Where the Sky Fell

Exploring the “Rock Elm Disturbance”

In the hills of far western Wisconsin, there is a hole that, when first made, was four miles across and three quarters of a mile deep. It is called, in a somewhat understated way, the “Rock Elm Disturbance,” and it was made by a giant rock that hit the ground from outer space.

I drove there because I wanted to see an impact crater with my own eyes. It was something I’d wanted to do since a few years ago, when I was happily reading along in Bill Bryson’s witty and informative book, A Short History of Nearly Everything, when I came across some startling facts.

According to Bryson, some “two thousand asteroids big enough to imperil civilization regularly cross our orbit,” and as many as “millions” of smaller ones—big enough to destroy a city—do, too. The number of known “near-earth asteroids” has gone from ninety-seven in 1980 to 6,384 today. The first planet killer wasn’t even spotted until 1991, and near misses are thought to happen as many as two or three times a week.

Since then, I have been quietly haunted by this prospect, and when I heard about the crater in Rock Elm, I knew I had to see it for myself because it was certainly big enough to destroy a city, and possibly an entire region.

First I stopped in the office of Nugget Lake Park and picked up a copy of a booklet written by UW–River Falls geologist Bill Cordua, and got directions to the spot where you can look out over the crater.

Cordua writes that the rock was “about the size of Lambeau Stadium” and hit the earth at about 65,000 miles an hour, causing an explosion 63,000 times bigger than Hiroshima as well as a 6.5 magnitude earthquake. For forty-five miles around everything would have been destroyed.

On the crater’s south rim, I parked and got out. Looking over the impact zone, or what was left of it, I found it it hard to imagine that kind of violence. The sky was a perfect summer blue and the only sounds were crickets chirping and the grass rustling in the wind.

The “disturbance” admittedly took place a long time ago: 470 million years, to be exact. Since then, the crater’s edges have softened and rounded. Trees have grown across it. If I didn’t know better, I would have mistaken it for more rolling hills. In fact, we probably wouldn’t know about the crater at all if it weren’t for the sleuthing of Cordua and others.

Rock Elm is one of around 180 known impact craters on land. One of the biggest occurred not far south of Rock Elm in Manson, Iowa, which hollowed out the ground twenty-two miles across.

Last year, in a cover story for The Atlantic, Gregg Easterbrook warned that scientists are beginning to look underwater, too, and are finding more and more craters there, suggesting that this happens much more often than previously thought. For example, a huge meteor landed just north of Australia in 536 A.D. and was seen as far away as Turkey. Another, which measured five kilometers across, hit the Indian Ocean around 2,800 B.C. Just this year, a massive asteroid was seen hitting Jupiter’s gaseous surface, leaving a crater the size of the Pacific Ocean.

In other words, they’re out there, and you never know where they’re going to land. But at least two have landed in Wisconsin, not counting a third near Pepin, which has yet to be verified. The second is called the Glover Bluff Crater, and no one knows much about it, except that it’s about five miles across, and is less than five hundred million years old. It’s one of the least studied of all the craters and will probably remain so, given that it’s in the middle of a stone quarry and is being slowly and steadily dismantled.

But I still wanted to see what it was like, too, so I headed up Interstate 39 and exited at Coloma. It took me a while to find it, but I eventually located the entrance to the quarry. An old woman sat in the shack at the entrance. I told her I was here to see the crater and asked if I could go in.

“Oh, I suppose so,” she said, “seeing as how there’s not much going on today. The economy, you know.”

She gave me a hard hat, said she didn’t really know exactly where the crater was and sent me on my way. So I drove in and stopped to pick up some oddly mottled rocks, which may or may not have been “shattercones,” those stones that still bear the marks of impact.

I wandered around for a little while longer, trying again to picture what such a massive explosion would have looked like, and what it would mean for us today. Finally, I started back to my car. But before I left, I looked up at the sky, then around the quarry, then at the rock in my hand. It all made me feel kind of small, like I was part of something bigger than I could really imagine. And it made the rocks under my feet feel a little less solid.

Contributing writer Frank Bures’s work appears in the Best American Travel Writing 2009.

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