How Archaeologists Are Using Radar to Visualize Subterranean Structures

Two weeks of virtual digging at a fabled site upends two decades' worth of preconceived ideas

By Heather Pringle
Oct 24, 2005 5:00 AMNov 12, 2019 6:23 AM


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Five circular depressions in the desert north of Bluff, Utah, have long been a source of tantalizing frustration to archaeologists. For the past two decades, the prevailing theory was that the desert hollows conceal five great kivas—subterranean circular masonry structures approximately 40 feet in diameter where ancient Pueblo people gathered more than 700 years ago to perform religious rituals. Although researchers have longed to excavate the site, called Comb Wash, the cost—roughly $1 million—and the time—about five years—have been prohibitive, not to mention the opposition by Native Americans to disturbing sacred grounds.

Then along came a pair of archaeologists from the University of Denver with a noninvasive, nondestructive technology to topple conventional thinking. Using ground-penetrating radar and software originally written for scans of the human brain, archaeology graduate student Tiffany Osburn and ground-penetrating-radar expert Larry Conyers have visualized the subterranean structures buried beneath the sediment. Rather than revealing great kivas similar to those at Chaco Canyon, New Mexico, capable of accommodating hundreds of pilgrims, Osburn's analysis showed only small family kivas suitable for sheltering no more than 20 or so people. Although the results seem disappointing, "it's an important study," says Winston Hurst, an independent consultant with the Comb Wash Archaeological Project.

Gaining a better understanding of the relationship between the great kivas and great houses in Chaco Canyon and the vestiges of similar buildings in 150 other communities scattered across the Four Corners region could help shed light on the rise and fall of one of the most fabled ancient civilizations in North America.

Researchers previously theorized that the communities—many linked to Chaco by prehistoric roads—formed part of a powerful religious society that spread its tentacles far into outlying areas. Comb Wash was presumed to be a major hub in this sacred network.

The new radar studies suggest otherwise. "With two weeks of research, 20 years' worth of preconceived ideas were shown to be false, and now we have to start developing new hypotheses," Conyers says. He now believes that the roads in the Comb Wash region "were probably nothing more than pathways that were used to connect little hamlets of agriculture."Impressed, several southwestern archaeologists have asked Conyers to test other Pueblo outlier sites.

The potential of ground-penetrating radar and other remote-sensing technologies to answer key archaeological questions is universal. Conyers is using radar in Tunisia to map third-century Christian catacombs and in northern Peru to scout for buried tombs and other architecture at the Moche site of El Brujo.

Archaeologists hope such systems will eliminate the need for large excavations and help locate artifacts lodged under ruins. Conyers's system can detect objects as small as golf balls buried beneath five feet of sediment, but he cannot tell his colleagues exactly what they are. "You can make out individual artifacts," he jokes, "but rarely are you bright enough say what they are."

NASA imaging technology reveals Angkor was larger than New York City

The lavish temple complexes of Angkor, the capital of the Khmer Empire from the 9th to the 16th centuries, offer few clues about what led to the collapse of the city. Even estimating the geographic size of the city was once considered a daunting task because the Angkorians used perishable thatch to build their homes. "You can be standing right in the middle of a 12th-century settlement and not even know it," says Damian Evans, deputy director of the Greater Angkor Project. But archaeologists are finally piecing together a comprehensive portrait of Angkor, thanks to data gathered by NASA Jet Propulsion Laboratory imaging experts. Remote-sensing devices that are sensitive to minute variations in the water content of soil revealed the footprints of vanished houses, water tanks, canals, and even historic rice fields, leading researchers to conclude that Angkor is most likely the world's largest archaeological site, a sprawling low-density metropolis covering an area larger than New York City. The remote-sensing data have also provided researchers with a plausible explanation for the fall of Angkor. To feed the burgeoning city, farmers deforested hills to the north for rice fields, greatly increasing erosion and the prospect of ecological disaster. Moreover, they constructed a massive irrigation system of canals in order to control flooding and store water for the dry season. "So it could have been that this system just got so intricate and complex to manage that irrigation became impossible," explains Evans.

Brian Fagan is a professor emeritus of anthropology at the University of California at Santa Barbara whose concern about conserving existing archaeological sites is spreading.

There is a great deal of talk today about archaeological sites being finite, rather like fossil fuels, but most research involves extensive excavation. Are archaeologists destroying sites as they go? F:

Well, we are caught in a catch-22. On the one hand, yes, archaeological sites are a finite resource that is rapidly being exhausted by looting, industrial development, the massive expansion of cities, roads, strip-mining, deep plowing, you name it. This means that archaeologists often have to mitigate the destructive effects of development. In some cases you can redirect a road and save a site from being overrun, but in others all you can do is retrieve as much information about the past as possible before the bulldozers move in. The problem is that excavation destroys sites, and we're in a crisis of sorts—as serious or more serious than deforestation—because while you can regrow trees, you sure can't regrow archaeological sites. As Kent Flannery, a University of Michigan archaeologist, once said, we're the only anthropologists who murder our informants in the process of studying them.

Is archaeological excavation just looting by another name? F:

It is, in a sense, if you don't publish the results of field research as thoroughly as you can. One of the dirty secrets of archaeology, as someone once put it, is that people really lapse when it comes down to laboratory work or writing the results up. It really is a scandal, the amount of archaeology that is not published.

Which noninvasive techniques hold the greatest promise? F:

Clearly, ground-penetrating radar has enormous possibilities, as does remote sensing. And the use of geographic information systems, which allow us to put archaeological and environmental data into digital landscapes and play with it and develop different scenarios, is a major revolution. All these methods are a far cry from vast area excavations, which are of course relics of Victorian times. As a colleague in New Zealand said to me, a large number of archaeologists are still behaving as if they were 19th-century adventurers.

How easy will it be to persuade them to adopt new approaches? F:

It's a very complex issue. A lot of people love going into the field—I do—getting their feet dirty, digging, surveying, watching the countryside. This will definitely continue, and so it should, but what I think is doomed are the huge long-term excavations of classical cities. They are an old concept. It's a fascinating time to be an archaeologist, but you're not going to be an Indiana Jones or a Flinders Petrie. You're probably going to be a lab rat.

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