CHARLES DOWNIE Dept. Geology, University of Sheffield, Sheffield, England

CHARLES DOWNIE Dept. Geology, University of Sheffield, Sheffield, England Glaciations of Mount Kilimanjaro, Northeast Tanganyika Abstract: On Kilimanjaro six glacial episodes are glacial features belong to the Fourth Glaciation recognized. At the principal volcanic center of which covered about 150 sq mi. The Little and Kibo these were interrupted by volcanic activity. Recent Glaciations are smaller in extent and post- The smaller volcanic center of Mavvenzi has been Pleistocene. The climatic pattern was probably extinct longer, and the glaciations have been super- similar at all times to that of today, and the thick- imposed. Shira, the lowest of the three volcanoes est and longest glaciers were generally always on in the group, has been only slightly affected by the south and west slopes. Comparison with other glaciation. The successive glacial episodes are glaciated regions in East Africa shows some sim- named the First, Second, Third, Fourth (Main), ilarities, and a similar sequence has been suggested Little, and Recent, of which the Third was the for the East African pluvial periods. most extensive; however, most of the obvious CONTENTS Introduction and acknowledgments 1 2. Details of the section in the Bastionsbach, south- Previous investigations 2 west of Kibo Peak, Mount Kilimanjaro, at Erosional features produced by the glaciers ... 3 13,100 feet showing the moraine of the Depositional features produced by the glaciers . 4 Second Glaciation ........... 8 Relationships between volcanic activity and ice cover 5 Plate Facing Sequence of glaciations on Kibo 6 1. Kibo Peak, Mount Kilimanjaro from the north- Sequence of glaciations on Mawenzi 10 west ................ 6 Sequence of glaciations on Shira 11 2. Kibo Peak, Mount Kilimanjaro from the south- Fourth (Main) Glaciation 11 east ................. 7 General statement 11 3. Moraines of Mount Kilimanjaro, northeast Tan- Main Glaciation on Kibo 11 ganyika ............... 16 Main Glaciation on Mawenzi 13 Little Glaciation 13 Table Recent Glaciation 14 1. Correlation of glaciations on Mount Kiliman- Comparisons and conclusions 14 jaro, northeast Tanganyika 7 References cited 15 2. Altitudes of moraines on Mount Kilimanjaro, Figure northeast Tanganyika 12 1. Cross section along the Machame Escarpment, 3. Comparison of the sequence of glaciations on southwest of Kibo Peak, Mount Kiliman- Mount Kilimanjaro with other Pleistocene jaro, showing the relationships between the sequences 14 moraines and the lava series 8 INTRODUCTION AND since disappeared from all but the last three, ACKNOWLEDGMENTS and on these it is clear that the glaciers have Kilimanjaro, 19,340 feet in height, is the retreated a long way from their maximum ex- highest of the three mountain groups in Africa tent. that still carry glaciers. During the Pleistocene, The climatic contrasts between the past and however, glaciers were present on several East the present indicated by these events on the African mountains, among them Mount mountain tops are more widely reflected in Elgon, the Aberdare Mountains, the Abys- tropical regions by the dwindling and disap- sinian Highlands, Mount Ruwenzori, Mount pearance of large lakes that once existed in the Kenya, and Mount Kilimanjaro. They have area and by other signs of a once heavier, more Geological Society of America Bulletin, v. 75, p. 1-16, 2 figs., 3 pis., January 1964 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/1/1/3416924/i0016-7606-75-1-1.pdf by guest on 30 September 2021 CHARLES DOWNIE—GLACIATIONS OF MT. KILIMANJARO, TANGANYIKA continuous rainfall. There has long been a The author would like to stress that the tendency to equate these pluvial periods with field work on which this paper was based was the glacial periods of Europe, but Flint (1959) done while participating in the Sheffield ex- has pointed out some of the difficulties under- peditions to Kilimanjaro in 1953 and 1957 and lying such a simple assumption. that he is indebted to all the members of these It is even more tempting to correlate the expeditions for assistance in various ways. He African pluvial periods with the period of is particularly grateful to Mr. P. Wilkinson maximum glaciation on the local mountains, for drawing his attention to the occurrence of but so far no direct evidence linking the events striations outside the Main moraines and to on the plains with those on the mountains has Dr. G. P. Leedal for information about the been found; the two areas are invariably separa- glacial deposits north of Kibo. The expeditions ted by long, forest-covered slopes extending up- received financial support from the Govern- ward for many thousands of feet. ment of Tanganyika, the Royal Society, and It was hoped when the expeditions from Shef- the University of Sheffield, and for this the field went to Kilimanjaro in 1953 and 1957 author as a member of the expeditions is very that it would be possible to