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Published 1984 | Published
Journal Article Open

Convection experiments in a centrifuge and the generation of plumes in a very viscous fluid


«Plumes» originating from unstable· thermal boundary layers have been proposed to be the preferred mode of small-scale convection in the Earth's mantle. However, doubts have been cast on the validity of the extrapolation from laboratory to mantle-like conditions. In particular, it was feared that inertial effects might be the origin of the observed instabilities. In this paper, experiments are described fbr which inertial effects are negligible. A small aspect-ratio tank filled with a very viscous fluid (Pr = 106) is used to observe the behaviour of convection for Rayleigh numbers up to 6.3 x 10^5. These high values are reached by conducting the experiment in a centrifuge which provides a 130-fold increase in apparent gravity. Rotational effects are small, but cannot be totally dismissed In this geometry thermal boundary layer instabilities are indeed observed, and are found to be very similar to their lower Prandtl number counterparts. It is tentatively concluded that once given a certain degree of «vulnerability», convection can develop «plume»-like instabilities, even when the Prandtl number is infinite. The concept is applied to the earth's mantle and it is speculated that «plumes» could well be the dominant mode of small-scale convection under the lithospheric plates.

Additional Information

© 1984 EGS-Gauthier-Villars. Received August 7, 1983; accepted December 19, 1983. Our thanks go to Don Anderson who made this project come to light We are thankful to John Lee and John Ting for precious help in running the centrifuge. Bill Barber and Nino Victor provided most valuable technical assistance. The differential interferometer was kindly given to one of us (HCN) by its inventor, Maurice Françon. We are grateful to Pierre Bergé and Monique Dubois for exciting discussions, and to Frank Richter for helpful criticisms. We acknowledge valuable discussions with D. J. Tritton, and Greg Houseman who also gave us a preprint of his paper. We are indebted to an anonymous reviewer who made important suggestions and comments that helped put this paper in its present form. This work was supported by the National Aeronautics and Space Administration grant N° NSG-7610. Contribution N° 3953, Division of Geological Sciences, California Institute of Technology, Pasadena, Ca, 91125.

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August 19, 2023
October 18, 2023