Post-eruption erosion and deposition in the 1980 crater of Mount St Helens,Washington, determined from digital maps

The crater of Mount St Helens shows one of the world's highest known rates of mass wasting. On many summer days, rockfall is almost continuous, and many large rock and dirty-snow avalanches have travelled several kilometres from their sources on the crater walls. Since formation of the crater on 18 May 1980, talus cones exceeding 100 m in thickness have formed at the base of the unstable 600 m high crater walls. To estimate rates of erosion and deposition, a series of digitized topographic maps made from aerial photographs taken of the crater in 1980, 1981, 1983, 1986 and 1988 were analysed using a geographic information system. Between 1980 and 1988, 30 × 10⁶ m³ of rock were eroded from the crater wall, representing a mean retreat rate of 2.1 m yr^?1. To account for the volume increase that occurs when bedrock is transformed into scree, this volume is multiplied by 4/3; this provides an estimate of the rock-debris volume supplied to the crater floor of 40 × 10⁶ m³. The actual volume of deposits that accumulated during this 8 year period, however, is 68 × 10⁶ m³. The difference of 28 × 10⁶ m³ is presumably the volume of snow intercalated between insulating layers of rock debris. Similar calculations for each of four time intervals between 1980 and 1988 suggest that wall erosion and thus talus accumulation rates are declining, but that rates will probably remain high for decades to come.     

Great-circle Rayleigh wave attenuation and group velocity,Part I: Observations for periods between 150 and 600 seconds for seven great-circle paths

Rayleigh wave attenuation coefficients and group velocities have been estimated for seven great-circle paths. The attenuation coefficient measurements cover the period range from 100 to 500 s, and group velocities the range from 100 to 600 s. Global average group velocities and attenuation coefficients have also been estimated for these period ranges. The spread of the individual path group velocities for 20-s averaging windows centred at 290, 250, 210, 180 and 150 s is less than 0.034, 0.028, 0.024, 0.048 and 0.071 km/s, respectively. Global average attenuation coefficients, when combined with global average group velocities, show that Q for Rayleigh waves has an approximately constant value of about 145 for periods between 150 and 220 s and slowly increases to a value of about 200 at a period of 400 s.     

Estimating relative bed-load contributions by lithology counts

In gravel-bedded streams where bed material of a tributary differs distinctly in lithology from that of the main stream, rock-type percentages can be used to estimate bed-load contributions of the two streams. The rock type that shows the greatest difference in abundance between the two streams is selected as the indicator lithology. Percentages of this lithology are estimated in both the main stream and tributary stream above their junction, and also in the main stream at a distance sufficiently downstream from the junction to allow complete mixing. The fraction of bed load contributed by the main stream, p,is estimated by ,where is an estimate of the proportion of indicator rock fragments in the bed of the main stream above the junction, is an estimate of the proportion in the bed of the tributary above the junction, and is an estimate of the proportion in the bed of the main stream below the junction. The variance of is obtained as var ( )= [p₁q₁(p_r – p₂)²/n(p₁ – p₂)⁴] + [p₂q₂(p_r – p₁)²/n(p₁ – p₂)⁴] + [p_rq_r/n(p₁ – p₂)²].Although no estimate of actual quantity of bed load is provided, the indicator rock technique supplies data that can serve as a check on data obtained by means of empirical formulas or actual transport measurements.     

Geometric assessment of the kodak DCS Pro back

This paper reports on an investigation into the suitability of the Kodak DCS Pro Back for use in close range photogrammetric measurement. The camera back, being used in conjunction with a medium-format non-metric camera, has been assessed with a view to using it for low- to medium-order photogrammetric work in architectural recording. Examinations centred upon the stability of the camera back with respect to the camera body and the effects of the removable infrared filter that is present immediately above the camera's focal plane. Ultimately the camera combination was deemed suitable for application in recording of this kind and is now in active use by the Metric Survey Team at English Heritage.     

