WALTER BUCHER'S LAST FIELD TRIP AND CONVERSION TO THE IMPACT ORIGIN OF METEOR CRATER: A TRIBUTE TO AN OPEN MIND

Into the 1960’s, Walter H. Bucher (1888-1965) eloquently defended cryptovolcanic origin of explosion structures against R. E. Dietz’s astrobleme interpretation, even invoking endogenic control of Meteor Crater by the Holbrook anticline. I was present when E. M. (Gene) Shoemaker changed his mind, on May 2, 1964.

Bucher had arrived armed with anti-impact arguments. H. H. Nininger had described augite in crater ejecta, which reminded Bucher of euhedral pyroxenes scattered at Monument Butte, a diatreme within sight of Meteor Crater. Gene showed him vesicular droplets of fused Kaibab dolomite with microscopic radial cpx aggregates. Having seen Permian Kaibab limestone at the Grand Canyon, Bucher wondered if dolomite crater ejecta could be Mississippian (Leadville) from depth. Within minutes of arrival, he identified brachiopods in ejecta as Permian. On an earlier visit, he had noted reverse grading in rim ejecta. Gene interpreted this deposit as a Pleistocene terrace. Finally, Gene’s meticulous structural mapping convinced Bucher of the realities of the overturned rim and outward thrusts. As we left, he conceded Meteor Crater, “but the Ries, that’s different.” He died nine months later.

Walter Bucher presciently recognized the planetary importance of cratering and taught all aspects of the problem. Although wrong on impact (and fixed continents), his students fondly remember ”Uncle Walt’s” enthusiasm, generosity, legendary absentmindedness, and, above all, his open mind. These characteristics are evident in my 1949 Columbia class notes, copies of 1964 letters between Bucher and C. S. Beals (Dominion Observatory, Ottawa) on Canadian craters, personal correspondence about our trip to Meteor Crater, and my recollections of the trip, written shortly afterwards. The evidence for impact cratering and plate tectonics became overwhelming within three years after Bucher’s death. Judging by his Meteor Crater conversion at age 76, is it possible that he would have accepted these novelties, had he lived?