Long ridges on Mars were caused by landslides, not ice, say scientists
While experts have not ruled out the presence of ice, they state that it was not needed to form the “long run-outs” analyzed on Martian landscape.
The unusually large and long ridges and furrows formed about 400 million years ago on Mars are not conclusive evidence of ice, say scientists.
The findings, according to the research team, show that the unique structures on the Martian landscape, from mountains several kilometers high, could have formed at high speeds of up to 360 km per hour due to underlying layers of unstable, fragmented rocks. This, says the team, challenges the idea that underlying layers of slippery ice can only explain such long vast ridges, which are found on landslides throughout the solar system.
“The presence of longitudinal ridges documented in long run-out landslides across our solar system is commonly associated with the existence of a basal layer of ice. However, their development, the link between their occurrence and the emplacement mechanisms of long-runout landslides, and the necessity of a basal ice layer remain poorly understood,” says the study published in Nature Communications.
According to the research team, while they have not ruled out the presence of ice, they state that ice was not needed to form the “long run-outs” analyzed on Mars. They suggest that the longitudinal ridges should not be considered as “unequivocal evidence” for the presence of ice.
"Landslides on Earth, particularly those on top of glaciers, have been studied by scientists as a proxy for those on Mars because they show similarly shaped ridges and furrows, inferring that Martian landslides also depended on an icy substrate. However, we have shown that ice is not a prerequisite for such geological structures on Mars, which can form on rough, rocky surfaces,” says doctoral student Giulia Magnarini from University College London (UCL) Earth Sciences.
“This helps us better understand the shaping of Martian landscapes and has implications for how landslides form on other planetary bodies, including Earth and the moon,” adds Magnarini.
The researchers — from ULC, Natural History Museum (London), Ben Gurion University of Negev (Israel), and University of Wisconsin Madison (USA) — used images taken by NASA's Mars Reconnaissance Orbiter to analyze some of the landslides remotely. They studied detailed three-dimensional images of an extensive landslide on Mars, which spans an area of over 55 kilometers wide.
"Cross-sections of the Martian surface in the Coprates Chasma in the Valles Marineris were analyzed to investigate the relationship between the height of the ridges and width of the furrows compared to the thickness of the landslide deposit," says the team.
Where landslide deposits are thickest, ridges form 60 meters high and furrows are as wide as eight Olympic-sized swimming pools end-to-end, shows analysis. The structures change as deposits thin out towards the edges of the landslide. Here, says the research team, ridges are shallow at 10 meters high and sit closer together.
"The Martian landslide we studied covers an area larger than Greater London and the structures within it are huge. Earth might harbour comparable structures but they are harder to see and our landforms erode much faster than those on Mars due to rain,” says co-author, Dr Tom Mitchell, associate professor of earthquake geology and rock physics, UCL Earth Science.
Dr Mitchell adds, “The vibrations of rock particles initiate a convection process that caused upper denser and heavier layers of rock to fall and lighter rocks to rise, similar to what happens in your home where warmed less dense air rises above the radiator. This mechanism drove the flow of deposits up to 40 km away from the mountain source and at phenomenally high speeds.”
According to Apollo 17 astronaut, Professor Harrison Schmitt from the University of Wisconsin Madison, who was part of the research team, the current work on Martian landslides relates to further understanding of lunar landslides such as the “Light Mantle Avalanche I have studied in the valley of Taurus-Littrow during Apollo 17 exploration and have continued to examine using images and data collected more recently from lunar orbit.”
"Flow initiation and mechanisms on the Moon may be very different from Mars," says Schmitt. However, comparisons often help geologists to understand comparable features, says Schmitt, who walked on the moon in December 1972 and completed geologic fieldwork while on the lunar surface.
“As on the Earth, the lunar meteor impact environment has modified the surface features of the Light Mantle Avalanche of the 75-plus million years since it occurred. The impact redistribution of materials in the lunar environment has modified features that ultimately may be found to resemble those documented in the Martian landslide study,” says Schmitt.