Channel and floodplain sediment dynamics in a reach of the tropical meandering Rio Beni (Bolivian Amazonia)

The study investigates interactions, water and sediment exchanges, between a rapidly migrating meander and its associated floodplain at fine temporal and spatial scales. The Beni River, an Amazonian free meandering river, makes the transition between Andean ranges and Amazonian lowlands. For the period 2002–2006, an assemblage of tools and methods (water and sediment discharges, topometric and bathymetric surveys, sedimentation rate estimations from unsupported ²¹⁰Pb and sediment trapping system) was used to jointly analyse the influence on the sediment budget of external factors (mainly water and sediment discharge) and the inherent behaviour of the system. The main issue addressed is the investigation of the complex relationship between ‘morphological conditioning’ of fluvial landform and process. The first part of the study was undertaken with the aim of linking erosion–deposition in an active meander with water and sediment fluxes. The three inter‐annual evolutions are characterized by very unequal sediment budgets; the first two intervals underwent predominant erosion, and the latter slight accumulation. Digital elevation models, evaluated for the active meander, demonstrate that sedimentation on the point bar depends more on external factors than erosion of the concave bank, which fluctuates slightly. The second part of the study, focusing on water and sediment exchanges between active bend and floodplain, examines the respective parts played by overbank flow and by an abandoned channel on the diffusion and sequestration of sediment. The association of short‐ and long‐term estimation of sedimentation rates suggests that floodplain construction is associated with two different processes and rhythms of sediment transportation. Finally, a sediment budget is proposed for the Beni River in the upper part of the Amazonian lowlands. Copyright © 2010 John Wiley & Sons, Ltd.     

Radio maps of the Sun at λ = 1.95 cm

Two radio maps of the Sun at = 1.95 cm, taken at the N.R.A.O. (Green Bank) with a resolving power of 2.1 are studied and compared with H pictures: both bright and dark features appear to be strongly correlated. The emitted flux and the angular extent of the bright regions are given; from the observed radio-darkening of a region, the height of a prominence is derived.On leave from Osservatorio Astrofisico di Arcetri, Firenze.     

Magnetic and microwave structure in solar active regions

The structure of six active regions observed at 2.8 cm with the Stanford interferometer is compared with the configuration of the underlying photospheric magnetic fields, as given by the Kitt Peak magnetograph.The similar resolution and accuracy on the measured positions of both instruments allowed us to establish a more detailed spatial correspondence between radio and magnetic features than previously reached.The radio features which correspond to the cores of the active sources are always found to overlay regions of enhanced magnetic fields. Different spatial associations have been found depending on the brightness temperature of the sources. The possibility that this effect might be due to the development of the active region is also considered.     

New insights on diapirism in the Adriatic Sea: the Tremiti salt structure (Apulia offshore,southeastern Italy)

The reinterpretation of public seismic profiles in the Adriatic offshore of Gargano (Apulia, southern Italy) allowed the detection of a kilometre‐scale salt‐anticline, the Tremiti diapir, within the larger Tremiti Structure. This anticline was generated by diapirism of Upper Triassic anhydrites within a thick Mesozoic to Quaternary sedimentary succession. Both internal stratal patterns and shapes of Plio‐Quaternary units, and the occurrence of an angular unconformity between early Tortonian and Pliocene rocks on the Tremiti Islands, suggest that halokinesis began during the late Miocene and is still active today. An ancient extensional SE‐dipping fault, cutting an older Mesozoic low‐amplitude anhydritic ridge, played an important role during salt mobilization, which was promoted by NW‐SE shortening. The diapir grew in the footwall of this fault, causing its upward propagation. In some places, the ancient fault served as a preferential channel for the upward migration of the anhydrites.