Melt regimes, internal stratigraphy, and flow dynamics of three glaciers in the Alaska Range

We used ground-penetrating radar (GPR), GPS and glaciochemistry to evaluate melt regimes and ice depths, important variables for mass-balance and ice-volume studies, of Upper Yentna Glacier, Upper Kahiltna Glacier and the Mount Hunter ice divide, Alaska. We show the wet, percolation and dry snow zones located below 2700 m a.s.l., at 2700 to 3900 m a.s.l. and above 3900 m a.s.l., respectively. We successfully imaged glacier ice depths upwards of 480 m using 40–100 MHz GPR frequencies. This depth is nearly double previous depth measurements reached using mid-frequency GPR systems on temperate glaciers. Few Holocene-length climate records are available in Alaska, hence we also assess stratigraphy and flow dynamics at each study site as a potential ice-core location. Ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in GPR profiles collected on Upper Yentna Glacier suggest that regions below 2800 m a.s.l. are inappropriate for paleoclimate studies because of chemical diffusion, through melt. Flow complexities on Kahiltna Glacier preclude ice-core climate studies. Minimal signs of melt or deformation, and depth–age model estimates suggesting 4815 years of ice on the Mount Hunter ice divide (3912 m a.s.l.) make it a suitable Holocene-age ice-core location

Flow dynamics of an accumulation basin: a case study of upper Kahiltna Glacier, Mount McKinley, Alaska

We interpreted flow dynamics of the Kahiltna Pass Basin accumulation zone on Mount McKinley, Alaska, USA, using 40, 100 and 900 MHz ground-penetrating radar profiles and GPS surface velocity measurements. We found dipping, englacial surface-conformable strata that experienced vertical thickening as the glacier flowed westward from a steep, higher-velocity (60 m a–1) region into flat terrain associated with a 908 bend in the glacier and lower velocities (15 m a–1) to the south. Stratigraphy near the western side of the basin was surface-conformable to 170 m depth and thinned as flow diverged southward, down-glacier. We found complex strata beneath the conformable stratigraphy and interpret these features as buried crevasses, avalanche debris and deformed ice caused by up-glacier events. We also suggest that basin dimensions, bed topography and the sharp bend each cause flow extension and compression, significantly contributing to conformable and complex strata thickness variations. Our findings show that surface-conformable stratigraphy continuous with depth and consistent strata thicknesses cannot be assumed in accumulation basins, because local and upglacier terrain and flow dynamics can cause structural complexities to occur under and within surfaceconformable layers

Advancements in the Measurement of the Cryosphere Using Geophysics — Introduction

Frozen regions of the earth are known as the cryosphere. The arctic, Antarctica, permafrost, ice sheets, and glaciers are some of the most challenging places to measure subsurface parameters, but they can also be some of the most important places to science and engineering research due to their susceptibility to environmental change. Ground-based, airborne, and space-borne geophysical methods are deployed to observe targets below the ground or in ice that may be difficult or impossible to measure using conventional direct observations and measurements. The papers in this special section address recent advances in instrumentation development and deployment and computational capabilities that have advanced cryosphere geophysical sciences. As such, many of these papers discuss the science that the methodology has helped reveal

Case study: A GPR survey on a morainic lake in northern Italy for bathymetry, water volume and sediment characterization

We carried out an extensive waterborne GPR survey consisting of 50 profiles with a total length of nearly 37 km on the morainic lake of Candia northerly Turin (Italy). Our aim was to test the capability of GPR to estimate the bathymetry, the water volume and the sediment type. We enhanced and controlled the GPR data processing and interpretation with bathymetry acquired with an acoustic echo sounder and measured conductivity and temperature profile of the water column with a multiparametric probe. We also analyzed the diffraction hyperbola that originated within the sediments in order to estimate the velocity and relative permittivity. With the permittivity and dielectric mixing rules, we estimated the porosity of the sediments above the diffracting objects and drew a map of the bottom lake porosit

Autonomous FMCW Radar Survey of Antarctic Shear Zone

Radar survey of the Antarctic shear zone was conducted using an ultra-wideband (2-10 GHz) frequency modulated continuous wave (FMCW) radar. The radar was mounted on a sled and pulled by a robot that was specifically designed to operate in a harsh polar environment. Our FMCW radar had good penetration through Antarctic snow and we observed snow stratigraphy to a depth of 20 m. The radar images also revealed multiple crevasses in the shear zone. Our results demonstrate that autonomous survey using high frequency radar is feasible and safe approach for detecting hidden crevasses

