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Anaerobic oxidation of methane (AOM) by methanotrophic archaea is an important sink of this greenhouse gas in marine sediments. However, evidence for AOM in freshwater habitats is rare, and little is known about the pathways, electron acceptors, and microbes involved. Here, we show that AOM occurs in anoxic sediments of a sulfate-rich lake in southern Switzerland (Lake Cadagno). Combined AOM-rate and 16S rRNA gene-sequencing data suggest that Candidatus Methanoperedens archaea are responsible for the observed methane oxidation. Members of the Methanoperedenaceae family were previously reported to conduct nitrate- or iron/manganese-dependent AOM. However, we demonstrate for the first time that the methanotrophic archaea do not necessarily rely upon these oxidants as terminal electron acceptors directly, but mainly perform canonical sulfate-dependent AOM, which under sulfate-starved conditions can be supported by metal (Mn, Fe) oxides through oxidation of reduced sulfur species to sulfate. The correspondence of high abundances of Desulfobulbaceae and Candidatus Methanoperedens at the same sediment depth confirms the interdependence of anaerobic methane-oxidizing archaea and sulfate-reducing bacteria. The relatively high abundance and widespread distribution of Candidatus Methanoperedens in lake sediments highlight their potentially important role in mitigating methane emissions from terrestrial freshwater environments to the atmosphere, analogous to ANME-1, -2, and -3 in marine settings.

Garnet is one of the most robust and ubiquitous minerals that record element zoning during crustal metamorphism. In addition to major elements, zoning in trace elements can provide a wealth of information to document the changing conditions of garnet growth and modification. However, mapping trace elements at low concentrations, over large areas and with high resolution has remained a major challenge. We present a comprehensive investigation of the TE distribution in garnet from three Alpine samples that underwent a complex evolution at different metamorphic conditions. The TE distribution in garnet grains is mapped in 2D in thin section with a novel approach using laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOFMS) to achieve a lateral resolution of 5 µm and limits of detection for the heavy rare earth elements (REE) down to 0.2 µg/g. Comparison with major element zoning measured by electron probe microanalysis and trace elements measured by conventional LA-ICPMS spot analysis testifies to the accuracy of the measurements. Garnet in an amphibolite-facies metapelite from Campolungo, Central Alps, that recorded metamorphism to 600 °C preserves Y + REE trace element zoning that closely matches that of Ca. In this sample, there is no notable diffusive modification for trace elements. Y + REE zoning is dominated by Rayleigh fractionation in the core and by the sporadic breakdown of accessory phases producing annuli in the rim of the garnet. A granulite-facies garnet from Malenco, Eastern Central Alps, formed during subsolidus heating, followed by peritectic melting reactions up to temperatures of 800–850 °C. Major and trace element zoning are decoupled indicating diffusional resetting of major elements, whereas trace elements still largely document the growth history. Enrichment of trace elements in the garnet mantle may be related to the consumption of biotite (V, Cr) and the dissolution of zircon (Zr) and monazite (Y + REE) in the melt. Diffusion of Y + HREE at the core–mantle boundary occurred over a length scale of ~ 200 µm. Garnet in an eclogite from the Sesia Zone, Western Alps (P ~ 2 GPa, T ~ 600 °C), displays pronounced fluid-related veinlets, visible in FeO, MgO and MnO, which cross-cut the primary growth zoning. Surprisingly, complex Y + REE and Cr zoning is not affected by the veinlets, indicating that they did not form by a crack-seal mechanism but are rather related to a selective replacement process. The trace element maps provide a detailed insight into the growth and modification of garnet and thus allow assessment of equilibrium versus disequilibrium processes, and assist in determination of P–T conditions, garnet dating, diffusion modelling as well as documenting fluid-induced modifications.

