GeoResJ最新文献

Coastal dunes are the primary defence protecting the coastline from the destructive forces of the sea in The Netherlands. Aeolian processes are important in this context as they contribute to dune accretion and thus the safety of the coastal hinterland. In this study, we analyze horizontal and vertical variability of event scale aeolian sand transport on a wide beach on the island of Ameland, The Netherlands. Data were obtained from a meteorological station, groundwater monitoring wells and a camera installed on the beach. Fifteen aeolian transport events (two involving onshore winds, seven longshore and six offshore) were measured using a comprehensive grid of 37 customized MWAC traps. The highest sand transport rates and largest variability was found for alongshore events. Surface moisture, governed by groundwater, was found to be an important controlling parameter for aeolian transport rates and vertical flux profiles. Groundwater levels were largely dominated by beach inundation, influencing the groundwater table for a two week period. Variations in vertical flux profiles between traps were larger for wet sand transport events than dry ones. In general, sand transport rates were highest at the foreshore and lowest at the dune toe. Sand transport dynamics are dependent on local conditions such as beach dimensions, beach orientation and also meteorological and surface characteristics. Moderate (high frequency, low magnitude) events are also capable of transporting large amounts of sand. Future studies should include spatially explicit measurements of elevation and surface moisture to obtain a more complete understanding of the complex sand transport dynamics.

We investigated the Holocene palaeo-environmental record of the Tuggerah Lake barrier estuary on the south-east coast of Australia to determine the influence of local, regional and global environmental changes on estuary development. Using multi-proxy approaches, we identified significant down-core variation in sediment cores relating to sea-level rise and regional climate change. Following erosion of the antecedent land surface during the post-glacial marine transgression, sediment began to accumulate at the more seaward location at ∼8500 years before present, some 1500 years prior to barrier emplacement and ∼4000 years earlier than at the landward site. The delay in sediment accumulation at the landward site was a consequence of exposure to wave action prior to barrier emplacement, and due to high river flows of the mid-Holocene post-barrier emplacement. As a consequence of the mid-Holocene reduction in river flows, coupled with a moderate decline in sea-level, the lake experienced major changes in conditions at ∼4000 years before present. The entrance channel connecting the lake with the ocean became periodically constricted, producing cyclic alternation between intervals of fluvial- and marine-dominated conditions. Overall, this study provides a detailed, multi-proxy investigation of the physical evolution of Tuggerah Lake with causative environmental processes that have influenced development of the estuary.

The Greater Caucasus Mountains contain the highest peaks in Europe and define, for over 850 km along strike, the leading edge of the second-largest active collisional orogen on Earth. However, the mechanisms by which this range is being constructed remain disputed. Using a new database of earthquake records from local networks in Georgia, Russia, and Azerbaijan, together with previously published hypocenter locations, we show that the central and eastern Greater Caucasus Mountains are underlain by a northeast-dipping zone of mantle seismicity that we interpret as a subducted slab. Beneath the central Greater Caucasus (east of 45°E), the zone of seismicity extends to a depth of at least 158 km with a dip of ∼40°NE and a slab length of ∼130–280 km. In contrast, beneath the western GC (west of 45°E) there is a pronounced lack of events below ∼50 km, which we infer to reflect slab breakoff and detachment. We also observe a gap in intermediate-depth seismicity (45–75 km) at the western end of the subducted slab beneath the central Greater Caucasus, which we interpret as an eastward-propagating tear. This tear coincides with a region of minimum horizontal convergence rates between the Lesser and Greater Caucasus, as expected in a region of active slab breakoff. Active subduction beneath the eastern Greater Caucasus presents a potentially larger seismic hazard than previously recognized and may explain historical records of large magnitude (M 8) seismicity in this region.

Dust devils are convective vortices rendered visible by lofted dust, and may be a significant means of injecting dust into the atmosphere, on both Earth and Mars. The fraction of vortices that are dust-laden is not well-understood, however. Here we report a May/June 2013 survey on a Nevada desert playa using small stations that record pressure and solar flux with high time resolution (2 Hz): these data allow detection of vortices and an estimate of the dust opacity of the subset of vortices that geometrically occult the sun. The encounter rate of vortex pressure drops of 0.3 hPa or larger is 50–80 per 100 days, with 0.6 hPa or larger drops occurring about 3 times less often. Obscuration events associated with pressure drops occur less frequently, in part because near-misses must be in the sunward direction to cause attenuation of the solar beam and in part because some vortices are not dust-laden. 40% of vortex events had no detectable attenuation, and only 20% of events caused dimming greater than about 2% (a maximum of ∼35%), with stronger dimming tending to occur with larger pressure drops. The distribution suggests dust lifting may be dominated by a few intense devils, complicating estimation of the total flux into the atmosphere.

The transition between the crust and mantle across the Australian continent shows considerable variations in both depth and sharpness. Recent extensive seismic reflection profiling provides a comprehensive data set to investigate the nature of the Moho in a wide range of geological environments. In reflection seismology the crust is normally characterized by distinct reflectivity whose base is taken as the location of the reflection Moho. This attribution to the base of the crust ties well to refraction and receiver function studies that make a more direct estimate of the depth to the base of the crust. The character of the reflection Moho varies widely across the Precambrian areas of Australia with no consistent link to the surface geology or the estimated age of the crust. In a number of places a double Moho is preserved with underthrusting, suggesting that the reflection Moho is a very ancient feature (at least 1400 Ma in the Capricorn Orogen). Elsewhere, the current Moho reflects multiple generations of crustal reworking.

