Abstract

Earth fissures are large open cracks in sediment and are controversial factors for siting waste facilities in the United States. Fissures were cited as potential hazards at each of the last two Texas radioactive waste sites. The fissures were considered potential conduits to the surface or to underlying aquifers. This research describes the behavior of earth fissures near Fort Hancock, Texas, and presents a method for estimating fissure depth using standard soil strength measurements. Observations described in the literature indicate that fissures open suddenly and episodically, swallowing large volumes of sediment and water. The author's observe that once a fissure is flooded and eroded, the fissure may become inactive and water may episodically pond in it for several years. This study suggests that during fissure flooding and erosion, the walls of the fissure weaken and collapse, closing the fissure until the sediment dries and hardens. Results indicate that fissures are limited in depth by the strength of the materials they form in. Using data from studies by previous researchers, we calculated maximum depths ranging from 2.3 to 17 m, within the fissures. The fissures in this study were in silty sand with an estimated depth of 5 m. Resistivities above the fissures indicated wetting and drying of the sediments to a 6 to 8 m depth, slightly deeper than the theoretical crack depth. Because wetting can extend below the depth of the fissure, these results are compatible. Trenches in fissures nearby bottomed in what was believed to be the fissure base at 6 m.

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