In this paper, we describe the investigations and actions taken to reduce risk and prevent casualties from a catastrophic 210,000 m 3 rockslope failure, which occurred near the village of Preonzo in the Swiss Alps on May 15, 2012. We describe the geological predisposition and displacement history before and during the accelerated creep stage as well as the development and operation of an efficient early warning system. The failure of May 15, 2012, occurred from a large and retrogressive instability in gneisses and amphibolites with a total volume of about 350,000 m 3 , which formed an alpine meadow 1250 m above the valley floor. About 140,000 m 3 of unstable rock mass remained in place and might collapse partially or completely in the future. The instability showed clearly visible signs of movements along a tension crack since 1989 and accelerated creep with significant hydromechanical forcing since about 2006. Because the active rockslide at Preonzo threatened a large industrial facility and important transport routes located directly at the toe of the slope, an early warning system was installed in 2010. The thresholds for prealarm, general public alarm, and evacuation were derived from crack meter and total station monitoring data covering a period of about 10 years, supplemented with information from past failure events with similar predisposition. These thresholds were successfully applied to evacuate the industrial facility and to close important roads a few days before the catastrophic slope failure of May 15, 2012. The rock slope failure occurred in two events, exposing a compound rupture plane dipping 42° and generating deposits in the midslope portion with a travel angle of 39°. Three hours after the second rockslide, the fresh deposits became reactivated in a devastating debris avalanche that reached the foot of the slope but did not destroy any infrastructure. The final run-out distance of this combined rock collapse–debris avalanche corresponded to the predictions made in the year 2004.

Form and function are two major characteristics of hydrological systems. While form summarizes the structure of the system, function represents the hydrological response. Little is known about how these characteristics evolve and how form relates to function in young hydrological systems. We investigated how form and function evolve during the first millennia of landscape evolution. We analyzed two hillslope chronosequences in glacial forelands, one developed from siliceous and the other from calcareous parent material. Variables describing hillslope form included soil physical properties, surface, and vegetation characteristics. Variables describing hydrological function included soil water response times, soil water storage, drainage, and dominant subsurface flow types. We identified links between form and hydrological function via cluster analysis. Clusters identified based on form were compared in terms of their hydrological functioning. The comparison of the two different parent materials shows how strongly landscape evolution is controlled by the underlying geology. Soil pH appears to be a key variable influencing vegetation, soil formation and subsequently hydrology. At the calcareous site, the high buffering capacity of the soil leads to less soil formation and fast, vertical subsurface water transport dominates the water redistribution even after more than 10,000 years of landscape evolution. At the siliceous site, soil acidification results in accumulation of organic material, a high water storage capacity, and in podsolization. Under these conditions water redistribution changes from vertical subsurface water transport at the young age classes to water storage in the organic surface layer and lateral subsurface water transport within 10,000 years. Key Points The underlying geology controls landscape evolution in glacial forefields After 10,000 years of evolution, hillslope form and hydrological functioning differ between the calcareous and siliceous sites Soil pH is a key variable indicative of differences in soil evolution and hydrological response between the two forefields

