In situ atomic force microscopy measurements of biotite basal plane reactivity in the presence of oxalic acid

We have used a direct imaging technique, in situ atomic force microscopy (AFM), to observe the dissolution of the basal biotite surface by oxalic acid over a range of temperatures close to ambient conditions, using a specially designed AFM liquid cell and non-invasive intermittent contact mode of operation. From the 3-dimensional nanometre-resolution data sets, we observe a process characterised by the slow formation of shallow etch pits in the (0 0 1) surface and fast growth of etch pits from the resulting steps, which represent proxies for the {h k 0} surface. Measurements of dissolution rates as a function of temperature allow a determination of an apparent activation energy (E_a,app) for the process, via mass-loss calculations from image analysis. We obtain a value of E_a,app = 49 ± 2 kJ mol⁻¹, which is consistent with separate calculations based on planar area etch pit growth, and measurements of etch pit perimeters, indicating that this value of E_a,app is representative of {h k 0} surface dissolution. The measurement of etch pit perimeters also enables an estimation of apparent activation energy as a function of step density indicating substantially higher apparent activation energy, up to E_a,app = 140 kJ mol⁻¹, on extrapolation towards a pristine surface with no defects. We suggest that this higher value of E_a,app represents the slow formation of etch pits into the (0 0 1) surface.     

Assessing probability of surface manifestation of liquefaction at a given site in a given exposure time using CPTU

This paper is a follow-up to a previous paper on the subject of liquefaction potential index (LPI), a parameter that is often used to characterize the potential for surface manifestation of liquefaction at a given site subjected to a given shaking level (represented by a pair of peak ground surface acceleration a_max and moment magnitude M_w). In the previous paper by Juang and his coworkers, the LPI was re-calibrated for a piezocone penetration test (CPTU) model, and a simplified model based on LPI was created for computing the conditional probability of surface manifestation of liquefaction (P_G). In this paper, the model for this conditional probability P_G is extended into a complete framework for assessing the probability of surface manifestation of liquefaction in a given exposure time at a given site subjected to all possible ground motions at all seismic hazard levels. This new framework is formulated and demonstrated with an example site in 10 different seismic regions in the United States.     

Algal pigments in sediments as a measure of eutrophication in the Baltic environment

A method of quantitative comparison of eutrophication of an area is proposed for the Baltic Sea, based on pigment content in sediments. The pigments concerned were chlorins a (i.e. chlorophylls a, b and selected chlorophyll a derivatives) and chlorophylls c. The analyses were performed on 300 samples from different layers of recent (0–10 cm) sediments, collected from about 50 stations, at different sites of the southern Baltic, including the estuaries of the two largest Polish rivers, in different seasons between 1992 and 2001, before and after the great flood of July 1997. The results are related to sampling site, sediment layer and hydrological conditions and also to organic carbon and E_h in sediments, oxygen and salinity in near-bottom waters. Depending on different chlorin a content in 0–1 and 0–10 cm layers, the sampling sites are classified into one of three groups: 1. Szczecin Lagoon and the Deep of Gda sk stations (permanently eutrophic, chl a in 0–1 cm >40 nmol/g, Σchlns a in 0–1 in 0–10 cm layer, Σchlns a_A in Σchlns a=55–65%), 2. Open sea stations (mesotrophic/oligotrophic, chl a in 0–1 cm <10 nmol/g, Σchlns a in 0–1 in 0–10 cm layer, Σchlns a_A in Σchlns a 50%; and 3. Coastal stations (periodically eutrophic, chl a in 0–1 cm 10–40 nmol/g, Σchlns a_A in Σchlns a 40%). The correlation coefficient between chlorophyll a and chlorophylls b and c indicates the classes of algae, which could be the main source of organic matter in the sediments. A high correlation with chlorophylls c is a marker of diatoms; a high correlation with chlorophyll b is a marker of green algae; and low correlation both with chlorophylls b and c—indicates a high blue–green algae input.     

