Sliding of Ice Past an Obstacle at Engabreen, Norway

At Engabreen, Norway, an instrumented panel containing a decimetric obstacle was mounted flush With the bed surface beneath 210 m of ice. Simultaneous measurements of normal and shear stresses, ice velocity and temperature were obtained as dirty basal ice flowed past the obstacle. Our measurements were broadly consistent with ice thickness, flow conditions and bedrock topography near the site of the experiment. Ice speed 0.45 m above the bed was about 130 mm d(-1), much less than the surface velocity of 800 mm d(-1) Average normal stress on the panel was 1.0-1.6 MPa, smaller than the expected ice overburden pressure. Normal stress was larger and temperature was lower on the stoss side than on the lee side, in accord with flow dynamics and equilibrium thermodynamics. Annual differences in normal stresses were correlated with changes in sliding speed and ice-flow direction. These temporal variations may have been caused by changes in ice rheology associated with changes in sediment concentration, water content or both. Temperature and normal stress were generally correlated, except when clasts presumably collided with the panel. Temperature gradients in the obstacle indicated that regelation was negligible, consistent with the obstacle size. Melt rate was about 10% of the sliding speed. Despite high sliding speed, no significant ice/bed separation was observed in the lee of the obstacle. Frictional forces between sediment particles in the ice and the panel, estimated from Hallet's (1981) model, indicated that friction accounted for about 5% of the measured bed-parallel force. This value is uncertain, as friction theories are largely untested. Some of these findings agree with sliding theories, others do not.

Assessing the Environmental Hazard of Using Seawater for Ore Processing at the Lasail Mine Site in the Sultanate of Oman

The Lasail mining area (Sultanate of Oman) was contaminated by acid mine drainage during the exploitation and processing of local and imported copper ore and the subsequent deposition of sulphide-bearing waste material into an unsealed tailings dump. In this arid environment, the use of seawater in the initial stages of ore processing caused saline contamination of the fresh groundwater downstream of the tailings dump. After detection of the contamination in the 1980s, different source-controlled remediation activities were conducted including a seepage water collection system and, in 2005, surface sealing of the tailings dump using an HDPE-liner to prevent further infiltration of meteoric water. We have been assessing the benefits of the remediation actions undertaken so far. We present chemical and isotopic (δ18O, δ 2H, 3H) groundwater data from a long-term survey (8–16 years) of the Wadi Suq aquifer along a 28 km profile from the tailings dump to the Gulf of Oman. Over this period, most metal concentrations in the Wadi Suq groundwater decreased below detection limits. In addition, in the first boreholes downstream of the tailings pond, the salinity contamination has decreased by 30 % since 2005. This decrease appears to be related to the surface coverage of the tailings pond, which reduces flushing of the tailings by the sporadic, but commonly heavy, precipitation events. Despite generally low metal concentrations and the decreased salinity, groundwater quality still does not meet the WHO drinking water guidelines in more than 90 % of the Wadi Suq aquifer area. The observations show that under arid conditions, use of seawater for ore processing or any other industrial activity has the potential to contaminate aquifers for decades.

Recharge Areas and Geochemical Evolution of Groundwater in an Alluvial Aquifer System in the Sultanate of Oman

A regional hydrogeochemical model was developed to evaluate the geochemical evolution of different groundwaters in an alluvial aquifer system in the Interior of Oman. In combination with environmental isotopes the model is able to extract qualitative and quantitative information about recharge, groundwater flow paths and hydraulic connections between different aquifers. The main source of water to the alluvial aquifer along the flow paths ofWadi Abyadh andWadi M’uaydin in the piedmont is groundwater from the high-altitude areas of the Jabal Akhdar and local infiltration along the wadi channels. In contrast, the piedmont alluvial aquifer alongWadi Halfayn is primarily replenished by lateral recharge from the ophiolite foothills to the east besides smaller contributions from the Jabal Akhdar and local infiltration. Further down gradient in the Southern Alluvial Plain aquifer a significant source of recharge is direct infiltration of rain and surface runoff, originating from a moisture source that approaches Oman from the south. The model shows that the main geochemical evolution of the alluvial groundwaters occurs along the flow path from the piedmont to the Southern Alluvial Plain, where dedolomitization is responsible for the observed changes in the chemical and carbon isotope composition in these waters.

