Drainage basin characteristics,their selection,derivation and analysis for a flood study of the British isles

A large data bank of morphometric, cover and climatic data for over a thousand drainage basins of all sizes in the British Isles was set up by the N.E.R.C. Flood Study. The paper describes the selection of these ‘independent’ variables, their degree of correlation, their portrayal of regional variability in the British Isles and their success as predictors of flood variables. The internal adjustment of drainage basins is confirmed, as is the basic physical division of Britain.     

Heat flow and heat generation in the Churchill Province of the Canadian Shield, and their palaeotectonic significance

Six new heat flow determinations are presented for Proterozoic mobile belts of the Churchill Province of the Canadian Shield, an area that was affected by several stages of the Hudsonian orogenic sequence (1.9-1.6 Ga ago). With other, previously published, values the mean of eight determinations considered reliable and representative and corrected for the effects of Pleistocene glaciation is 44 ± 7 mW m⁻². Heat generation measurements have also been made; values range from 0.1–1.04 μW m⁻³.A linear relation between heat flow and heat production is apparent. The heat flow axis intercept is 37 mW m⁻², and the scale depth is 11 km, compared with 28 mW m⁻² and 13.6 km for the Archaean Superior Province. Approximately 20% of the Churchill heat flow appears to be derived from radioactive decay in the upper crust, compared with 30% for the Superior Province and shields as a whole. The observations imply that the heat flow-heat production relation for the Churchill Province should be written as Q = Q_c + Q_e + A₀b where Q_c is equivalent to the reduced heat flow for the Archaean terrain, b is similar for the two, and Q_e is an additional component of heat flow in the Proterozoic mobile belts of the Churchill Province.A speculative tectonic model is presented. It is suggested that rifting along two axes of an original craton, which had lateral variations in near surface radiogenic element concentration, followed by erosion of the radiogenic layer and subsequent reconvergence of the cratonic segments, led to widespread redistribution of radioactive elements into the reactivated inter-rift crustal block. One result would be that crustal temperatures are higher in that part of the Churchill Province than in the Superior.     

V p /V s anomalies in dilatant rock samples

Summary In a series of triaxial experiments we have measuredV _p ,V _s and volumetric strain simultaneously in dilating dry and saturated rocks. For the first time these data permit quantitative comparison of seismic velocities or their ratio and dilatant volumetric strain. In air-dry samplesV _p /V _s decreases by a few per cent at strains of 10^–3; in saturated materials with high pore pressure,V _p /V _s increases by a comparable amount. Decreases in seismic velocity ratio are difficult to generate in initially saturated rocks even with low pore pressures and at strain rates of 10^–4/sec. A liquid-vapor transition will not produce a significant drop inV _p /V _s . If dilatancy and fluid flow are responsible for seismic travel time anomalies prior to earthquakes, our results suggest that such anomalies will occur only in regions where pore fluid source to sink dimensions are of the order of 10 km or more, or in regions where the rocks are not saturated to begin with.     

Pore water pressure and stability conditions on a motorway embankment

Prior to the occurrence of a shallow surface slip on a clay embankment a tensiometer system was installed to continuously monitor pore water conditions. It is shown that high pore water pressures can develop in clay embankments after periods of continuous low intensity precipitation. Using stability analyses it is demonstrated that for this first time slide, the clay fill material had a shear strength above residual values and a small but finite cohesion.     

Behavioural responses of estuarine mysids to hypoxia and disruption by cadmium

Neomysis integer (Peracarida: Mysidacea) occupies the upper, low-salinity regions of estuaries in Europe, where it can experience periods of reduced oxygen concentration associated with the maximum turbidity zone. The present study reports the distribution of N. integer in response to gradients of dissolved oxygen in combination with environmentally realistic cadmium concentrations (0.1, 0.5 and 1.0 microg Cd2+ l(-1). Control and 0.1 microg Cd2+ l(-1) mysids were distributed evenly along a flume containing an oxygen gradient, and demonstrated no avoidance to hypoxia (down to 30% air saturation). In contrast, mysids exposed to 1.0 microg Cd2+ l(-1) migrated away from areas of low dissolved oxygen and, after 90 min, no mysids were found in regions of <75% air saturation. These results indicate that cadmium poses an increased risk to estuarine organisms inhabiting upper estuarine areas subjected to reduced dissolved oxygen concentrations.     

Subsurface structure across the axis of the Tongariro Volcanic Centre,New Zealand

The relationship between structure and volcanism in the Tongariro Volcanic Centre, New Zealand, is largely masked by a mantle of young volcanic deposits. Here we report the results of an integrated geophysical investigation (using gravity, multi-level aeromagnetic and magnetotelluric methods) of subsurface deposits and structures in the upper 1–2 km across the axis of the Tongariro Volcanic Centre. Modelling of these data across the Tama Lakes saddle shows that the outcropping volcanic deposits are up to 800 m thick, underlain by Tertiary sediments (of a few 10's to a few 100 m in thickness) and in turn lying above a basement of probable Mesozoic greywacke. Basement faulting is shown to be concentrated in the centre of the rift, which is 18 km wide at this location, but no vertical offset is resolved at the rift axis. Vertical displacements on basement faults of 250–300 m are modelled giving a minimum total basement subsidence of 650 m. A 5 km-wide, deep low resistivity zone occurs at the axis of the rift which is interpreted as either resulting from extensive fracturing and/or hydrothermal alteration within the basement. Steep-sided volcanic bodies with a high proportion of lavas/dykes coincide with the Waihi fault and the rift axis. Coincidence with the Waihi Fault suggests that this fault system may have provided magma pathways to the surface and a focus for dyke emplacement, which could have contributed to rift extension. The lack of offset at the rift axis may reflect the juvenile nature of faulting at this location, which is consistent with the notion of a migration of faulting towards the centre of the graben, alternatively, rifting may have been entirely accommodated by dyke emplacement.