Abstract:
In March 1971, seven members of the Woods Hole Oceanographic Institution
were engaged in a multidisciplinary study of Lake Kivu. This expedition represents
part of a long-range program concerned with the structural and hydrographical
settings of the East African Rift Lakes and their relationships to
the Red Sea and the Gulf of Aden Rifts. The program started in May 1963 with
a geophysical study on Lake Malawi (von Herzen and Vacquier, 1967). Several
expeditions of our Institution into the Red Sea and Gulf of Aden area in 1964,
1965 and 1966 (Degens and Ross, 1969) provided detailed geological information
on the "northern" extension of the East African Rift. And finally our study of
last year on Lake Tanganyika c1osed a major gap in the program; it allowed
us to out1ine a model on the evolution of a rift which starts with (i) bulging
of the earth's crust, (ii) block-faulting, (iii) volcanism and hydrothermal
activity, and which has its final stage in (iv) sea floor spreading (Degens
et al. 1971). In the case of Lake Tanganyika, only the second stage of this
evolution series has been reached, i.e. block-faulting. In contrast, the Red
Sea and the Gulf of Aden had already evolved to active sea floor spreading, almost
25 million years ago. Somewhere along the line between Lake Tanganyika
and the Gulf of Aden must lie the "missing link" of this evolution series.
Lake Kivu, almost 100 miles to the north of Lake Tanganyika is situated
at the highest point of the Rift Valley and is surrounded by active volcanoes
and geothermal springs. As recently as 1944, lava flows reached the lake
shore. This lake was therefore, a natural choice to test our hypothesis on
the origin and development of rifts. Furthermore, the occurrence of large
quantities of dissolved gases, e.g., CO2 and methane, represented an interesting
geochemical phenomenon worthwhile to investigate.
