bluuebunny/crossref_metadata_2025 huggingface dataset:
A pocos kilómetros, pero en otro país. El retiro de jubilados estadounidenses en Baja California, México
Authors: Lardiés Bosque Raúl
Published: September 2017

México se ha convertido en el principal país de Iberoaméricaen recibir jubilados procedentes de Estados Unidos. Este colectivo deinmigrantes se ha extendido por varios enclaves del país, pero unaimportante comunidad se localiza en la zona fronteriza (en el corredor‘Ensenada-Tijuana’, estado de Baja California). Este artículo pretendeconocer las razones que influyen en el traslado residencial de los jubiladosa esta zona de México, y se basa en la realización de 29 entrevistasen profundidad. Los resultados apuntan a que, sobre todo, factoresambientales y también socioeconómicos determinan el traslado; en concreto,el buen clima, las diferencias de precios y de nivel de vida entreambos países, además de otras razones como la cercanía y el desarrollode un entorno cultural y lingüístico propicio, favorecen la movilidadresidencial de este colectivo de personas.
Políticas públicas para el desarrollo rural: un análisis multiescalar
Authors: Molina Ibáñez Mercedes , Farris Massimiliano
Published: September 2017

El artículo reflexiona sobre el papel de las políticas públicasy de la sociedad local como protagonistas de un cambio necesario parael desarrollo de los territorios rurales marginales, desde una perspectivamultiescalar que considere la dimensión territorial. Nueva economía,multifuncionalidad rural, territorio y políticas públicas constituyen labase de este análisis.
Subsidios gubernamentales para riesgos de mercado en granos: el caso del sorgo en México
Authors: Echánove Huacuja Flavia
Published: September 2017

En un contexto de gran volatilidad de los precios internacionalesde los granos, como el vivido en los últimos años, la protección alos productores adquiere gran relevancia. Con este fin, el gobierno deMéxico implementó un programa de subsidios llamado agricultura porcontrato, cuyas características y limitantes son el objeto central de nuestroestudio. Entre los hallazgos, se encontró que si bien dicho programaofrece importantes ventajas para los participantes, es sumamante vulnerablepor los inclumplimientos de contratos motivados por los efectosadversos del clima, la relación de precios relativos (precios internacionalesvs precios en el mercado libre) y la evolución del tipo de cambio.Otras limitantes son la reducida cobertura nacional y la concentración delos apoyos en un reducido grupo de beneficiarios, entre los que figurangrandes empresas alimentarias.
Evolución de las relaciones transfronterizas en el Bidasoa: de la conurbación a la communauté
Authors: Alberdi Collantes Juan Cruz
Published: September 2017

Con la entrada de España en la Unión Europea y la desapariciónde la frontera se intensifican las relaciones internacionales. Pero tambiénvecinos que habían permanecido alejados se acercan unos a otros.Los municipios de Bajo Bidasoa, es decir, Irún, Hondarribia y Hendaia,conforman una conurbación y como tal deciden hacer frente a las necesidadesde su población. Para ello crean el Consorcio transfronterizo delBidasoa el año 1998 pero las dificultades que supone trabajar en dos paísesdiferentes limita su desarrollo. Frente a ello surgen nuevas instituciones,de origen comarcal, que comienzan a superar algunas de las barrerascon las que se topaba el Consorcio, hasta el punto de poner lacontinuidad de esta entidad en entredicho.
Creación de una base de datos homogeneizada de temperaturas para los Pirineos (1950-2010)
Authors: Cuadrat José María , Serrano Roberto , Saz Miguel Ángel , Tejedor Ernesto , Prohom Marc , Cunillera Jordi , Esteban Pere , Soubeyroux Jean Michel , Deaux Nathalie
Published: September 2017

En este artículo se describe el proceso y metodología para lacreación de una base de datos térmica del Pirineo para el periodo temporal1950-2010, y se avanzan los primeros resultados del análisis espacial de lastemperaturas y del cálculo de la tendencia de las mismas a escala anual.Para el control de calidad y homogeneización se ha empleado el métodoHOMER que incorpora los últimos métodos y técnicas de gestión de datos,incluyendo la eliminación de valores atípicos, la detección por paresy la selección de punto de ruptura (reforzada por los metadatos). Las seriesfinales proporcionan datos homogeneizados para analizar la evolucióndel clima y el comportamiento climático del conjunto del Pirineo.
Agentes locales y proyectos transfronterizos en el eje transpirenaico Barcelona-Toulouse
Authors: Oliveras González Xavier , Durà Guimerà Antoni
Published: September 2017

