Eruption dynamics of Hawaiian-style lava fountains
Abstract
Hawaiian-style lava fountains are episodic, not continuous. Existing models view a typical Hawaiian fountain as driven by a sustained, steady-state process. However, eyewitness observations show that, within a single fountain, the height pulsates implicating fluctuations in the fluxes of gas and magma The short-lived but powerful 1959 eruption at Kīlauea Iki contained 17 fountaining episodes and produced a cone and tephra blanket as well as a lava lake which interacted with the vent during all but the first episode of the eruption. We have conducted a detailed investigation of tephra from the episode 1 deposit in order to examine ascent and eruption conditions of Hawaiian lava fountaining. Density measurements (300 to 1600 kg/m3) and vesicularity calculations (42% - 88%) of closely spaced lapilli-sized samples from the episode 1 tephra indicate a wide textural diversity reflecting variability in vesiculation processes. Micro-textures in the least vesicular clasts have polymodal size distributions of bubbles with thick walls, whereas clasts with higher vesicularity offer bimodal distributions of bubbles with thin walls. Modal vesicularity clasts have bi- to poly-modal vesicle size distributions which lie between these two end members as well as exterior macro-textures of frequent occurrences of centimeter-sized bubbles. Early quenched rims of the highest vesicularity clasts have vesicle-number densities approaching 107 cm- 3 which offers a valid approximation to magma conditions immediately at fragmentation. However, modal vesicularity clasts with vesicle-number densities of 106 cm-3 strongly indicate that this number density, represented by the majority of magma driving the eruption, has dropped away from the maximum. Partial bubble loss occurred through the process of coalescence and outgassing during two-phase flow in the conduit. Combining the macro- and micro-textural observations we therefore propose a more complex story for Hawaiian lava fountaining from conduit ascent through to eruption than currently exists within the literature.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.V14A..08S
- Keywords:
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- 8428 Explosive volcanism;
- 8430 Volcanic gases;
- 8434 Magma migration and fragmentation;
- 8499 General or miscellaneous