Convection and thermal mixing in super-confined systems

The destabilizing geothermal gradient across the Earth's lithosphere can drive convection in subsurface water reservoirs, especially in regions considered hot spots, where geothermal energy peaks. Such regions include mid-ocean ridges and tectonically active areas on Earth, where deep hot waters meet cold surface water that penetrates from the surface through open faults. Investigating the thermo-fluid dynamics of these super-confined systems is not only stimulating but also relevant for better understanding (1) thermal ecosystems that depend on minerals transport and mixing; and (2) geothermal reservoirs. Adopting the canonical features of Rayleigh-Bénard convection to establish a destabilizing thermal gradient through a fluid, we utilize Hele-Shaw cells as an analogue to investigate convection and thermal mixing in fault systems. Combining experimental and numerical experiments, we examine the relationship between thermal forcing, energy transport's spatial distribution, and global mixing quantified by the scalar fluctuations destruction rate. We aim to give insights into the fluid dynamics that can be expected in hard-to-reach hydrothermal systems.