{{Short description|Volcanic caldera in Chad's Tibesti Massif}} {{Use dmy dates|date=April 2025}} [[File:Trou_au_Natron_caldera_satellite_photo.jpg|thumb|The soda lake is visible as the white area to the bottom of the crater in this satellite image of the Trou au Natron caldera in Chad.]]
'''Trou au Natron''' (French: "hole of [[natron]]") or {{lang|tuq|Doon Orei}} ([[Teda language|Teda]]: "big hole")<ref>{{Cite book |url=https://books.google.com/books?id=-SNmAAAAMAAJ&q=%22doon+orei%22 |title=Il Sahara centro-orientale dalla preistoria ai tempi dei nomadi Tubu |last1=Beltrami |first1=Vanni |last2=Proto |first2=Harry |date=2007 |publisher=Archaeopress |isbn=9781407301020 |language=it }}</ref> is a [[volcano|volcanic]] [[caldera]] of the [[Tibesti Mountains|Tibesti Massif]] in the nation of [[Chad]] in Northern Africa.<ref name="readersnatural">{{Cite book |title=Natural Wonders of the World |publisher=Reader's Digest Association, Inc |year=1980 |isbn=0-89577-087-3 |editor-last=Scheffel |editor-first=Richard L. |location=United States of America |pages=377 |editor-last2=Wernet |editor-first2=Susan J. }}</ref><ref>{{Cite book |url=https://books.google.com/books?id=toYRAQAAMAAJ&q=trou+au+natron |title=Annual Field Conference |last=al-Arḍ |first=Jamʻīyah al-Lībīyah li-ʻUlūm |date=1966 |publisher=Earth Sciences Society of the Libyan Arab Republic |quote=The Trou au Natron has a caldera diameter of six to eight km... }}</ref> The volcano is extinct. It is unknown when it last erupted.<ref name=":2">{{Cite gvp |name=Tarso Toussidé |vn=225010 |access-date=3 October 2017 }}</ref><ref>{{Cite web |url=http://www.bgs.ac.uk/vogripa/searchVOGRIPA.cfc?method=detail&id=363 |title=VOGRIPA |website=www.bgs.ac.uk |access-date=3 October 2017 |archive-date=3 October 2017 |archive-url=https://web.archive.org/web/20171003075408/http://www.bgs.ac.uk/vogripa/searchVOGRIPA.cfc?method=detail&id=363 |url-status=live }}</ref> Its [[Volcano Number|volcano number]] is 0205–01.<ref name=":1">{{Cite book |url=https://books.google.com/books?id=0DZrfpL9_DMC&pg=PA396 |title=Volcanoes of the World: Third Edition |last1=Siebert |first1=Lee |last2=Simkin |first2=Tom |last3=Kimberly |first3=Paul |date=9 February 2011 |publisher=University of California Press |isbn=9780520947931 }}</ref> Trou au Natron is located just south-east of [[Toussidé]], the westernmost volcano of the Tibesti Mountains. Its edge cuts into the nearby [[Yirrigue|Yirrigue caldera]].
[[File:Natron deposits, Trou au Natron, Chad.jpg|thumb|Natron deposits, Trou au Natron, Tibesti, Chad]]
== Geology == The caldera sits at an elevation of {{cvt|2450|m|}}.<ref>{{Cite book |url=https://books.google.com/books?id=qJc9AAAAIAAJ&pg=PA248 |title=Mountain Weather and Climate |author-link=Roger G. Barry |last=Barry |first=Roger Graham |date=1981 |publisher=CUP Archive |isbn=9780416737301 }}</ref> It has an irregular diameter of approximately {{cvt|6–8|km||0}} and is up to {{cvt|1000|m}} deep.<ref name="readersnatural" /> Four smaller volcanic cones, made of [[scoria]] or [[andesite|andesitic]] [[tuff]] sit on the floor of the caldera.<ref name="readersnatural" /><ref name=":0">{{Cite book |url=https://books.google.com/books?id=6iZRBAAAQBAJ&pg=PA61 |title=Volcanic Landforms and Surface Features: A Photographic Atlas and Glossary |last1=Green |first1=Jack |last2=Short |first2=Nicholas Martin |date=6 December 2012 |publisher=Springer Science & Business Media |isbn=9783642651502 }}</ref> Numerous smaller vents and hot springs on the caldera's floor emit hot steam and mineral water.<ref name="readersnatural" />
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.<ref name="readersnatural" /> During these explosions, chunks of debris up to {{Cvt|5|m3|}} in size may have been hurled up to {{Cvt|10|km|}} from the crater.<ref name="readersnatural" /> Its exact period of formation is unconfirmed, although a [[Pleistocene]] formation has been suggested.<ref name=":1" /> It is known to be one of the youngest formations on the Tibesti Massif.<ref name=":2" />
Much of the surface of the caldera is lined with a white crust of [[carbonate]] salts such as [[Sodium carbonate|sodium carbonite]] and [[natrolite]].<ref name=":0" /> 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.<ref name="readersnatural" /><ref>{{Cite book |url=https://books.google.com/books?id=v911L1sq1FkC&pg=PA95 |title=Great Warm Deserts of the World: Landscapes and Evolution |last=Goudie |first=Andrew |date=2002 |publisher=Oxford University Press |isbn=9780199245154 }}</ref> 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.<ref name="readersnatural" />
Both the slopes and the floor of the caldera contain thick layers of fossilized aquatic [[Gastropoda|gastropods]] and [[Diatom|diatoms]], indicating that the caldera was once home to a deep lake. During the [[Last Glacial Maximum]], the lake may have been up to {{Cvt|500|m||abbr=}} deep. Radiocarbon dating on some of these samples indicates an age of approximately 14,500–15,000 years [[Before Present]].<ref>{{Cite journal |last1=Soulié-Märsche |first1=I. |last2=Bieda |first2=S. |last3=Lafond |first3=R. |last4=Maley |first4=J. |last5=M'Baitoudji |last6=Vincent |first6=P. M. |last7=Faure |first7=Hugues |date=1 July 2010 |title=Charophytes as bio-indicators for lake level high stand at "Trou au Natron", Tibesti, Chad, during the Late Pleistocene |journal=Global and Planetary Change |series=Quaternary and Global Change: Review and Issues Special issue in memory of Hugues FAURE |volume=72 |issue=4 |pages=335 |doi=10.1016/j.gloplacha.2010.05.004 |bibcode=2010GPC....72..334S |issn=0921-8181 }}</ref>
== Gallery == <gallery> File:Trou au Natron (Toussidé) ASTER.jpg|Satellite image of Trou au Natron via Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) File:Tousside, Tibesti Mountains, Chad.jpg|Satellite image of the Tousside volcano (large dark area in centre). Trou au Natron is visible below and to the right (smaller white area). File:Tibesti Worldwind.jpg|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. File:Chad Trou au Natron 2301-2.jpg|Overview of Trou au Natron's caldera from its summit </gallery>
== References == *{{GEOnet2|32FA88363C853774E0440003BA962ED3}} {{Reflist|30em}}
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{{DEFAULTSORT:Trou Au Natron}} [[Category:Tibesti Mountains]] [[Category:Calderas of Chad]]