Los agentes públicos locales, por ser la administración territorial más próxima, detectan necesidades o conflictos, pero pueden no tener las competencias administrativas para gestionarlos. En el artículo se recoge la propuesta y rechazo de proyectos territoriales a administraciones superiores en un contexto transfronterizo. El análisis se centra en el ámbito territorial del eje transpirenaico Barcelona-Toulouse (frontera España-Andorra-Francia), y en dos contextos político administrativos diferentes, anterior y posterior a la regulación jurídica de la cooperación transfronteriza. En concreto se analizan seis casos, en los ámbitos de las infraestructuras de transporte (la línea ferroviaria Barcelona-Toulouse, y la carretera E-09), la sanidad (el Hospital Transfronterizo de Cerdanya) y la gestión del agua (trasvases de aguas y las depuradoras de la cuenca alta del Segre). Se evalúa el rol de los agentes así como el de los proyectos en la construcción regional transfronteriza.
Dinámica y caracterización geoecológica de comunidades vegetales a partir de valores indicadores de Ellenberg y del método fitoindicación/fitoacción. Ensayo de aplicación en los tarajales del arroyo Aceitero (cuenca del Guadaíra, Sevilla)
Authors: Gómez Montblanch David Cristel , Laguna Lumbreras Emilio , Meaza Rodríguez Guillermo
Published: September 2017

Se realiza la caracterización geoecológica de una formación riparia de galería de taraje común (Tamarix gallica) en el Arroyo Aceitero (provincia de Sevilla), usando dos aproximaciones: 1) el uso combinado de los valores indicadores de Ellenberg y las coberturas, propuesto por Laguna (2012), y 2) el método Fi/Fa (Interactividad Fitoindicación/Fitoacción) de Meaza y Cuesta (2010). Previamente, se realiza un análisis de estructura y dinámica mediante el uso combinado de algunos estadísticos y la propuesta de clasificación sociológica de pies de formaciones leñosas empleado por el Sistema Agro-Forestal (Harold, 1984). Ambos métodos indican que el tarajal muestreado es una comunidad vegetal que combina especies higrófilas y nitrófilas, estando de hecho dominada por plantas higronitrófilas. Se concluye que ambas aproximaciones metodológicas pueden usarse de modo complementario.
Análisis de la afección del deporte de escalada en la biología reproductora del quebrantahuesos (Gypaetus barbatus L.) en el Pirineo central (Aragón-España)
Authors: Blasco Ibáñez Ignacio , Longares Aladrén Luis Alberto , Gil Gallús Juan Antonio
Published: September 2017

En todas las poblaciones naturales de aves rapaces existen unidades reproductoras (UR) cuya productividad, entendida como pollos volados/año, es baja o nula. Las molestias humanas en las zonas de nidificación han sido una de las causas más relacionadas con el descenso de la productividad de muchas aves rapaces (Richardson y Miller, 1997). Según Arroyo y Razin (2006) las actividades humanas cercanas a los nidos del Quebrantahuesos (Gypaetus barbatus L.) pueden causar molestias en la reproducción. Los vigentes planes de recuperación de la especie en la Cordillera pirenaica contemplan acciones específicas para evitar el fracaso reproductivo, mediante la aplicación de medidas preventivas de factores de perturbación: molestias por batidas de caza, escalada deportiva, etc. Durante los últimos 10 años el deporte de escalada en Aragón (en todas sus modalidades) ha experimentado un aumento en cuanto al número de escaladores y sectores donde se practica. Con el fin de conocer las posibles repercusiones de la escalada en roca en la conservación del Quebrantahuesos se ha recopilado información sobre sectores de escalada en la provincia de Huesca. Posteriormente dicha información ha sido georreferenciada espacialmente y se le han aplicado diversos métodos de análisis geoespacial con técnicas SIG en el entorno ArcGis. El objetivo ha sido realizar una aproximación al análisis de la posible relación entre el deporte de escalada y la nidificación de la especie. De un total de 315 nidos conocidos de Quebrantahuesos en Aragón (2011), se ha comprobado que el 11,75% de estos (n= 37) podrían estar afectados por la escalada en roca.
El proceso de ordenamiento ambiental en Cuba. Propuesta y aplicación de su procedimiento metodológico a nivel nacional y regional
Authors: Cárdenas López Obllurys , Mateo Rodríguez Juan Manuel , Martínez Suárez Juan Mario
Published: September 2017

La necesaria interacción entre el ordenamiento territorial y ordenamiento ambiental fue promulgada en la Ley 81 y en las Estrategias Ambientales Nacionales (EAN) desde 1997, en Cuba. Varias situaciones frenaron su cumplimiento, la falta de procedimientos metodológicos que guiaran el proceso, fue una de ellas por lo que la EAN de 2011-2015 y los Lineamientos del Partido Comunista de Cuba (PCC), en el año 2011, lo ratifican como objetivo. En el abordaje de este problema y en la inclusión de los resultados de los estudios de peligro, vulnerabilidad y riesgo y de los escenarios de cambio climático radica la actualidad de la presente investigación. Teniendo como hipótesis que: el empleo de procedimientos metodológicos integradores y participativos facilitará la elaboración de modelos de ordenamiento ambiental (MOA) que aporten regulaciones, lineamientos y normas ambientales al proceso de ordenamiento territorial; se persigue como objetivo principal: proponer los procedimientos metodológicos para la elaboración de los MOA y realizar su validación a nivel nacional y municipal. Son empleados métodos teóricos y empíricos combinados en la elaboración de los procedimientos y en su validación a diferentes escalas. Se concluye en la pertinencia de utilizar el procedimiento propuesto para la elaboración de los MOA, a diferentes escalas, teniendo como base el enfoque participativo y a las unidades de paisaje, como unidad de análisis.
Apoyos para maíz en México: el programa gubernamental de agricultura por contrato
Authors: Echánove Huacuja Flavia
Published: September 2017

