Free convection is a process by which mixing of fluids occurs over larger scales and at faster rates than Fickian transport; this process is of critical importance for a range of environmental issues. Despite decades of research, the understanding of this phenomenon still largely stems from theoretical studies, lab experiments, numerical modeling, and secondary field observations. In this contribution, we present a time-lapse field study of free convection in a coastal sabkha in the United Arab Emirates. Using electrical resistivity imaging data collected during three field campaigns, we demonstrate that free convection at this site originates from episodic large rainfall events that drive salt dissolution at the surface and infiltration of a dense brine to the water table. Our observations, including the rates of downward migration and dissipation of the dense fingers, are corroborated by hydrodynamic modeling of the system.