Geological Clues Connect Arizona Meteor Impact To Massive Landslide In Grand Canyon

Forbes

3 days ago

Aerial view of Meteor Crater in Arizona. getty
A new study highlights the striking coincidence in the geologic ages of the famous Meteor Crater in Arizona and a landslide dam that blocked the Colorado River, forming a paleolake in the Grand Canyon 56,000 years ago.
Driftwood and lake sediments have been long known in a cave called Stanton's cave in Marble Canyon of eastern Grand Canyon. The mouth of the cave is 45 meter above the river, so how did they end up there?
'It would have required a ten-times bigger flood level than any flood that has happened in the past several thousand years. Or maybe they are very old deposits left as the river carved down, or maybe they floated in from a paleolake caused by a downstream lava dam or landslide dam? We needed to know the age of the cave deposits,' explains Karl Karlstrom, emeritus earth science professor at the University of New Mexico and lead author of the study.
In the mid 1960's, Karlstrom's father, Thor, was in the cave as part of a cross-disciplinary geology-archeology research. They found evidence of species that went extinct in Grand Canyon like the California condor and Harrington's Mountain goat; they also found split twig figurines made 3,000 to 4,000 years ago by the ancestors of tribes that live around Grand Canyon. The driftwood was dated to be greater than 35,000 years which was near the limit of the radiocarbon dating method at the time; this age got recalculated in 1984 to 43,500 years. The new study, using new methods and analyses from two labs in New Zealand and Australia reports a date of 56,000 years old.
In the 1980's Richard Hereford of the USGS in Flagstaff had proposed that there was a rockslide near Nankoweap Canyon, about 35 kilometers downstream of Stanton's Cave, that might have formed a dam and a paleolake that backed up water and that allowed driftwood to float into Stanton's cave. If so, driftwood should be found also in other caves, flooded at the same time.
'From numerous research trips, Karl and I knew of other high-accessible caves that had both driftwood and sediment that could be dated,' says coauthor Dr. Laurie J. Crossey. The additional wood samples provided ages around 55,600 years. In one — now almost inaccessible — cave there were even beaver tracks preserved in the sand, suggesting that high water levels persisted for quite some time. Based on sedimentation rates in the canyon, the paleolake likely existed for at least 1,000 years before filling up or breaching the landslide dam.
Conceptualization of Nankoweap landslide that brought down large boulders of Kaibab Limestone from ... More the cliffs at left and created a geologically short-lived paleolake in Grand Canyon. Karl Karlstrom/University of New Mexico
Landslides can be triggered by erosion, earthquakes or volcanic eruptions, but in theory also the shock waves of an asteroid impact could be
Coauthor Dr. David Kring, head of the Center for Lunar Science and Exploration, University of Colorado Boulder, and an expert on the famous Meteor Crater in Arizona, had been working to recalculate the age of the crater, concluding that the impact happened 53,000 to 63,000 years ago.
Was the Meteor Crater impact enough to cause such a landslide? Kring has written about the physics of this and other impacts and has calculated that the impact would have set off a magnitude 5.4 earthquake (or even M6 using different assumptions) and that the shock wave would still have been ~M3.5 after traveling (in seconds) the 160 kilometers north to Grand Canyon. So, the impact could have 'shaken loose' the steep cliffs of Grand Canyon that were 'waiting and ready to go,' as shown by numerous rock falls that happen in Grand Canyon still today.
"The meteorite impact, the massive landslide, the lake deposits, and the driftwood high above river level are all rare and unusual occurrences. The mean of dates from them converge into a narrow window of time at 55,600 ± 1,300 years ago which gives credence to the hypothesis that they were causally related,' concludes Karlstrom.
The full study, "Grand Canyon landslide-dam and paleolake triggered by the Meteor Crater impact at 56 ka," was published in the journal Geology and can be found online here.
Additional material and interviews provided by University of New Mexico.