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1.
The quantification of debris‐flow hazard requires estimates of debris‐flow frequency and magnitude. Several methods have been proposed to determine the probable volume of future debris flows from a given basin, but most have neglected to account for debris recharge rates over time, which may lead to underestimation of debris‐flow volumes in basins with rare debris flows. This paper deals with the determination of debris recharge rates in debris‐flow channels based on knowledge of debris storage and the elapsed time since the last debris flow. Data are obtained from coastal British Columbia and a relation is obtained across a sample of basins with similar terrain and climatic conditions. For Rennell Sound on the west coast of the Queen Charlotte Islands, the power‐law relation for area‐normalized recharge rate, Rt, versus elapsed time, te was Rt = 0·23te?0·58 with an explained variance of 75 per cent. A difference in recharge rates may exist between creeks in logged and unlogged forested terrain. The power function for undisturbed terrain was Rt = 0·20te?0·49, while the function for logged areas was Rt = 0·30te?0·77. This result suggests that for the same elapsed time since the last debris flow, clearcut gullies tend to recharge at a slower rate than creeks in old growth forest. This finding requires verification, particularly for longer elapsed times since debris flow, but would have important implications for forest resource management in steep coastal terrain. This study demonstrates that commonly used encounter probability equations are inappropriate for recharge‐limited debris flow channels. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

2.
There exists a need to advance our understanding of debris-covered glacier surfaces over relatively short timescales due to rapid, climatically induced areal expansion of debris cover at the global scale, and the impact debris has on mass balance. We applied unpiloted aerial vehicle structure-from-motion (UAV-SfM) and digital elevation model (DEM) differencing with debris thickness and debris stability modelling to unravel the evolution of a 0.15 km2 region of the debris-covered Miage Glacier, Italy, between June 2015 and July 2018. DEM differencing revealed widespread surface lowering (mean 4.1 ± 1.0 m a-1; maximum 13.3 m a-1). We combined elevation change data with local meteorological data and a sub-debris melt model, and used these relationships to produce high resolution, spatially distributed maps of debris thickness. These maps were differenced to explore patterns and mechanisms of debris redistribution. Median debris thicknesses ranged from 0.12 to 0.17 m and were spatially variable. We observed localized debris thinning across ice cliff faces, except those which were decaying, where debris thickened. We observed pervasive debris thinning across larger, backwasting slopes, including those bordered by supraglacial streams, as well as ingestion of debris by a newly exposed englacial conduit. Debris stability mapping showed that 18.2–26.4% of the survey area was theoretically subject to debris remobilization. By linking changes in stability to changes in debris thickness, we observed that slopes that remain stable, stabilize, or remain unstable between periods almost exclusively show net debris thickening (mean 0.07 m a-1) whilst those which become newly unstable exhibit both debris thinning and thickening. We observe a systematic downslope increase in the rate at which debris cover thickens which can be described as a function of the topographic position index and slope gradient. Our data provide quantifiable insights into mechanisms of debris remobilization on glacier surfaces over sub-decadal timescales, and open avenues for future research to explore glacier-scale spatiotemporal patterns of debris remobilization. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

3.
This study assessed the levels of marine debris pollution and identified its main sources in Korea. The surveys were bimonthly conducted by NGO leaders and volunteers on 20 beaches from March 2008 to November 2009. The quantities of marine debris were estimated at 480.9 (±267.7) count ⋅ 100 m−1 for number, 86.5 (±78.6) kg ⋅ 100 m−1 for weight, and 0.48 (±0.38) m3 ⋅ 100 m−1 for volume. The level of marine debris pollution on the Korean beaches was comparable to that in the coastal areas of the North Atlantic ocean and South Africa. Plastics and styrofoam occupied the majority of debris composition in terms of number (66.7%) and volume (62.3%). The main sources of debris were fishing activities including commercial fisheries and marine aquaculture (51.3%). Especially styrofoam buoy from aquaculture was the biggest contributor to marine debris pollution on these beaches.  相似文献   

4.
In 1996 a large debris flow occurred on the fan of the Chalance torrent system, a tributary of the Séveraisse river, French Alps. To investigate the magnitude and frequency of such debris flows on this fan, fieldwork was carried out in the summer of 1998. Detailed investigation revealed that several debris flows have occurred in the past 200 years. Lichenometry was used as a dating technique to obtain the frequency of these debris‐flow events. Also the volume of these flows was estimated. With these data a magnitude–frequency relationship was constructed. This relationship shows a maximum magnitude of at least 50 × 103 m3. Based on data for the past c. 150 years, a debris flow of such a volume appears to have a recurrence interval of approximately 34 years. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

