Earth is a geologically active planet, which means it has plate tectonics and volcanic eruptions that have not ceased. This activity extends all the way to the core, where action between a liquid outer core and a solid inner core generates a planetary magnetic field. In comparison, Mars is an almost perfect example of a “stagnant lid” planet, where geological activity billions of years ago and the surface has remained stagnant ever since.

But as indicated by the many mountains on Mars, which includes the tallest in the Solar System (Olympus Mons), the planet was once a hotbed of volcanic activity. And according to a recent NASA-supported study, there is evidence that thousands of “super-eruptions” happened in the Arabia Terra region in northern Mars 4 billion years ago. These eruptions occurred over the course of 500-million years and had a drastic effect on the Martian climate.

The research, which was recently published in the Geophysical Research Letters, was led by geologist Patrick Whelley of NASA’s Goddard Spaceflight Center. He was joined by researchers from the University of Maryland, Pennsylvania State University, the Johns Hopkins University Applied Physics Laboratory (JHUAPL), and the geotechnical engineering consulting firm Landau Associates.

This image taken by the Hi-RISE camera on NASA’s Mars Reconnaissance Orbiter shows several basins in Arabia Terra. Credits: NASA/JPL-Caltech/University of Arizona

Here on Earth, volcanoes can sometimes produce eruptions that release a tremendous amount of dust and toxic gases into the air, blocking out sunlight and changing the climate for decades. When these eruptions happen, they blast about 1015 liters of molten rock and gas through the surface and spread a thick blanket of ash up to several thousand km from the eruption site. Rather than leaving behind mountainous remains, volcanoes of this magnitude collapse into a giant hole (a “caldera”) that can measure dozens of km in diameter.

In Arabia Terra, on Mars, the existence of seven calderas were the first indications that the region may have once hosted volcanoes capable of super-eruptions. At one time, scientists believed that they were a series of impact basins created by asteroids billions of years ago. However, in 2013, a team of scientists published a study where they proposed that these depressions were actually calderas.

Some key indications, they argued, included the fact that the depression were weren’t perfectly round like craters, and the very deep floors and benches of rock near the walls (signs of collapse). Whelley and his team, which included co-author Alexandra Matiella Novak (a volcanologist with the JHUAPL) decided to investigate this possibility further. But instead of looking for volcanoes themselves, they looked for signs of ash.

Already, Matiella Novak had been using data from NASA’s Mars Reconnaissance Orbiter (MRO) to look for signs of ash elsewhere on Mars. After partnering with Whelley and his team, they began looking for similar data in the region of Arabia Terra. As Matiella Novak explained in a recent NASA press release:

“So we picked it up at that point and said, ‘OK, well these are minerals that are associated with altered volcanic ash, which has already been documented, so now we’re going to look at how the minerals are distributed to see if they follow the pattern we would expect to see from super-eruptions.”