Epidemiologia lesional en un club d'hoquei sobre herba

Objectiu: Descriure la incidència, la severitat, el tipus i la distribució anatòmica de les lesions en un club d'hoquei sobre herba espanyol durant 3 temporades consecutives (2002-03, 2003-04 i 2004-05). Material i mètodes: Es van recopilar retrospectivament totes les lesions esdevingudes en els equips de divisió d'honor, masculí i femení, integrats ambdós per un total de 18 jugadors i jugadores. Es va comptabilitzar el nombre total d'hores d'entrenaments i de partits per quantificar les hores d'exposició i es va calcular la incidència lesional mitjançant la fórmula següent (nombre de lesions/hores d'exposició) x 1.000 hores. Resultats: La severitat va dependre del temps de baixa esportiva del jugador/a (lleu: < 7 dies, moderada: 8-28 dies i severa: > 28 dies). Les dones van presentar una incidència lesional discretament superior als homes (27,70/1.000 h respecte de 27,64/1.000 h). La incidència lesional durant els partits oficials va ser superior a la dels entrenaments en ambdós sexes (38,37/1.000 h respecte de 24,32/1.000 h en homes i 30,74/1.000 h respecte de 27,70/1.000 h en dones). La majoria de lesions va afectar les extremitats inferiors (64,6%), seguides per les del tronc (25,6%), les extremitats superiors (8,89%) i el cap (0,84%). La regió anatòmica més afectada va ser el cuixa (23,9%), seguida de la cama (11,53%) i el turmell (10,27%). La lesió amb més incidència va ser el DOMS (15,45/1.000 h), seguit de les sobrecàrregues (3,84/1.000 h) i distensions musculars (3,24/1.000 h). La majoria de lesions van ser de caràcter lleu (90%); i van presentar més incidència lesional els períodes de març a maig i els mesos d'octubre i novembre

GPR Reflection Profiles of Clark and Commonwealth Glaciers, Dry Valleys, Antarctica

Englacial horizons deeper than 100 m are absent within 100 MHz ground-penetrating radar (GPR) surface profiles we recorded on Clark and Commonwealth Glaciers in the Antarctic Dry Valleys region. Both glaciers show continuous bottom horizons to 280 m, with bottom signal-to-noise ratios near 30 dB. Density horizons should fade below 50 m depth because impermeable ice occurred by 36 m. Folding within Commonwealth Glacier could preclude radar strata beneath about 80 m depth, but there is no significant folding within Clark Glacier. Strong sulfate concentrations and contrasts exist in our shallow ice core. However, it appears that high background concentration levels, and possible decreased concentration contrasts with depth placed their corresponding reflection coefficients at the limit of, or below, our system sensitivity by about 77 m depth. Further verification of this conclusion awaits processing of our deep-core chemistry profiles

Melt Regimes, Stratigraphy, Flow Dynamics and Glaciochemistry of Three Glaciers in the Alaska Range

We used ground-penetrating radar (GPR), GPS and glaciochemistry to evaluate melt regimes and ice depths, important variables for mass-balance and ice-volume studies, of Upper Yentna Glacier, Upper Kahiltna Glacier and the Mount Hunter ice divide, Alaska. We show the wet, percolation and dry snow zones located below 2700ma.s.l., at 2700 to 3900ma.s.l. and above 3900ma.s.l., respectively. We successfully imaged glacier ice depths upwards of 480m using 40–100MHz GPR frequencies. This depth is nearly double previous depth measurements reached using mid-frequency GPR systems on temperate glaciers. Few Holocene-length climate records are available in Alaska, hence we also assess stratigraphy and flow dynamics at each study site as a potential ice-core location. Ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in GPR profiles collected on Upper Yentna Glacier suggest that regions below 2800ma.s.l. are inappropriate for paleoclimate studies because of chemical diffusion, through melt. Flow complexities on Kahiltna Glacier preclude ice-core climate studies. Minimal signs of melt or deformation, and depth–age model estimates suggesting 4815 years of ice on the Mount Hunter ice divide (3912ma.s.l.) make it a suitable Holocene-age ice-core location