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Travels & Troubles in Geology: Africa

The views expressed are those of the author and are not necessarily those of Scientific American.


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We locked the doors, armed for a fight with gun, knife and hammers, …[]. The expectation for an adventure and the fleas hold us awake for a long time…
Austrian geologist Guido Stache in 1870 describing field work on the borders of the Austro-Hungarian Empire

Summer time is also time for holidays and travels – so let us follow some geologist(s) on their travels and expeditions and their experiences, discoveries, joys and troubles of field work.

John “Jack” Walter Gregory was born in London in the year 1864. Already in early years his interest in the natural world and its exploration emerged – during his later career he will visit Europe, Africa, Australia, India, North- and South America, even the remote islands of Spitsbergen. His interest in geology came from the necessity to know where he actually was:

… my attention was first directed to geology in order to understand the geography of the districts through which I rambled, and the, often, apparently erratic course of the rivers … and to understand local topography’.
Gregory in 1906

After graduation he found work at the British Museum for Natural History, where he worked on the collections of rocks, fossil echinoderms and corals.
In October 1892 Gregory was asked if he would join an expedition to East Africa, exploring the area of today Kenya, Ethiopia and Somalia – regions at the time still poorly known or mapped, but geopolitically important.

Gregory however showed interest in the geology of Africa long before this expedition, impressed by the hypothesis of Austrian geologist Eduard Suess. The origins of the mountains and depressions of the African continent were an unexplained geological mystery at the time. Suess summarized in 1891 the results of an expedition to Lake Rudolf by Count Samuel Teleki (de Szek; 1845-1916) and suggested that the valleys crossing East Africa were the results of periodic tectonic movements.

Fig.1. “The Great Rift Valley: some associated fractions are marked by broken lines.” The part of the valley system explored by Gregory in 1892-1893 (located east of Lake Victoria) is today also referred as Gregory Rift (GREGORY 1920).

November 20, 1892 the expedition unloaded 300 tons of equipment in the harbour of Lamu, 110 camels and 40 donkeys were needed to transport the material and 300 soldiers were hired to protect the caravan. Destination of the expedition was Lake Rudolf, a destination that they however would never reach.
Despite the 300 tons of equipment soon problems arouse, there was not enough food to feed all the men. Fever and various diseases spread among the members of the expedition, Gregory was first plagued by ulcers on the legs that immobilized him for weeks and January 17, 1893 he fell sick with malaria. In Mombasa the expedition was officially cancelled.
Gregory, still interested to see for himself the great depressions of East Africa, decided to take advantage of this situation. He was already in Africa and the equipment of the abandoned expedition could still be useful – with the financial help of his family and the British Museum he organized a new expedition. March 23, 1893 the new expedition, comprising this time 41 men, left Mombasa. Gregory’s old peculiarities emerged; he loved to walk alone for miles, collecting specimens of plants, animals and rocks. For most of the time he didn’t sleep at night, sneaking trough the camp controlling if the sentries were on duty.

… the geology was so tempting that I went off alone. By this time the men were accustomed to my going by myself, for I did so whenever the country was safe and the next camping-place easy to find. These solitary rambles were to me the most delightful incidents in the expedition. Free from the bother of the caravan, I could climb a mountain, track a river, visit a neighbouring lake, chase butterflies, and collect plants as careless as a schoolboy.
Gregory in 1896

Fig.2. Geological sketch map of British East Africa (Kenya) showing the locations of Lamu Island, Witu, Mombasa, Lake Baringo and Mount Kenya, all visited by Gregory in 1892 and 1893, plus an outline of the Rift Valley (GREGORY 1896).

The main geological work was carried out from the village of Njemps on the shores of Lake Baringo, where they mapped the geology of the western wall of the Kamasin Scarp. Gregory confirmed Suess interpretation of the tectonic origin of this valley and deduced from the weak erosion seen on the mapped faults that this process must have been very recent. But Gregory recognized also similarities between the geology of the Red Sea and the African Rift Valley and proposed that these landscapes are connected – and the dimensions of this feature surprised him as he had discovered a mayor element of earth’s crust.
Gregory described this discovery in an article published in the journal of the Royal Geographical Society in 1920, where he coined also the modern term of Rift Valley and connected it to tectonic movement of the earth – a controversial hypothesis at the time, when most landscapes were regarded as results of erosion.

For this type of valley I suggested the term Rift Valley, not implying that the whole valley was formed by the two sides being simply pulled apart, but as a breach due to a subsidence between two series of rents.
Gregory in 1920

Fig.3. Section across the Rift Valley (GREGORY 1896), F=faults, Gregory suggested that the faults, forming the characteristic elements in the section of the rift valley, were formed by vertical uplift – apparently also Scar from “Lion King” is singing in an area with active tectonic uplift…

Bibliography:

GREGORY, J. W. (1920): The African rift valleys. The Geographical Journal, Vol. 56 (1): 13-41
GREGORY, J. W. (1896): The Great Rift Valley: being the narrative of a journey to Mount Kenya and Lake Baringo : with some account of the geology, natural history, anthropology and future prospects of British East Africa. John Murray, London: 500
LEAKE, B.E. (2011): The Life and Work of Professor J.W. Gregory FRS (1864-1932). Geological Society Memoir, No. 34: 234

David Bressan About the Author: Freelance geologist dealing with quaternary outcrops interested in the history and the development of geological concepts through time. Follow on Twitter @David_Bressan.

The views expressed are those of the author and are not necessarily those of Scientific American.



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