Who doesn’t love gigantic, ancient volcanoes? Mars has a ton of volcanoes that range from huge to ridiculous. Today we learn that NASA scientists discovered evidence of explosive supervolcanoes in Arabia Terra, a devastated highland region that we believe is one of the oldest areas on earth.
NASA’s JPL explains that a team of its scientists found the volcanoes after another team of JPL researchers realized that some of the depressions in Terra Arabia that we held for billion-year-old asteroid impact craters could actually be volcanic calderas. When they looked at the pits, they found that there were features that did not match craters. For one thing, they weren’t perfectly round. They were also pretty deep and showed some signs of collapse. However, Terra Arabia is covered in other impact craters and terrain features that could disrupt the study. “We read this paper and were keen to follow up, but instead of looking for volcanoes themselves, we looked for the ashes because you can’t hide that evidence,” said Patrick Whelley, who led the Terra Arabia analysis.
“So we picked it up at that point and said, ‘Okay, these are minerals associated with altered volcanic ash, which has already been documented if they follow the pattern we would expect from super-eruptions,” said Alexandra Matiella Novak, also from JPL. By a stroke of luck, Novak was already using the Mars Reconnaissance Orbiter to investigate ashes on Mars at that time. So she teamed up with Wheeley’s team for the Terra Arabia study.
The team of scientists looked downwind of their candidate caldera into the walls of craters and canyons and found the ash using the MRO’s CRISM imaging spectrometer. Since Mars is a dry and tectonically silent place, the suffocating, kilometer-thick blanket lay undisturbed in its original layers.
“It was then that I realized this was not a coincidence, it was a real signal,” said Jacob Richardson, a geologist at NASA Goddard who worked with Whelley and Novak. “We actually see what was predicted and that was the most exciting moment for me.”
Mars has no plate tectonics, it has stagnant lid tectonics. This means that the material does not sink towards the core. But it also means that weak points and mantle superplums don’t move. On Earth after Chicxulub, the almost antipodal Deccan Traps erupted for another two million years. And the quality of its lava changed, became thinner and more basaltic.
On Mars, Olympus Mons, the youngest of the great volcanoes in the giant Tharsis bulge, could lie on top of another such super cloud. These persistent eruptions occur when a hotspot stays in the same place for a long time and drains material through the same place in the crust. But where Tharsis is a shield volcano that releases thin and liquid lava, this work suggests that the calderas of Terra Arabia originated from explosive volcanoes. The idea here is that they are releasing internal pressure and heat similar to eruptions on Earth, they could have been released as massive explosions that tore through weak or thin spots in the Martian crust. And the calderas of Arabia Terra are the only evidence of such an explosive found on Mars.
In addition, the minerals that make up the ash layer include allophane, a weathering by-product of volcanic glass, and montmorillonite, a volcanic clay formed by water weathering. (Montmorillonite also occurs here on Earth and is widely used industrially.) This means that this work also builds up the corpus of information that suggests that Mars was once really wet. At the moment it’s mostly just really cold and sometimes covered in carbon dioxide frost.