Using Spatial Statistics to Examine the Pattern of Urban Land Development in Halifax–Dartmouth

This article examines the locational patterns of population and employment and the resultant changes in urban form in the Halifax–Dartmouth region between 1970 and 1996. The article employs the univariate and bivariate K function to measure spatial dependence or clustering within and between the classes of residential and commercial land parcels. The results of the K function estimates suggest that residential land parcels cluster together, commercial land parcels cluster together, and residential and commercial land parcels have become more clustered over time. Evidence of clustering provides insight into the changing urban form of the region and possible multinucleation.     

Synclinal-horst basins: examples from the southern Rio Grande rift and southern transition zone of southwestern New Mexico, USA

In areas of broadly distributed extensional strain, the back‐tilted edges of a wider than normal horst block may create a synclinal‐horst basin. Three Neogene synclinal‐horst basins are described from the southern Rio Grande rift and southern Transition Zone of southwestern New Mexico, USA. The late Miocene–Quaternary Uvas Valley basin developed between two fault blocks that dip 6–8° toward one another. Containing a maximum of 200 m of sediment, the Uvas Valley basin has a nearly symmetrical distribution of sediment thickness and appears to have been hydrologically closed throughout its history. The Miocene Gila Wilderness synclinal‐horst basin is bordered on three sides by gently tilted (10°, 15°, 20°) fault blocks. Despite evidence of an axial drainage that may have exited the northern edge of the basin, 200–300 m of sediment accumulated in the basin, probably as a result of high sediment yields from the large, high‐relief catchments. The Jornada del Muerto synclinal‐horst basin is positioned between the east‐tilted Caballo and west‐tilted San Andres fault blocks. Despite uplift and probable tilting of the adjacent fault blocks in the latest Oligocene and Miocene time, sediment was transported off the horst and deposited in an adjacent basin to the south. Sediment only began to accumulate in the Jornada del Muerto basin in Pliocene and Quaternary time, when an east‐dipping normal fault along the axis of the syncline created a small half graben. Overall, synclinal‐horst basins are rare, because horsts wide enough to develop broad synclines are uncommon in extensional terrains. Synclinal‐horst basins may be most common along the margins of extensional terrains, where thicker, colder crust results in wider fault spacing.     

Sediment deposition from flow at low gradients into a buffer strip—a critical test of re-entrainment theory

The spatial and size distribution of sediment deposited from short periods of overland flow due to the effect of a simulated grass buffer strip was measured for low slopes of 1.6, 3.4 and 5.1%. These data were analysed so as to critically evaluate two alternative models of the process of re-entrainment of recently deposited sediment. A model of re-entrainment, previously thought to be appropriate only for a steady-state or equilibrium situation, was found to give better agreement with experiments than did a model previously used in the literature on this subject.     

Simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel

Topographic interactions generate multidirectional and unsteady air?ow that limits the application of velocity pro?le approaches for estimating sediment transport over dunes. Results are presented from a series of wind tunnel simulations using Irwin‐type surface‐mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp‐crested model dunes. Findings complement existing theories on secondary air?ow effects on stoss transport dynamics and provide new information on the in?uence of lee‐side air?ow patterns on dune morphodynamics. For all speeds investigated, turbulent unsteadiness at the dune toe indicates a greater, more variable surface shear, despite a signi?cant drop in time‐averaged measurements of streamwise shear stress at this location. This effect is believed suf?cient to inhibit sediment deposition at the toe and may be responsible for documented intermittency in sand transport in the toe region. On the stoss slope, streamline compression and ?ow acceleration cause an increase in ?ow steadiness and shear stress to a maximum at the crest that is double that at the toe of the isolated dune and 60–70 per cent greater than at ?ow reattachment on the lower stoss of closely spaced dunes. Streamwise ?ow accelerations, rather than turbulence, have greater in?uence on stress generation on the stoss and this effect increases with stoss slope distance and with incident wind speed. Reversed ?ow within the separation cell generates signi?cant surface shear (30–40 per cent of maximum values) for both spacings. This supports ?eld studies that suggest reversed ?ow is competent enough to return sediment to the dune directly or in a de?ected direction. High variability in shear at reattachment indicates impact of a turbulent shear layer that, despite low values of time‐averaged streamwise stress in this region, would inhibit sediment accumulation. Downwind of reattachment, shear stress and ?ow steadiness increase within 6 h (h = dune height) of reattachment and approach upwind values by 25 h. A distance of at least 30 h is suggested for full boundary layer recovery, which is comparable to ?uvial estimates. The Irwin sensor used in this study provides a reliable means to measure skin friction force responsible for sand transport and its robust, simple, and cost‐effective design shows promise for validating these ?ndings in natural dune settings. Copyright © 2003 John Wiley & Sons, Ltd.     

