Volcanoes on Venus

Venus wears its volcanism on the outside. NASA's summary of the Magellan radar results counts at least 85 percent of the surface as volcanic flows and the rest as highly deformed mountain belts, with no sign of Earth-style plate tectonics, and with no water to wear it down, a lava flow there can keep its shape for hundreds of millions of years. Combing Magellan's global mosaics, Rebecca Hahn and Paul Byrne catalogued about 85,000 volcanic edifices in 2023, some 99 percent of them less than 5 km across. Alexander Basilevsky of the Vernadsky Institute and Wojciech Markiewicz of the Max Planck Institute for Solar System Research (MPS) cite a geological map on which volcanic plains alone cover about 70 percent of the planet. Why expect any of this? Volcanism, the two write, is how a planet sheds surplus heat, and a world almost as large and dense as Earth stored comparable heat when it formed and keeps making more from radioactive potassium, thorium and uranium.

Soviet landers brought rock chemistry into the question. On 22 October 1975 Venera 9 sent back a view of a field of fairly large stones, and NPO Lavochkin drew a bold conclusion: a surface like that cannot be older than about a million to ten million years, so Venus is geologically active. Radioactive-element readings at the Venera 9 and 10 sites matched basalt. At the Venera 13 site the soil sampler found rock close to potassium-rich alkaline basalt, while Venera 14 found far less of the alkali elements. The older Venera 8 result is harder to place: NPO Lavochkin likens its potassium, uranium and thorium to terrestrial granites, while Basilevsky and Markiewicz call the same concentrations slightly above typical basalt and suggest the probe sampled one of the steep-sided domes thought to be made of stickier, non-basaltic lava.

Radar gave the planet a geography. Venera 15 made its first radar survey of the surface on 16 October 1983 and, with Venera 16, mapped the north of the planet into 1984. NPO Lavochkin lists small volcanoes on the plains and enormous ones on the Lakshmi plateau, the caldera Colette with radiating frozen lava flows, a lava flow 300 km long, rings 150 to 600 km across that it calls ovoids, and a terrain it names 'parquet'. O. N. Rzhiga's 1988 book counts cone-shaped volcanoes ten times more common on the plains of Venus than on Earth and records the names that stuck. The rings' Russian name means crown; in English they are coronae. The ridged, criss-crossed ground, which Rzhiga describes as found on no other planet, became tessera, from the Greek for tile.

Magellan, which mapped 98 percent of the surface between 1990 and 1992, showed the volcanoes in detail. Maat Mons, a broad shield, is 395 km across in the IAU gazetteer, centred at 0.5 degrees north, 194.6 degrees east in Atla Regio (NASA's 1992 caption says near 0.9 north, 194.5 east). NASA's caption for its 1992 perspective view puts the summit 8 km above the planet's mean surface and almost 5 km above the surrounding terrain; Basilevsky and Markiewicz give about 9 km above the mean level and call it the highest volcano on Venus, and neither source explains the kilometre between them. Either way the flanks are gentle, like those of Mauna Loa, because fluid basaltic lava spreads before it can pile up. Steep-sided domes, which the two compare with Novarupta in Alaska, imply viscous lava, on Earth usually andesite, dacite or rhyolite, though lava frothed with gas under Venus's heavy atmosphere could also do it.

The craters told a stranger story, the one known as global resurfacing. Gerald Schaber and colleagues catalogued 842 impact craters on the first 89 percent of Venus that Magellan mapped, spread almost uniformly, 62 percent pristine and just 4 percent embayed by lava, and implying an average surface age of about 500 million years. Steady, patchy repaving ought to leave some old craters half drowned, so the team read the pattern as a global event or events that ended about 500 million years ago, after which volcanism declined without stopping. Robert Strom, Schaber and Douglas Dawson, classifying differently in 1994, counted 84 percent pristine and 2.5 percent embayed and argued for a global event about 300 million years ago that ended in under 10 million years, with only about 4 to 6 percent of the planet repaved since.

Roger Phillips and colleagues read the same craters another way in 1992. They could not reject a completely random distribution, yet the embayed and faulted craters clustered where craters were scarce overall, mainly in the Aphrodite volcanic and tectonic zone. Their end-member equilibrium model repaves Venus continuously in small patches, about 1 square kilometre a year on average, and the fit they preferred confines resurfacing to a few regions at a time; Strom's team replied that such models leave at least 17 times more embayed craters than are seen. NASA's Magellan summary still lists sudden against gradual repaving as a major unanswered question. The 2025 review led by Justin Filiberto concludes that the evidence for present activity fits ongoing regional events better than catastrophic models. Basilevsky and Markiewicz, counting craters plain by plain, describe volcanism that ran at about the pace of Earth's mid-ocean ridges for the first fifth of roughly the last billion years, then fell by about two orders of magnitude.

