Showing papers in "The Geographical Journal in 1959"

Some Recent Geological Deposits in the Egyptian Nile Valley

Abstract: Several years ago G. W. Murray I contributed a discussion to the Geographical Journal which m rked the first successful attempt o sketch the Upper Pleistocen and Holocene climatic history of Egypt in a truly modern fashion. The wealth of personal observations and intimate knowledge of the material described reflected Mr. Murray's long years of experience in Egypt, since 1941 as Director of the Topographi? cal Survey. During the winter of 1958 the present writer collected geological data in Middle and Upper Egypt which adds in some way to our present knowledge of Postglacial climates in that country. Although the Recent, or Holocene, deposits of Egypt form but a minute fraction of the surface area, their significance for the inhabited riverain zone is paramount. Climate and sedimentation must have played as important a role in modelling the geographical environment in ancient times as they do today. For example, it is not at all obvious that the precious Nile alluvium has been distributed and laid down at a uniform rate since the close of the Pleistocene, as is widely supposed. These Holocene deposits in the Nile Valley are of aeolian and fluviatile origin: sand dunes, nilotic mud and wadi deposits. The aeolian deposits.?Wind-borne sediments in the valley are more or less limited to the western margins, particularly between Gebel Deshasha (near Biba) and the monas? tery Deir el-Miharraq by el Qusiya, a stretch of over 80 miles. These sand fields are of considerable hindrance to cultivation. Their development is both complex and interesting, so that it is regrettable that, apart from reference to their existence, little attention has ever been paid to them. Firstly one can speak of an irregular line of marginal valley dunes lying exlusively upon Nile mud to a width of one half to two miles between Deshasha and a point about three miles south of Balansura (west of Abu Qurqas). After a small interruption similar dune fields occur between Tuna el Gebel (west of Mallawi) and Dashlut (west of Dairut), and again between Nazlet Bawit (west of Sanabu) and el-Miharraq. In contrast to the dunes upon the Pleistocene gravels west of the desert margin, these are to a fair extent fixed by vegetation deriving its moisture from the ground-water. Although the fields between Deshasha and Bal? ansura can only be classified with difficulty as generally transversal arrays running paral? lel to the border desert-alluvium, those between Tuna and Dashlut are developed as specific geomorphological forms. Three rows of 10 feet high transversal dunes run NNE.-SSW. while another line abuts the desert in the lee of the Pleistocene gravels. In the Meir area, between Sanabu and Qusiya, two immense longitudinal dunes of four miles in length are blown up in the lee of the steep limestone scarp running NNW.-SSE. All these dunes overlie nilotic sediments and were apparently deposited during the last few centuries. From behind the Black Hills due west of Beni Mazar a chain of NNW.-SSE. longitudinal dunes, generally averaging one or two miles in length, extends over 30 miles across the desert surface to the nummulitic headland a little south of Balansura.

The Movement of Shingle Over the Sea Bed Close Inshore

Abstract: A recent paper in the Journal1 described experiments, carried out early in 1957 in the Orfordness area of S ffolk, into the movements of beach material. These experiments employed an improved version of a technique of radioactive marking first used on shingle at Scolt Head Island, Norfolk, in 1956.2? 3 The present paper describes further work carried out at Orfordness between 6 February and 13 April !959, which employed essentially the same methods for marking and tracing as were used in 1957. This new work was designed to extend and consolidate the information gained in the earlier experiments. Additional data on the extent to which material passed between the sea bed in the offshore zone and the beach were sought. It was hoped also to trace the precise manner in which material moved in and across the estuary of the River Ore. Plate 1 gives an aerial view of the experimental sites.

