Wed February 20, 2013
Earth Notes: Protecting The Plateau's Ancient Walls
In the latest installment of KNAU's environmental series, Earth Notes, we hear about some of the best practices for preserving ancient rock buildings on the Colorado Plateau.
Of the many ancient rock buildings on the Colorado Plateau, even the most solidly built eventually succumb to decay. The walls typically have hard outer veneers over a rubble core. Over centuries wide swings in temperature and moisture cause them to crumble and collapse.
Opinions vary widely on the best preservation methods. Officials at sites such as national parks once covered many rock walls with a hard cemented cap, giving a false illusion of stability. But cracks tend to develop in the caps. They allow water to enter the mortar core. Once there, the water allows damaging ice and salt crystals to form.
So some archaeologists say it's best to simply re-bury old walls to preserve them. Many Native Americans advocate a different approach: They favor letting ruins decay naturally.
In recent years, archaeologists have tried a new tactic at sites like Far View House at Mesa Verde National Park. It's called "soft capping," and it involves placing alternating layers of soil and geo-composite fill on top of old walls. Topped by grass, the covering seems to strengthen masonry walls.
Because the vegetation takes up water, percolation into the stone wall is reduced. Moisture seeps in from rain and snowmelt, but intervening dry periods allow the wall to dry out. Fibrous organic additives help wick moisture away, just as straw does in traditional adobe walls.
Should ancient rock walls be preserved? That's a value judgment. But if so, then low-tech soil and grass may be some of the best tools available.