Volatile characteristics of peralkaline rhyolites from Kenya: an ion microprobe,infrared spectroscopic and hydrogen isotope study

Peralkaline rhyolites of the Greater Olkaria Volcanic Complex, Kenya Rift Valley, were derived from separated, though closely related, magma chambers. Ion microprobe analyses of glass inclusions in quartz phenocrysts show pre-eruptive water contents of up to 3.4 wt% contrasting with previous estimates that the magmas were anhydrous. The values approach predicted solubility levels corresponding to water saturation at low crustal pressures (1 kbar). The glass matrices of the rhyolites have low water contents, ranging from 0.07 to 0.46 wt%, suggesting significant degassing during, or prior to, eruption. Infrared measurements of the matrix glasses show variation in the relative proportions of the two hydrous species dissolved in the glasses. The amount of molecular water, determined semi-quantitatively, apparently increases with increased fluorine content and peralkalinity. This suggests a competition between hydroxyl groups and fluoride ions for similar sites within the melt structure. The mechanism of degassing has been investigated using hydrogen isotopes. The range of D values in most rocks can be produced by varied degrees of open-system degassing of rhyolite melt initially in equilibrium with water of a fixed, or limited, D value. There is evidence to suggest that closed-system degassing may also have been a significant component in some rhyolites. The exact mechanisms of degassing remain uncertain. Particular problems include the relative contribution of open-and closed-system degassing during eruption and the initial vapour compositions and solubility relationships.     

Population change in the upper Braldu Valley,Baltistan, 1900-1990: all is not as it seems

"This paper examines population change in the upper Braldu Valley of the Karakoram range in northern Pakistan between 1900 and 1990. Population has declined over the 90-year period of observation and the majority of that decline is accounted for by females.... The paper discusses apparent demographic trends in a contemporary and historical context and questions the extension of vague, unqualified, context-independent population statistics to an area where apparently they do not apply. It argues that only by interpreting demographic change from within such a local context can the relevance of population control policies be scrutinized. This paper is not an exhaustive demographic analysis but presents data from a little-studied region of the Himalayan area and is meant to open avenues for future research there." (EXCERPT)     

Activity of Hawaiian Volcanoes during the years 1940–1950

Summit eruptions of Mauna Loa, on the Island of Hawaii, occurred in 1940 and 1949, and flank eruptions in 1942 and 1950. Lava poured out in 1940 and 1942 was about equal in amount, totaling approximately 76 million cubic meters in each eruption. The 1949 eruption was somewhat smaller, liberating approximately 59 million cubic meters. The 1950 eruption was one of the largest on record, producing five large lava flows and several smaller ones, totaling approximately 459 million cubic meters. Three of the 1950 flows entered the sea. In 1942 a lava flow threatened the city of Hilo, and was bombed from the air in an effort to divert it. Calculations indicate that the gas content of the lava extruded during the 1940 eruption probably was in the vicinity of one percent by weight of the total magma. Other calculations indicate the viscosity of fluid Hawaiian lava to be in the range of 10³ to 10⁵ poises. Temperature readings on the 1950 lava ranged from 1090⁰ to 900⁰ C. Kilauea Volcano showed signs of uneasiness in 1944, with an apparent increase of magmatic pressure indicated by outward tilting of the moutain flanks and a series of earthquakes progressing toward the surface. In December 1950 a series of earthquakes accompanied a subsidence of the summit of Kilauea Volcano.     

Influence of Changing Atmospheric Circulation on Precipitation δO–Temperature Relations in Canada during the Holocene

Postglacial precipitation δ¹⁸O history has been reconstructed for two regions of Canada. Long-term shifts in the oxygen-isotope composition of annual precipitation (δ¹⁸O_p) in southern Ontario appear to have occurred with a consistent isotope–temperature relation throughout the past 11,500¹⁴C yr. The modern isotope–temperature relation in central Canada near present boreal treeline evidently became established between 5000 and 4000 years ago, although the relation during the last glacial maximum and deglaciation may also have been similar to present. In the early Holocene, however, unusually high δ¹⁸O_papparently persisted, in spite of low temperature locally, probably associated with high zonal index. A rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in Pacific air masses traversing the western Cordillera, perhaps accompanied by a higher summer:winter precipitation ratio, could have been responsible for the observed effect. Equivalent isotope–temperature “anomalies” apparently occurred elsewhere in western North America in response to changing early-Holocene atmospheric circulation patterns, suggesting that a time-slice map of δ¹⁸O_pfor North America during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers.     

Large and growing environmental reservoirs of Deca-BDE present an emerging health risk for fish and marine mammals

Polybrominated diphenyl ethers (PBDEs) have been the subject of intense scientific and regulatory scrutiny during recent years. Of the three commercial forms (Penta, Octa and Deca) of PBDEs that have been widely used as flame retardants in textiles, furniture upholstery, plastics, and electronics, only Deca-BDE remains on the general market in North America, while a recent ruling of the European Court spells an impending end to its use in Europe. We review here highlights of aquatic research documenting the rapid emergence of PBDEs as a high priority environmental concern in Canada. PBDEs are being introduced in large quantities to the aquatic environment through sewage discharge and atmospheric deposition. In certain environmental compartments, the single congener BDE-209, the main ingredient in the Deca-BDE formulation, has surpassed the legacy PCBs and DDT as the top contaminant by concentration. Limited biomagnification of BDE-209 in aquatic food webs reflects its high log K_ow and preferential partitioning into the particle phase. As a result, large environmental reservoirs of BDE-209 are being created in sediments, and these may present a long-term threat to biota: BDE-209 breaks down into more persistent, more bioaccumulative, more toxic, and more mobile PBDE congeners in the environment.     

