Climatic changes in the Chalbi Desert,North Kenya

The Chalbi flat, located 60 km outside the rift to the east, forms a moist, salt-clay encrusted playa which also functions as an inland sink for alluvial fans. Residual lacustrine beds, including freshwater carbonates and travertines, crop out along its higher periphery. Mammalian bones of lacustrine and terrestrial elements, and K/Ar dating of the capping lava suggest a lake or a swamp environment 2–2.5 million years ago. Radiocarbon dating of Melanoides tuberculata and Planorbis and a sediment assemblage composed of clotted micrite, calcareous molds, root marks and stromatolites point to an additional early Holocene Chalbi lake or swamps 11000-9500 yr BP. The data suggest wet environmental conditions outside the rift, which is consistent with the occurrence of a wet period in the early to middle Holocene in intertropical Africa, but out of phase with the climatic conditions in Sinai and Israel and with the high-latitude maximum lake levels and glacier advance. These relations have probably been caused by migration of climatic belts.     

Sea-level changes,coastal dune building and sand drift,North-Western Jutland,Denmark

Christiansen, C. & Bowman, D.: Sea-level changes, coastal dune building and sand drift, North-Western Jutland, Denmark. Geografisk Tidsskrift 86: 28–31. Copenhagen, June 1986.

Two main models linking dune building and sea level changes have so far been proposed. Application of the low sea level model suggests that the major Danish dune building period from 1550 to 1750 need not necessarily be the result of human activity. The dune building period is probably related to a low sea level and the reworking of exposed shallow marine sand.     

Developing coastal adaptation to climate change in the New York City infrastructure-shed: process, approach, tools, and strategies

While current rates of sea level rise and associated coastal flooding in the New York City region appear to be manageable by stakeholders responsible for communications, energy, transportation, and water infrastructure, projections for sea level rise and associated flooding in the future, especially those associated with rapid icemelt of the Greenland and West Antarctic Icesheets, may be outside the range of current capacity because extreme events might cause flooding beyond today??s planning and preparedness regimes. This paper describes the comprehensive process, approach, and tools for adaptation developed by the New York City Panel on Climate Change (NPCC) in conjunction with the region??s stakeholders who manage its critical infrastructure, much of which lies near the coast. It presents the adaptation framework and the sea-level rise and storm projections related to coastal risks developed through the stakeholder process. Climate change adaptation planning in New York City is characterized by a multi-jurisdictional stakeholder?Cscientist process, state-of-the-art scientific projections and mapping, and development of adaptation strategies based on a risk-management approach.     

The philosophy,design and applications of the New South Wales geological survey's metallogenic mapping programs

The metallogenic mapping program of the Geological Survey, Department of Mines, New South Wales has two aims, to provide an inventory of information on all known mineral deposits in New South Wales, and to enable the recognition and delineation of metallogenic districts and provinces.

Each deposit is described on a standardized data sheet. Selected information is symbolized on a coloured geological or tectonic background map at a scale of 1:250 000. This scale is considered to be suitable for locating deposits in the field and at the same time gives an impression of the regional distribution of deposits. The tectonic map is constructed using a plate tectonic model.

Each map is accompanied by interpretative notes which are not of standard form but in which one of three approaches may be adopted: an interpretation according to the geological association, the delineating of groupings of deposits in structural zones, and the recognition of metallogenic units based on a plate tectonic model. In many, but not all cases, mineral districts were first delineated before the above approaches were adopted.

The New South Wales Geological Survey's metallogenic maps may be used to develop concepts in ore genesis, and prognostic concepts for exploration. They assist in understanding the relationships between tectonic process and the concentration of ore minerals. They are valuable in land use and resource management studies.     

The 1988 Tennant Creek,northern territory,earthquakes: A synthesis

Three large earthquakes with surface‐wave magnitudes 6.3–6.7 on 22 January 1988 were associated with 32 km of surface faulting on two main scarps 30 km southwest of Tennant Creek in the Northern Territory. These events provide an excellent opportunity to study the mechanics of midplate earthquakes because of the abundance of geological and geophysical data in the area, the proximity of the Warramunga seismic array and the ease of access to the fault zone. The 1988 earthquakes were located in the North Australian Craton in an area that had no history of moderate or large earthquakes before 1986. Additionally, no smaller earthquakes from the fault zone were identified at the Warramunga array, which is situated only 30 km from the nearest scarp, between the 1965 installation of the array and 1986. The main shocks were preceded by a swarm of moderatesized (magnitude 4–5) earthquakes in January 1987 and many smaller aftershocks throughout 1987. Careful relocation of all teleseismically recorded earthquakes from the fault zone shows that the 1987 activity was concentrated in an area only 6 km across in the gap between the two main fault scarps. The main shocks also nucleated in the centre of the fault zone near the 1987 activity. Field observations of scarp morphology indicate that the scarp is divided into three segments, each showing primarily reverse faulting. However, whereas the western and eastern segments show movement of the southern block over the northern, the central scarp segment shows the opposite, with the northern block thrust over the southern block.

Analysis of the first arrival times at Warramunga suggests that the three main shocks were associated with the western, central and eastern scarp segments, respectively. The locations of aftershocks determined using data from temporary seismograph arrays in the epicentral area define three inclined zones of activity that are interpreted as fault planes. In the western and eastern portions of the aftershock zone, these concentrations of activity dip to the south at 45° and 35°, respectively, but in the central section the aftershock zone dips to the north at 55°. Focal mechanisms derived from modelling broadband teleseismic data show thrust and oblique thrust faulting for the three main shocks. The first event ruptured unilaterally up and to the northwest on the westernmost fault segment, while the third main shock ruptured horizontally to the southeast. Modelling of repeat levelling data from the epicentral area requires at least three distinct fault planes, with the eastern and western planes dipping to the south and the central plane dipping to the north. The combination of scarp morphology, aftershock distribution and elevation data makes a strong case for rupture of fault planes in conjugate orientation during the 22 January 1988 Tennant Creek earthquakes. More than 20000 aftershocks have been recorded at Warramunga and activity continues to the present‐day with occasional shocks felt in the town of Tennant Creek and some recent off‐fault aftershocks located directly under the Warramunga seismic array. Stratigraphic relationships exposed in trenches excavated across the scarps suggest that during the Quaternary, a large earthquake ruptured the surface along one segment of the 1988 scarps.     