The exhumed Infrahelvetic Flysch Units in the eastern central Alps in Switzerland are a field analog to modern accretionary wedges at active plate boundaries. In these seismically active convergent settings, water‐saturated sediments undergo consolidation, and diagenetic to low‐grade metamorphic processes cause complex fluid‐rock interactions. To contribute to the understanding of structural and fluid processes and their interaction with seismic activity, we present quantitative information on the geometrical and spatial distribution of slate‐hosted calcite veins from the Infrahelvetic Flysch Units that show mutual overprinting relationships with the ductile phyllosilicate‐rich matrix. Two vein systems that form in the deeper part of the inner wedge are characterized: (a) layer‐parallel veins (meter‐scale) forming spatially repetitive vein‐arrays and (b) pervasively distributed, steep micron‐veinlets, that cross‐cut the thicker layer‐parallel veins and the ductile matrix. Synchrotron X‐ray Fluorescence Microscopy (XFM) is instrumental in detecting previously unseen densely spaced micron‐veinlets. The spatial distribution of micron‐veinlets indicates pervasive layer‐perpendicular fluid transport in response to dissolution‐precipitation creep through the wedge. Layer‐parallel veins form vein‐arrays with thicknesses on the meter‐scale suggesting that fluids are progressively localized in channels up‐scale. Both vein sets form in an alternating fashion with two different enhanced flux directions, which could be indicative for a critically stressed wedge with near‐lithostatic fluid pressures. The layer‐parallel veins and vein‐arrays could represent seismic events with low magnitude earthquakes (Mw up to 4.0) or slow‐slip events currently found at active plate boundaries, while micron‐veinlets and dissolution‐precipitation processes accommodate slow interseismic deformation. Plain Language Summary Convergent plate boundaries are locations where lithospheric plates collide. Plate collision produces a wide variety of seismic activity, which is a major natural hazard posing socio‐economic risks. When oceanic plates are involved in collision, an accretionary wedge made of sediments forms near the plate boundary. Here, we study an ancient accretionary wedge in the Swiss Alps to examine the potential traces of paleo‐seismic activity left in the rock record. We focus on ubiquitous veins, mineralized fractures that acted as fluid pathways in such active seismic domains. We documented veins from the field (m‐scale) to the grain scale (μm‐scale). Synchrotron X‐ray Fluorescence Microscopy (XFM) enabled mapping of trace‐element concentrations in the vein minerals, capturing tracers of paleo‐fluid transport at 2 μm resolution. The innovative XFM technique unveiled the presence of micron‐veinlets with widths less than that of a human hair. These micron‐veinlets form widespread, densely spaced clusters throughout these rock sequences. Our microanalytical observations demonstrate that these micron‐veinlets facilitate fluid transport via dissolution‐precipitation creep during interseismic deformation of the wedge while the m‐scale veins could potentially represent small earthquakes or slow slip events. Key Points Cyclic fracturing, veining, and pressure solution are characteristic in the sediment‐rich inner part (>250°C) of the accretionary wedge Synchrotron XFM documents pervasive micron‐veinlets enabling layer‐perpendicular fluid migration during slow wedge deformation Layer‐parallel veins arrange in vein‐arrays indicating localized fluid transport and potentially small seismic or slow‐slip events

The timing and dynamics of fluid-induced melting in the typical Barrovian sequence of the Central Alps has been investigated using zircon chronology and trace element composition. Multiple zircon domains in leucosomes and country rocks yield U–Pb ages spanning from ~32 to 22 Ma. The zircon formed during Alpine melting can be distinguished from the inherited and detrital cores on the basis of their age, Th/U (<0.1) and trace element composition. Ti-in-zircon thermometry indicates crystallization temperatures around 620–700°C. Their composition allows discriminating between (1) zircon formation in the presence of early garnet, (2) zircon in equilibrium with abundant L-MREE-rich accessory phases (allanite, titanite and apatite) typical of metatonalites, and (3) zircon formed during melting of metasediments in feldspar-dominated assemblages. The distribution of zircon overgrowths and ages indicate that repeated melting events occurred within a single Barrovian metamorphic cycle at roughly constant temperature; that in the country rocks zircon formation was limited to the initial stages of melting, whereas further melting concentrated in the segregated leucosomes; that melting occurred at different times in samples a few meters apart because of the local rock composition and localized influx of the fluids; and that leucosomes were repeatedly melted when fluids became available. The geochronological data force a revision of the temperature–time path of the migmatite belt in the Central Alps. Protracted melting over 10 My followed the fast exhumation of Alpine eclogites contained within the same region and preceded fast cooling in the order of 100°C/Ma to upper crustal levels.

The Central Alpine lower crustal migmatitic Gruf complex was exhumed in contact to the greenschist-grade Chiavenna ophiolite and gneissic Tambo nappe leading to a lateral gradient of ~ 70 °C/km within the ophiolite. The 14 km long, E-W striking subvertical contact now bridges metamorphic conditions of ~ 730 °C, 6.6 kbar in the migmatitic gneisses and ~ 500 °C, 4.2 kbar in the serpentinites and Tambo schists 2–4 km north of the contact. An obvious fault, mylonite or highly sheared rock that could accommodate the ~ 8.5 km vertical displacement is not present. Instead, more than half of the movement was accommodated in a 0.2–1.2 km thick orthogneiss of the Gruf complex that was heterogeneously molten. Discrete bands with high melt fractions (45–65%) now contain variably stretched enclaves of the adjacent MOR-derived amphibolite. In turn, the adjacent amphibolites exhibit tonalitic in-situ leucosomes and dikes i.e., were partially molten. The H2O necessary for fluid-assisted melting of the orthogneiss and amphibolites was likely derived from the tectonic contact metamorphism of the Chiavenna serpentinites, at the contact now in enstatite + olivine-grade. U–Pb dating of zircons shows that partial melting and diking occurred at 29.0–31.5 Ma, concomitant with the calc-alkaline Bergell batholith that intruded the Gruf. The major driving forces of exhumation were hence the strong regional North–South shortening in the Alpine collisional belt and the buoyancy provided by the Bergell magma. The fluids available through tectonic contact metamorphism led to self-enhanced magmatic weakening and concentration of movement in an orthogneiss, where melt-rich bands provided a low friction environment. Continuous heating of the originally greenschist Chiavenna ophiolite and Tambo gneisses + schists by the migmatitic Gruf complex during differential uplift explains the skewed temperature profile, with intensive contact heating in the ophiolite but little cooling in the portion of the now-exposed Gruf complex.