Helium transfer from water into quartz crystals: A new approach for porewater dating

Several important fundamental and applied problems require a quantification of slow rates of groundwater flow. To resolve these problems helium appears to be a promising tracer. In this contribution we discuss a new approach, which gives the helium inventory in a rock – pore water system by using the relevant mineral record, i.e., without extraction and investigation of the porewater samples. Some U- and Th-poor minerals such as quartz (quartz separates from Permo-Carboniferous Formation, sandstone–shale interlayering, Molasses Basin, Northern Switzerland, hereafter PCF, are used in this study) contain excessive helium having migrated into their internal helium-accessible volume (HAV) from the surrounding porewater [I.N. Tolstikhin, B.E. Lehmann, H.H. Loosli, A. Gautschi, Helium and argon isotopes in rocks, minerals and related groundwaters: a case study in Northern Switzerland, Geochim. Cosmochim. Acta 60 (1996) 1497–1514]. These volumes are estimated by using helium as a nano-size penetrating tool, i.e., by saturation of the minerals with helium under controlled pressure–temperature conditions and subsequent measurements of the helium-saturated concentrations. In the quartz separates HAV/total volume ratios vary from 0.017% to 0.16%; along with the measured initial (unsaturated) He concentration the HAV gives the internal helium pressure, the mean value obtained for 7 samples (25 sample aliquots) is P=0.45F0.15 atm (1 r). The product of helium pressure and solubility (7.35_10_3 cc STP He/cc H2O for the temperature and salinity of PCF aquifers reported in [F.J. Pearson, W. Balderer, H.H. Loosli, B.E. Lehmann, A. Matter, T. Peters, H. Schmassmann, A. Gautschi, Applied Isotope Hydrogeology–A Case Study in Northern Switzerland, Elsevier Amsterdam, 1991, 439 pp.]) is the mineral-derived He concentration in the respective porewater, CPW=0.0035F0.0017 cc He/cc H2O. This value is in full accord with measured He concentrations in PCF aquifers, CPCF, varying from 0.0045 to 0.0016 cc He/cc H2O. This agreement validates the proposed approach and also shows that the mineral–porewater helium–concentration equilibrium has been established. Indeed, estimates of the He-migration rates through our quartz samples show that in ~6000 years the internal pressure should equilibrate with He-concentration in related porewater of PCF, and this time interval is short compared to independent estimates [I.N. Tolstikhin, B.E. Lehmann, H.H. Loosli, A. Gautschi, Helium and argon isotopes in rocks, minerals and related groundwaters: a case study in Northern Switzerland, Geochim. Cosmochim. Acta 60 (1996) 1497–1514]. The helium inventory in the rock–porewater assemblage shows that helium abundance in pore waters is indeed important. In shale samples (with ~15% porosity) porewaters contain more helium than the host minerals altogether. Porewater heliumconcentration profiles, available from the mineral record, along with helium production rates are input parameters allowing model(s) of helium migration through a hydrological structure to be developed. Quite high helium concentrations in PCF porewaters imply slow removal mechanisms, which will be discussed elsewhere.