bridge this gap grateful. using characteristic lava flows to link events on The photographs forming Plates 1 and 2 are the summit with those on the surrounding reproduced by permission of the Air Survey plains. To some extent this has been done. A Division, Ministry of Lands, Forests and Wild- succession of glaciations interspersed with peri- life, Dar-es-Salaam, Tanganyika. ods of volcanic activity has been determined on the mountain top, and many of the lava PREVIOUS INVESTIGATIONS flows have been traced to the plains both to The former great extent of the glaciers on the north, where they pass under the Amboseli Kilimanjaro has been known since the first Lake Beds, and to the south where they meet exploration of Meyer (1900) at the end of the the Pangani River deposits. Unfortunately 19th century. He photographed and recorded these extensive areas of sedimentary deposits large moraines and glacial striae far below the are still imperfectly examined and as far as is glacier snouts and in addition discovered fluvio- known have yielded no fossils or artifacts which glacial sands below lava flows on the west permit correlation with other lacustrine or slopes of Kibo. Early in the present century alluvial beds in East Africa or with any of the Jaeger (1909) saw the moraines southwest of pluvial periods. Kibo and Klute (1920) travelled widely over Nevertheless Kilimanjaro provides much the summit area and published the first accurate additional information about the succession map. On this map he showed many of the large of glaciations in East Africa, and it is considered moraines, recognizing two series, the outer worth-while to record the sequence of events older group and the inner younger group. on the summit in the hope that at some future Others which he found in intermediate posi- date the geology of the surrounding plains tions he interpreted as retreat stadia. will be better known and the correlation be- In 1932 Nilsson published an account of his tween glacial and pluvial periods firmly es- studies of the lacustrine and glacial deposits tablished. of East Africa, in the course of which he In determining the succession of glaciations briefly visited Kilimanjaro. There he examined Kilimanjaro has certain advantages over the in detail the large moraines in the southern other mountains in East Africa. On Mt. valleys of Mawenzi and some smaller moraines Ruwenzori, a horst of Precambrian rocks, and farther west. He summarized the previous on Mt. Kenya, which became extinct before work and recognized a number of stages in the glaciation began, each successive glaciation glaciation which he correlated with the pluvial largely obliterated the evidence for those pre- periods. ceding. Whereas this is true for parts of Kili- The present account is based on two visits manjaro, activity continued at the main Kibo extending over four months during which center and at several small parasitic centers nearly all the mountain above the forest was until Recent time so that glacial deposits have explored. The data collected considerably at many places been protected beneath various amplify those given by Klute (1920) regarding groups of lava flows; consequently, a greater the distribution of moraine and also amplify the number of glacial episodes are distinguished sequence of glaciations deduced by Nilsson than on any of the other East African moun- (1932). Many additional occurrences of glacial tains. deposits among the lava flows have been dis- Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/1/1/3416924/i0016-7606-75-1-1.pdf by guest on 30 September 2021 PREVIOUS INVESTIGATIONS covered and placed in relationship to the lava fined but short and extend only for about a succession. It was also observed that the ice is mile from the caldera edge. Excellent examples still retreating and has receded a long way from are found on the south and west slopes of Kibo, its position when Meyer first visited the glacier probably the finest on the mountain being the snouts, but these recent changes will not be 500-foot-deep trough of the upper Garanga discussed in this account. Tal. In contrast, on the north and west slopes The work of these expeditions has not yet of Kibo the valleys seldom exceed 200 feet in been published in full. Preliminary reports of depth, and none can be described as U-shaped. the first expedition have been published by That this contrast is mostly due to fresh lava Wilcockson (1956) and Downie and others flows continuing until fairly recently is shown (1956). Subsequent discoveries necessitate by the presence on the northern slopes of Ma- some modification of these reports but not in wenzi of well-marked U-shaped valleys. These any way that substantially affects this paper. are somewhat shallower than the main valleys on the south slopes, and it appears that the EROSIONAL FEATURES PRODUCED thickness of the ice was greater on the southern BY THE GLACIERS slopes.

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