Source: Dissertation Abstracts International, Volume: 54-06, Section: B, page: 2959.

Adviser: Neil Ribe.

The interaction of a viscous, buoyant, deformable drop with a fluid surface is applied to mantle convection problems. First, the instantaneous deformation of a spherical drop is considered to study the effect of lateral viscosity variations on mantle convection. Solution for the progressive deformation of a drop approaching the fluid surface is then used to model mantle plumes, with particular application to Venus.

The effects of lateral viscosity variations on mantle convection are modeled by solving analytically for the motion of an instantaneously deforming, buoyant drop near a fluid surface. The high viscosity of a shallow load can increase topography by as much as a factor of five. The effects of lateral viscosity variations decrease with load depth. The model also indicates that 'slabs' approaching a high viscosity lower mantle should be mostly in down dip compression, and that this does not indicate that they are unable to penetrate into the lower mantle.

The progressive deformation of a buoyant drop as it approaches and spreads laterally below a fluid surface is calculated numerically using the boundary integral method. The solutions are used to model evolving volcanic features which result from the encounter of a plume head with a planet surface. Early stages produce dome shaped topography, large geoid to topography ratio (GTR), and radial extensional deformation. After plume spreading, plateau-like topography, low GTR, and concentric deformational features evolve. Comparison of model results with data indicates that the Venus highlands can be produced by plume heads which started with radii of about 500 km, and are now in various stages of spreading. Smaller scale plumes may produce features such as the novae, with coronae evolving as the plumes spread.

After the spreading drop has become thin, asymptotic solutions can be used to approximate its motion. Three solutions are derived for different values of the drop's viscosity contrast relative to its aspect ratio. Slender body theory, lubrication theory, and 'stiff' drop theory are used to solve for the spreading of drops with low, intermediate, and high viscosity contrasts respectively.