Ways and Means

Accretionary Wedge #43 has the theme of “my favorite geological illustration.” Hollis chose this theme at my urging based on her post about one of the spectacular old “birds-eye” oblique views of Black Hills geology. There are plenty of truly artistic geological figures and illustrations from the era before computer aided drafting, and I’d be hard pressed to choose among them. Indeed, I’m also a great fan of the Hudson River School of painters, and though many drew inspiration from geology, whether they can accurately be called geological illustrations is somewhat questionable – as I’m reminded daily by the Bierstadt print in my dining room (others, of course, are more true to nature).

During my summer internship at the USGS in Menlo Park, CA in 1996 I became familiar with more recent works of cartographic art, such as the oblique illustrations of geological phenomena in the Sierra Nevada by Tau Rho Alpha (yes, that’s his name). See some of the figures in The Geologic Story of Yosemite National Park (1987) by N. King Huber, for examples of his work.

Ways and MeansLazarus, Duke of YorkNonetheless, from the moment I suggested this theme for an Accretionary Wedge there was really only one figure I gave serious consideration to selecting as my favorite geological illustration. And that is Figure 5 (at left) from the 1877 printing of Grove Karl Gilbert‘s Report on the Geology of the Henry Mountains. Captioned “Ways and Means,” the hand drawn illustration of a mule’s head is a reminder of the remote nature of the Henry Mountains – the last significant region of the conterminous United States to be explored and scientifically documented – and the realities of fieldwork in the mid-1870s in the West. The figure is actually a partial reproduction of a sketch of the mule “Lazarus, Duke of York” (reproduced at right) that Gilbert himself sketched in one of his own field notebooks. What draws me to this image even more, however, is that it was removed from the second (and much more widely circulated) printing of this famous report (though I was fortunate that UW-Madison had a first edition in its library collection when I was a grad student there). I learned the history of this figure through the scholarly work of Charles B. Hunt (of ‘cactolith’ fame), in his “Geology of the Henry Mountains, Utah: as recorded in the notebooks of G.K. Gilbert 1875-76″ (Geological Society of America Memoir 167). Hunt raises the possibility that the figure was cut to save printing costs, but suggests that resetting the rest of the type would have likely had the opposite effect. I prefer to think that some humorless editor gave old Lazarus the ax, in an effort to make the report more professional looking (it was, after all one of the first USGS Professional Papers). I’d like to think G.K. Gilbert would have enjoyed publishing about his work and travels in a less formal medium, such as the geoblogosphere. I certainly feel that modern geologic communication could use some of the more personal, humorous touches of which “Ways and Means” is symbolic.

Xenobombs on the Half Shell

This morning Callan Bentley at Mountain Beltway published a blog post that included the photo of a beautiful sample of a Kilbourne Hole xenolith cut in half to reveal the mantle peridotite core surrounded by a thin selvage of basaltic rock. These sorts of basalt covered xenoliths are not so uncommon as they might at first seem – indeed, Siim Sepp at Sandatlas proceeded to produce his own sample from Lanzarote in the Canary Islands. In fact, I’ve collected samples like this at Kilbourne Hole in New Mexico and Dish Hill in California’s Mojave Desert, and I’ve seen similar samples described from the cinder cones on Mauna Kea in Hawaii. In all of these localities the xenolithic core of the sample was ejected pyroclasticly from cinder cones that produced broadly alkaline basaltic lava compositions (though Kilbourne Hole was more of a dry heave, if you ask me). I’ve also collected mantle xenoliths with a similar basalt selvage from Haulalai Volcano in Hawaii, however in that case the xenoliths were left behind as a lag deposit in a basaltic lava channel.

What I want to push back on here, though, is the term that Callan coined for these samples, “xenobomb”. Though the samples of this type from cinder cones could arguably be called volcanic bombs, the samples cited by Callan and Siim lacked the streamlined features of a true lava bomb. In fact, I’ve seen a spectacular sample of a xenolith-cored lava bomb, complete with a beautiful aerodynamic basaltic bomb coating in the petrology lab collection of the University of Wisconsin-Madison (sadly I don’t have a photo). What really irks me about “xenobomb” is not the shape of the particular samples that Callan and Siim used to define it, but the etymology of the word. “Xenobomb” suggests a “foreign” bomb. That’s just not what these samples are. Perhaps in their new lab environments they’re xenobombs, of a sort, but on the volcanoes where they were collected “xenobomb” suggests bomb pieces that are foreign to the eruption from which they originated, and that’s just plain wrong. Plus, I’d hate to think of the cinder cones that formed them as xenobombers – can you imagine the hatred that would be heaped on them by American politicians? Before long there’d be campaigns to rid America of the xenobombers and innocent cinder cones like Wizard Island and Sunset Crater could be swept up in the hysteria. Words have meaning – use them cautiously.

Could this be the end for innocent cinder cones?