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Meteorite Craters and Impact Structures of the Earth
by Paul Hodge (University of Washington)
Cambridge University Press, Cambridge, 1994, 124 pp.
Black and white photographs and illustrations. Hardcover. $49.95
We have created a nation of Chicken Littles.
With all the attention Chicxulub, Shoemaker-Levy 9, and the South Pole- Aitken Basin have received lately, planetary impact cratering is riding the crest of a popularity tsunami right now. But the growing awareness of impacts is producing some strange encounters at Space City. Even the woefully inadequate monosyllabic grunts of post-grunge Texabilly have been replaced by crater-speak around these parts. Just last week, I overheard a rather harried check-out clerk at the corner Stop and Go exclaim, "This job exceeds my Hugoniot-elastic limit, man; I am going irreversible!" Unfortunately, he pulled out a rather hefty Muong Nong tektite and tried to bludgeon the old patron who was buying 25 Lottos with a sack full of pennies. The geezer shifted deftly away from the strike and rapped the youngster's knuckles sharply with the pointy end of a shatter cone he had concealed in his pocket. "Decompress, sonny, the pressure just means you're near ground zero. Lower your Z and go with the flow; you'll rebound soon enough." Sonny licked his bruised hand and tried his best to fit 2500 pennies into the cash drawer.
I read Paul Hodge's book, Meteorite Craters and Impact Structures of the Earth, last week; I note this because I have the task of reviewing the book, and if there is one thing that I have learned from my many years at the knee of the master it is this: You should probably read a book before you review it. This simple truth is not universally adhered to, however. For instance, another book on cratering was reviewed recently by two people (who shall go unnamed) who, judging from their mistakes, could not possibly have read the book first. These tag- team reviewers clearly thought of themselves as true scientists because they, the great analytical thinkers that they are, wrote papers with lots of integral signs and inverted triangles and numbers with lots of decimal places and stuff. And the author? Well he was a poor misguided geologist, practicing the antiquated and totally unnecessary act of gathering empirical constraints. The problem arose because the author's observations didn't support the reviewers' theories. And any fool (well, two fools in this case) knows that when observations don't support model predictions, you discredit the observations. I suspect that these two wizened scientists would go irreversible if they tried to read Paul Hodge's book. It doesn't contain a single equation.
What Hodge's book does have a lot of is craters and suspected craters on Earth: 139 to be exact. It's sort of like a catalog of crater localities with some photographs and some text. The craters are organized geographicalphabetically. [Sorry, a geologist feels a strong need to invent a word now and again, and this one seems to fit here: The major divisions are geographical (Canada, Asia, Latin America, etc.) but within each major group, the individual craters are listed alphabetically.] The book's listing of craters is uncritical in the sense that a lot of controversy surrounds many of the listed features. But the author is upfront about this wherever possible, and, in my opinion (which is the only one that counts here), the major importance of the book might be that it motivates geologists to go to these places and look for themselves (except of course, for the ones that are really far away and hard to get to, like Rio Cuarto, or are in really primitive localities like suburban Chicago).
On average Hodge dedicates less than a page to each crater. But the kinds of information and how much space an individual site receives in the book vary greatly. In some cases this is scholastic; for instance, there is a lot of space given to the Barringer Crater and the Ries Crater; after all, these are well-studied and very important features. (Actually, those of us in the cratering business have long recognized that there is little need to study any other craters, but we don't want the funding to dry up.) In other cases, it seems like the author depended upon contributions from established researchers. Those that responded most generously were justly rewarded; consequently, we are treated to pages of photomicrographs from the Canadian Geological Survey in sections on Slate Islands and Saint Martin, even though there is no explanation or discussion of the microscopic features shown. Judging from the section on the Marquez Dome, I was out of town.
There is also a lot of information on Australian craters, mainly because Hodge attended the now-famous Australian Crater Expedition in 1990. That was where about 50 crazed curiosity seekers followed Gene Shoemaker across about a kajillion miles of dirt tracks, sucking dust and ogling the marvelous outback scenery that all too infrequently held, in near field, an impact crater. Hours or days of cramped travel in a crowded bus were momentarily rewarded by a brief stop at a crater, on occasion arriving just as the Sun was departing. So we visited over a dozen craters--some of the best examples on Earth--in less than three weeks. The trials of such an ambitious trip brought out extremes in personalities and brought home an important lesson to me: Some of the strongest men on that trip were the women, unflinching, always pitching in, never complaining through it all. Some of the men, however, griped and whined incessantly. Okay, we made camp a couple of nights after midnight, and maybe (just once) we had to drink water that dead birds floated in. So what if we didn't get a hot meal each and every night or that mechanical breakdowns were a daily occurrence. It was the bush a thousand miles from nowhere where feral camels, endless acres of termite mounds, and spinifex punctuated a landscape red as rust. It was roller coaster rides over 30-meter-tall sand dunes, and a night sky so bright it is forever burned on my retinas. It was an experience I will never forget and neither, apparently, will Paul Hodge.
This book is clearly not intended to be a heavyweight treatise on impact, but rather a light, short, entry-level catalog of terrestrial craters. Hodge has faithfully summarized current views on most craters from existing publications and provides a brief list of references at the end of each discussion. In all cases, Hodge's book gives enough information so that a curious outsider could go to the university library and dive into virtually any crater's literature head first (caution: literature may be dangerously shallow in some areas). In that regard it is a very useful resource.
But this prince is not without a few blemishes, and the big nose-wart, as it were, sits prominently in the book's introduction. Hodge attempts to summarize in less than a page the key aspects of the cratering process; for the most part, this suffices and is appropriate for the lay person for which it is intended. But what was he thinking when he was composing the tektite section (bottom, p. 3)? ". . . The frontal layer of compressed gas is capable of melting and ejecting blobs of rock before the solid object touches the Earth's surface. These blobs are the tektites and . . ." I don't think so. Also, on page 4 Hodge discusses "shock lamellae and linear features in quartz" and states that "these kinds of features are common in lunar rocks. . . ." This is, at best, misleading to the uninitiated student for which this book would otherwise be most useful.
Other than these deficiencies, the errors are minor and the annoyances are few. In the next edition I would like to see more use made of the photographs; some are so small they are useless, some are not described, most need scale bars, and virtually all seem simply to be expedient ways to fill the pages of, even so, a very short book. And speaking of artwork, who thought up the bright idea of putting midnight blue print on a black cover? This virtually ensures that the book will go unnoticed on library shelves.
While this book will be of limited use to impact specialists, it could be a valuable resource for students or anyone else interested in learning more about impact features. This in itself is a laudable purpose given that so many of the major contributions in terrestrial cratering come from outside the professional community. So, if you have a repressed desire to learn about terrestrial craters but don't know where to start, this book is for you. Who knows, maybe you'll discover something that the theorists will attempt to discredit. At that point, congratulations would be in order.