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1.
Assessment of gully erosion rates through interviews and measurements: a case study from northern Ethiopia 总被引：3，自引：0，他引：3
Jan Nyssen Jean Poesen Maude Veyret‐Picot Jan Moeyersons Mitiku Haile Jozef Deckers Joke Dewit Jozef Naudts Kassa Teka Gerard Govers 《地球表面变化过程与地形》2006,31(2):167-185
Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation. In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi‐structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case‐study areas. In Dingilet, gullying started around 1965 after gradual environmental changes (removal of vegetation from cropland in the catchment and eucalyptus plantation in the valley bottom); rill‐like incisions grew into a gully, which increased rapidly in the drier period between 1977 and 1990. The estimated evolution of the total gully volume in the other areas show patterns similar to those of the Dingilet gully. Average gully erosion rate over the last 50 years is 6·2 t ha?1 a?1. Since 1995, no new gullies have developed in the study area. Area‐specific short‐term gully erosion rates are now on average 1·1 t ha?1 a?1. The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human‐induced environmental degradation. Under the present‐day conditions of ‘normal’ rain and catchment‐wide soil and water conservation, gully erosion rates are decreasing. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
Croft William Lee Shi Wei Sack Jörg-Rüdiger Corriveau Jean-Pierre 《Journal of Geographical Systems》2017,19(3):221-248
Journal of Geographical Systems - Given the large volumes of detailed data now being collected, there is a high demand for the release of this data for research purposes. In particular,... 相似文献
3.
James D. Ford Tristan Pearce Jason Prno Frank Duerden Lea Berrang Ford Tanya R. Smith Maude Beaumier 《Climatic change》2011,109(3-4):399-415
A survey documenting how climate change is perceived and responded to by Canadian mine operations was administered to a random sample of practitioners working at mine sites across Canada. Key findings include: (1) Mines are sensitive to climatic hazards; (2) There is concern about climate change among mine practitioners, but the majority have not yet noticed climate change to be affecting operations; (3) Future climate change is expected to have negative impacts for mine operations; (4) Mines are responding to climate change mainly through efforts to reduce greenhouse gas emissions but also through adaptation, although to a lesser degree; and (5) Knowledge of future climate change projections and impacts is limited, potentially constraining understanding of the nature of climate change risks. The survey compliments previous work documenting perceptions among upper level management on climate change in the Canadian mining industry. The results from both surveys are largely consistent, establishing that the mining sector perceives climate change as an emerging risk and is developing response options, but needs to invest more time and resources for adaptation to what are inevitable changes in climate. The results support the need for targeted in-depth research to assess the vulnerability of mining to climate change and to evaluate response options. 相似文献
4.
A rocket C.W. radio propagation experiment has been used to measure electron density profiles and the results compared with values calculated from ionograms. In general the agreement is satisfactory but significant discrepancies in the rocket measurements, during the up-leg portions of several rocket flights above 110 km were observed and possible causes are discussed. In one flight the effect of a travelling ionospheric disturbance on the N(h) profile was recorded. Sporadic E strata with thicknesses of 0.6–0.8 km were recorded in these flights. 相似文献
5.
Three intrusive systems of detection and quantification of coastal erosion events (using thermocouples and thermal pins) were developed and tested from 2005 to 2008 in different regions of the Gulf and maritime estuary of the St Lawrence (Quebec, Canada). The 3‐m‐long thermal pins inserted inside unconsolidated deposits allow the monitoring of erosion for a time period sometimes extending over several seasons. The thermocouple or thermocable method allows not only the instrumentation of unconsolidated deposits but also of rocky and cohesive substrate to a depth of 85 cm. An autonomous microclimatic station located near the experimental sites simultaneously samples temperature parameters, precipitation, snow cover, wind speed and direction as well as global radiation. The differential analysis of cliff thermal regime performed simultaneously with an analysis of air temperature makes it possible to determine the activation periods of coastal erosion processes. The results also make it possible to establish with precision the actual influence of rapid variations of certain climatic and microclimatic parameters (radiation, presence of snow cover, precipitation, etc.) on the physical state of surfaces and also on the activation of certain physical processes connected to coastal erosion events. The automated thermal erosion pin system (ATEPS) allows high temporal resolution (i.e. continuous) monitoring, enabling a real coupling of coastal erosion rates and climatic parameters. Preliminary results with the ATEPS system indicate that mild winter temperature and direct solar radiation are significant factors controlling cliff retreat rates. Moreover, the melting of segregation ice during the spring thaw contributed for more than 70% of cliff retreat against only 30% for frost shattering. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