5.
Calcitic stalagmites from caves in the Sauerland, Germany, prove the existence of sub-Milankovitch cycles in precipitation during the last 6000 yr. The δ18O record dated with Th/U is interpreted as an indicator of paleohumidity. Spectral analysis of δ18O from 6000 a BP up to the recent top of a stalagmite from the Atta cave yields statistically significant peaks at 1450, 117, 64 and 57 a. Additionally we find a good correlation of the stalagmite’s δ18O and Δ14C from European tree rings. The 1450 a cycle in the stalagmite probably is analogous to the pervasive millennial scale climate cycle described by Bond et al. [Science 278 (1997) 1257-1266; 294 (2001) 2130-2136] derived from the amount of ice rafted debris in deep sediments from the North Atlantic. Our results suggest that the centennial to millennial shifts observed in the North Atlantic are accompanied by synchronous shifts of the climate in Northern and Central Europe, which most probably can be attributed to solar irradiation variations.  相似文献   

6.
Based on the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy, this paper presents an approach to simulate debris flow maximum run‐out. On the basis of the flow source areas and an average thickness of 1·2 m of the scarps, we estimated debris flow volumes of the order of 104 and 105 m3. Flow mobility ratios (ΔH/L) derived from the x, y, z coordinates of the lower‐most limit of the source areas (i.e. apex of the alluvial fan) and the distal limit of the flows ranged between 0·27 and 0·09. We performed regression analyses that showed a good correlation between the estimated flow volumes and mobility ratios. This paper presents a methodology for predicting maximum run‐out of future debris flow events, based on the developed empirical relationship. We implemented the equation that resulted from the calibration as a set of GIS macros written in Visual Basic for Applications (VBA) and running within ArcGIS. We carried out sensitivity analyses and observed that hazard mapping with this methodology should attempt to delineate hazard zones with a minimum horizontal resolution of 0·4 km. The developed procedure enables the rapid delineation of debris flow maximum extent within reasonable levels of uncertainty, it incorporates sensitivities and it facilitates hazard assessments via graphic user interfaces and with modest computing resources. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

7.
While many surface foraging seabirds ingest plastic, the spatial overlap of these far-ranging predators with debris aggregations at-sea is poorly understood. We surveyed concurrent distributions of marine birds and debris along a 4400 km cruise track within a debris accumulation area in the North East Pacific Ocean using line and strip transect methods. Analysis of debris and bird distributions revealed associations with oceanographic and weather variables at two spatial scales: daily surveys and hourly transects. Hourly bird abundance (densities; 0-9 birds km−2) was higher in lower wind and shallower water. Hourly debris abundance (densities; 0-15,222 pieces km−2) was higher in lower wind, higher sea-level atmospheric pressure and deeper water. These results suggest that debris and seabird abundance and community structure are influenced by similar environmental processes, but in opposing ways, with only three far-ranging seabird species (Black-footed Albatross, Cook’s Petrel and Red-tailed Tropicbird) overlapping with high debris concentrations over meso-scales.  相似文献   

8.
Terrestrial cosmogenic nuclide concentrations in sediment are used to quantify mean denudation rates in catchments. This article explores the differences between the 10Be concentration in fine (sand) and in coarse (1–3 or 5–10 cm pebbles) river sediment. Sand and pebbles were sampled at four locations in the Huasco Valley, in the arid Chilean Andes. Sand has 10Be concentrations between 4.8 and 8.3·105 at g−1, while pebbles have smaller concentrations between 2.2 and 3.3·105 at g−1. It appears that the different concentrations, systematically measured between sand and pebbles, are the result of different denudation rates, linked with the geomorphologic processes that originated them. We propose that the 10Be concentrations in sand are determined by the mean denudation rate of all of the geomorphologic processes taking place in the catchment, including debris flow processes as well as slower processes such as hill slope diffusion. In contrast, the concentrations in pebbles are probably related to debris flows occurring in steep slopes. The mean denudation rates calculated in the catchment are between 30 and 50 m/Myr, while the denudation rates associated with debris flow are between 59 and 81 m/Myr. These denudation rates are consistent with those calculated using different methods, such as measuring eroded volumes.  相似文献   

