![The hydrothermal system of Dallol](https://upload.wikimedia.org/wikipedia/commons/9/97/The_hydrothermal_system_of_Dallol.png)
Dallol is a unique, terrestrial hydrothermal system around a
cinder cone volcano in the
Danakil Depression
The Danakil Depression is the northern part of the Afar Triangle or Afar Depression in Ethiopia, a geological depression that has resulted from the divergence of three tectonic plates in the Horn of Africa.
Geology
The Danakil Depression lies ...
, northeast of the
Erta Ale Range
Erta Ale Range is the most important axial volcanic chain of the Afar Depression, Afar Region, Ethiopia. It consists mostly of shield volcanoes. The active volcano Erta Ale is a prominent feature of the range. The highest volcano of the range is ...
in
Ethiopia
Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...
. It is known for its unearthly colors and mineral patterns, and the very acidic fluids that discharge from its
hydrothermal springs.
Etymology
The term ''Dallol'' was coined by the
Afar people
The Afar ( aa, Qafár), also known as the Danakil, Adali and Odali, are a Cushitic-speaking ethnic group inhabiting the Horn of Africa. They primarily live in the Afar Region of Ethiopia and in northern Djibouti, as well as the entire southern co ...
and means dissolution or disintegration, describing a landscape of green acid ponds and geysers (
pH-values less than 1) and
iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
,
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
and salt desert plains. The area somewhat resembles the
hot springs areas of Yellowstone National Park.
Description
Dallol mountain has an area of about , and rises about above the surrounding salt plains. A circular depression near the centre is probably a collapsed crater. The southwestern slopes have water-eroded salt canyons, pillars, and blocks. There are numerous saline springs and fields of small
fumarole
A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...
s.
Numerous
hot spring
A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...
s discharge
brine
Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
and acidic liquid here. Small, widespread, temporary
geyser
A geyser (, ) is a spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam. As a fairly rare phenomenon, the formation of geysers is due to particular hydrogeological conditions that exist only in ...
s produce cones of salt. The Dallol deposits include significant bodies of
potash
Potash () includes various mined and manufactured salts that contain potassium in water-soluble form. found directly at the surface. The yellow, ochre and brown colourings are the result of the presence of iron and other impurities. Older, inactive springs tend to be dark brown because of
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
processes.
[
]
Formation
It was formed by the intrusion of basaltic magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
into Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
salt deposits and subsequent hydrothermal activity. Phreatic eruption
A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evapo ...
s took place here in 1926, forming Dallol Volcano; numerous other eruption craters dot the salt flats nearby. These craters are the lowest known subaerial In natural science, subaerial (literally "under the air"), has been used since 1833,[Subaerial](_blank)
in the Merriam ...
volcanic vents in the world, at or more below sea level. In October 2004 the shallow magma chamber beneath Dallol deflated and fed a magma intrusion southwards beneath the rift. The most recent signs of activity occurred in January 2011 in what may have been a degassing
Degassing, also known as degasification, is the removal of dissolved gases from liquids, especially water or aqueous solutions. There are numerous methods for removing gases from liquids.
Gases are removed for various reasons. Chemists remove gas ...
event from deep below the surface.
Physical properties
''Dallol'' lies in the evaporitic plain of the Danakil depression
The Danakil Depression is the northern part of the Afar Triangle or Afar Depression in Ethiopia, a geological depression that has resulted from the divergence of three tectonic plates in the Horn of Africa.
Geology
The Danakil Depression lies ...
at the Afar Triangle
The Afar Triangle (also called the Afar Depression) is a geological depression caused by the Afar Triple Junction, which is part of the Great Rift Valley in East Africa. The region has disclosed fossil specimens of the very earliest hominins; th ...
, in the prolongation of the Erta Ale
Erta Ale (or Ertale or Irta'ale; Amharic: ኤርታሌ) is a continuously active basaltic shield volcano in the Afar Region of northeastern Ethiopia. It is situated in the Afar Depression, a barren desert area. Erta Ale is the most active volcan ...
basaltic volcanic range. The intrusion of basaltic magma in the marine sedimentary sequence of Danakil resulted in the formation of a salt dome
A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered using ...
structure, where the hydrothermal system is hosted. The age of the hydrothermal system is unknown and the latest phreatic eruption that resulted in the formation of a diameter crater within the dome, took place in 1926. The wider area of Dallol is known as one of the driest and hottest places on the planet. It is also one of the lowest land points, lying below mean sea level. Other known hydrothermal features nearby Dallol are Gaet'Ale Pond
Gaet'ale Pond is a small hypersaline lake located near the Dallol crater in the Danakil Depression (Afar Region, Ethiopia). It is located over a hot spring of tectonic origin and has no apparent inlet or outlet streams. The water of Gaet'ale Pon ...
and Black Lakes.
The hydrothermal springs of Dallol discharge anoxic, hyper-acidic (pH < 0), hyper-saline (almost 10 times more saline than seawater), high temperature (> ) brines that contain more than 26 g/L of iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
. The main gases emitted from the springs and fumaroles are carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
, nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
; and traces of hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
, argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
, and oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
. Although several other hyper-acidic (pH < 2) volcanic systems exist, mainly found in crater lakes and hydrothermal sites, the pH values of Dallol decrease far below zero. The coexistence of such extreme physicochemical characteristics (pH, salinity, high temperature, lack of oxygen, etc.) render Dallol one of the very few ‘poly-extreme’ sites on Earth. This is why Dallol is a key system for astrobiological
Astrobiology, and the related field of exobiology, is an interdisciplinary scientific field that studies the origins, early evolution, distribution, and future of life in the universe. Astrobiology is the multidisciplinary field that investig ...
studies investigating the limits of life. Parts of the region are nearly sterile, except for a diverse array of "ultrasmall" archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
.