210Pb dating of the Miaoergou ice core from the eastern Tien Shan, China

In 2005, two ice cores with lengths of 58.7 and 57.6 m respectively to bedrock were recovered from the Miaoergou flat-topped glacier (43 degrees 03 ' 19 '' N, 94 degrees 19 ' 21 '' E; 4512 m a.s.l.), eastern Tien Shan. Pb-210 dating of one of the ice cores (57.6 m) was performed, and an age of AD 1851 +/- 6 at a depth of 35.2 m w.e. was determined. For the period AD 1851-2005, a mean annual net accumulation of 229 +/- 7 mm w.e. a(-1) was calculated. At the nearby oasis city of Hami (similar to 80 km from the Miaoergou flat-topped glacier) the annual precipitation rate is 38 mm w.e. a(-1), hence glacial meltwater is a major water supply for local residents. The surface activity concentration of Pb-210(ex) was found to be similar to 400 mBq kg(-1), which is higher than observed at other continental sites such as Belukha, Russia, and Tsambagarav, Mongolia, which have surface activity concentrations of 280 mBq kg(-1). The Pb-210 dating agrees well with the chronological sequence deduced from the annual-layer counting resulting from the seasonalities of delta O-18 and trace metals for the period AD 1953-2005, and beta-activity horizons resulting from atmospheric nuclear testing during the period AD 1962-63. We conclude that Pb-210 analysis is a suitable method for obtaining a continuous dating of the Miaoergou ice core for similar to 160 years, which can also be applied to other ice cores recovered from the mountains of western China.

Continental degassing of 4He by surficial discharge of deep groundwater

Radiogenic He is produced by the decay of uranium and thorium in the Earth’s mantle and crust. From here, it is degassed to the atmosphere and eventually escapes to space. Assuming that all of the 4He produced is degassed, about 70% of the total He degassed from Earth comes from the continental crust. However, the outgoing flux of crustal He has not been directly measured at the Earth’s surface and the migration pathways are poorly understood. Here we present measurements of helium isotopes and the long-lived cosmogenic radio-isotope Kr in the deep, continental-scale Guarani aquifer in Brazil and show that crustal He reaches the atmosphere primarily by the surficial discharge of deep groundwater. We estimate that He in Guarani groundwater discharge accounts for about 20% of the assumed global flux from continental crust, and that other large aquifers may account for about 33%. Old groundwater ages suggest that He in the Guarani aquifer accumulates over half- to one-millionyear timescales. We conclude that He degassing from the continents is regulated by groundwater discharge, rather than episodic tectonic events, and suggest that the assumed steady state between crustal production and degassing of He, and its resulting atmospheric residence time, should be re-examined.

The geomorphology and morphometry of the banded terrain in Hellas basin, Mars

Hellas basin is a large impact basin situated in the southern highlands of Mars. The north-western part of the basin has the lowest elevation (-7.5 km) on the planet and contains a possibly unique terrain type, which we informally call “banded terrain”. The banded terrain is made up of smooth-looking banded deposits that display signs of viscous behavior and a paucity of superimposed impact craters. In this study, we use newly acquired high spatial resolution images from the High Resolution Imaging Science Experiment (HiRISE) in addition to existing datasets to characterize the geomorphology, the morphometry and the architecture of the banded terrain. The banded terrain is generally confined to the NW edge of the Alpheus Colles plateau. The individual bands are ~3–15 km-long, ~0.3 km-wide and are separated by narrow inter-band depressions, which are ~65 m-wide and ~10 m-deep. The bands display several morphologies that vary from linear to concentric forms. Morphometric analysis reveals that the slopes along a given linear or lobate band ranges from 0.5° to 15° (average~6°), whereas the concentric bands are located on flatter terrain (average slope~2–3°). Crater-size frequency analysis yields an Amazonian-Hesperian boundary crater retention age for the terrain (~3 Gyr), which together, with the presence of very few degraded craters, either implies a recent emplacement, resurfacing, or intense erosion. The apparent sensitivity to local topography and preference for concentrating in localized depressions is compatible with deformation as a viscous fluid. In addition, the bands display clear signs of degradation and slumping at their margins along with a suite of other features that include fractured mounds, polygonal cracks at variable size-scales, and knobby/hummocky textures. Together, these features suggest an ice-rich composition for at least the upper layers of the terrain, which is currently being heavily modified through loss of ice and intense weathering, possibly by wind.

