A Cheap, Quick and Safe Way of Surveying Glaciers

The use of a 35 mm or similar camera set up over a theodolite is described for surveying mountain and polar glaciers where conditions do not allow for extensive detailed surveying or the use of heavy phototheodolites. Though used initially by Spender and Wright in the 1930s on Mount Everest and in Greenland and Arctic Canada, but apparently not by others since then, it was again tried out by Wright in Iceland in 1992. Modern analytical techniques have shown that heights accurate to within 2 m can be obtained from these photographs at distances up to 5 km. In addition, five times as many points can be identified and intersected in the laboratory from the photographs as was possible using sketches in difficult field conditions. Some reasons are suggested for the lack of use of this technique by others. The potential of existing survey photographs taken in Arctic Canada for large scale surveys of high polar glaciers in 1938 is described, with the hope that glaciologists and photogrammetrists might undertake their analysis.     

Regional travel-time and slowness measurements for P-waves in the distance range 40–57°

A method for analysing travel times measured at a large array or a network of seismographs from many earthquakes within a specific region has been developed. Approximate relative station corrections are calculated from the residuals on a least-squares line or least-squares quadratic form fitted through the times for each earthquake, and may be improved by iteration after a preliminary travel-time curve has been derived. Accurate relative baseline corrections for each earthquake are also calculated iteratively, and an optimum slowness-distance curve is determined from the combined corrected travel times from all earthquakes using a trade-off procedure. Calculations using synthetic travel-time data suggest that abrupt changes in slowness of ～ 0.4 s deg^?1 due to the presence of triplications are generally resolvable, provided that the effects of lateral variations are small, even with random epicentre mislocations in the range ± 0.5°. Slowness measurements at a network of temporary stations deployed across Australia do not show any discontinuities in slowness greater than 0.2 s deg^?1 in the distance range 45–54°. Similar measurements at the Warramunga array from the same source regions, however, suggest the presence of complexity in the slowness curve at distances close to 50°. Relative arrival times at the temporary network generally have standard deviations less than 0.25 s, thus suggesting that details of structure finer than those derived from conventional travel-time studies can be resolved.     

Metal accumulation in four molluscs

Specimens of mussels (Mytilus edulis), winkles (Littorina littorea), dogwhelks (Nucella lapillus) and limpets (Patella vulgata) were collected from the north-east coast of England in 1980–1981 in order to analyse the dried whole soft tissue for zinc, copper and iron. In each case, only a narrow size range of organisms was collected from a small environmentally homogeneous site and sex was taken into account. Most of the frequency distributions of metal concentrations obtained were found to show significant positive skewness. This skewness could not be explained either by the degree of mobility or type of feeding mechanism of the organisms or by any other known parameter, e.g. size, sex, habitat variation. Some individual mussels were found to be extremely good regulators of their zinc concentrations. On the other hand, other individual mussels had the ability to accumulate unusually high levels of zinc.     

Dispersal and characteristics of pyroclastic fall deposits from Mt. Misery Volcano,West Indies

Mt. Misery volcano, near the northern end of the Lesser Antilles island arc, produced late Quaternary airfall layers that have different dispersal patterns. These are controlled by: a) the style of explosive activity which determined the heights of the eruption columns and b) a layered atmospheric system with contrasted bipolar wind directions at different altitudes. Isopach and isopleth maps are given for 10 eruptions belonging to the Mansion Series (>41, 730–1, 750 yrs. B.P.). Basaltic strombolian-type scoria-fall deposits were dispersed mainly by surface/lower tropospheric winds to the NW and W. In contrast green and brown andesitic sub-plinian and plinian falls with higher eruption columns were dispersed to the SE and E by upper tropospheric winds. Thinly laminated phreatomagmatic ashes within the Mansion Series are again dispersed to the NW and controlled by surface winds.The green andesite layers most commonly contain microvesicular, angular clasts due to some limited interaction of magma and external water which partly drove these eruption columns. These deposits also contain carbonized wood up to 11 km from the vent. Vegetation is thought to have been ignited by large juvenile bombs of dense green and esite which have been measured up to 15 cm at 8 km from the vent.

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Zusammenfassung Der Vulkan Mt. Misery im Norden des Inselbogens der Kleinen Antillen hat im späten Quartär Aschelagen hervorgebracht, die unterschiedliche Verteilungsmuster aufweisen. Diese werden bestimmt durch a) die Art der Explosionen, die die Höhe der Eruptionssäulen bestimmte und b) durch das geschichtete atmosphärische System mit gegenläufigen bipolaren Windrichtung in verschiedenen Windrichtungen. Es werden Isopachen-Isoplethen-Karten für 10 Ausbrüche dargestellt, die zu den Mansion-Serien (>41, 730-1, 750 Jahre B.P.) gehören. Basaltische Schlackenlagen vom Stromboli-Typ wurden hauptsächlich durch Oberflächen- bis untertroposphärische Winde nach Nordwesten und Westen verteilt. Im Gegensatz dazu vertrifteten grüne und braune andisitische subplinische und plinische Aschen aus höheren Eruptionssäulen nach SE und E durch Winde der oberen Troposphäre. Dünn laminierte phreatomagmatische Aschen innerhalb der Mansion-Serie wurden wiederum nach NW ausgebreitet durch oberflächennahe Winde. Die grünen Andesitlagen enthalten besonders häufig schaumige, eckige Komponenten, bedingt durch die Interaktion von Magma und Oberflächenwasser, die teilweise diese Eruptionssäulen beeinflußt hat. Diese Ablagerungen enthalten außerdem verkohltes Holz bis 11 km Entfernung vom Ausbruchszentrum. Es ist anzunehmen, daß die Vegetation durch große juvenile Bomben von dichtem, grünem Andesit verbrannt ist, die bis zu 15 cm ø in 8 km Entfernung vom Ausbruchszentrum beobachtet wurden.

