A vibration study of the archeological ruins, Hovenweep National Monument, Utah-Colorado

King, Kenneth; Algermissen, S.

Hovenweep National Monument is located on the Colorado Plateau north of the San Juan River. The National Monument straddles the border of southwest Colorado and southeast Utah (fig. 1). Hovenweep National Monument contains six groups of unique, ancient, stone-adobe structures. Four of these groups are in Colorado and two in Utah. The builders of the structures now in ruins were part of the Anasazi culture that developed along the San Juan River system in the Four Corners region. Around 1200 A.D. the Hovenweep Anasazi people began building the existing structures at the head of small draws and on the rims of box canyons. The Hovenweep ruins are unlike any other Anasazi structures of the southwest in architecture and general setting. Most of the structures are tall stone towers that, except for narrow peepholes, generally have no windows and very narrow entrances. Due to their appearance, the massive masonry pueblos were referred to as "castles" by the early explorers. The Hovenweep archeological ruins are noted for their square and D-shaped towers, which can exceed 6 m in height. The structures are constructed of excellent masonry of layered coursed-stone style and most have their foundations on the sandstone bedrock. The only evident structural weaknesses of the archeological ruins are the top plate sections which show damage caused by the failure or removal of the horizontal logs that were used for the roof supports. These logs had either failed or had been removed for other construction or firewood by people who occupied the area after the demise of the Anasazi culture. These unique archeological structures in the Monument show general deterioration from natural erosion and human destruction. Fortunately, the National Park Service protection has stemmed the relic hunters and general damage by the public but there is a need for further regulations which will protect the unique sites from potential future damage from vibrations induced by commercial activities and public use. The most effective regulations would protect the archeological ruins without being an unnecessary impediment to exploration and to development of natural resources and without undue restriction of public access to the areas adjacent to the structures. Artificially-induced vibration from commercial endeavors may be a potential hazard to the Hovenweep .archeological ruins. Typical sources of induced vibrations are explosions from oil or mineral explorations and activities of earth-moving equipment such as bulldozers, rippers, and graders for pipeline and road construction. This report describes the results of a vibration study of the more fragile of the archeological structures and a study of vibration attenuation of induced ground motions from explosions, trench construction, and local traffic in the areas adjacent to the Square Tower group of ruins. The results of these tests are used to suggest a vibration zoning of the archeological sites. The zoning shows the areas that are acceptable for public use, traffic, general construction and exploration work.

A vibration study of the archeological ruins, Hovenweep National Monument, Utah-Colorado

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