Investigation of the stable isotope fractionation in speleothems with laboratory experiments

Many speleothems show evidence for calcite precipitation under disequilibrium conditions. To improve the understanding of these kinetic processes, several laboratory experiments were performed to study the fractionation of stable oxygen and carbon isotopes during the precipitation of calcite. Carbonate was precipitated under controlled conditions from both a body of standing water (beaker experiments) and a solution flowing along a channel (channel experiments) at a relative humidity of 100%. Slow degassing of CO₂, simulated by the beaker experiments, results in δ¹⁸O values in equilibrium with the solution. In contrast, the δ¹³C values show a significant enrichment, inversely proportional to the height of the solution in the beakers. Fast degassing of CO₂, simulated by the channel experiments, showed an enrichment of both δ¹³C and δ¹⁸O and a slope of Δδ¹³C/Δδ¹⁸O of 1.4±0.6. These results represent experimental evidence for the Hendy effect, which is manifested in (i) a progressive increase in δ¹⁸O and δ¹³C away from the growth axis and (ii) a positive correlation between δ¹⁸O and δ¹³C along a single growth layer of a stalagmite.     

Polarized single-crystal FTIR-spectra of natural staurolite

Polarized infrared absorption spectra of thin single-crystal slabs parallel to (010) and (001) of a staurolite from Pizzo Forno, Ticino, with analyzed composition (Fe_2.9Mg_0.9Zn_0.1Mn_0.1)Al_17.5Ti_0.1(Si_7.7Al_0.3)O₄₈H₃ have been measured in the range of 3000–4000 cm^?1. From the pleochroitic behaviour of the OH-vibrations three groups of bands can be distinguished: the bands of group I, a strong band at 3445 cm^?1 plus a weak shoulder at 3358 cm^?1, and the bands of group II, a weak band centered at 3677 cm^?1 plus a shoulder at 3635 cm^?1, are assigned to the H1 and H2 protons, respectively. The bands of group III, a weak band at 3577 cm^?1 plus a shoulder, cannot be interpreted on the basis of the proton positions known so far. We assign them to an additional proton H3, which is bonded to O1 and shows a bifurcated hydrogen bridge to two O5 in a vacant T2 site.     

A new hypothesis for the origin of the supposed giant snail Dinocochlea from the Wealden of Sussex, England

When first described in 1922, Dinocochlea ingens, an Early Cretaceous (Valanginian) fossil from the Wadhurst Clay Formation (Wealden) of Hastings in Sussex, England, was regarded as the steinkern of a huge gastropod over 2 m in length and claimed to be the largest gastropod ever to have lived. Most subsequent researchers have doubted the identity of D. ingens as a gastropod, usually believing it to be a pseudofossil, but no convincing explanation has been proposed for its origin. Restudy of the type material leads to the new hypothesis that Dinocochlea originated as a horizontal, corkscrew-shaped burrow resembling Helicodromites that acted as a nucleus for concretion growth. Sectioned specimens of Dinocochlea are filled with concentrically banded sediment interpreted to be growth rings of a concretion. Modification of a computer simulation designed to illustrate gastropod shell growth shows how the development of a concretion around a corkscrew-shaped burrow could lead to the morphology seen in Dinocochlea. The most likely tracemaker for Dinocochlea was a capitellid polychaete (‘threadworm’) with a body just a few mm in diameter.     

Sur la présence de nickel dans un gisement de bauxite près de Mégare

Résumé L'exploitation récente d'un gisement de bauxite près de Mégare (Grèce) a fait apparaître sur les calcaires de base une concentration verte d'oxyde de nickel relativement élevée. La présence dans le gisement d'argiles rouges, renfermant de fortes proportions d'oxyde de fer avec des teneurs relativement faibles en alumine et des traces d'oxyde de nickel, induit à penser qu'il s'agit d'un produit latéritique dérivé d'une roche ultrabasique et transporté ultérieurement sur la région calcaire karstifiée avec ses remplissages bauxitiques. L'étude se termine par une hypothèse sur la genèse de ce gîte singulier.

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The recent mining of a bauxite deposit near Megara (Greece) has shown on the footwall limestone a relatively high concentration of a green nickel oxide. The occurrence in the same deposit of red clays with a rather high percentage of iron oxide and a low content of alumina, together with some traces of nickel, induces to think that this material is composed of a lateritic soil derived from an ultrabasic rock and subsequently transported on karstified limestone with its bauxitic fillings. — The study ends with an hypothesis on the genesis of this unusual deposit.