The Influence of European Contacts on the Landscape of Southern Nigeria

Abstract: IN West Africa, as in many other parts of the world, man's activities have con? siderably modified the landscape. Even before the first contacts with Europe West African cultivators cut down vast areas of forest and replaced it by cropland and fallow. Pastoralists annually set fire to grassland and bush. European inter? vention brought economic changes which are reflected in new attitudes to land, cultivation and stock rearing, and these have produced further landscape modifi? cations. In the French territories the settler with his plantation has introduced landscape elements which are at once obvious in their departure from West African traditions. In the British territories settlers are for the most part lacking, and yet European influences have produced marked changes through the medium of the peasant cultivator and the artisan. Southern Nigeria, with its policy of development through the African peoples themselves, affords several excellent examples.* Southern Nigeria includes politically the Western and Eastern Regions and the Southern Cameroons; for convenience, reference will occasionally be made to neighbouring portions of Northern Nigeria with which it has or has had close economic or social contacts. Before the arrival of European traders in the fifteenth century the peoples of the territories now included in Southern Nigeria had pro? duced a variety of social systems and agricultural practices which were, in part, responses to the different physical environments. The latter are defined broadly in terms of vegetation, soil and moisture distributions in so far as these are significant for man, i.e. the physical environments are "milieux" in the sense used by RichardMolard.1 Relief features produce only local differences except in the extreme east where the range of altitude is much greater. Since the physical factors vary in their significance for man from place to place the environmental boundaries differ in character according to local conditions. In Southern Nigeria two of these bound? aries are defined mainly by vegetation distribution, and one by rainfall distribution, as will be shown below. Due to the modifications by man (with which this paper is concerned) physical environments are not static. The constant cutting and burn? ing of trees, shrubs and grass, the modification of soils by cultivation and pastoralism, all produce changes in the appearance of the landscapes concerned?and even movement of the physical environment boundaries. Keay has pointed, for example, to the degradation of rainforest to savanna on a large scale.2 Two of the following physical environments are based on Keay's "vegetation zones" which it is suggested may be more usefully recognized as broad physical regions of the type defined

Variations of the Ice Margins in East Antarctica

Abstract: Since THE last century, glaciers over most of the earth have been shrinking. A mass of evidence of his trend has been collected by Ahlmann in comprehensive survey of glacier variations,1 while other writers, too numerous to mention, have brought forward proof of recent glacier recessions in Europe, North and South America, Africa, Asia, New Zealand, and the Arctic regions. Since about 1940-50, however, there are signs that the recession has become less general in the Northern Hemisphere and there is some evidence that the temperature rise in the Arctic culminated about 1940.* Glacial recession has been widespread throughout the Arctic and Sub-arctic, and numerous examples have been reported from Alaska, Canada, Iceland, Jan Mayen, Spitsbergen, Franz Josef Land, Novaya Zemlya, Norway, and the outflow glaciers of the Greenland ice cap. It would seem reasonable, then, to consider the possibility of some corresponding process in Antarctica and, indeed, some reports 3 give the im? pression that ice recession was occurring in west Antarctica in 1940. Further reports of recent glacier retreat at Heard Island have been made by several members of the A.N.A.R.E. (Australian National Antarctic Research Expeditions). Against this, how? ever, Schytt4 was able to state that no appreciable thinning of the ice had occurred in Dronning Maud Land for many years prior to 1950. In these circumstances the writer, while working at Mawson with the A.N.A.R.E. during the International Geophysical Year, approached the question of ice margin variations in east Antarctica with an open mind. The studies in this field were divided into two broad categories: an attempt to show whether or not there had been fluctuations of the ice margins during the past century or so, and a search for evidence of changes on a larger time scale, i.e. post-Pleistocene variations. These will be considered in turn.

The Survey of South Georgia, 1951-7

Abstract: "South Georgia willbe remembered as journey's end for a great British polar ex? plorer, Sir Ernest Shackleton; and that alone is enough to assure it of a place in history. His grave, marked by a rectangular headstone of rough granite, lies in the cemetery near the head of King Edward Cove on the south-west side: the Cairn and Cross, a memorial tribute set up by his former comrades, stands on the tussocky nub of Hope Point at the mouth of the Cove on the north-east side. And on a calm clear summer}s day?when the water shows blue and the tussock green, when scree and crag look sandyhot in the sun and the high tops are dazzlingly free of cloud, when perhaps the only proof of latitude and longitude is a wisp of brash ice in the bay and the 'quark' of a penguin?no environment could be more peaceful, and few more beautiful. But that is a misleading impression: the Island is in siesta." The Times, 30 July 1954.

