bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new continuous high-resolution detection system for sulphate in ice cores
Authors: Bigler Matthias , Svensson Anders , Steffensen Jørgen Peder , Kaufmann Patrik 
Published: December 2007

AbstractSulphate (SO42–) is a major ion found in polar ice cores and is related to different aerosol sources and processes. Explosive volcanic eruptions, even far away, can cause distinct sulphate peaks in ice core records. Thus, a robust sulphate detection system which is suitable for fieldwork and which enables the measurement of sulphate at high temporal resolution is of great interest. In this study, we present the adaptation of a new continuous flow analysis system for sulphate that is based on a spectrophotometric method using dimethylsulfonazo III and an inline reactor column containing barium sulphate particles. The method shows a detection limit of ∽70 ng g–1 and a linear range up to at least 3000 ng g–1. It is simple, robust and less prone to interferences compared to the previously used method.
Modelling coupled hydraulics and sediment transport of a high-magnitude flood and associated landscape change
Authors: Carrivick Jonathan L. 
Published: December 2007

AbstractProcesses and mechanisms of erosion, transport and deposition within high-magnitude outburst floods such as jökulhlaups and lahars are poorly understood and remain largely unquantified. This study therefore applies a two-dimensional or depth-averaged hydrodynamic model, with fully integrated sediment transport, to reconstruct a Holocene jökulhlaup to have occurred from Kverkfjöll volcano, Iceland. Results indicate simultaneous inundation of multiple channels, flow around islands, hydraulic jumps and multi-directional flow including backwater areas and hydraulic ponding. These flow characteristics are typical of outburst floods that are volcanically triggered, flow through steep volcanic terrain and contain high concentrations of volcaniclastic sediment. Kverkfjöll jökulhlaups had low frontal flow velocities but as stage increased, velocities reached 5–15ms–1. Peak stage was prolonged in zones of hydraulic ponding, but generally attenuated in magnitude and duration downstream. Suspended load transport persisted over the entire hydrograph but bed load transport was spatially discontinuous and comprised distinct pulses. A hierarchy of landforms is proposed, ranging from highest energy zones (erosional gorges, scoured bedrock, cataracts and spillways) to lowest (valley-fills, bars and slackwater deposits). Bedrock erosion was generally where flow exceeded ∽3m flow depth, ∽7ms–1 flow velocity, ∽1×102Nm–2 shear stress and 3 ×102Wm–2 stream power. Deposition occurred below ∽8m flow depth, 11 ms–1 flow velocity, 5 ×102Nm–2 shear stress and 3 ×103Wm–2 stream power. Hydraulic ranges associated with erosion and deposition have considerable overlap due to transitional flow phenomena, transitions in sediment concentration and the influence of upstream effects, such as hydraulic ponding behind topographic constrictions. These results are the first of coupled hydraulic and sediment transport phenomena in high-magnitude outburst floods with fluid rheology and high sediment content, such as jökulhlaups and dilute lahars. Modelled changes in sediment mass closely resembled field-mapped zones of erosion and deposition. This paper therefore introduces a capability to simulate rapid landscape change due to high-magnitude outburst flood.
Habits of a glacier-covered volcano: seismicity patterns and velocity structure of Katla volcano, Iceland
Authors: Jónsdóttir Kristín , Tryggvason Ari , Roberts Roland , Lund Bjoörn , Soosalu Heidi , Böðvarsson Reynir 
Published: December 2007

AbstractThe Katla volcano, overlain by the Mýrdalsjökull glacier, is one of the most active and hazardous volcanoes in Iceland. Earthquakes show anomalous magnitude-frequency behaviour and mainly occur in two distinct areas: within the oval caldera and around Goðabunga, a bulge on its western flank. The seismicity differs between the areas; earthquakes in Goðabunga are low frequency and shallow whereas those beneath the caldera occur at greater depths and are volcano-tectonic. The seismicity shows seasonal variations but the rates peak at different times in the two areas. A snow budget model, which gives an estimate of the glacial loading, shows good correlation with seismic activity on an annual scale. Data recorded by the permanent network South Iceland Lowland (SIL), as well as by a temporary network, are used to invert for a 3D seismic velocity model underneath Eyjafjallajökull, Goðabunga and the Katla caldera. The tomography resolves a 15 km wide, aseismic, high-velocity structure at a depth of more than 4 km between the Eyjafjallajökull volcano in the west and the Katla volcano in the east. Anomalously low velocities are observed beneath the Katla caldera, which is interpreted as being a significantly fractured area of anomalously high temperature.
Heat transfer in volcano–ice interactions on Earth
Authors: Wilson L. , Head J.W. 
Published: December 2007

