Small volcano

Any volcano on Venus less than 20 km across is classed as a “small volcano”.

Small volcanoes are round structures. They may be shaped like a shield, a dome or a cone, and some have a flat top. A vent may sit at the centre (Kreslavsky and Head 1999; Hansen 2005).

They are up to about 1 km high. They form when a small volume of magma rises to the surface from a shallow magma chamber.

Some small volcanoes stand alone (see the plate). Most, however, are loosely scattered across the shield plains or packed into denser groups in the shield fields. These plains may have formed only at certain times. If so, small volcanoes – especially groups of them – also formed mainly in particular periods. There are so many small volcanoes that their lavas together cover a large area.

Venus may have anywhere from a hundred thousand to a million small volcanoes. Hahn and Byrne (2022) catalogued 84,000 of them. All of these are smaller than 5 km, and most are hard to make out on the available radar images. A detailed survey would need higher-resolution images. On such images, artificial intelligence could help to find the small circular features.

In density, size and distribution, small volcanoes resemble the basaltic seamounts of Earth’s ocean floor.

The first images sharp enough to show small volcanoes came from the Soviet Venera probes.

See also: shield plains