Potential desiccation cracks on Mars: A synthesis from modeling, analogue-field studies, and global observations

Potential desiccation polygons (PDPs) are polygonal surface patterns that are a common feature in Noachian-to-Hesperian-aged phyllosilicate- and chloride-bearing terrains and have been observed with size scales that range from cm-wide (by current rovers) to 10s of meters-wide. The global distribution of PDPs shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes. They are mostly associated with sedimentary deposits that display spectral evidence for the presence of Fe/Mg smectites, Al-rich smectites or less commonly kaolinites, carbonates, and sulfates. In addition, PDPs may indicate paleolacustrine environments, which are of high interest for planetary exploration, and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water. A collective synthesis with new data, particularly from the HiRISE camera suggests that desiccation cracks may be more common on the surface of Mars than previously thought. A review of terrestrial research on desiccation processes with emphasis on the theoretical background, field studies, and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on Mars.

The role of climate-driven chemical weathering on soil production

Climate plays an important role in controlling rates of weathering and weathered regolith production. Regolith production functions, however, seldom take climate parameters into account. Based on a climate-dependent weathered regolith production model, at low denudation rates, relative regolith thicknesses are less sensitive to changes in precipitation rates, while at high denudation rates, small changes in climatic parameters can result in complete stripping of hillslopes. This pattern is compounded by the long residence times and system response times associated with low denudation rates, and vice versa. As others have shown, the transition between regolith-mantled and bedrock slopes is dependent on the ratio of denudation to production. Here, we further suggest that this is itself a function of precipitation rate and temperature. We suggest that climatic parameters can be easily incorporated into existing soil production models and that such additions improve the predictive power of soil production models. (C) 2013 Elsevier B.V. All rights reserved.

Drilling into debris-rich basal ice at the bottom of the NEEM (Greenland) borehole

After the NEEM (Greenland) deep ice-core drilling was declared terminated with respect to developing stratigraphic climate reconstructions, efforts were turned toward collecting basal ice-sheet debris and, if possible, drilling into the bedrock itself. In 2010, several meters of banded debris-rich ice were obtained under normal ice-drilling operations with the NEEM version of the Hans Tausen (HT) drill, but further penetration was obstructed by a rock in the path of the drill head at 2537.36 m. During short campaigns in 2011 and 2012, attempts were made to penetrate further using various reinforced ice cutters mounted on the HT drill head, tailored to cut through rock. These had some success in penetrating coarse material, but produced severely damaged cutters. Additionally a 51 mm diameter diamond cutting tipped rock drill was adapted to fit the NEEM drill. With this device, several additional meters of core containing subglacial sediments, rocks and rock fragments were collected. With these tools 1.39 m of additional material were obtained during the 2011 field season, and 7.1 m during 2012. Subglacial water refreezing into the newly formed borehole hindered further penetration, and the bedrock interface was not reached before final closure of the NEEM Camp.

Ce(III) and Ce(IV) (re)distribution and fractionation in a laterite profile from Madagascar: Insights from in situ XANES spectroscopy at the Ce LIII-edge

