Pattern formation in dry lakes

Salt lakes are natural water basins loaded in minerals. Due to aridity, but also to human interventions and climate changes, some salt lakes become progressively water depleted. As the water of a salt lake evaporates, the minerals contained in the lake are brought to the surface and form a crust. During rain episodes, the crust gets soaked and some of the rain infiltrates the porous soil, leading to evaporation through the crust upon the return of hot weather.

Dry lakes can be useful in providing a source of sodium or lithium which are some of the benefits of Salar de Uyuni in Bolivia. However, dry lakes are not always as beneficial. Salton Sea, located about 80km east of San Diego, was originally created to divert the Colorado River and provide water supplies for agriculture. Due to the use of fertilizers and pesticides in agriculture and of the fact that Salton Sea was used as an agricultural runoff, the lake became overwhelmingly polluted, leading to the death of its natural fish, to fetid hydrogen sulfide air currents reaching nearby cities and to the transport of other toxic compounds through winds. Another lake associated with health hazards is Owens Lake, located between Los Angeles and Las Vegas. Of natural origin, this lake dried in the early 20th century due to human intervention: the city of Los Angeles diverted the Owens river to an aqueduct, depriving Owens Lake from its source. Owens lake now represents a major health hazard for the city of Los Angeles, as its salt crust includes a number of carcinogens such as arsenic.

In spite of their major impact on the environment, dry lakes are not well understood. In particular, their impact on atmospheric dust production and on mineral transport to the oceans is largely due to their salt crusts and, more specifically, to their protruding polygonal ridges. The formation of these ridges has been studied as part of the crust dynamics but without coupling with the subsurface flow and through the subsurface flow patterns but without any
modelling of the crust. No modelling of the coupling has yet been attempted. The objective of this project is to explain the formation of polygonal ridges on the crust of dry lakes. To achieve this, we will couple, for the first time, the subsurface porous convection and the crust dynamics using numerical simulation.