Surface textures of turbidite sand grains, Laurentian Fan and Sohm Abyssal Plain

Surface textures of quartz grains have been examined from five samples from the Laurentian Fan and Sohm Abyssal Plain, representing varied transport distances and power of the depositing turbidity current. The grains retain their primary irregular shape derived from glacial erosion, and glacial surface textures are preserved in dish-shaped depressions. These features have been superimposed by a slight rounding of edges and an abundance of collision-induced markings, particularly mechanical V-forms. The most intense current modification of this sort occurs in mid-Wisconsinan or earlier sands that have been transported over 1000 km to the distal Sohm Abyssal Plain by turbidity currents. Collision textures probably develop during grain flow on the steep continental slope: delicate resedimented shelf foraminifera are preserved in the same turbidites and most have been transported exclusively in suspension.     

The visualization of socio-economic GIS data using virtual reality tools

This paper addresses two issues: the use of 'realistic' environments for the visualization of socio-economic data, and the use of virtual reality tools for the exploration of data from existing GIS databases. 'Realistic' is here used in a narrow sense to imply the reconstruction of real-world scenes in which major components of the physical environment are reconstructed to facilitate geographical visualization. A review of visualization techniques for geographically-referenced 3-D data is presented, and the translation of an existing urban GIS database into virtual reality modelling language (VRML) demonstrated for a study area in Cardiff, UK. This work shows that the export of conventional 2-D GIS data into virtual reality toolkits can be relatively straightforward, and offers exciting new avenues for visualization and exploration. We argue that some of the parameters of the true scene such as colour, building shape, and texture may be directly modified in order to represent otherwise unobservable socio-economic characteristics, in the spirit of exploratory data analysis. These issues are of particular importance in the context of current advances towards the dynamic linkage of GIS and virtual reality modelling.     

Decision makers' perspectives on European geographic information policy issues

The proposals for a European policy framework for Geographic Information (GI) recently put forward by Directorate General XIII raise three sets of issues about measures required to facilitate the dissemination of GI in the European Union: (1)'hot topics' such as privacy and the legal protection of databases that apply to information generally; (2) GI issues such as reference data and metadata services that may require action by the European Commission; and (3) perceived barriers to the development of a European GI market. This paper examines the views of 20 experts responsible for the provision and management of GI in key organizations throughout Europe. A Delphi-style strategy was used to identify the relative importance of the issues raised by the proposals and to ascertain the level of agreement as to the importance of these issues between the experts. The results show that issues relating to copyright, the protection of intellectual property rights, data quality, and data access policies were ranked highly by most of the respondents. A lack of awareness, education, and training (as opposed to the lack of public domain data and metadata services) were viewed as the main barriers to the deveiopment of the GI market in Europe.     

The Atomic Ratios of Natural Ferruginous Biotites with reference to 'The Stability Relations of the Ferruginous Biotite, Annite'

The atomic ratios given by Eugster and Wones (1962) for analysesof high FeO-low MgO micas cited by Foster (1960) are in error.The recalculated atomic ratios herein presented show that onlythree of the thirteen have low (OH+F), and only one has characteristicsthat may possibly be due to loss of water during determination.None of the analyses exhibit characteristics suggestive of oxidationof iron and loss of H, as in progression towards oxyannite. The average recalculated octahedral occupancy is 2.69, not 2.91as in the previous calculation. The differences between atomic ratios calculated on the basisot determined H₂O⁺ and F and those calculated on the basis ofthe theoretical O₁₀ (OH)₂ content are not great enough to changethe essential compositional character of these micas as interpretedby Foster (1960). However, they do affect significantly thecalculated octahedral occupancy.     

Bedload abrasion and the in situ fragmentation of bivalve shells

The aim of this study was to determine how Unio bivalve shells fragment within the channel of the Sakmara River (southern Urals, Russia). The Sakmara River has an abundant bivalve population and a highly variable flow regime which, at low flow, allowed much of the channel bed to be examined. A large data set of 1013 shells (Unio sp.) was examined and these were shown to have consistent patterns of orientation, aspect, shell abrasion, perforation and fracture. The close spatial relationship between areas of shell abrasion, shell perforation and shell fracture showed that they form part of a continuum whereby areas of abrasion evolve into perforations and perforations coalesce and enlarge into fractures. The mechanism of shell damage proposed is one of abrasion in place, whereby the shell remains stationary on the surface of the point bar and is impacted by bedload. Underpinning this process are the hydrodynamic properties of the bivalve shell, with consistency in the orientation and aspect of the valve in a flowing current producing consistency in the distribution of damage on the shell surface. Valves preferentially lie in a convex‐up position and orientate in the flow such that the umbo faces upstream. The elevated, upstream‐facing umbo region is exposed to particle impact and is the first to be abraded and perforated. The vulnerability of the umbo to perforation is greatly increased by the thinness of the shell at the umbo cavity. The in situ abrasion process is enhanced by the development of an armoured gravel bed which restricts valve mobility and maintains shells within the abrasion zone at the sediment–water interface. The in situ abrasion process shows that broken shells are not a reliable indicator of long distance transport. The study also raises the issue that tumbling barrel experiments, which are generally used to simulate shell abrasion, will not replicate the type of directionally focused sand‐blasting which appears to be the principal cause of shell fragmentation in the Sakmara River.     

