A Conceptual Model for the Development and Persistence of Soap Holes (Unique Prairie Groundwater Discharge Features)

Abstract

Soap holes manifest as localized areas of water-saturated, weak sediments which render farmland uncroppable and hazardous. The formation mechanisms and global distribution are largely unknown, despite being inferred as groundwater discharge phenomena on the Alberta prairies over 50 years ago. Here, the first conceptual model for soap hole development and persistence is created using time-series hydraulic and temperature data, electrical resistivity tomography, sediment analyses, and geochemical data (sediment and groundwater) from two locations in Alberta, Canada. The soap holes developed in smectite-rich, dominantly colloidal-size glacial sediments under strong flowing artesian conditions, resulting in quick conditions and liquefaction. Geoelectric and hydraulic conductivity contrasts (2-5 orders of magnitude), as well as groundwater geochemistry, suggest preferential groundwater flow of artesian aquifer provenance through a low permeability confining layer. In addition to natural occurrences, a proportion of soap holes may be the consequence of explosive-source seismic conducted for oil and gas exploration in Alberta.