The Ngauruhoe lava erupted in 1954 is an olivine-bearing basaltic andesite, and belongs to the Taupo volcanic association of basalts, basaltic andesites, pyroxene andesites, dacites, rhyolites, and ignimbrites. This association, as indicated by a variation diagram, is divided into three distinct series: (a) a main basic series, displaying continuous variation from basalts to dacites; (b) a continuous acid series of rhyolites and ignimbrites; and (c) an accumulative series of basalts and basaltic andesites.