The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a pressure that is 90 times that of Earth's atmosphere.
There are over 80,000 volcanoes on Venus detected through radar mapping. For many years scientists debated on whether Venus was currently active or if the volcanic structures were remnants from the past. There are few impact craters on Venus's surface which pointed to relatively recent resurfacing. The most likely resurfacing event would have been volcanic flows. Radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank. Although many lines of evidence such as this suggest that volcanoes on Venus have been recently active, present-day eruptions at Maat Mons have not been confirmed. Nevertheless, other more recent studies, in 2020, suggest that Venus, though not Maat Mons specifically, is indeed currently volcanically active. In 2023, scientists reexamined topographical images of the Maat Mons region taken by the Magellan orbiter. Using computer simulations they determined that the topography had changed during an 8-month interval, and have concluded that active volcanism was the cause. Until 2023, there had only been hints of active volcanism. In March 2023, Herrick et al. announced that they had imaged a vent expanding in Magellan images, indicating active volcanism on Venus.
Types of volcanoes
Venus has shield volcanoes, widespread lava flows and some unusual volcanoes called pancake domes and "tick-like" structures which are not present on Earth. Pancake dome volcanoes are up to in diameter and less than in height and are 100 times larger than lava domes formed on Earth. They are usually associated with coronae and tesserae (large regions of highly deformed terrain, folded and fractured in two or three dimensions, which are unique to Venus). The pancakes are thought to be formed by highly viscous, silica-rich lava erupting under Venus's high atmospheric pressure.
The "tick-like" structures are called scalloped margin domes. They are commonly called ticks because they appear as domes with numerous legs. They are thought to have undergone mass wasting events such as landslides on their margins. Sometimes deposits of debris can be seen scattered around them.
On Earth, volcanoes are mainly of two types: shield volcanoes and composite or stratovolcanoes. The shield volcanoes, for example those in Hawaii, eject magma from the depths of the Earth in zones called hot spots. The lava from these volcanoes is relatively fluid and permits the escape of gases. Composite volcanoes, such as Mount St. Helens and Mount Pinatubo, are associated with tectonic plates. In this type of volcano, the oceanic crust of one plate is sliding underneath the other in a subduction zone, together with an inflow of seawater, producing a gummier lava that restricts the exit of the gases, and for that reason, composite volcanoes tend to erupt more violently.
On Venus, where there are no tectonic plates or seawater, volcanoes are mostly of the shield type. Nevertheless, the morphology of volcanoes on Venus is different: on Earth, shield volcanoes can be a few tens of kilometres wide and up to high in the case of Mauna Kea, measured from the sea floor. On Venus, these volcanoes can cover hundreds of kilometres in area, but they are relatively flat, with an average height of . Large volcanoes cause the Venusian lithosphere to flex downward because of their enormous vertical loads, producing flexural moats or ring fractures around the edifices.[McGovern and Solomon, 1998] Large volcano edifice loading also causes magma chambers to fracture in a sill-like pattern, affecting magma propagation beneath the surface.
Other unique features of Venus's surface are novae (radial networks of dikes or grabens) and arachnoids. A nova is formed when large quantities of magma are extruded onto the surface to form radiating ridges and trenches which are highly reflective to radar. These dikes form a symmetrical network around the central point where the lava emerged, where there may also be a depression caused by the collapse of the magma chamber.
Arachnoids are so named because they resemble a spider's web, featuring several concentric ovals surrounded by a complex network of radial fractures similar to those of a nova. It is not known whether the 250 or so features identified as arachnoids actually share a common origin, or are the result of different geological processes.A New Episode of Volcanism on Venus. ESA: Science and technology. December 2, 2012
Recent volcanic activity Volcanism on Venus has taken place within the last 2.5 million years; however, until recently there had been no absolute proof that any volcano on Venus has erupted recently. Recent radar imagery shows more than 1,000 volcanic structures and evidence of possible periodic resurfacing of the planet by floods of lava. In addition to the radar images, there is supporting evidence that volcanism has taken place, including an unusual change in the amount of sulphur dioxide gas in the upper atmosphere. Sulphur dioxide is an important component of volcanic outgassing. However, the sulphur dioxide in the lower atmosphere remains stable. This could mean that a change in the global atmosphere caused the sulphur dioxide concentration to increase above the clouds. Even though the change in the atmosphere may be evidence that there have been volcanoes that erupted in Venus, it is difficult to determine whether they occurred or not. In 2014, the first direct evidence for ongoing volcanism was located, in the form of infrared "flashes" over the edges of rift zone Ganis Chasma, near the shield volcano Sapas Mons. These flashes were detectable during two or three consecutive Earth days in 2008 and 2009 and are thought to be caused either by hot gases or lava released from volcanic eruptions. Scientists suspect that there are four volcanoes that may be active: Maat Mons, Ozza Mons, Sapas Mons and Idunn Mons.Venus Volcano Watch. Mattei, M. F. The Journal of the Association of Lunar and Planetary Observers, Volume 53, Number 2, p.6. March 2011.Venus Volcano Observing List for Spring 2018. Mattei, M. F. The Journal of the Association of Lunar and Planetary Observers, Volume 60, Number 2, p.38–39. March 2018.