Desde hace poco más de una década, el gobierno mexicano ha venido aplicando dos programas de subsidios para proteger a productores y empresas compradoras de granos de los riesgos de las fluctuaciones de los precios de esos bienes a nivel internacional. Este tipo de apoyos, plasmados en los programas denominados “agricultura por contrato” y “coberturas de precios”, son el objeto de la investigación. Se estudian sus características centrales, así como sus limitantes y efectos, tanto en los productores de maíz del estado de Puebla, como en las firmas pecuarias compradoras de dicho grano. Entre los hallazgos de la investigación figura el hecho de que si bien los programas ofrecen importantes ventajas a los participantes, son frecuentes los incumplimientos de contratos debidos a desastres climáticos, relación de precios (internacionales vs. mercado libre) y evolución del tipo de cambio. Se reseña también el carácter regresivo de los apoyos y su concentración geográfica. La necesidad de reorientar la política de subsidios agrícolas en México es una de las conclusiones del artículo, señalando las posibles alternativas.
Las posibilidades de integración del transporte escolar y regular en Aragón
Authors: Badía Lázaro Ricardo
Published: September 2017

El presente artículo explora las ventajas y el potencial de integrar las líneas de transporte escolar en la red de transporte regular de viajeros en Aragón. Con este propósito, se ha recopilado información sobre los puntos de origen, destino y características básicas de todas las rutas escolares. Los resultados muestran la incipiente aparición de dos modelos de integración diferentes. El primero de ellos se corresponde con las rutas escolares integradas cuya principal ventaja es la mejora en la accesibilidad de la población rural a los servicios. El segundo son las rutas regulares con reserva de plaza cuyos beneficios son un menor coste para la administración y una mejora de la rentabilidad de las líneas regulares. Ambos modelos todavía cubren una pequeña parte de la demanda por lo que atendiendo a sus ventajas tienen un gran potencial de expansión.
Projection, Scale, and Accuracy in the 1721 Kangxi Maps
Authors: Jupp David L.B.
Published: September 2017

The Kangxi Emperor employed Jesuit brothers (1708–18) to produce maps of the provinces of China using a combination of Western and Chinese survey methods. The maps were completed by 1721. They were sent back to Europe and became the basis for maps of China produced by Jean Baptiste Bourguignon d'Anville in 1735. The main changes from traditional Chinese mapping were to use latitude and longitude as primary coordinates, map them using a spherical projection, and use astronomical measurements of latitude and longitude to establish baselines. Changes in latitude and longitude were found using traditional metric survey and relationships between distance north–south and latitude and distance east–west and longitude to convert to degrees. A digitized facsimile of the 1721 map series is available from the US Library of Congress. In this article, the digitized images were used to reconstruct the parameters of the sinusoidal projection, establish scale, and re-project and mosaic the maps into various forms for presentation. The accuracy of five of the province maps is discussed in detail. It is found that poor astronomical measurements of longitude are the most serious issue for the maps, but that apart from areas distorted by the poor longitude estimates, the accuracy was commensurate with that of European land maps of the time.
Land and Power: Making a New Map of Ireland's Border
Authors: Carr Garrett
Published: September 2017

The author discusses the process behind a map of his creation, “A View of the Border.” It charts Ireland's north/south frontier and has been used to illustrate the author's 2017 monograph, The Rule of the Land: Walking Ireland's Border. Defending or questioning the legitimacy of Ireland's border is still a defining force in Ireland's politics, especially in Northern Ireland. In addition, this border is soon to become the United Kingdom's only land border with the European Union. The author takes issue with the borderline symbol on maps, suggesting that the reduction of Ireland to a binary has negative ramifications in political discourse – contributing to an us-versus-them stalemate. On the ground, Ireland's border is largely invisible and almost completely permeable; the author wondered if the border could be mapped in a way that would reflect this. To identify original modes of mapping the frontier, the author travelled the borderline from end to end. The resulting map charts defensive architecture and historical sites, as well as unofficial cross-border routes and other subjects. Many topographic elements on “A View of the Border” do not generally appear on maps; the author explains the thinking behind the inclusion of some of these elements and discusses designing the icons used represent them. The conclusion asks if any of the creative decisions made in “A View of the Border” could be applied to maps other border regions.
Glacier Flow and the Growth of the Glacier Grain
Authors: Seligman G.
Published: September 2017

The crystallographic results of the Jungfraujoch Research Party’s investigations were published in the Proceedings of the Royal Society in August 1939. It has since occurred to me that insufficient attention was drawn to another factor affecting the movement and growth of the glacier grain, namely the possibility of pressure melting, followed by regelation. There are numerous air spaces between glacier grains at all stages until they approach the state of pure ice, and it seems natural that while two neighbouring grains (which are continually moving differentially to one another) arc in contact, pressure melting, will take place, and that when the film of water reaches an air space it will refreeze. The effect will become less as the firn passes into ice owing to the decrease in the amount of air space and the increased interlocking, of the grains, which makes their differential movement more difficult. Naturally, also, pressure melting would not take place at those points in the glacier which were appreciably below freezing point.
Microstructural change in ice: I. Constant-deformation-rate tests under triaxial stress conditions
Authors: Melanson P. M. , Meglis I.L. , Jordaan I.J. , Stone B. M.
Published: September 2017

