Catastrophic ice avalanches may have blasted down kilometers of polar ice craters of Mars at speeds of up to 80 meters per second on at least two occasions.
According to new research, these massive ice avalanches, also called fast running glacier surges, might solve a mystery about strange features on the Red Planet.
“This is the result of catastrophic flow of downslope material,” said Sergey Krasilnikov, a postdoctoral researcher at the Vernadsky Institute of Geochemistry and Analytical Chemistry at the Russian Academy of Sciences and the lead author of a study published recently in Planetary and Space Science.
Mars is full of strange features like fast shifting sand dunes and surface carbonates. Researchers had long noticed strange, linear features that traveled down the sides of craters in the north polar region. Given that the lines appear to be moraines, researchers “thought they might be from carbon dioxide glaciers, which is super cool and exotic sounding,” said Mike Sori, a planetary scientist at the University of Arizona who was not involved in Krasilnikov’s study.
Data, Models, Geometry, and Strange Features
Krasilnikov and his coauthors wanted to test an alternate theory, believing that water ice avalanches may be responsible for creating moraine-like ridges in two craters. The fast moving, destructive forces may have pushed debris to their edges as they tumbled down the slopes of these craters.
The researchers used open-source multispectrum and radar data from NASA. They ran this information through a 3-D model software program called Rapid Mass Movement Simulation in addition to using a separate math and geometry approach.
The simulations and calculations revealed that ice avalanches indeed could have created these moraine-like ridges that travel down the craters.
A massive amount of ice tumbled down the craters, Krasilnikov said: about 2.42 square kilometers in the first case they looked at and about 1.1 square kilometers in the second.
“It’s a very big mass,” he said.
Krasilnikov said that Mars accumulates ice similarly to the way frost forms on Earth, layer by layer. This ice can build up enormous weight and pressure in areas such as the tops of craters. He and his coauthors calculated that the first crater they studied had an ice massif buildup of 150 meters, whereas the second was about 100 meters.
Once the pressure gave out, the speed of these avalanches was fast, with the flow of ice traveling about 80 meters per second—similar to the speed of snow avalanches on Earth, Krasilnikov said. But the lower gravity of Mars means that they traveled much farther than Earth avalanches. The ice avalanches on the first crater traveled about 15 kilometers, whereas those on the second flowed for about 12 kilometers. The larger one had a width of about 5 kilometers at its thickest point and covered 104 square kilometers in total.
Ice Avalanches or Moraines?
Sori said that he thinks Krasilnikov’s paper is a nice advance in the scientific debate over these features, but he isn’t completely convinced it settles the debate and hopes it inspires more tests or observations.
“It’s a nice alternative explanation,” he said, adding that we know avalanches occur on other parts of Mars today. He also said that these researchers have shown that an avalanche can cover the right distance to produce these moraine-like features.
For Sori, the drawback in this new theory has to do with the fact that the ridges look so much like moraines, though he concedes that different processes could produce something that looked similar.
The theory on carbon dioxide (CO2) glaciers is that they can occur when Mars has a low axial tilt, which has occurred every few million years. At these times, conditions are cold enough that CO2 freezes, accumulates, and flows like the snow glaciers we know on Earth.
But Krasilnikov said that although the craters in question were formed more than 10 million years ago, the moraine-like ridges in these two craters were likely formed in the past few million years. The oblique angle of the planet necessary for CO2 glaciers to form hasn’t happened in the past 10 million or so years, he said.
As to why these ice avalanches seem to have happened only in these two places, Krasilnikov is unsure. “I think it’s [because of] very special physical conditions,” he said.
—Joshua Rapp Learn (@JoshuaLearn1), Science Writer