Cliff-top storm deposits on Banneg Island, Brittany, France: Effects of giant waves in the Eastern Atlantic Ocean     

Serge Suanez  Bernard Fichaut  Rudy Magne   《Sedimentary Geology》2009,220(1-2):12-28

This study is based on the morphosedimentary analysis of the cliff-top storm deposits accumulated on the coast of Banneg Island located in the archipelago of Molène (Brittany, France). These CTSDs comprise large, tabular clasts quarried from the upper part of the cliff and the backing scoured platform by giant oceanic storm waves impacting directly the western coast of the island. An analysis of the distribution and the geomorphology of these accumulations were carried out using the DGPS topographic surveys. Most of the clasts are organised into imbricate boulder clusters or ridges deposited between 7.5 and 14.5 masl. 52 accumulations were inventoried from the north to the south of the island, representing a global volume of 1000 m³. The median size of the clasts calculated is equivalent to 0.8 × 0.6 × 0.4 m and a weight of 0.6 t. The largest one measuring 5.3 × 3.9 × 0.5 m (≈ 32 t) is located in the centre of the island (ridge #28). It has been deposited 14 m inland from the edge of the cliff at the elevation of 9 m. Sediment analysis shows that clast sizes become smaller with increasing distance from the shoreline, but there is no relationship between the sorting and the distance inland. A study of the hydrodynamic conditions inducing clast transport was undertaken by an analysis of the wave data from the 1989 to the 1990 winter storms. Models of wave runup indicate that their highest water levels may have reached up to 19 masl, 5 to 10 m higher than the top of the cliff. Submersion by giant storm waves has been more important and frequent in the centre and the south of the island. Wave data over the 1979 to the 2007 period shows that no events as powerful as those of the 1989 to the 1990 winter were recorded during the last 30 years. Yet, it appears that the 1979–1990 decade was characterized by important morphogeneous events while the following period (1990–2007) has experienced a sharp decrease in storm events. These variations could be attributed to the inversion from a negative towards a positive phase in the North Atlantic Oscillation index.  相似文献   

The Rapid X-Ray Variability of V4641 Sagittarii (SAX J1819.3-2525 = XTE J1819-254)     

Wijnands R  van Der Klis M 《The Astrophysical journal》2000,536(2):L93-L96

A theoretical light-curve model of the 1985 outburst of RS Ophiuchi based on a thermonuclear runaway model is presented. The system consists of a very massive white dwarf (WD) with an accretion disk and a red giant. The early phase of the V light curve is well reproduced only by the bloated WD photosphere of the thermonuclear runaway model on a 1.35+/-0.01 M middle dot in circle WD, while the later phase is dominated both by the irradiated accretion disk and by the irradiated red giant underfilling the inner critical Roche lobe. The UV light curve is also well reproduced by the same model with a distance of 0.6 kpc to RS Oph. The envelope mass at the optical peak is estimated to be 2x10-6 M( middle dot in circle), indicating a rather high mass accretion rate of 1.2x10-7 M( middle dot in circle) yr(-1) between the 1967 and 1985 outbursts. About 90% of the envelope mass is blown off in the outburst wind, while the residual 10% (2x10-7 M( middle dot in circle)) has been left and added to the helium layer of the WD. The net increasing rate of the WD mass is 1.2x10-8 M( middle dot in circle) yr(-1). Thus, RS Oph is certainly a strong candidate for a Type Ia supernova progenitor.  相似文献