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Résumé Le volcan Misery, situé dans la partie N de l'arc des petites Antilles a donné lieu, au cours du Quaternaire, au dépôt de couches de cendres, dont la dispersion s'est opérée de diverses manières. Cette dispersion est fonction: a) du style de l'activité explosive du volcan, dont dépend la hauteur de la colonne de projections; b) du système stratifié de l'atmosphère caractérisé par des vents dont la direction varie avec l'altitude. Des cartes d'isopaques et d'isoplethes ont été établies pour 10 éruptions de la série Mansion (>41, 790–1, 750 ans B.P.). Des scories basaltiques de type strombolien ont été dispersées principalement vers le NW et l'W par des vents de surface ou de la basse troposphère. Par contre, des produits andésitiques verts et bruns de type plinien et subplinien, provenant de colonnes d'éruption élevées, ont été dispersés vers le SE et l'E par des vents de la troposphère supérieure. Des cendres finement stratifiées, d'origine phréatomagmatique montrent une dispersion vers le NW provoquée par des vents de surface.Les dépôts andésitiques verts renferment couramment des fragments elastiques, microvésiculaires, anguleux, témoins de l'interaction du magma et des eaux de surface, responsable en partie de la hauteur des colonnes d'éruption. Les mêmes dépôts contiennent du bois carbonisé jusqu'à 11 km du cratère. On pense que la végétation a été incendiée par de grosses bombes d'andésite verte de forte densité, dont la dimension atteint encore 15 cm à 8 km du cratère.

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A thermochemical study of the distribution of cobalt and nickel between diopsidic pyroxene and melt

Glasses and crystals of compositions MgCaSi₂O₆, CoCaSi₂O₆ and NiCaSi₂O₆ were studied by high temperature solution calorimetry, x-ray diffraction, and pycnometry. These data were combined with trace element distribution data to obtain values for ΔAG⁰, ΔH⁰, ΔS⁰, and ΔV⁰ for M-Mg exchange reactions. Enthalpies of vitrification increase in the order Co, Mg, Ni as do volumes of vitrification and apparent melting points. The mixing of Co and Mg, Ni and Mg, and Co and Ni is almost ideal in crystals and glasses, with small negative heats of mixing and small volume changes. The exchange reactions MgCaSi₂O₆ (xl) + MCaSi₂O₆ (liq) = MgCaSi₂O₆ (liq) + MCaSi₂O₆ (xl) are exothermic for Ni and endothermic for Co. The volumes and entropies of the exchange reaction are small.     

The carbon and nitrogen isotopic composition of ureilites: Implications for their genesis

Fourteen ureilites were analyzed for stable C isotopic composition using stepped combustion. The δ¹³C values over the temperature range 500 to 1000°C are fairly constant for any particular meteorite although there are differences between samples. The similarity in combustion temperatures of pure diamond (600–1000δC) and pure graphite (600–800°C) makes it difficult to ascertain the relative proportions of either component within each sample. However, the constant δ¹³C values observed over the range 500 to 1000°C strongly suggests that ureilite diamond and graphite have the same isotopic composition. This would seem to confirm that the diamond in ureilites formed from the graphite during a process, presumably an impact event, which did not fractionate C isotopes.There is a variation in C isotopic composition of graphite/diamond intergrowths among ureilites, which is not continuous—the samples fall into two groups, with δ¹³C values clustered around ?10%. and ?2%. PDB. These groups are also distinguishable on the basis of the Fe content of their olivines, which may reflect the existence of more than one ureilite parent body. The brecciated ureilite North Haig has a δ¹³C value of ?6.5%. and it is thus possible that this sample contains components from mixed parent materials.Nitrogen abundance and stable isotope measurements were made on five samples using stepped combustion analysis. Nitrogen concentrations range from 25 to 150 ppm and $\text{C}\text{N}$ ratios are substantially less than for carbonaceous chondrites. Variation in N isotopic composition is wide and there is evidence of different ratios in diamond/graphite, silicate and metal.     

The identification of radial velocity anomalies in the lower mantle using an interference method

A radial velocity anomaly in the lower mantle may cause a triplication in the travel-time curve for short-period P waves, but the first two arrivals may not be separable visually on seismograms over a distance range of about 4–10°. However, the changes of slowness and azimuth as a function of time can be used to infer the presence of interfering signals. Some of the interference effects that can be generated synthetically are often observed on seismograms of earthquakes recorded at the Yellowknife array at distances close to 50°, 80° and 90°. The data from Yellowknife provide evidence for the presence of regions of high velocity gradients at depths of about 1250, 2400 and 2730 km that also show rapid lateral variations. Numerous P arrivals from South American earthquakes that traverse the lowest 500 km of the mantle beneath the Caribbean region have been used to illustrate the main features of the interference method.     

Earthquake response of steel-framed multistorey buildings with set-backs

A study is made of the dynamic behaviour of multistorey steel rigid-frame buildings with set-back towers. The effects of set-backs upon the building frequencies and mode shapes are examined. Then the effects of set-backs on seismic response are investigated by analysing the response of a series of set-back building frame models to the El Centro ground motion. Finally, the computed responses to the El Centro earthquake are compared with some code provisions dealing with the seismic design of set-back buildings. The conclusions derived from the study include the following:

• 1. The higher modes of vibration of a set-back building can make a very substantial contribution to its total seismic response; this contribution increases with the slenderness of the tower.
• 2. Some of the important response parameters for the tower portion of a set-back building are substantially larger than for a related uniform building.
• 3. For very slender towers, the transition region between the tower and the base may be subjected to very large storey shears.