A dynamic model for the formation of vesicular zones in ponded lava flows
Thick (>30 m) flows of Columbia River basalt contain internal vesicular zones within otherwise dense, sparsely vesicular basalt. These zones are continuous over distances ranging from 2 to 30 km; most are characterized by abrupt transitions from vesicle-rich to vesicle-poor rock above and by gradational lower margins. The zones were formed by post-emplacement migration, coalescence, and entrapment of aqueous vapor bubbles. Under appropriate physicochemical conditions, bubbles nucleate at the lower solidification front and rise buoyantly until retarded by the higher viscosities preceding the upper solidifications front. Accumulation of bubbles against this ceiling occurs before freezing-in of the vesicles by the downward passage of the upper front. We have developed a one-dimensional dynamic model of the process of vesicular-zone emplacement by starting with the measured distribution of vesicles in a lava flow and calculating their movement according to Stokes' law as the flow is ''melted'' in the reverse of its solidification history. Estimates of the solidification history of the Cohassett flow were based on a previously developed cooling model. Simulated melting of the flow was accomplished by movement of the upper and lower solidification fronts in reverse time. 13 refs., 8 figs.
- Research Organization:
- Pacific Northwest Lab., Richland, WA (USA)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 6392584
- Report Number(s):
- PNL-SA-16268; CONF-881254-1; ON: DE89005226
- Resource Relation:
- Conference: American Geophysical Union fall meeting, San Francisco, CA, USA, 5 Dec 1988; Other Information: Paper copy only, copy does not permit microfiche production
- Country of Publication:
- United States
- Language:
- English
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