High-resolution photos of Martian lava flows show coiling spiral patterns that resemble snail or nautilus shells. Such patterns have been found in a few locations on Earth, but never before on Mars. The discovery appears in a paper in Science published by Andrew Ryan and Philip Christensen (both Arizona State University).
The new result came out of research into possible interactions of lava flows and floods of water in the Elysium volcanic province of Mars.
“Athabasca Valles has an extensive literature,” Ryan says, “as well as an intriguing combination of seemingly fluvial and volcanic features.” Among the features are large slabs or plates that resemble broken floes of pack ice in the Arctic Ocean on Earth. In the past, a few scientists have argued that the plates in Elysium are in fact underlain by water ice.
Assessing claims that ice was present today beneath the lava plates drove Ryan to study the area. This led him to look closely at every available image of the region, with an emphasis on those from the HiRISE camera on Mars Reconnaissance Orbiter.
“I first noticed puzzling spiral patterns in an image near the southern margin of Cerberus Palus,” Ryan explains. “The coils become noticeable in the full-resolution HiRISE image only when you really zoom in. They also tend to blend in with the rest of the light-gray terrain until you stretch the contrast a bit.”
On Earth, lava coils can be found on the Big Island of Hawaii, mainly on the surface of ropey pahoehoe lava flows. They have also been seen in submarine lava flows near the Galapagos Rift on the Pacific Ocean floor.
As Ryan explains, “The coils form on flows where there’s a shear stress — where flows move past each other at different speeds or in different directions. Pieces of rubbery and plastic lava crust can either be peeled away and physically coiled up — or wrinkles in the lava’s thin crust can be twisted around.”
Similarly, he notes, scientists have documented the formation of rotated pieces of oceanic crust at mid-ocean ridge spreading centers. “Since the surface of active lava lakes, such as those on Hawaii, can have crustal activity like spreading centers do, it’s conceivable that lava coils may form there in a similar way, but at a smaller scale.”
The size of Martian lava coils came as a surprise. “On Mars the largest lava coil is 30 meters across — that’s 100 feet. That’s bigger than any known lava coils on Earth,” he says. Ryan and Christensen’s work has inventoried nearly 200 lava coils in the Cerberus Palus region alone.
Looking ahead, Ryan says, “Lava coils may be present in other Martian volcanic provinces or in outflow channels mantled by volcanic features. I expect that we’ll find quite a few more in Elysium as the HiRISE image coverage grows over time.”