In 2020, a study by University of Maryland supported by Swiss National Science Foundation and NASA discovered that 37 of Venus's coronae show signs of ongoing activity. Maryland professor Laurent Montesi said, "we are able to point to specific structures and say 'Look, this is not an ancient volcano but one that is active today, dormant perhaps, but not dead...'" The active coronae are clustered near each other, so positioning geologic survey instruments would now be easier.
In March 2023, at the 54th Lunar Planetary Science Conference, a team revealed the first images of volcanic activity on the surface of Venus. The announcement consisted of two radar images from different cycles of Magellan data (8 months apart) that displayed a volcanic vent that had expanded by almost 2 square kilometers. This data was over 30 years old at the time of this discovery. The scientists checked that this expansion could not be explained by the angle at which the images were taken through computer simulations, which revealed that the change must be structural. A new research published in May 2024 in the journal Nature Astronomy using too data from Magellan pointed in the same direction.Volcanoes on Venus might be erupting right now, space.com, May 28, 2024.
Lightning Lightning on Venus may serve as a diagnostic of volcanism or atmospheric convection, so some effort has been devoted to detecting possible lightning on Venus.Lightning detection on Venus: a critical review. Ralph D. Lorenz. Prog Earth Planet Sci (2018) 5: 34. 20 June 2018. No lightning has been directly observed, but the most compelling evidence is the very low frequency (VLF) radio emissions recorded beneath the clouds by all four of the Venera landers. The Japanese orbiter Akatsuki was searching for visible lightning on Venus, among other science objectives.Hunt for optical lightning flash in Venus using LAC onboard Akatsuki spacecraft. Takahashi, Yukihiro; Sato, Mitsuteru; Imai, Masataka. 19th EGU General Assembly, EGU2017, proceedings from the conference held 23–28 April 2017 in Vienna, Austria., p.11381.
Atmospheric phosphine In 2020, Greaves et al. detected phosphine levels of 1–5 parts per billion in Venus's atmosphere using ALMA and JCMT. Historic data from Pioneer Venus also shows the possible detection of phosphine. Phosphine (PH3) is derived from phosphide (P3−) through the following interaction with sulfuric acid in Venus's atmosphere:
Phosphide comes from metals such as iron and magnesium, which should exist in great quantities in Venus's mantle. The phosphines were detected at a height of 70 km, which implies a volcanic eruption on the explosive scale of Krakatau or Yellowstone on Earth. The implication of this is not only that Venus has experienced recent volcanism, but that it is capable of explosive eruptions despite the lack of hydrated melts similar to those created at subduction zones on Earth. It is thought that Venus may have primordial water in the mantle that could be concentrated through fractionation.
Biological activity has been suggested as an alternate explanation for the phosphines in Venus's atmosphere, but this is unlikely due to the absence of any other biosignatures. Another hypothesis states that the phosphine could be produced in Venus's clouds, but this process requires water which is generally unavailable on Venus. Some scientists question that the phosphine levels found are truly as high as indicated. If the phosphine is present in amounts of 1–5 ppb and can be determined to originate in the mantle, it will imply a deep mantle plume system which contains enough volatiles to produce explosive volcanism.
Exploration In 2010, Suzanne E. Smrekar et al. published that Venus Express observed three volcanoes that have had eruptions about 250,000 years ago or less, which suggests that Venus is periodically resurfaced by lava flows... She has proposed two missions to Venus to elucidate the planet: Venus Origins Explorer (VOX), and VERITAS. Meanwhile, the Japanese spacecraft, Akatsuki's goals were to scan for active volcanism using its infrared cameras, although the infrared detector that was supposed to do this failed in December 2016 after a relatively short period of observations.Initial products of Akatsuki 1-μm camera . Earth, Planets and Space. 2018, vol. 70, nbr. 6.
Three missions are expected to launch in the 2030s, VERITAS, DAVINCI, and EnVision, all of which will help detect volcanism. Both VERITAS and EnVision will use radar remote sensing to map the surface of Venus at resolution 10 times better than that of Magellan. These missions will allow mapping over different time periods that could display more, higher resolution, evidence of current day volcanism.