Early Cretaceous Basaltic and Rhyolitic Magmatism in Southern Uruguay Associated with the Opening of the South Atlantic

The Early Cretaceous volcanic rocks of southern Uruguay comprisemafic and felsic volcanics. The position of these outcrops atthe southern edge of the Paraná–Etendeka continentalflood basalt province provides an opportunity to investigatepossible lateral variations in both mafic and more evolved rocktypes towards the margins of such an area of plume-related magmatism.The mafic lavas are divided into two compositionally distinctmagma types. The more voluminous Treinte Y Trés magmatype is similar to the low-Ti basalts of the Paraná floodbasalt province. The Santa Lucía magma type is a distinctand rare basalt type with ocean-island basalt type asthenosphericaffinities (high Nb/La, low ⁸⁷Sr/⁸⁶Sr_i). The felsic volcanicsare divided into two series, the Lavalleja Series and the AigüaSeries. The Lavalleja Series are chemically and isotopicallysimilar to the Paraná–Etendeka low-Ti rhyolites,and are considered to be related to the Treinte Y Tréslavas by extensive fractionation and crustal assimilation. TheAigüa Series have low ¹⁴³Nd/¹⁴⁴Nd_i and low ⁸⁷Sr/⁸⁶Sr_i andunlike the rhyolites of the Paraná, are interpreted asmelts of pre-existing mafic lower crust that subsequently underwentextreme fractionation. The differences observed in the felsicsuites may be linked to differences in the volumes of the associatedbasalts and the amounts of extension. KEY WORDS: South America; flood basalts; felsic volcanics; crustal melts; plume     

Geomorphology of the eastern Badia basalt plateau, Jordan

The eastern Badia of the Hashemite Kingdom of Jordan is a landscape developed predominantly on late Tertiary and Quaternary basalt lava flows, which vary in age between 8.9 million and 0.1 million years. Pyroclastic deposits are associated with remnant volcanic cones. There is limited, seasonal rainfall. Natural vegetation regenerates during cool, damp months. Slopes, which range from concave to convex forms and have varying relief, can be related to different basalts and the time since emplacement. Much of the ground surface is mantled with boulders. In many places the continuity of boulder cover produces a desert pavement. Clasts show differing degrees of burial or exhumation, depending on the surrounding topography. Water and sediment movement are important to landscape development. Much sediment is deposited in pans, which evolve at topographic lows. The pans, known locally as Qa, vary in form depending on drainage network development. Transitional forms, known as Marab, develop where wadis widen out and sediments are deposited along ephemeral channels. Groundwater is significant, with three aquifers beneath much of the eastern Badia. Recharge of the upper aquifer is predominantly on the footslopes of the Druze Mountains, with north to south flow. Groundwater extraction has resulted in the expansion of agriculture, with consequent changes in soil and water quality.     

Geochemical and Isotopic Evolution of Loihi Volcano, Hawaii

A 680m thick section from the deeply dissected east flank ofLoihi Volcano was sampled using the Pisces V submersible toevaluate the volcano's geochemical evolution. Three types oflavas were recovered: tholeiitic, weakly alkalic and stronglyalkalic. The ratio of alkalic to tholeiitic lavas varies systematicallywith depth, from predominantly alkalic at the base of the sectionto tholeiitic at the top. Glasses from these rocks have similarratios of highly incompatible elements and Pb, Sr and Nd isotopes,but distinct ratios of highly to moderately incompatible elements.Partial melting modeling indicates that these tholeiitic andalkalic lavas could be derived by variable degrees of partialmelting of a slightly heterogeneous source. Many distinct parentalmagmas were generated for each rock type during the 100–150k.y. that the east flank section was formed. Crystal fractionationand olivine accumulation were the dominant processes controllingcompositional variation among lavas of the same rock type. Magmamixing features were observed in only a few of the lavas collected. Loihi typifies the preshield stage of Hawaiian volcanism whenthe volcano drifts closer to the focus of the hotspot. The compositionalvariation in Loihi's east flank section, which may represent40% of the volcano's extrusive history, is consistent with thepredicted increase in partial melting during this drift. Thetransition from dominantly alkalic to tholeiitic volcanism onLoihi was fitful but relatively rapid and is now nearly complete.This transition is the opposite of that which occurs duringthe post-shield stage of Hawaiian volcanism as the volcano migratesaway from the hotspot focus. Loihi's tholeiitic lavas overlap in ratios of incompatible traceelements and Pb, Sr and Nd isotopes with lavas from its moreactive neighbor, Kilauea. The small differences in major elementcontents between lavas from these adjacent volcanoes can beexplained by high-pressure orthopyroxene fractionation of Loihimagmas, which may be a consequence of a low magma-supply rate,or by slightly shallower depths of melt segregation for Kilaueamagmas. KEY WORDS: Loihi volcano; Hawaii; geochemistry; Sr-Nd-Pb isotopes     

Developers in the public interest? The role of urban development corporations in the Anglophone Caribbean

