Trou au Natron

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Satellite image of Trou au Natron caldera in Chad. The soda lake is visible as the white area to the bottom of the crater.

Trou au Natron (French: "hole of natron") or Doon Orei (Teda: "big hole")[1] is a volcanic caldera of the Tibesti Massif in the nation of Chad in Northern Africa.[2][3] The volcano is extinct. It is unknown when it last erupted.[4][5] Its volcano number is 0205–01.[6] Trou au Natron is located just south-east of Toussidé, the westernmost volcano of the Tibesti Mountains. Its edge cuts into the nearby Yirrigue caldera.

The caldera sits at an elevation of 2,450 m (8,040 ft).[7] It has an irregular diameter of approximately 6–8 km (4–5 mi) and is up to 1,000 m (3,300 ft) deep.[2] Four smaller volcanic cones, made of scoria or andesitic tuff sit on the floor of the caldera.[2][8] Numerous smaller vents and hot springs on the caldera's floor emit hot steam and mineral water.[2]

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]

Soda lake[edit]

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]



  1. ^ Beltrami, Vanni; Proto, Harry (2007). Il Sahara centro-orientale dalla preistoria ai tempi dei nomadi Tubu (in Italian). Archaeopress. ISBN 9781407301020. 
  2. ^ a b c d e f g h Scheffel, Richard L.; Wernet, Susan J., eds. (1980). Natural Wonders of the World. United States of America: Reader's Digest Association, Inc. p. 377. ISBN 0-89577-087-3. 
  3. ^ al-Arḍ, Jamʻīyah al-Lībīyah li-ʻUlūm (1966). Annual Field Conference. Earth Sciences Society of the Libyan Arab Republic. The Trou au Natron has a caldera diameter of six to eight km... 
  4. ^ a b "Global Volcanism Program | Tarso Toussidé". Retrieved 2017-10-03. 
  5. ^ "VOGRIPA". Retrieved 2017-10-03. 
  6. ^ a b Siebert, Lee; Simkin, Tom; Kimberly, Paul (2011-02-09). Volcanoes of the World: Third Edition. University of California Press. ISBN 9780520947931. 
  7. ^ Barry, Roger Graham (1981). Mountain Weather and Climate. CUP Archive. ISBN 9780416737301. 
  8. ^ a b Green, Jack; Short, Nicholas Martin (2012-12-06). Volcanic Landforms and Surface Features: A Photographic Atlas and Glossary. Springer Science & Business Media. ISBN 9783642651502. 
  9. ^ Goudie, Andrew (2002). Great Warm Deserts of the World: Landscapes and Evolution. Oxford University Press. ISBN 9780199245154. 

Coordinates: 20°59′00″N 16°32′00″E / 20.98333°N 16.53333°E / 20.98333; 16.53333