AbstractThe very high temperature contrast between magma/ lava and water ice commonly leads to the assumption that significant melting will take place immediately upon magma/ lava ice contact, yet observations of active flows show little evidence of voluminous melting upon contact. We use analytical thermal models to reassess the efficiency with which heat can be transferred from magma to ice in three situations: lava flows erupted on top of glacial ice, sill intrusions beneath glacial ice evolving into subglacial lava flows and dyke intrusions into the interiors of glaciers. We find that the maximum ratios of thickness of ice that can be melted to the thickness of magmatic heat source are likely to be ∽2–5 for subaerial lava flows encroaching onto glaciers, ∽6–7 for subglacial lava flows and ∽10 for dykes intruded into glacial ice. Rates of ice melt production are not linear functions of time and flow thickness, however, and this may account for the observations of minimal immediate water release from beneath advancing lava flows. Field observations during future eruptions should be directed at measuring the temperature of released water.
Survival of the Mýrdalsjökull ice cap through the Holocene thermal maximum: evidence from sulphur contents in Katla tephra layers (Iceland) from the last ∽8400 years
Authors: Oladottir Bergrun A. , Thordarson Thor , Larsen Gudrun , Sigmarsson Olgeir 
Published: December 2007

AbstractThe climate in Iceland was drier and warmer during the Holocene thermal maximum than it is today and it has been suggested that ice caps disappeared entirely. Katla, a volcano covered by the Mýrdalsjökull ice cap in southern Iceland, has erupted rather steadily throughout the Holocene. Pre-and post-eruption sulphur concentrations in its products have been determined in previous studies, through melt inclusions trapped in phenocrysts (pre-eruption mean values of 2155±165 ppm) and fully degassed magmatic tephra (post-eruption mean values of 445±130 ppm). The phreatomagmatic tephra has much more variable S contents (550–1775 ppm) and spans the compositional gap between magmatic tephra and melt inclusions. These variable sulphur values are attributed to arresting of degassing as the magma is quenched upon contact with external water in the shallow levels of the volcano conduit. Sulphur in Katla tephra can thus be used to evaluate whether Mýrdalsjökull survived the warm spells of the Holocene. In this study, sulphur concentrations in tephra layers representing the last ∽8400 years of the volcano’s eruption history were measured, revealing concentrations in the phreatomagmatic range (600–1600 ppm). Hence, we conclude that over the last ∽8400 years, explosive activity at Katla has been dominated by phreatomagmatic eruptions, implying that the Mýrdalsjökull ice cap has been present throughout the Holocene.
Modeling the dynamic response of a crater glacier to lava-dome emplacement: Mount St Helens, Washington, USA
Authors: Price Stephen F. , Walder Joseph S. 
Published: December 2007

AbstractThe debris-rich glacier that grew in the crater of Mount St Helens after the volcano’s cataclysmic 1980 eruption was split in two by a new lava dome in 2004. For nearly six months, the eastern part of the glacier was squeezed against the crater wall as the lava dome expanded. Glacier thickness nearly doubled locally and surface speed increased substantially. As squeezing slowed and then stopped, surface speed fell and ice was redistributed downglacier. This sequence of events, which amounts to a field-scale experiment on the deformation of debris-rich ice at high strain rates, was interpreted using a two-dimensional flowband model. The best match between modeled and observed glacier surface motion, both vertical and horizontal, requires ice that is about 5 times stiffer and 1.2 times denser than normal, temperate ice. Results also indicate that lateral squeezing, and by inference lava-dome growth adjacent to the glacier, likely slowed over a period of about 30 days rather than stopping abruptly. This finding is supported by geodetic data documenting dome growth.
Will subglacial rhyolite eruptions be explosive or intrusive? Some insights from analytical models
Authors: Tuffen H. , McGarvie D.W. , Gilbert J.S. 
Published: December 2007