The Tamins rock avalanche lies adjacent to the Flims rock avalanche, the largest in the Alps. Its deposit forms a ridge across the Rhine Valley just downstream of the confluence of the Vorderrhein and Hinterrhein rivers. The deposit is dominated by a 1.6-km-long longitudinal ridge, Ils Aults, and two roughly 600-m-long transverse ridges. Several extensional scarps bear witness to spreading of the deposit. A breach through the deposit, where the Rhine River presently flows, reveals a carapace and intense fragmentation. Exposure dating using cosmogenic 36Cl yields an age of 9420 ± 880 years. This suggests that the Tamins event occurred in a time frame similar to the Flims event but was slightly earlier than the Flims rock avalanche, as also required by stratigraphic relationships. 3D volume modeling reveals bulking of only 14%. The motion of the rock avalanche seems to have occurred first as a flexible block, which underwent fragmentation and simple shearing where the top moved faster than the bottom. The ensuing spreading led to the formation of extensional scarps. There is no identified weak layer along the sliding surface; nevertheless, modeling suggests a friction angle of 10°.

Unlike fragmental rockfall runout assessments, there are only few robust methods to quantify rock-mass-failure susceptibilities at regional scale. A detailed slope angle analysis of recent Digital Elevation Models (DEM) can be used to detect potential rockfall source areas, thanks to the Slope Angle Distribution procedure. However, this method does not provide any information on block-release frequencies inside identified areas. The present paper adds to the Slope Angle Distribution of cliffs unit its normalized cumulative distribution function. This improvement is assimilated to a quantitative weighting of slope angles, introducing rock-mass-failure susceptibilities inside rockfall source areas previously detected. Then rockfall runout assessment is performed using the GIS- and process-based software Flow-R, providing relative frequencies for runout. Thus, taking into consideration both susceptibility results, this approach can be used to establish, after calibration, hazard and risk maps at regional scale. As an example, a risk analysis of vehicle traffic exposed to rockfalls is performed along the main roads of the Swiss alpine valley of Bagnes.

Physically based hydrological models describe natural processes more accurately than conceptual models but require extensive data sets to produce accurate results. To identify the value of different data sets for improving the performance of the distributed hydrological model TOPKAPI we combine a multivariable validation technique with Monte Carlo simulations. The study is carried out in the snow and ice‐dominated Rhonegletscher basin, as these types of mountainous basins are generally the most critical with respect to data availability and sensitivity to climate fluctuations. Each observational data set is used individually and in combination with the other data sets to determine a subset of best parameter combinations out of 10,000 Monte Carlos runs performed with randomly generated parameter sets. We validate model results against discharge, glacier mass balance, and satellite snow cover images for a 14 year time period (1994–2007). While the use of all data sets combined provides the best overall model performance (defined by the concurrent best agreement of simulated discharge, snow cover and mass balance with their respective measurements), the use of one or two variables for constraining the model results in poorer performance. Using only one data set for constraining the model glacier mass balance proved to be the most efficient observation leading to the best overall model performance. Our main result is that a combination of discharge and satellite snow cover images is best for improving model performance, since the volumetric information of discharge data and the spatial information of snow cover images are complementary. Key Points Multivariable calibration improves overall model performance Satellite snow cover images and discharge data lead to good model performance Glacier mass balance with high spatial resolution leads to adequate model performance