New Zealanders were recently reminded why our country is known as ‘the land of fire and ice’ after the Whakaari/White Island eruption which tragically took the lives of many who were visiting the tourist destination. We are all too familiar with catastrophic events in Aotearoa, having experienced volcanic eruptions and violent earthquakes throughout our history. New Zealand has been home to some of the most powerful volcanic eruptions in geologically recent times, like the Taupo caldera. The Christchurch earthquakes of 2011 destroyed much of the garden city and took the lives of over 180 people, and the Kaikoura earthquake in 2016 was one of the most complex and powerful earthquakes ever recorded in the world. Our home planet is an active world that is always changing, whether it be due to climate, weather, or geological processes. So, why is Earth so geologically active? Most of the other planets in our Solar System were very active at some point in history, but Earth remains the only one today.

The planets of our Solar System formed at around the same time, right after the birth of our Sun 4.6 billion years ago. The gas giant planets were further out, while the rocky planets, Mercury, Venus, Earth, and Mars, stayed close to the Sun. The early planets were very different to those we know today. Their surfaces would have been extremly hot, fueled by asteroid collisions and extreme volcanism from within. The surfaces eventually cooled off and atmospheres formed, but the cores of the planets remained very hot. For Earth, the outer layers cooled to form the crust that eventually broke apart into what we call tectonic plates. These plates quite literally ‘float’ on the Earth’s mantle, meaning our planet’s surface is always changing. As the mantle slowly moves, tension builds up at the plate boundaries. The sudden release of this energy results in what we know as earthquakes. Volcanoes usually form along these tectonic boundries. The infamous ‘Ring of Fire’ is the most geologically active area on Earth that spans the entire Pacific basin. This ring runs right through New Zealand, which is why we experience so many earthquakes and volcanoes. The other countries within the ring of fire also experience these events frequently like Japan or the Californian coast. This process was only accepted by scientists in the 1960s, and it made many curious as to what the other planets are like compared to Earth.

Venus is a world dominated by volcanoes. Most of the surface features are volcanic in origin, and it has more volcanoes than any other planet in our Solar System. The surface is over 90% basalt, and scientists have noted over 1,600 volcanoes dotting its surface. However, Venus is not known to show any signs of tectonic plates like Earth, and despite having so many volcanoes, none are known to be active today. Scientists are still not sure why this is, seeing as Venus is roughly the same size as Earth. Mars seems to have suffered a similiar fate to Venus. It too has many volcanoes that dot its surface, but none today are known to have erupted in recent times and it does not show any sign of plate tectonics. The most famous volcano on Mars is Olympus Mons, a huge sheild volcano that is almost 22km high. For reference, Mount Everest on Earth is a measly 8.8km! Scientists believe that Mars’ smaller size allowed its core to cool quicker than Earth’s, meaning its volcanism died out much quicker.

NASA’s InSight mission landed on the red planet in 2018 to learn more about its internal structure and geology. InSight detected the first signs of ‘marsquakes’ just months after landing, though these siesmic events would have been comparable to a magnitute 1-2 earthquake on Earth. This would not have been felt by any human who were to stand on Mars, so Mars’ geological activity remains low today.

There is one place in our Solar System that takes the spot from Earth as the most geologically active place but it’s not a planet – Io, a moon of Jupiter! This moon has over 400 active volcanoes all across its surface, and is coloured in bright hues of orange and yellow sulphur deposits much like Rotorua here in New Zealand. However, Io does not have any plate tectonics. The intense volcanism is caused by what scientists call tidal heating. Io orbits very close to Jupiter and does so in just 1.7 days. The close proximity and fast orbital speed means Io is quite literally pulled and strected by Jupiter’s intense gravity. This moon is also tugged at by Jupiter’s three other large moons, heating the core to high temperatures that result in near-constant eruptions. Io has been observed erupting by the many spacecraft that have visited the Jovian system. The NASA’s New Horizons probe spotted a 330km high plume eruptiong off Io’s Tashtar Paterae volcano while enroute to Pluto, while the Galileo probe saw lava lakes that stretch over 50km across.

Earthquakes and volcanones are a reminder to us on Earth that our home planet is a complex and changing world. Although these events are often tragic and can cause a loss of human life, they serve a purpose to our home planet. The core of Earth is flowing molten metal which generates electric currents, and Earth’s spin on its axis causes these electrical currents to form a magnetic field that surrounds the planet. This magnetic field creates a barrier that protects our planet from intense solar wind from the Sun. If we did not have this magnetic field, solar wind would strip away our atmosphere and life on Earth would be impossible.

Also, volcanism contributes to the slow carbon cycle and the enrichment of the land with nutrients for plant life!

Josh Kirkley, Astronomy Educator 

IMAGES: Top left – The Galileo probe observed this large lava fountain erupting from Io’s Tvashtar volcano. Top right – Russia’s Klyuchevskaya Sopka volcano erupting in 1994, seen from the Space Shuttle Endeavour. Above – A 300km high volcanic plume eruptiong off Io in 2007. Credits: NASA.