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Impact of reduced near-field entrainment of overpressured volcanic jets on plume development

Journal of Geophysical Research

By:
, , ,
DOI: 10.1029/2011JB008862

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Abstract

Volcanic plumes are often studied using one-dimensional analytical models, which use an empirical entrainment ratio to close the equations. Although this ratio is typically treated as constant, its value near the vent is significantly reduced due to flow development and overpressured conditions. To improve the accuracy of these models, a series of experiments was performed using particle image velocimetry, a high-accuracy, full-field velocity measurement technique. Experiments considered a high-speed jet with Reynolds numbers up to 467,000 and exit pressures up to 2.93 times atmospheric. Exit gas densities were also varied from 0.18 to 1.4 times that of air. The measured velocity was integrated to determine entrainment directly. For jets with exit pressures near atmospheric, entrainment was approximately 30% less than the fully developed level at 20 diameters from the exit. At pressures nearly three times that of the atmosphere, entrainment was 60% less. These results were introduced into Plumeria, a one-dimensional plume model, to examine the impact of reduced entrainment. The maximum column height was only slightly modified, but the critical radius for collapse was significantly reduced, decreasing by nearly a factor of two at moderate eruptive pressures.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Impact of reduced near-field entrainment of overpressured volcanic jets on plume development
Series title:
Journal of Geophysical Research
DOI:
10.1029/2011JB008862
Volume
117
Issue:
B05209
Year Published:
2012
Language:
English
Publisher:
American Geophysical Union
Publisher location:
Washington, D.C.
Contributing office(s):
Cascades Volcano Observatory
Description:
13 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Number of Pages:
13
Country:
United States