Jean-Fran?ois?MontreuilEmail author Louise?Corriveau Eric?G.?Potter 《Mineralium Deposita》2015,50(3):293-325
Uranium and polymetallic U mineralization hosted within brecciated albitites occurs one kilometer south of the magnetite-rich Au–Co–Bi–Cu NICO deposit in the southern Great Bear magmatic zone (GBMZ), Canada. Concentrations up to 1 wt% U are distributed throughout a 3 by 0.5 km albitization corridor defined as the Southern Breccia zone. Two distinct U mineralization events are observed. Primary uraninite precipitated with or without pyrite–chalcopyrite?±?molybdenite within magnetite–ilmenite–biotite–K-feldspar-altered breccias during high-temperature potassic–iron alteration. Subsequently, pitchblende precipitated in earthy hematite–specular hematite–chlorite veins associated with a low-temperature iron–magnesium alteration. The uraninite-bearing mineralization postdates sodic (albite) and more localized high-temperature potassic–iron (biotite–magnetite ± K-feldspar) alteration yet predates potassic (K-feldspar), boron (tourmaline) and potassic–iron–magnesium (hematite ± K-feldspar ± chlorite) alteration. The Southern Breccia zone shares attributes of the Valhalla (Australia) and Lagoa Real (Brazil) albitite-hosted U deposits but contains greater iron oxide contents and lower contents of riebeckite and carbonates. Potassium, Ni, and Th are also enriched whereas Zr and Sr are depleted with respect to the aforementioned albitite-hosted U deposits. Field relationships, geochemical signatures and available U–Pb dates on pre-, syn- and post-mineralization intrusions place the development of the Southern Breccia and the NICO deposit as part of a single iron oxide alkali-altered (IOAA) system. In addition, this case example illustrates that albitite-hosted U deposits can form in albitization zones that predate base and precious metal ore zones in a single IOAA system and become traps for U and multiple metals once the tectonic regime favors fluid mixing and oxidation-reduction reactions. 相似文献
7.
The Mesoproterozoic Rivard minette dyke provides a case example of dyke-parallel fracturing induced by propagation of low-viscosity
melts at deep crustal levels. The dyke constitutes a xenolith-choked intrusion breccia and provides samples of an extensive
section of the lithosphere underlying the southwestern Grenville Province of Québec at 1.08 Ga. The xenoliths occupy approximately
50% of the volume of the breccia. They are extremely diverse and include pyroxenites and mafic granulites from the upper mantle
and lower crust, and Grenvillian gabbroids, gneisses and quartzites. Wall-rock fragments are detached to various extents along
dyke-parallel fractures and apophyses. The host lamprophyre magma has a calculated viscosity of ca. 40 Pa·s. Rapid ascent
of magma and turbulence are suggested by the presence of large dense fragments and the brittle-to-ductile deformation at the
margins of some xenoliths. A minimum ascent velocity of ca. 50 cm·s–1 is estimated from the settling velocity of a 40 cm long pyroxenite xenolith. The progressive addition of xenoliths increased
the effective viscosity of the liquid-solid mixture to 103 Pa·s during emplacement. This favoured Bingham behaviour and laminar flow of the magma, and xenolith suspension. Field evidence
suggests that xenoliths were formed through (1) early fracturing of wall rock by inelastic deformation during dyke propagation,
and (2) continuous delamination of wall rock by intrusion of magma along the dyke-parallel fractures. This led to removal
of chilled margins, and to fluid infiltration, partial melting and microbrecciation in the wall rock. Pre-existing discontinuities
played a minor role in the fracturing process. Xenoliths may thus be abundant in alkaline magmas not only because these magmas
ascend rapidly and can transport xenoliths, but possibly also, because their low viscosities promote intense fracturing of
wall rock.
Received: 10 June 1995 / Accepted: 10 February 1996 相似文献
8.
Anik Daigle Andr St-Hilaire Valrie Ouellet Julie Corriveau Taha B.M.J. Ouarda Laurent Bilodeau 《Journal of Hydrology》2009,370(1-4):29-38
A data-driven model is designed using artificial neural networks (ANN) to predict the average onset for the annual water temperature cycle of North-American streams. The data base is composed of daily water temperature time series recorded at 48 hydrometric stations in Québec (Canada) and northern US, as well as the geographic and physiographic variables extracted from the 48 associated drainage basins. The impact of individual and combined drainage area characteristics on the stream annual temperature cycle starting date is investigated by testing different combinations of input variables. The best model allows to predict the average temperature onset for a site, given its geographical coordinates and vegetation and lake coverage characteristics, with a root mean square error (RMSE) of 5.6 days. The best ANN model was compared favourably with parametric approaches. 相似文献
9.
