By Martha Demas
The evocative sight of temple and palace ruins engulfed by dense jungle has long attracted the imagination of poets, the interest of archaeologists, the avaricious eye of the tomb robber, and the curiosity of the general public.
Such scenes abound in parts of Asia and Central America. These geographically and culturally distinct regions have in common long-abandoned ancient settlements and humid tropical environments. The fate of these settlements is predictable as the tropical forestkept at bay by human effortrapidly returns to overwhelm the structures when the site is abandoned.
The initial damage to structures caused by the return of the jungle is exacerbated when ruins are excavated. Liberating buildings from their jungle cover exposes fragile materials and weakened structures to further deterioration from the erosive effects of wind and rain, microfloral growth, and changes in humidity and temperature. Large numbers of tourists visiting an excavated site can accelerate the process of destruction already at work.
Preserving these tropical sites for the future presents an enormous challenge. The ancient Maya cities of Central America and Mexico exemplify the problems faced by archaeologists, conservators, and site managers. While many Maya sites remain virtually inaccessible because of their remoteness and jungle cover, others have long been subject to excavation and, more recently, to high levels of visitation.
In 1992, the Getty Conservation Institute began a collaborative effort with archaeologists and government authorities in the Central American country of Belize to address some of the problems of conserving archaeological sites in humid tropical zones. The venue for project activities is Xunantunich, an ancient Maya city of the Late Classic and Terminal Classic periods (700-1000). Here, archaeologists from the University of California, Los Angeles (UCLA), directed by Dr. Richard M. Leventhal, are undertaking a long-term research and excavation project, which includes development of the site for tourism. The site was selected by the Institute in part because conservation efforts could be fully integrated with excavation activitiessomething that rarely occurs during most archaeological work.
Located near the Guatemalan border, Xunantunich has been Belize's national symbol of its Maya past. The site is dominated by a 40-meter (130- foot) high pyramid, the "Castillo." Still the tallest building in Belize, the Castillo was probably the primary ritual building for the site and once displayed a 3-meter (10-foot) high stucco frieze on all four sides. The last unexcavated segment of the frieze, which features a three-dimensional figure of a Maya ruler, is currently being excavated by the UCLA team. Surrounding the central area are numerous outlying settlements that remain largely uninvestigated, still covered by the verdant tropical forest.
Primary goals of the Conservation Institute's Xunantunich project are to understand more fully processes of deterioration in humid, tropical environments and to develop methods for conservation of architectural and decorative stone, stucco, and mortar. Most architectural elements in tropical areas experience weathering degradation that differs significantly from such processes in colder, drier, or more temperate regions. Foremost among these differences is the growth of lichens, algae, fungi, and mosses on the almost continuously damp surface of exposed structures. Microflora penetrate stone, loosening grains and thereby decreasing the stone's cohesive strength. Even in the absence of biodeterioration, the degradation of mortar, plaster, and stone in tropical environments can be severe, as high relative humidity and frequent rainfall result in the gradual dissolution of soluble components in these materials.
With these problems in mind, the Institute is researching the use of chemical consolidants for strengthening limestone, and the use of biocides for controlling microfloral growth. Parallel with laboratory work at the Institute, experiments began at Xunantunich to test the ability of selected water-based consolidants to penetrate limestone and cure in a high-humidity atmosphere, thereby increasing the stone's resistance to temperature and humidity fluctuations. Field testing consists of treating limestone samples with consolidants and exposing them to the weather. Environmental monitoring stations, equipped with battery-powered systems recharged by solar panels, have been installed at the test locations to record weather data, which will be used to define test conditions for artificial aging tests in the laboratory, and to evaluate the testing in the field.
To control the microfloral growth that weakens masonry, the testing program will identify biocides that are effective, long lasting, inexpensive, and have negligible adverse impact on the environment. Selected biocides are currently being field-tested at Xunantunich. Field testing of consolidants and the biocides will continue for at least another two years.
The structural damage to Maya monuments caused by the intrusion of roots of shrubs and trees into the building fabric is a consequence not only of the tropical environment, but also of the building techniques employed by the Maya. The Maya built their pyramids in stages, each stage constituting a separate structural unit. During their period of use, the structural equilibrium of these buildings was assured by the application and continuous maintenance of an impermeable stucco facing on a structure's exterior. Once a building was abandoned, its stuccoed floors and walls cracked, and vegetation and water invaded, causing weakness and the potential for collapse. Ironically, although vegetation was the initial source of damage, in time it became the agent of stability by literally binding together, through root penetration, the collapsing structure. Removal of the vegetation in order to excavate the structure disrupts once again the equilibrium and exposes the structure to a fresh cycle of deterioration.
Conservation of excavated structures often necessitates intrusive interventions, such as dismantling and rebuilding of walls and the addition of new materials. Developing methods for structural consolidation and stabilization that conform to conservation principlesincluding minimal interventionwhile providing visitors with an understanding of the original appearance and construction is a challenging goal of conserving Maya monuments. All too frequently, the necessity for intrusive interventions has led to a too-heavy-handed approach, involving total reconstruction and a liberal interpretation of the original structure's appearance.
At Xunantunich, excavation is now exposing two of the pyramidal structures in the central plazathe monumental Castillo and a smaller pyramid. As excavation proceeds, the Conservation Institute is providing expertise and on-site training in architectural and stucco conservation to the UCLA archaeological team and the Belizean authorities, to create a model for conservation of other structures. Architectural conservator Rudy Larios, with over twenty years of experience in conserving Maya structures in Guatemala and Honduras, together with experienced stucco conservators from the Instituto Nacional de Antropología e Historia in Mexico, provide this professional expertise. Their work has the additional benefit of helping to strengthen the network of practitioners in the region.
Although archaeological documentation during excavation is a well-developed practice, the same cannot always be said of documentation for conservation purposes. Institute staff and consultants, working with members of the archaeological team, developed guidelines for conservation documentation, including a format for recording the condition of structures prior to intervention, and photographic protocols for capturing the transformation of jungle-covered mounds into consolidated structures.
In keeping with the Getty Conservation Institute's larger goals of promoting appropriate conservation and management of archaeological sites, the Institute's Training Program is organizing workshops and short courses at the local and regional level. Two recent activities in support of conservation needs were a three-day seminar on management policy with members of the Belize Department of Archaeology, and a collections management workshop for staff members of the Belize departments of Archaeology and Museums.
Martha Demas is a Fellow with GCI's Special Projects.