Supervolcanoes ripped up early Mars

Mars may have had giant explosive volcanoes in its ancient past that spewed billions upon billions of tonnes of rock and ash into the sky. Vast areas of collapsed ground in a region of the planet called Arabia Terra are their likely remains, believe Joe Michalski and Jacob Bleacher. The two scientists report their findings in Nature journal.

They say such supervolcanoes would have had a profound impact on the early evolution of Mars. Their gases would have influenced the makeup of the atmosphere and perturbed the climate. And the ash fall would have covered the landscape across great swathes of the planet. It is quite likely some of the deposits the rovers are now encountering on Mars have their origin in colossal blasts.

“Scientists know the planet must have been more active in its deep past, in its first billion years. But we’ve always struggled to find evidence for these early volcanoes. The supervolcanoes we report in Nature may solve this puzzle,” said Michalski, who is affiliated to the Natural History Museum in London, and the Planetary Science Institute in Tucson, Arizona.

Supervolcano is an informal term to describe an immense eruptive event that expels in excess of a 1,000 cubic kilometres of rock and ash. Earth has experienced this type of cataclysm numerous times, although not for many thousands of years. The US Yellowstone National Park, for example, sits on top of a past supervolcano. But these behemoths are not so straightforward to identify.

Unlike, familiar volcanoes — such as Etna or St. Helens on Earth, or indeed Olympus Mons on Mars — supervolcanoes do not build mountains out of layers of lava.

Rather, their great scale means that, when they erupt, the whole landscape lets go with multiple vents and fissures. And after the eruption, the ground will fall back into the void left by all the ejected material, producing a large bowl or caldera.

Michalski and Bleacher, from NASA’s Goddard Space Flight Center, have identified a number of potential supervolcanoes in an area of Mars’s northern hemisphere known as Arabia Terra. It is assumed to be one of the oldest terrains on the planet. The researchers say their calderas are unlikely to be old meteorite impacts sites because they are irregular in shape, and lack the raised rim and central peak often found at impact craters.

“Our best example is Eden Patera,” Michalski told the BBC’s “Science In Action” programme. “Thousands of cubic kilometres of material would have been erupted, and that’s a minimum. In terms of size, it would be very similar to Yellowstone — about 70 kilometres across.”

The supervolcanoes’ gases would have influenced the composition of the early atmosphere and the evolution of the climate thereafter. But they may also have had an impact on Mars’ potential for habitability, by pulling up substantial quantities of water and the essential elements needed for life from deep inside the planet.

“If future work shows that supervolcanoes were present more widely on ancient Mars, it would completely change estimates of how the atmosphere formed from volcanic gases, how sediments formed from volcanic ash and how habitable the surface might have been,” emphasised Michalski.