The volcanic eruption on Tristan da Cunha in 1961

On 10th October 1961, after two months of localized earth tremors, a dome of lava was extruded, about 300 yards east of the island settlement, on the northern coast of Tristan da Cunha. The dome grew rapidly to about 300 feet above its surroundings, and its seaward margin slowly moved outwards. Between 20th and 27th October the seaward side of the dome collapsed or was carried away, and mobile lava was emitted. This formed two series of lobes, extending into the sea along a front of about 1300 yards. This activity had ceased by the end of January 1962. In February, a dome up to 130 yards wide and 320 yards long, was pushed up 100 feet above the lava field, extending along the line of the lava stream from the central vent. By mid-March, this activity had ceased, and the only subsequent activity has been the continuation of fumarolic vents in the lava field. The trachyandesitic lava was of almost identical composition at each stage of the eruption, and closely resembled that from a previous eruption about 300 years ago at the other end of the island. The island has many well-preserved volcanic cones and scoria mounds. Such features as explosion craters, lava levees and lava channels also occur. The rocks of the Tristan da Cunha group range from ankaramites through basalts and trachybasalts to trachyandesites and trachytes. Leucite-bearing rocks are frequent and all the rocks have relatively-high contents ofK, Ba, Sr andNb. The origin of such a group of potassic rocks in a mid-oceanic environment is of considerable petrological interest. The 1961 eruption and the general geology of the Tristan da Cunha group was studied by members of the Royal Society Expedition to Tristan da Cunha. Their findings will be published in the Philosophical Transactions of the Royal Society (P. E. Baker, I. G. Gass, P. G. Harris andR. W. Le Maitre).     

Deep Hubble space telescope ultraviolet imaging of the M87 jet

Near-ultraviolet imaging with HST offers the best possible spatial resolution currently available for optical/UV astronomical imaging. The giant elliptical galaxy M87 hosts one of the most spectacular, best studied and nearest (d=16 Mpc) galactic-scale relativistic (synchrotron emitting plasma) jets. We have extracted from the HST archive all 220 nm images of the jet of M87, taken with the STIS MAMA camera and co-added them to provide the deepest image ever at this wavelength. The combination of highest spatial resolution and long integration time, 42500 seconds, reveals a wealth of complex structure, knots, filaments and shocks. We compare this image with deep X-ray observations obtained with the Chandra X-ray telescope.     

High seas marine protected areas: Benthic environmental conservation priorities from a GIS analysis of global ocean biophysical data

Designing a representative network of high seas marine protected areas (MPAs) requires an acceptable scheme to classify the benthic (as well as the pelagic) bioregions of the oceans. Given the lack of sufficient biological information to accomplish this task, we used a multivariate statistical method with 6 biophysical variables (depth, seabed slope, sediment thickness, primary production, bottom water dissolved oxygen and bottom temperature) to objectively classify the ocean floor into 53,713 separate polygons comprising 11 different categories, that we have termed “seascapes”. A cross-check of the seascape classification was carried out by comparing the seascapes with existing maps of seafloor geomorphology and seabed sediment type and by GIS analysis of the number of separate polygons, polygon area and perimeter/area ratio. We conclude that seascapes, derived using a multivariate statistical approach, are biophysically meaningful subdivisions of the ocean floor and can be expected to contain different biological associations, in as much as different geomorphological units do the same. Less than 20% of some seascapes occur in the high seas while other seascapes are largely confined to the high seas, indicating specific types of environment whose protection and conservation will require international cooperation. Our study illustrates how the identification of potential sites for high seas marine protected areas can be accomplished by a simple GIS analysis of seafloor geomorphic and seascape classification maps. Using this approach, maps of seascape and geomorphic heterogeneity were generated in which heterogeneity hotspots identify themselves as MPA candidates. The use of computer-aided mapping tools removes subjectivity in the MPA design process and provides greater confidence to stakeholders that an unbiased result has been achieved.     

