 Holocene lava flows are more alkalic than the Pleistocene lava flows and comprise several xenoliths of chromium-spinel lherzolite, spinel clinopyroxenite, and rare ferroan websterite and spinel wehrlite.Xenoliths do not exist in the older lava flows.However, chemical evidence indicates that every lava flow was produced in a similar way by low degrees of piecemeal melting.