Extensive damage to ice occurs during ice structure interaction by microcracking, recrystallization and melting. The objective of this work was to investigate this damage process under confined-stress conditions believed to be associated with impact zones that occur during ice–structure interaction. “Damage” refers to microstructural modification that causes deterioration of the mechanical properties. Prior experimental work has shown that a small amount of deformation causes permanent damage in ice, leading to enhanced creep rates during subsequent loading. To investigate this softening, freshwater granular ice was deformed under moderate confinement (20 MPa) at –10°C, at two rates which bracket ductile and brittle behavior (10−2 s−1 and 10−4 s−1). Samples were deformed to different levels of axial strain up to 28.8%. Thin sections were examined to assess the progressive changes in microstructure.

Both grain-boundary and intra-granular cracking began at strains corresponding to the peak stress (1–2%) for tests at both strain rates. The peak stresses were 23.4 MPa for the tests at 10−2 s−1 and 9.8 MPa for the tests at 10−4 s−1. At strains of > 1–2%, dense clusters of intra-granular cracks began to develop in the samples tested at the higher rate. At the lower rate, dynamic recrystallization was apparently the dominant deformation mechanism beyond the peak stress. The average grain-size decreased strongly during the first few per cent strain and then maintained a relatively stable value.
Microstructural change in ice: II. Creep behavior under triaxial stress conditions
Authors: Meglis I. L. , Melanson P. M. , Jordaan I.J.
Published: September 2017

This work investigates the deformation of ice under deviatoric stresses and confining pressures expected during ice–structure interaction. Granular ice was tested under a range of confining pressures (5–60 MPa) and deviatoric stresses (up to 25 MPa), with sample temperatures between –8° and –10°C. Samples were deformed to increasing end-levels of axial strain, and were thin-sectioned and photographed immediately following testing.

At all confinement levels, the original texture of the sample is completely transformed within the first 10–15% strain, to a fine-grained matrix with a few larger, isolated grains. At low confinements, grain-size reduction is associated with extensive microcracking. At high confinements, few cracks are observed. Observations suggest that microcracking, melting and recrystallization are active at all levels of confinement, though the relative importance of each depends on the confinement, stress and accumulated strain.

Deviatoric stress is a strong factor in controlling the creep, reflected in both the time required for the sample to reach accelerated creep and the tertiary creep rate itself. Two exceptions to this pattern were noted. First, some samples experienced strain localization and eventual rupture. These specimens tended to have higher creep rates even in the initial stages of strain. Second, prior damage resulted in rapid softening compared with the behavior of undamaged specimens. However, when strain rates are compared among all samples at a given level of cumulative axial strain, the creep behavior obeys a power law over the whole range of strain levels tested. Effective viscosity decreased from 107.8 to l06.4 MPa−n s within the first 10% strain, during which the most substantial microstructural changes occurred, and then stayed relatively stable. The stress exponent, n, remained within the range 4.0–4.6.

The dominant deformation mechanism appears to depend strongly on confining pressure (cracking at low pressure and dynamic recrystallization at high pressure). Creep rates at high confinement appear to increase relative to those at intermediate confinement, but the influence of temperature must be addressed further.
A computer-based system simulating snowpack structures as a tool for regional avalanche forecasting
Authors: Durand Y. , Giraud G. , Brun E. , Mérindol L. , Martin E.
Published: September 2017

This paper describes the current state of a complete automatic system of three numerical models that simulate snow-cover stratigraphy and avalauche risks for operational avalanche forecasting. The first model, SAFRAN, estimates relevant meteorological parameters affecting snowpack evolution. The second Crocus, is a snow numerical model which simulates the physical processes inside the snowpack and its stratigraphy. The last model, MÉPRA, is an expert system; based on an assessment of snowpack stability, it deduces natural and accidental avalanche risks. To describe the great Variability of the snowpack and the associated avalanche risks, this automatic system simulates snow-cover evolution and its stability for many typical slopes, elevations and aspects representative of the different French massifs. To achieve this result, different kinds of validations have been carried out since winter 1981; they are mainly based on comparisons with different sets of measurements and on the opinion of users.

