By Annalee Newitz | io9.com

For six months in the winter and fall of 1969, Niagara’s American Falls were "de-watered", as the Army Corps of Engineers conducted a geological survey of the falls’ rock face, concerned that it was becoming destabilized by erosion. During the interim study period, the dried riverbed and shale was drip-irrigated, like some mineral garden in a tender establishment period, by long pipes stretched across the gap, to maintain a sufficient and stabilizing level of moisture. For a portion of that period, while workers cleaned the former river-bottom of unwanted mosses and drilled test-cores in search of instabilities, a temporary walkway was installed a mere twenty feet from the edge of the dry falls, and tourists were able to explore this otherwise inaccessible and hostile landscape.