MODELING OF A MICROWAVE BURST EMISSION

We applied model computations on a microwave burst observed with the Westerbork Synthesis Radio Telescope (WSRT) at 6 cm. We used additional data from H, soft and hard X-rays in order to reproduce the flaring loop and to compute the microwave total intensity and circular polarization. We examined both cases of thin and thick target. The computations show a large emission source in an optically thick loop. We compare our results with the observation.     

HYDROLOGICAL RESPONSE OF SMALL WATERSHEDS FOLLOWING THE SOUTHERN CALIFORNIA PAINTED CAVE FIRE OF JUNE 1990

Following the Painted Cave Fire of 25 June 1990 in Santa Barbara, California which burned 1214 ha, an emergency watershed protection plan was implemented consisting of stream clearing, grade stabilizers and construction of debris basins. Research was initiated focusing on hydrological response and channel morphology changes on two branches of Maria Ygnacio Creek, the main drainage of the burned area. Research results support the hypothesis that the response of small drainage basins in chaparral ecosystems to wildfire is complex and flushing of sediment by fluvial processes is more likely than by high magnitude debris flows. During the winter of 1990–1991, 35–66 cm of rainfall and intensities up to 10 cm per hour for a five-minute period were recorded with a seasonal total of 100% of average (normal) rainfall (average=63 cm/year). During the winter of 1991–1992, 48–74 cm of rainfall and intensities up to 8 cm per hour were recorded with a seasonal total of 115% of normal. Even though there was moderate rainfall on barren, saturated soils, no major debris flows occurred in burned areas. The winter of 1992–1993 recorded total precipitation of about 170% of normal, annual average intensities were relatively low and again no debris flows were observed. The response to winter storms in the first three years following the fire was a moderate but spectacular flushing of sediment, most of which was derived from the hillslopes upstream of the debris basins. The first significant storm and stream flow of the 1990–1991 winter was transport-limited resulting in large volumes of sediment being deposited in the channel of Maria Ygnacio Creek; the second storm and stream flow was sediment-limited and the channel scoured. Debris basins trapped about 23 000 m³, the majority coming from the storm of 17–20 March 1991. Sediment transported downstream during the three winters following the fire and not trapped in the debris basins was eventually flushed to the estuarine reaches of the creeks below the burn area, where approximately 108 000 m³ accumulated. Changes in stream morphology following the fire were dramatic as pools filled with sediment which greatly smoothed longitudinal and cross-sectional profiles. Major changes in channel morphology occur following a fire as sediment derived from the hillslope is temporarily stored in channels within the burned area. However, this sediment may quickly move downstream of the burned region, where it may accumulate reducing channel capacity and increasing the flood hazard. Ecological consequences of wildfire to the riparian zone of streams in the chaparral environment are virtually unknown, but must be significant as the majority of sediment (particularly gravel necessary for fish and other aquatic organisms) entering the system does so in response to fires. © 1997 John Wiley & Sons, Ltd.     

Natural and imposed injustices: the challenges in implementing 'fair' flood risk management policy in England

This paper examines the challenges facing English flood risk management (FRM) policy and practice when considering fair decision-making processes and outcomes at a range of spatial scales. It is recognised that flooding is not fair per se : the inherent natural spatial inequality of flood frequency and extent, plus the legacy of differential system interventions, being the cause. But, drawing on the three social justice models – procedural equality, Rawls' maximin rule and maximum utility – the authors examine the fairness principles currently employed in FRM decision-making. This is achieved, firstly, in relation to the distribution of taxpayer's money for FRM at the national, regional and local levels and, secondly, for non-structural strategies – most notably those of insurance, flood warnings and awareness raising, land use control, home owner adaptation and emergency management. A case study of the Lower Thames catchment illustrates the challenges facing decision-makers in 'real life': how those strategies which appear to be most technically and economically effective fall far short of being fair from either a vulnerability or equality perspective. The paper concludes that if we are to manage flood risk somewhat more fairly then a move in the direction of government funding of nationally consistent non-structural strategies, in conjunction with lower investment decision thresholds for other local-level FRM options, appears to offer a greater contribution to equality and vulnerability-based social justice principles than the status quo.     

Petrology and Geochemistry of Volcan Cerro Azul: Petrologic Diversity among the Western Galapagos Volcanoes

Cerro Azul, one of the large shield volcanoes in the westernGalápagos archipelago, has erupted a wide range of tholeiiticto alkalic basalts. These diverse compositions include someof the most primitive yet reported from the western archipelagoand are unlike those of the other, well-studied, neighboringvolcanoes of Sierra Negra and Alcedo, which have erupted basaltof fairly uniform composition. Major- and trace-element modelingshows that Cerro Azul, Alcedo and Sierra Negra share a similardepth of melting and source composition. Modeling also revealsthat there are small, systematic differences in the extent ofpartial melting between the volcanoes that can be related totheir distance from the proposed plume center below the westernmostisland of Fernandina. However, even though melts segregatingfrom the plume in the western Galápagos reflect a narrowrange of temperatures and source compositions, there are widevariations in the enrichments of major and trace elements betweenCerro Azul, Alcedo and Sierra Negra that cannot be attributedto mantle processes. We believe the observed intershield geochemicaldifferences result from magma supply and cooling rates thatare unique to each volcano, and reflect the variations in lithospherictransport and storage processes across the western archipelago. KEY WORDS: basalt; Galápagos; magma supply; mantle plume; ocean island