Although the routinely obtained results do not yet take into account all small-scale effects such as wind transport, they have been considered as valuable information by avalanche forecasters since 1992 93 and used operationally since then.
Subglacial drilling at Black Rapids Glacier, Alaska, U.S.A.: drilling method and sample descriptions
Authors: Truffer M. , Motyka R.J. , Harrison W.D. , Echelmeyer K. A. , Fisk B. , Tulaczyk S.
Published: September 2017

We employed a commercial wireline drill rig to investigate the subglacial conditions of Black Rapids Glacier, a well-studied surge-type glacier in the central Alaska Range. The four main goals were: to assess the capabilities of the commercial drilling industry for sampling subglacial material, to investigate the basal morphology, to determine the subglacial geology and to emplace borehole instruments. The drilling was done in an area where seasonal and secular variations in speed are large, and where seismic studies suggested the presence of a till layer. Four holes were drilled at three locations to a maximum depth of 620 m. Three holes yielded samples of basal ice and till, although recovery of the latter was generally poor. Bedrock was sampled in one or possibly two of the holes. In the area sampled, t he glacier is underlain by a till layer some 4–7 m thick, confirming the seismic interpretation. It consists of a sandy matrix at least 20–30% of which comprises larger clasts. Limited samples of the matrix indicate that near the top of the till the porosity is 40%, and t hat some of the pore water is frozen. Geologic studies suggest that the drilling area lies to the north of the Denali Fault, a major tectonic boundary followed by the glacier, and that most of the till is locally derived with transport distances of <2 km.
Combining SAR interferometry and the equation of continuity to estimate the three-dimensional glacier surface-velocity vector
Authors: Reeh Niels , Madsen Søren Nørvang , Mohr Johan Jakob
Published: September 2017

Until now, an assumption of surface-parallel glacier flow has been used to express the vertical velocity component in terms of the horizontal velocity vector, permitting all three velocity components to be determined from synthetic aperture radar interferometry. We discuss this assumption, which neglects the influence of the local mass balance and a possible contribution to the vertical velocity arising if the glacier is not in steady state. We find that the mass-balance contribution to the vertical surface velocity is not always negligible as compared to the surface-slope contribution. Moreover, the vertical velocity contribution arising if the ice sheet is not in steady state can be significant. We apply the principle of mass conservation to derive an equation relating the vertical surface velocity to the horizontal velocity vector. This equation, valid for both steady-state and non-steady-state conditions, depends on the ice-thickness distribution. Replacing the surface-parallel-flow assumption with a correct relationship between the surface velocity components requires knowledge of additional quantities such as surface mass balance or ice thickness.
Automatic reconstruction of polycrystalline ice microstructure from image analysis: application to the EPICA ice core at Dome Concordia, Antarctica
Authors: Gay Michel , Weiss Jerome
Published: September 2017

A digital image-processing approach is proposed which allows the extraction of two-dimensional polycrystalline ice microstructure (grain boundaries) from thin sections observed between cross-polarisers. It is based on image segmentation of colour images. The method is applied to the preliminary analysis of the shallow ( Holocene) ice of the European Project for Ice Coring in Antarctica (EPICA) ice core at Dome Concordia. Structural parameters, such as the mean cross-sectional area, shape anisotropy and grain morphology, are obtained. The interest and limitations of this automatic procedure are discussed.
Application of a mass-balance model to a Himalayan glacier
Authors: Kayastha Rijan Bhakta , Ohata Tetsuo , Ageta Yutaka
Published: September 2017

A mass-balance model based on the energy balance at the snow or ice surface is formulated, with particular attention paid to processes affecting absorption of radiation. The model is applied to a small glacier, Glacier AX010 in the Nepalese Himalaya, and tests of its mass-balance sensitivity to input and climatic parameters are carried out. Calculated and observed area-averaged mass balances of the glacier during summer 1978 (June-September) show good agreement, namely -0.44 and -0.46 m w.e., respectively.

Results show the mass balance is strongly sensitive to snow or ice albedo, to the effects of screening by surrounding mountain walls, to areal variations in multiple reflection between clouds and the glacier surface, and to thin snow covers which alter the surface albedo. In tests of the sensitivity of the mass balance to seasonal values of climatic parameters, the mass balance is found to be strongly sensitive to summer air temperature and precipitation but only weakly sensitive to relative humidity.
Modelling mass balance using photogrammetric and geophysical data: a pilot study at Griesgletscher, Swiss Alps
Authors: Kääb Andreas , Funk Martin
Published: September 2017

The kinematic boundary condition al the glacier surface can be used to give glacier mass balance at a point as a function of changes in the surface elevation, and of the horizontal and vertical velocities. Vertical velocity can in turn be estimated from basal slope, basal ice velocity and surface strain. In a pilot study on the tongue of Griesgletscher, Swiss Alps, the applicability of the relation for modelling area-wide ice flow and mass-balance distribution is tested. The key input of the calculations, i.e. the area-wide surface velocity field, is obtained using a newly developed photogrammetric technique. Ice thickness is derived from radar-echo soundings. Error estimates and comparisons with stake measurements show an average accuracy of approximately ±0.3 ma-1 for the calculated vertical ice velocity at the surface and ±0.7 ma-1 for the calculated mass balance. Due to photogrammetric restrictions and model-inherent sensitivities the applied model appeared to be most suitable for determining area-wide mass balance and ice flow on flat-lying ablation areas, but is so far not very well suited for steep ablation areas and most parts of accumulation areas. Nevertheless, the study on Griesgletscher opens a new and promising perspective for the monitoring of spatial and temporal glacier mass-balance variations.
Intra-seasonal changes in deformation profiles revealed by borehole studies, Storglaciären, Sweden
Authors: Hooke Roger LeB. , Pohjola Veijo Allan , Jansson Peter , Kohler Jack
Published: September 2017

