Earth and Mars Experience Mysterious Mega-avalanches


Satellite image of western Tibet's Aru Mountains on July 21, 2016, after it had experienced the second largest ice avalanche in recorded history just days before. NASA Earth Observatory

In July 2016, a massive avalanche ripped through the Aru Mountains in western Tibet. The circumstances surrounding the event were highly mysterious. There was no obvious trigger, and the gentle slope that the icy debris barreled down wasn't considered a risk, even for the smallest of avalanches. Nevertheless, nine people and hundreds of livestock in the village of Dungru died as a result.

It was the second largest ice avalanche in recorded history, bested only by the 2002 avalanche of Kolka Glacier in the Caucasus. The 2016 natural disaster left a debris field up to 98 feet (30 meters) deep and covering 4 square miles (10 square kilometers) in its wake.

Then, just two months later, at an adjacent Aru mountainside a few miles to the south, another mega-avalanche occurred (apparently) independently of the first event.

"Even one of these gigantic glacier avalanches is very unusual," Andreas Kääb, a glaciologist who works at the University of Oslo, said at the time. "Two of them within close geographical and temporal vicinity is, to our best knowledge, unprecedented."

Now, according to a study published in Nature Geoscience, a team of researchers led by Kääb have used Earth-observing satellites to study the Tibetan region and collected samples of the debris to decipher why two historic avalanches happened on the same unlikely slopes within weeks of one another.

They found that the circumstances surrounding the mega-avalanches in Tibet may also apply to another location. An extraterrestrial one.

Like Wet Talcum Powder

Mega-avalanches occur when something catastrophic happens at a glacier's base. In the case of the Aru avalanches, meltwater had been penetrating the base, though there was little indication that the resulting avalanches would be so extensive and destructive.

Usually, the glacier would be anchored (frozen) to the slope material, preventing any sudden mass movement from occurring, but a buildup of meltwater in this permafrost region would have allowed a mudlike slurry to form under the ice. Samples collected from the debris confirmed that the glacier bed is composed primarily of fine-grained sedimentary rocks, like siltstone, sandstone and clay.

Jeffrey Kargel, senior scientist at the Planetary Science Institute, says the composition of the rock and the deep penetration of meltwater — possibly driven by climate change — was a recipe for disaster. Kargel co-authored the study.

Kargel noted a lot of phyllosilicates in the samples collected: "These are clay minerals, platy minerals like mica that can form a very slippery material ... like talcum powder," he says. "When wet, it forms a very slippery mud." This mud, continues Kargel, can form a non-Newtonian fluid. With non-Newtonian fluids, once deformation starts, it gets faster and faster as the viscosity of this lubricating layer precipitously declines. Should this fluid form under a massive glacier, devastating flows of ice and rock can suddenly occur down an otherwise gentle slope.

Mars Glaciation

Kargel's interest in avalanches goes well beyond Tibet, however.

When Kargel was a graduate student at the University of Arizona in 1989, for fun, he would pore over the hundreds of observations sent back from NASA's Viking spacecraft that orbited Mars in the late 1970s and early 1980s.The hi-resolution photographs the university collected provided geological detail like nothing planetary scientists had ever seen before.

A map of Mars' Argyre impact basin captured courtesy of the Mars Global Surveyor
NASA/JPL-Caltech/Arizona State University

Although Kargel's research focused on the icy moons of the outer solar system, his interest was piqued when he saw what he thought was a network of sinuous channels meandering through the Argyre impact basin, a region in the southern highlands of the red planet. When he started inspecting nearby craters to work out the direction of the sunlight and shadows, however, he realized that those channels weren't channels at all; they were ridges of material and possible evidence for glacial deposits.

Here's why he thought that. On Earth, raised ridges called "eskers" form when water flows under glaciers, depositing sediment. When the glaciers melt and disappear, this sediment is left behind, like inverted river channels. In the late 1980s and early 1990s, claiming to see glacial features at mid-latitudes on Mars, however, was "highly controversial," Kargel says. When NASA's Mars Global Surveyor observed further evidence for ancient glacial deposits on Mars after it arrived in 1997, the idea became less outlandish. Now, after decades of Mars exploration, we know that, yes, Mars has a fascinatingly active geology and is littered with evidence for glaciation.

And guess what? There's also evidence for mega-avalanches that would dwarf what happened in Tibet.

Mars, Like Earth

"I have a hunch that a lot of these giant landslides on Mars, especially those that have been noted for their very long run-out distance — the horizontal distance traveled by the landslide divided by the vertical fall distance — is very large," says Kargel. "We might have a case for an Aru avalanche-type process going on, especially if there were massive ice bodies — ice-rich permafrost or glaciers — I think that when melting begins at depth, you get this formation of a slippery mud then the conditions are present for a big avalanche, potentially much bigger than the Aru avalanches if the scale of the [glacier] is bigger."

Mars is a dusty planet, and this dust provides a clue as to the possible mechanism that might drive massive avalanches.

"There have been discoveries of phyllosilicates on Mars, and we've known for a very long time, at least since Mariner 9, that Mars is a dusty world and we know that the dust that is preferentially carried by the wind is fine-grained, just a few microns in size," he says.

Like the fine grains sampled in the Aru avalanche debris, Martian dust is talcum powder-sized particles of platy phyllosilicate minerals. This suggests that, should they become wetted, the rocks on Mars are conducive to the "runaway deformation processes where the ice mass can slip off its bed on the same kind of slurry (to the Tibetan case)," he adds.

"There are indications that the kinds of processes that happened with the Aru avalanches may have occurred many hundreds of thousands of times the scale of the Aru avalanches in the Argyre basin."

We know that Mars was once a lot wetter than it is now, and we know it was also covered in glaciers that have come and gone as the Martian climate has radically changed, driven by drastic periodic changes in the planet's axial tilt over the eons. It stands to reason that similar processes may drive these kinds of mega-avalanches on Mars and on Earth; orbital imagery certainly seems indicative of this conclusion.

Now we just need to send a rover to a Martian glacial deposit to find out if this is the case.



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