Sediment resuspension events induced by the wake wash of deep-draft vessels

Hydrodynamics and sediment resuspension events, induced at the shoreline by a deep-draft vessel passing nearby, are described. Measurements (pressure, currents and turbidity) were obtained at 4 Hz, on a lower beach ~50 m from a channel where large car ferries operate in Wootton Creek, Isle of Wight. The study focuses on a representative 8-min 32-s-long record, during which two large vessels passed the channel section. At the shore, the passage of each vessel induced a long-period water-level drawdown, followed by a water-level oscillation (seiche) of similar period, and the short-period waves of the wake. Both drawdowns were the main constituents of the prevailing wave pattern. The second drawdown was the largest in amplitude, in response to a higher speed of the ferry, and the influence of the seiche which had been activated during the preceding event. Two successive peaks of turbidity were observed shortly after this drawdown. Analyses of current velocity and direction indicate that the sediments resuspended originated from the shallower upper beach. Anthropogenically induced erosion of the foreshore is predicted at Wootton Creek.     

Recovery of Bennu’s orientation for the OSIRIS-REx mission: implications for the spin state accuracy and geolocation errors

The goal of the OSIRIS-REx mission is to return a sample of asteroid material from near-Earth asteroid (101955) Bennu. The role of the navigation and flight dynamics team is critical for the spacecraft to execute a precisely planned sampling maneuver over a specifically selected landing site. In particular, the orientation of Bennu needs to be recovered with good accuracy during orbital operations to contribute as small an error as possible to the landing error budget. Although Bennu is well characterized from Earth-based radar observations, its orientation dynamics are not sufficiently known to exclude the presence of a small wobble. To better understand this contingency and evaluate how well the orientation can be recovered in the presence of a large 1\(^{\circ }\) wobble, we conduct a comprehensive simulation with the NASA GSFC GEODYN orbit determination and geodetic parameter estimation software. We describe the dynamic orientation modeling implemented in GEODYN in support of OSIRIS-REx operations and show how both altimetry and imagery data can be used as either undifferenced (landmark, direct altimetry) or differenced (image crossover, altimetry crossover) measurements. We find that these two different types of data contribute differently to the recovery of instrument pointing or planetary orientation. When upweighted, the absolute measurements help reduce the geolocation errors, despite poorer astrometric (inertial) performance. We find that with no wobble present, all the geolocation requirements are met. While the presence of a large wobble is detrimental, the recovery is still reliable thanks to the combined use of altimetry and imagery data.     

Geophysical characterization of the lithological control on the kinematic pattern in a large clayey landslide (Avignonet,French Alps)

Lithology variation is known to have a major control on landslide kinematics, but this effect may remain unnoticed due to low spatial coverage during investigation. The large clayey Avignonet landslide (French Alps) has been widely studied for more than 35 years. Displacement measurements at 38 geodetic stations over the landslide showed that the slide surface velocity dramatically increases below an elevation of about 700 m and that the more active zones are located at the bottom and the south of the landslide. Most of the geotechnical investigation was carried out in the southern part of the landslide where housing development occurred on lacustrine clay layers. In this study, new electrical prospecting all across the unstable area revealed the unexpected presence of a thick resistive layer covering the more elevated area and overlying the laminated clays, which is interpreted as the lower part of moraine deposits. The downslope lithological boundary of this layer was found at around 700 m asl. This boundary coincides with the observed changes in slide velocity and in surface roughness values computed from a LiDAR DTM acquired in 2006. This thick permeable upper layer constitutes a water reservoir, which is likely to influence the hydromechanical mechanism of the landslide. The study suggests a major control of vertical lithological variations on the landslide kinematics, which is highlighted by the relation between slide velocity and electrical resistivity.     

Abrupt axial variations along the slow to ultra-slow spreading centers of the northern North Fiji Basin (SW Pacific): Evidence for short wave heterogeneities in a back-arc mantle

This study presents results of surveys conducted along the slow to ultra-slow spreading axis of the Northern North Fiji Basin (NNFB), including the Hazel Holmes, Tripartite and South Pandora Ridges, and the newly discovered Futuna and North Cikobia spreading centers. Spreading segments along these axes display highly contrasted axial morphologies, ranging from a rift valley to a prominent axial high. In some places, abrupt inversions of topography are observed between neighboring segments. Detailed analyses of bathymetry and backscatter maps reveal that axial highs are spotted with numerous coalescent volcanoes forming features ranging from irregular terrains to well-organized ridges. The volcanic edifices are distributed over a wide neovolcanic zone, which corresponds to the axial relief, suggesting on important contribution of volcanism to the relief construction. Comparisons between various ridge-shaped segments reveal that axial volcano-tectonic patterns are directly related to the local magma production and delivery, in a context of tectonic extension related to plate divergence, and suggest that coalescent volcanoes are fed from multiples short-lived and unconnected magma lenses. In the competition between horizontal and vertical accretion of oceanic crust, the spreading centers of the NNFB represent a special case where lava production is locally high enough and spreading rate is low enough to allow prominent axial highs to develop. The along axis morphologic variability is related to intermittent volcanic activity that may result from rapid temporal and spatial variations in the distribution of upper mantle convection cells below accretion centers, superimposed on the regional thermal anomaly located under the whole basin.     

