Rift-related volcanic hazards in Tanzania and their mitigation

Abstract

Both the western and eastern branches of the Late Cenozoic East African rift system traverse the country of Tanzania, and historic volcanic eruptive activity has occurred in both branches (e.g., Harkin, 1960; Dawson, 1962). Within Tanzania, Quaternary eruptive centres are located along most of the length of the Eastern (Gregory) rift system, whereas one isolated volcanic province lies along the Western rift system (Fig. 1). Both the Western and Eastern rift valleys and their uplifted rift flanks in Tanzania are seismically active, although earthquakes have been of larger magnitude and more numerous in the Western rift during the last century (e.g., Adams and Ambraseys, this volume; Iranga, this volume). 01 Doinyo Lengai lies within the central part of the Eastern rift between Lakes Natron and Manyara, and is the only active volcano within the Eastern rift system in Tanzania, having been active throughout the years 1880 to 1990 (Dawson, 1962; Nyamweru, 1988) (Fig. 2a). Some of these eruptions have been confined to the northern crater, whereas others distributed considerable volumes of carbonatitic ash over the surrounding countryside. In 1917 vegetation on the mountain was destroyed and ash deposited as far as 72 km away from the volcano (Dawson, 1962).