GEOLOGIC HAZARDS IN OKLAHOMA

Natural geologic processes that have caused or may cause a hazardous condition in Oklahoma include earthquakes, landslides, floods, karst/salt dissolution, radon, and expansive soils. At least four principal seismic areas, El Reno-Mustang, central Oklahoma, Love and Carter Counties, and the Arkoma Basin, occur in Oklahoma. Typical earthquake-magnitude values range from 1.8 to 2.5 and focal depths are generally less than 3 miles. Most of Oklahoma landslides occur in the eastern third of the State owing to a wetter climate and steeper slopes associated with a more mountainous terrain. Major foods frequently occur in the spring and fall months in Oklahoma. Flood-prone areas in Oklahoma are identified and mapped by the U.S. Geological Survey, the U.S. Army Corps of Engineers, and private contractors. The mapping program is intended to delineate areas that have, on the average, 1 chance in 100 of being inundated in any particular year. Water-soluble rocks, such as limestone, dolomite, gypsum/anhydrite, and/or salt are prone to the development of karst and dissolution features from the dissolving action of circulating ground waters. The sinkholes and caverns thus developed are potential hazards owing to possible settlement or collapse of the land surface into the underground openings. Principal areas in Oklahoma where karst features are present in limestone and dolomite are in the Ozark Mountains, the Arbuckle Mountains, and the Limestone Hills (north of the Wichita Mountains). Gypsum and shallow salt deposits are present in many areas of western Oklahoma. Approximately 80% of the State is underlain by formations with uranium contents that are equal to, or less than the crustal average (2.5 ppm). The U.S. Environment Protection Agency identified 9 Oklahoma counties that have a moderate potential for elevated indoor radon levels. Clay-rich shales, or soils derived from the weathering of shale, may contain clay minerals, such as montmorillonite, that swell to as much as 1.5 to 2.0 times their original dry volume when they are wetted. Over 75% of Oklahoma contains bedrock units that have the ability to serve as sources for expansive soils. The saturation of soil from rainfall, lawn watering, or sewer leakage may cause major damage through the expansion of soils beneath sidewalks, highways, utility lines, and foundations.