Dallol is highly dynamic; active springs go inactive and new springs emerge in new places in the range of days, and this is also reflected in the colors of the site that change with time, from white to green, lime, yellow, gold, orange, red, purple and ochre. In contrast to other hydrothermal systems known for their colorful pools (e.g. Grand Prismatic Spring
The Grand Prismatic Spring in Yellowstone National Park is the largest hot spring in the United States, and the third largest in the world, after Frying Pan Lake in New Zealand and Boiling Lake in Dominica. It is located in the Midway Geyser Ba ...
), where the colors are generated by biological activity, the color palette of Dallol is produced by the inorganic oxidation of the abundant iron phases. Another fascinating feature of Dallol is the wide array of unusual mineral patterns, such as, salt-pillars, miniature geysers, water-lilies, flower-like crystals, egg-shaped crusts, and pearl-like spheres. The main mineral phases encountered at Dallol are halite
Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
, jarosite
Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe3(SO4)2(OH)6. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byproduct duri ...
, hematite
Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
, akaganeite
Akaganeite, also written as the deprecated Akaganéite,Ernst A.J. Burke (2008):Tidying up Mineral Names: an IMA-CNMNC Scheme for Suffixes, Hyphens and Diacritical marks. ''Mineralogical Record'', volume 39, issue 2. is a chloride-containing iro ...
and other Fe-oxyhydroxides, gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...
, anhydrite
Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...
, sylvite
Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite ( NaCl). The two are, in fact, isomorphous. Sylvite is colorless to white with shades of ...
and carnallite
Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rare ...
.
Supposed absence of life
In October 2019, a French-Spanish team of scientists published an article in ''Nature Ecology and Evolution
''Nature Ecology and Evolution'' is an online-only monthly peer-reviewed scientific journal published by Nature Publishing Group covering all aspects of research on ecology and evolutionary biology. It was established in 2017. Its first and curre ...
'' that concludes that while the salt plains are teeming with halophile
The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...
microorganisms, there is no life in Dallol's multi-extreme ponds due to the combination of hyperacidic and hypersaline environments, and the abundance of magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
(which catalyzes the denaturation of biomolecule
A biomolecule or biological molecule is a loosely used term for molecules present in organisms that are essential to one or more typically biological processes, such as cell division, morphogenesis, or development. Biomolecules include large ...
s). However another team reported for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea
Nanohaloarchaea is a clade of diminutive archaea with small genomes and limited metabolic capabilities, belonging to the DPANN archaea. They are ubiquitous in hypersaline habitats, which they share with the extremely halophilic haloarchaea.
Nan ...
History
The Dallol area lies up to below sea level, and has been repeatedly flooded in the past when waters from the Red Sea
The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
have flowed into the depression. The last separation from the Red Sea was about 30,000 years ago.
The discovery of the volcano by the first European settlers certainly dates from the first colonization and expeditions in the region, in the 17th or 18th century. But the hostility of the depression, the unbearable heat which reigns there, and the dangers of the site (acid basins, toxic fumes), did not favour the exploration of the zones close to the crater. On the contrary, the Erta Ale
Erta Ale (or Ertale or Irta'ale; Amharic: ኤርታሌ) is a continuously active basaltic shield volcano in the Afar Region of northeastern Ethiopia. It is situated in the Afar Depression, a barren desert area. Erta Ale is the most active volcan ...
was much more accessible, especially because the part of the rift where it is located (called the Erta Ale Range), is significantly higher. The last eruption of this phreato-magmatic volcano dates back to 2011.
Gallery
File:ET Afar asv2018-01 img15 Dallol.jpg, The Danakil desert seen from Dallol
File:ET Afar asv2018-01 img36 Dallol.jpg, Salt and sulfur formations at Dallol
File:ET Afar asv2018-01 img55 Dallol.jpg, Salt canyons
File:ET Afar asv2018-01 img43 Dallol.jpg, Sulfur ponds
File:Ethiopia Dallol GuideStanding.JPG, Guide walking on Dallol
See also
* List of volcanoes in Ethiopia
This is a list of volcanoes in Ethiopia. It includes both active and extinct vents.
See also
* Geography of Ethiopia
* Lists of volcanoes
References
{{Global Volcanism Program
Volcanoes
Ethiopia
Ethiopia, , om, Itiyoophiyaa, so ...
* Dallol – a ghost town
Ghost Town(s) or Ghosttown may refer to:
* Ghost town, a town that has been abandoned
Film and television
* Ghost Town (1936 film), ''Ghost Town'' (1936 film), an American Western film by Harry L. Fraser
* Ghost Town (1956 film), ''Ghost Town'' ...
in the Dallol crater. It had the record high average temperature for an inhabited location on Earth.
References
Bibliography
* ''On the Volcanoes of the World'' episode ''The Horn of Africa'' (2008; Science Channel
Science Channel (often simply branded as Science; abbreviated to SCI) is an American pay television channel owned by Warner Bros. Discovery. The channel features programming focusing on science related to wilderness survival, engineering, manu ...
)
External links
Photos from Dallol taken during an expedition to the Danakil in February 2008
YouTube
Wired
BBC
BBC
{{Portal bar, Earth sciences, Evolutionary biology, Africa, Geology
Afar Region
Astrobiology
Geologic formations of Ethiopia
Geochemistry
Hydrothermal vents
Iron minerals