The thermospheric semiannual density response to solar EUV heating

The goal of this study was to characterize the thermospheric semiannual density response to solar heating during the last 35 years. Historical radar observational data have been processed with special orbit perturbations on 28 satellites with perigee heights ranging from 200 to 1100 km. Approximately 225,000 very accurate average daily density values at perigee have been obtained for all satellites using orbit energy dissipation rates. The semiannual variation has been found to be extremely variable from year to year. The magnitude of the maximum yearly difference, from the July minimum to the October maximum, is used to characterize the yearly semiannual variability. It has been found that this maximum difference can vary by as much as 100% from one year to the next. A high correlation has been found between this maximum difference and solar EUV data. The semiannual variation for each year has been characterized based on analyses of annual and semiannual cycles, using Fourier analysis, and equations have been developed to characterize this yearly variability. The use of new solar indices in the EUV and FUV wavelengths is shown to very accurately describe the semiannual July minimum phase shifting and the variations in the observed yearly semiannual amplitude.     

Neotectonic Deformation of Pleistocene Deposits Along the Sudetic Marginal Fault,Southwestern Poland

The 160 km long Sudetic Marginal Fault (SMF) of Middle Silesia, southwestern Poland, is a main Alpine fault oriented NW–SE. This paper provides evidence of possible neotectonic activity in front of the SMF. The data are based on three exposures in the Roztoka–Mokrzeszow Graben near the city of Swidnica. Morphotectonic evidence in front of the SMF is also examined. Two sets of extensional deformation features are exposed and analysed. The main one includes gently inclined normal faults and flexures, with displacements in the bedrock of at least several metres. Based on the Quaternary stratigraphy of the region, the age of deformation is most probably Lower Saalian (Upper Pleistocene). The trigger for the deformation was probably the re-reactivation of the SMF and other faults due to the advance of the Lower Saalian Scandinavian ice-sheet into the Sudetic Mountains. The secondary deformation system includes sub-vertical, often conjugate faults with displacements up to 0·5 m superimposed on former structures. Its dominant normal faulting mode suggests an extensional stress regime that apparently coincides with the post-glacial glacioisostatic rebound. © 1997 John Wiley & Sons, Ltd.     

Triple splitting with the F2-region of the ionosphere at high and mid-latitudes

The occurrence of the third (z-ray) component of the F2-trace on ionograms is investigated at high- and mid-latitudes. Diurnal variations show a systematic shift, with magnetic inclination, of the time of maximum occurrence. Seasonal variations show a winter maximum, and an inverse sunspot-cycle relationship exists. Maximum occurrence appears between a magnetic inclination of 70° and 80° with a fall-off either side.

Evidence is presented to suggest a z-ray association with “Spread-F” fronts, and a possible mechanism for the recording of the z-ray trace at the transmitter site is described. This involves longitudinal propagation of the o-mode at its normal reflection level, coupling at this point, and ultimate reflection for the z-ray mode as a result of sloping ionization contours belonging to “Spread-F” fronts extending in directions perpendicular to the magnetic meridian.

An association with V.L.F. emissions (“dawn-chorus”) is discussed.     

Rare earth and other trace elements in historic azorean lavas

Rare earth element (REE) and other trace element compositions of 16 lavas from all historic and 2 prehistoric eruptions on 5 islands of the Azores Archipelago show notable intra-and inter-island differences. Fe enrichment and “compatible” element depletion due to fractional crystallization have been superimposed on variations established in the source area. Fractionation of La/Sm, U/Th, K/Na and “large ion lithophile” (LIL) element abundances are probably related to variable fusion of a source peridotite whose LIL element distribution cannot be exactly specified in view of its possible heterogeneity. Relative light-REE enrichment in basalt appears greatest on the “potassic” island São Miguel, the more sodic island Fayal and one lava from Pico, and least in basalts from the “sodic” islands Terceira, São Jorge and Pico. This variation is matched by most other LIL elements, although P shows unexpected enrichment in Terceira lavas, otherwise the least LIL element-enriched and most heavy-REE-enriched. Upper mantle phase chemistry is probably critical in establishing the patterns. In particular, P—REE covariance may reflect phase stabilities of apatite and (P-bearing) garnet in the upper mantle. Distribution patterns of REE in the historic lavas are similar to those of basalts from the Atlantic median rift at the crest of the Azores “platform”. Transition to light-REE-depleted rift-erupted basalts to the southwest is believed to be step-wise with increasing water depth, possibly indicating retention of a light-REE-rich phase in the residue from partial fusion as intersection of geotherm and peridotite solidus occur at lower pressures. The source mantle for the Azores basalts is probably light-REE- and LIL element-enriched but we find no evidence so far to suggest its emplacement by thermal “plume” activity.     

Dounreay oil spill: Major implications of a minor incident

Few reports of oil spills on an exposed rocky shore have taken into account the background of natural events and the period over which the possible consequences of pollution and its treatment may come to light. This small incident has served as a cautionary tale, illustrating the pitfalls of instant assessment, and the type of baseline experience required for biological interpretation. It has also underlined the continuing inadequacy of the ecological advice available when treatment decisions have to be made.