A caustic chemical bath
Lake Magadi is an extreme environment, a 100-square-kilometer saline, alkaline lake in the southern Kenyan Rift Valley. During the dry season, up to 80% of its surface is covered by a solid white crust of sodium carbonate minerals. The lake water is a dense brine with a pH that can reach 11.5, similar to ammonia solution. This intense alkalinity comes from a unique geological setting. The lake has no river outlets and is recharged primarily by saline hot springs. Underground water percolates through volcanic rocks, picking up sodium and carbonate ions. It is then heated and discharged into lagoons around the lake margins at temperatures up to 86°C (187°F). The intense equatorial sun causes rapid evaporation, concentrating the salts and precipitating vast quantities of a mineral called trona (sodium sesquicarbonate).
This process has been happening for millennia. The trona crust is up to 40 meters (130 feet) thick in places, representing an accumulation of at least 9,000 years. The lake sits in a basin containing more than 30 billion metric tons of this mineral. The distinctive pink and red colors of the brine are not from the minerals themselves, but from immense populations of salt-loving microorganisms. Halophilic archaea, a type of single-celled life, produce protective carotenoid pigments that give the water its dramatic hue, which is most pronounced in the dry season when salinity peaks.