By studying the topography and mineral composition of a portion of the Arabia Terra region in northern Mars, scientists recently found evidence of thousands of massive volcanic eruptions, or “super eruptions”. Spewing water vapour, carbon dioxide, and sulfur dioxide into the air, these explosions tore through the Martian surface over a 500-million-year period about 4 billion years ago, Phys.org reports. Scientists reported this estimate in a paper published in the journal Geophysical Research Letters. “Each one of these eruptions would have had a significant climate impact – maybe the released gas made the atmosphere thicker or blocked the Sun and made the atmosphere colder,” said Patrick Whelley, a geologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who led the Arabia Terra analysis. “Modellers of the Martian climate will have some work to do to try to understand the impact of the volcanoes.” After blasting molten rock and gas through the surface and spreading a thick blanket of ash up to thousands of kilometres from the eruption site, a volcano of this magnitude collapses into a giant hole called a caldera. Calderas, which also exist on Earth, can be dozens of kilometres wide. Seven calderas in Arabia Terra were the first giveaways that the region may once have hosted volcanoes capable of super eruptions. Once thought to be depressions left by asteroid impacts to the Martian surface billions of years ago, scientists first proposed in a 2013 study that these basins were volcanic calderas. They noticed that they weren’t perfectly round like craters, and they had some signs of collapse, such as very deep floors and benches of rock near the walls. “We read that paper and were interested in following up, but instead of looking for volcanoes themselves, we looked for the ash, because you can’t hide that evidence,” Whelley said. On Earth, volcanoes capable of super eruptions – the most recent erupted 76,000 years ago in Sumatra, Indonesia – are dispersed around the globe and exist in the same areas as other volcano types. Mars, too, has many other types of volcanoes, including the biggest known volcano in the solar system, called Olympus Mons. Olympus Mons is 100 times larger by volume than Earth’s largest volcano of Mauna Loa in Hawaii, and is known as a “shield volcano,” which drains lava down a gently sloping mountain. Arabia Terra so far has the only evidence of explosive volcanoes on Mars.