A surprising slab of salt shines at the summit of the Sahara's tallest peak — Earth from space

A rare and striking sight was captured from space: a thick layer of bright white salt sits at the summit of Emi Koussi, the highest peak in the Sahara desert. This extinct volcano, located in northern Chad, stands at an impressive 11,204 feet (3,415 meters) above sea level and is part of the Tibesti Massif, a volcanic mountain range that straddles the border between Chad and Libya.

The white salt crust, up to 3,300 feet (1,000 meters) across, covers the lowest part of Emi Koussi's caldera system, which is a complex depression surrounded by various volcanic vents and cones. The salt, known as natron, is a mixture of sodium carbonate decahydrate, sodium bicarbonate, sodium chloride, and sodium sulfate, and was left behind by an ancient lake that filled the caldera but has since evaporated.

This unique feature is not the only salt deposit in the Tibesti Massif, as another significant deposit lies nearby in the Trou au Natron caldera, which is shaped like a giant skull when viewed from above. Despite the harsh and arid environment of Emi Koussi, a pair of volcanic cones on the mountain's northern flank may contain permanent waterways that can hold liquid water due to their deep and narrow ravines, which are often shadowed and much cooler than the surrounding area.