Science Spotlight: Volcanism on Planet Venus

Venusian Volcanism

There are four types of volcanic features unique to Venus: coronae, novae, “pancake” domes, and arachnoids. These features are classified by their geomorphology and formation mechanisms.

Coronae

Coronae (singular corona) have diameters of 100-1000 km. They are circular with ridges and fractures, have an interior that is topographically inflated or deflated, have a surrounding moat, and inner volcanic or tectonic structures. Corona shapes can vary. Radial fracturing, concentric fracturing, and compressional tectonic structures are common features of coronae. Coronae result from doming and fracturing due to the interaction of mantle diapirs with the gravitational relaxation of the lithosphere.

Novae

Novae (singular nova) are 100-300 km in diameter and radially fractured. Their fractures form starburst consisting of multiple blocks. A nova commonly features uplifted topography or inflation.. Novae are the result of doming and fracturing of the surface due to interaction of mantle diapirs with the lithosphere. Radial fracturing results from dike emplacement.

Pancake domes

A pancake dome is an unusual “pancake” shaped lava dome only found on Venus. These features often form in groups or clusters. They are generally associated with other forms of Venusian volcanism, such as coronae and novae.

Arachnoids

Arachnoids are characterized by circular patterns of ridges and radial fracture patterns or ridges extending outward. They are 50-175 km diameter depressions with small amounts of associated volcanism. They are formed by the evolution of mantle diapirs. High tangential stress during the formation of arachnoids leads to radial fractures. Some arachnoids resemble coronae.

Global Resurfacing Events

The geologic evolution of Venus is still uncertain due a lack of samples and age constraints. Radar images obtained by the Magellan mission revealed a low number of craters. The impact crater record gives a mean production age of 300–600 million years ago (Ma) and a uniform distribution over the entire surface of the planet. No more than 10% of the craters have been altered by volcanism. These observations suggest a catastrophic volcanic event removed all evidence of older surface material and previous cratering. In other words, Venus underwent a resurfacing event—a gradual resurfacing or global resurfacing event ending at 300–600 Ma. The last global resurfacing took place in less than 100 Ma and was followed by decreased volcanic activity. Two potential resurfacing mechanisms have been suggested to explain the above observations: resurfacing by plate tectonics and resurfacing by plume activity.

Plate tectonics, the creation of lithosphere at spreading ridges and subduction at trenches, could account for resurfacing. Because the last resurfacing event took 100 Ma to complete, the average surface age during this time must have been 50 Ma. This age corresponds to the average age of the oceanic lithosphere on Earth. The lack of evidence for present-day plate tectonics on Venus does not mean that plate tectonics could not have existed before the event, or that plate tectonics could not have accounted for it. However, it is not clear whether plate motions could stop within the 100-Ma time scale required by the crater record.

The other suggested mechanism of resurfacing is plume generation. Because less than 20% of the planet has been resurfaced over the last 500 Ma, the global production rate must have been at least 25 times higher than the present-day rate for the duration of the event. Such a rate could be achieved by increasing the number of plumes, increasing the potential temperature by 200 degrees Celsius, reducing the lid thickness, or reducing the solidus temperature. However, it is not clear that any of these processes could produce a resurfacing event over 100 Ma. Plume activity is not sufficient to explain the style of resurfacing required by the crater record. Therefore, the true mechanism for periodic resurfacing events on Venus is not yet evident and remains up for debate. Venus might exhibit similar behavior in the future, but there is no guarantee that it will occur within our human lifetime.

Sources / references

• Guest, J.E., et al 1992. Small volcanic edifices and volcanism in the plains of Venus. Journal of Geophysical Research, V. 97, E10, Pgs. 15949-15966.
• Head, J.W., et al 1992. Venus volcanism: Classification of volcanic features and structures, associations, and global distribution from Magellan data. Journal of Geophysical Research: Planets, V. 97, E8, Pgs. 13153-13197.
• Krassilnikov, A.S. 2006. Relationship Between Radial/Concentric Volcanic/Tectonic Features of Venus (Coronae, Novae, Arachnoids, and Calderas. Lunar and Planetary Science XXXVII Conference papers.
• Magee K.R. and Head, J.W. 1993. Large‐scale volcanism associated with coronae on Venus: Implications for formation and evolution . Geophysical Research Letters V. 20, No. 12, Pgs. 1111-1114.
• Nimmo, F. and McKenzie, D. 1998. Volcanism and Tectonics of Venus. Annu. Rev. Earth Planet. Sci. V. 226, Pgs. 23–51.
• NASA website, retrieved July 2022.
• Romeo, I. and Turcotte, D.L. 2010 Resurfacing on Venus. Planetary and Space Science, V.58, I. 10, Pgs. 1374-1380.