     

Determining melt productivity of mantle sources from U-Th and U-Pa disequilibria; an example from Pico Island, Azores

We use coupled ²³⁸U-²³⁰Th and ²³⁵U-²³¹Pa disequilibria measurements from Pico Island, Azores to examine the melting behavior of the underlying mantle. U-series disequilibria in young, mafic lavas are dependent on the melting rate of their source, which in most cases is primarily controlled by its melt productivity. Mafic lithologies such as eclogite and pyroxenite have much higher melt productivities than peridotite and so U-series measurements may provide constraints on the mineralogy of the melting mantle. Recent Pico Mountain lavas show limited geochemical variations and a restricted range of U-series disequilibria with (²³⁰Th/²³⁸U) = 1.22-1.25 and (²³¹Pa/²³⁵U) = 1.46-1.50. Using a simple, dynamic melting model of a homogeneous source, these results can be reproduced with melting rates of <1 × 10⁻⁴ kg/m³/a and melt porosities of <0.7% near the onset of melting. For a plausible range of upwelling rates, this implies that the melt productivity is <6%/GPa. This value is consistent with a garnet peridotite source but not with more highly productive mafic lithologies. Given independent evidence for the involvement of mafic lithologies such as recycled oceanic crust in Pico magmagenesis, we suggest a scenario in which initial eclogitic melts are dispersed through melt-rock reaction into a larger volume of surrounding peridotite. Subsequent re-melting of the resultant incompatible element enriched peridotite carries a geochemical signature of the mafic lithologies but not necessarily a record of their high melt productivity.     

Pressure-Temperature Evolution of a Late Palaeozoic Paired Metamorphic Belt in North-Central Chile (34{degrees}-35{degrees}30'S)

In the Chilean Coastal Cordillera, two units, the Western andEastern Series, constitute coeval parts of a Late Palaeozoicpaired metamorphic belt dominated by siliciclastic metasediments.The Western Series also contains rocks from the upper oceaniccrust and represents an accretionary prism. Omnipresent high-pressureconditions are reflected by Na–Ca-amphibole and phengitein greenschists. Peak PT conditions of 7·0–9·3kbar, 380–420°C point to a metamorphic gradient of11–16°C/km. Three unique occurrences of blueschistyield deviating conditions of 9·5–10·7 kbar,350–385°C and are interpreted as relics from the lowermostpart of the basal accretion zone preserving the original gradientof 9–11°C/km along the subducting slab. Pervasiveductile deformation related to basal accretion occurred nearpeak PT conditions. Deformation and PT evolution of the metapsammopeliticrocks is similar to that of the metabasites. However, a raregarnet mica-schist yields peak PT conditions of 9·6–14·7kbar, 390–440°C reflecting a retrograde stage aftercooling from a high-temperature garnet-forming stage. It isconsidered to be an exhumed relic from the earliest siliciclasticrocks subducted below a still hot mantle wedge. A retrogradeoverprint of all rock types occurred at 300–380°C.Continuous reactions caused crystal growth and recrystallizationwith abundant free water mostly under strain-free conditions.They record a pressure release of 3–4 kbar without erasingpeak metamorphic mineral compositions. The Eastern Series lacksmetabasite intercalations and represents a less deformed retro-wedgearea. In the study area it was entirely overprinted at a uniformdepth at 3 ± 0·5 kbar with temperatures progressivelyrising from 400°C to 720°C towards the coeval Late Palaeozoicmagmatic arc batholith. The interrelated pattern of PT datapermits a conceptual reconstruction of the fossil convergentmargin suggesting a flat subduction angle of 25° with continuousbasal accretion at a depth of 25–40 km and a short mainintrusion pulse in the magmatic arc. The latter was accompaniedby the formation of a thermal dome in the retro-wedge area,which remained stable relative to the vertically growing accretionaryprism characterized by cyclic mass flow. KEY WORDS: paired metamorphic belt; greenschist; blueschist; central Chile; thermobarometry     

Implications for conifer glacial refugia and postglacial climatic variation in western Beringia from lake sediments of the Upper Indigirka basin

A c. 13 800 cal. a BP palynological record from Tschuch'ye Lake (eastern Yakutia), when combined with other palaeobotanical records from western Beringia, supports previous conclusions that Larix and Pinus pumila spread from multiple cryptic refugia during the Lateglacial period and middle Holocene, respectively. The antiquity and spatial distribution of Larix in many of these records suggest that full‐glacial landscapes probably had a small but important tree component. The Tschuch'ye record further indicates the absence of a Younger Dryas climatic reversal and is in accord with the preponderance of other data from western Beringia, which indicate warmer than present climates between c. 12 900 and 9100 cal. a BP. The subsequent spread of Pinus pumila, which has similar temperature requirements as Larix, denotes a shift to wetter but still warm climates during the middle Holocene, with palynological data suggesting optimal conditions in far western areas of western Beringia c. 7000–5000 cal. a BP. The postglacial occurrence of relatively warm/dry and warm/wet intervals is consistent with results of a regional climate‐model simulation that indicates warmer than present temperatures and decreased effective moisture at 11 000 cal. a BP and persistence of warm conditions but with greater moisture and longer growing season at 6000 cal. a BP.     

