Helium resonance lines in the flare of 15 June, 1973

Time sequences of He i and He ii resonance line intensities at several sites within the flare of 15 June, 1973 are derived from observations obtained with the Naval Research Laboratory's Slitless Spectroheliograph on Skylab. The data are compared with predictions in six model flare atmospheres based on two values for the heating rate and three for the flux of photoionizing coronal X-rays and EUV. A peak ionizing flux more than 10³ times that in the quiet Sun is indicated. For most conditions in flare kernels the He ii L and L lines are found to be formed by collisional excitation, thereby contributing to the local cooling of the plasma at temperatures above 6 × 10⁴ K. Emission in the higher Lyman lines is generally the result of a mixture of collisional excitation at these temperatures and photoionization and recombination at temperatures near 2.5 × 10⁴ K. We discuss implications for the common practice of deriving stellar coronal fluxes from He ii 1640 Å fluxes assuming dominance of the recombination mechanism.Chief, Quantum Physics Division, National Institute of Standards and Technology.Operated jointly by the National Institute of Standards and Technology and the University of Colorado.Operated by the National Optical Astronomy Observatories of the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.     

Permeability development in vesiculating magmas: implications for fragmentation

 Fragmentation, or the "coming apart" of magma during a plinian eruption, remains one of the least understood processes in volcanology, although assumptions about the timing and mechanisms of fragmentation are key parameters in all existing eruption models. Despite evidence to the contrary, most models assume that fragmentation occurs at a critical vesicularity (volume percent vesicles) of 75–83%. We propose instead that the degree to which magma is fragmented is determined by factors controlling bubble coalescence: magma viscosity, temperature, bubble size distribution, bubble shapes, and time. Bubble coalescence in vesiculating magmas creates permeability which serves to connect the dispersed gas phase. When sufficiently developed, permeability allows subsequent exsolved and expanded gas to escape, thus preserving a sufficiently interconnected region of vesicular magma as a pumice clast, rather than fully fragmenting it to ash. For this reason pumice is likely to preserve information about (a) how permeability develops and (b) the critical permeability needed to insure clast preservation. We present measurements and calculations that constrain the conditions (vesicularity, bubble size distribution, time, pressure difference, viscosity) necessary for adequate permeability to develop. We suggest that magma fragments explosively to ash when and where, in a heterogeneously vesiculating magma, these conditions are not met. Both the development of permeability by bubble wall thinning and rupture and the loss of gas through a permeable network of bubbles require time, consistent with the observation that degree of fragmentation (i.e., amount of ash) increases with increasing eruption rate. Received: 5 July 1995 / Accepted: 27 December 1995     

Uncertainty in adaptive capacity

The capacity to adapt is a critical element of the process of adaptation: it is the vector of resources that represent the asset base from which adaptation actions can be made. Adaptive capacity can in theory be identified and measured at various scales, from the individual to the nation. The assessment of uncertainty within such measures comes from the contested knowledge domain and theories surrounding the nature of the determinants of adaptive capacity and the human action of adaptation. While generic adaptive capacity at the national level, for example, is often postulated as being dependent on health, governance and political rights, and literacy, and economic well-being, the determinants of these variables at national levels are not widely understood. We outline the nature of this uncertainty for the major elements of adaptive capacity and illustrate these issues with the example of a social vulnerability index for countries in Africa. To cite this article: W.N. Adger, K. Vincent, C. R. Geoscience 337 (2005).     

An examination of the resettlement program at Mayon Volcano: what can we learn for sustainable volcanic risk reduction?

This paper investigates a resettlement program for communities impacted by volcanic hazards from Mayon volcano in the Philippines. Two resettlement sites are selected, the first FVR–FNM village (named after President Fidel V. Ramos and Mayor Florencio N. Munoz) was settled after the 1993 eruption. The second, Bungkaras Village, was settled after the 2006 eruption and associated typhoon Reming lahar event. These two sites were selected in order to explore the process of relocation over the short and longer term, although the main focus of the study is in the more recently settled Bungkaras Village. The overall aim is to determine if exposure to volcanic hazards has decreased without adding to vulnerability through loss of livelihood, community and culture, and exposure to new risks. A mixed method qualitative approach was utilized including semistructured interviews, participant observations, and a participatory workshop. This enabled an in-depth understanding of life and the challenges faced at the resettlement sites vis-à-vis the original settlements. In order to document the process of site selection, planning, and building, semistructured interviews were conducted with key government officials, emergency managers, and donors of the resettlement projects. This research demonstrates that a volcanic resettlement program must be directed by meaningful consultation with the impacted community who also share in the decision making. Successful resettlement must consider aspects of livelihood security, house design, and the availability of public and lifeline facilities.     

Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization

Crystal size distributions (CSDs) measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates, growth times, and the degree of overstepping (T) of reactions during metamorphism. CSDs are described through use of a population density function n=dN/dL, where N is the cumulative number of crystals per unit volume and L is a linear crystal size. Plots of ln (n) vs. L for olivine+pyroxene and magnetite in high-temperature (1000° C) basalt hornfelses from the Isle of Skye define linear arrays, indicating continuous nucleation and growth of crystals during metamorphism. Using the slope and intercept of these linear plots in conjunction with growth rate estimates we infer minimum mineral growth times of less than 100 years at T<10° C, and nucleation rates between 10^–4 and 10^–1/cm³/s. Garnet and magnetite in regionally metamorphosed pelitic schists from south-central Maine have CSDs which are bell-shaped. We interpret this form to be the result of two processes: 1) initial continuous nucleation and growth of crystals, and 2) later loss of small crystals due to annealing. The large crystals in regional metamorphic rocks retain the original size frequency distribution and may be used to obtain quantitative information on the original conditions of crystal nucleation and growth. The extent of annealing increases with increasing metamorphic grade and could be used to estimate the duration of annealing conditions if the value of a rate constant were known. Finally, the different forms of crystal size distributions directly reflect differences in the thermal histories of regional vs. contact metamorphosed rocks: because contact metamorphism involves high temperatures for short durations, resulting CSDs are linear and unaffected by annealing, similar to those produced by crystallization from a melt; because regional metamorphism involves prolonged cooling from high temperatures, primary linear CSDs are later modified by annealing to bell shapes.     