The distribution of trivalent and tetravalent cerium, Ce(III) and Ce(IV) respectively, in a lateritic profile from Madagascar, has been characterized by X-ray-absorption near-edge structure (XANES) spectroscopy at the Ce LIII-edge on the LUCIA beamline (SOLEIL synchrotron, France). XANES spectra were acquired on bulk-rock samples as well as on specific lateritic minerals or polymineral zones (in-situ measurements) of the tonalite bedrock and the three overlying weathered horizons (C-, B- and A-horizons). Geochemically, the bedrock, and the A- and C-horizons show similar rare earth element content (REE = 363–405 mg/kg). They also display the same positive Ce-anomaly (CeCN/Ce∗ = 1.12–1.45), which is therefore likely to be inherited from the bedrock. In the B-horizon, the higher REE content (REE = 2194 mg/kg) and the larger Ce-anomaly (CeCN/Ce∗ = 4.26) are consistent with an accumulation zone caused by the evaporation of groundwater during the dry season. There is a good agreement between the Ce(III)/Cetotal ratio (XCe(III)) deduced from the positive Ce-anomaly (bulk-rock geochemical data) and that derived from XANES spectroscopy on the same bulk-rock samples (BR-XCe(III)-XANES) in the bedrock, and the C- and B-horizons. In the A-horizon, XANES measurements on bulk rock and minerals revealed a higher BR-XCe(III)-XANES (up to 100%) compared to the XCe(III) deduced from geochemical data (XCe(III) = 79%). The preservation of a positive Ce-anomaly in the A-horizon suggests that the Ce mobilization and redistribution during weathering occurred with no significant Ce fractionation from other trivalent REE. Remarkably, the only investigated sample where cerianite is observed belongs to the B-horizon. Within this horizon, Ce oxidation state varies depending on the microstructural position (porosity, cracks, clay-rich groundmass). The highest Ce(IV) concentrations are measured in cerianite (and aluminophosphates) localized in pores at the vicinity of Mn-rich domains (XCe(III)-XANES = 30–51%). Therefore, Ce fractionation from other REE is attributed to a Ce oxidation and precipitation potentially assisted by oxyhydroxide scavenging. In the C-horizon, Ce(III) and Ce(IV) are mainly distributed in REE-minerals of the rhabdophane group found in pores and cracks. The similarity between the Ce(III) proportion of rhabdophane grains (XCe(III)-XANES = 74–89%) with that of the bedrock (BR-XCe(III)-XANES = 79%) suggests no significant fractionation of Ce(III) and Ce(IV) between solution and mineral during the successive stages of primary REE-mineral alteration, transport in solution and secondary precipitation in the incipient stages of weathering. Overall, our novel spectroscopic approach shows that Ce is not necessarily oxidized nor fractionated from other REE during weathering in lateritic conditions. This implies that like Ce(III), Ce(IV) can be mobilized in aqueous fluids during weathering, possibly thanks to complexation with organic molecules, and can precipitate together with Ce(III) in secondary REE-bearing minerals. The corollary is that (paleo)redox reconstructions in soils and/or sediments based on Ce-anomaly in weathered rocks or minerals must be interpreted with caution.

Plate fixation of extra-articular fractures of the proximal phalanx: do new implants cause less problems?

BACKGROUND Limited range of finger motion is a frequent complication after plate fixation of phalangeal fractures. The purpose of this study was to evaluate the results of plate fixation of extra-articular fractures of the proximal phalanx using current low-profile mini-fragment-systems. METHODS From 2006 to 2012, 32 patients with 36 extra-articular fractures of the proximal phalanx of the triphalangeal fingers were treated with open reduction and plate fixation (ORPF) using 1.2 and 1.5 mm mini-fragment systems. Patients presenting with open fractures grade 2 and 3 or relevant laceration of adjacent structures were excluded from the study. We retrospectively evaluated the rate of mal-union or non-union after ORPF, the need for revision surgery, for plate removal, and for tenolysis. Data were analyzed for further complications with regard to infections or complex regional pain syndrome (CRPS). RESULTS No infections were noted. Five patients developed transient symptoms of CRPS. Six weeks postoperatively, total active finger motion (TAM) averaged 183°, and all 32 patients underwent formal hand therapy. At the latest follow-up or at the time of plate removal, respectively, the mean TAM improved to 213°. Extension lag of proximal interphalangeal joints was found in 67 % of all fractured fingers. Secondary surgery was necessary in 14 of 32 patients (2 corrective osteotomies, 12 plate removals including 7 procedures explicitly because of reduced mobility). CONCLUSIONS Despite of new implant designs significant problems persist. Adhesions of extensor tendons leading to limited range of finger motion are still the most frequent complications after ORPF of proximal phalangeal fractures, even in absence of significant soft-tissue damage. LEVEL OF EVIDENCE Therapeutic, Retrospective, Level IV.

