As the largest and most famous cliff dwelling in Mesa Verde National Park, Cliff Palace is the park's interpretive centerpiece. Many of the half million visitors each year make it a point to stop and see Cliff Palace, either through magnificent views from one of the nearby overlooks or by taking a ranger-guided interpretive hike into the cliff dwelling itself. Until recently, one of the key components of a Cliff Palace interpretive tour was Kiva F, a 13th century circular structure located in the southern portion of the alcove. Partially subterranean, the structure was built on top of loose fill, sandstone slabs, and cultural debris. Surrounding Kiva F are Kivas C and G, an assemblage of multistory rooms, and retaining walls that ascend toward the back of the alcove. As each ranger-guided hike (on average 15 tours and 740 visitors per day or roughly 3,962 tours and 160,600 visitors per year ) moved through the site, they walk up a short set of steps and stand around Kiva F on a heavily stabilized pathway. Here the ranger discusses the character, function, and significance of a kiva to the Ancestral Pueblo people, and visitors have the opportunity to spend a few moments in thought. It was during one of these hikes in early summer, 2011 that a ranger observed what appeared to be a problem.
Just below the stabilized path, a small void had appeared in the masonry bench or banquette accompanied by the north wall now leaning precariously into the structure. In response, National Park Service archeologists began an evaluation of Kiva F to determine overall condition and potential causes. The team reviewed previous preservation treatments that had addressed water penetration, localized cracks, displaced segments of wall, and loss of mortar and stone. They then examined the void and extent of wall deflection, and weighed various options to stabilize the problem. As a remedial measure, a wooden brace was installed to support the north wall over a weekend, and the ranger-guided hikes were re-routed to avoid Kiva F.
When the team returned the following Monday, they were confronted with a more complex problem. While they focused on the north wall of Kiva F, a large portion of the south wall unexpectedly fell onto the Kiva floor. With no prior indication of an impending collapse, this event suggested underlying conditions that extended far beyond the structural boundaries of the kiva, potentially threatening much of the southern half of Cliff Palace. Further assessment of the surrounding structures, notably Kiva G just to the north of Kiva F, further reinforced these observations. What followed was the decision to expand the scope of investigation beyond Kiva F to include more detailed study of earlier stabilization efforts, comprehensive condition assessment of 102 architectural units (roughly the southern half of the site), and yet another look at the long-standing problem of water entering the alcove through cracks on the mesa top above Cliff Palace.
After months of exhaustive study, by July of 2012, it appeared that both localized deterioration of individual structures and features, as well as site wide systemic problems indicative of structural failure, were working in tandem.
Localized effects include loss, or substantial damage of stone, wood, mortar, and plastered/painted surfaces; compromised foundations; damaged architectural features (e.g. doorways, vents, wall niches, wall pegs, etc.); relatively small to severe wall cracks; and partially collapsed walls. These conditions were the result of both natural and cultural processes affecting the fabric of Cliff Palace in a fairly predictable, widespread manner. These same processes, however, can affect standing architecture and site deposits in different ways; as in the rate, magnitude, character, and distribution of specific problems. A simple example of this would be how one piece of sandstone remains intact while the one next to it crumbles into powder.
Systemic problems, while more difficult to detect, posed an equal or greater threat to the preservation of Cliff Palace. Studies suggested that much of the architecture in the southern portion of the alcove was predominantly footed onto small, irregularly shaped roof slabs or unconsolidated alcove deposits spread across a steeply pitched alcove floor. Over time these deposits, and the structures built on top of them, had begun to 'slide' downslope. This process could have been gradual, rapid or a combination of the two. Evidence in the form of a distinct linear crack and significant structural deformation extended from Kiva A at the south end to Kivas F, G, and H at the center of the alcove. In effect, what we saw was a fault line running parallel to the back of the alcove that may indicate a difference in the rate and magnitude of movement above and below the line. Further complicating the picture is the likelihood that a few larger roof slabs on the alcove floor provided a more stable footing for some structures, and thereby created both vertical and lateral thrust working to literally tear prehistoric structures apart. Large cracks, structural deformation, and rapid collapse - as illustrated in Kivas F and G - supported this interpretation.
While the collapse of Cliff Palace was and is not imminent, the combination of ongoing deterioration of individual features and structures along with an unpredictable foundation will eventually result in loss of architecture and archeological deposits. Fortunately, the cracks, voids, and leaning walls noted above provided critical clues to understanding what was causing the deterioration at time, how quickly it was occurring, if it was happening throughout the site or only in specific areas, and what steps we could take to slow or stop the process.
Summary and What's Next
The root of Cliff Palace's structural problems is the foundation –or the lack of a stable foundation –upon which the entire southern end of the community was built in the 13th century. Although the northern areas appear firmly based on bedrock, the southern end is footed in loose, unconsolidated soil and rubble. After nearly eight centuries, this lack of a solid base has caused the structures in the southern end of the site to slide downhill at uneven rates, leading to cracks, falling walls, and general instability. Work will continue on the site as needed to monitor, assess, and stabilize Cliff Palace as needed.
Some of the steps that have been or will be taken in the future include:
Completion of a comprehensive condition assessment in the north half of Cliff Palace
Careful study of preservation history and treatments
Geological and hydrological analysis of the alcove
Structural analysis of architecture
Installation of monitoring systems
Evaluation of visitor management objectives
Development of alternative preservation treatments
Why is it important to take these steps to stabilize and preserve Cliff Palace now? Cliff Palace is a significant place to millions of people who have walked its ancient pathways. It is particularly important in the traditions of the Pueblo people of the American Southwest. It also is a much-beloved part of Mesa Verde. National parks, including Mesa Verde, exist thanks to citizens who, more than 100 years ago, committed to setting aside these special places for the future. We are the beneficiaries of that trust. In what condition shall we pass Cliff Palace along to our children?