This trace visible since the space testifies to an unsuspected past.
View from the terrestrial orbit, intriguing white formation attracts attention to the heart of the Sahara, at the top of an isolated volcano. Captured thanks to very powerful observation instruments by astronauts aboard the international space station, this “white spot” contrasts significantly with the surrounding dark rocks. Due to its high altitude (more than 3,400 meters), it was first interpreted as a snow deposit – a hypothesis quickly called into question by scientists from NASA.
The geological investigations revealed that these were in reality saline deposits, residue of an old lake that occupied the crater of the Emi Koussi volcano, in northern Chad. This stratovolcancan now extinct retains the brands of an environment radically different from that we know: the “green Sahara”, a more humid climate phase marked by the presence of lakes, rivers and regular precipitation.
The image makes it possible to identify clear clues of a water erosion: channels, canyons, fossil river beds … So many geomorphological traces which testify to an ancient climate regime, much more humid, having shaped the region about 5,000 years ago. The interaction between volcanic activity and ancient hydrography gave birth to a landscape then much more conducive to life.
This orbital observation, captured as part of NASA surveys, illustrates how spatial remote sensing contributes to reconstructing the climates of the earth. It highlights the climatic variability of the Sahara and recalls that large deserts are not frozen environments, but the products of long geological and atmospheric developments. The “white spot” of the Emi Koussi volcano thus becomes a precious marker of a past where life, water and vegetation reigned where the aridity extends.
