Venus has a famously thick atmosphere, approximately 95 times thicker than Earth’s. It also has volcanos. So if a volcano erupted, would there be a plume or would everything just travel along the surface?
The solid components of the eruption, e.g. ejected magma, would still be ejected, but they wouldn’t be thrown as far as on Earth because atmospheric drag would be much higher. The gaseous components of the plume would rise only if they’re lighter than the atmosphere of Venus, which is almost entirely carbon dioxide. Assuming the gases to be of the same composition as on Earth, the plume would actually rise higher than on Earth because the relative density of the gas compared to the surrounding atmosphere would be lower.
Wouldn’t that also apply to the ash and stuff? I get what you’re saying about drag, but any particles that DO make it up into the atmosphere should take much longer to drift down, no?
A very rough analogy to a Venus volcano would be an Earth underwater volcano.
Eruptions on Earth are generally categorized as more “oozing” or more “explosive”. Those are my terms, but you get the idea. See here for lots more on this: Types of volcanic eruptions - Wikipedia.
It seems the OP is considering mostly the explosive sort.
Yes. Terminal velocity of an object falling through an atmosphere scales with the square root of fluid density. Atmospheric pressure on the surface of Venus is about 92 times that of Earth, and CO2 has a density about 1.5 times that of air when at earth-surface conditions. So the density of the Venusian atmosphere is about 138 times that of Earth. With a density ratio of 1/138, ash on Venus would fall about (1/138)^0.5 = 0.085 times as fast as on Earth (8.5%).
According to Wikipedia, there are very strong winds on Venus. All in all, it seems like atmospheric dispersion of a volcanic plume would probably be very substantial.
Although Venus has what appear to be shield volcanoes, there are no cryptodomes or stratovolcanoes present on the surface today, and no apparent plate tectonics which means that any hotspots would be relatively stationary. So, we see no evidence of the kind of violent ejection or high viscosity magma. Even if there were active volcanic vents with sufficient pressure to produce airborne ejecta comparable to what we experience on volcanoes on Earth, the ejecta would actually be not that much hotter than the ambient atmosphere (~740 K), and so the massive updrafts and pyroclastic clouds would not form, and would instead just fall back onto the surface very close to the ejection site. The heat of the atmosphere would make lava less viscous and capable of moving further, and the atmospheric pressure would tend to flatten and prevent the formation of cinder cones.
We know almost nothing for certain about the geological composition of the Venusian surface because of the difficulty of landing or performing direct spectroscopic analysis through the thick atmosphere, but it is assumed to be an alkali and plagioclase feldspar bedrock comparable of that to ancient terrestrial bedrock on Earth, albeit with enhanced non-hydrological chemical weathering and wind erosion, and very little oxidation. The surface is overall pretty flat and from the landers that have made it to the surface, mostly featureless.
Stranger
ETA: @Machine_Elf two posts up. …
At the same time, a given particle of ash or pumice or whatever of size X that exits the Venusian vent at vertical speed Y will experience far more atmospheric drag on the way up than the same X-sized particle exiting a vent at speed Y on Earth. So will not tend to be lofted as high before beginning its descent.
Hence my comment that a volcano erupting explosively into the Venusian atmosphere might have results very similar to the same volcano erupting in a shallow sea on Earth.
I think most of the fine ash that drifts downwind from a volcano doesn’t ascend ballistically during the eruption. If it’s small/fine enough to descend like snow as it drifts downwind, then it will decelerate quickly after being ejected from the volcano. After that, most of its ascent will be via buoyancy-driven convection - that is, a volcanically hot plume will rise violently because it’s much hotter (and much less dense) than the surrounding atmosphere, and it will drag that fine ash upward with it - even while that ash is falling, at its own turtle-speed terminal velocity, through the rapidly ascending plume.
Agree with that. The fine ash is carried by the convective currents or wind with very little ballistic upward impetus or subsequent gravity-driven sink rate. And the finer the ash the more that’s true. An “ash” particle 100 feet across will feel lots of gravity and relatively little atmospheric drag. Both going up and coming back down.
Conversely, a particle of PM2.5 size will feel almost all atmospheric drag and nearly zero gravity. Both going up, going sideways, and coming back down.
But when the upward-rushing gas column exits the vent into an atmosphere that thick, the inertia of the whole column depletes rapidly before it has traveled very far. Even PM2.5-sized fine ash will not be carried too far aloft.
@Stranger_On_A_Train also pointed out that given the temperature of Venus’s atmosphere, an exiting gas column won’t be all that much hotter than ambient and therefore not nearly as thermally buoyant as those seen on Earth.
All assuming of course, Venus actually had volcanoes. Which, ref Stranger again, to all indications it does not and cannot.
Don’t you hate it when very recent news puts a foot in your mouth?
From that article:
This latest discovery builds on the historic 2023 discovery of images from Magellan’s synthetic aperture radar that revealed changes to a vent associated with the volcano Maat Mons near Venus’ equator. The radar images proved to be the first direct evidence of a recent volcanic eruption on the planet. By comparing Magellan radar images over time, the authors of the 2023 study spotted changes caused by the outflow of molten rock from Venus’ subsurface filling the vent’s crater and spilling down the vent’s slopes.
…
The two locations studied were the volcano Sif Mons in Eistla Regio and the western part of Niobe Planitia, which is home to numerous volcanic features. By analyzing the backscatter data received from both locations in 1990 and again in 1992, the researchers found that radar signal strength increased along certain paths during the later orbits. These changes suggested the formation of new rock, most likely solidified lava from volcanic activity that occurred during that two-year period. But they also considered other possibilities, such as the presence of micro-dunes (formed from windblown sand) and atmospheric effects that could interfere with the radar signal.
These are shield volcanoes in an area where the terrain is indicative of previous volcanic activity.
Stranger
Thanks for the corrections. I read more into the comments upthread than was actually said. D’oh on me!
Venus seemingly has at least one area featuring oozy low volume / low ejection rate shield volcanos. So Hawaiian / Strombolian eruptive types.
But not the sort of violently eruptive Plinian volcanoes I interpreted the OP to be interested in.
The almost total lack of water and any active plate tectonics might suggest that there is less scope for dissolved volatiles in magma compared to here on Earth. So current day volcanic eruptions likely don’t have the preconditions for an explosive event.
Maybe there is still primordial CO2 in the magma but I would expect it is long gone, and without processes to recharge it, no more explosive eruptions.
There were some objects found by a couple of landers that were suggestive of volcanic tufts. So maybe a little bit of an indication of maybe a small amount of explosive processes. But I wouldn’t be betting on it. There is so much we have no clue about.