News Release, Kansas Geological Survey, Dec. 16, 1994
The Canyon Revisited--A Rephotography of the Grand Canyon, 1923-1991, published this fall by the University of Utah Press, features 45 pairs of black-and-white photos of the Canyon. One set was taken in 1923, the second set was taken 68 years later from the same locations.
The 1923 photographs were shot during a trip, sponsored by the U.S. Geological Survey, aimed at mapping the canyon and examining possible dam sites. The geologist on that trip, Raymond C. Moore was the state geologist of Kansas, and his photographs and field notes from that trip reside today in the KU archives. The 1991 photographs were taken by Survey photographer John Charlton. Text in the new book was written by Survey staff members Don Baars and Rex Buchanan.
"The purpose of rephotography is to compare a set of old photos with new ones to determine what changes have occurred in the meantime," said Don Baars. "The 1923 trip was probably the most important trip down the Colorado River since John Wesley Powell's 1867 expedition. The 1923 crew saw the Canyon before the advent of human changes that began with the construction of Hoover Dam in the 1930s and continued with Glen Canyon Dam in the 1960s."
In September 1991, the Survey crew spent three weeks in the Canyon, pinpointing sites where the 1923 photos were taken. The 1991 crew took new photographs, then compared old and new for changes.
Some of the photo pairs show little change in the Canyon over 68 years. Except for rapids, where flooding had rearranged boulders, many geologic features appear much the same--most canyon walls show little erosion and it's possible to recognize the same rocks in both the old and the newer photos.
"The most striking thing about some of these photos is the lack of change," said Baars. "The geology is virtually the same. The photo pairs give a good sense of just how long it took erosion to form the Grand Canyon."
Other photos, however, show substantial change, much of it related to human activity. The Colorado River is considerably less silty in the modern photos, for example, because Glen Canyon Dam, above the Grand Canyon, allows sediment to settle out of the river before it enters the Canyon. The photos also show locations where the river, now starved for silt, has eaten away sandbars along the Canyon.
Probably the most noticeable change in the Canyon between 1923 and 1991 is the explosive growth of new vegetation. Because Glen Canyon Dam has restricted flooding, vegetation has grabbed a strong hold along the river's edge. Non-native plants, like the tamarisk or salt cedar, have invaded the river bank in huge numbers.
"Many of these photographic pairs show a dramatic increase in vegetation," said Baars. "In some spots close to the river, the new growth was so great that it was impossible to replicate the photos. The vegetation was just too thick."
Vegetation wasn't the only impediment to photography in the Canyon, according to Charlton. Heat, dirt, and even the occasional Grand Canyon rattlesnake made for challenging working conditions. "Simply finding the exact locations where the original 45 photographs were taken proved to be difficult," said Charlton. "And each vantage point offered its own problems. At several locations, for example, the original vantage point had been destroyed by erosion."
In addition to this book, Charlton's photographs have appeared in a number of geology books and journals. Don Baars is the author of several books about southwestern geology, including The Colorado Plateau: A Geologic History (University of New Mexico Press, 1983). Buchanan is the co-author of Roadside Kansas: A Traveler's Guide to Its Geology and Landmarks (University Press of Kansas, 1987).
"The photos in The Canyon Revisited show the slow pace of erosion. That may help give people an appreciation for the concept of geologic time," said Baars. "The photos also show that human activities can have great impact, even in a place as vast as the Grand Canyon."