (300 m) of shale fill. The channel thalweg bifurcates updip into two meandering steep-walled channels which display numerous side gullies. The channel grew from the youthful to the mature stage through massive erosive mechanisms and during the mature stage may have been further enlarged by more active erosional agents such as turbidity currents. Old age began with increased peralic sedimentation and infilling of the channel with deep-marine shale. Eventually, progradation and eustatic drop in sea level dried the channel, its younger fill and older adjacent deposits. Paleo-channels are silient economic features. The deep-marine shale infill of the channel acts as a source of oil and gas and a seal for adjacent reservoir rock. Upward migration of oil through fractures, faults, and sediments fills reservoirs in overlying structures formed in nearshore deposits of the upper Wilcox. Most of the major oil and gas fields of the Wilcox Group in Tyler and Hardin Counties are localized in the structures above the underlying channel fill.

Early Late Cretaceous to Holocene Seismic Stratigraphy and Geologic History of Southeastern Gulf of Mexico

Multifold seismic reflection profiles were used in conjunction with results from Deep Sea Drilling Project (DSDP) Leg 77 to interpret the early Late Cretaceous to Holocene geologic history of the southeastern Gulf of Mexico. During the mid-Cenomanian(?) to early Paleocene(?), this region began to record the effects of a collision between a northward-migrating island arc (now part of Cuba) and a salient of the North American plate. More than 2 km (6,560 ft) of gravity-flow deposits accumulated in an elongate structural corridor or foredeep along the base of the modern Cuban slope, while the slope itself was the site of both folding and overthrusting. Clastics continued to dominate the depositional regime until the late Eocene, at which time the Cuban arc had been firmly we ded to North America. A late middle to early late Eocene hiatus in Site 540, which coincides with a prominent regional seismic unconformity, marks the transition from predominantly terrigenous input to pelagic/hemipelagic deposition. Since the late Eocene, the southeastern gulf has recorded multiple cycles of deposition and erosion. Unconformities displayed on seismic profiles are numerous. Erosional agents have included the Gulf Stream system, and turbidity currents and debris flows concentrated in the vicinity of submarine canyons. Continuing slope instability is indicated by slide/slump planes along canyon walls.

Surface geology from Viking landers on Mars: A second look

Aside from reddish dust, products of martian weathering are not abundantly obvious on Viking lander images. Surface stones appear sound, spalls and disintegration fragments are largely lacking, pitting of stones is probably not due to differential weathering, and reddish stone colors more likely result from adhered dust than from patination. Judging from wind-scoured drifts, deflated ground, rippled bed forms, lee-side tails, basal scours, fretted rocks, and ubiquitous dust, wind is currently the most effective transportive and erosive agent. The dogma that martian eolian material is almost exclusively of 10–100 µ size is challenged by granule ripples and the possibility that wind-drifted deposits consist largely of sand-sized particles. Fretting is more common than faceting on martian ventifacts. Crusts on martian surface fines are more akin to case-hardened rinds than to true duricrust. Crusting, a possibly continuing process, may be the product of atmospheric breathing of the regolith. Pits on surfaces of many martian stones are probably vesicles modified by eolian erosion. Pits on nonvesicular rocks may be solely the product of wind blasting. Vesicular lava, dense lava, and breccias are the most likely rocks among surface stones around the landers. The “bedrock” outcrops near VL-1 may be large boulders embedded in a breccia substrate. Pyroclastics seem a likely constituent of surface deposits.

Néotectonique et morphogénèse insulaire en Grèce : le massif du Mont Ida (Crète)

The limestone high moutains of the Crète island, and their margins present remarkable patterns and formations brought up during neotectonic and bioclimatic controls very active on erosion agents. Many old landscapes have been shaped again (tropical karst to nivo karst ...). Even monogenic landscapes exist : gorges, detritic fans ... For the first time also a tropical glacial relief is described at this latitude in the south of the mediterranean regions.

Catabolin???A Cartilage Catabolic Factor from Synovium

Resorption of cartilage matrix is usually considered to be due to extrinsic proteases, generally thought to be the neutral metalloproteases, including collagenase. Such enzymes can be secreted from synovial tissue and in acute forms of arthritis they are believed to be the main agents of pannus erosion. However, such enzyme secretion has not been clearly demonstrated to be the causative agent in either rheumatoid arthritis or in osteoarthritis. For example, no specific inhibitors of these proteinases have yet been proved effective in vivo. Recent experiments at the Strangeways Research Laboratory have demonstrated that viable chondrocytes of animal and human articular cartilage are capable of resorbing their surrounding matrix without the aid of extrinsic enzymes. We now know that such resorption can be stimulated by the action of a low molecular weight peptide released from living synovial and other connective tissues. These messengers (catabolins) are capable of stimulating chondrocytes to degrade totally both proteoglycan and collagen. The purification, properties, regulation and action of catabolism are under investigation to determine the role for catabolin in arthritis.

Ice Processes and Related Sedimentary Features in Tidal Flats, St. Lawrence Estuary, Quebec, Canada: ABSTRACT

Four to five months each year, ice is an active agent of erosion, transportation, sedimentation, and protection in tidal-flat environments along the St. Lawrence Estuary. Characteristic erosional and sedimentary features include chaotic microrelief up to 60 cm high, circular depressions 20 to 50 cm deep and up to a few meters in diameter, furrows 20 to 35 cm deep and up to 2 km long, ice-push ridges, deformational structures, ice-rafted boulders, and clumps of coarse and fine-grained material scattered throughout tidal flats. Every year, millions of tons of sediment of various texture are incorporated into ice, removed from the shore and nearshore zones, and transported over various distances ranging from a few decimeters to many kilometers. During the winter, the ice cov r protects the tidal flats from wave and current erosion and allows deposition of 20 to 35 cm of soft mud under the ice sheet in the macrotidal zone. Modern cold region tidal flats show characteristic sedimentary features, structures, and sequences that can be useful in identifying ancient shelf sedimentary environments. End_of_Article - Last_Page 919------------

The application of erosion slowness theory to hillslope formation

AbstractA method of analysis for predicting the time development of hillslope profiles is presented. The technique is based upon the assumption of weathering limited erosion and assumes that the local surface normal erosion rate is dependent upon the local flux of erosional agent and a function of the local slope gradient. This technique has been previously applied with success to analogous erosional processes in the sand blasting, chemical and energetic atom bombardment induced ablation of solids. The analysis shows how linearly segmented profiles can develop from initially curved surfaces and indicates the progress of profiles to stable end forms. Actual application to geomorphological situations is limited by lack of knowledge of micro‐environmental erosion fluxes and the gradient dependence of erosion and it is suggested that field observations and laboratory simulations could be helpful in determining the utility of the analysis technique outlined here.