On the Mechanisms of Lava Flow Emplacement and Volcano Growth: Arenal, Costa Rica

Abstract

Arenal Volcano is composed of a hierarchical series of geologic units: unit flow, composite flow, lava field, and lava armor. Volume-limited unit flows are emplaced at short time intervals to make up composite flows. Composite flows form lava fields, and lava fields in turn, constitute the lava armor (the volcano). Tephra and lava breccias are selectively eroded from the steep slopes of the volcano by heavy rains and contribute little to the actual shape of the cone. This constructive process has important consequences for the distribution of the age of lava on a composite cone. We show that lava of significantly different ages may be juxtaposed at all scales from the unit flow, to the composite flow, to the lava field, and to the lava armor. These relations are applicable to the time sequential sampling of a composite volcano.Detailed observations of the dynamic behavior of unit flows indicate that two dimensionless parameters determine the distribution of lava between an active, flowing component and a passive, stationary component. The first parameter, f, is a measure of how much lava the front uses to advance relative to how much it uses to build up levees. The second parameter, q, is the fraction of lava that is able to drain out of the channel when no more lava from the vent feeds the flow. Both parameters have a primary role in determining the final dimensions of a lava flow. These parameters may be calculated from observations of lava flowing onto different topography and at different times after effusion. This data set may allow the prediction of f and q for future flows, and as a consequence, the final flow length along possible flow paths is also predictable.The development of a thermal structure within the flow plays a critical role in the dynamic evolution of a unit flow. The weight of a cold, highly viscous crust at the surface of the flow actively modifies the stress distribution in the flow and controls the rate of processes such as front velocity, levee formation, and growth of surges. We propose that for a given flux of lava there is a critical channel length beyond which the flow accelerates triggering the separation of the flow from its source near the vent. Thus, the unit flows are volume-limited. Based on this hypothesis we derive a relation for the velocity and position of the flow front at any time after effusion has started, assuming the time functions of f, q, and flow rate are known. We find that the length of a unit flow is directly proportional to f, q, and the flow rate and it is inversely proportional to the cross-sectional area of the channel and to the sine of the slope. These relations also hold for composite flows.Finally, by making the approximation that a composite flow grows to a constant slope we derive equations for the evolution of lava fields and the growth of the volcanic structure. These relations explain the asymmetric distribution, areal extent, and slope of the various lava fields at Arenal and allow us to infer the position of buried craters and contacts. Re...

Numerical modelling of strain in lava tubes

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Risk evaluation, detection and simulation during effusive eruption disasters

“…Following discussions at the European Commission's Joint Research Centre (JRC) during the VALgEO meeting, held at the JRC (Ispra, Italy) in October 2011, the theme grouping was extended to the operational response community. That is, the remote sensing and modelling communities would have to provide products that were Hulme (1974) t 0 u, E r , 1 Rheology and surface morphology Borgia et al (1983) Heat, kinetic and potential energy m, t 0 X, u, 1 Channel-fed flow emplacement Fink (1980) m 1 Flow surface folding Cigolini et al (1984) f, m u , h, w, u Flow velocity profile Park & Iversen (1984) q rad 3 t 0 , m u , h, u Dynamics of Bingham fluid q rad m X, h, u, E r , t Time-dependent flow profile Dragoni et al (1986) m, t 0 u, h, w, u, E r , 1 Velocity profile for laminar flow q rad q adv 3 E r , X Effusion rate and cooling controls on flow area Baloga (1987) m X, h, w, u Lava flow as kinematic wave Moore (1987) t 0 , m u , h, w, u, E r Channel flow and rheological model Baum et al (1989) m u Rhyolite: folds and Taylor instability Dragoni (1989) q rad 3 T, m, t 0 u, h, u, E r , 1 Temperature-dependent rheology and velocity Heslop et al (1989) m, t 0 u, h, w, u, E r , 1 Super-elevated flow Borgia & Linneman (1990) m, t 0 u, X, h, E r , t Channel-fed flow field growth Crisp & Baloga (1990a, b) q rad q adv 3 t Surface thermal structure and q rad Fink & Griffiths (1990) 3 Spreading of crusted viscous-gravity current Oppenheimer (1991) heat budget 3 Flow heat loss model Dragoni et al (1992) q rad 3 T, m, t 0 u, 1 Velocity profile for laminar flow Fink & Griffiths (1992) q conv 3 u, Pe Flow surface morphology Manley (1992) 3 f, m u Silicic flow thermo-rheology model Griffiths & Fink (1993) 3 Effects of surface cooling on the lava spreading Stasiuk et al (1993) 3 Influence of cooling on lava-flow dynamics Crisp & Baloga (1994) q rad , q ent q adv , L 3 f Thermal effects of entrainment and L Dragoni & Tallarico (1994) q rad T, f, m, t 0 u, h, u f-dependent rheology and velocity Keszthelyi (1994) q rad 3 Ra Effect of vesicles on cooling A. HARRIS ET AL. et al (1995) m u , h, w, u, E r , Re High velocity flow Dragoni et al (1995) q cond 3 m, t 0 u, h, u, 1 Roofing over of a channel Keszthelyi (1995) heat...…”

La geomorfología de la colada de Cervantes, volcán Irazú (Costa Rica): Descripción de uno de los campos de lava más grandes de América Central

“…En Arenal, a partir de dos focos eruptivos, se desarrolló entre 1968 y 1974 un campo de lavas Inferior (cráter A) y entre 1975 y finales del 2010 un campo de lava Superior (cráter C). El campo Inferior posee espesores acumulados significativamente mayores de hasta 170 m, y su tasa de efusión fue también más alta, mientras que el campo de lavas Superior fue relativamente más pequeño, con coladas cortas y menos espesas, y una tasa de efusión inferior (Borgia et al, 1998;Borgia & Linneman, 1990;Wadge et al, 2006). Thomas (1983) razonablemente piensa que no pudo solo haber habido un único foco eruptivo para cada campo de lavas en Cervantes, porque el tiempo de erupción habría sido de muchos años; entre 21,9 y 111,8 años para el campo de lava Occidental, por ejemplo.…”