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Unraveling Mars's Hidden Plume History Through Wrinkle Ridges
A Giant Volcanic Mystery on the Red Planet
You can't really miss Mars's Tharsis region. It's a massive volcanic bulge, roughly 6,000 kilometers across and rising more than 20 kilometers high—picture a dome the size of North America, heaped with volcanic material that piled up over 4 billion years. For decades people have asked the obvious question: what built this thing? And the one I find even more tantalizing—did the volcanism stay put, or did it wander?
To get at those questions, we turned to wrinkle ridges, the odd wave-like features that ripple across the Martian surface like creases in a rug. They're more than geological curiosities. Each one is a frozen record of the ancient stresses that squeezed and compressed the crust while Tharsis was growing.
Mapping 77,000 Kilometers of Martian Wrinkles
So we set ourselves a fairly ambitious task: map 650 individual wrinkle ridges, stretching a combined 77,294 kilometers across Mars's western hemisphere. That's nearly twice the circumference of Earth, which still amazes me when I say it out loud. We broke those ridges into 34,741 smaller segments, each about 2 kilometers long, and worked through them using high-resolution images and elevation data.
The idea behind it is simple. If a ridge formed because of stress from a rising plume of hot material beneath the crust, it should curve in a roughly circular pattern around the stress source—the way ripples spread out from where you drop a stone in a pond. By measuring how far each segment strays from that perfect circle, we could trace the stress back to where it came from.
Five Stress Centers Tell a Story of Migration
What came out of the analysis genuinely surprised us: not one stress center, but five distinct ones scattered across Tharsis:
- C1 : Near the southern edge of Alba Mons caldera in the north
- C2 : Between Jovis Tholus and Ceraunius Fossae
- C3 : Between Ulysses Patera and Pavonis Chasma
- C4 : At Phoenicis Lacus, near Noctis Labyrinthus
- C5 : At Claritas Rupes in the south
These centers span 4,518 kilometers from north to south—a strong hint that the source of volcanic stress moved around over geological time rather than sitting in one place.
Reading the Timeline: Which Came First?
Five centers was a start, but it left us with a question: in what order were they active? This is where it turned into detective work. Much like an investigator reading which bloodstain lies on top of another, we looked at where wrinkle ridges cross-cut each other. When one ridge slices across another, the one doing the cutting has to be younger.
After working through dozens of these intersections, we pieced together the sequence: C2 → C3 → C1 → C4 → C3 (again) → C5 → C4 (again)
I love what this tells us. The stress didn't simply march from north to south. It jumped around, and some centers switched back on more than once. C4 in particular looks like it was the most recently active spot of all.
The Critical Taper: Mars as a Gently Sloping Wedge
Here's where things got even more interesting for me. We didn't stop at mapping where the ridges sit—we tried to work out what's underneath them. From the ridges' heights and widths, we estimated how much the crust had shortened (between 1.5 and 3.8 kilometers along different profiles) and how deep the faults reach below the surface (between 2.9 and 8.8 kilometers).
When we plotted those detachment depths against distance from each stress center, a clean pattern jumped out: both the surface topography and the buried faults form a very gentle wedge, with angles of just 1.2° to 2.2°. That's remarkably shallow—much gentler than anything in Earth's mountain belts.
And that wedge shape matters, because it follows what geologists call "critical taper theory"—the very same principle behind Earth's fold-and-thrust mountain belts. In effect, the Tharsis dome behaved like a colossal accretionary wedge, with material shoved outward and upward by the plume rising beneath it.
The Water Beneath: An Unexpectedly Slippery Layer
The finding I keep coming back to is what must have been greasing these faults. Wedge angles this gentle demand unusually low friction along the detachment zones—far lower than ordinary rock sliding on rock.
We calculated friction coefficients between just 0.055 and 0.093. To put that in context, normal rock friction usually sits around 0.6 to 0.85. Something was knocking the friction way down.
Our best explanation? Liquid water trapped beneath an impermeable permafrost layer.
Here's the picture. The detachment depths we found (3–9 km) line up with depths where Mars's internal heat would keep water liquid, even with that frigid surface above. Higher up, frozen ground—permafrost—would form a seal, with nowhere for the water to escape. The weight of the rock above would drive up the fluid pressure below, essentially "floating" the upper crust and letting it slide far more easily.
There are other candidates, of course: layers of clay minerals or salt deposits, both known on Mars, can also act as lubricants. The evaporite deposits—sulfates and the like—found in the nearby Valles Marineris canyons lend some weight to that idea.
What It All Means: A Migrating Plume Beneath Ancient Mars
Put it all together, and the story of how Tharsis formed looks more tangled and more alive than we used to think:
- The plume wasn't stationary : Instead of a single fixed hotspot, the volcanism migrated across the region over hundreds of millions of years, between the Late Noachian and Early Hesperian periods (roughly 3.7–3.1 billion years ago).
- Multiple reactivations occurred : The stress centers didn't just fire once and fall silent—C3, and especially C4, switched back on, which points to either plume branching or the main plume rocking back and forth.
- Water played a crucial role : The weak detachment zones we mapped suggest liquid water was present at depth while the ridges were forming, sealed under an icy lid and helping the crust deform.
- The overall motion was northward to southward : For all the messiness, there's a broad drift of the stress centers from north (C2, C1) toward the south (C4, C5), with C4 marking the final major phase.
That migration may reflect the plume bumping into changes in crustal thickness, especially near Mars's dramatic hemispheric boundary—the dichotomy—where the northern lowlands give way to the southern highlands. The thick crust in the south might have steered or stalled the plume, nudging it to branch or shift.
Why This Matters
Tharsis isn't just a Martian curiosity—it's a window into how a whole planet works. It dominates Mars's topography, tugged at its rotation, shaped its climate, and may have had a hand in whatever water once ran across the surface.
What we've put together is the most detailed reconstruction so far of how this enormous feature evolved, and it reveals a history far more dynamic than anyone suspected. Five stress centers, a clear migration pattern, and those low-friction detachments all point to a rich interplay between rising mantle plumes, crustal structure, and fluids hiding underground.
It's also a good reminder that even "dead" planets carry remarkably complicated stories. Mars hasn't had real volcanic activity for millions of years, yet the wrinkle ridges hold a detailed record of its violent past—if you know how to read them.
This research was published in the Journal of Geophysical Research: Planets by Oguzcan Karagoz, Thomas Kenkmann, and Stefan Hergarten from Albert-Ludwigs-University Freiburg, Germany.