Cause of dominance by sheetflood vs. debris-flow processes on two adjoining alluvial fans, Death Valley, California

Two large, adjoining alluvial fans of the Panamint Range piedmont, Death Valley, California, are composed of different facies assemblages deposited by contrasting sedimentary processes. The Anvil Spring fan was built solely by water-flow processes (incised-channel floods and sheetfloods), whereas the neighbouring Warm Spring fan has been constructed principally by debris flows. The boundary between these fans delineates a sharp provincial piedmont contact between sheetflood-dominated fans to the south and debris-flow-dominated fans to the north. Factors such as climate, catchment area, fan area, catchment relief, aspect, vegetation types and density, and neotectonic setting are essentially identical for these two fans. The key difference between them is that their catchments are underlain by dissimilar bedrock types, which weather to yield distinctive sediment suites. Weathering of the granite and andesite of the Anvil fan catchment produces significant volumes of medium to very coarse sand, granules, pebbles, cobbles and boulders, but minimal silt and clay. In contrast, the shale, quartzite and dolomite that dominate bedrock in the Warm Spring catchment weather to yield a wide suite of sedimentary particles spanning from clay to boulders. The abundance of mud, and the unsorted character of the yielded sediment, cause precipitation-induced slope failures in the Warm Spring catchment to transform readily into debris flows. This propensity is due to the low permeability of the colluvial sediment, which causes added water to become trapped quickly and pore pressure to rise rapidly, promoting transformations to debris flows. In contrast, the limited volume of sediment finer than medium sand yielded from the Anvil fan catchment causes the colluvium to have high permeability. This factor prevents the transformation of wet colluvium to a debris flow during hydrologically triggered slope failures, instead maintaining sediment transport as entrained bed load or suspended load in a water flow.     

五大连池近代火山老黑山火烧山火山喷发过程的考察研究

作者在已有工作的基础上,以当代火山学的研究思路和观点,为恢复五大连池两个近代火山,老黑山火烧山的喷发历史过程进行了野外考察研究工作。老黑山火山锥是由三套不同的碎屑堆积物组成。在锥体的南侧、东侧和西侧以及北测和北西侧有５个熔岩溢出口,按它们形成先后关系,认为有早、中、晚三期熔岩流。本文还对老黑山火山锥上的寄生火山、结壳熔岩与渣状熔岩的分布、流动特点及形成的控制因素进行了分析讨论。最后得出结论：老黑山火山是经多期次喷发活动形成的。火烧山火山锥是一碎屑化泡沫化程度很低的浮岩块和熔岩碎块组成,同老黑山有明显区别。     

The spatial implications of the functional proximity deriving from air passenger flows between European metropolitan urban regions

Until recently the traditional spatial configuration of the European geography was based upon the core-periphery model. The ‘pentagon’, broadly defined as lying between London, Paris, Milan, Munich and Hamburg, was seen as the core area characterised by having the highest concentration of economic development in the European Union (EU), with the remainder of the European territory viewed as peripheral, albeit to varying degrees. In a number of cases such peripheral areas equated with clear regional disparities. The elaboration of the European Spatial Development Perspective (ESDP) (CEC, European spatial development perspective, towards balanced and sustainable development in the territory of the European Union, 1999) challenged this core-periphery model. European spatial planning policies, aimed at encouraging social and economic, and with ever increasing importance, territorial cohesion, seek amongst other aspects to encourage the development of a balanced and polycentric urban system. This paper adopts a network analysis approach to the analysis of air passenger flows between some 28 principal European metropolitan urban regions. The evaluation of these flows contributes to an enhanced comprehension of the spatial dynamics of the European metropolitan territory which goes beyond that deriving from the more standard analyses of the individual components of the urban system. Several indicators are used, deriving from gravitational modelling techniques, to analyse the complexity of the air passenger flows. A multidimensional scaling (MDS) technique is introduced in order to interpret and visualise the resulting spatial configuration and positioning of the different metropolitan centres within the conceptual European ‘space of air passenger flows’, thereby contrasting with the more traditional map-based geographical image of Europe, based upon Cartesian coordinates.

Mass constraints from multiphase cooling flow models

I review the multiphase cooling flow equations that reduce to a relatively simple form for a wide class of self-similar density distributions described by the single parameter, k , first introduced by Nulsen. It is shown that steady-state cooling flows are not consistent with all possible emissivity profiles, which can therefore be used as a test of the theory. In combination, they provide strong constraints on the temperature profile and mass distribution within the cooling radius. The model is applied to ROSAT HRI data for three rich clusters. At one extreme ( K  ∼ 1) these show evidence for cores in the mass distribution of size 110–140 h ⁻¹₅₀ kpc and have temperatures that decline towards the flow centre. At the other ( k ∈ ∞), the mass density and gas temperature both rise sharply towards the flow centre. The former are more consistent with observations which usually show a lower emission-weighted temperature within the cooling flow than from the cluster as a whole. The requirement that the solutions have a temperature gradient that is non-increasing towards the cluster centre limits the matter density gradient to be shallower than ρ_grav ∝∼  r ^−1.2 in the cluster core.     