Climate change and human impact in a sensitive ecosystem: the Holocene environment of the Northwest Icelandic highland margin

Complex interactions of climate and volcanic activity have shaped the environment of Iceland during the Holocene. Palaeoecological records from Iceland offer a unique look at a Holocene environment that was uninhabited by humans and free of mammal herbivores until about AD 870. We present a new reconstruction of Holocene vegetation and landscape dynamics from a small lake, Barðalækjartjörn, located near the highland margin in Northwest Iceland. A multi‐proxy approach was used to reconstruct vegetation based on pollen and plant macrofossil analysis and landscape stability based on lithological proxies. The record covers the period c. 10 300–200 cal. a BP. For the first two millennia aeolian processes probably played a part in vegetation development. This period is characterized by high input of minerogenic material into the lake and a vegetation assemblage in which plants tolerant of aeolian deposition are prominent. Betula pubescens woodland reached a maximum between c. 7400 and 6500 cal. a BP. Betula nana‐dominated dwarf shrub heath replaced woodland after c. 4000 cal. a BP, following the onset of Neoglaciation. Land use following human settlement caused an environmental shift at the highland margin. Betula pubescens probably disappeared from the vicinity of the lake soon thereafter. Large‐scale soil erosion began at c. 1000 cal. a BP in the wake of human activities, such as introduction of grazing livestock and woodcutting. This study offers an important long‐term perspective of the development of the highland ecosystem under both wholly natural and human‐influenced conditions.     

Phase relations of phlogopite with magnesite from 4 to 8 GPa

To evaluate the stability of phlogopite in the presence of carbonate in the Earth’s mantle, we conducted a series of experiments in the KMAS–H₂O–CO₂ system. A mixture consisting of synthetic phlogopite (phl) and natural magnesite (mag) was prepared (phl₉₀-mag₁₀; wt%) and run at pressures from 4 to 8 GPa at temperatures ranging from 1,150 to 1,550°C. We bracketed the solidus between 1,200 and 1,250°C at pressures of 4, 5 and 6 GPa and between 1,150 and 1,200°C at a pressure of 7 GPa. Below the solidus, phlogopite coexists with magnesite, pyrope and a fluid. At the solidus, magnesite is the first phase to react out, and enstatite and olivine appear. Phlogopite melts over a temperature range of ~150°C. The amount of garnet increases above solidus from ~10 to ~30 modal% to higher pressures and temperatures. A dramatic change in the composition of quench phlogopite is observed with increasing pressure from similar to primary phlogopite at 4 GPa to hypersilicic at pressures ≥5 GPa. Relative to CO₂-free systems, the solidus is lowered such, that, if carbonation reactions and phlogopite metasomatism take place above a subducting slab in a very hot (Cascadia-type) subduction environment, phlogopite will melt at a pressure of ~7.5 GPa. In a cold (40 mWm⁻²) subcontinental lithospheric mantle, phlogopite is stable to a depth of 200 km in the presence of carbonate and can coexist with a fluid that becomes Si-rich with increasing pressure. Ascending kimberlitic melts that are produced at greater depths could react with peridotite at the base of the subcontinental lithospheric mantle, crystallizing phlogopite and carbonate at a depth of 180–200 km.     

Boron concentrations in carbonaceous chondrites

We have analyzed B in carbonaceous chondrites in order to clarify a factor of 100 difference between the solar system B abundance derived from the solar photosphere and that inferred from previous meteorite data. Consistent results were obtained from two instrumental methods for B analysis: (a) counting of the high energy betas from ¹²B produced by the ¹¹B(d,p) reaction, and (b) measurement of particle track densities from ¹⁰B(n,α)⁷Li in a plastic track detector affixed to a homogenized meteorite sample. Contamination is a major problem in B analyses, but extensive testing showed that our results were not seriously affected. Our B concentrations are typically 1–2 ppm and are a factor of 2–6 lower than previous carbonaceous chondrite measurements. Our data for the Cl chondrites Ivuna and Orgueil would indicate a solar system B/Si atomic abundance ratio of 58 × 10^?6, but this is still a factor of 2–10 higher than the photospheric estimates. It may be that B is depleted in the sun by thermonuclear processes; however, the similarity of photospheric and meteoritic Be abundances is a problem for this point of view. Alternatively, B may be enhanced in carbonaceous chondrites, but this would make B a cosmochemically unique element. A mm-sized (Fe,Mn,Mg)CO₃ crystal from Orgueil shows no B enrichment. We find ¹⁰B ≤ 10¹⁶ atoms/g in two Allende fine-grained inclusions suggesting that B is not a refractory element under solar nebula conditions. This ¹⁰B limit, when taken as a limit on ¹⁰Be when the inclusion formed, puts constraints on the possibility of a solar system synthesis of ²⁶Al. For a proton spectrum of E^?a, a must be ≥ 3 if a solar gas is irradiated or a ≥1.5 if dust of solar composition is irradiated.     

