How long could volcanic plumes persist in the Venus atmosphere?

Is Venus volcanically active today? Resolving the ambiguity surrounding current Venusian volcanism is a primary objective for upcoming missions like EnVision and VERITAS. One potential unambiguous sign of volcanic activity would be the detection of gas plumes from an explosive volcanic eruption. If such plumes exist, their detectability will be limited by dispersion and dilution in the active Venus atmosphere.

To constrain the lifetime of plumes from possible explosive volcanism, we used the Venus Planetary Climate Model to simulate the dispersal of plumes containing water vapour (H₂O), hydrogen chloride (HCl), carbon monoxide (CO), and carbonyl sulphide (OCS) within a three-dimensional atmospheric environment. We model localised gas enhancements at altitudes probed by nightside spectral windows (8.62, 20.91, and 35.45 km above surface).

Figure 1: Localised enhancements in trace gas species caused by a simulated volcanic plume

Our results indicate that plumes persist longest in the deep atmosphere (8.62 km) at equatorial latitudes, where H₂O enhancements remain distinguishable from low background variability for up to 100 hours, forming distinct downstream streaks. In contrast, at 35 km, high intrinsic variability in chemically active species (CO and OCS) driven by atmospheric dynamics obscures plume signatures. While the impact of trace gas enhancements on measured spectra is larger at this altitude, planetary-scale waves induce travelling maxima in CO and OCS abundances which could easily be mistaken for plumes. Chemically inert species (H₂O, HCl) are less intrinsically variable, but disperse within 0.5-2 Earth days due to the relatively high wind speeds at 35 km.

We perform sensitivity tests with trace gas increases of 50%, 40%, 30%, 20%, 10%, and 3% above background levels. Higher enhancements, simulating bigger eruptions, take longer to disperse, but qualitative findings that plume lifetimes are longer at lower latitudes and altitudes and for chemically inert gases are largely consistent across simulations. We conclude that observing inert gases, in particular H₂O, at low altitudes and latitudes offers the best opportunity for successful plume detection. Even in the best case scenario, however, plume lifetimes in our study reach a maximum of only a few days. These results should be taken into consideration when planning observation strategies and interpreting potential observations of variability in trace gas species.

Figure 2: Maximum persistence time of water vapour plume enhancements for five different increases (50%, 40%, 30%, 20%, 10%, and 3% above background level) and three altitudes (8.62 km, 20.91 km, 35.45 km).