January 17, 2014
Idaho, Mars Canyons Share Similarities: Carved By Massive Megafloods
redOrbit Staff & Wire Reports - Your Universe Online
The shared geological features found in U-shaped bedrock canyons both in south-central Idaho and on the surface of Mars are likely the result of massive floods, according to research appearing in the journal Proceedings of the National Academy of Sciences (PNAS).California Institute of Technology (Caltech) geology professor Michael P. Lamb and his colleagues explain that while there have been other explanations for the formation of each canyon, it was likely that these structures were “carved rapidly by outburst flooding” approximately 46,000 years ago.
Furthermore, the researchers wrote that – in contrast to the amphitheater-headed canyons found in Idaho – those with more pointed heads might have evolved as a result of tens of thousands of years’ worth of river erosion. Megafloods, not groundwater seepage, were probably the cause of the Martian canyons as well, they added.
Satellite images have shown that these amphitheather-headed canyons, which are found in both Idaho’s Malad Gorge State Park and on Mars, have tall vertical headwalls. Those found in Idaho were carved into an essentially flat plain composed of basalt, a volcanic rock that originated from a hotspot in modern-day Yellowstone Park.
“Two canyons in Malad Gorge, Woody's Cove and Stubby Canyon, are characterized by tall vertical headwalls, roughly 150 feet high, that curve around to form an amphitheater,” Caltech explained in a statement. “Other amphitheater-headed canyons can be found nearby, outside the Gorge – Box Canyon, Blue Lakes Canyon, and Devil's Corral – and also elsewhere on Earth, such as in Iceland.”
In order to determine how these canyons formed, Lamb and former Caltech postdoctoral fellow Benjamin Mackey conducted a series of field surveys, collecting rock samples from three canyons in Malad Gorge: Woody's Cove, Stubby Canyon and a non-amphitheater canyon known as Pointed Canyon.
“Geologists have a good understanding of how the rocks in Woody's Cove and Stubby Canyon achieved their characteristic appearance. The lava flows that hardened into basalt were initially laid down in layers, some more than six feet thick. As the lava cooled, it contracted and cracked, just as mud does when it dries,” the institute said.
This effect resulted in the creation of vertical cracks across the entire layer of basalt that had been formed by lava. As additional sheets of lava covered the land, they too cooled and cracked vertically. The result was a wall that, when viewed vertically, resembles a stack of tall blocks – a structure type known as columnar basalt.
“While the formation of columnar basalt is well understood, it is not clear how, at Woody's Cove and Stubby Canyon, the vertical walls became exposed or how they took on their curved shapes,” the institute said. “The conventional explanation is that the canyons were formed via a process called ‘groundwater sapping,’ in which springs at the bottom of the canyon gradually carve tunnels at the base of the rock wall until this undercutting destabilizes the structure so much that blocks or columns of basalt fall off from above, creating the amphitheater below.”
The researchers were unable to corroborate those observations, however, as they found no evidence of undercutting, despite the existence of springs at the base of both amphitheater canyons. In addition, such a process should have left massive boulders at the foot of both canyons that would not have been carried away or dissolved as of yet.
“These blocks are too big to move by spring flow, and there's not enough time for the groundwater to have dissolved them away, which means that large floods are needed to move them out. To make a canyon, you have to erode the canyon headwall, and you also have to evacuate the material that collapses in,” Lamb explained.
That led the Caltech researchers to conclude that waterfall erosion occurring during a large flood was the only likely remaining candidate to explain canyon formation in Malad Gorge. Furthermore, the investigative team said that the evidence collected from the site suggests that amphitheater-shaped canyons could be “diagnostic of very large-scale floods,” implying that larger water discharges and shorter flow durations were involved.
Canyons with the same type of features as those found in Malad Gorge also exist on Mars, though some of them are much larger, according to the study authors. Based on the evidence collected by their research in Idaho, Lamb and his colleagues said that it is more likely that they were caused by megafloods than by groundwater seeping out of cracks at the base on the canyon headwalls.