Stress fields about strike-slip faults inferred from stylolites and tension gashes

In general, the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress (σ₁). This is the case in the Languedoc for structures developed in the Jurassic limestones during the N-S Pyrenean compression. Exceptionnally, however, these microstructures turn in direction and become oblique (even orthogonal) one to the other, probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault. This mechanism also occurs in a larger scale structure involving segments of pre-tectonic joints that act as “en échelon” microfaults in a brittle “kink-band” equivalent to a peculiar type of potential wrench-fault.     

Temporal and chemical connections between plutons and ignimbrites from the Mount Princeton magmatic center

The Mount Princeton magmatic center, located in central Colorado, consists of the epizonal Mount Princeton batholith, the nested Mount Aetna caldera, and volumetrically minor leucogranites. New CA-TIMS U/Pb zircon ages indicate the majority of the Mount Princeton batholith was emplaced during a period of regional ignimbrite quiescence. The structurally highest unit of quartz monzonite yields a ²⁰⁶Pb/²³⁸U age of 35.80 ± 0.10 Ma, and the youngest dated unit of the quartz monzonite is a porphyritic unit that yields a ²⁰⁶Pb/²³⁸U age of 35.37 ± 0.10 Ma. Using the exposed, dated volume of the quartz monzonite and new geochronology yields an estimated pluton filling rate of ~0.002 km³/a. This rate is comparable to the accumulation rates published for other plutons, and at least an order of magnitude slower than fluxes necessary to support accumulation of large eruptible magma volumes. Geochronology for the two large ignimbrites spatially associated with the batholith indicates a temporal disconnect between the vast majority of pluton building and explosive eruption of magma. The Wall Mountain Tuff erupted from a source in the same geographic area as the Mount Princeton batholith at 37.3 Ma (Ar/Ar sanidine), but no structural evidence of a caldera or temporally associated plutonic rocks is known. The Badger Creek Tuff erupted at 34.3 Ma (Ar/Ar sanidine) during the formation of the Mount Aetna caldera in the southern portion of the batholith. Our ²⁰⁶Pb/²³⁸U age for the Badger Creek Tuff is 34.47 ± 0.05. The only analyzed plutonic rocks of similar age to the Badger Creek Tuff are an extra-caldera dike with a ²⁰⁶Pb/²³⁸U age of 34.57 ± 0.08 Ma, a ring dike with a ²⁰⁶Pb/²³⁸U age of 34.48 ± 0.09 Ma, and a portion of the Mount Aetna pluton with a ²⁰⁶Pb/²³⁸U age of 34.60 ± 0.13 Ma. The small volume intrusions related to the eruption of the Badger Creek Tuff are chemically similar to the ignimbrite and show no signature of crystal–liquid separation in the shallow crust.     

Geochemical and isotopic characteristics of the Cretaceous Orikabe Plutonic Complex,Kitakami Mountains,Japan: magmatic evolution in a zoned pluton and significance of a subduction-related mafic parental magma