Smoothing and Change Point Detection for Gamma Ray Count Data

Gamma ray detectors are used to measure the natural radioactivity of rocks. For a number of boreholes drilled at a site the gamma ray detector is lowered into each borehole and counts of gamma ray emissions at different depths are recorded as the instrument is gradually raised to ground level. The profile of gamma counts can be informative about the geology at each location. The raw count data are highly variable, and in this paper we describe the use of adaptive smoothing techniques and change point models in order to identify changes in the geology based on the gamma logs. We formulate all our models for the data in the framework of the class of generalized linear models, and describe computational methods for Bayesian inference and model selection for generalized linear models that improve on existing techniques. Application is made to gamma ray data from the Castelreagh Waste Management Centre which served as a hazardous waste disposal facility for the Sydney region between March 1974 and August 1998. Understanding the geological structure of this site is important for further modelling the transport of pollutants beneath the waste disposal area.     

A Reappraisal of Rb, Y, Zr, Pb and Th Values in Geochemical Reference Material BHVO-1

The geochemical reference material BHVO-1 was analysed by a variety of techniques over a six year period. These techniques included inductively coupled plasma-mass spectrometry and atomic emission spectroscopy (ICP-MS and ICP-AES, respectively), laser ablation ICP-MS and spark source mass spectroscopy. Inconsistencies between the published consensus values reported by Gladney and Roelandts (1988, Geostandards Newsletter) and the results of our study are noted for Rb, Y, Zr, Pb and Th. The values reported here for Rb, Y, Zr and Pb are generally lower, while Th is higher than the consensus value. This is not an analytical artefact unique to the University of Notre Dame ICP-MS facility, as most of the BHVO-1 analyses reported over the last ten to twenty years are in agreement with our results. We propose new consensus values for each of these elements as follows: Rb = 9.3 ± 0.2 μg g-1 (compared to 11 ± 2 μg g-1), Y = 24.4 ± 1.3 μg g-1 (compared to 27.6 ± 1.7 μg g-1), Zr = 172 ± 10 μg g-1 (compared to 179 ± 21 μg g-1), Pb = 2.2 ± 0.2 μg g-1 (compared to 2.6 ± 0.9 μg g-1) and Th = 1.22 ± 0.02 μg g-1 (compared to 1.08 ± 0.15 μg g-1).     

Recent Rapid Regional Climate Warming on the Antarctic Peninsula

The Intergovernmental Panel on Climate Change (IPCC) confirmed that mean global warming was 0.6 ± 0.2 °C during the 20th century and cited anthropogenic increases in greenhouse gases as the likely cause of temperature rise in the last 50 years. But this mean value conceals the substantial complexity of observed climate change, which is seasonally- and diurnally-biased, decadally-variable and geographically patchy. In particular, over the last 50 years three high-latitude areas have undergone recent rapid regional (RRR) warming, which was substantially more rapid than the global mean. However, each RRR warming occupies a different climatic regime and may have an entirely different underlying cause. We discuss the significance of RRR warming in one area, the Antarctic Peninsula. Here warming was much more rapid than in the rest of Antarctica where it was not significantly different to the global mean. We highlight climate proxies that appear to show that RRR warming on the Antarctic Peninsula is unprecedented over the last two millennia, and so unlikely to be a natural mode of variability. So while the station records do not indicate a ubiquitous polar amplification of global warming, the RRR warming on the Antarctic Peninsula might be a regional amplification of such warming. This, however, remains unproven since we cannot yet be sure what mechanism leads to such an amplification. We discuss several possible candidate mechanisms: changing oceanographic or changing atmospheric circulation, or a regional air-sea-ice feedback amplifying greenhouse warming. We can show that atmospheric warming and reduction in sea-ice duration coincide in a small area on the west of the Antarctic Peninsula, but here we cannot yet distinguish cause and effect. Thus for the present we cannot determine which process is the probable cause of RRR warming on the Antarctic Peninsula and until the mechanism initiating and sustaining the RRR warming is understood, and is convincingly reproduced in climate models, we lack a sound basis for predicting climate change in this region over the coming century.