Urban centres in the Caribbean face a wide variety of infrastructural and planning challenges. One of the key strategies that has been adopted by national governments to address these challenges is the formation of urban development corporations. These are governmental agencies with powers to facilitate urban regeneration in specific areas. This paper examines the history, role and function of urban development corporations in Jamaica, Antigua and Barbuda, and Trinidad and Tobago. The Urban Development Corporation (UDC) was formed in Jamaica in 1968, the St John's Development Company (SJDC) in Antigua and Barbuda was created in 1986, and the Urban Development Corporation of Trinidad and Tobago (UDeCOTT) was established in 1994. These bodies share the characteristic of having far-reaching planning and development powers within specific areas. For example, the SJDC is able 'to acquire, manage, or dispose of lands and to lay out, construct, and maintain roads, buildings, public parks, piers, car parks, and other public amenities' within specified designated areas, whilst Jamaica's UDC is empowered 'to carry out and/or secure the laying out and development of "designated areas". These three urban development corporations can be seen to act as developers in the public interest, as agents of modernisation, and as responses to neoliberalisation. However, whilst they have succeeded in effecting large-scale transformations to the urban landscape, this has often been achieved through a top-down development process with exemption from planning regulations and little accountability to the residents of the cities.     

EFFECTS OF CLIMATE CHANGE ON INLAND WATERS OF THE PACIFIC COASTAL MOUNTAINS AND WESTERN GREAT BASIN OF NORTH AMERICA

The region designated as the Pacific Coastal Mountains and Western Great Basin extends from southern Alaska (64°N) to southern California (34°N) and ranges in altitude from sea level to 6200 m. Orographic effects combine with moisture-laden frontal systems originating in the Pacific Ocean to produce areas of very high precipitation on western slopes and dry basins of internal drainage on eastern flanks of the mountains. In the southern half of the region most of the runoff occurs during winter or spring, while in the northern part most occurs in summer, especially in glaciated basins. Analyses of long-term climatic and hydrological records, combined with palaeoclimatic reconstructions and simulations of future climates, are used as the basis for likely scenarios of climatic variations. The predicted hydrological response in northern California to a climate with doubled CO₂ and higher temperatures is a decrease in the amount of precipitation falling as snow, and substantially increased runoff during winter and less in late spring and summer. One consequence of the predicted earlier runoff is higher salinity in summer and autumn in San Francisco Bay. In saline lakes, the incidence of meromixis and the associated reduction in nutrient supply and algal abundance is expected to vary significantly as runoff fluctuates. In subalpine lakes, global warming will probably will lead to increased productivity. Lacustrine productivity can also be altered by changes in wind regimes, drought-enhanced forest fires and maximal or minimal snowpacks associated with atmospheric anomalies such as El Niño–Southern Oscillation (ENSO) events. Reduced stream temperature from increased contributions of glacial meltwater and decreased channel stability from changed runoff patterns and altered sediment loads has the potential to reduce the diversity of zoobenthic communities in predominately glacier-fed rivers. Climatic warming is likely to result in reduced growth and survival of sockeye salmon in freshwater, which would, in turn, increase marine mortality. Further research activities should include expanded studies at high elevations and of glacier mass balances and glacial runoff, applications of remote sensing to monitor changes, further refinement of regional climatic models to improve forecasts of future conditions and continued analyses of long-term physical, chemical and biological data to help understand responses to future climates. © 1997 John Wiley & Sons, Ltd.     

WIDESPREAD EFFECTS OF CLIMATIC WARMING ON FRESHWATER ECOSYSTEMS IN NORTH AMERICA

Freshwaters in different regions show many similarities and differences in their responses to climatic warming. Bases for comparison include reports from regional committees, long-term records for several sites where climate has warmed in the past two decades and other human alterations to freshwaters that simulate some of the expected results of climatic warming, such as reservoir construction. Palaeoecological studies of freshwaters under climatic warming and differences in communities under different climatic regimes are also considered. Major changes in the physical, chemical and biological characteristics of lakes occur. Many of the changes to lakes and streams are the result of strong effects of climatic warming on terrestrial catchments. Inputs from catchments can be either dampened or amplified by in-lake processes, in some cases causing counter-intuitive responses, such as the acidification of streams but alkalinization of lakes in areas where supplies of base cations are limited. Consideration of land–water interactions and interactions between climatic warming and other human stresses are important for the accurate prediction of the effects of climatic change. © 1997 John Wiley & Sons, Ltd.     

BEYOND TWISTER: A GEOGRAPHY OF RECREATIONAL STORM CHASING ON THE SOUTHERN PLAINS*

ABSTRACT. Storm chasing is widely perceived as a new form of extreme sport or adventure travel. Each spring increasing numbers of tourists descend on the Southern Plains, the center of storm chasing in the United States, but little is known about their activities. According to longtime chasers, popular portrayals of storm pursuits are highly misleading, and growing participation in the sport is affecting storm chasing in the region. This study introduces the storm-chasing enterprise. Using route information and comments supplied by veteran chasers, I describe the spatial patterns of storm-chasing on the Southern Plains. Comparing the behavior and motivations of longtime enthusiasts with popular portrayals of the activity permits me to dispel many myths and to discuss the nature and future of this growing but little-understood recreational pursuit.