Quaternary glaciation of the Bale Mountains,Ethiopia     

Henry A. Osmaston  Wishart A. Mitchell  J. A. Nigel Osmaston 《第四纪科学杂志》2005,20(6):593-606

Central Ethiopia comprises a high plateau at 2000–3000 m, formed from Tertiary lava flows and bisected by the Eastern African Rift. Ten volcanic mountains rise to altitudes of just over 4000 m, but on only three has Quaternary glaciation been substantiated by published field observations. On the Bale Mountains (4400 m), a previous report based on limited evidence proposed an ice‐cap extending to 600 km². Based on aerial photographs and ground surveys, this paper reports evidence of a more complex situation. A wide spread of large erratic boulders on the plateau records a central ice cap of 30 km², though ice probably extended for a further 40 km². Further north two groups of deeply incised and clearly glaciated valleys contain moraines and roches moutonnées (60 km²). On interfluves between them and on the open north slopes are moraines from an earlier stage of the same glaciation or from a distinct older event. Altogether about 180 km² may have been glaciated. Cores dated by ¹⁴C from inside and outside the glaciated area suggest that at least the northern valley glaciers may date from the Last Glacial Maximum. Estimated equilibrium line altitudes for these glaciers and the ice‐cap are 3750–4230 m. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Inclusion of ice cover in a storm surge model for the Beaufort Sea     

M. B. Danard  M. C. Rasmussen  T. S. Murty  R. F. Henry  Z. Kowalik  S. Venkatesh 《Natural Hazards》1984,2(2):153-171

Storm surges in the Beaufort Sea present a severe problem for navigation as well as for offshore oil drilling activities. Influence of ice cover on storm surges in the Beaufort Sea is examined making use of a numerical model as well as a set of observations.The automated shallow-water model of Henry has been modified to incorporate ice cover and is adapted to the Beaufort Sea. The leading edge of the permanent ice is calculated from the loci of identifiable points. Generalized similarity theory is employed to compute wind stresses. Simulations are made using model-predicted ice concentrations and observed ice concentrations. Ice motion is relatively small in units of model grid distance (approximately 18 km) during surges. Spherical effects are important and should be included in future adaptations of the model. Comparison of the computed surges with observed surges for eight different events showed reasonable agreement.  相似文献   

The Fe xii 195.1 Å/1242 Å emission line ratio in the solar corona     

F. P. Keenan  S. S. Tayal  R. J. W. Henry 《Solar physics》1990,128(1):61-65

Recent R-matrix calculations of electron impact excitation rates in Fe xii are used to derive the theoretical emission line ratio R ₁ = I(195.1 Å)/I(1242 Å), which is potentially a useful electron density diagnostic for the solar inner corona (r 1.05 61-01). These results are found to be significantly different from the earlier estimates of Withbroe and Raymond (1984), but are in good agreement with the observed values of R ₁, for the quiet Sun and an active region. Adoption of the R-matrix atomic data for the 1242 Å line in the coronal iron abundance determination removes an existing discrepancy between results derived from the EUV transition and other iron lines in the solar XUV spectrum. The R-matrix calculations confirm the prediction of Withbroe and Raymond that the earlier discrepancies in R ₁ and the iron abundance were due to the 1242 Å line excitation rates being underestimated by a factor of ~2. Withbroe and Raymond's paper is, therefore, an excellent example of how astronomical observations can be used to accurately predict atomic physics data.  相似文献   

