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Volcanism

Venus was very volcanically active 200 to 500 million years ago. On the maps that Magellan managed to complete we see thousands of volcanoes of at least 10km diameter and 274 volcanoes between 20 and 100km in diameter. 156 are larger than 100 km and there are craters of over 1.5 km diameter of which the largest attains 280 km.


Les cratères d’impact sont répartis de manière aléatoire sur l’entièreté de la surface de Vénus. La plupart (points blancs) sont restés inchangés et sont concentrés dans certaines zones telles que l’Aphrodite Terra. Des régions de faible densité de cratères (zones bleues) sont souvent situées sur des plateaux élevés. Les régions de plus forte densité correspondent en général aux plaines.

The impact crater are spread in a random way across the entire surface of Venus.
(credit: NASA) Read more

We also see lava domes (roughly circular mound resulting from the slow eruption of lava) of 15 to 90km in diameter, plateaus, and huge hills, of which the tallest is Mount Maxwell that is 11 000 m high. We also see "coronae" – strange circles of wrinkles and cracks in the crust, of which the largest is 2 600 km.

However, in 3 years of observations, the Magellan probe never witnessed an eruption on Venus, as if the volcanoes were currently dormant.

Images obtained by various probes sent to Venus allowed us to see many impact craters of average size, and even distribution, which implies that the surface is relatively young. There are no small craters on Venus.

The dense atmosphere of the planet burns most small asteroids and comets up and only large objects hit the ground: there are fewer than 1000 impact craters on Venus.

The dominant theory with planetologists is that a ‘recent’ increase in internal activity with large scales eruptions resurfaced the majority of the planet.

Les terrains sur Vénus consistent principalement de plaines volcaniques (bleu). Au sein de ces plaines, existent des régions déformées telles que les tesserae (rose), des structures volcaniques telles que des couronnes (pêche), des rivières de lave (rouge) et des volcans de différentes tailles (orange). Les volcans ne sont pas concentrés en chaînes comme sur Terre, indiquant l’absence de tectonique des plaques.
Cette carte géologique indique les différents types de terrain et leur âge respectif déduit de la densité de cratères. Les volcans et couronnes semblent être localisés le long des zones de rift équatoriales plus jeunes (bleu). Les tesserae, plaines et crêtes sont plus âgées (jaune).

The terrain of Venus is mostly made up of plains (blue).
(credit: NASA) Read more

This geological map indicates different types of terrain and their respective ages. (credit: NASA) Read more

In 3 years of radar mapping (1990 to 1993), Magellan did not detect any new lava flows in the landscape, suggesting that volcanism on Venus is not currently very active.

In fact their amazing state of preservation is perhaps misleading: there is little erosion on Venus because there is no rain and the thick atmosphere of carbonic gas plays more of a protective role than that of a destructive agent.
 Markings that seem recent could in fact me tens or even thousands of millions of years old.

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