In 1985, 1987 and 1988, we measured deformation of boreholes in the ablation zone of Storglaciären. A different hole was used each year. Deformation profiles were determined for four consecutive time periods between mid-July and early September. All three holes were in an area where the glacier lies in an overdeepened part of the bed, up-glacier from a riegel. The first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin. Despite large standard errors, variations in the deformation profiles during the melt season are broadly consistent with other data. We thus believe that they are real, and that they reflect changes in the stress field resulting from changes in drag at the bed. A decrease in drag early in the melt season, coupled with convergence of the bed contours towards the riegel, is believed to be responsible for a previously documented increase in vertical velocity just up glacier from the riegal at this time of year. Also noteworthy, but perhaps problematical, was an abrupt transverse shear of at a depth of ~25 m near the center of the glacier in July 1985. The shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier.
Climate at the Equilibrium Line of Glaciers
Authors: Ohmura Atsumu , Kasser Peter , Funk Martin
Published: September 2017

The relationships between temperature, precipitation and radiation on glacier equilibrium lines are investigated, using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods. It is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months’ temperature in a free atmosphere, annual total precipitation, and the sum of global and long-wave net radiation. All of these are measured at or very near the equilibrium-line altitudes. Then, it is shown how the shift of the equilibriumline will occur as a result of a climatic change. Finally, the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations. The present results make it possible to identify the altitudes in climate models where glacierization should begin, and to evaluate the mass-balance changes as a result of possible future changes in the climate.
Air clathrate crystals from the GRIP deep ice core, Greenland: a number-, size- and shape-distribution study
Authors: Pauer F. , Kipfstuhl S. , Kuhs W. F. , Shoji H.
Published: September 2017

We performed microscopic observations and a statistical study of the number, size and shape distribution of clathrates in the GRIP (Greenland Ice Core Project) deep ice core, using 185 samples from a depth range of 1016–3014 m, spanning a period of 6 to >110 ka BP and encompassing the Holocene, Wisconsin and Eemian periods. The number concentration of the clathrates varied considerably with climatic changes. It was possible to detect the rapid climatic oscillations in the last glacial between 13 and 110 ka BP, the Dansgaard–Oeschger cycles, in the number-concentration profile of clathrates. The mean volume of clathrates is less clearly influenced by climatic factors, with a tendency towards greater volumes in warmer periods, but also a growth of clathrates with depth could be detected. This growth rate was calculated to be 3.1 × 10-12 cm3 a-1. The amount of gases captured in the clathrates is estimated to be significantly smaller than the total amount of air determined by gas-concentration measurements. This points to diffusion processes of atmospheric gases within the ice matrix.
Coupling between a glacier and a soft bed: I. A relation between effective pressure and local shear stress determined from till elasticity
Authors: Iverson Neal R. , Baker Robert W. , Hooke Roger LeB. , Hanson Brian , Jansson Peter
Published: September 2017

To predict the distribution of motion beneath glaciers on soft beds, the strength of the coupling between the ice and the bed and its variation with effective pressure must be known. A record of shear strain, acquired with a tiltmeter emplaced in till beneath Storglaciären, Sweden, indicates that fluctuations in water pressure cause variations in the local shear stress on the bed and that the bed deforms elastically in response to these variations. To estimate the shear stress from the elastic component of the total shear strain, the shear modulus of the till was measured in relaxation tests conducted in the laboratory with a ring-shear device. After accounting for the elastic compliance of the device, these tests yielded shear moduli of about 1000 and 1800 kPa at confining pressures of 85 and 280 kPa, respectively. These values are comparable to those of other granular materials undergoing recoverable shear strains of the same magnitude. The local shear stress on the till, calculated by applying the measured shear moduli to the tilt record, scales with Pe1.7, where Pe is the effective pressure. This relation implies that as Pe decreases at the ice/till interface, shear stresses on the till are reduced and concentrated elsewhere on the bed, perhaps where the till is absent or the glacier is frozen to the bed. When compared with the strength of the till determined from ring-shear tests, this relation also accounts for the lack of permanent deformation at depth in the bed during periods of low Pe and indicates that most basal motion was by sliding or ploughing.
Coupling between a glacier and a soft bed: II Model results
Authors: Iverson Neal R.
Published: September 2017

The relation between the local effective pressure and shear stress on till beneath Storglaciären, Sweden, discussed in Iverson and others (1999), provides an empirical basis for studying the processes that control the strength of the ice/bed coupling. Particles in the bed that protrude into the glacier sole support shear stresses that are limited by either ploughing or the traditional sliding mechanisms. Model calculations, based on studies of cone penetration through fine-grained sediment and sliding theory, agree with the observed relation between shear stress and effective pressure if the water layer at the ice/bed interface is assumed to thicken rapidly as the effective pressure approaches zero. Studies of the hydraulics of linked cavities provide support for this assumption, if the mean thickness of the water layer reflects the extent of microcavity development at the interface. Comparison of the calculated shear stress with the ultimate strength of till suggests that bed deformation limits the shear stress on till beneath Storglaciären only at intermediate effective pressures; at very low effective pressures, like those inferred at the site of the tiltmeter discussed in Iverson and others (1999), and at sufficiently high effective pressures, ploughing and sliding should focus motion near the glacier sole. A calculation using parameter values appropriate for Ice Stream B, West Antarctica, suggests that ploughing may occur there at shear stresses not sufficient to deform the bed at depth. This conclusion is reinforced by the likelihood that pore pressures in excess of hydrostatic should develop down-glacier from ploughing particles, thereby weakening the bed near the glacier sole. However, given the apparent sensitivity of the ice/bed coupling to basal conditions that may be highly variable, any blanket assumption regarding the flow mechanism of ice masses on soft beds should probably be viewed with skepticism.
An investigation of the debris-rich basal ice from Worthington Glacier, Alaska, U.S.A.
Authors: Hart Jane K. , Waller Richard I.
Published: September 2017

