"Ethnic identity is accompanied by ethnic stigmatization, and the [ruins of the] Basque hotels, set within the larger building community that is the West, are reminders of the both the region's cultural diversity and cultural divisions. "
The fabric of Square Tower, its stonework crafted by the ancestors of Arizona's and New Mexico's Pueblo Indians, has withstood the test of centuries. But during the last three decades, nature—perhaps unwittingly abetted by an early preservation plan—has been getting the upper hand. To deal with the problem, the Park Service has put together a repair kit packed with the tools of an unusual range of professionals. This meeting of the minds promises to pioneer a new way of caring for the nation's prehistoric landmarks.
The edifice rises up in a complex of intriguingly shaped houses, dams, and towers, situated at the head of Little Ruin Canyon in southeastern Utah's Hovenweep National Monument. Not much is known about the prehistory of Hovenweep—declared a national monument in 1923 because of its spectacular Puebloan architecture—since there has been little excavation here. The construction of the complex, wet-laid, single- and double-coursed walls of carefully shaped stones interrupted here and there by raised doorways, is typical of the Northern San Juan Puebloans, evidenced in the towers, great houses, kivas, dams, and walls they built throughout the region in the 13th century. It is the location and durability of this complex that sets it apart. One- and two-story structures cluster at the heads of canyons—on the rims, on the slopes, on boulders, even tucked into the cliff faces. For some, only rubble remains; others are superbly preserved except for their roofs. Square Tower, the centerpiece of the Park Service unit in which it resides, is one of these.
The tower's high, nearly intact walls rest on a sandstone boulder immediately adjacent to the main drainage at the foot of the canyon, next to where a spring empties out. And there lies the problem. In 1960, with water eroding the rock and threatening to topple the tower, the Park Service constructed a protective wall of local sandstone set in Portland cement mortar. Then, obscured by overgrowth and forgotten as personnel changed over the next 30 years, nature went to work.
When the vegetation was cut in 1990, it became apparent that the wall, far from staving off the erosion, had possibly accelerated it, with sizable areas eroding out of the rock face on the northeast and southeast corners. Deposits of calcium sulfate on the boulder and the wall meant either a dissolving of the natural bonding material in the sandstone or salt from the concrete eating its way in. Or both. The cause of the problem was obvious—water. But what were the forces feeding the erosion? The relatively high water table? Surface runoff? Or water moving underground from the mesa into the drainage?
Park Service managers took immediate action. Mary Griffitts, geologist at Mesa Verde National Park, undertook a study of consolidants that could keep the sandstone grains from dissolving (with erosion, the grains flake off to the touch). She soon focused on ethyl silicate as the most promising. The monument's staff pruned back the vegetation and—to channel possible flash floods—constructed a gabion along the bank adjacent to the boulder. Runoff patterns were also modified to direct water away. The deep cavity between the wall and the boulder was filled with mud mortar, a natural material, to keep out water. Historic photographs of the tower and boulder were collected (the earliest dates to 1892), and the public trail was closed so visitors would not get hurt by a collapsing wall.
Meanwhile, an advisory group was recruited with the professional depth that could not only solve the problem at hand, but also pioneer a new paradigm for preserving such structures, which dot the Southwest. Present on the team were a geologist, several historic architects and structural engineers, a fabric conservator, and a number of archeologists, representing the Park Service, the U.S. Geological Survey, the Bureau of Reclamation, the University of Pennsylvania, and the Utah Historic Preservation Office.
There was a crosscurrent of ideas that one would expect given the group. There is a twist in the tower, possibly induced by recent events. Believing that, unchecked, it could hasten the structure's demise, one of the architects suggested erecting a rigid armature inside. An engineer countered that an inflexible skeleton could restrict natural shifts caused by changes in temperature. So, among other short-term recommendations, the group advised measuring the movement scientifically as a first step.
The work of the Historic American Building Survey, a Park Service unit who fielded a project team in 1993, is the result of this interdisciplinary ferment (see Federal Archeology, spring 1995). Under the direction of HABS architect Joseph Balachowski, the team deployed the tools of architectural photography—Linhoff Metrika 150mm and 90mm photogrammetric cameras—with paper bulls-eyes affixed to the stonework. The bulls-eyes acted as data points, ensuring a record as precise as an architect's drawing, a first for a Park Service archeological site.
Past documentation of such ruins has generally been accurate, but elevations, almost by necessity, have been drawn with a good deal of artistic license. The highly irregular surfaces make conventional measuring all but impossible. In this case, HABS produced elevations directly from the photogrammetric images, which were digitized, stone by stone, into Autocad software at the computer-aided drafting studio the survey shares with the Historic American Engineering Record (part of the reason for such exactitude was to have a record of this architectural mastwork should it ever be lost).
With these data as a baseline, the Park Service monitored the movement using a program designed by Park Service engineer Dave Keough. A year's worth of measurements helped determine whether the twist was introduced during the tower's construction in the 13th century, between its abandonment and the earliest photographs in the late 1800s, or recently. The data showed no movement significant enough to be a threat, and the vintage photos evidenced no twisting since the turn of the century.
Not all of the plans unfolded as expected. The engineers had recommended burying a French drain in the rock debris against the boulder on its west and south sides. But excavators under the supervision of Mesa Verde archeologist Dave Johnson found a well-preserved kiva just below the surface. Consequently the drain was not installed. Instead, the kiva was covered up (to protect it from the elements) and moisture meters were sunk in the backfill to measure the water flow. The meters, which also record temperature, have been read monthly since 1995.
The park archeologist advised installing ceramic pins in three places on the boulder to monitor surface erosion. And, on the recommendation of conservator Frank Matero, deep voids in the sandstone were packed with hydrated hydraulic lime and sand, a dry, natural mixture softer than the rock itself (harder materials like the concrete tend to accelerate erosion).
During this time, Griffitts was testing the ethyl silicate on boulders near the tower, and the surrounding water was tested for salts to determine if it was the origin of the eroding forces. Several stones were removed from the wall but no erosion was noted behind them. The stones were reset in a mud mortar (again, a natural material) for easy removal and checking in the future.
Al Decker, a retired member of the crew who built the wall, was interviewed, but could remember little of the specific rationale behind its construction. The obvious concern at the time was that the eroding boulder would lead to the collapse the tower.
The joints in the tower's stonework were filled with mud mortar hardened by a liquid acrylic polymer to extend its life. This work was carried out by the Mesa Verde masonry workers Raymond Begay, Gene Trujillo, Willie Begay, and Kee John—assisted by myself and Phil Wilson. Before repointing, Mesa Verde archeologist Larry Nordby wrote an historic structures report documenting the details of the mortar and other features of the tower.
After three years of successful lab and field tests, it was time to apply the ethyl silicate to the boulder. But first, conservator Anne Oliver did detailed photographic and graphic documentation of the sandstone surface. Salts were removed too. I worked with Griffitts and Matero to apply the ethyl silicate, in 1996 and last year.
The project continues. The ethyl silicate has definitely hardened the boulder, but the real cause of the deterioration has not been addressed. The rain falls and the stream still flows into Little Ruin Canyon, with the water table only inches below the surface at the base of the boulder much of the year. It is hoped that the erosion has been reduced but only monitoring will tell. Now, with the short term recommendations carried out, we plan to reconvene our advisors to take on the long term preservation of the boulder—and the precious piece of our nation's heritage perched precariously upon it.
For more information, contact Kathleen Fiero, Site Preservation (Stabilization) Archeologist, Mesa Verde National Park, Mesa Verde National Park, Colorado 81330, (970) 529-4510, fax (970) 529-4498.