The crust has kept moving in its own fashion. In 2021 Byrne, Richard Ghail and colleagues described lowland crustal blocks that have rotated or slid against one another like jostling pack ice, some after the youngest local plains were laid down, with stresses that mantle convection can supply. Coronae, the rings of the Venera maps, reach 2,600 km across at Artemis Corona and are read as places where hot mantle plumes press on the lithosphere. Anna Gülcher and colleagues reproduced their shapes in 2020 with plumes that drip, briefly subduct or spread beneath the crust, and judged at least 37 large coronae, Artemis among them, to be active. In 2025 Gael Cascioli and colleagues found buoyant mantle material beneath 52 of the 75 coronae that Magellan's gravity field can resolve; VERITAS, they add, would resolve 427.

Tesserae, NASA says, may be the oldest surfaces on the planet, and they are where the argument about water meets the volcanoes. NASA puts them at about 8 percent of the surface, found so far only on Venus: cracked and wrinkled highlands that resemble rugged mountains on Earth. Byrne and colleagues reported in 2020 curved, parallel bands in several tesserae, like terraced layers of stacked lava or sediment on Earth, and called tesserae locally the stratigraphically oldest units preserved. Composition is open. George Hashimoto and colleagues found in Galileo's night-side infrared images that most lowlands seem to emit more efficiently than most highlands, and offered silica-rich, granite-like highland rock as one reading; since large bodies of granite need water, Venus may once have had an ocean. Byrne's layers could be volcanic or sedimentary, so they do not settle it. NASA notes that none of the probes that descended between 1966 and 1985 studied or photographed a tessera; its DAVINCI probe is designed to descend over one, Alpha Regio. The water question continues on Oceans and the greenhouse.

Is Venus volcanically active today? One line of evidence comes from above the clouds. In 1984 Larry Esposito reported that Pioneer Venus had watched sulfur dioxide at the cloud tops, and the haze above them, fall more than tenfold over the spacecraft's first five years. Venus had looked similar in the late 1950s, so he proposed episodic injection, perhaps by eruptions as energetic as Krakatoa's in 1883. Emmanuel Marcq and colleagues then saw another tenfold fall between 2007 and 2012 with the SPICAV spectrometer on Venus Express. Sunlight destroys the gas above the clouds within a couple of days, Marcq told ESA, so any rise means something lifted it recently. His team did not choose between buoyant volcanic plumes and slow swings in the atmospheric circulation needing no volcanism at all. See Pioneer Venus Orbiter, Venus Express and, for the chemistry, Atmosphere of Venus.

A second line comes from heat leaking through the clouds. Near 1 micrometre the atmosphere lets through the infrared glow of the hot ground, and weathering changes how strongly a rock glows. In 2010 Suzanne Smrekar and colleagues used the VIRTIS spectrometer to show that lava flows at three Hawaii-like hotspot rises, Imdr, Themis and Dione Regiones, glow more strongly than their surroundings: too fresh, they argued, for the corrosive atmosphere to have altered them. How fresh is disputed. The paper puts them under 2.5 million years and probably about 250,000 or less, ESA's Italian release a few hundred thousand to 2.5 million, and ESA's later mission summary perhaps a few thousand to a few tens of thousands. Basilevsky and Markiewicz object that those ages come from dividing lava volumes by eruption rates, which measures how long a flow took to build up and leaves open when it erupted. In 2020 Filiberto and colleagues measured olivine weathering under Venus-like conditions and concluded that flows lacking its signature are no more than several years old. The 2025 review names Idunn Mons in Imdr Regio, with Maat Mons and Aramaiti Corona, as the places where combined datasets make the best case. A 2010 microwave study by N. V. Bondarenko, James Head and Mikhail Ivanov adds a flow in Bereghinya Planitia that was still warm, they argue, in 1993, though Basilevsky and Markiewicz note that faulty calibration could explain the excess.

The third line, the Ganis Chasma hotspots, is what the lead author, quoted by ESA in 2015, called the most tantalising evidence yet for active volcanism. A team led by Eugene Shalygin of MPS, including Markiewicz and Basilevsky, took night-side images from the Venus Monitoring Camera on Venus Express through the same window and removed the temperature expected from altitude. Along a young rift near Ozza Mons and Maat Mons they found four transient hotspots. The brightest, Object A, brightened between 22 and 24 June 2008 and had faded by 13 October. Clouds smear each spot over more than 100 km, so size and temperature trade against each other. ESA's release of 18 June 2015 gives about 1 square kilometre at 830 degrees C against a 480 degree average; Basilevsky and Markiewicz, writing in Russian in 2016, give about 1,200 degrees C, fully molten basalt, for about 10 square kilometres, or about 1,000 degrees C for 10,000. A smaller source must be hotter to give the same glow, so those figures sit uneasily together; the 2015 paper's own figures were not accessible for this check. ESA's later mission summary calls the volcanic reading by no means certain.

