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Published October 1993 | public
Book Section - Chapter

Experimental simulations of explosive degassing of magma


Explosive flows of strongly gas-supersaturated liquids have been investigated experimentally in two different configurations to simulate conditions in violent volcanic eruptions. i) Decompression of water saturated with dissolved C0_2 at pressures up to 0.7 MPa causes explosive bubble growth and foaming. The large volume increase accelerates the two-phase mixture upward to velocities as large as 14 m/s at nearly constant accelerations up to more than 200 g. Constant acceleration implies that the bubble growth rate is proportional to t^(2/3), measurably larger than the t^(1/2) law expected for diffusive growth of spherical bubbles. ii) Rapid mixing of concentrated K_2CO_3 and HCl solutions generates CO_2 supersaturated to a few MPa. In this case, reaction and degassing generate an increasingly accelerating flow until the reactants become depleted at peak accelerations of about 100g and velocities up to 45 m/s. In both experiments the rapid expansion causes the foam to fragment into a heterogeneous spray. The experimental flows are comparable to explosive volcanic flows in terms of decompression ratio, velocities, accelerations and in the large range of scales present. The large accelerations cause strong extensional strain and longitudinal deformation of the foam. Tube pumice is a major component of Plinian deposits and ignimbrites, and preserves evidence of these flow conditions.

Additional Information

"The International Seminar ... was held ... under the sponsorship of the Japan Society for the Promotion of Science (JSPS) and the Fujihara Foundation of Science (FFS)"--Preface. This work was supported by the National Environmental Research Council. (U.K.), B.P. Venture Fund, the California Institute of Technology and the University of Michigan.

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