The effects of air transportation on the movement of labor   总被引：1，自引：0，他引：1  

Kenneth John Button  Henry Vega 《GeoJournal》2008,71(1):67-81

The effects of the deregulation of airlines markets and the new technologies that have been introduced into air transportation have been heavily studied. Much of this analysis has been on the impacts on the industry and the immediate welfare implications for passengers and, to a lesser extent, cargo consignors. This study looks at the longer-term effects of the modern air transportation system on labor markets and labor migration. The growth of the service sector, the emergence of more flexible manufacturing techniques, the reduction in trade-barriers, and the creation of more sophisticated financial markets have led to greater mobility in production and in capital movement. This has been explored to some extent. Labor is, however, also more mobile - for example, since the admission of Poland to the European Union some 465,000 Polish workers have joined the UK labor market. Air transportation facilitates easier migration, makes short-term, long-distance migration viable, and allows migrants to maintain contact with their home country. Within larger countries, such as the US, there has also been a growth in long distance “week-day” migration as spouses work in different parts of the country to be reunited at weekends. The study makes use of aggregate data to look at trends in international labor movements particularly concerning the European situation, and, to a lesser extent, at recent developments within the US. It is concerned both with what is going on in terms of the use being made of air transportation by migrants and the light that this may shed on migration theory.

Kenneth John ButtonEmail:

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New palaeomagnetic results from the Kerguelen Islands     

Bernard Henry  Claude Plessard 《Geophysical Journal International》1997,128(1):73-83

New palaeomagnetic analyses have been carried out in the Kerguelen Islands on 32 lava flows of well-established age (20–22 Ma). Combined with previous studies, they yield a reliable pole for the Lower Miocene for the Antarctic plate: N = 59 flows. 349.9°E, 83.5°S, A⁹⁵= 6.1°. A reversal sequence reversed-normal has been identified in the Port Jeanne d'Arc section.  相似文献   

Analytical descriptions of subaqueous groundwater seepage     

Henry J. Bokuniewicz 《Estuaries and Coasts》1992,15(4):458-464

Direct measurements of groundwater seepage show the importance of subaqueous discharges as sources of fresh water and of dissolved chemicals to lakes and the coastal ocean. The rate of seepage decreases rapidly offshore; an analytical solution was developed that describes the discharge as Ki(In(coth πxk/4l))/k where i is the hydraulic gradient, K is the vertical hydraulic conductivity,l is the aquifer thickness, x is the distance from the shoreline, and k² is K divided by the horizontal hydraulic conductivity. In addition to variations due to the inhomogeneities in the aquifer, seepage into the coastal ocean involves some recirculation of the salt water. In Great South Bay, New York measured fluxes were as great as 150 I m^?2 d^?1. The discharge near the shore was typically 50 I m^?2 d^?1, decreasing to 30 1 m^?2 d^?1 at a distance of 100 m offshore. Secondary convection due to an unstable density structure at the sediment-water interface may also be superimposed on the seepage distribution. Fingers of salt should be capable of carrying marine water many decimenters downward against the fresh groundwater advection. As a result, care must be exercised in interpreting direct measures of seepage flux to recognize the contribution of recirculated seawater.  相似文献   

Variability in latent heat flux over the tropical pacific in association with recent two ENSO events     

Fu Congbin  Henry Diaz  Fan Huijun 《大气科学进展》1992,9(3):351-358

This paper analyzed the variations of latent heat flux (LHF) over the tropical Pacific in the period 1978-1988 by using COADS (Comprehensive Ocean and Atmospheric Data Set). It has been founded that the interannual variabili ty of LHF exhibits strong ENSO signal, with the significant increasing LHF during the recent two warm events, i.e., 1982 / 83 and 1986 / 87 and decreasing LHF in the cold episodes. However the longitudinal distribution of the LHF departures varies from event to event. In the eastern Pacific, the specific humidity difference at air-sea interface (qs -qa) makes a dominant contribution to the interannual variability of LHF ( r = 0.73 ), while in the western Pacific the surface wind speed, W and the qs - qa make nearly equal contribution to that of LHF.  相似文献   

Investigations in Kenya and Malawi using as-dug laterite as bases for bituminous surfaced roads     

