Did You Know

Venusian volcanoes tend to be broad but not as high as those on Earth. The highest volcano on Venus is Maat Mons, which rises 8.5 km above the surrounding plains. By comparison, the volcanoes on Hawaii rise 10 km above the sea floor.

Radar images from Magellan suggest there have been recent lava flows on Venus. Such volcanic activity provides evidence about the interior processes of a planet. Venus appears to lose heat from its interior via hot-spot volcanism rather than via convection as in the case of Mercury. Hot spots produce shield volcanoes and flood volcanism, and these features are common on the present-day Venusian landscape. Magellan also revealed surface features called arachnoids, which look like craters with spider legs radiating from them. These features are thought to form when molten magna pushes up from the interior with such force that the surrounding crust gets cracked.

Figure 5.7 The Magellan probe found four distinctive 'pancake domes' on the eastern edge of the Alpha Regio highland plateau. These volcanic features are about 25 km in diameter and 750 m high. (Photo: NASA)

Tectonic movement that has resulted in crustal shortening, stacking of crustal blocks and wrinkle ridges on the lowlands and rolling plains has also shaped the surface of Venus. Also seen on the lowlands and plains are fractures formed when the crust was stretched or pulled apart. Diana Chasma is the deepest fracture on Venus, with a depth around 2 km below the surface and a width of nearly 300 km.

The oldest terrains on Venus are about 800 million years old. Lava flows at that time probably wiped out earlier surface features and larger craters from early in Venus's history.

Venus probably once had large amounts of water like Earth but the high temperature boiled all this away, so Venus is now very dry.

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