AbstractSimple analytical models of subglacial eruptions are presented, which simulate evolving subglacial cavities and volcanic edifices during rhyolitic eruptions beneath temperate glaciers. They show that the relative sizes of cavity and edifice may strongly influence the eruption mechanisms. Intrusive eruptions will occur if the edifice fills the cavity, with rising magma quenched within the edifice and slow melting of ice. Explosive magma–water interaction may occur if a water- or steam-filled gap develops above the edifice. Meltwater is assumed to drain away continuously, but any gap above the edifice will be filled by meltwater or steam. Ductile roof closure will occur if the glacier weight exceeds the cavity pressure and is modelled here using Nye’s law. The results show that the effusion rate is an important control on the eruption style, with explosive eruptions favoured by large effusion rates. The models are used to explain contrasting eruption mechanisms during various Quaternary subglacial rhyolite eruptions at Torfajökull, Iceland. Although the models are simplistic, they are first attempts to unravel the complex feedbacks between subglacial eruption mechanisms and glacier response that can lead to a variety of eruptive scenarios and associated hazards.
A full Stokes-flow thermo-mechanical model for firn and ice applied to the Gorshkov crater glacier, Kamchatka
Authors: Zwinger Thomas , Greve Ralf , Gagliardini Olivier , Shiraiwa Takayuki , Lyly Mikko 
Published: December 2007

AbstractThe Gorshkov crater glacier at Ushkovsky volcano, Kamchatka, is characterized by a large aspect ratio and special thermodynamic conditions at the bedrock caused by a locally enhanced and spatially varying geothermal heat flux. Furthermore, large parts of this glacier consist of firn rather than pure ice, which alters the rheological properties (such as viscosity and compressibility) of the glacier. We present a newly developed, thermo-mechanically coupled, three-dimensional flow model based on the finite-element (FE) modeling software Elmer, and apply it to the Gorshkov crater glacier. By assuming steady-state conditions, the present-day velocity field, temperature field, basal melting rate and age distribution are simulated. We find that flow velocities are generally small (tens of centimeters per year). Horizontal and vertical velocities are of comparable magnitude, which shows that the shallow-ice approximation is not applicable. Owing to the spatially variable volcanic heat flux, the thermal regime at the ice base is cold in the deeper parts of the glacier and temperate in the shallower parts. The measured temperature profile and age horizons at the K2 borehole are reproduced quite well, and remaining discrepancies may be attributed to transient (non-steady-state) conditions. Firn compressibility is identified as a crucial element for the modeling approach.
Heat transfer in volcano–ice interactions on Mars: synthesis of environments and implications for processes and landforms
Authors: Head James W. , Wilson Lionel 
Published: December 2007

AbstractWe review new advances in volcano–ice interactions on Mars and focus additional attention on (1) recent analyses of the mechanisms of penetration of the cryosphere by dikes and sills; (2) documentation of the glacial origin of huge fan-shaped deposits on the northwest margins of the Tharis Montes and evidence for abundant volcano–ice interactions during the later Amazonian period of volcanic edifice construction and (3) the circumpolar Hesperian-aged Dorsa Argentea Formation, interpreted as an ice sheet and displaying marginal features (channels, lakes and eskers) indicative of significant melting and interior features interpreted to be due to volcano–ice interactions (e.g. subglacial volcanic edifices, pits, basins, channels and eskers). In this context, we describe and analyse several stages and types of volcano–ice interactions: (1) magmatic interactions with ice-rich parts of the cryosphere; (2) subglacial volcanism represented by intrusion under and into the ice and formation of dikes and moberg-like ridges, intrusion of sills at the glacier–volcano substrate interface and their evolution into subglacial lava flows, formation of subglacial edifices, marginal melting and channels; (3) synglacial (ice contact) volcanism represented by flows banking up against glacier margins, chilling and forming remnant ridges and (4) post-glacial volcanism and interactions with ice deposits.
Glacier retreat during the recent eruptive period of Popocaté petl volcano, Mexico
Authors: Andrés Nuria , Zamorano Josè J. , Sanjosé Josè J. , Atkinson Alan , Palacios David 
Published: December 2007

