London, May 23 : A new analysis of a canyon in the US state of Idaho lends support to the idea that Mars, which boasts similar canyons, had substantial rainfall and megafloods early in its history.
According to a report in New Scientist, it has been suggested by researchers that Idaho's Box Canyon, which resembles a snake, with a sinuous body and a rounded head, had a giant lake existing at its "head".
But the canyon's containing walls might have given way, unleashing a megaflood 45,000 years ago.
One theory suggests that such "amphitheater-headed" canyons form slowly, as seeping groundwater gradually erodes canyon walls in the snake's head.
That process might create some canyons in softer rock, according to researchers led by Michael Lamb of the University of California, Berkeley, US.
But they say such slow seepage could not have transported the metre-sized boulders that were carried downstream in Box Canyon, which is carved into harder basaltic bedrock.
"It requires a lot of water to remove them," said Lamb.
In fact, it would have required a megaflood - a catastrophic outpouring of massive amounts of water in a relatively short period.
Such megafloods occurred numerous times in the western US several tens of thousands of years ago and played a significant role in shaping the landscape.
The discharges are thought to have resulted when structures that held large lakes in place - such as rockfalls or glaciers - eroded or melted away, releasing the lakes' water in a sudden flood.
Basalt forms much of Mars's surface. If similar Martian canyons were carved in solid basaltic bedrock as well, they would have required a release of some large body of water, according to Lamb.
"That implies a substantial rainfall cycle, since that is the best explanation for how water filled such a lake in the first place," Lamb told New Scientist.
"If, on the other hand, such canyons formed from seeping groundwater, that allowed the hypothesis that there could never have been any rainfall on Mars," he added.