Additional Theory of Origin of Fiamme in Ignimbrites

Abstract

THE pantelleritic Quaternary volcano Fantale (lat. 8° 58′ N., long. 39° 54′ E.) is situated at the northern end of the main Ethiopian rift valley. During a field excursion to this volcano, we made a brief examination of a recent ignimbrite. This pale green ash flow, which was probably erupted in association with the formation of the Fantale Caldera¹, is particularly rich in fiamme. Fiamme are flattened, black, glassy inclusions with flame-like cross sections. These are usually considered to have formed by the collapse of included molten pumice under the load of the overlying portions of the pyroclastic flow². As we shall show, it seems unlikely that the fiamme in the Fantale ignimbrite originated in this way; the purpose of this communication is to suggest an alternative origin.