9.
As marine debris levels continue to grow worldwide, defining sources, composition, and distribution of debris, as well as potential effects, becomes increasingly important. We investigated composition and abundance of man-made, benthic marine debris at 1347 randomly selected stations along the US West Coast during Groundfish Bottom Trawl Surveys in 2007 and 2008. Anthropogenic debris was observed in 469 tows at depths of 55-1280 m. Plastic and metallic debris occurred in the greatest number of hauls followed by fabric and glass. Mean density was 67.1 items km−2 throughout the study area but was significantly higher south of 36°00′N latitude. Mean density significantly increased with depth, ranging from 30 items km−2 in shallow (55-183 m) water to 128 items km−2 in the deepest depth stratum (550-1280 m). Debris densities observed along the US West Coast were comparable to those seen elsewhere and provide a valuable backdrop for future comparisons.  相似文献   

10.
In 2008 two male sperm whales (Physeter macrocephalus) stranded along the northern California coast with large amounts of fishing net scraps, rope, and other plastic debris in their stomachs. One animal had a ruptured stomach, the other was emaciated, and gastric impaction was suspected as the cause of both deaths. There were 134 different types of nets in these two animals, all made of floating material, varying in size from 10 cm2 to about 16 m2. The variability in size and age of the pieces suggests the material was ingested from the surface as debris rather than bitten off from active gear. These strandings demonstrate that ingestion of marine debris can be fatal to large whales, in addition to the well documented entanglements known to impact these species.  相似文献   

11.
A new theory is described for the uptake of U in an open system applied to the dating of archaeological bones. Analytical solutions are obtained for the rate of radioactive decay of 238U, 234U and 230Th as a function of position for the case where both 238U and 234U diffuse across a bone, and where external supply of 234U is not in equilibrium with 238U. The new theory constitutes a forward model for predicting 238U, 234U and 230Th activity profiles across a bone given an age and diffusion coefficient. The forward model can be used in an inversion process whereby observations of activity profiles of 238U, 234U and 230Th as a function of position are used to infer the bone age of a sample together with robust measures of uncertainty. Differences from previous studies are that no closed system assumptions are required and no apparent age calculations necessary, while diffusion of 234U across the bone is accounted for in the inversion process. The procedure also does not require U-concentration profiles for the calculation of model parameters. The measurement of U-concentration profiles are, however, useful for the assessment of the reliability of the calculated results. Because of the assumption of constant 234U/238U ratios at the boundaries of the bone, DAD age results are generally older than closed system U-series results derived from the same isotopic data. Allowance is made for both correlated and uncorrelated errors in activity measurements as well as theoretical error caused by inhomogeneities in the sample. The implementation of the new approach (which we term the DAD model for Diffusion–Adsorption–Decay) is straightforward and efficient enough to allow estimation of age and its uncertainty on a desktop computer. Software for performing age estimation with the new model is available from the corresponding author.  相似文献   

12.
Debris flows generated from landslides are common processes and represent a severe hazard in mountain regions due to their high mobility and impact energy. We investigate the dynamics and the rheological properties of a 90 000 m3 debris‐flow event triggered by a rapid regressive landslide with high water content. Field evidence revealed a maximum flow depth of 7–8 m, with an estimated peak discharge of 350–400 m3 s?1. Depositional evidence and grain‐size distribution of the debris pose the debris flow in an intermediate condition between the fluid‐mud and grain‐flow behaviour. The debris‐flow material has silt–clay content up to 15 per cent. The rheological behaviour of the finer matrix was directly assessed with the ball measuring system. The measurements, performed on two samples at 45–63 per cent in sediment concentration by volume, gave values of 3·5–577 Pa for the yield strength, and 0·6–27·9 Pa s for the viscosity. Based on field evidence, we have empirically estimated the yield strength and viscosity ranging between 4000 ± 200 Pa, and 108–134 Pa s, respectively. We used the Flo‐2D code to replicate the debris‐flow event. We applied the model with rheological properties estimated by means of direct measurements and back‐analyses. The results of these models show that the rheological behaviour of a debris‐flow mass containing coarse clasts can not be assessed solely on the contribution of the finer matrix and thus neglecting the effects of direct grain contacts. For debris flows composed by a significant number of coarse clasts a back‐analysis estimation of the rheological parameters is necessary to replicate satisfactorily the depositional extent of debris flows. In these cases, the back‐estimated coefficients do not adequately describe the rheological properties of the debris flow. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