AbstractPopocatépetl (19°02’ N, 98°62’W; 5424 m) is one of the largest active stratovolcanoes in the Transmexican Volcanic Belt. A glacier located on the north side has undergone severe ablation since the volcano reinitiated eruptive activity in December 1994. In our study, we calculate the extent of the glacier recession and the loss in glacial mass balance during the period of greatest laharic activity (1994–2002), using photogrammetric treatment of 20 pairs of aerial photographs. The results indicate that from November 1997 to December 2002, the glacier released approximately 3 967 000 m3 of water. A period of intense glacier melting occurred from 4 November 2000 to 15 March 2001 during which time 717 000 m3 of water was released. Much of the melting was attributed to the pyroclastic flow that took place on 22 January 2001 and produced a 14.2 km lahar with 68 000 m3 of water. Among the many types of volcanic events, pyroclastic flows were the most effective in causing sudden snowmelt, although small explosions were also effective since they deposited incandescent material on the glacier. The collapse of the plinian columns covered the glacier with pyroclasts and increased its volume. The existence of control points for georeferencing and a knowledge of the topography underlying the glacier previous to the eruption would have provided more accurate and useful results for hazard prevention.
Whither Arctic sea ice? A clear signal of decline regionally, seasonally and extending beyond the satellite record
Authors: Meier Walter N. , Stroeve Julienne , Fetterer Florence 
Published: December 2007

AbstractThe Arctic sea ice has been pointed to as one of the first and clearest indicators of climate change. Satellite passive microwave observations from 1979 through 2005 now indicate a significant –8.4±1.5% decade–1 trend (99% confidence level) in September sea-ice extent, a larger trend than earlier estimates due to acceleration of the decline over the past 41 years. There are differences in regional trends, with some regions more stable than others; not all regional trends are significant. The largest trends tend to occur in months where melt is at or near its peak for a given region. A longer time series of September extents since 1953 was adjusted to correct biases and extended through 2005. The trend from the longer time series is –7.7±0.6% decade–1 (99%), slightly less than from the satellite-derived data that begin in 1979, which is expected given the recent acceleration in the decline.
Geometry change between 1990 and 2003 at Finsterwalderbreen, a Svalbard surge-type glacier, from GPS profiling
Authors: Hodgkins Richard , Fox Adrian , Nuttall Anne-Marie 
Published: December 2007

AbstractSurface mass-balance and geometry data are key to quantifying the climate response of glaciers, and confidence in data synthesis and model interpretations and forecasts requires data from as wide a range of locations and glacier types as possible. This paper presents measurements of surface elevation change at the Svalbard surge-type glacier Finsterwalderbreen, by comparing a 1990 digital elevation model (DEM) with a surface GPS profile from 2003. The pattern of elevation change is consistent with that previously noted between 1970 and 1990, and reflects the continued quiescent-phase evolution of the glacier, with mass loss in the down-glacier/receiving area of up to –1.25mw.e. a–1, and mass gain in the up-glacier/reservoir area of up to 0.60 mw.e. a–1; the area-weighted, mean change for the whole glacier is 0.19mw.e. a–1. The spatial pattern of elevation increase and decrease is complex, and the boundary between thickening and thinning determined by combining GPS and DEM data does not appear to correspond with the equilibrium-line altitude determined from surface mass-balance measurements. There is no evidence yet of a decrease in the rate of reservoir area build-up driven by mass-balance change resulting from the warmer winter air temperatures, and decreased proportion of snowfall in total precipitation, noted at meteorological stations in Svalbard.
Glaciological conditions in seven contrasting regions estimated with the degree-day model
Authors: Braithwaite Roger J. , Raper Sarah C.B. 
Published: December 2007

AbstractWe apply the degree-day model to seven glacial regions that offer contrasting conditions and are well documented in the World Glacier Inventory. The regions are: Axel Heiberg Island in Arctic Canada; Svalbard; northern Scandinavia; southern Norway; the Alps; the Caucasus; and New Zealand. We estimate the average equilibrium-line altitude (ELA) for each half-degree latitude/longitude grid square from the median elevations of glaciers within the square and we extrapolate temperature from the UEA/CRU (Climate Research Unit of the University of East Anglia) gridded climatology. Using the degree-day model, we calculate annual accumulation at the ELA, equal to ablation at the ELA, and other quantities like summer mean temperature, length of melt season, balance gradients and the sensitivity of mass balance to temperature and/or precipitation changes. Glaciers can be characterized on a scale from cold-dry (Axel Heiberg Island) to warm-wet (New Zealand) corresponding to the contrast between maritime and continental climates. Mass-balance sensitivities to temperature and/or precipitation changes are relatively small for dry-cold climate and relatively high for warm-wet climate. We could extend the approach to other glacier regions but we note that there are large areas for which ELA data are not available as they are still not covered by the World Glacier Inventory.
Energy-balance model validation on the top of Kilimanjaro, Tanzania, using eddy covariance data
Authors: Cullen Nicolas J. , Mölg Thomas , Kaser Georg , Steffen Konrad , Hardy Douglas R. 
Published: December 2007

