Moussa Alli (Musa Alli)

Moussa Alli is a large strata volcano nearly 1500 m in height and 25 km in diameter the eastern part of which is in Djibouti. There is a large, complex caldera on the upper part of the volcano. The earliest flows were of basalt and hawaiite and these were followed by mugearite, trachyte and rhyolite. There followed the caldera-forming event which was post-dated by development of trachytic and rhyolitic domes and finally by emission of alkali olivine basalt flows, frequently ankaramitic, from numerous small centres. Eleven rock analyses (Fino et al., 1973) indicate the volcanic series to be slightly alkaline with a little normative acmite in rhyolites. Trachytes contain phenocrysts of green pyroxene, anorthoclase and fayalite. A further suite of analyses is in Piguet and Vellutini (1991).