13.
Measurements of uranium concentration and the234U/238U activity ratio in oceanic basalts which have undergone low-temperature seafloor alteration indicate that uranium uptake is a pervasive occurrence but that the various phases involved behave differently with respect to this process. Palagonite exhibits uranium contents 8–20 times higher than unaltered glass coupled with low234U/238U, suggesting ongoing preferential leaching of234U. Altered crystalline interiors of several old basalts have234U/238U > 1, indicative of recent uranium exchange with seawater. The data also provide evidence for uranium sources with234U/238U higher than the seawater value of 1.14. Manganese crusts on basalts of a variety of ages have isotopic ratios indicating that they either are recent deposits or also have experienced continuing uranium exchange with seawater.  相似文献   

14.
The abundance and composition of marine debris including floating marine debris (FMD), seafloor marine debris (SMD) and beached marine debris (BMD) were investigated in coastal seawaters/beaches around the northern South China Sea during 2009 and 2010. The FMD density was 4.947 (0.282-16.891) items/km2, with plastics (44.9%) and Styrofoam (23.2%) dominating. More than 99.0% of FMD was small or medium size floating marine debris. The SMD and BMD densities of were 0.693 (0.147-5.000) and 32.82 (2.83-375.00) items/km2, respectively. SMD was composed of plastics (47.0%), wood (15.2%), fabric/fiber (13.6%) and glass (12.1%), while BMD was composed of plastics (42.0%) and wood (33.7%). More than 90% of FMD, 75% of SMD and 95% of BMD were not ocean-based sources but land-based sources, mostly attributed to coastal/recreational activity, because of the effect of human activities in the areas.  相似文献   

15.
Calcitic crusts of calcareous red algae could be suitable material for age determination of raised marine deposits and palaeothermometry at annual to sub-annual resolution. We examined the potential of U–Th dating of cold-water calcareous algae by analysing fossil specimens (n=10) from Kapp Ekholm (Svalbard) and recent specimens from Norway (n=3) and Scotland (n=1). After initial measurements using α-spectrometry, thermal ionisation mass spectrometry (TIMS) was used to study the material in more detail. Recent specimens contain 0.19–1.55 μg g−1 U, and the measured (234U/238U) activity ratios vary between 1.12 and 1.30. Fossil specimens contain 1–168 μg g−1 U, and display variable and highly elevated initial (234U/238U) activity ratios. In general, the TIMS results show increasing (234U/238U) activity ratios and concentrations of U and Th with increasing stratigraphic age. From this it is evident that marine calcareous red algae contain U in-vivo and they experience substantial post-mortem uptake of U. We conclude that direct U–Th dating of fossil calcareous algae from raised marine deposits is not viable without further geochemical understanding of the in-vivo uptake and post-depositional pathways of U and Th in such deposits. Despite the convincing open-system behaviour of the material, comparison with previously published chronostratigraphy from the site shows that the calcareous algae generally yield ages that are too old. This is in contrast to the expected result based on simple continuous post-mortem U accumulation and calls for a complex model comprising migration of U and multi-component addition of Th (detrital/colloidal) to explain the observed trends.  相似文献   

16.
Supra‐glacial lakes and ponds can create hotspots of mass loss on debris‐covered glaciers. While much research has been directed at understanding lateral lake expansion, little is known about the rates or processes governing lake deepening. To a large degree, this knowledge gap persists due to sparse observations of lake beds. Here we report on the novel use of ground penetrating radar (GPR) surveys to simultaneously collect supra‐glacial lake bathymetry and bottom composition data from Spillway Lake (surface area of 2.4 × 105 m2; volume of 9.5 × 104 m3), which is located in the terminus region of the Ngozumpa Glacier in the Khumbu region of the Nepal Himalaya. We identified two GPR bottom signals corresponding to two sedimentary facies of (1) sub‐horizontal layered fine sediment drape and (2) coarse blocky diamict. We provide an understanding of the changes in subaqueous debris distribution that occur through stages of lake expansion by combining the GPR results with in situ observations of shoreline deposits matching the interpreted facies. From this, we present an updated conceptual model of supra‐glacial lake evolution, with the addition of data on the evolving debris environment, showing how dominant depositional processes can change as lakes evolve from perched lakes to multi‐basin base‐level lakes and finally onto large moraine‐dammed lakes. Throughout lake evolution, processes such as shoreline steepening, lakebed collapse into voids and conduit interception, subaerial and subaqueous calving and rapid areal expansion alter the spatial distribution and makeup of lakebed debris and sediments forcing a number of positive and negative feedbacks on lake expansion. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

