Composite Lava Flows on Haleakala Volcano, Hawaii

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Composite lava flows of ankaramite and alkalic olivine basalt on the western flank of Haleakala contain abundant phenocrysts of olivine and augite in their upper parts, but are nearly devoid of phenocrysts in their lower parts. They resulted from crystal settling in the magma column below the volcano, followed by eruption first of the phenocryst-poor upper part of the magma, and later the phenocryst-enriched lower part. The latter overrode the earlier lava of the same flow while the flow was still hot and active.