I’ve already talked about these oblique craters in Oblique Impacts in Nevada. I want to talk about them a little more. And share a few stereo views of them.
To see the images in 3D, simply focus on the center line, and cross your eyes a little until you see a 3d image in the middle.
The largest of these three is about a mile from end to end.
The lake had water in it up to the level of the lowest set of beach lines at the time of impact. This accounts for the strange shape of the ejecta splashes downrange from the impact points.
To the best of my knowledge no formal field work to collect specimens for C14 dating has ever been done here. And I don’t think an impact scientist has been on the ground there yet either. But, among the meteorite hunting community, the dry lakes of northern Nevada already have a strong reputation as a happy hunting ground. From what we can see here, it’s no wonder.
And we may not have any tested dates yet. But we can still come up with a pretty good educated guess that puts us in the ball park. That set of beach lines we see lying across an ejecta splash can be dated with high degree of confidence to the early Holocene, or right around the end of the last ice age.
These Nevada meteorites fell into a shallow lake. But downrange, to the northeast, in Southwest Montana, we come to another set of oval craters. There, we see where many pieces of something fell into the soft sedimentary deposits of the Red Rock River valley. And with exactly the same trajectory.
Again we have a location that can give us a good indication of the age of the event. It’s where one of the ejecta curtains fell across an ancient meander of the river. That meander is about the same age as the beach lines lying across the ones in Nevada.
The odds of two different, low angle, impact events, happening at different times, in locations so close together, yet having exactly the same trajectory are inconceivable. So it’s a good bet the two crater fields are related, that the craters are all part of the same fall, and are some of the remaining scars of a major, multiple fragment impact event.
Here’s where my curiosity get’s set on fire. Those features are all about the same age as the Grand Coulee, and the ‘Channeled Scablands’ of eastern Washington.
If we look further downrange to the northeast, we come to the huge basin of Glacial Lake Missoula. During the Pleistocene, it’s waters were being held back by a glacial ice dam on the Clark Fork River in northern Idaho. That ice dam had been stable for tens of thousands of years when it suddenly, an inexplicably, broke up, and released a catastrophic mega flood downstream that gouged out the Channeled Scablands of eastern Washington in a matter of days.
That flood happened right around the same time those pieces of something plowed into the wet sediments on the bottom of that shallow lake in Nevada, and when the ejecta splash from an oval crater fell across a meander of the Red Rock River, in southwest Montana.
The ages are about right. Did the same regional impact storm that left all those oblique impact craters cause the breakup of the ice dam on the Clark Fork River at the end of the last ice age? Was this the trigger event for Harlan Bretz’s flood?