Early Proterozoic,basaltic andesite tuff-breaccia: downslope,subaqueous mass transport of phreatomagmatically-generated tephra

At Bear Lake, in the Flin Flon-Snow Lake greenstone belt of Manitoba, 400⁺ m of thick-to very thick-bedded, generally ungraded, basaltic andesite tuff-breccia, breccia, and lapilli-tuff are intercalated with pillowed lava flows in the upper part of an early Proterozoic submarine basaltic andesite shield volcano. The fragmental rocks comprise angular, amygdaloidal blocks and lapilli, many with partial chilled selvages, in a matrix of blocky, non-amygdaloidal to highly amygdaloidal vitric basaltic andesite ash and small lapilli. Minor thin-to medium-bedded, commonly normally graded tuff occurs in the upper part of the sequence. Clasts in fragmental beds consistently have higher amygdule contents than intercalated lava flows. Although similar to pillow-fragment breccias, the Bear Lake fragmental rocks were produced by extended surtseyan-type, phreatomagmatic eruptions, with associated fire fountain activity, at a progressively subsiding, shallow water vent. Periodic tephra slumping generated debris flows that transported particles down the uppe, gentle slope of the volcano to a depositional site at a water depth of less than 1 km. Turbidity currents probably carried much fine tephra to deeper water; tuff was deposited in the preserved section only after explosive volcanism ceased.     

Challenges in urban water management in the United States

The growing intensity of use of water in the urban environment of the United States is posing significant challenges for its supply, utilization, and protection. The development of traditional water sources is becoming more difficult, and water suppliers are turning to conservation and reuse as alternatives. Price disincentives and better water use management are being utilized to attempt to deal with limited capacity for distribution of water in periods of high demand. Urban runoff presents significant localized flooding problems. Management of floods and floodplains is given focus under the National Flood Insurance Act of 1968, which has as its goal the deterrence of development in flood-prone areas. Water quality goals, being developed and pursued under the Safe Drinking Water Act of 1974, are becoming more encompassing as the breadth of pollutants identified in the urban environment expands. Wastewater control strategies developed under the Federal Water Pollution Control Act of 1972 are expanding their emphasis upon nonpoint source pollution, as opposed to traditional emphasis upon point source pollution. Integrated management of the water resource will become increasingly necessary to adequately address water problems in the urban environment. State and local responsibilities for urban water management and control will likely increase.     

Transient Behaviour of Tropospheric Ozone Precursors in a Global 3-D CTM and Their Indirect Greenhouse Effects

The global three-dimensional Lagrangian chemistry-transport model STOCHEM has been used to follow the changes in the tropospheric distributions of the two major radiatively-active trace gases, methane and tropospheric ozone, following the emission of pulses of the short-lived tropospheric ozone precursor species, methane, carbon monoxide, NO_x and hydrogen. The radiative impacts of NO_x emissionswere dependent on the location chosen for the emission pulse, whether at the surface or in the upper troposphere or whether in the northern or southern hemispheres. Global warming potentials were derived for each of the short-lived tropospheric ozone precursor species by integrating the methane and tropospheric ozone responses over a 100 year time horizon. Indirect radiative forcing due to methane and tropospheric ozone changes appear to be significant for all of the tropospheric ozone precursor species studied. Whereas the radiative forcing from methane changes is likely to be dominated by methane emissions, that from tropospheric ozone changes is controlled by all the tropospheric ozone precursor gases, particularly NO_xemissions. The indirect radiative forcing impacts of tropospheric ozone changes may be large enough such that ozone precursors should be considered in the basket of trace gases through which policy-makers aim to combat global climate change.     

POPULATION CENSUS WITH THE AID OF AERIAL PHOTOGRAPHS: AN EXPERIMENT IN THE CITY OF LEEDS

This study shows how aerial photographs can be of value in a population census. The census and the enumeration district maps were used initially to obtain population data and the housing stock was derived from the aerial photographs. From these the population densities were determined of a number of sample enumeration districts containing a single type of house. Another set of enumeration districts was selected and the housing stock again derived from the aerial photographs. By considering the type and quantity of housing stock and the population density of each housing type, the population figures were estimated for each enumeration district. The values of these population estimates were then compared with the values recorded in the census. The overall population estimate had an error of only 2%, but the estimates for some of the individual enumeration districts showed greater errors. These errors are assessed and analysed and some suggestions are made to improve the methodology used in this study.     

Elasticity of an upper mantle clinopyroxene

The ambient pressure elastic properties of a natural clinopyroxene (C2/c symmetry) from Kilbourne Hole, NM have been determined. In terms of end-members, diopside (CaMgSi₂O₆), hedenbergite (CaFeSi₂O₆), jadeite (NaAlSi₂O₆), cosmochlor (NaCrSi₂O₆), and Mg-Tschermak (MgAl(AlSi)O₆), its composition is Di₇₂He₉Jd₃Cr₃Ts₁₂. The analytic density, based on chemistry and cell parameters is 3.327 (0.003) g/cm³. The elastic constants [c₁₁, c₁₂, c₁₃, c₁₅, c₂₂, c₂₃, c₂₅, c₃₃, c₃₅, c₄₄, c₄₆, c₅₅, c₆₆] are [273.8 (0.9), 83.5 (1.3), 80.0 (1.1), 9.0 (0.6), 183.6 (0.9), 59.9 (1.6), 9.5 (1.0), 229.5 (0.9), 48.1 (0.6), 76.5 (0.9), 8.4 (0.8), 73.0 (0.4), 81.6 (1.0)] GPa where uncertainties are reported at the 95% confidence level. The aggregate (mean of Hashin-Strikman bounds) adiabatic bulk modulus is 117.2 (0.7) GPa, and the shear modulus is 72.2 (0.2) GPa. Although measured moduli are broadly consistent with trends in elasticity versus atomic volume, deviations from the systematics would produce significant (percent level) changes in calculated velocities for candidate mantle mineral assemblages. The compositional dependence of elasticity for several clinopyroxenes is explored on the basis of just the Di+He and Jd+Ts mole fractions. The bulk modulus lies within experimental uncertainties of the linear mixture of end-member properties while the shear modulus deviates by 3%. Received: 29 September 1997 / Revised, accepted: 4 March 1998     

Measurements of Reaction Coefficients of NO2 and HONO on Aerosol Particles

The reaction coefficients of nitrogen dioxide and nitrous acid with monodisperse sodium chloride and ammonium sulphate aerosols have been measured in a flow reactor at atmospheric pressure. These experiments were performed at relative humidities above and below the deliquescence points of both aerosols (r.h. 50 and 85%) at 279 K. The results for NO₂ afford a reaction coefficient in the range (2.8–10) × 10^-4 and for HONO, (2.8–4.6) × 10^-3. For both species, there appears to be an enhancement of the reaction coefficient on sodium chloride aerosol at 50% r.h. The results are compared with reaction coefficients determined by other experimental methods. A good agreement is found for both gases between this method and the coated denuder method previously developed in our research laboratories (Msibi et al., 1993) and with the majority of other published data for NO₂. In the case of HONO, our estimate of reaction coefficient is smaller than, or at the lower limits of the ranges reported by other published studies.