THE PROBLEM OF LAKE CHAD.

Otago Witness, Issue 2928, 27 April 1910, Page 79

THE PROBLEM OF LAKE CHAD.

THE SHRINKING OF THE SURFACE., Lake Chad presents one of the mosfc puzzling problems in hydrography to b* found in any part of the African Continent—or, indeed,, of the whole world. For several years past private explorers an« Government commissions have reported that the lake, which used to be regarded as a great inland sea, was rapidly drying up an4_ assuming the character of a vast swamp. Native tradition, however, represented the lair as subject to periodical fluctuations, and the question arose whether the shrinkage of recent years was simply the result of one of these fluctuations, or whether it represented a stage in the desiccation-of the Chad region. Other interesting problems have presented themselves for solution. Is Lake Chad the lowest part of the vast plains which extend from its shores on all sides, or are some of the surrounding plains of lower elevation? And is there any truth in the affirmation of the old geographers thai 1 , the waters of this region used to find their way eastwards to the Nile?. Completa answers to these questions have still to bri provided, and the Lake Chad region con-* tinues to offer a fascinating field for re--search to the scientific explorer. But though much remains to be done befora knowledge of the geography of Lake Chadl and the surrounding region is complete, great additions to knowledge on the sub< ject have been made in recent years* British explorers, notably Lieutenant Boyd Alexander, have done their part in investigating the character of the lake region; but it is to the French that the greatest credit is due for activity ht seeking to provide a solution of the blems presented by the lake. An excellent illustration of their zeal was afforded in 1908, at the close of the survey by, an Anglo-French commission 01 the fronn tier extending from the Niger to Lake Chad. On the completion of the survey) the British section of the commission returned home, but the members of the French section, acting under instructions from their Government, remained behind for several months, and carried out a most interesting series of investigations in and around the lake. The results of the French researches were ' laid before the Royal Geographical Society by Captair Tilho, the chief of the French mission, and Lieutenant Mercadier.

Some four years before the mission in 1908 Captain Tilho had visited Lake Chad, and obtained abundant evidence of the shrinkage in the lake .urface. In 1908 he found that in the interval between his two visits the process of shrinkage had) been steadily continued. Where before he had navigated a vast open expanse at water in the northern portio of the lake bed, caravans were crossing over dry land. The central portion of the lake was reduced to a marsh, in which navigation was quite impossible. Only in the southern portion of the lake, around the mouth of the Shari River, wa<? there any consider-, able expanse of open water to be found.. Here in 1908 channels had been opened' up which were formerly impracticable, baH the vegetation had also developed with Temarkable rapidity, so that, except in the immediate vicinity of the mouth of the Shari, navigation was confined to a multitude of narrow channels. It gives some idea" of the great size >f Lake Chad that, restricted as it was in 1908, Captain Tilho found an expanse of open water, about the mouth of the Shari an area roughly equal to that of the department of the Seine. This formed only about one-fiftieth part of the total area oi the lake bed, which Captain Tilbo estimates to be about four-fifths the size ol Belgium. The average depth of the laktf is no more than about sft, and so gentle is the slope of its shores that at times even a strong wind will suffice to submerge or leave bare large areas of the lake bed.. Captain Tilho sees no reason t- suppose that Lake Chad will disappear, an*his view that it is subject to fluctuations in size, governed by some meteorological law which cannot be formulated in the present state of knowledge, finds confirmation in the latest news from Lake Chad, according to which the lake has been rapidly expanding again during the past; year. To the east and north-east of the lake the French exolorers made several •interesting journeys, which resulted in the discovery that to the north-east the ground falls away very slowly, but surely, a point less then 250 miles from Lake Chad being found to be over 200 ft lower than the level of the lake. The researches of the mission could not be carried far enough to enable Captain Tilho to determine the lowest point of the vast plains that stretc away from Lake Chad, or to say definitely whether the lower-lying country once received an overflow of water from the lake. He thinks it not improbable, however, that such was the case, while even to-day some of the waters of Lake Chad which are lost by infiltration may find their wav to the lower-lying areas. The French mission was interesting from other points of view than that of the study of Lake Chad's hydrographical problems. The big game in the neighbourhood of the lake consists principally of the rhinoceros, hippopotamus, elephant, and boar. These animals, like everything else along the lake shores, had been seriously affected bv the shrinkage in ite volume, and had followed the waters of the lake southwards. So rapid had been the cVying up of the northern portion that forge quantities of fish were left behind in muddy pools, where they quicklyi died. The water in the pools became, in tuxa. charged with decomposed matter.

which rendered it poisonous., and the aative cattle perished by hundreds. One of the peculiarities of Lake Chad is the growth in its waters of dense masses of the •nibuch tree, which attains in two years a height oi from eight to nine yards with a diameter of from 12in to 15in. Itdies when the water falis below a certain lev**l or contains too much salt; and its

wood, when dry, is the lightest in the world, its density being ten times less than that of water and two and a-half times less than that of cork. Its lightness was illustrated in a novel manner during Captain Tilho's lecture by the projection on the screen of a photograph of a French baby girl holding with ease a

great log of wood cut from the ambuch tree. Major O'Shea, the chief of the British mission, was present at the lecture, and the exchange .of courtesies which took place testified to the excellent relations between the British and French sections of th£ joint boundary commission.