This is a large, dome-shaped basalt volcano surmounted by a truncated cone and rising to over 3000 m. Apart from the dominant olivine basalts, which pass into basanites, the summit region is essentially trachytic. The trachytes are flow-banded lavas with sanidine microphenocrysts in a matrix of sanidine, aegirine-augite, opaque minerals and riebeckite. Phonolite also occurs. A few cones of scoria, agglomerate and tuff are present, particularly on the lower northern and southern flanks. There are four analyses of basalt and basanite, including trace element and Sr, Nd and Pb isotope data, in Paslick et al. (1995).