Henry Grace 《Geotechnical and Geological Engineering》1991,9(3-4):183-195

Summary In Kenya 1974/5 and in Malawi 1984/5 trial sections of bituminous-surfaced low volume roads were constructed using as-dug laterite in place of stone or stabilized material as a base course.The laterite did not conform with any accepted specifications but performed equally well when compared with adjoining sections of road using stone or stabilized material as a base.The construction procedures employed are described. A period of 4–6 weeks between the compaction of the base and its surfacing is considered essential if the road is to perform satisfactorily. During this period it is exposed to the weather and traffic or to periodic watering and rolling. This treatment fills any cracks with dust or mud and closes them by the kneading action of rubber-tyred traffic. The bituminous surfacing is applied where the base has dried out to about half the optimum moisture content and is extended about 1.5 m beyond each edge of the carriageway.In 1984, $40000 US per km was saved in Malawi in this way, approximately 70% being in convertible currency without incurring additional maintenance or vehicle operating costs.  相似文献   

Distinguishing strongly rheomorphic tuffs from extensive silicic lavas   总被引：2，自引：6，他引：2  

Christopher D Henry  John A Wolff 《Bulletin of Volcanology》1992,54(3):171-186

High-temperature silicic volcanic rocks, including strongly rheomorphic tuffs and extensive silicic lavas, have recently been recognized to be abundant in the geologic record. However, their mechanisms of eruption and emplacement are still controversial, and traditional criteria used to distinguish conventional ash-flow tuffs from silicic lavas largely fail to distinguish the high-temperature versions. We suggest the following criteria, ordered in decreasing ease of identification, to distinguish strongly rheomorphic tuffs from extensive silicic lavas: (1) the character of basal deposits; (2) the nature of distal parts of flows; (3) the relationship of units to pre-existing topography; and (4) the type of source. As a result of quenching against the ground, basal deposits best preserve primary features, can be observed in single outcrops, and do not require knowing the full extent of a unit. Lavas commonly develop basal breccias composed of a variety of textural types of the flow in a finer clastic matrix; such deposits are unique to lavas. Because the chilled base of an ashflow tuff generally does not participate in secondary flow, primary pyroclastic features are best preserved there. Massive, flow-banded bases are more consistent with a lava than a pyroclastic origin. Lavas are thick to their margins and have steep, abrupt flow fronts. Ashflow tuffs thin to no more than a few meters at their distal ends, where they generally do not show any secondary flow features. Lavas are stopped by topographic barriers unless the flow is much thicker than the barrier. Ash-flow tuffs moving at even relatively slow velocities can climb over barriers much higher than the resulting deposit. Lavas dominantly erupt from fissures and maintain fairly uniform thicknesses throughout their extents. Tuffs commonly erupt from calderas where they can pond to thicknesses many times those of their outflow deposits. These criteria may also prove effective in distinguishing extensive silicic lavas from a postulated rock type termed lava-like ignimbrite. The latter have characteristics of lavas except for great areal extents, up to many tens of kilometers. These rocks have been interpreted as ash-flow tuffs that formed from low, boiling-over eruption columns, based almost entirely on their great extents and the belief that silicic lavas could not flow such distances. However, we interpret the best known examples of lava-like ignimbrites to be lavas. This interpretation should be tested through additional documentation of their characteristics and research on the boiling-over eruption mechanism and the kinds of deposits it can produce. Flow bands, flow folds, ramps, elongate vesicles, and probably upper breccias occur in both lavas and strongly rheomorphic tuffs and are therefore not diagnostic. Pumice and shards also occur in both tuffs and lavas, although they occur throughout ash-flow tuffs and generally only in marginal breccias of lavas. Dense welding, secondary flow, and intense alteration accompanying crystallization at high temperature commonly obliterate primary textures in both thick, rheomorphic tuffs and thick lavas. High-temperature silicic volcanic rocks are dominantly associated with tholeiitic flood basalts. Extensive silicic lavas could be appropriately termed flood rhyolites.  相似文献   

Cloud Fields Over Irrigated Areas In Southwestern Kansas—Data And Speculations     

G. A. Marotz  J. Clark  J. Henry  R. Standfast 《The Professional geographer》1975,27(4):457-461

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