Comparing flow regime,channel hydraulics,and biological communities to infer flow–ecology relationships in the Mara River of Kenya and Tanzania

Abstract

Equatorial rivers of East Africa exhibit unusually complex seasonal and inter-annual flow regimes, and aquatic and adjacent terrestrial organisms have adapted to cope with this flow variability. This study examined the annual flow regime over the past 40 years for three gauging stations on the Mara River in Kenya and Tanzania, which is of international importance because it is the only perennial river traversing the Mara-Serengeti ecoregion. Select environmental flow components were quantified and converted to ecologically relevant hydraulic variables. Vegetation, macroinvertebrates, and fish were collected and identified at target study sites during low and high flows. The results were compared with available knowledge of the life histories and flow sensitivities of the riverine communities to infer flow–ecology relationships. Management implications are discussed, including the need to preserve a dynamic environmental flow regime to protect ecosystems in the region. The results for the Mara may serve as a useful model for river basins of the wider equatorial East Africa region.

Editor Z.W. Kundzewicz; Guest editor M. Acreman     

基于GIS的坡面泥石流危险性评价

综合不同的泥石流评价因子对泥石流危险性进行了研究,利用地理信息系统（ GIS）来计算潜在的泥石流危险区域。选取虹口乡高原村与庙坝村共处坡面为研究区域,在ArcGIS中生成研究区域的坡面立体图。选取适当的评级指标,确定了流域内主要的泥石流影响因子。采用层次分析法得出各主要因子的权重值,将各因子划分为五个不同等级,并分别对各个因子进行数值化和归一化处理。利用ArcGIS形成各评价因子专题层,再分别给不同评价栅格赋权重值,最终运用叠置分析与插值分析得出研究坡面的不同色带所表示的危险等级区划图,从而实现单坡面泥石流危险性的评价。     

The role of the hyporheic zone across stream networks

Many hyporheic papers state that the hyporheic zone is a critical component of stream ecosystems, and many of these papers focus on the biogeochemical effects of the hyporheic zone on stream solute loads. However, efforts to show such relationships have proven elusive, prompting several questions: Are the effects of the hyporheic zone on stream ecosystems so highly variable in place and time (or among streams) that a consistent relationship should not be expected? Or, is the hyporheic zone less important in stream ecosystems than is commonly expected? These questions were examined using data from existing groundwater modelling studies of hyporheic exchange flow at five sites in a fifth‐order, mountainous stream network. The size of exchange flows, relative to stream discharge (Q_HEF:Q), was large only in very small streams at low discharge (area ≈ 100 ha; Q < 10 l/s). At higher flows (flow exceedance probability > 0·7) and in all larger streams, Q_HEF:Q was small. These data show that biogeochemical processes in the hyporheic zone of small streams can substantially influence the stream's solute load, but these processes become hydrologically constrained at high discharge or in larger streams and rivers. The hyporheic zone may influence stream ecosystems in many ways, however, not just through biogeochemical processes that alter stream solute loads. For example, the hyporheic zone represents a unique habitat for some organisms, with patterns and amounts of upwelling and downwelling water determining the underlying physiochemical environment of the hyporheic zone. Similarly, hyporheic exchange creates distinct patches of downwelling and upwelling. Upwelling environments are of special interest, because upwelling water has the potential to be thermally or chemically distinct from stream water. Consequently, micro‐environmental patches created by hyporheic exchange flows are likely to be important to biological and ecosystem processes, even if their impact on stream solute loads is small. Published in 2011 by John Wiley & Sons, Ltd.     

A 24 h investigation of the hydrogeochemistry of baseflow and stormwater in an urban area impacted by mining: Butte,Montana

Changes in water quality during a storm event were continuously monitored over a 24 h period at a single location along an urban stormwater drain in Butte, Montana. The Butte Metro Storm Drain (MSD) collects groundwater baseflow and stormwater draining Butte Hill, a densely populated site that has been severely impacted by 130 years of mining, milling, and smelting of copper‐rich, polymetallic mineral deposits. On the afternoon of 26 June 2002, a heavy thunderstorm caused streamflow in the MSD to increase 100‐fold, from 0·2 ft³ s⁻¹ to more than 20 ft³ s⁻¹. Hourly discharge and water quality data were collected before, during, and following the storm. The most significant finding was that the calculated loads (grams per hour) of both dissolved and particulate copper passing down the MSD increased more than 100‐fold in the first hour following the storm, and remained elevated over baseline conditions for the remainder of the study period. Other metals, such as zinc, cadmium, and manganese, showed a decrease in load from pre‐storm to post‐storm conditions. In addition to the large flush of copper, loads of soluble phosphorus increased during the storm, whereas dissolved oxygen dropped to low levels (<2 mg l⁻¹). These results show that infrequent storm events in Butte have the potential to generate large volumes of runoff that exceed Montana water quality standards for acute exposure of aquatic life to copper, as well as depressed levels of dissolved oxygen. This study has important implications to ongoing reclamation activities in the upper Clark Fork Superfund site, particularly with respect to management of storm flow, and may be applicable to other watersheds impacted by mining activities. Copyright © 2005 John Wiley & Sons, Ltd.