THE GREAT RIFT VALLEY

Rotorua Morning Post, Volume 2, Issue 441, 27 January 1933, Page 7

THE GREAT RIFT VALLEY

IN EASTERN AFRICA NEW ZEALAND'S SOUTHWARD DRIFT. (By Emeritus Professor James Park.) The African Riff Valley ranks as one of the seven geological wonders of the world, but its discovery is so recent that thoi^gh jwell-kpown to geologists, accounts of it are only now finding their way into current literature. Heredotus (445 B.C.), the celebrated Greek historian, had much to say of the mysteries of "The Dark Continent." Be it said that of the wonders of ancient Egypt and Ethiopia, of pigmy meil- and the man-like gorilla, of the rhythmie rise and fall of the life-giving waters of the Nile. of the devouring Sahara and Mountains of the Moon he wrote with restraint and sweet amazement; but of the Rift Valley he knew nothing or of the true nature of physical phenomena, for his vision was limited by the supernatural, wrhich invaded every channel of thought and every activity of life in the Pagan days in which he lived. The progress of modern thought is like a flood that cannot he stayed, and 1 much that puzzled the Greek histor- ! ian is now everyday knowledge. But ! to return to the Rift Valley. In the ■ last century explorers in Central East ■ Africa brought baclc accounts of a j chain of lakes lying in a trough-like j depression that was pimpled with' volcanoes and drained by rivers that did not conform to the rules of wellbehaved rivers are expected to follow. j Armed with a mass of carefully j verified facts, it was left to the fer- j tile brain of the world-famed geolo- j gist, Suess, to formulate the startling , view that these lakes, volcanoes, and : strangely-behaving rivers actually oc- ; curred on the floor of an earth rent, cyclopean in length and width. The late Professor J. W. Gregory ) was not slow to reeognise the vast j importance of this generalisation, and : ip 1893 he travelled into the hinter- I land of the then remote Tanganyika j country — the land of the hostile Ma- | sai — and after some months of ardu- ! ous exploration returned to England j bearing abundant evidence of the ex- ( istence of Suess' hypothetical fault- | trough, which he called by the arrest- j ing name "The Great Rift Valley." j His work created a sensation in the geological world, and thereafter he became distinguished, for his name was now associated with the most famous geologist of modern times. In a second journey to Central East Africa in 1919, Gregory confirmed his earlier work. Before that year and since then many other geologists have traversed the great rift, if not throughout its whole length, at any rate in part, and some have placed their observations on record. Among these observers is Dr. Wayland, of the Uganda Geological Survey, who has made a notable contrihution to the discussion regarding the origin of the rift-trough. The Rift Valley of Central East Africa is a system of meridional rifts extending from the south of Zambesi to the Sudan and Abyssinia,a distance ef many thousand miles. Generally throughout its great length, which dwarfs all other known fault-systems, it is bounded l)y parallel walls that are in most places steep escarpments some 1500 feet in height. The floor, in part rich pastoral plains, in part desert, is broken with volcanoes, old and new, large and small, and dotted with lakes ranging from a few acres to thousands of square miles in area. Notable among the many volcano piles to the south of Lake Edward there rises from the floor a remarkahle chain of volcanoes, ranging from 10,000ft to nearly 15,000ft in height, and running in a transverse row right across the rift-valley from wall to wall. North of Lake Nyassa the rift forks, and its two branches enclose Lake Victoria. There are also many tributary rifts that are divaricating branches of the main rift-system. Many geologists consider there is J good reason for the belief that the I Red Sea and the Gulf of Aden oecupy , a typical rift-depression. From the j northern end of the Red Sea there runs northwards a rift-trough on the course of which lie the Gulf of Akaba, the Dead Sea, the Jordan Valley, and the Sea of Galilee. The Red Sea rift is thought by some to be connected by a diagonal rift with Lake Rudolf, and if this be so, the rift system of Eastern Africa extends in all for 6000 miles, girdling a quarter of the earth's circumference. The Rift Valley, be it said, is not a valley worn down by river erosion, and it has no connection with the existing drainage system of the country. In this we see one of its unique features; and at once the question arises, IIoav was it formed? Once formed, the scarp-walls and the slopes of the volcanoes -that rise from its floor had to submit to the wear and tear of rain and running water. The walls were sculptured and frayed and the floor" piled with rocky material. Two main theories have been advanced to account for the formation of the Rift Valley. It is admitted by all that the escarpment walls lie along two parallel faults. It is also clear that th'e floor before the faultinfe stood at the same level as the sides. That is to say, two parallel cracks app'eared in the peneplane, and either the strip of land between them sank relatively to the crust on each side, or the strip remained stationary or nearly so while the sides were forced upwards. Professor Gregory supported the forrner view. He believed that the rift is a strip that has collapsed. He conceived that by the action of slow compression an arch raised along a meridional arc and that when the elastie limit of the rocks was reached the arch sagged and eventually fell in, forming th'e floor of thq trough. There is now a tendency to break away in some measure from GregoiYs view. In recent years bones of the Dinotherium have been found in deposits laid down by Lake Victoria. This strange creature, which is related to the elephant, existed elsewhere in early Miocene times. Evidently Lake Victoria had already been formed before the Miocene. Th'e contention is that lake and rift had their origin together. Slow faulting continued without arching till the Pleistocene, thus affording additional crustal relief, either by further sinking of the , trough, depression or heightening of

the fault-scarps, whichever view is preferred. The second theory of the origin of the Rift Valley is based on the fascinatin hypothesis of Professor Wegener which postulates that the continents are not fixed but drifting on the ocean of liquid rock generally believed to exist at a considerable depth helow the surface. If free, the continental crusts would tend to drift slowly to the westward on account of the earth's rotation. If one side was free to move, the free bit would crack | and drift off from the!, other. Wegener and his supporters, who | are many and distinguished, find confirmation of their view in the remarkahle correspondence between the east i coast of America and the west coast : of Africa, and in the resemblances j that exist in the late Carboniferous i epoeh between the plants and animals | of South Africa, Southern India, South j America and Australia. They further contend that New Zealand is a bit ! broken off the south-east corner of j Australia, its drift being towards the | Antarctic. i These regions were not connected j by great land-bridges, as some bei lieve, but were all part and parcel ' of a single land mass that cracked in | pieces. In the course of geological j aeons the pieces slowly drifted apart J The connection between Wegener's view and the origin of the African ' Rift Valley is this: The Rift' Valley, he postulates, is a system of crustal cracks that will in time develop1 in length and depth till East Africa and West Africa slowly drift apart as two | sub-eontinents. At first they will be j separated by a narrow sea like the Red Sea. Later an ocean will lie be tween them. It is seen that in the theories that attempt to account for the origini of the African Rift Valley the authors enlist the aid of powerful cracks, and one is tempted to ask what originated the cracks? It may be frankly admitted that nohody knows or is ever likely to lcnow with any degree of certainty. The only course open to the geologist is to speculate on forhat. seem to him to be the probable causes. Cracks may arise from the shrink- , ing apd v/arping of thc crust due to cooling, or from regional expansion oi portions of the deeper material arising from the accumulation of the heat of radio-activity. Evidently faulting and warping are merely an expression oi the throes of the earth's discomfort arising from some internal trouble. Evidence 'of relief of growing pains is the effusion of floods of , lava along the course of major faults , in every corner of the globe. Perhaps the globe is getting tired of the everlasting spinning, and is slowing down. Retardation, we .are i assured by astronomers, would most surely impose powerful stresses on the crust, with consequent deformation; ( so, also, they say, would acceleration. Here again we are at liberty to make our choice of two opposing. postulates.