Monitoring estuaries using non-permanent stations: practical aspects and data examples

This paper deals with the performances of non-permanent environmental monitoring stations when recording at high-sampling interval (hour) over a long term (months, years) within estuarine waters. Information about data quality and system maintenance requirements are provided based on the experience gained with an autonomous station deployed during 2?years at the Guadiana Estuary (southern Portugal–Spain border). The station includes (1) a multi-parameter probe for water quality (temperature, conductivity, dissolved oxygen, turbidity, chlorophyll and pH) inserted in a tube through a surface-floating buoy; and, (2) a bottom-mounted current meter. The main issues for the continuous acquisition of valid data were biofouling on the optical (chlorophyll, turbidity, dissolved oxygen), conductivity sensors of the probe and high sediment dynamics at the bed. The definition of a detailed maintenance programme is required for the lengthening of (valid) data time series. The typical variability of the parameters is described at seasonal and tidal time scales and episodic events are identified (coastal upwelling and high freshwater inputs). These examples illustrate how integrated data analysis is fundamental to define and understand the changes induced by specific events on several interrelated parameters, and, more generally, how these systems can contribute to a better understanding of the hydro-ecological processes operating in estuaries.     

Permeability profiles in granular aquifers using flowmeters in direct-push wells

Numerical hydrogeological models should ideally be based on the spatial distribution of hydraulic conductivity (K), a property rarely defined on the basis of sufficient data due to the lack of efficient characterization methods. Electromagnetic borehole flowmeter measurements during pumping in uncased wells can effectively provide a continuous vertical distribution of K in consolidated rocks. However, relatively few studies have used the flowmeter in screened wells penetrating unconsolidated aquifers, and tests conducted in gravel-packed wells have shown that flowmeter data may yield misleading results. This paper describes the practical application of flowmeter profiles in direct-push wells to measure K and delineate hydrofacies in heterogeneous unconsolidated aquifers having low-to-moderate K (10(-6) to 10(-4) m/s). The effect of direct-push well installation on K measurements in unconsolidated deposits is first assessed based on the previous work indicating that such installations minimize disturbance to the aquifer fabric. The installation and development of long-screen wells are then used in a case study validating K profiles from flowmeter tests at high-resolution intervals (15 cm) with K profiles derived from multilevel slug tests between packers at identical intervals. For 119 intervals tested in five different wells, the difference in log K values obtained from the two methods is consistently below 10%. Finally, a graphical approach to the interpretation of flowmeter profiles is proposed to delineate intervals corresponding to distinct hydrofacies, thus providing a method whereby both the scale and magnitude of K contrasts in heterogeneous unconsolidated aquifers may be represented.     

Non-climatic growth of the saline Lake Beseka,Main Ethiopian Rift

When using rift lakes as proxies for palaeoclimate it is essential to know if water level changes are of geological or climatic origin, and whether a reinterpretation of palaeo-lake levels derived from lithostratigraphic sequences is required. The saline, endorheic Lake Beseka is located in the tectonically active Main Ethiopian Rift. Despite the aridity of the rift valley the lake's surface area quadrupled from 11.1 km² in 1973 to 39.5 km² in 2002. We quantify the lake growth by means of a detailed bathymetric model and high-resolution satellite time series. We analyse the potential climatic, anthropogenic, and tectonic agents of Lake Beseka's growth. Multitemporal remote sensing data and meteorological records were compared with in-situ measurements of hydrochemical parameters and water depth to address the reason for the lake level rise. Our results suggest that Lake Beseka's expansion originates from an increased discharge of the hot springs. The combined analysis of satellite data and in-situ measurements proved to be a valid tool for the quantification of lake level changes and can help to detect the causes of these variations.     

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.     

Emplacement of a Debris Avalanche during the 1883 eruption of Krakatau (Sunda Straits,Indonesia)

Conclusion The data collected during the Mentawai cruise help to clarify understanding of the 1883 eruption of Krakatau. We have previously discussed the weaknesses of the interpretation of Williams (1941) and others (Self and Rampino 1981) and emphasized that only a Mount St. Helens-type collapse during the course of the eruption could account for all the characteristics of the eruption and of the related deposits.The discovery on land of deposits attributable to a debris-avalanche, in the stratigraphic position where they were expected, is a strong argument for the validity of our scenario.Marine surveys confirm that the sea bottom around Krakatau is covered by a thick ignimbritic deposit. But the presence of this deposit does not invalidate the presence of a debris-avalanche deposit under the ignimbrites. The hummocky morphology favours this hypothesis.Flank-failure of volcanoes is generally considered as a very efficient mechanism for triggering tsunamis (Kienle et al. 1987; Siebert et al. 1987). However, the majority of the volcanoes where flank-failure has been described are tall and bulky and the collapse of a broad edifice like Krakatau may be surprising. However the geological evidence shows that such a mechanism can act at various scales; for example the flank collapse of Mayu Yama volcano (height 700 m, volume 0,3 km³), a parasitic cone of Unzen volcano (Japan), triggered a debris-avalanche into the sea that was 1 km long, with a characteristic hummocky surface; the resulting tsunami killed 9528 people (Katayama 1974). In the same way, a partial collapse of Iliwerung volcano, Indonesia (50 × 10⁶ m³) in July 1979, triggered a tsunami which killed several hundred people (McClelland et al. 1989). At Krakatau, the main summit was 822 m asl; the collapse took place along the edge of the prehistoric caldera and this structural unconformity probably facilitated the triggering of the process.     

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.