The one-point PDF of the initial conditions of our local Universe from the IRAS PSC redshift catalogue

The algorithm ztrace of Monaco & Efstathiou is applied to the IRAS PSCz catalogue to reconstruct the initial conditions of our local Universe with a resolution down to ~5  h ¹ Mpc. The one-point probability distribution function (PDF) of the reconstructed initial conditions is consistent with the assumptions that: (i) IRAS galaxies trace mass on scales of ~5  h ¹ Mpc and (ii) the statistics of the primordial density fluctuations are Gaussian. We use simulated PSCz catalogues, constructed from N -body simulations with Gaussian initial conditions, to show that local non-linear bias can cause the recovered initial PDF (assuming no bias) to be non-Gaussian. However, for plausible bias models, the distortions of the recovered PDF would be difficult to detect using the volume finely sampled by the PSCz catalogue. So, for Gaussian initial conditions, a range of bias models remain compatible with our PSCz reconstruction results.     

Land-use planning for natural hazards in New Zealand: the setting,barriers, ‘burning issues’ and priority actions

Land-use planners have a critical role to play in building vibrant, sustainable and hazard resilient communities in New Zealand. The policy and legal setting for natural hazards planning provides a solid foundation for good practice. But there are many examples of ‘bad practice’ that result in unnecessary risks and, in some cases, exposure to repeat events and potentially devastating impacts. Much, therefore, remains to be done to improve hazards planning policy and practice in New Zealand. This article explores the questions: What role does land-use planning play in managing hazard risks in New Zealand; and what needs to be done to reduce hazard risks and build community resilience? The article starts by describing the milieu within which natural hazards planning takes place. It goes onto outline the stakeholders and institutional and legal setting for natural hazards planning in New Zealand, including barriers to realising the potential of natural hazards planning. This synthesis reveals a number of ‘burning issues’, including the need to: (a) Improve understanding about the nature of hazards; (b) Prioritise risk avoidance (reduction) measures; (c) Provide national guidance for communities exposed to repeat events and address the relocation issue and (d) Mainstream climate change adaptation. Each ‘burning issue’ is discussed, and priority actions are recommended to realise the potential of land-use planning to reduce natural hazard risks and build community resilience in New Zealand. Ultimately, the challenge is to develop a cooperative hazards governance approach that is founded on coordinated policies, laws and institutions, cooperative professional practice and collaborative communities.     

Volatiles in submarine volcanic rocks from the spreading axis of the East Scotia Sea back-arc basin

The volatile content of glassy pillow rims from East Scotia Sea back-arc basin (BAB) lavas are unlike those of mid-ocean ridge (MOR) pillow-rim glasses, although non-volatile compositions of the two rock groups overlap. The East Scotia Sea samples have three to ten times greater water contents and nearly twice the average CO₂ and Cl contents of MOR samples; F contents are similar. S contents are only one-third those from MOR samples. H₂O and CO₂ contents of glassy pillow rims from Mariana island arc andesites are similar to those in the BAB lavas studied. Nevertheless, volatiles in the East Scotia Sea BAB magmas are probably not directly derived from the subducted slab, because there is no seismic evidence that the slab extends within 200 km of the spreading axis of the East Scotia Sea. Available data do not preclude the possibility that the magmas were contaminated by seawater prior to eruption or that the mantle under the East Scotia Sea spreading center is volatile-rich. The volatiles may have been added to the mantle during an earlier period of subduction, perhaps during the initial formation of the East Scotia Sea basin.     

San Quintín volcanic field, Baja California, Mexico: 'within-plate' magmatism following ridge subduction

The Holocene San Quintín volcanic province in northern Baja California comprises spinel-lherzolite-bearing alkali basalts. Trace element (La/Nb = 0.57–0.73; K/Rb = 402–479; La_N/Yb_N= 8.4, 9.9) and isotopic ratios (⁸⁷Sr/⁸⁶r = 0.70323–0.70352; ¹⁴³Nd/¹⁴⁴Nd = 0.512924–0.512996; ²⁰⁶Pb/²⁰⁴Pb = 19.108, 19.250; ²⁰⁷Pb/²⁰⁴Pb = 15.567, 15.589; ²⁰⁸Pb/²⁰⁴Pb = 38.82, 38.85) show that the lavas are compositionally indistinguishable from some ocean island, plume-associated basalts such as Hawaii and the Azores, and testify to an asthenospheric source for the magmas. The occurrence in Baja of such lavas may be related to the nature of the cessation of plate subduction beneath the peninsula; at present, San Quintín (and volcanic provinces to the north) are underlain by a 'no-slab window', whereas immediately to the south, remanent oceanic lithosphere may be preserved as a relict slab. This may act as a bamer to the upward passage of diapirs or magmas from the asthenosphere.     

Predicting the peculiar velocities of nearby PSCz galaxies using the Least Action Principle

We use the Least Action Principle to predict the peculiar velocities of PSC z galaxies inside cz =2000 km s⁻¹. Linear theory is used to account for tidal effects to cz =15 000 km s⁻¹, and we iterate galaxy positions to account for redshift distortions. As the Least Action Principle is valid beyond linear theory, we can predict reliable peculiar velocities even for very nearby galaxies (i.e., cz ≤500 km s⁻¹). These predicted peculiar velocities are then compared with the observed velocities of 12 galaxies with Cepheid distances. The combination of the PSC z galaxy survey (with its large sky coverage and uniform selection) with the accurate Cepheid distances makes this comparison relatively free from systematic effects. We find that galaxies are good tracers of the mass, even at small (≤10  h ⁻¹ Mpc) scales; under the assumption of no biasing, 0.25≤ β ≤0.75 (at 90 per cent confidence). We use the reliable predicted peculiar velocities to estimate the Hubble constant H ₀ from the local volume without 'stepping up' the distance ladder, finding a confidence range of 65–75 km s⁻¹ Mpc⁻¹ (at 90 per cent confidence).     

Preliminary laboratory studies of the optical scattering properties of the crystal clouds

Ice crystal clouds have an influence on the radiative budget of the earth; however, the exact size and nature of this influence has yet to be determined. A laboratory cloud chamber experiment has been set up to provide data on the optical scattering behaviour of ice crystals at a visible wavelength in order to gain information which can be used in climate models concerning the radiative characteristics of cirrus clouds. A PMS grey-scale probe is used to monitor simultaneously the cloud microphysical properties in order to correlate these closely with the observed radiative properties. Preliminary results show that ice crystals scatter considerably more at 90° than do water droplets, and that the halo effects are visible in a laboratorygenerated cloud when the ice crystal concentration is sufficiently small to prevent masking from multiple scattering.