Debris flood risk assessment for Mosquito Creek, British Columbia, Canada

Mosquito Creek drains a 15.5 km² watershed on the North Shore Mountains north of Vancouver, British Columbia, Canada, and flows through the densely urbanized District and then City of North Vancouver. Previous studies determined that the creek is subject to debris floods (hyperconcentrated flows). The National Research Council of Canada is applying multi-hazard risk assessment procedures for various regions in B.C. and chose Mosquito Creek as one of its target areas. As part of its natural hazard management plan, the District of North Vancouver (DNV) requested an assessment of debris flood hazards and associated risk to life. Using a combination of empirical methods, dendrochronology and some judgment, BGC Engineering Inc. assessed debris flood hazard extent, velocity and depth for estimated 100-, 200-, 500- and 2,500-year debris flow return periods. Based on the results from the hazard assessment, risk for individuals and groups living within the hazard area, including residential homes and a fire hall, was estimated. Compared to risk tolerance criteria accepted on an interim basis by the DNV, we estimate that societal risk exceeds tolerable standards and that individual risk exceeds tolerable standards for 10 homes. The results from the risk to loss of life study have prompted DNV to implement a series of risk reduction measures including installation of a debris containment net and watershed restoration measures.     

New triple oxygen isotope data of bulk and separated fractions from SNC meteorites: Evidence for mantle homogeneity of Mars

We report precise triple oxygen isotope data of bulk materials and separated fractions of several Shergotty–Nakhla–Chassigny (SNC) meteorites using enhanced laser‐assisted fluorination technique. This study shows that SNCs have remarkably identical Δ¹⁷O and a narrow range in δ¹⁸O values suggesting that these meteorites have assimilated negligibly small surface materials (<5%), which is undetectable in the oxygen isotope compositions reported here. Also, fractionation factors in coexisting silicate mineral pairs (px‐ol and mask‐ol) further demonstrate isotopic equilibrium at magmatic temperatures. We present a mass‐dependent fractionation line for bulk materials with a slope of 0.526 ± 0.016 (1SE) comparable to the slope obtained in an earlier study (0.526 ± 0.013; Franchi et al. 1999). We also present a new Martian fractionation line for SNCs constructed from separated fractions (i.e., pyroxene, olivine, and maskelynite) with a slope of 0.532 ± 0.009 (1SE). The identical fractionation lines run above and parallel to our terrestrial fractionation line with Δ¹⁷O = 0.318 ± 0.016‰ (SD) for bulk materials and 0.316 ± 0.009‰ (SD) for separated fractions. The conformity in slopes and Δ¹⁷O between bulk materials and separated fractions confirm oxygen isotope homogeneity in the Martian mantle though recent studies suggest that the Martian lithosphere may potentially have multiple oxygen isotope reservoirs.     

An assessment of climate change impacts and adaptation for the Torres Strait Islands, Australia

Adaptive practices are taking place in a range of sectors and regions in Australia in response to existing climate impacts, and in anticipation of future unavoidable impacts. For a rich economy such as Australia’s, the majority of human systems have considerable adaptive capacity. However, the impacts on human systems at the intra-nation level are not homogenous due to their differing levels of exposure, sensitivity and capacity to adapt to climate change. Despite past resilience to changing climates, many Indigenous communities located in remote areas are currently identified as highly vulnerable to climate impacts due to their high level of exposure and sensitivity, but low capacity to adapt. In particular, communities located on low-lying islands have particular vulnerability to sea level rise and increasingly intense storm surges caused by more extreme weather. Several Torres Strait Island community leaders have been increasingly concerned about these issues, and the ongoing risks to these communities’ health and well-being posed by direct and indirect climate impacts. A government agency is beginning to develop short-term and long-term adaptation plans for the region. This work, however, is being developed without adequate scientific assessment of likely ‘climate changed futures.’ This is because the role that anthropogenic climate change has played, or will play, on extreme weather events for this region is not currently clear. This paper draws together regional climate data to enable a more accurate assessment of the islands’ exposure to climate impacts. Understanding the level of exposure and uncertainty around specific impacts is vital to gauge the nature of these islands’ vulnerability, in so doing, to inform decisions about how best to develop anticipatory adaptation strategies over various time horizons, and to address islanders’ concerns about the likely resilience and viability of their communities in the longer term.     

Mediated climate change in Britain: Scepticism on the web and on television around Copenhagen

Copenhagen 2009 was a major moment in the development of climate change as an issue. But climate sceptics before and during this event, sought to influence the nature of debate, and for this reason, the way Copenhagen was covered in the mass media was particularly important. This paper outlines the contours of contrarian arguments and claims, and assesses their reflection in the coverage at Copenhagen. The focus is on television, and extends to the assessment of internet - both modes of mass communication underrepresented in the existing literature. The results suggest a higher profile for contrarians and scepticism than is perhaps healthy, and speak to the role of these mass media, now and in the future, particularly with regard to the issue of public comprehension of the issues involved.     