The origin of clay minerals in active and relict hydrothermal deposits

Samples of Fe-oxide-rich hydrothermal sediments were collected from active and inactive portions of the TransAtlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge. Clays separated from TAG metalliferous sediments in this study all consist of Al-poor nontronite. Oxygen isotope thermometry of the clays yields formation temperatures of 54-67°C for samples from the inactive Alvin mound compared with 81-96°C for samples from the active TAG site. The latter are the highest recorded temperatures for authigenic hydrothermal clays. Sr isotope analysis of the clays from the active mound suggests that they precipitated from seawater-dominated fluids, containing less than 15% hydrothermal end-member fluid. In contrast, nontronite from the inactive Alvin mound has ⁸⁷Sr/⁸⁶Sr values that closely resemble that of detrital North Atlantic clays, suggesting a dominantly continental source for the Sr. Rare earth element data are consistent with a significant detrital input to the inactive site but also demonstrate the extent of hydrothermal input to the low temperature fluid. Crystallographic fractionation of the trivalent REE is apparent in the heavy REE enrichments for all nontronite samples. The inferred formation-mechanism for nontronite-rich Fe-oxyhydroxide deposits at the surface of the active mound is by direct precipitation from low temperature fluids. At the inactive Alvin site, in contrast, the deposits form during alteration of pelagic sediments by diffuse fluids and replacement of biogenic carbonate with nontronite and Fe-oxyhydroxide. These two modes of formation are both important in seafloor hydrothermal settings where clay minerals are a significant component of the hydrothermal deposit.     

Photogrammetry from Archived Digital Imagery for Seal Monitoring

This paper discusses the use of near vertical aerial photographs archived onto Kodak Photo CD in the production of a digital elevation model of the Isle of May, Scotland. Control for the survey was obtained using differential GPS receivers and the photogrammetric processing was carried out using low cost PC hardware and software. The elevation model is being used in a GIS to enable the spatial analysis of the island's seal population.     

Progress toward sustainable settlements: a role for urban climatology

Summary Sustainable development can be defined as that which meets the needs of the current generation while leaving sufficient resources for the needs of future generations. A central objective is to decouple conventional resource use (and its corollary, waste generation) from economic development through technological innovation, improved efficiency and changes in individual practices. As the global population becomes urbanized and human activity is concentrated in urban areas, settlement planning is a key aspect of sustainability. The widespread inclusion of environmental objectives in urban plans at all scales provides an opportunity for the incorporation of urban climate knowledge into the planning process on a routine basis. Many of the stated objectives have both direct and indirect connections to climate. However, for this to happen, climate research and results must be linked more explicitly to the objectives of the sustainable settlement. In this paper, the relevance of sustainability to urban design and climate is discussed and the potential contribution of current urban climatology is assessed, identifying areas of special consideration for transfer to achieve sustainable urban planning and design.     

Metal-silicate partitioning of cesium: Implications for core formation

Here we present the first set of metal-silicate partitioning data for Cs, which we use to examine whether the primitive mantle depletion of Cs can be attributed to core segregation. Our experiments independently varied pressure from 5 to 15 GPa, temperature from 1900 to 2400 °C, metallic sulfur content from pure Fe to pure FeS, silicate melt polymerization, expressed as a ratio of non-bridging oxygens to tetrahedrally coordinated cations (nbo/t) from 1.26 to 3.1, and fO₂ from two to four log units below the iron-wüstite buffer. The most important controls on the partitioning behavior of alkalis were the metallic sulfur content, expressed as X_S, and the nbo/t of the silicate liquid. Normalization of X_S to 0.5 yielded the following expressions for D-values as a function of nbo/t: log D_Na = −2.0 + 0.44 × (nbo/t), log D_K = −2.4 + 0.67 × ( nbo/t), and log D_Cs = −3.2 + 1.17 × (nbo/t). Normalization of nbo/t to 2.7 resulted in the following equations for D-values as a function of S content: log D_Na = −4.1 + 6.4 × X_S, log D_K = −7.7 + 13.9 × X_S, and log D_Cs = −12.1 + 23.3 × X_S.There appears to be a negative pressure effect up to 15 GPa, but it should be noted that this trend was not present before normalization, and is based on only two measurements. There is a positive trend in cesium’s metal-silicate partition coefficient with increasing temperature. D_Cs exhibits the largest change and increased by a factor of three over 500 °C. The effect of oxygen fugacity has not been precisely determined but in general, lowering fO₂ by two log units resulted in a rise in all D-values of approximately an order of magnitude. In general, the sensitivity of partition coefficients to changing parameters increased with atomic number.The highest D-value for Cs observed in this study is 0.345, which was obtained at nbo/t of 2.7 and a metal phase of pure FeS. This metallic composition has far more S than has been suggested for any credible core-forming metal. We therefore conclude that the depletion of Cs in Earth’s mantle is either caused by radically different behavior of Cs at pressures higher than 15 GPa or is not related to core formation. Even so, we have shown that a planet with a sufficient S inventory may incorporate significant amounts of alkali elements into its core.