Modelling The Mean Velocity Profile In The Urban Canopy Layer

A simple model originally derived for meanwind speed profiles in vegetative canopy flows ismodified for application to arrays ofthree-dimensional surface obstacles (cubes), whichcould be representative of a simple urban-typesurface. It is shown that for cube arrays that arenot too densely packed, the predicted exponentialvelocity profile provides an adequate fit to thespatially averaged velocity profile (u(z))within the obstacle canopy. Application of the model to a set of wind-tunnel dataallows for the evaluation of an empirical fittingparameter called the attenuation coefficient. This isrelated to the turbulence length scale, which can befound by manipulating the results of thegradient-diffusion model used to derive the velocityprofile. The results show a reduction of theturbulence length scale with increasing obstaclepacking density. By assuming a linear transition fromthis length scale at the top of the canopy to theclassical Prandtl length scale in the overlyinginertial sublayer, an acceptable model is obtained forthe full velocity profile within simple obstaclearrays, from the ground up to the overlyingsemi-logarithmic region.     

Responses of infaunal composition, biomass and production to discharges from a marine outfall over the past decade

The largest municipal outfall on the west coast of Canada discharges into the southeastern Strait of Georgia, where high sedimentation from the Fraser River has maintained stable sediment geochemical and contaminant conditions from 2001 to 2011. Outfall exposure has not affected trophic structure or diversity (H'), but has significantly affected faunal composition and species richness, resulting in loss of crustaceans and echinoderms near-field. Organic biomass and production have mostly remained within expected background ranges for the Strait, due to recent increases in a low oxygen tolerant polychaete in the high deposition zone. A significant regional shift in faunal composition occurred after 2003, followed by gradual declines in richness, abundance, calcareous organisms and production. This cannot be attributed to changes in outfall exposure, but is exaggerated by it. We hypothesize that changing river flow, extreme events and shifts in offshore upwelling water temperature, oxygen and pH may be increasing geochemical stress in benthos.     

Impacts of sediment supply and local tectonics on clinoform distribution: the seismic stratigraphy of the mid Pleistocene-Holocene Indus Shelf

We present results from the first high-resolution seismic reflection survey of the inner Western Indus Shelf, and Indus Delta, Arabian Sea. The results show major regional differences in sedimentation across the shelf from east to west, as well as north to south, both since the Last Glacial Maximum (~20?ka) and over longer time scales. We identify 10 major regional reflectors, interpreted as representing sea level lowstands. Strong compressive folding is observed underlying a reflector we have called Horizon 6 in the north-western shelf, probably compression associated with the transpressional deformation of the Murray Ridge plate boundary. Downslope profiles show a series of well developed clinoforms, principally at the shelf edge, indicating significant preservation of large packages of sediment during lowstands. These clinoforms have developed close to zones of deformation, suggesting that subsidence is a factor in controlling sedimentation and consequently erosion of the Indus Shelf. These clinoforms fan out from dome features (tectonic anticlines) mostly located close to the modern shoreline.     

Invasive crayfish as drivers of fine sediment dynamics in rivers: field and laboratory evidence

Despite increasing recognition of the potential of aquatic biota to act as ‘geomorphic agents’, key knowledge gaps exist in relation to biotic drivers of fine sediment dynamics at microscales and particularly the role of invasive species. This study explores the impacts of invasive signal crayfish on suspended sediment dynamics at the patch scale through laboratory and field study. Three hypotheses are presented and tested: (1) that signal crayfish generate pulses of fine sediment mobilisation through burrowing and movement that are detectable in the flow field; (2) that such pulses may be more frequent during nocturnal periods when signal crayfish are known to be most active; and (3) that cumulatively the pulses would be sufficient to drive an overall increase in turbidity. Laboratory mesocosm experiments were used to explore crayfish impacts on suspended sediment concentrations for two treatments: clay banks and clay bed substrate. For the field study, high frequency near‐bed and mid‐flow turbidity time series from a lowland river with known high densities of signal crayfish were examined. Laboratory data demonstrate the direct influence of signal crayfish on mobilisation of pulses of fine sediment through burrowing into banks and fine bed material, with evidence of enhanced activity levels around the mid‐point of the nocturnal period. Similar patterns of pulsed fine sediment mobilisation identified under field conditions follow a clear nocturnal trend and appear capable of driving an increase in ambient turbidity levels. The findings indicate that signal crayfish have the potential to influence suspended sediment yields, with implications for morphological change, physical habitat quality and the transfer of nutrients and contaminants. This is particularly important given the spread of signal crayfish across Europe and their presence in extremely high densities in many catchments. Further process‐based studies are required to develop a full understanding of impacts across a range of river styles. Copyright © 2013 John Wiley & Sons, Ltd.