Direct measurements of latent heat during crystallization and melting of a ugandite and an olivine basalt

Step-scanning calorimetric measurements using a Setaram HT1500 calorimeter were performed between 800 and 1400°C on two natural samples: a ugandite from the East African rift and an olivine basalt from the western Mexican arc. Our measurements provide the first in-situ quantitative assessment of enthalpy during melting of initially crystalline natural samples. The distribution of latent heat across the liquidus-solidus intervals of the two samples is distinctly different, reflecting significant variation in the sequence and abundance of mineral phases during melting (clinopyroxene and leucite in the ugandite; olivine, clinopyroxene, and plagioclase in the basalt). Our data further indicate that the common assumption of a uniform distribution of latent heat across the liquidus-solidus interval of a magma is a reasonable approximation for the olivine basalt, but is grossly in error for the ugandite. This is due to cotectic precipitation of leucite and clinopyroxene, leading to a large, disproportionate release of latent heat early in the crystallization sequence. The implication for the thermal history of a crystallizing ugandite magma is that therate of heat loss during conductive cooling will unitially be more rapid than the average rate. The net result will be to produce lower magmatic temperatures after a given cooling interval relative to models assuming a uniform release of latent heat. An additional series of scanning calorimetric experiments were performed at variable rates (1,2 and 3°/min) to evaluate the role of kinetics on the distribution of enthalpy during both melting and crystallization of the ugandite and olivine basalt. The results indicate that clinopyroxene is the most important mineral phase in controlling the shapes of the enthalpy profiles during cooling; this is due to its large enthalpy of fusion and its tendency for sluggish nucleation, followed by rapid crystallization at temperatures that vary with cooling rate. The resolution of the calorimeter (in terms of heat detected per unit time) is also important in determining the shapes of theobserved enthalpy profiles during these rapid scans. Estimates based on the observed calorimetric signal associated with melting of olivine, and the lack of a calorimetric signal during melting of leucite, combined with known enthalpies of fusion for the two phases, indicate detection limits of approximately 0.6–1.2 kJ per 5 min increments.     

Volcanic hazard communication using maps: an evaluation of their effectiveness

Hazard maps are considered essential tools in the communication of volcanic risk between scientists, the local authorities and the public. This study investigates the efficacy of such maps for the volcanic island of Montserrat in the West Indies using both quantitative and qualitative research techniques. Normal plan view maps, which have been used on the island over the last 10 years of the crisis, are evaluated against specially produced three-dimensional (3D) maps and perspective photographs. Thirty-two demographically representative respondents of mixed backgrounds, sex, education and location were interviewed and asked to complete a range of tasks and identification on the maps and photographs. The overall results show that ordinary people have problems interpreting their environment as a mapped representation. We found respondents’ ability to locate and orientate themselves as well as convey information relating to volcanic hazards was improved when using aerial photographs rather than traditional plan view contour maps. There was a slight improvement in the use of the 3D maps, especially in terms of topographic recognition. However, the most striking increase in effectiveness was found with the perspective photographs, which enabled people to identify features and their orientation much more readily. For Montserrat it appears that well labelled aerial and perspective photographs are the most effective geo-spatial method of communicating volcanic risks.

Diagnostic analysis of future climate scenarios applied to urban flooding in the Chicago metropolitan area

Past heavy precipitation events in the Chicago metropolitan area have caused significant flood-related economic and environmental damages. A key component in flood management policies and actions is determining flood magnitudes for specified return periods. This is a particularly difficult task in areas with a complex and changing climate and land-use, such as the Chicago metropolitan area. The standard design storm methodology based on the NOAA Atlas 14 and ISWS Bulletin 70 has been used in the past to estimate flood hydrographs with variable return periods in this region. In a changing climate, however, these publications may not be accurate. This study presents and illustrates a methodology for diagnostic analysis of future climate scenarios in the framework of urban flooding, and assesses the corresponding uncertainties. First, the design storms are calculated using data downscaled by a regional climate model (RCM) at 30-km spacing for the present and 2050s under the IPCC A1Fi (high) and B1 (low) emissions scenarios. Next, the corresponding flood discharges at six watersheds in suburban Chicago are estimated using a hydrologic event model. The resulting scenarios in flood frequency were first assessed through a set of diagnostic tests for precipitation timing and frequency. The study did not reveal any significant changes in the 2050s in the average timing of heavy storms, but their regularity decreased. The average timing did not exhibit any significant spatial variability throughout the region. The precipitation frequency analysis revealed distinct differences between the northern and southeastern subregions of the Chicago metropolitan area. The quantiles in the northern subregion averaged for 2-year, 5-year, and 10-year return periods exhibited a 20% and 16% increase in daily precipitation for scenarios B1 and A1Fi, respectively. The southeastern subregion, however, exhibited a decrease of 12% for scenario B1 and a minor increase of 3% for scenario A1Fi. The hydrologic effects of changing precipitation on the flood quantiles were illustrated using six small watersheds in the region. The relative increases or decreases in precipitation translated into even larger relative increases or decreases in flood peaks, due to the nonlinear nature of the rainfall-runoff process. Simulations using multiple climate models, for longer periods, finer spatio-temporal resolution, and larger areal coverage could be used to more accurately account for numerous uncertainties in the precipitation and flood projections.