Hidden deep in the heart of the Sahara Desert lies a pitch-black volcano, covered in the remains of ancient lava flows, alongside one of the most astonishing geological features on Earth, a volcanic crater so perfectly shaped as a skull that it looks almost intentional.
A photo taken by an unnamed astronaut aboard the International Space Station on September 23, 2019 captured both formations in one image, revealing the Tussian volcano and the Trou-O-Natron caldera rising from the sand-covered plateau in northern Chad in extraordinary detail. The image provides a rare window onto one of the planet’s least visited and most geologically attractive landscapes, an area where millions of years of volcanic activity have left dramatic, permanent scars across the desert floor that remain virtually unchanged to this day.
A cushion volcano and why it looks so dramatically different from its surroundings
Tousidi, also known as Tarso Tousidi, is a potentially active stratovolcano located within the Tibesti Mountains, a remote volcanic region covering approximately 100,000 square kilometers of northern Chad and southern Libya. The peak is 3,265 meters above sea level, making it the second tallest mountain in the entire Tibesti region. What makes it instantly striking from space is its color. The volcano and the sprawling mass of rock surrounding it appear almost entirely black on the pale, sand-colored plateau, because the land surrounding it is covered by a geological structure called a massif, built from layer upon layer of overlapping molten rock left by multiple ancient lava flows that slowly poured from the volcano’s summit over an enormous period of geological time.
The massif extends up to 32 kilometers at its widest point, its dark surface standing out sharply against the surrounding plateau, which over eons of wind has carved into a network of criss-crossing canyons, as documented by NASA’s Earth Observatory.
What does the name Toussidé actually mean?
The name of the volcano is not just a geographical designation. According to historical records referenced in the JSTOR archive of geographical journal studies, Toussidé roughly translates to a phrase meaning something close to “he who killed the locals with fire” in the language of indigenous communities living near the Tibesti mountain range, suggesting a long cultural memory of violent or destructive volcanic activity at or near the site. Despite this troubling origin, the Smithsonian’s Global Volcanism Program has found no confirmed evidence that Tussidi volcanism actually erupted during the Holocene, the current geological epoch that began about 12,000 years ago, meaning that the period of truly dangerous volcanic production predates recorded human history in the region by a very large margin.
A skull-shaped caldera hides southeast of the volcano
Southeast of the dark massif, which can be seen in the upper right of the astronaut’s photo as a small white circle surrounding several dark spots, lies Trou aux Natron, a volcanic caldera that drops about 1,000 meters from its rim to its floor and is about 8 kilometers wide. When viewed directly from above, the combination of the pale white salt floor and a pair of dark volcanic cones rising from within it creates a striking resemblance to a human skull staring up from the desert, an effect that has made the crater one of the most photographed geological formations in the region despite its extraordinary remoteness.
The caldera is believed to have formed during an explosive volcanic eruption more than 120,000 years ago, well before the Holocene epoch, placing its violent origins in the Pleistocene epoch. It was once filled with a large salt lake that supported ancient algae and other microorganisms, but as the climate dried out and the lake evaporated at the beginning of the Holocene, the receding waters left behind thick white salt deposits that now cover its floor and give the skull formation a distinctive pale, skull-like appearance.
Why did the entire Tibesti region look as dark as the lava mass does today?
The massif surrounding Tusidi is not an isolated piece of local geology but a visible remnant of a much broader volcanic history that once shaped the entire Tibesti landscape. One of the younger mountains in the chain is Tusidi, which itself was formed by similar patterns of lava eruption long before Tusidi was born as a distinct volcanic structure. According to the Earth Observatory, the entire Tibesti Plateau likely once matched the dark color of the present-day massif centuries before sand was blown away by desert winds that gradually buried and illuminated the surrounding terrain.
Given enough time, perhaps another 100,000 years or so, the same process may eventually cause the dark Tussidian massif to blend into the surrounding plateau just as older parts of the range have already done, slowly erasing one of the most visually dramatic geological signatures currently visible anywhere in Africa from space.
The volcano is dormant but not dead
While the Tusidi has shown no confirmed eruptive activity throughout the Holocene, it has never completely subsided. The European Space Agency, which took its own satellite images of the area in 2021, notes that the volcano sometimes releases steam through small vents called fumaroles located near its summit, a clear indication that heat and geological activity are continuing below the surface and that the volcano is still technically active and not completely extinct. Geologists have not yet undertaken a comprehensive formal assessment of the potential for a Tusidic eruption, largely because the Tibesti area is very remote and has historically been difficult to access for scientific fieldwork, meaning that important questions about the future behavior of the volcano and the precise chronology of past eruption cycles currently remain unanswered.