The dynamics of rapidly emplaced terrestrial lava flows and implications for planetary volcanism

Stephen BalogaProxemy Research, Inc., Laytonsville, MarylandNASA Goddard Space Flight Center, Greenbelt, MarylandPaul D. SpudisLunar and Planetary Institute, Houston, TexasJohn E. GuestUniversity of London Observatory, London, EnglandAbstract. The Kaupulehu 1800-1801 lava flow of Hualalai volcano and the 1823 Keaiwaflow from the Great Crack of the Kilauea southwest rift zone had certain unusual and possiblyunique properties for terrestrial basaltic lava flows. Both flows apparently had very lowviscosities, high effusion rates, and uncommonly rapid rates of advance. Ultramafic xenolithnodules in the 1801 flow form stacl_s of cobbles with lava rinds of only millimeter thicknesses.The velocity of the lava stream in the 1801 flow was extremely high, tit least 10 m s _ (morethan 40 km h l). Observations and geological evidence suggest similarly high velocities for the1823 flow. The unusual eruption conditions that produced these lava flows suggest a floodlikemode of emplacement unlike that of most other present-day flows. Although considerableeffort has gone into understanding the viscous fluid dynamics and thermal processes that oftenoccur in basaltic flows, the unusual conditions prevalent for the Kaupulehu and Keaiwa flowsnecessitate different modeling considerations. We propose an elementary flood model fl)rthis type of lava emplacement and show that it produces consistent agreement with theoverall dimensions of the flow, channel sizes, and other supporting field evidence. Thereconstructed dynamics of these rapidly emplaced terrestrial lava flows provide significantinsights about the nature of these eruptions and their analogs in planetary volcanism.IntroductionThe 1800-1801 eruption of the Hualalai volcano and the1823 eruption of Kilauea volcano provide unique opportunitiesfor investigating the dynamics of rapidly emplaced lava flows.These eruptions featured unusually high rates of dischargecombined with relatively low lava viscosities, conditionsthought to be present in certain planetary settings. The overalldimensions, planimetric forms, and general morphologic char-acteristics of these Hawaiian flows seem to suggest physicalprocesses of emplacement that are usually considered com-monplace in basaltic volcanism, for example, laminar viscousfluid flow, cooling by radiation, incipient crystallization, andthe formation of an insulating surficial crust. However, it haslong been known that these flows are relatively unusual amongterrestrial basaltic eruptions [e.g., Stearns, 1926; Richter andMurata, 1961] in featuring such high volumetric rates of effu-sion and low magma viscosities.More than 50 years ago, Nichols [1939] correctly pointed outthat sufficiently slow-moving lava flows should be treated quan-titatively by laminar viscous fluid dynamics, rather than asemiempirical formalism for turbulent water flow. Nichols alsonoted, in effect, the defining condition for a sufficiently slow-moving laminar flow, namely, that the movement of any ilia-Copyright 1995 by the American Geophysical Union.Paper number 95JB02844.0148-0227/95/95J B-02844505.00ment within the flow is locally parallel to all other filaments.With noteworthy insight, Nichols [1939, p. 294] proclaimed thatinferences about the dynamics of lawl flows "can be deter-mined only if it is known whether the flow was turbulent orlaminar. " A slight overstatement of the case for viscous fluidflow precedes this insightful remark, that "'gravity does notsucceed in making the liquid of low viscosity flow more rapidlythan the more viscous liquid, because the liquid of low viscosityuses up energy in turbulence . " When a free, unconfinedupper surface is present, additional volumetric flow rate canalways be used to increase the mean flow velocity, although thisis not as efficient for turbulent flows. Inferences drawn byNichols for the Alika flow of the 1919 Mauna Loa eruptkm anda distal segment of the McCartys flow in New Mexico includeda laminar flow regime and flow adwmce rates of about 2 m/sand (I.2 m/s, rcspectively.Numcrous works treating lava emplaccmcnt with the con-cept of laminar, viscous tluid flow have appeared since Nichols'publication. With the aid of more detailed observations ofbasaltic lava flow emplacement, wc know today that thc con-cept of laminar flow with all elements moving in parallel iscertainly not always valid. In addition, advancc rates for manybasaltic lava flows havc been significantly greater than thcrange of values infcrrcd by Nichols.Thc classical view of turbulence in fluid flow features statis-tically correlated, timc-dcpcndcnt fluctuations in thc compo-nents of flow velocity. We still cannot make the assertion ofturbulence in lava flows in the classical sense. Howcvcr, pure24,5O9