Lake Magadi soda

In the dry season this lake is four-fifths solid, and the salt in places is forty metres thick.

Lake Magadi is the southernmost lake in the Kenyan Rift Valley, sitting in a catchment of faulted volcanic rock north of Tanzania's Lake Natron. It covers roughly 100 square kilometres in an endorheic basin formed by a graben, meaning nothing drains out of it, and it is a textbook saline pan. The water is a dense sodium carbonate brine, and it precipitates vast quantities of trona, sodium sesquicarbonate, which is the soda the place is mined for.

It keeps going because it is fed from below. Saline hot springs, some reaching 86 degrees Celsius, discharge into alkaline lagoons around the lake margins, and there is almost no surface runoff in this region to speak of. Most of those springs lie along the north-western and southern shorelines.

The lake changes character twice a year. In the rains a thin layer of brine, less than a metre deep, spreads across much of the pan. It evaporates fast, and what it leaves is an expanse of white salt that dries and cracks into enormous polygons.

It was not always this salty. Several thousand years ago, in the late Pleistocene to mid-Holocene, conditions here were very different, and the sediments record it. A 2020 paper in Scientific Reports by Luis A. Buatois, Robin W. Renaut and colleagues, working across the University of Saskatchewan, Hong Kong Baptist University, the Smithsonian and Mount Royal University, describes animal burrows preserved in Pleistocene magadiite at the lake, and uses them to work out what the depositional environment of bedded magadiite actually was. Burrows mean animals, and animals mean water that something could live in.

Go for the flamingos and the heat shimmer rather than for specimens. This is a working industrial soda operation on a fragile alkaline lake, so stay on the roads and treat the pans as off limits.