Observations by the Pioneer Venus orbiter and many different types of analyses have suggested the possibility of contemporary explosive volcanism on Venus. The rise of volcanic eruption plumes on Venus is reexamined using recent improvements in buoyant plume modeling. The first-order model applied to Venus by previous authors features nonphysical discontinuous solutions for all of the model parameters and lacks internal consistency in the formulation of the governing equations. This makes it difficult to assess the validity of the Venus applications and conclusions derived from these models. The model used here contains several improvements including two corrections to the formulation and a change in the criterion for the transition of the plume from the jet region to the buoyancy-driven region. The model used in earlier works assumed a discontinuous transition between these two regions, resulting in an overestimate of the transition height as well as the maximum plume height. The effect of the transition criterion is magnified on Venus, where the continuous solution appears to have very little dependence on initial vent size. In contrast, the discontinuous solution shows a very strong dependence on initial vent size. The continuous solution used here indicates that plumes on Venus become dominated by buoyancy effects almost immediately above the vent. Use of the discontinuous solution, however, suggests that jets up to 10 km above the vent are possible for the boundary conditions considered. The combined effect of using the older model for conditions on Venus is a 5-8% overestimate of the maximum plume height for vent radii ranging from 20 to 250 m. The influence of latitude and elevation are also explored. For large eruptions on Venus, plumes rising in the Northern Highlands would rise much higher than plumes with identical boundary conditions erupted in the equatorial Lowlands. This is due to the greater stability of the upper atmosphere at higher latitudes and the sharp decrease in atmospheric pressure as a function of altitude. To examine the net effect of all the model assumptions and ambient influences, eruptions are simulated for a range of conditions at Maat Mons and compared with results in the literature. These simulations indicate that for small mass fluxes, the new model predicts smaller plumes than the older model. For larger mass fluxes, however, the new model predicts larger plumes than the older model. Because the Maat Mons summit elevation is already more than 9 km above the mean planetary radius, the reduced atmospheric pressure results in a plume with enough buoyancy to more than compensate for all of the model effects. These results continue to support the possibility that explosive eruptions on Venus may be capable of producing plumes that rise buoyantly to heights detected by the Pioneer Venus orbiter.
Journal of Geophysical Research
- Pub Date:
- August 1999
- Planetology: Solid Surface Planets: Atmospheres-composition and chemistry;
- Planetology: Solid Surface Planets: Volcanism;
- Planetology: Solar System Objects: Venus;
- Volcanology: Planetary volcanism