at Mesa Verde
Using Lasers to Help Save History >> By Elizabeth Lee
hen the CyArk team was asked to fly to Mesa Verde National Park for an on-location shoot for PBS s WIRED Science, they brought the scanner along as a prop for the show. Upon arriving at the park it became clear that the National Park Service was in need of much more than an expensive prop. Located in Southwest Colorado, Mesa Verde National Park is home to more than 4,800 archaeological sites. Six hundred of these sites are the famous cliff dwellings built almost 800 years ago by the Ancestral Pueblo Outside western walls of Room 11 at Spruce Tree House people. Sometimes referred to by their Navajo name, Anasazi, the Ancestral Puebloans are the Native American culture responsible for the adobe and sandstone dwellings found in the present day American Southwest. Although they occupied what is now Mesa Verde National Park for more than 700 years, most of the impressive structures we see today were built in the last 100 years of the Ancestral Puebloans time in the region, around 1200 AD. Despite their long period of occupation in the area, the site was abandoned in the span of two generations. The reasons behind the site abandonment are not entirely clear as the Ancestral Puebloans left no written records. Instead, the clues they left behind were the dwellings they once inhabited. As the most significant remains of this culture, protecting the cliff dwellings is crucial in preserving the heritage of the Ancestral Puebloans. Cliff Dwelling sites were constructed in the sheltering alcoves of the steep mesa canyon walls, and as such are somewhat more protected than free standing archaeological sites. However, the sites are still subject to deterioration caused by modern tourists and nature. Wind, rain, temperature changes and erosion have presented a clear and present danger to the continuing structural stability and integrity of the shelters. As a result, all of Mesa Verde s sites are in need of documentation, conservation and monitoring. The park s Square Tower House site became the perfect example of this need. In December 2006, a large boulder detached from the alcove face and damaged a two-story structure and one of the kivas on site. Currently, Square Tower House is one of the most significant sites in the park. It is known for its very unusual four-story tower and its ceremonial kivas with intact roofs. It is a popular spot for tourists visiting the park despite having to view the site from a designated observation area. Although the obvious damage from the rock fall had already been documented by the Park Service, when CyArk arrived at the site in August of 2007 there were still questions about what other unseen damage might have been done. Prior to the TV shoot, the CyArk team was taken on a tour of Square Tower House by the Field Director of the Archaeology Program, Julie Bell, who told the story of the rock fall. The site, although damaged by the rock fall, is still largely intact. The setting of Square Tower house is particularly compelling. Nestled into the alcove, the site overlooks one of the many canyons that cut through the mesa. The fourstory tower is the dominant feature of the site. The rock face serves as the back wall of the structure. A closer look at the site reveals footholds, worn doorways, and rock art glimpses into the everyday life of the people who once lived there. I just fell in love with it, said CyArk founder Ben Kacyra. On the spot, he decided that CyArk should help in recording the site and collect enough information to do a
Kiva G at Square Tower House is located against the easternmost rear wall of the alcove, and has a ventilation shaft emerging in the open area to its south. Near its hearth is a large vertical slab rather than the single wall course found in other Kivas at Square Tower House. Kiva G is in good condition. View of Kiva E, Rooms 35-36, and Room 26 at Spruce Tree House. When excavations and repair work were conducted on site in 1908, the lower-story wall of Room 26 (to the left) was in excellent condition and little work was needed. The curved west wall contains a fireplace in the northeast corner of the room. There is a passageway between the room and Kiva D. Kiva E has a passageway, visible in this picture, that leads to steps near an opening in the floor of Room 35.
Archaeologists carefully lower heavy and fragile laser scanning equipment 100 feet to the Fire Temple, which is accessible primarily by handholds, footholds, and ladders. structural analysis of parts of the site. Capturing the site with a laser scanner meant that CyArk would not only have a complete documentation of one of the park s most interesting sites, but that the survey data could be used to create a model of the recently damaged site. Without the aid of a complete set of survey equipment and with a limited time on site, it was decided that the tower should be the focus of data collection. The excitement of the project started even before the scanning. The equipment had to be lowered more than 100 feet off the cliff face down to the site. In order to meet the equipment at the bottom, team members had to descend using hand ropes, ladders and steps carved into the rock face. ScanStation Meets Square House Working within the limited time frame and around the WIRED Science production schedule, the site was scanned using a Leica ScanStation from six different locations. Given the condensed field time and lack of supplemental equipment, it was decided that the scans would be registered to one another using common points in overlapping scans. This cloud to cloud registration can be used to merge the scans fixed targets and a permanent control network are not accessible. By carefully planning the scan locations and scanning with significant overlap, the team was able to ensure accuracy across the site. The most challenging part of the scanning actually came from not only getting the scanner inside the tower, but to register the inside and outside of the building to each other. Great care had to be taken when the scanner was placed inside the tower so as to not damage the original plaster floor. By scanning the outside of the tower from several locations and by getting a very detailed scan of the inside, the two scans were able to be registered to one another through common points in the tower s several doorways. To say the CyArk work is important to the park personnel in charge of preservation is a bit of an understatement. Larry T. Wiese, Superintendent of the Park and overseer of the work done by CyArk, put it this way: Mesa Verde is both a National Park and World Heritage Site. The park s 52,000 acres hold nearly 5,000 archeological sites that we must care for and document. The detailed documentation, 3D imaging, structural analysis, and modeling that once would have taken many months can now be done in days. CyArk provides quick access from computer files to be used by field personnel, and remote access by researchers and students. Part of CyArk s mission is to increase awareness about heritage sites by making their information readily accessible to the public. The initial data collected at Square Tower House is already up on the their website, although additional research on the stability of the tower is still in progress. Visit www.cyark. org for more information on CyArk s current projects. It is hoped that these technologies will assist the scientific community and the general public in perceiving and understanding the threat to heritage sites and encourage discussion as to how people can help protect these sites.
Sending the equipment down to the site was no small feat! Room 28 at Square Tower House is built partially atop a large boulder towards the central front (south) of the complex, to the south of Kiva F. Its east wall is missing a large chunk.
While Superintendent Wiese joked during the filming of WIRED Science that the CyArk team could not leave until it had documented the thousands of important sites in the park, the need is real, not only at this site, but at threatened places of antiquity throughout the world. The work of CyArk continues. Square Tower House overlooks Navajo Canyon. Like many cliff dwelling sites, it faces south, which optimized winter sun. Originally there were more than 80 rooms; today there are remains of 60 rooms and 7 kivas, two of which are still partially covered by original roof construction. A spring below provided water. Access was seemingly by hand and toe holds carved into the sandstone. Lacking even a most rudimentary access path, it is inaccessible to visitors today. For more on laser archaeology and a great video of Ben Kacyra and Ziya Tong at Mesa Verde, visit: www.pbs.org/kcet/wiredscience/ story/91-laser_archaeology.html Elizabeth Lee is the Manager of Documentation Projects at CyArk. She has conducted field work at Neolithic sites in Turkey, and Hungary, Incan sites in Peru in addition to her most recent work at Mesa Verde National Park and Chichén Itza in Mexico. At the University of California at Berkeley Ms. Lee founded the UC Berkeley/CyArk Visualization Lab and served as instructor for the UC Berkeley/CyArk Internship Program. She has also conducted HDD training workshops for the U.S. National Park Service, the Presidio Trust, US/ICOMOS, and the University of Notre Dame. Spruce Tree House is 216 feet wide and 89 feet deep. Cliff dwellings were adapted to the topography of each location, making each site unique.