The Orikabe Plutonic Complex, northeast Japan, is a zoned pluton and one of the Cretaceous intrusions in the Circum-Pacific area. In the Main body, K-rich calc-alkaline rocks composed of marginal gabbro and a large amount of monzodiorite–quartz monzonite–monzogranite are intruded successively by innermost calc-alkaline rocks of granodiorite. The gabbro and monzodiorite–monzogranite have a continuous chemical variation, while the granodiorite has lower concentrations of K, Rb, Y, Zr, Nb and F at the same SiO₂ content. The gabbro and monzodiorite–quartz monzonite have a Rb-Sr whole-rock age of 119±12 Ma with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70392±0.00007. The initial ⁸⁷Sr/⁸⁶Sr ratio of the innermost granodiorite is estimated to be about 0.7042. The ¹⁸O values of fresh rocks range from +6.7 to +8.3, indicating a positive correlation with SiO₂ contents. The K-rich calc-alkaline rocks were derived through fractional crystallization from a mafic parental magma with a slightly high ¹⁸O value, implying a major contribution of a sub-arc mantle at a continental margin. Trace element modeling indicates that the source could have been a fertile lherzolite enriched in LILE and depleted in HFSE. The innermost granodiorite was the differentiation product of a distinct parental magma, suggesting the involvement of a small amount of crustal component in the source and partial melting under a more hydrous condition.Editorial responsibility: J. Hoefs     

The application of fuzzy risk in researching flood disasters

To perform a fuzzy risk assessment the simplest way is to calculate the fuzzy expected value and convert fuzzy risk into non-fuzzy risk, i.e., a crisp value. In doing so, there is a transition from a fuzzy set to a crisp set. Therefore, the first step is to define an α level value, followed by selecting the elements x with a subordinate degree A(x) ≥ α. The fuzzy expected values, E_a (x) \underline{E}_{\alpha } (x) and [`(E)]_a (x) \overline{E}_{\alpha } (x) , of a possibility–probability distribution represent the fuzzy risk values being calculated. Therefore, we can obtain a conservative risk value, a venture risk value and a maximum probability risk value. Under such an α level, three risk values can be calculated. As α adopts all values between the set [0, 1], it is possible to obtain a series of risk values. Therefore, the fuzzy risk may either be a multi-valued risk or a set-valued risk. Calculation of the fuzzy expected value of a flood risk in the Jinhua River basin has been performed based on the interior–outer-set model. The selection of an α value is dependent on the confidence in different groups of people, while the selection of a conservative risk value or a venture risk value is dependent on the risk preference of these people.     

Predicting the risk of saltwater contamination of freshwater aquifers during aquifer thermal energy storage

Aquifer thermal energy storage (ATES) is an underground thermal energy storage technology with a large potential to decarbonise the heating and cooling of buildings. ATES installations typically store thermal energy in aquifers that are also exploited for potable water, so a major consideration during development is ensuring that system operation will not lead to groundwater pollution. In this study, the risk of contamination due to upconing of a shallow freshwater/saltwater interface during ATES operation is investigated. Fluid flow, and heat and salt (chloride ion) transport are simulated in a homogeneous aquifer during ATES operation via a well doublet. The impact of geological, hydrological and operational parameters is investigated in a sensitivity analysis. Two new dimensionless numbers are proposed to characterise salt upconing and redistribution during ATES operation and provide a close match to simulated concentrations: C_R,w characterises the contamination risk at the ATES installation, and C_R,d characterises the risk at locations downstream of the ATES installation with respect to background groundwater flow. ATES systems with C_R,w and C_R,d < 10 introduce low risk of contamination in a homogenous aquifer, with chloride concentration at, and downstream of, the ATES system, remaining below the World Health Organisation’s advised limit. ATES installations with C_R,w and C_R,d > 10 cause a rapid increase in aquifer chloride concentration. The results are used to estimate an exclusion distance beyond which ATES system operation will not cause contamination in a homogenous aquifer. The dimensionless parameters proposed allow rapid assessment of the potential for saltwater contamination during ATES operation.

     

Bedload-to-suspended load ratio and rapid bedrock incision from Himalayan landslide-dam lake record

About 5400 cal yr BP, a large landslide formed a > 400-m-tall dam in the upper Marsyandi River, central Nepal. The resulting lacustrine and deltaic deposits stretched > 7 km upstream, reaching a thickness of 120 m. ¹⁴C dating of 7 wood fragments reveals that the aggradation and subsequent incision occurred remarkably quickly (∼ 500 yr). Reconstructed volumes of lacustrine (∼ 0.16 km³) and deltaic (∼ 0.09 km³) deposits indicate a bedload-to-suspended load ratio of 1:2, considerably higher than the ≤ 1:10 that is commonly assumed. At the downstream end of the landslide dam, the river incised a new channel through ≥ 70 m of Greater Himalayan gneiss, requiring a minimum bedrock incision rate of 13 mm/yr over last 5400 yr. The majority of incision presumably occurred over a fraction of this time, suggesting much higher rates. The high bedload ratio from such an energetic mountain river is a particularly significant addition to our knowledge of sediment flux in orogenic environments.