Trou au Natron

Geology

The caldera sits at an elevation of 2,450 m (8,040 ft).

Because of its irregular shape, it has been theorized that the caldera was formed as a result of multiple massive explosions, each of which deepened the enormous pit.[2] During these explosions, chunks of debris up to 5 m³ (180 cu ft) in size may have been hurled up to 10 km (6.2 mi) from the crater.^[2] Its exact period of formation is unconfirmed, although a Pleistocene formation has been suggested.^[6] It is known to be one of the youngest formations on the Tibesti Massif.^[4]

Much of the surface of the caldera is lined with a white crust of carbonate salts such as sodium carbonite and natrolite.^[8] This substance is also known as natron, leading to the French name for the site. This crust is sometimes known as the Tibesti Soda Lake.^[2][9] The crusts are formed when mineral-rich steam is emitted from small vents on the crater's floor. When this water evaporates in the desert heat, the minerals remain behind as part of the crust.^[2]

Both the slopes and the floor of the caldera contain thick layers of fossilized aquatic gastropods and diatoms, indicating that the caldera was once home to a deep lake. During the Last Glacial Maximum, the lake may have been up to 500 m (1,600 ft) deep. Radiocarbon dating on some of these samples indicates an age of approximately 14,500–15,000 years Before Present.^[10]

Gallery

• 
  Satellite image of Trou au Natron via Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
• 
  Satellite image of the Tousside volcano (large dark area in centre). Trou au Natron is visible below and to the right (smaller white area).
• 
  Satellite overview of the Tibesti Massif. Trou au Natron is located to the left; it is highlighted in the full-size view of the image.
• 
  Overview of Trou au Natron's caldera from its summit.

References

• Trou au Natron at GEOnet Names Server