Luke Ootes Steve Goff Valerie A. Jackson Sarah A. Gleeson Robert A. Creaser Iain M. Samson Norman Evensen Louise Corriveau A. Hamid Mumin 《Mineralium Deposita》2010,45(6):549-566
The timing of Cu–Mo–U mineralisation at the Nori/RA prospect in the Paleoproterozoic Great Bear magmatic zone has been investigated
using Re–Os molybdenite and 40Ar–39Ar biotite geochronology. The Re–Os molybdenite ages presented are the first robust sulphide mineralisation ages derived from
the Great Bear magmatic zone. Cu–Mo–U mineralisation is hosted in early to syn-deformational hydrothermal veins consisting
of quartz and K-feldspar or more commonly tourmaline-biotite-quartz-K-feldspar, with associated wall-rock alteration assemblages
being predominantly biotite. Sulphide and oxide minerals consist of chalcopyrite, molybdenite and uraninite with lesser pyrite
and magnetite. Elevated light rare earth elements and tungsten concentrations associated with the Cu–Mo–U mineralisation have
also been reported at the prospect by previous workers. Molybdenite and uraninite occur intimately in dravitic tourmaline
growth zones and at grain margins, attesting to their syngenetic nature (with respect to hydrothermal veining). Two molybdenite
separates yield Re–Os model ages of 1,874.4 ± 8.7 (2σ) and 1,872.4 ± 8.8 Ma (2σ) with a weighted average model age of 1,873.4 ± 6.1 Ma (2σ). Laser step heating of biotite from the marginal alteration of the wall-rock adjacent to the veins yields a 40Ar–39Ar maximum cooling age of 1,875 ± 8 Ma (MSWD = 3.8; 2σ), indistinguishable from the Re–Os molybdenite model age and a previously dated ‘syn-tectonic’ aplitic dyke in the region.
Dravitic tourmaline hosts abundant primary liquid–vapour–solid-bearing fluid inclusions. Analytical results indicate liquid–vapour
homogenisation at >260°C constraining the minimum temperature of mineralisation. The solids, which are possibly trapped, did
not homogenise with the liquid–vapour by 400°C. Salinities in the inclusions are variable. Raman spectra identify that at
least some of the solids are calcite and anhydrite. Raman spectra also confirm the vapour phases contain some CO2; whereas clathrates or CH4 was not observed or detected. Quartz grains only host secondary fluid inclusions, which fluoresce under ultraviolet light,
indicating trapped hydrocarbons. We speculate that these resulted from Phanerozoic fluid circulation through the Proterozoic
basement. The collective interpretation of the age, hydrothermal character and associated metals, high temperature and variable
salinity suggests that the Nori/RA Cu–Mo–U mineralisation can be linked with the earliest stages of plutonism in the Great
Bear magmatic zone. From a regional perspective, the mineralisation may pre-date the extensive multi-element mineralisation
now recognised as part of the iron oxide copper–gold (IOCG) spectrum of deposits. As IOCG provinces generally contain a variety
of mineralisation styles, we interpret this as the earliest phase of the extensive mineralising system. 相似文献
10.
M.C. Corriveau H.E. Jamieson M.B. Parsons J.L. Campbell A. Lanzirotti 《Applied Geochemistry》2011,26(9-10):1639-1648
Windblown and vehicle-raised dust from unvegetated mine tailings can be a human health risk. Airborne particles from As-rich abandoned Au mine tailings from Nova Scotia, Canada have been characterized in terms of particle size, As concentration, As oxidation state, mineral species and texture. Samples were collected in seven aerodynamically fractionated size ranges (0.5–16 μm) using a cascade impactor deployed at three tailings fields. All three sites are used for recreational activities and off-road vehicles were racing on the tailings at two mines during sample collection. Total concentrations of As in the <8 μm fraction varied from 65 to 1040 ng/m3 of air as measured by proton-induced X-ray emission (PIXE) analysis. The same samples were analysed by synchrotron-based microfocused X-ray absorption near-edge spectroscopy (μXANES) and X-ray diffraction (μXRD) and found to contain multiple As-bearing mineral species, including Fe–As weathering products. The As species present in the dust were similar to those observed in the near-surface tailings. The action of vehicles on the tailings surface may disaggregate material cemented with Fe arsenate and contribute additional fine-grained As-rich particles to airborne dust. Results from this study can be used to help assess the potential human health risks associated with exposure to airborne particles from mine tailings. 相似文献