17.
A method for U–Pb isotopic dating using secondary ion mass spectrometer (SIMS) was developed for uraninite. Correlation between 251(UO)+/235U+ and 206Pb+/235U+ obtained by a sensitive high‐resolution ion microprobe (SHRIMP) was adopted for a calibration from secondary ion ratios (Pb+/U+) to the atomic abundance ratios (Pb/U). In this study, a uraninite sample (206Pb/238U = 0.1647) collected from Faraday mine, Bancroft, Canada, is used as a reference material for the U–Pb calibration. The established method was applied to three uraninite samples collected from the Chardon, Ecarpière, and Mistamisk mines. The calibrated 206Pb*/238U ratios of the three uraninites show correlation with Pb/U elemental ratios obtained using an electron probe microanalyzer (EPMA) (correlation coefficients: 0.98, 0.99, and 0.97, respectively), which indicates the reliability of the SHRIMP calibration method used in this study. The analysis of Ecarpière uraninite provides concordant U–Pb data, and a weighted average of the 206Pb*/238U age is 287 Ma ±8 Ma (95 % conf.) which is consistent with the previous chronological results by SIMS. Mistamisk uraninite provides discordant U–Pb data with the upper and lower intercept ages of 1 729 and 421 Ma, which correspond to uraninite formation in association with the Hudsonian orogeny and the remobilization of uranium as pitchblende, respectively. The U–Pb age of Chardon uraninite (315 Ma) is consistent with the igneous activity of Mortagne granite, but is older than the previously reported age (264 Ma). Marcasite in the Chardon uraninite altered to goethite under the oxidizing condition, which indicates that U–Pb system in the uraninite crystallized at 315 Ma was disturbed under the oxidizing condition. The established calibration method using Faraday uraninite is useful for U–Pb isotopic dating on the scale of a few micrometers to tens of micrometers, which make it possible to obtain the accurate age of uraninite.  相似文献   

18.
Strong isotopic fractionation between234U and238U has been noted in deep oil-well brines. The waters are stratigraphically and structurally isolated from fresh-water inflow and have remained stagnant for more than five half-lifes of234U. Excess234U is explained by the234Th alpha-recoil nucleus event.  相似文献   

19.
During a 3-year period, several aspects of the glacier-rock interface were studied in a cavity beneath 5–8 m of ice near the terminus of Grinnell Glacier, Montana, U.S.A. Continuous week-long records of the summer sliding rate revealed a very uniform speed of about 12 m a?1 during the summer, a value about 20 per cent higher than the average annual sliding rate. Several decimetre-sized rock fragments were broken from the glacier bed near the lee sides of bedrock ledges and transported down-glacier. In the course of a two-week long experiment, the glacier abraded its bed significantly and non-uniformly. It is of interest that significant quarrying and abrasion occurred under thin ice with relatively little entrained debris.  相似文献   

20.
The geochronology of cave deposits in the Cradle of Humankind UNESCO World Heritage Site in South Africa provides a timeframe essential for the interpretation of its fossils. The uranium-lead (U–Pb) and uranium-thorium disequilibrium (U/Th) dating of speleothems, mostly flowstones that underlie and blanket the fossil-bearing sediments, have been effective in this sense, but U–Pb is limited by the requirement of ∼1 ppm U concentrations and low common Pb contents, and U/Th has a c. 500 ka limit of applicability. Here we report age results for calcite-aragonite speleothems obtained using a new combined uranium-thorium-helium ((U,Th)–He) and U/Th dating routine. We reproduced within analytical uncertainty, the published U–Pb or U/Th ages for (a) flowstone in three drill core samples in the range 2000–3000 ka, (b) a flowstone hand sample taken at surface with an age of 1800 ka, and (c) five underground flowstone samples in the range 100–800 ka. Calcite retentivity for He under cave conditions is thus demonstrated. In the few cases where helium loss was observed in speleothems, only some of the subsamples were affected, and to varying degrees, suggesting loss by lattice damage not related to diagenetic processes, rather than volume diffusion. In the 100 to 800 ka range, the combined U/Th disequilibrium and (U,Th)–He method also yielded reliable values for initial (230Th/238U) and (234U/238U) activity ratios. Importantly, most subsamples had high initial (230Th/238U) values, ranging from 1.0 to 19.7, although having low Th/U ratios. This is probably due to incorporation of Fe–Mn oxides-hydroxides dust, on which 230Th was previously adsorbed. Such samples are mostly not dateable by U/Th without the additional input from the He analysis. If not detected and corrected for, such high initial (230Th/238U) values can lead to inaccurate U/Th and U–Pb ages. Our study shows that the incorporation of He analysis in U/Th dating has broad potential application, with four methods for calculating the ages, in carbonates from different environments where U-Pb or U/Th dating would not work.  相似文献   

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