Controls on Rayleigh wave amplitudes: attenuation and focusing

A large data set of amplitude measurements of minor and major arc Rayleigh waves in the period range 73–171 s is collected. By comparing these amplitudes with the amplitudes of synthetic waveforms calculated by mode summation, maps of lateral variations in the apparent attenuation structure of the Earth are constructed. An existing formalism for predicting the effects of focusing is employed to calculate amplitude perturbations for the same data set. These perturbations are used to construct 'pseudo‐attenuation' maps and these results are compared with the apparent attenuation maps calculated from the data. It is shown that variations in Rayleigh wave amplitude perturbations in the Earth are dominated by attenuation at long wavelengths (below about degree 8) and by elastic structure at shorter wavelengths. It is also shown that the linear approximation for focusing is successful at predicting Rayleigh wave amplitudes using existing phase velocity maps. These results indicate that future attempts to model the velocity structure of the Earth would be assisted by incorporating amplitude data and by jointly inverting for Q structure.     

The genesis and tectonic control on archaean gold deposits of the Western Australian Shield — A metamorphic replacement model

Gold deposits occur in greenstone belts world wide, and contribute to anomalously high gold production from Archaean terranes. As in other cratons, Archaean gold mineralization of Western Australia represents a complex array of deposit styles. Despite this, most deposits are clearly epigenetic, and large deposits have a number of features in common, including their strong structural controls, distinctive wallrock alteration (Fe-sulphide, K-mica±albite, Ca---Mg---Fe carbonates), consistent metal associations (Au---Ag---As---Sb---W---B; low base metals), commonly Fe-rich host rocks, great depth extension and lack of appreciable vertical zonation. These shared characteristics, combined with their ubiquitous occurrence, indicate that Archaean gold deposits had a common origin related to the tectonic evolution of greenstone belts.Auriferous hydrothermal systems were broadly synchronous with regional metamorphism and emplacement of synkinematic granitoids and felsic (porphyry) intrusions. Although these gold systems involved low-salinity, lowdensity, reduced, near-neutral H₂O---CO₂ fluids carrying gold as reduced sulphur complexes, the origin of the fluids is equivocal. Most timing evidence and stable isotope data cannot distinguish metamorphic from magmatic (granitoid or felsic porphyry) orggins, but the lack of consistent spatial relationships between specific, volumetrically significant intrusive phases and large gold deposits in a number of cratons strongly favours metamorphic derivation of fluids.The metamorphic-replacement model for gold mineralization involves devolatilization of the lower portions of the greenstone pile, with high geothermal gradients inhibiting significant melting. CO₂ possibly formed by the decarbonation of early alteration, related to mantle degassing along crustal-scale, synbasinal fault zones. Auriferous fluids were channelled along greenstone-scale faults, in part developed during reactivation of crustal-scale faults in a strike-slip regime. Gold deposition occurred largely under greenschist facies conditions (about 300–400°C, 1–2 kb) in response to decreasing gold solubility with declining temperature. However, a major control on gold deposition was fluid/wallrock interaction. Many large deposits formed by sulphidation of Fe-rich host rocks, with synchronous deposition of Fe-sulphides and gold. However, the variable nature of gold-depositing reactions, including lowering of fO₂ and pH, allowed a multitude of small, and some large, deposits to form wherever that fluid circulation occurred. In consequence, several of the relatively small deposits currently worked from open pit are hosted by ultramafic and felsic rocks. There are few constraints on the source of components (Au, S, K, CO₂) added to gold deposits, but even giant deposits such as the Golden Mile, Kalgoorlie could have formed from a realistic greenstone source volume (ca. 8×8×5 km). Convective circulation of fluids could have contributed to the generation of high fluid-rock ratios.On the regional scale, the markedly heterogeneous distribution of large gold deposits, gold productivity and host rocks to deposits can be accommodated by the metamorphic-replacement model. The most favourable conditions for development of auriferous hydrothermal systems operated in younger (ca. 2.7±0.1 Ga) rift-phase greenstones where greatest extension and crustal thinning produced high geothermal gradients, crustal-scale synbasinal faults, and rapid extrusion and burial of volcanics, including abundant komatiites. Iron-rich tholeiitic basalts and dolerites were preferred host rocks for large gold deposits. The least favourable conditions existed in older (ca. 3.5-3.4 Ga) platformphase greenstones, where gentle sagging on submerged continental crust produced eruption of mainly mafic volcanics with few komatiites, commonly in very shallow-water environments. This allowed intense synvolcanic alteration of both gold source rocks and potential host rocks. The generally smaller gold deposits formed mainly in ultramafic or greywacke hosts. Younger (ca. 3.0 Ga) platform-phase greenstones appear intermediate in nature but, unlike other greenstones, have significant epigenetic gold deposits in originally oxide-facies BIF, which were deposited on relatively deep-water platforms. Similar controls appear to exist on a world scale, with gold mineralization peaking at ca. 2.7±0.1 Ga in response to development of major rift zones in thickened, relatively mature continental crust. Interestingly, the giant Witwatersrand goldfield formed at about the same time.     