Mesoscale physical variability affects zooplankton production in the Labrador Sea

Surface distribution (0–100 m) of zooplankton biomass and specific aminoacyl-tRNA synthetases (AARS) activity, as a proxy of structural growth, were assessed during winter 2002 and spring 2004 in the Labrador Sea. Two fronts formed by strong boundary currents, several anticyclonic eddies and a cyclonic eddy were studied. The spatial contrasts observed in seawater temperature, salinity and fluorescence, associated with those mesoscale structures, affected the distributions of both zooplankton biomass and specific AARS activity, particularly those of the smaller individuals. Production rates of large organisms (200–1000 μm) were significantly related to microzooplankton biomass (63–200 μm), suggesting a cascade effect from hydrography through microzooplankton to large zooplankton. Water masses defined the biomass distribution of the three dominant species: Calanus glacialis was restricted to cold waters on the shelves while Calanus hyperboreus and Calanus finmarchicus were widespread from Canada to Greenland. Zooplankton production was up to ten-fold higher inside anticyclonic eddies than in the surrounding waters. The recent warming tendency observed in the Labrador Sea will likely generate weaker convection and less energetic mesoscale eddies. This may lead to a decrease in zooplankton growth and production in the Labrador basin.     

Morphology and geotechnique of active-layer detachment failures in discontinuous and continuous permafrost, northern Canada

Fifty active-layer detachment failures triggered after forest fire in the discontinuous permafrost zone (central Mackenzie Valley, 65° N.) are compared to several hundred others caused by summer meteorological triggers in continuous permafrost (Fosheim Peninsula, Ellesmere Island, 80°N). Most failures fall into compact or elongated morphological categories. The compact type occur next to stream channels and have little internal disturbance of the displaced block, whereas the elongated types can develop on any part of the slope and exhibit greater internal deformation. Frequency distributions of length-to-width and length-to-depth ratios are similar at all sites. Positive pore pressures, expected theoretically, were measured in the field at the base of the thawing layer. Effective stress analysis could predict the instability of slopes in both areas, providing cohesion across the thaw plane was set to zero and/or residual strength parameters were employed. The location of the shear planes or zones in relation to the permafrost table and the degree of post-failure secondary movements (including headwall recession and thermokarst development within the failure track) differed between the localities, reflecting dissimilarity in the environmental triggers and in the degree of ground thermal disturbance.     

Dynamical evolution of cometary asteroids

We present results from long-term numerical integrations of hypothetical Jupiter-family comets (JFCs) over time-scales in excess of the estimated cometary active lifetime. During inactive periods these bodies could be considered as 'cometary' near-Earth objects (NEOs) or 'cometary asteroids'. The contribution of cometary asteroids to the NEO population has important implications not only for understanding the origin of inner Solar system bodies but also for a correct assessment of the impact hazard presented to the Earth by small bodies throughout the Solar system. We investigate the transfer probabilities on to 'decoupled' subJovian orbits by both gravitational and non-gravitational mechanisms, and estimate the overall inactive cometary contribution to the NEO population. Considering gravitational mechanisms alone, more than 90 per cent of decoupled NEOs are likely to have their origin in the main asteroid belt. When non-gravitational forces are included, in a simple model, the rate of production of decoupled NEOs from JFC orbits becomes comparable to the estimated injection rate of fragments from the main belt. The Jupiter-family (non-decoupled) cometary asteroid population is estimated to be of the order of a few hundred to a few thousand bodies, depending on the assumed cometary active lifetime and the adopted source region.     

Vietnamese activity in the Adelaide real estate market

Significant real estate activity by Vietnamese households in Adelaide did not occur until 1979, and since then the groups buying activity has been heavily concentrated in the northwest region of the metropolitan area. Therefore, the median housing price paid by Vietnamese buyers has not kept pace with the median price paid by all buyers. Concentration also causes Vietnamese buyers to be disproportionately active in the middle‐to‐lower end of the market, within which there has been a strong preference for rural properties and for houses rather than home units and maisonettes. Amongst Vietnamese buyers who subsequently sell their properties, the majority have not re‐entered the market and their capital gain from ownership has been marginal.