The rift also has a naming problem. The 2015 paper and ESA's release call it Ganiki Chasma, a name the IAU gazetteer does not contain: the rift is Ganis Chasma, approved in 1982 and centred at 18.0 degrees north, 189.0 degrees east, while Ganiki Planitia is a plain centred at 40.0 degrees north, 202.0 degrees east. Basilevsky and Markiewicz, two of the paper's authors, use the gazetteer name in their Russian review.

Magellan may have caught an eruption itself, though it took three decades to notice: this is the Maat Mons volcanic change. Robert Herrick of the University of Alaska Fairbanks spent about 200 hours comparing images of the same ground from different orbits and found a vent on Maat Mons that changed between February and October 1991. In February it was nearly circular, about 2.2 square kilometres; eight months later it had doubled in size, lost its shape and appeared filled to the rim, apparently by a lava lake. The two images looked from opposite directions, so Herrick and Scott Hensley of JPL modelled the vent in different configurations, testing alternatives such as landslides, and concluded that an eruption best explained the change. JPL's release called it the first direct geological evidence of recent volcanic activity on the surface of Venus. The paper in Science, dated 24 March 2023, is more guarded: flows downhill from the vent appear in the second image, but the authors cannot rule out that they were already there and invisible in the first because of the different geometry.

A year later an Italian team reported two more. Davide Sulcanese, Giuseppe Mitri and Marco Mastrogiuseppe compared radar images from 1990 and 1992 and found flow-shaped areas that had grown brighter on the western flank of Sif Mons, a volcano in Eistla Regio, and in western Niobe Planitia. Having weighed microdunes and atmospheric effects, they read the changes as new lava 3 to 20 metres thick. The paper appeared in Nature Astronomy on 27 May 2024, and Mitri told the Italian news agency ANSA that clues had become certainty. On 22 April 2026 the same journal published a rebuttal by S. S. Bhiravarasu and colleagues, Filiberto among them, arguing that the brightness differences are fully consistent with the different viewing geometries of the two cycles and that new flows are implausible in the local geology. The reply, printed alongside, holds that geometry alone cannot produce coherent bright patterns without a steep, continuous slope the topography does not show. Imperial College London, which co-led the challenge, stressed on 28 April 2026 that its team does not rule out present-day volcanism; this radar evidence, it said, is not definitive. We found no further exchange in print by 4 November 2026.

Why the argument turns on geometry can be seen in Magellan's own archive. Slopes facing the radar look bright and slopes facing away look dark, so the same ground changes appearance with look direction and angle. When bright patches appeared in a second-cycle image of the Imdr region from November 1991, mission scientists repeated the first cycle's geometry in July 1992, tentatively ruled out moving soil and blamed ripples or small dunes that look different from east and west. Magellan's resolution is quoted as better than 100 metres (NSSDCA), about 120 metres (a NASA image caption) or 120 to 280 metres depending on geometry (the Trento team). Basilevsky and Markiewicz, who put the best at 100 to 200 metres, want images at least ten times sharper; the Bhiravarasu team asks for clear changes in shape, change detection built for radar taken under varying conditions, and better topography. Two of its members published such a method with Imperial colleagues in September 2026, tested on simulated lava flows and on Iceland's Holuhraun flow.

The newest Magellan result concerns the plumbing: the Nyx Mons lava tube. On 9 February 2026 Leonardo Carrer, Elena Diana and Lorenzo Bruzzone of the University of Trento reported in Nature Communications that a collapse pit near Nyx Mons opens into an empty conduit. They inverted radar echoes from inside the pit, a skylight where a tube's roof has fallen in, about 110 km west of the gazetteer centre of Nyx Mons. Beneath it they infer a conduit about a kilometre across, followed by the radar for at least 300 metres, with a roof at least 150 metres thick and an empty void at least 375 metres high, each figure uncertain by about 75 metres. The paper says the feature is hypothesised to be a lava tube; the university's release says it has shown for the first time that one exists, and describes the 375 metre figure as a depth. Bruzzone suggests the tunnel may run at least 45 km, which sharper radar would have to confirm.

Akatsuki, for about a decade the only spacecraft orbiting Venus, lost contact at the end of April 2024, and JAXA ended its operations on 18 September 2025; its 1 micrometre camera, IR1, meant partly to check for active volcanoes, had been out of action since December 2016. There should be something to see: in 2022 Byrne and Siddharth Krishnamoorthy scaled Earth's eruption record to Venus and estimated as many as 120 eruptions a year. None of the missions meant to look has launched. In October 2026 the teams were aiming for late December 2030 for DAVINCI and November 2032 for VERITAS, though NASA's mission overview still said no earlier than 2031 (checked 4 November 2026). ESA's pages give November 2031 for EnVision; Ars Technica reported 2032 in September and October, after NASA pulled out of supplying its radar. Basilevsky and Markiewicz ended their 2016 review hoping for Russia's Venera-D.