Empirical Catchment-wide Rainfall Erosivity Models for Two Rivers in the Humid Tropics of Australia

The concept of rainfall erosivity is extended to the estimation of catchment sediment yield and its variation over time. Five different formulations of rainfall erosivity indices, using annual, monthly and daily rainfall data, are proposed and tested on two catchments in the humid tropics of Australia. Rainfall erosivity indices, using simple power functions of annual and daily rainfall amounts, were found to be adequate in describing the interannual and seasonal variation of catchment sediment yield. The parameter values of these rainfall erosivity indices for catchment sediment yield are broadly similar to those for rainfall erosivity models in relation to the R-factor in the Universal Soil Loss Equation.     

Kinetic isotopic fractionation during diffusion of ionic species in water

Experiments specifically designed to measure the ratio of the diffusivities of ions dissolved in water were used to determine . The measured ratio of the diffusion coefficients for Li and K in water (D_Li/D_K = 0.6) is in good agreement with published data, providing evidence that the experimental design being used resolves the relative mobility of ions with adequate precision to also be used for determining the fractionation of isotopes by diffusion in water. In the case of Li, we found measurable isotopic fractionation associated with the diffusion of dissolved LiCl (D_⁷Li/D_⁶Li=0.99772±0.00026). This difference in the diffusion coefficient of ⁷Li compared to ⁶Li is significantly less than that reported in an earlier study, a difference we attribute to the fact that in the earlier study Li diffused through a membrane separating the water reservoirs. Our experiments involving Mg diffusing in water found no measurable isotopic fractionation (D_²⁵Mg/D_²⁴Mg=1.00003±0.00006). Cl isotopes were fractionated during diffusion in water (D_³⁷Cl/D_³⁵Cl=0.99857±0.00080) whether or not the co-diffuser (Li or Mg) was isotopically fractionated. The isotopic fractionation associated with the diffusion of ions in water is much smaller than values we found previously for the isotopic fractionation of Li and Ca isotopes by diffusion in molten silicate liquids. A major distinction between water and silicate liquids is that water surrounds dissolved ions with hydration shells, which very likely play an important but still poorly understood role in limiting the isotopic fractionation associated with diffusion.     

Tidal and Groundwater Fluxes to a Shallow, Microtidal Estuary: Constraining Inputs Through Field Observations and Hydrodynamic Modeling

Increased nutrient loading to estuaries has led to eutrophication, degraded water quality, and ecological transformations. Quantifying nutrient loads in systems with significant groundwater input can be difficult due to the challenge of measuring groundwater fluxes. We quantified tidal and freshwater fluxes over an 8-week period at the entrance of West Falmouth Harbor, Massachusetts, a eutrophic, groundwater-fed estuary. Fluxes were estimated from velocity and salinity measurements and a total exchange flow (TEF) methodology. Intermittent cross-sectional measurements of velocity and salinity were used to convert point measurements to cross-sectionally averaged values over the entire deployment (index relationships). The estimated mean freshwater flux (0.19?m³/s) for the 8-week period was mainly due to groundwater input (0.21?m³/s) with contributions from precipitation to the estuary surface (0.026?m³/s) and removal by evaporation (0.048?m³/s). Spring?Cneap variations in freshwater export that appeared in shorter-term averages were mostly artifacts of the index relationships. Hydrodynamic modeling with steady groundwater input demonstrated that while the TEF methodology resolves the freshwater flux signal, calibration of the index?Csalinity relationships during spring tide conditions only was responsible for most of the spring?Cneap signal. The mean freshwater flux over the entire period estimated from the combination of the index-velocity, index?Csalinity, and TEF calculations were consistent with the model, suggesting that this methodology is a reliable way of estimating freshwater fluxes in the estuary over timescales greater than the spring?Cneap cycle. Combining this type of field campaign with hydrodynamic modeling provides guidance for estimating both magnitude of groundwater input and estuarine storage of freshwater and sets the stage for robust estimation of the nutrient load in groundwater.