Dynamics of degassing at Kilauea Volcano, Hawaii
- Univ. Paris 7 (France)
In the volcano chamber, gas bubbles rise through magma and accumulate at the roof in a foam layer. The foam flows toward the conduit, and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit. The bubbles in the foam deform under the action of buoyancy. If the critical thickness is reached, the foam collapses into a large gas pocket which erupts into the conduit. Foam accumulation then resumes, and a new cycle begins. The attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity, suface tension, and bubble size. Hence two different eruption regimes are predicted: (1) alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and (2) steady foam flow at the roof leading to continuous bubbly flow in the conduit. Data on eruption rates and repose times between fountaining phases from the 1969 Mauna Ulu and the 1983-1986 Pu'u O'o eruptions yield constraints on three key variables. The area of the chamber roof must be a few tens of square kilometers, with a minimum value of about 8 km{sup 2}. Magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone. Close to the roof, the gas volume fraction is a few percent, and the gas bubbles have diameters lying between 0.1 and 0.6 mm. These estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts, as well as to the observations on deep submarine basalts. The transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 10{sup 3} kg/s. In this model, changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof.
- OSTI ID:
- 5015181
- Journal Information:
- Journal of Geophysical Research; (United States), Vol. 95:B3; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HAWAII
VOLCANOES
DEGASSING
BUBBLES
DENSITY
DIMENSIONS
FLUID FLOW
FLUID MECHANICS
FOAMS
GEOLOGIC MODELS
MAGMA
MAGMA SYSTEMS
SIZE
SURFACE TENSION
TIME DEPENDENCE
VISCOSITY
VOLUME
COLLOIDS
DEVELOPED COUNTRIES
DISPERSIONS
FEDERAL REGION IX
GEOTHERMAL SYSTEMS
MECHANICS
NORTH AMERICA
PHYSICAL PROPERTIES
SURFACE PROPERTIES
USA
580000* - Geosciences