PEOPLE KNEW FOR a long time that there was something odd about the earth behManson, Iowa. In 1912, a man drilling a well for the town water supply reported bringing up alot of strangely deformed rock—「crystalline clast breccia with a melt matrix」 and 「overtura flap,」 as it was later described in an official report. The water was odd too. It wasalmost as soft as rainwater. Naturally soft water had never been found in Iowabefore.
Though Manson』s strange rocks and silken waters were matters of curiosity, forty-oneyears would pass before a team from the Uy of Iowa got around to making a trip to theunity, then as now a town of about two thousand people in the northwest part of thestate. In 1953, after sinking a series of experimental bores, uy geologists agreed thatthe site was indeed anomalous and attributed the deformed rocks to some a, unspecifiedvolic a. This was in keeping with the wisdom of the day, but it was also about aswrong as a geological clusion get.
The trauma to Manson』s geology had e not from within the Earth, but from at least 100million miles beyond. Sometime in the very a past, when Manson stood on the edge of ashallow sea, a rock about a mile and a half across, weighing ten billion tons and traveling atperhaps two huimes the speed of sound ripped through the atmosphere and puo the Earth with a violend suddehat we scarcely imagine. Where Mansonnow stands became in an instant a hole three miles deep and more thay miles across.
The limestohat elsewhere gives Iowa its hard mineralized water was obliterated andreplaced by the shocked basement rocks that so puzzled the water driller in 1912.
The Manson impact was the biggest thing that has ever occurred on the mainland Uates. Of any type. Ever. The crater it left behind was so colossal that if you stood on oneedge you would only just be able to see the other side on a good day. It would make the Grandyon look quaint and trifling. Unfortunately for lovers of spectacle, 2.5 million years ofpassing ice sheets filled the Manson crater right to the top with rich glacial till, then graded itsmooth, so that today the landscape at Manson, and for miles around, is as flat as a tabletop.
Which is of course why no one has ever heard of the Manson crater.
At the library in Manson they are delighted to show you a colle of neer articlesand a box of core samples from a 1991–92 drilling program—ihey positively bustle toproduce them—but you have to ask to see them. Nothing perma is on display, andnowhere iown is there any historical marker.
To most people in Manson the biggest thing ever to happen was a tornado that rolled upMain Street in 1979, tearing apart the business district. One of the advantages of all thatsurrounding flatness is that you see danger from a long way off. Virtually the whole townturned out at one end of Main Street and watched for half an hour as the tornado came towardthem, hoping it would veer off, then prudently scampered when it did not. Four of them, alas,didn』t move quite fast enough and were killed. Every June now Manson has a weeklocalled Crater Days, which was dreamed up as a way of helping people fet that unhappyanniversary. It doesn』t really have anything to do with the crater. Nobody』s figured out a wayto capitalize on an impact site that isn』t visible.
「Very occasionally we get people ing in and asking where they should go to see thecrater and we have to tell them that there is nothing to see,」 says Anna