Palaeoenvironments of early hominins in temperate and Mediterranean Eurasia: new palaeobotanical data from Palaeolithic key-sites and synchronous natural sequences

The present study focuses on new palaeobotanical data (pollen, phytoliths and fruits) from three of the oldest Early Palaeolithic sites in Eurasia (Dmanisi in Georgia, Ca’ Belvedere di Monte Poggiolo in Italy and Pont-de-Lavaud in France). The main aim is to examine the ecological factors associated with the first human dispersals out of Africa into Eurasia. The palaeoecological data are discussed with regards to chronology and geographical location of the settlements. The vegetation pattern of each site consists of temperate Eurasian and Mediterranean taxa, subtropical trees being more or less recorded depending on climatic and geographic features. The new palaeobotanical data show that different vegetation structures occurred between the first human dispersal in Caucasus and the later dispersals in western Eurasia. However, in all cases hominins seemed to be adapted to temperate ecosystems. In Caucasus, human occupation took place at 1.7 Ma in a forest-steppe environment, while at ca 1 Ma human populations occupied various settings such as open landscapes or dense forests. These data suggest that during the Early Pleistocene, human populations evolved and dispersed in western Eurasia, gradually increasing their degree of adaptation to diversified environments.     

Orbit determination of the Lunar Reconnaissance Orbiter

We present the results on precision orbit determination from the radio science investigation of the Lunar Reconnaissance Orbiter (LRO) spacecraft. We describe the data, modeling and methods used to achieve position knowledge several times better than the required 50–100 m (in total position), over the period from 13 July 2009 to 31 January 2011. In addition to the near-continuous radiometric tracking data, we include altimetric data from the Lunar Orbiter Laser Altimeter (LOLA) in the form of crossover measurements, and show that they strongly improve the accuracy of the orbit reconstruction (total position overlap differences decrease from ~70 m to ~23 m). To refine the spacecraft trajectory further, we develop a lunar gravity field by combining the newly acquired LRO data with the historical data. The reprocessing of the spacecraft trajectory with that model shows significantly increased accuracy (~20 m with only the radiometric data, and ~14 m with the addition of the altimetric crossovers). LOLA topographic maps and calibration data from the Lunar Reconnaissance Orbiter Camera were used to supplement the results of the overlap analysis and demonstrate the trajectory accuracy.     

Non-Newtonian effects during injection in partially crystallised magmas

Injection of Newtonian crystal-free magmas into a partially crystallised host which may exhibit non-Newtonian properties produces magmatic structures such as pipes, syn-plutonic dikes or dendritic structures. Field relationships between the structure and the host rock commonly indicate what the rheological contrasts during the injection were. The manner in which a magma deforms in response to injection is mainly linked to crystal content and strain rate (i.e., injection rate). Three kinds of behaviour can be distinguished: (1) Newtonian at low crystal contents; (2) Non-Newtonian at intermediate (40–60%) crystal contents, or at high crystal contents if the strain rate is small; and (3) brittle failure at high crystal content or strain rates.Petrologic observations indicate that injection can take place when the host magma still behaves as a fluid. To investigate the physics of the injection process we review the results of injection experiments in non-Newtonian fluids. These experiments were performed to study viscous fingering in 2-D Hele Shaw cells. They provide the first step to establishing the main non-Newtonian effects during the formation of interfacial instabilities arising when a Newtonian fluid is injected into a more viscous fluid or paste. The qualitative comparison of the morphological features of the interfaces between the fluids in the experiments with those in nature suggests that, in magmas, irregularities of the interfaces (dikes and dendrites) result from non-Newtonian properties of the host. We conclude that fluid-like deformation, rather than brittle behaviour of the host, during injection is likely to produce the general features observed on the field. Cooling effects might be responsible for the widespread phenomenon of fragmentation. We emphasise that the main effect of non-Newtonian properties in partially crystallised magmas is to generate strongly heterogeneous media producing discontinuities which could explain the main morphological features of syn-plutonic injection structures.     

Physical models of magmatic intrusion during thrusting

To investigate how magma rises through the brittle upper crust in a context of compressional tectonics, we have performed experiments on scaled physical models. Powdered silica (having a cohesion of 300 Pa and an angle of internal friction of 38°) was used to represent brittle crust. A vegetable oil (with a Newtonian viscosity of 10^?2 Pa·s at 50 °C) was used to represent magma. A moving piston shortened the models in a box, while oil was injected steadily at the base. On cooling to room temperature, the oil solidified. The resulting intrusions were thin sills, dykes and laccoliths. Their shapes and emplacement modes depended on the ratio R between rates of shortening and injection. From shapes and orientations of intrusions, we infer that hydraulic fracturing was one mechanism of emplacement. Unconsolidated intrusions strongly influenced thrust formation. On the basis of our experiments, we suggest that magmas in orogenic belts can rise along thrust faults.