Explosive volcanic activity on Venus: The roles of volatile contribution, degassing, and external environment

Abstract

We investigate the conditions that will promote explosive volcanic activity on Venus. Conduit processes were simulated using a steady-state, isothermal, homogeneous flow model in tandem with a degassing model. The response of exit pressure, exit velocity, and degree of volatile exsolution was explored over a range of volatile concentrations (H2O and CO2), magma temperatures, vent altitudes, and conduit geometries relevant to the Venusian environment. We find that the addition of CO2 to an H2O-driven eruption increases the final pressure, velocity, and volume fraction gas. Increasing vent elevation leads to a greater degree of magma fragmentation, due to the decrease in the final pressure at the vent, resulting in a greater likelihood of explosive activity. Increasing the magmatic temperature generates higher final pressures, greater velocities, and lower final volume fraction gas values with a correspondingly lower chance of explosive volcanism. Cross-sectionally smaller, and/or deeper, conduits were more conducive to explosive activity. Model runs show that for an explosive eruption to occur at Scathach Fluctus, at Venus’ mean planetary radius (MPR), 4.5% H2O or 3% H2O with 3% CO2 (from a 25 m radius conduit) would be required to initiate fragmentation; at Ma’at Mons (~9 km above MPR) only ~2% H2O is required. A buoyant plume model was used to investigate plume behaviour. It was found that it was not possible to achieve a buoyant column from a 25 m radius conduit at Scathach Fluctus, but a buoyant column reaching up to ~20 km above the vent could be generated at Ma’at Mons with an H2O concentration of 4.7% (at 1300 K) or a mixed volatile concentration of 3% H2O with 3% CO2 (at 1200 K). We also estimate the flux of volcanic gases to the lower atmosphere of Venus, should explosive volcanism occur. Model results suggest explosive activity at Scathach Fluctus would result in an H2O flux of ~107 kg s−1. Were Scathach Fluctus emplaced in a single event, our model suggests that it may have been emplaced in a period of ~15 days, supplying 1–2×104 Mt H2O to the atmosphere locally. An eruption of this scale might increase local atmospheric H2O abundance by several ppm over an area large enough to be detectable by near-infrared nightside sounding using the 1.18 µm spectral window such as that carried out by the Venus Express/VIRTIS spectrometer. Further interrogation of the VIRTIS dataset is recommended to search for ongoing volcanism on Venus

Pyroclastic flow deposits on Venus as indicators of renewed magmatic activity

“…Even the smaller units mapped here, assuming they were originally up to a few meters thick, imply a substantial total mass of volatiles (concentrations of up to 5% H 2 O or CO 2 ) in the rising magma [ Airey et al ., ] and a chain of vents extending along the fractured terrain [ Glaze et al ., ]. In general, discharges of volatile‐rich magma occur during the early phases of a magma source's interaction with the surface.…”

Why Deep-Water Eruptions Are So Different From Subaerial Eruptions

“…This principle also applies to sub-glacial settings and other planetary bodies with dense atmospheres. For example, on Venus, the atmospheric pressure is 9.2 MPa (Taylor, 2010;Airey et al, 2015), which is equivalent to a depth of ∼1 km in the Earth's oceans.…”

Hot climate inhibits volcanism on Venus: Constraints from rock deformation experiments and argon isotope geochemistry

“…Furthermore, the Martian surface and atmosphere are both very water poor, but we know that the crust on Mars is hydrated (Carr and Head, 2010;. A volatile-rich interior on Venus (or at least a hydrated mantle) could result in explosive volcanism (Thornhill, 1993;Fagents and Wilson, 1995;Glaze et al, 2011;Airey et al, 2015), and some workers have proposed that some morphological units on the Venusian surface are pyroclastic deposits (Campbell and Rogers, 1994;McGill, 2000;Grosfils et al, 2011;Ghail and Wilson, 2013). Therefore, it is difficult to definitively conclude whether the crust and upper mantle on Venus is desiccated or hydrous, and only future missions to Venus can resolve this question.…”