New evidence of volcanic activity on Venus

30 year old images have been reanalysed, and might show a lava flow.
17 March 2023

Interview with 

David Rothery, Open University


global view of the surface of Venus


Despite Venus being as close to us as Mars, much less is known about its surface and inner workings. That’s because Venus is a very hostile environment. The atmosphere is 100 times thicker than Earth’s, which makes peering through the gloom and studying the surface with satellites very difficult, and the high temperatures - hot enough to melt lead on the surface - also mean that most probes cook: the longest any man-made structure has lasted on Venus is two hours! But now, by revisiting 30 year old images of the surface of Venus, scientists from Alaska Fairbanks University have discovered two photos taken 8 months apart that show an apparent lava flow coming out from one of Venus’ volcanoes. So how much light does this shed on how Venus operates? Will Tingle asked Open University planetary geologist David Rothery to take a look at the findings for him…

David - I've lost track of how many times active volcanism has been "discovered" on Venus. And this was just another attempt to see if anything had changed in an eight month period that was possible by the repeated imagery. Venus' surface is clearly young. There are plenty of places where lots of lava flows and volcanoes and it's not been blasted to smithereens by impact craters coming in. It's clearly a young surface, but how young? This has been a debate and if it's all relatively young, surely some of it should still be erupting today.? After all, the Earth, same size, mass and density as Venus, has got plenty of active volcanoes.

Will  -Purely for the listeners at home, not me at all, do volcanoes work the same way on Venus as they do on Earth?

David - Well, Venus is Earth-like in terms of its gravity, size, mass and density, so you're melting the same kind of stuff. It's got a much denser atmosphere, 90 times denser than ours, and also a much hotter surface, about 400 Celsius all the time. So if molten rocks rise to the surface and start to spread out like a lava flow, they'll cool down slower than they will on the Earth. If the rocks erupt explosively, which is hard to do because there's a denser atmosphere confining the volcanic gases, but if they do erupt explosively, you can get a sustained eruption column with convection going on, but it won't reach as high as it would on the Earth. But you can get convecting eruption columns like you get on volcanoes in Indonesia lately, for example, where there have been eruption columns on volcanoes. So, many of the processes, volcanologically, on Venus are very similar to Earth and more similar to Earth than on an atmosphere-less body like Mercury, or a body with very little atmosphere like Mars. So Venus is going to be the best analogue elsewhere in our solar system for finding volcanic processes that in all stages look very similar to Earth's.

Will - What does this apparent volcanic activity signify about the planet?

David - Well Venus, although it's the same size mass and density as the Earth, is behaving perplexingly differently. Earth gets most of its heat out through plate tectonics, warm stuff rises at mid-ocean, cools down, forms an oceanic plate, which then disappears below the continents at the subduction zone like the ring of fire around the Pacific. And those volcanoes are an indirect manifestation of plate tectonics. It doesn't work that way on Venus. We don't have young plates forming and cold plates descending. As far as we can see, all the heat is either getting out through just conduction or through hotspots where the volcanoes are operating. Finding out the balance of how this is happening and whether it goes on at a steady state on Venus, or whether it's episodic. There was a theory, a decade or so ago, that Venus had some rigid lid which kept all the heat in and then every few hundred million years it overturned in a vast orgy of global resurfacing that would be very catastrophic and that's gone out of fashion now and people are saying no, it probably erupts here and it erupts there and we have to use a special pleading to understand why they can't see particularly young regions and particularly old regions manifested by the number of impact craters they can count. So it's not well understood. So there are some very important differences between the global heat transport outwards on Venus and the global heat transport outwards on the earth. And it's understanding why these two planets, which should be the same but aren't, are so different and yet so similar. That's the fascination of doing volcanology on Venus.

Will - So by better understanding what's going on in terms of the volcanic activity, we might be able to get a better look at what's going on under the hood as it were?

David - Absolutely looking under Venus' hood. That's a good strapline for a talk. I might try and nick that one

Will - It's all yours. So what's next then? As you say, there's a few more flights going past Venus. Are they hoping to shed a bit more light?

David - There are two NASA missions to go to Venus. There's Da Vinci and there's Veritas. There's a European one - Envision. So after many decades of nothing concentrated on Venice's surface, we now have a fleet of spacecraft going there which will peer through the clouds, one will send a descender on a balloon to go through the clouds and see the surface for a while before it cooks and we'll have better radar mapping of the surface. So we're going to understand Venus much better and these exciting hints that have been building up over the past 30 years that there is ongoing volcanic activity, we'll be able to really test those and if in eight years time we don't know for sure whether or not there's volcanic activity on Venus, I'll be very surprised. I think these missions are going to cleans it for us.

Will - Very exciting. Set our watches for eight years time, then?

David - Something like that, yeah.


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