This paper examines the debris-rich basal ice layer from Worthington Glacier, Alaska, U.S.A., a small valley glacier overlying rigid bedrock. The debris-rich basal ice layer studied shows evidence for large-scale longitudinal compressive deformation (isoclinal folds and nappes), similar in style and magnitude features to that reported from push moraines formed in glacial sediments. The debris-rich ice largely comprisedstratified solid ice(layers of alternating debris-rich and debris-poor ice) which we suggest results from the tectonic attenuation of folds produced from the deformation of the frozen debris, glacier ice and bubble-rich ice that comprise the initial basal layer of Worthington Glacier. Beneath the glacier lies a thin bed of saturated diamicton which contains evidence of limited movement. It is suggested that this is the result of the partial melt-out of the debris-rich basal ice layer which then behaved as a local (and seasonal) thin deforming layer.

It is suggested that this example, from a valley glacier flowing over rigid bedrock, provides further evidence that the processes of sediment transport, incorporation and deposition in the debris-rich basal ice are similar to and linked with those in the deforming layer.
Faceted crystal formation in the northeast Greenland low-accumulation region
Authors: Steffen Konrad , Abdalati Waleed , Sherjal Isabelle
Published: September 2017

Snow-pit analysis in the tow-accumulation region in northeast Greenland indicated a mean annual accumulation of 12 ± 1.6 cm. It also revealed numerous faceted layers that were not related to the summer horizon of previous years. In general, the faceted crystals were found under a wind crust. These crusts appear to originate during the winter. Snow- and air-temperature data from automatic weather stations suggest that the katabatic storms are responsible for the formation of the wind crusts and the faceted layers. Frequent, abrupt temperature changes up to 30°C were observed within two days, due to turbulent mixing of cold-air inversions. The near-surface air-temperature variations are correlated with wind speed, the latter leading the former by 6–9 hours for increasing wind, and 1–4 hours for decreasing wind. Because of low accumulation, katabatic storms affect the same snow surface for several months, causing repealed air-temperature fluctuations. This leads to strong vapor-pressure gradients and faceted crystal growth in the top snow layer. On average we found two faceted layers (in addition to the summer layer) per year for a 4 year record. In addition to its climatological significance in the snow record, the formation of these layers is especially important to understand for the interpretation of microwave satellite observations of the firn.
A distributed temperature-index ice- and snowmelt model including potential direct solar radiation
Authors: Hock Regine
Published: September 2017

Hourly melt and discharge of Storglaciären, a small glacier in Sweden, were computed for two melt seasons, applying temperature-index methods to a 30 m resolution grid for the melt component. The classical degree-day method yielded a good simulation of the seasonal patient of discharge, but the pronounced melt-induced daily discharge cycles were not captured. Modelled degree-day factors calculated for every hour and each gridcell from melt obtained from a distributed energy-balance model varied substantially, both diurnally and spatially. A new distributed temperature-index model is suggested, attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography. This is accomplished by including a radiation index in terms of potential clear-sky direct solar radiation, and thus, without the need for other data besides air temperature. This approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates. The incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance.
Conditions for bubble elongation in cold ice-sheet ice
Authors: Alley Richard B. , Fitzpatrick Joan J.
Published: September 2017

Highly elongated bubbles are sometimes observed in ice-sheet ice. Elongation is favored by rapid ice deformation, and opposed by diffusive processes. We use simple models to show that vapor transport dominates diffusion except possibly very close to the melting point, and that latent-heat effects are insignificant. Elongation is favored by larger bubbles at pore close-off, but is nearly independent of bubble compression below close-off. The simple presence of highly elongated bubbles indicates only that a critical ice-strain rate has been exceeded for significant time, and provides no information on possible disruption of stratigraphic continuity by ice deformation.
Reliability analysis for design of stake networks to measure glacier surface velocity
Authors: David Chadwell C.
Published: September 2017

