On a recent visit to New Zealand’s North Island I stayed in a hotel next to a Maori village in Rotorua. There was a constant sulphurous smell of bad eggs and white steam clouds rising from the village caused by superheated boiling water gushing out of the ground showing it was very hot down under. This country was formed by the Pacific tectonic plate diving under the Australian plate causing volcanoes, mountains and earthquakes hence the hot water spurting out. While taking atmospheric night photos of the village planet Venus shone through the steam. Venus is about the same size as our Earth with roughly the same number of volcanoes yet Venusian volcanoes are completely different from ours and are formed by large floods of magma rather than by tectonic plate movement. This deforms the landscape by magma pushing up and outward.
When we look up at our familiar Moon we see light and dark patches creating the face of “the Man in the Moon”. The Japanese see a rabbit, the Chinese a toad. Scientists see volcanism. In 1969 Apollo 11 landed on the dark grey flat “Sea of Tranquility”. However, this was not liquid water but between 4.3 and 3.1 billion years ago it was a flood of liquid magma which eventually cooled to ancient basalt rock. Because the Moon is small its heat escaped into space relatively quickly and there is now not enough internal heat to cause any volcanic eruptions and has been volcanically dead for 1 billion years.
Mars is only half the size of Earth but has old volcanoes concentrated in four areas with the biggest one called Olympus Mons standing 25 kilometres high and 500km wide (about the size of Poland!) and much bigger than any of our volcanic mounds. Mars doesn’t seem to have tectonic plates that rub together so it is probably weak “hot spots” in the crust that allowed the magma to burst through in the past. On Mars no plates moved so the magma just spilled out in the same place creating much bigger flatter volcanoes whereas on Earth the plates move over the same hot spot eventually creating strings of volcanic islands like the Galapagos Islands.
The closest moon to Jupiter is little Io which is slightly bigger than our Moon. In 1979 the Voyager spacecraft passed by Io and discovered a 300km high volcanic plume. The surface is red, orange and yellow and pockmarked with large calderas and lava flows which is constantly changing due to magma spewing out, making it resemble a huge pizza! The Hubble telescope and Galileo spacecraft have shown the lava is even hotter than any ejected from our volcanoes and all this violent hot activity is caused by the huge gravity from Jupiter pushing and pulling on Io’s interior. Spectacular volcanic worlds all around us!
Glynn Bennallick