Tectonic and Geologic Activity on Venus

Venus's Surface Has Processes Different from Earth's Plate Tectonics

Apr 20, 2009

With 80% of its surface covered with volcanoes or solidified lava flows, Venus is very tectonically active, but tectonics on Venus differ from plate tectonics on Earth.

Astronomers are unable to directly observe the cloud-shrouded surface of Venus. With the advent of the space program, however, they can map the surface using radar. NASA's Magellan mission to Venus orbited the planet and made detailed radar maps of the surface. Radar maps have revealed a very tectonically active surface. Studying how geology on Venus differs from plate tectonics on Earth helps astronomers and geophysicists understand tectonic activity and geology on both worlds.

What Is Tectonic Activity?

Tectonic activity is any geologic activity that moves or distorts a solid surface of a planet or moon. Tectonic activity can in principle occur on any planet or moon with a solid surface, however smaller worlds often do not have hot interiors needed to supply energy to drive tectonic activity. Examples of tectonic activity include: earthquakes, movement along fault lines, volcanoes and other volcanic activity, crust folding, and uplifting.

Plate Tectonics on Earth

On Earth tectonic plates float on the mantle. Slowly moving convection currents in Earth's mantle move the plates. As plates collide considerable tectonic activity takes place along the plate boundaries. This activity includes earthquake and volcanic activity and is a major mountain building process on Earth. On Earth such tectonic activity is concentrated on the boundaries between slowly drifting tectonic plates. Tectonic movement on Earth is mostly horizontal.

Tectonics on Venus

Astronomers do not know whether Venus is still volcanically active, but Venus has had a large amount of tectonic activity in its geologic history. Venus has about 1600 large volcanic features and perhaps hundreds of thousands of smaller volcanic features. Solidified lava flows cover about 80% of its surface. Unlike on Earth, however, the volcanoes on Venus are not concentrated on tectonic plate boundaries. In fact Venus may not have tectonic plates as found on Earth.

In addition to shield volcanoes similar to those found on Earth, Venus has some volcanic features that are unique to Venus and that form from vertical tectonic motions. Lava dome, also called pancake dome, volcanoes form on Venus when lava flows up from the mantle then retreats. Coronae are large (a few hundred kilometers across) volcanic features that form on Venus when lava pushes up from the mantle and swells the crust. The continental masses on Venus, such as Istar Terra, seem to be larger scale versions of the same process. All of these tectonic features on Venus result from vertical rather than horizontal movement of the crust.

Comparing Tectonics on Venus and Earth

Earth's crust is divided into tectonic plates. Tectonic activity results when these plates slowly drift horizontally and is concentrated on the boundaries between the plates.

The crust of Venus does not seem to have plates as found on Earth. Tectonic features on Venus therefore do not result from crustal plates drifting horizontally. Rather Venus has tectonic features not found on Earth that result from vertical motions of the crust.

Detailed comparison of tectonic activity on Venus and Earth will help astronomers and geophysicists better understand the geology and tectonic activities on both planets.