THE DYNAMICS OF RAPIDLY EMPLACED TERRESTRIAL LAVA FLOWS AND IMPLICATIONS FOR PLANETARY VOLCANISM

The Kaupulehu 1800-1801 lava flow of Hualalai volcano and the 1823 Kea iwa flow from the Great Crack of the Kilauea southwest rift zone had c ertain unusual and possibly unique properties for terrestrial basaltic lava flows. Both flows apparently had very low viscosities, high effu sion rates, and uncommonly rapid rates of advance. Ultramafic xenolith nodules in the 1801 flow form stacks of cobbles with lava rinds of on ly millimeter thicknesses. The velocity of the lava stream in the 1801 flow was extremely high, at least 10 m s(-1) (more than 40 km h(-1)). Observations and geological evidence suggest similarly high velocitie s for the 1823 flow. The unusual eruption conditions that produced the se lava flows suggest a floodlike mode of emplacement unlike that of m ost other present-day flows. Although considerable effort has gone int o understanding the viscous fluid dynamics and thermal processes that often occur in basaltic flows, the unusual conditions prevalent for th e Kaupulehu and Keaiwa flows necessitate different modeling considerat ions. We propose an elementary flood model for this type of lava empla cement and show that it produces consistent agreement with the overall dimensions of the flow, channel sizes, and other supporting field evi dence. The reconstructed dynamics of these rapidly emplaced terrestria l lava flows provide significant insights about the nature of these er uptions and their analogs in planetary volcanism.