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.
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.”
Their approach builds on the work of another research team, which also learned of the theory that the Arabia Terra basins could be calderas and calculated where the ash from possible super-eruptions in that region would have settled. According to their results, the ash would have traveled downwind to the East, where it would thin out away from the center from what remained of the volcanoes (i.e., the calderas).
Using images from MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument, the team looked for signs of minerals on the surface and in the canyon walls and craters hundreds to thousands of km from the calderas, where the ash would have been carried by the wind. Eventually, they identified volcanic minerals like montmorillonite, imogolite, and allophane that were turned to clay by water.
They then laid the mineral data over a topographic map made using images taken by the MRO’s cameras, which yielded a three-dimensional topographic map of Arabia Terra. From this, the team was able to see that the layers of ash were very well preserved in the mineral-rich deposits, rather than being mixed up by winds and water. As the team had anticipated beforehand, the ash was layered in the same way it would have been if the deposits were fresh.
Said Jacob Richardson, a geologist at NASA Goddard who worked with Whelley and Novak:
“That’s when I realized this isn’t a fluke, this is a real signal. We’re actually seeing what was predicted and that was the most exciting moment for me. People are going to read our paper and go, ‘How? How could Mars do that? How can such a tiny planet melt enough rock to power thousands of super-eruptions in one location?’ I hope these questions bring about a lot of other research.”
Based on the volume of each caldera, the same scientists who proposed that Arabia Terra was once volcanically active also calculated how much material would have been released by each super-eruptions. This information allowed Whelley and his colleagues to calculate the number of eruptions needed to produce the amount of ash they found and concluded that 1000 to 2000 super-eruptions took place over a 500 million year period.
“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 Whelley. “Modelers of the Martian climate will have some work to do to try to understand the impact of the volcanoes.”
In addition to the question of how these volcanoes affected the Martian climate, there is also the question of why so many calderas are concentrated in this single region. On Earth, volcanoes capable of super-eruptions are dispersed across the planet and co-exist with other types of volcanoes. Mars has many other types of volcanoes, such as Olympus Mons and the three major mountains that make up the Tharsis Montes chain – Ascraeus Mons, Pavonis Mons and Arsia Mons.
So far, Arabia Terra is the only region on Mars where evidence of super-volcanoes has been found. This raises questions about whether calderas were concentrated in regions here on Earth but have eroded physically over time or moved due to plate tectonics. In the meantime, this research could also inform future searchers for super-volcanoes on other bodies in our Solar System.
For instance, Jupiter’s moon Io is known for releasing powerful lava plumes that can reach 500 km (310 mi) into space. There’s also evidence that volcanic activity continues on Venus, which creates the possibility that there are caldera clustered in certain regions. It will be fascinating to see what role these and other geological processes could have played in the evolution of extraterrestrial bodies.