Late Pleistocene Eolian Sediments Related to Pyroclastic Eruptions of Mauna Kea Volcano, Hawaii

Loess and dune sands that mantle volcanic rocks on the northwest flank of Mauna Kea volcano consist predominantly of fine-grained pyroclasts of the alkalic Laupahoehoe Volcanics produced by explosive eruptions. The loess is divided into lower and upper units, separated by a well-developed paleosol, while older and younger dune sands are separated by loess. Four interstratified tephra marker horizons aid in regional stratigraphic correlation. Radiocarbon ages of charcoal fragments within the loess, U-series ages of rhizoliths in the dune sand, and K/Ar ages and relative stratigraphic positions of lava flows provide a stratigraphic and temporal framework. The lower loess overlies lava flows less than 103,000 ± 10,000 K/Ar yr old, and¹⁴C dates from the paleosol developed at its top average ca. 48,000 yr. Loess separating the dune sand units ranges from ca. 38,000 to 25,000¹⁴C yr old; the youngest ages from the upper loess are 17,000–18,000¹⁴C yr B.P. Dips of sand-dune foreset strata, isopachs on the upper loess, and reconstructed isopachs representing cumulative thickness of tephra associated with late-Pleistocene pyroclastic eruptions suggest that vents upslope (upwind) from the sand dunes were the primary source of the eolian sediments. Average paleowind directions during the eruptive interval (ca. 50,000–15,000 yr B.P.), inferred from cinder-cone asymmetry, distribution of tephra units, orientation of dune foreset strata, and the regional pattern of loess isopachs, suggest that Mauna Kea has remained within the trade-wind belt since before the last glaciation.     

全新世气候适宜期黄土高原及黄土／沙漠过渡区年降水量的初步恢复

通过黄土高原及其临区１０４个地点地表土壤磁化率值与当地的现代多年平均降水量的回归分析，建立了磁化率与降水量的转换函数。在遍布黄土高原不同地区典型的全新世黄土－古土壤剖面磁化率测量的基础上，利用所建立的转换函数，初步恢复了全新世气候适宜期，黄土高原及黄土／沙漠过渡区年降水量的分布状况。     

A mobile coherent low-frequency acoustic range

A portable system for the measurement of certain underwater acoustic propagation phenomena is described. Acoustic sources and receivers of special design are used. A precision tracking system enables coherent signal reception in the presence of source-receiver motion. The major elements of the acoustic range are described and examples of data are presented.     

Using tree stems in multi-temporal terrestrial lidar scanning data to monitor landslides on vegetated slopes

Landslides - Terrestrial lidar scanning (TLS) has become a widely accepted expert tool for monitoring geohazards on bare or sparsely vegetated slopes through change detection. While trees can be an...     

Dissimilatory sulfate reduction in hypersaline coastal pans: Activity across a salinity gradient

The impact of salinity on the metabolic activity of sulfate-reducing bacteria in five highly saline to hypersaline coastal pans was studied using a radioactive tracer technique. We recorded sulfate reduction at in situ porewater salinities of up to 422. Furthermore, enumeration of sulfate reduction rates in whole core incubations conducted under in situ conditions suggested a high variability in the activity of sulfate-reducers. Average reduction rates (27-3685 nmol cm⁻³ d⁻¹) varied according to depth, season and site sampled. The highest reduction rates measured in the hypersaline pan were comparable to the highest reported rates from highly productive salt marsh and microbial mat ecosystems. Correspondingly, the depth-integrated rates (integrated to 12 cm) varied from 6 to 241 mmol m⁻² d⁻¹ and were also among the highest ever reported rates. The reduction rates decreased down-core and, surprisingly, were highest in the winter season when the lowest sediment temperatures were encountered.High salt concentrations did not inhibit sulfate reduction rates. Rather, higher rates were measured at pans with higher in situ salinities. In laboratory slurry incubation experiments, sediments from the saltpans were treated with increasing salt concentrations. Regression analysis suggested that the short term response of microbial consortia to up-shock was an increase in sulfate reduction activity up to salinities of 272-311 and 134-244, in hypersaline and highly saline pans, respectively. Beyond these salinities, the cells showed evidence of reduced activities.     

Playing the 'disabled role' in local travel

Summary This paper describes how people with a range of physical impairments use the 'disabled role' to enable them to make local journeys in Swansea. It examines the processes by which interaction between people and social institutions serves to overcome transport disability and to reinforce prevailing meanings and structures of disability.     

Spectroscopy on Small Telescopes: The Echelle Spectrograph

In recent years there has been a trend toward the automation ofmodest sized observatories, especially those involved withphotoelectric photometry. Although undoubtedly useful, there isclearly a need for more advanced instrumentation such asspectrographs. The relatively small telescope sizes places severelimits on the choice of spectrograph configuration. A fiber-fedechelle spectrograph is arguably the most suitable design forthese applications.Presented here is a brief discussion of the design philosophy andoperating principles. Both theoretical and measured performancedata for the prototype University of Queensland EchelleSpectrograph are also presented.     

Acceleration and evolution of faults: An example from the Hunter Mountain–Panamint Valley fault zone,Eastern California

We present new space geodetic data indicating that the present slip rate on the Hunter Mountain–Panamint Valley fault zone in Eastern California (5.0 ± 0.5 mm/yr) is significantly faster than geologic estimates based on fault total offset and inception time. We interpret this discrepancy as evidence for an accelerating fault and propose a new model for fault initiation and evolution. In this model, fault slip rate initially increases with time; hence geologic estimates averaged over the early stages of the fault's activity will tend to underestimate the present-day rate. The model is based on geologic data (total offset and fault initiation time) and geodetic data (present day slip rate). The model assumes a monotonic increase in slip rate with time as the fault matures and straightens. The rate increase follows a simple Rayleigh cumulative distribution. Integrating the rate-time path from fault inception to present-day gives the total fault offset.     

Composite suspended sediment particles and flocculation in glacial meltwaters: preliminary evidence from Alpine and Himalayan basins

Research over the last decade has shown that the suspended sediment loads of many rivers are dominated by composite particles. These particles are also known as aggregates or flocs, and are commonly made up of constituent mineral particles, which evidence a wide range of grain sizes, and organic matter. The resulting in situ or effective particle size characteristics of fluvial suspended sediment exert a major control on all processes of entrainment, transport and deposition. The significance of composite suspended sediment particles in glacial meltwater streams has, however, not been established. Existing data on the particle size characteristics of suspended sediment in glacial meltwaters relate to the dispersed mineral fraction (absolute particle size), which, for certain size fractions, may bear little relationship to the effective or in situ distribution. Existing understanding of composite particle formation within freshwater environments would suggest that in‐stream flocculation processes do not take place in glacial meltwater systems because of the absence of organic binding agents. However, we report preliminary scanning electron microscopy data for one Alpine and two Himalayan glaciers that show composite particles are present in the suspended sediment load of the meltwater system. The genesis and structure of these composite particles and their constituent grain size characteristics are discussed. We present evidence for the existence of both aggregates, or composite particles whose features are largely inherited from source materials, and flocs, which represent composite particles produced by in‐stream flocculation processes. In the absence of organic materials, the latter may result solely from electrochemical flocculation in the meltwater sediment system. This type of floc formation has not been reported previously in the freshwater fluvial environment. Further work is needed to test the wider significance of these data and to investigate the effective particle size characteristics of suspended sediment associated with high concentration outburst events. Such events make a major contribution to suspended sediment fluxes in meltwater streams and may provide conditions that are conducive to composite particle formation by flocculation. Copyright © 2002 John Wiley & Sons, Ltd.