Measurement of glacier surface velocity provides some constraint on glacier flow models used to date ice cores recovered near the flow divide of remote high-altitude ice caps. The surface velocity is inferred from the change in position of a network of stakes estimated from the least-squares adjustment of geodetic observations – terrestrial and/or spaced-based – collected approximately 1 year apart. The lack of outliers in and the random distribution of the post-fit observation residuals are regarded as evidence that the observations contain no blunders. However, if the network lacks sufficient geometric redundancy, the estimated stake positions can shift to fit erroneous observations. To determine the maximum size of these potential undetected shifts, given the covariance of the observations and the approximate network geometry, expressions are developed to analyze a network for redundancy number and marginally detectable blunders (internal reliability), and the position shifts from marginally detectable blunders (external reliability). Two stake networks, one on the col of Huascar–n (9°–07'S, 77°–37'W; 6050 m a.s.l.) in the north-central Andes of Peru and one on the Guliya ice cap (35°–17'N, 81°–29'E; 6200 m a.s.l.) on the Qinghai–Tibetan Plateau in China, are examined for precision and internal and external reliability.
Snow chemistry of Agassiz Ice Cap, Ellesmere Island, Northwest Territories, Canada
Authors: Goto-Azuma Kumiko , Koerner Roy M. , Nakawo Masayoshi , Kudo Akira
Published: September 2017

Pit-wall samples were collected from two sites about 2 km apart on Agassiz Ice Cap, Ellesmere Island, Northwest Territories, Canada, in 1992, 1993 and 1994, and from a site a further 1 km distant, in order to study spatial and seasonal variations in snow chemistry. Two of the pits were dug in wind-scoured zones and one in an unscoured zone. Although a large part of the winter snow is removed from the scoured zones (which do not show very negative δ18O values) the winter/spring anion peaks are still evident; this may be due to the predominance of dry deposition in mid-winter. The Cl− and SO42– ions peak in late winter/early spring, while NO3− peaks both in late winter/early spring and in summer. Vertical concentration profiles of all anions did not significantly alter over a 2 year period, indicating that there are no serious post-depositional changes due to evaporation, snow melting or photochemical reactions. However, comparisons between stake/board snow-accumulation measurements and those derived from the least scoured pit indicate that a single pit will represent annual accumulation rates for a local area only.
Variations in basal conditions on Rutford Ice Stream, West Antarctica
Authors: Smith A. M.
Published: September 2017

Seismic reflection data from two lines on Rutford Ice Streem are presented and are compared with data already published from a third line on the ice stream. The amplitude and phase of the reflections have been used io investigate the properties ol the sub-ice material. Multiple reflections on long record-length data allowed calibration of the reflection coefficient at the ice-bed interlace and determination of the acoustic impedance of the bed material. The characteristics of the bed material vary both along and across the ice stream. The average acoustic impedance of the bed material across the glacier at the upstream line is 3.88 x 106 kg−2 s−1. This decreases to 3.19 x 10−6 kg m−2s−1 52 km further downstream. These values are within the rang which is typical of soft sediments. Using acoustic impedance as an indicator of subgiacial porosity, some areas of the ice-stream bed are interpreted as dilatant water-saturated sediments undergoing pervasive deformation. In other areas, the bed is not deforming and basal sliding may be a more important process. The proportional the ice-stream width over which bed deformation occurs increases downstream.
Depositional models for moraine formation in East Antarctic coastal oases
Authors: Fitzsimons Sean J.
Published: September 2017

This paper examines the origin of moraine ridges in East Antarctic coastal oases and derives depositional models appropriate for the reconstruction of Quaternary history. On the basis of morphology, structure and sedimentology, four principal types of ridge may be identified: (1) type A moraines from when the basal debris zone crops out near an ice margin; (2) type B moraines form when large recumbent folds develop in the basal debris zone; (3) type C moraines are ice-contact screes and fans which form when debris accumulates at steep or cliffed ice margins; and (4) type D moraines are thrust-block moraines that form when unconsolidated sediment is entrained by freezing, shearing and thrusting of sediment blocks at the base of the glacier. Simple calculations of the rate of debris accumulation at ice margins suggest that type A, B and C moraines take thousands of years to form and record stable ice margins. Type D moraines are structural features that may form relatively quickly when ice margins override unconsolidated sediment. Constructing models to explain the origin of the moraines is an important part of reconstructing the Quaternary history of Antarctic coastal oases, because the models provide a basis for reconstructing the position and behaviour of the ice sheet during advance and retreat
The response of two Icelandic glaciers to climatic warming computed with a degree-day glacier mass-balance model coupled to a dynamic glacier model
Authors: Jóhannesson Tómas
Published: September 2017

A degree-day glacier mass-balance model is coupled to a dynamic glacier model for temperate glaciers. The model is calibrated for two outlet glaciers from the Hofsjökull ice cap in central Iceland. It is forced with a climate scenario that has recently been defined for the Nordic countries for the purpose of outlining the hydrological consequences of future greenhouse warming. The scenario for Iceland specifies a warming rate of 0.25°C per decade in mid-summer and 0.35°C per decade in mid-winter with a sinusoidal variation through the year. The volume of the glaciers is predicted to decrease by approximately 40% over the next century, and the glaciers essentially disappear during the next 200 years. Runoff from the area that is presently covered by the glaciers is predicted to increase by approximately 0.5 m a−130 years from now due to the reduction in the volume of the glaciers. The runoff increase reaches a flat maximum of 1.5–2.0 m a−1100–150 years from now and levels off after that. The predicted runoff increase leads to a significant increase in the discharge of rivers fed by meltwater from the outlet glaciers of the ice cap and may have important consequences for the operation and planning of hydroelectric power plants in Iceland.