AN ASSESSMENT OF CLAST MACROFABRICS IN GLACIGENIC SEDIMENTS BASED ON A/B PLANE DATA

Previous studies of clast macrofabrics in glacigenic deposits have concentrated on A‐axis orientations and dips, and a variety of control samples are available based upon such measurements. Like clast A‐axes, A/B planes will also tend to rotate to parallelism with the direction of shear and therefore should also provide meaningful data on the direction and cumulative impact of shear by the depositing/deforming medium (i.e. glacier ice). The measurement of A/B plane dip and orientation avoids the potential problem of the transverse orientations observed for clast A‐axes and provides poles‐to‐plane data, thereby strengthening the modality of samples and providing clear visual impressions of stress directions. Such data also enable more significant inter‐sample comparisons of fabric strength and clast dip angles, which are significant when assessing the impact of shearing in sediment genesis. We present data on clast A/B plane dip directions and angles from subglacial tills, glacitectonite continuums, subglacially lodged clasts and glacimarine/glacilacustrine deposits using traditional methods of statistical and graphical macrofabric analysis. These sample sets will serve as control data for future macrofabric analyses that utilize A/B planes. The separation of the unequivocally lodged clast component from subglacial till samples allows us to demonstrate the influence of deformation and ploughing in the relative weakening of till fabrics as proposed by some researchers. High angles of A/B plane dip in glacigenic subaqueous deposits appear to be well developed in the glacilacustrine setting investigated here, confirming previous studies based on A‐axis dips, but less convincing in the glacimarine sediments of the Canadian Arctic, thereby widening the range of fabric strengths in subaqueous glacigenic deposits. Significant overlaps of A/B plane fabric shape envelopes reflect the strain history of subglacial and subaqueous depositional environments, which is unsurprising given the hybrid nature of glacigenic deposits, but the statistical isolation of the lodgement component from subglacial traction tills strongly suggests that the continuum of sample plots on modality/isotropy graphs reflects the range of strain histories in glacitectonites and subglacial traction till.     

Seismic and volcanic hazards in Peru: changing attitudes to disaster mitigation

Over the last 15 years there have been dramatic shifts in the consensus over how best to cope with natural hazards in economically developing regions such as South America. One very positive outcome of the United Nations sponsored International Decade for Natural Disaster Reduction (IDNDR 1990–2000) has been that there is now greater interchange between the work of earth scientists examining the processes and mechanics of hazard occurrence and impact, and social scientists exploring the causes of human vulnerability to hazard – and thereby disaster. This paper traces the development of this new understanding with reference to earthquakes and volcanic eruptions in Peru, one of the most hazardous countries in South America. Particular focus is placed on the excellent progress currently being made by scientists in better understanding the physical dimensions of natural hazard exposure, and the ground-breaking work by social scientists in promoting new approaches to understanding and mitigating human vulnerability to disaster. The paper concludes by emphasizing the need to build on this research to produce more inclusive, incultured and unified strategies of disaster mitigation at the local, national and international levels.     

Kilauea East Rift Zone Magmatism: an Episode 54 Perspective

On January 29–30, 1997, prolonged steady-state effusionof lava from Pu'u'O'o was briefly disrupted by shallow extensionbeneath Napau Crater, 1–4 km uprift of the active Kilaueavent. A 23-h-long eruption (episode 54) ensued from fissuresthat were overlapping or en echelon with eruptive fissures formedduring episode 1 in 1983 and those of earlier rift zone eruptionsin 1963 and 1968. Combined geophysical and petrologic data forthe 1994–1999 eruptive interval, including episode 54,reveal a variety of shallow magmatic conditions that persistin association with prolonged rift zone eruption. Near-ventlava samples document a significant range in composition, temperatureand crystallinity of pre-eruptive magma. As supported by phenocryst–liquidrelations and Kilauea mineral thermometers established herein,the rift zone extension that led to episode 54 resulted in mixtureof near-cotectic magma with discrete magma bodies cooled to