Remote thermal monitoring of active volcanoes has many important applications for terrestrial and planetary volcanic systems. In this study, we describe observations of active eruptions on Kilauea and Erta Ale volcanoes using a short-wavelength, high-resolution, consumer digital camcorder and other non-imaging thermal detectors. These systems revealed brightness temperatures close to the eruption temperatures and temperature distributions, morphologies and thermal structures of flow features, tube systems and lava fountains. Lava flows observed by the camcorder through a skylight on Kilauea had a peak in maximum brightness temperatures at 1230 °C and showed brightness temperature distributions consistent with most rapid flow at the center. Surface brightness temperatures of cooling lava flows on Kilauea were close to 850 °C. Centimeter-scale thermal features are evident around pahoehoe ropes and inflated flows and stalactites in lava tubes. Observations of the fountaining Erta Ale lava lake in February 2011 extend the baseline of observations of the eruptive episode begun in late 2010. We observed a fountain using the camcorder and found a peak in maximum brightness temperatures at 1164 °C, consistent with previous studies. Steep temperature gradients were observed across centimeter-scale distances between the highly exposed fountain and cracks and the much cooler lava lake surface and crater walls. The instrument and methods described here lead to robust pictures of the temperatures and temperature distributions at these volcanoes and reveal desired characteristics of planetary remote sensing platforms for the study of volcanically active bodies such as Io.

Atmospheric aerosol particles may undergo phase separation due to differences in miscibility. This alters the morphology of particles such that they are no longer well-mixed, simple spheres. As a result, scattering and absorption of sunlight in Earth’s atmosphere could be affected. In turn, this may alter direct climate forcing by aerosols. In this work we examine the impact of phase separation on aerosol optics for the bi-sphere, core–shell, and engulfed morphologies. We find bi-spherical particles often exhibit very different scattering and absorption cross-sections for a mid-visible wavelength (0.53 μm) relative to an equivalent, volume-weighted spherical case. Optical differences are largely driven by the particle shape, rather than differences in refractive index between phases. However, when averaged across a typical urban particle size distribution, the differences in light scattering largely vanish and bi-sphere and volume equivalent models generally agreed to within 10% for dielectric particles. For particles that are light absorbing, the bi-sphere and volume averaged cases often yielded dissimilar results with the volume-averaged case reflecting absorption >10% more than the phase separated particles. This was particularly true for bi-spheres in which one component particle is strongly light absorbing. Core–shell and engulfed morphologies yield volume scattering efficiencies within a few percent of volume-weighted spheres. However, modeled light absorption between the phase separated and volume averaged models frequently differ by >20% when inclusions absorb light strongly. Therefore, modeling light absorption of mixed-phase particles through the volume-mixing rule cannot be recommended.

The formation of base metal sulfide deposits requires not only a source of metals but also reduced sulfur. If incoming sulfur is present in ore fluids as sulfate, then a source of electrons is needed to drive the reduction of sulfate to sulfide. The oxidation of organic matter can release electrons that provide the reducing capacity, whether it be in low- or high-temperature settings that are conducive to biological or thermochemical sulfate reduction (BSR or TSR). The amounts of organic matter reacted and sulfide minerals formed can be estimated by mass balance calculations. In this study, an integrated mass balance expression is formulated that takes into account the sulfide mineral content and organic carbon content and H/C ratios of mineralised and non-mineralised rocks. Model calculations based on carbon, sulfur and redox budget balances suggest that the extent of oxidation of the organic matter present at the Here’s Your Chance (HYC) Pb–Zn deposit is insufficient for reduction of the required quantity of sulfate. The results imply that externally derived reducing capacity and/or reduced sulfur is required to form the metal resource. Possible sources include hydrocarbon-rich fluids from deeper parts of the sedimentary sequence or formation of sulfide and organic matter as products of BSR during sedimentation/early diagenesis. However, the observed oxidation of organic matter associated with the deposit suggests that at least some reducing capacity is locally derived. Therefore, our calculations are consistent with genetic models for HYC that have multiple sources of redox budget for sulfate reduction.

Equipment for performing low-altitude aerial photography for geomorphological studies on 10–1000 m scales is described, with particular reference to study of sand dunes. An automatic digital camera is lofted by a parafoil kite: the arrangement costs around $400, collapses into a volume of ∼2 l and can be deployed in a few minutes, making it convenient for field use when wind conditions (>4 m/s) permit. Some operational considerations are discussed and we demonstrate two scientific applications – change detection to show a dune at White Sands has not advanced in an 11-month interval and the generation of a digital elevation model of Bruneau Dune.

We present results from a series of experiments on the partitioning of chlorine between a hydrous fluid phase and a phonolitic melt that we then use to model specific aspects of volcanic degassing. Experiments were performed from 250 to 10 MPa on a phonolite from Erebus lava lake, Antarctica, at 1000 °C near the QFM solid buffer. Only one of 48 experimental samples shows coexistence of low-density vapour and high-density brine in the fluid phase while 35 samples are unambiguously in the vapour field. Large uncertainties in the H₂O–NaCl phase diagram at the P–T considered do not allow us to assign reliable phase behaviour to the remaining samples. We select a vapour-dominated subset of our dataset to establish an empirical HCl solubility law valid at low pressures and salinities. This law is incorporated into a thermodynamical model of degassing, which we use to compute equilibrium temperatures from gas measurements made at Erebus in 2010. The quiescent lake activity features cyclic temperature variations between 1000 and 1050 °C, which is consistent with thermal convection within the shallow plumbing system. Backward tracking of representative gas compositions and temperatures shows the evolution with pressure of the molar ratio of SO₂/HCl in the gas, a quantity that is often measured in volcanic plumes. Model outputs suggest that this ratio can vary by up to an order of magnitude when the pressure changes from atmospheric to 100 MPa, depending on degassing style (coupled vs. decoupled ascent of gas and melt).