EMPLACEMENT OF XENOLITH NODULES IN THE KAUPULEHU LAVA FLOW, HUALALAI VOLCANO, HAWAII

The basaltic Kaupulehu 1800-1501 lava flow of Hualalai Volcano, Hawaii contains abundant ultramafic xenoliths. Many of these xenoliths occur as bedded layers of semi-rounded nodules, each thinly coated with a v eneer (typically 1 mm thick) of lava. The nodule beds are analogous to cobble deposits of fluvial sedimentary systems. Although several mech anisms have been proposed for the formation of the nodule beds, it was found that, at more than one locality, the nodule beds are overbank l evee deposits. The geological occurrence of the nodules, certain diagn ostic aspects of the flow morphology and consideration of the inferred emplacement process indicate that the Kaupulehu flow had an exception ally low viscosity on eruption and that the flow of the lava stream wa s extremely rapid, with flow velocities of at least 10 m s(-1) (more t han 40 km h(-1)). This flow is the youngest on Hualalai Volcano and fu ture eruptions of a similar type would pose considerable hazard to lif e as well as property.