SGER: Documenting the Transient Nature of Natural Free Convection in Groundwater

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Geophysical imaging of a sabkha in the United Arab Emirates (UAE) following an extreme precipitation event in 2008 shows the first compelling evidence of free convection flow processes in a natural groundwater setting. The imaged pattern is consistent with fingering caused by precipitation-induced redissolution of a halite crust and a pre-existing convection pattern; the distribution of these fingers is similar to those observed in lab experiments and numerical simulations. Natural free convection, which is important for heat and solute transport across a range of hydrogeologic settings, has been studied for over a century but almost entirely in theory, numerical models, and laboratory experiments. Currently, very little is known about the growth and decay of convective instabilities because most research assumes steady state conditions. In order to resolve key questions about origins and persistence of convection, as well as their associated spatial and temporal scales, it is vital to resolve the transient nature of different interacting regimes.Our UAE field site is an ideal location to address some of these knowledge gaps. Precipitation records suggest that fingering at this site may only be initiated once every decade with a halite crust building up during dryer years. Our pilot data demonstrate the unique opportunity to monitor the dynamic nature of density fingering. We propose to integrate time-lapse geophysical, hydrological, and geochemical measurements with preliminary hydrological modeling. The exploratory research will provide a transformative advance for this important field. The results will be disseminated through research papers and conference presentations and will form the foundation for a continued research program including a full-scale modeling effort.