AbstractEddy covariance data collected over a horizontal surface on the largest ice body on Kilimanjaro, Tanzania, over 26–29 July 2005 were used to assess the uncertainty of calculating sublimation with a surface energy balance (SEB) model. Data required for input to the SEB model were obtained from an existing automatic weather station. Surface temperatures that were solved iteratively by the SEB model were used to compute emitted longwave radiation, turbulent heat fluxes using the aerodynamic bulk method and the subsurface heat flux. Roughness lengths for momentum and temperature, which were found to be the most important input parameters controlling the magnitude of modelled (bulk method) turbulent heat fluxes, were obtained using eddy covariance data. The roughness length for momentum was estimated to be 1.7×10–3 m, while the length for temperature was one order of magnitude smaller. Modelled sensible and latent heat fluxes (bulk method) compared well to eddy covariance data, with root-mean-square differences between 3.1 and 4.8 Wm–2 for both turbulent heat fluxes. Modelled sublimation accounted for about 90% of observed ablation, confirming that mass loss by melting is much less important than sublimation on the horizontal surfaces of the remaining plateau glaciers on Kilimanjaro.
20th-century variations in area of cirque glaciers and glacierets, Rocky Mountain National Park, Rocky Mountains, Colorado, USA
Authors: Hoffman Matthew J. , Fountain Andrew G. , Achuff Jonathan M. 
Published: December 2007

AbstractComparison of historic maps and aerial and ground-based photographs for the small cirque glaciers and glacierets of Rocky Mountain National Park in the northern Front Range of Colorado, USA, indicates modest change during the 20th century. The glaciers retreated through the first half of the 20th century, advanced slightly from the mid-1940s to the end of the century and have retreated slightly since. High interannual variability in area and temporal gaps in data complicate the trends. Local climate records indicate a lack of systematic change between 1950 and 1975, but significant warming afterwards. Local topographic effects (e.g. wind redistribution of snow and avalanching) are important influences. These small glaciers respond to changes in regional climate; summer temperature alone is a good predictor of the mass balance of Andrews Glacier (r = -0.93). Spring snowfall is also an important factor. That winter precipitation is not statistically significant supports the notion that these small glaciers gain much snow from wind drift and avalanching, making winter snow accumulation almost indifferent to variations in direct snowfall. Less than expected glacier retreat may be due to increased summer cloudiness.
Sensitivity of glacier runoff to summer snowfall events
Authors: Escher-Vetter Heidi , Siebers Matthias 
Published: December 2007

AbstractIn order to investigate the effect of changing precipitation type on glacier discharge due to air-temperature changes, the relation between summer snowfall and runoff is surveyed for the Vernagtbach basin, Austria, (2640–3630ma.s.l.; ~72% glaciated) for the period 1976–2005. Precipitation data were evaluated for each ablation season with respect to amount and type; the latter derived mainly from daily photographs of the catchment, but validated over 4 years with additional meteorological data. Winter snowfall amounts were determined on the basis of mass-balance measurements. Average ablation period air temperature showed a rise of 1.5 K from 1976 to 2005, and runoff increased from about 1100 mmw.e. to 2200 mmw.e. Snowfall amounts during the ablation period decreased between 1976 and 1991, but increased from 1992 to 2005, indicating a large year-to-year variation. The number of days with snowfall varies even more, with no clear trend discernible. The evolution of runoff is only partly explained by precipitation type during the ablation season, and accumulation amounts during winter deliver a not unambiguous picture. More important is the development of the ablation area from about 20% of glacier size in the 1970s to 100% in 2003.