Formation of the Wink Sink, A Salt Dissolution and Collapse Feature, Winkler County, Texas

The Wink Sink in Winkler County, Texas, formed on June 3, 1980. Within 24 hours it had expanded to a maximum width of 360 ft (110 m). On June 5, 1980, maximum depth of the sinkhole was 110 ft (34 m), and volume about 5.6 million ft3 (158,600 m3). Between June 3 and June 6, 1980, a large area bordering the south rim of the sink subsided about 10 ft (3 m) relative to the north side. Further subsidence of 1,456 ft (44.4 cm) occurred along the southern rim between July 19 and December 12, 1980. A probable precursor of the sinkhole was a solution cavity that migrated upward by successive roof failures, thereby producing a collapse chimney filled with brecciated rock. Dissolution of salt in the Permian Salado Formation is inferred to have produced the solution cavity. Depth of the Salado ranges from 1,300 to 2,200 ft (396 to 670 m). Data on the size and initial depth of the solution cavity are unavailable. The Salado Formation in the region contains several dissolution zones. Occurrence of dissolution in the middle of the Salado evaporite sequence may have resulted from groundwater flow along fractured anhydrite interbeds. Water may have come in contact with salt by downward movement from overlying aquifers or by upward movement from underlying aquifers under artesian pressure. The Wink Sink lies directly above the Permian Capitan Reef, which contains water that is unsaturated with respect to sodium chloride. Hydraulic head of water from the reef is higher than the elevation of the Salado Formation but lower than the head in the Triassic Santa Rosa Formation, a near-surface fresh-water aquifer. Fracture or cavernous permeability occurs above, within, and below the Salado Formation, as indicated by the loss of circulation of drilling fluid in wells drilled near the sinkhole. Consequently, a brine density-flow cycle may be operating: relatively fresh water moves upward under artesian pressure and dissolves salt; the denser brine moves downward under gravity flow in the same fracture system. Alternatively, downward flow of water from aquifers such as the Santa Rosa Formation or Quaternary sediments above the salt is also a possible explanation for dissolution. A plugged and abandoned well that was located within the circumference of the sinkhole may have provided a conduit for water movement. Composition of water in the Wink Sink resembles that of water in nearby wells producing from the Quaternary alluvium and from the Triassic Santa Rosa Formation. Hendrick well number 10-A was drilled in 1928 at a site now within the circumference of the sinkhole. The well, which initially produced about 80 percent water from the Permian Tansill Formation, was plugged with cement and abandoned in 1964. The well was not used for brine disposal. Over 12 million barrels of salt water produced from the Hendrick Field were disposed of by injection into the Permian Rustler Formation during 1961. Waterflood projects in the Hendrick Field began in 1963 and are still in progress. Sinkholes similar to the Wink Sink occur in other areas of North America. Their morphology, associated strata, and mode of formation suggest that dissolution, brecciation, and surface subsidence commonly occur during their formation