Bubble growth in highly viscous melts

Theory, experiments, and autoexplosivity of dome lavas

Oded Navon, Anatoly Chekhmir, Vladimir Lyakhovsky

Research output: Contribution to journalArticle

128 Citations (Scopus)

Abstract

We examine the physics of growth of water bubbles in highly viscous melts. During the initial stages, diffusive mass transfer of water into the bubble keeps the internal pressure in the bubbles close to the initial pressure at nucleation. Growth is controlled by melt viscosity and supersaturation pressure and radial growth under constant pressure is approximately exponential. At late stages, internal pressure falls, radial growth decelerates and follows the square-root of time. At this stage it is controlled by diffusion. The time of transition between the two stages is controlled by the decompression, melt viscosity and the Peclet number of the system. The model closely fit experimental data of bubble growth in viscous melts with low water content. Close fit is also obtained for new experiments at high supersaturation, high Peclet numbers, and high, variable viscosity. Near surface, degassed, silicic melts are viscous enough, so that viscosity-controlled growth may last for very long times. Using the model, we demonstrate that bubbles which nucleate shortly before fragmentation cannot grow fast enough to be important during fragmentation. We suggest that tiny bubbles observed in melt pockets between large bubbles in pumice represent a second nucleation event shortly before or after fragmentation. The presence of such bubbles is an indicator of the conditions at fragmentation. The water content of lavas extruded at lava domes is a key factor in their evolution. Melts of low water content (<0.2 wt%) are too viscid and bubbles nucleated in them will not grow to an appreciable size. Bubbles may grow in melts with ~0.4 wt% water. The internal pressure in such bubbles may be preserved for days and the energy stored in the bubbles may be important during the disintegration of dome rocks and the formation of pyroclastic flows.

Original languageEnglish
Pages (from-to)763-776
Number of pages14
JournalEarth and Planetary Science Letters
Volume160
Issue number3-4
DOIs
Publication statusPublished - 1998
Externally publishedYes

Keywords

  • Experimental studies
  • Lava
  • Numerical models
  • Pumice
  • Shield volcanoes
  • Vesicle
  • Vesicular texture
  • Viscosity

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