Structural features of South-Adamawa (Cameroon) inferred from magnetic anomalies: Hydrogeological implications

Structural directions of the southern part of the Adamawa plateau in Cameroon are highlighted by filters applied on the magnetic anomaly map. Determination of the magnitude maxima of (1) the horizontal gradient of the field reduced to the pole, and (2) the analytic signal, allowed a map to be produced showing various lineaments interpreted as the fault system of the studied area. In particular, the faults on the shaded relief map of the horizontal gradient magnitude suggest a slide to the left of the Foumban shear zone in the studied area. Interpretation of the observed anomaly along a profile directed SSE-NNW shows the presence of a magnetized body considered as an intrusion into the granitic basement of probably basaltic volcanic rocks, put in place during the reactivation of the Foumban shear zone. In addition, the observed correlation between the mapped structural directions, the sites of thermo-mineral springs and the hydrographical network shows that the results of this study will be helpful for further hydrogeological research in the studied area.     

A suggestion on the role of tidal forces in the deformation of the Earth's crust

It is proposed that a contribution to orogeny is made by tidal flexing of the Earth's crust. It is suggested that the crust of the Earth is continually expanding horizontally as a result of tidal flexing, and that the pressures caused by this expansion are relieved by folding, faulting and volcanism in zones of weakness which ultimately become zones of granitic accumulation. This expansion also helps account for the concentration of granitic materials of the crust into continental masses.     

Trapping of airborne dust by mosses in the Negev Desert,Israel

Airborne silt and clay containing calcium carbonate, quartz, clays, marine nannoplankton, and aquatic diatoms are trapped among stems of mosses in the Negev Highlands Desert. The mosses were studied in an area with 70 mm mean annual rainfall. They grow over the particles covering them and trap additional dust as it comes, resulting in the accumulation of loess sediments. The mosses protect the accumulated soil from erosion by wind or water. Remnants of the moss leaves and stems were found at a depth of 15 mm and more. No particles or minerals typical to basalt were found in the moss-trapped soil. The function of cushiony mosses may be used to explain the processes of loess trapping and protection in larger areas in moister areas such as the Northern Negev. Microscopic fossils in the dust may be used as guides to the origin of the (aeolian) sediments.     

Origin and flatness of ponds on asteroid 433 Eros

NEAR‐Shoemaker Multi‐Spectral Imager data reveal several hundred “ponds” on 433 Eros: smooth deposits that sharply embay the bounding depressions in which they lie, and whose spectra appear blue relative to that of the surrounding terrain. We investigate the topography of these ponds on Eros using a new shape model derived from stereophotoclinometric analysis, and validated against altimetry from the NEAR Laser Rangefinder, to constrain the mode of pond formation from three existing models. We update the locations of 55 pond candidates identified in images registered to the new shape model. We classify the flatness of these features according to the behavior of the first and second derivatives of the topography. We find that less than half of pond candidates have clearly flat floors. Based on the pond topography, we favor an external origin for the ponds' deposits. We suggest that fine dust may be transported into bounding depressions by electrostatic levitation, but may adhere to slopes, and that seismic shaking may not be sufficient to bring the deposits to an equipotential surface. Disaggregation of a central boulder should result in an obvious break in slope, such a variation is only observed in roughly half the pond candidates.     

Shoreline migration and beach-nearshore sand balance over the last 200 years in Haifa Bay (SE Mediterranean)

Several researchers have investigated morphological changes on the south-eastern Mediterranean coast during the late Holocene. However, very few of these studies include quantitative data covering the last 200 years. In this study, topographical maps, nautical charts and aerial photographs are used to estimate the shoreline migrations and beach–nearshore sand balance over the last 200 years in Haifa Bay, Israel, the northernmost final depositional sink of the Nile littoral cell. The findings reflect two main periods. During the first period, between 1799 and 1928, human intervention along the bay’s coast was negligible, a significant coastal expansion of ∼50 to 150 m (averages of 0.4–1.2 m/year) was measured, and sand accumulation was estimated at ∼70,000 m³ annually in the beach–nearshore area. A dramatic change in the sedimentological pattern was observed during the second period, between 1928 and 2006, following the completion of Haifa Port’s main breakwater (1929–1933). During this period, most of the bay’s coast was in a steady state, with seasonal fluctuations of less than about ±20 m, and slight erosion of ∼7,000 m³ annually. These findings are consistent with previous studies which conclude that from approximately 4,000 years ago until the construction of Haifa Port, sea level remained relatively stable, and a continuous accumulation of Nile-derived sand dried up the Zevulun Plain and shifted the Haifa Bay shoreline westwards to its present location. This long-term trend ceased after completion of the Haifa Port main breakwater.