Efficiency of frost-cracking processes through space and time: An example from the eastern Italian Alps

It is widely accepted that climate has a strong impact and exerts important feedbacks on erosional processes and sediment transport mechanisms. However, the extent at which climate influences erosion is still a matter of debate. In this paper we test whether frost-cracking processes and related temperature variations can influence the sediment production and surface erosion in a small catchment situated in the eastern Italian Alps. To this extent, we first present a geomorphic map of the region that we complement with published 10Be-based denudation rates. We then apply a preexisting heat-flow model in order to analyze the variations of the frost-cracking intensity (FCI) in the study area, which could have controlled the sediment production in the basin. Finally, we compare the model results with the pattern of denudation rates and Quaternary deposits in the geomorphic map. The model results, combined with field observations, mapping, and quantitative geomorphic analyses, reveal that frost-cracking processes have had a primary role in the production of sediment where the intensity of sediment supply has been dictated and limited by the combined effect of temperature variations and conditions of bedrock preservation. These results highlight the importance of a yet poorly understood process for the production of sediment in mountain areas.

The first major incision of the Swiss Deckenschotter landscape

The Swiss Deckenschotter (“cover gravels”) is the oldest Quaternary units in the northern Swiss Alpine Foreland. They are a succession of glaciofluvial gravel layers intercalated with glacial and/or overbank deposits. This lithostratigraphic sequence is called Deckenschotter because it “covers” Molasse or Mesozoic bedrock and forms mesa-type hill-tops. Deckenschotter occurs both within and beyond the extent of the Last Glacial Maximum glaciers. The Swiss Deckenschotter consist of two sub-units: Höhere (Higher) and Tiefere (Lower) Deckenschotter. Although the Höhere Deckenschotter sub-unit (HDS) is topographically higher than the Tiefere Deckenschotter, it is older. The only available age for the Swiss Deckenschotter is 2.5–1.8 Ma based on mammal remains found in HDS at the Irchel site. In this study, we present an exposure age for the topographically lowest HDS, calculated from a cosmogenic 10Be depth-profile. Our results show that the first phase of the Deckenschotter glaciations in the Swiss Alps terminated at least 1,020+80−120 ka ago, which is indicated by a significant fluvial incision. This line of evidence seems to be close to synchronous with the beginning of the Mid-Pleistocene Revolution, when the frequency of the glacial-interglacial cyclicity changed from 41 to 100 ka and the amplitude from low to high, between marine isotope stages 23 and 22.

Chronology of Lateglacial ice flow reorganization and deglaciation in the Gotthard Pass area, Central Swiss Alps, based on cosmogenic 10Be and in situ 14C

We reconstruct the timing of ice flow reconfiguration and deglaciation of the Central Alpine Gotthard Pass, Switzerland, using cosmogenic 10Be and in situ14C surface exposure dating. Combined with mapping of glacial erosional markers, exposure ages of bedrock surfaces reveal progressive glacier downwasting from the maximum LGM ice volume and a gradual reorganization of the paleoflow pattern with a southward migration of the ice divide. Exposure ages of ∼16–14 ka (snow corrected) give evidence for continuous early Lateglacial ice cover and indicate that the first deglaciation was contemporaneous with the decay of the large Gschnitz glacier system. In agreement with published ages from other Alpine passes, these data support the concept of large transection glaciers that persisted in the high Alps after the breakdown of the LGM ice masses in the foreland and possibly decayed as late as the onset of the Bølling warming. A younger group of ages around ∼12–13 ka records the timing of deglaciation following local glacier readvance during the Egesen stadial. Glacial erosional features and the distribution of exposure ages consistently imply that Egesen glaciers were of comparatively small volume and were following a topographically controlled paleoflow pattern. Dating of a boulder close to the pass elevation gives a minimum age of 11.1 ± 0.4 ka for final deglaciation by the end of the Younger Dryas. In situ14C data are overall in good agreement with the 10Be ages and confirm continuous exposure throughout the Holocene. However, in situ14C demonstrates that partial surface shielding, e.g. by snow, has to be incorporated in the exposure age calculations and the model of deglaciation.