The Influence of Climatic Changes on Animals and Plants

Abstract: Since the middle of the eighteenth century the climate of northern Europe has undergone a change. Several series of temperature recprds from different places show the same trend towards a more maritime climate (Angstrom, 1939; Manley, 1946; Ahlmann, 1949a). Winter temperatures have risen and the difference between summer and winter extremes has been reduced. This effect is clearly seen in Manley's account of the secular variation in running means of temperature for different months in Lancashire, where the January and December values alone show a definite rise. The rise in temperature has been more pronounced at higher lati? tudes. Thus whilst the rise in mean annual temperature between about 1870 and 1940 has been only a fraction of a degree centigrade in Britain (Manley, 1946), mean annual temperatures have increased by nearly one degree in Stockholm (Ahlmann, 1949a) and by nearly two degrees in northern Finland (Keranen, 1944). The rise in winter temperatures shows an even more pronounced trend with lati? tude, the increment amounting to four or five degrees in west Greenland and Spitsbergen (see Rubinstein, 1946; Hesselberg and Birkeland, 1940-4). The greater circulation of warm air into these northern latitudes has been accompanied by the anticipated increase in precipitation. During this same period there has been a general decrease in precipitation and a slight lowering of mean annual temperature over large land masses in lower latitudes (Lysgaard, 1948, 1949). These changes have left their mark on the great natural registers of climate, namely the mountain glaciers, the polar ice and the inland seas. Glaciers advance or recede in response to the difference between their rate of accumulation from snow? fall and their rate of melting in the warmer part of the year. Their size depends, therefore, both upon annual temperature and on precipitation integrated over a very long period. It is well known that a number of glaciers in northern Europe reached their maximum extent some 200 years ago and have since receded at a rate which has tended to increase in recent years (see Ahlmann, 1949b). Photographs of glaciers (e.g. Ahlmann, 1949a) taken from the same place at a time lapse of several decades show how dramatically this shrinkage has taken place. Since precipitation in these regions has, if anything, increased, the glacial recession must be entirely due to the longer and warmer melting season. The temperature of the Arctic Sea has risen, probably as a result of increasing atmospheric circulation causing an intensification of the North Atlantic drift (Smed,

Analysis of Regional Flood Frequency on the Nene and the Great Ouse

Abstract: Although the series of gauging records for British rivers are neither numerous Lnor (with few excepti ns) long, some f them appear adequate fo use n certain kinds of analysis. In particular, a preliminary study of the hydrometric statistics pub? lished in the ' Surface water year-books'1 indicates that flood-flow frequencies can be obtained for a region which includes large parts of two distinct river-systems. The region comprises 1811 square miles, of which 1180 are drained by the Great Ouse above Brownshill Staunch (grid reference 52/369727) and 631 by the Nene above Orton (grid reference 52/166972). Records from nine gauging-stations have been analysed to give the relationships between catchment area and flood-frequency for floods of recurrence-intervals up to 10 years. In this context, the term flood does not necessarily imply a discharge sufficient to inundate the floor of a valley, but merely means a high discharge. The floods discussed here are annual floods, i.e., the highest discharges in individual water years.2 The recurrence-interval is the average interval in which a flood of a given size (in units of discharge) will occur as an annual maximum. Thus the 5-year flood?the flood with a recurrence-interval of 5 years?can be expected to occur as the annual maximum once in a given 5-year period. Since not all the gauging-stations supply continuous records (Table I), it has been necessary to use records of maximum daily discharges; i.e., records of the highest mean daily discharges recorded in single years. Momentary peak discharges would be more to the purpose, but it will be shown that a simple relationship connects maximum daily and momentary peak discharges on the Nene, where a correcting factor can be employed. The techniques of analysis described in what follows are familiar to hydrologists and are standard practice in the U.S. Geological Survey.3 They include (1) the adjust? ment of available records to a base-period by interpolation of missing figures, (2) computation of recurrence-intervals for floods of given magnitudes at each station, (3) testing for homogeneity of records, and (4) graphing of the relationship of catch? ment area to floods of selected recurrence-interval for the region as a whole. 1. Adjustment of records to a base-period.?When some of the series of available records are short or broken (Table I), missing figures can be interpolated. Interpolated values have no reality, but interpolation is useful in making the actual records easy to handle, and is especially convenient when short series include both very high and very low annual floods. As will be shown, adjusted and unadjusted series give almost identical results, so that (in this instance at least) the increased convenience obtained by interpolation is not gained at the expense of accuracy. Interpolation is effected in the following manner: one station, normally a station with an unbroken record for the base-period, is selected as a station of reference; the highest annual discharges recorded at other stations are plotted, year for year, against the corresponding discharges at the station of reference; on each graph a line is drawn

