Trou au Natron (French: "hole of

natron Natron is a naturally occurring mixture of sodium carbonate decahydrate ( Na2CO3·10H2O, a kind of soda ash) and around 17% sodium bicarbonate (also called baking soda, NaHCO3) along with small quantities of sodium chloride and sodium sulfate. ...

") or ( Teda: "big hole") is a

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

of the Tibesti Massif in the nation of Chad in

Northern Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in t ...

. The volcano is extinct. It is unknown when it last erupted. Its

volcano number The Volcano Number (also Volcano Reference File Number, Volcano Numbering System, or VNUM) is a hierarchical geographical system to uniquely identify and tag volcanoes and volcanic features on Earth. The numbers consist of four numerals, a hyphen, ...

is 0205–01. Trou au Natron is located just south-east of

Toussidé Toussidé (also known as Tarso Toussidé) is a potentially Volcano#Active, active stratovolcano in Chad. Toussidé lies in the Tibesti Mountains, the large Yirrigué caldera and the smaller Trou au Natron and Doon Kidimi Volcanic crater, crater ...

, the westernmost volcano of the Tibesti Mountains. Its edge cuts into the nearby Yirrigue caldera. Natron deposits, Trou au Natron, Chad

Geology

The caldera sits at an elevation of . It has an irregular diameter of approximately and is up to deep. Four smaller volcanic cones, made of

scoria Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) '' ...

or andesitic tuff sit on the floor of the caldera. Numerous smaller vents and hot springs on the caldera's floor emit hot steam and mineral water. 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. During these explosions, chunks of debris up to in size may have been hurled up to from the crater. Its exact period of formation is unconfirmed, although a

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

formation has been suggested. It is known to be one of the youngest formations on the Tibesti Massif. Much of the surface of the caldera is lined with a white crust of

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

salts such as sodium carbonite and

natrolite Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany. It was named natrolite by Martin Heinrich Klapro ...

. This substance is also known as

, leading to the French name for the site. This crust is sometimes known as the Tibesti Soda Lake. 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. Both the slopes and the floor of the caldera contain thick layers of fossilized aquatic

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

and

diatoms A diatom (New Latin, Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group com ...

, indicating that the caldera was once home to a deep lake. During the Last Glacial Maximum, the lake may have been up to deep. Radiocarbon dating on some of these samples indicates an age of approximately 14,500–15,000 years

Before Present Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becau ...

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.

References

* {{DEFAULTSORT:Trou Au Natron Tibesti Mountains Volcanoes of Chad