Vents and channels in the Cerberus Plains of Mars
My research on Mars is finally in print, in the Journal of Geophysical Research: Planets! You can view it here, but here’s what I found in a nutshell.
The Cerberus Plains are one of the youngest surfaces on Mars: parts of them formed only a few million years ago. There’s been a lot of debate about whether they were formed by lava, water or a combination of both and what the source of this material was. Many say that Athabasca Valles, a channel system that runs from northeast to southwest within the plains, was carved by water and that this erupted from the Cerberus Fossae, a series of fractures spanning 1000 km in the north of the plains1. But that area, as you can see in the image (right), is cut off from the rest of the Cerberus plains in the east by a ridge. In the eastern part, it has been said that the plains were formed by flows of lava from low shield volcanoes. It’s likely part of them was, but the kind of lava that forms a volcanic edifice doesn’t flow far enough to make a flat plain – it’s too viscous2. The plains here are more likely to have been formed by eruptions from low fissures without surrounding volcanoes, and most of those fissures, on a flat plain, would have been buried by later lavas. To find fissures that are still visible, we need to look at a topographic high.
And lo and behold, on the ridge that separates the Athabasca Valles region from the plains in the east there are a whole series of vents with channels leading away from them down onto the surrounding plains. These are clearly a prime candidate source for the Cerberus plains material and, when I started my work, they’d just been imaged at super-high resolutions by the High Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter. I set out to map the vents and channels and work out whether they really did contribute to the formation of the Cerberus plains.
So what did I discover? A resounding yes: material from some of these vents really did form the plains surface south of the ridge, and also a 8 km-wide strip just to the north of the ridge. They did this through a complex series of channels, some of which incise down into the ridge and plains, and others that are built up on the surface between levees formed by the flow itself. The complexly overlapping channels suggest flow was episodic rather than sustained, though the depth of incision of some of the channels shows it was long-lived enough to remove a significant amount of material.
What formed these channels? The likely candidates are water or lava, and the most obvious explanation would be that water incised channels while lava piled up to make the constructed channels. It’s not as simple as that, though: some research indicates lava can erode out channels on Mars3, and concentrated mudflows can make constructed channels similar to the examples here. Similarly, there’s a polygonal texture to some of their deposits, which could show a high water-content (such mounds can form by periglacial processes), but can also form by lava cooling. As with so many aspects of Martian geomorphology, analogues can be found to fit either a volcanic or hydrous genesis and there doesn’t seem to be a smoking gun here. I’m currently working on rendering some of this area in 3D, so maybe, just maybe, I’ll find one that way.
As well as showing that these vents supplied the material to the south of the ridge, I was able to use the ridge’s position slap-bang between the Athabasca flows and the plains to the east to constrain the relative ages of those parts of the plains. I found that there was an inflow of material, probably lava, from the east just at the end of activity from the vents in the ridge, and found by crater-counting that that was laid down around 11 million years ago. I found that more thick flows from the north, probably lava from the region of Cerberus Fossae, were younger than activity from the ridge, so that makes those younger than 11Ma.
What we seem to have here is the eruption of a lot of material, much of it probably lava, from different sources at around the same time to make the Cerberus plains. The vents in the ridge have the same alignment as the Cerberus Fossae, another likely source, so all these fractures were probably caused by the same regional stress regime extending the crust, cracking it and allowing lava and/or water to reach the surface.
This is an excitingly recent date for so much tectonic and volcanic activity, and identifying it opens the door to the possibility that the region could still be active. In fact, the inSight mission plans to land there in 2016 and use seismometers to see if it is. It’s an exciting area of Mars, and I won’t be taking my eyes off it even as I delve into the mysteries of Mercury.