Foreward

Few who read this book live on the landscapes described in this book, which are inhospitable due to large accumulations of salt. This gives visitors the impression of being on another planet. Although few of us will personally experience this arid environment, it covers nearly 20% of the continental surface of the Earth and hence is an important terrain. It forms in response to a combination of arid or semi-arid climate and a topography that results in the pervasive formation of brine and associated mineral deposits. In closed basins, water from rainfall cannot escape by streamflow so the only way out is by evaporation, including evapotranspiration from a few salt-tolerant plants. When the water molecules evaporate, the dissolved salts are left behind to form brine with a salt concentration much higher than sea water. Accumulations of mineral deposits precipitate from the brines. These are referred to by different terms depending on the language of the region including sabkha (Arabic); salinas, salares, saladas, salars, and playas (Spanish); or salt pans, saline lakes, alkali flats, salt plains, dry lakes, and salt flats (English). The salts originate as dissolved solids in the rainfall and from the weathering of minerals in the geologic framework that makes up the terrain. The rain infiltrates in the uplands and flows as groundwater to discharge in the lowlands where salt accumulates. The story sounds simple but understanding the formation of the mineral species and solutes within the hydrologic landscape is complex.

There are more than a dozen different minerals, that form from the brines, often rich in chloride, sulphate or carbonate that are exquisitely beautiful when viewed under a microscope. Which mineral develops is a function of both the input of dissolved constituents (solutes) and, surprisingly to a large extent, the leakage of solutes from the basin. The process of increasing brine concentration depends on the thermodynamic state of the brine, the water vapor content of the atmosphere, and the dynamic interplay between hydrology and thermodynamics with varying temperature driving the mineral outcome. Although the book is written from a conceptual viewpoint, to fully appreciate the explanations provided in this book, the reader will need some prior understanding of groundwater flow systems, density dependent flow and introductory level thermodynamics. The scientific puzzles represented by brines and the minerals they produce are amongst the most sophisticated offered by multidisciplinary geoscience.

Dr. Warren Wood is one of the few scientists who has studied this complex interplay of factors governing brines and their minerals in surface and near surface conditions in several parts of the world. He has walked these barren landscapes with an eye to the evidence needed to unravel the mysteries.

John Cherry, The Groundwater Project Leader
Guelph, Ontario, Canada, December 2021