Explorations in Patagonia

Abstract: No one with a taste for strange country can fail to be impressed by the remark? able geography of the Andes of Southern Patagonia: the labyrinth of fjords which split the Chilean coast and bite deep into the mainland; the curiously similar pattern of lakes on the opposite side, many of which, Lagos San Martin and Buenos Aires for example, though lying well to the east of the main range, are drained by rivers flowing through it into the Pacific; the innumerable glaciers which radiate from the central ice caps and thrust their massive fronts into the intricate system of waterways surrounding them. That so much of the region remains unexplored is due almost entirely to its physical difficulties, for during the last sixty years many attempts have been made to penetrate it. Most parts of the main range, even on the eastern side, can only be reached by amphibious operations which are liable to be rendered hazardous by the violent and prolonged storms which prevail. The glaciers in their lower reaches are often so broken and crevassed that it is impossible to travel on them; lateral moraines rarely offer an easy line of approach, and the forest, which covers all but the steepest slopes and extends to an altitude of about 3000 feet, is usually dense, trackless and difficult to negotiate. Except on parts of the ice caps where sledges might possibly be used, back-packing is the only means of transport, and no porters can be hired locally to help with this. But the chief problem is presented by the prolonged periods of rain, the rarity and brevity of spells of fine weather and, above all, the savage wind-storms which sometimes con? tinue for weeks at a stretch, with gusts up to 130 m.p.h. It is these obstacles which have prevented most expeditions from achieving more than a very limited objective or covering more than a very small portion of this very large and exceedingly complex field. The redoubtable Salesian priest, Alberto de Agostini, has been a dominant figure in the exploration of the region. He has led no fewer than twelve expeditions to various parts of it, which have contributed the major part of our knowledge of the main range. A few of the high mountains have been climbed, notably the formidable peak of Fitzroy, the ascent of which was made in 1952 by a French expedition led by Lionel Terray. In 1956 H. W. Tilman and two com? panions crossed the range from the Calvo Fjord to the front of the Moreno Glacier on Lago Argentino. The chief objects of the small expedition which I took to the Patagonian Andes during the 1958/59 season were glaciological and botanical. Geoffrey Bratt, who had been with me in the Karakoram the previous year, shared both the initiative and the organization. He planned to make large-scale surveys of various glacier fronts which would serve as a basis for later observers. We invited John Mercer, who had already been twice to the area in which we proposed to operate, to join the party. He was anxious to continue a line of study on the trees bordering the glaciers, designed to ascertain the dates of successive glacial advances. The Trustees of the British Museum lent us the services of Peter James to make a comprehensive collection of plants and lichens, and furnished a grant of money to cover his expenses. We also invited Peter Miles to join us in Argentina to act as liaison officer and to make col? lections of birds and insects. Besides the British Museum, grants were also received from the Mount Everest Foundation and the Percy Sladen Trust, and surveying