Deriba is a
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), 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 fina ...
or
Holocene
The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
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 ...
in
Darfur
Darfur ( ; ar, دار فور, Dār Fūr, lit=Realm of the Fur) is a region of western Sudan. ''Dār'' is an Arabic word meaning "home f – the region was named Dardaju ( ar, دار داجو, Dār Dājū, links=no) while ruled by the Daju, ...
,
Sudan
Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...
. Part of the volcanoes of the
Marra Mountains, it lies on the
Darfur dome
Darfur Dome or Darfur Volcanic Province is an area of about 100x400 km in Western Sudan. As well as its best-known and central feature, Deriba Crater, it encompasses the surrounding Marra Mountains (Jebel Marra) and Tagabo Hills, both formed aro ...
and like the
Tagabo Hills
The Tagabo Hills is a volcanic field in the region of Darfur in Sudan. It lies north of the Marrah Mountains and southwest of the larger Meidob Volcanic Field. The Tagabo Hills are also known as the Kutum Volcanic Field, after the town of Kutu ...
and
Meidob Hills volcanism may be the product of a
mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...
. After the separation of
South Sudan
South Sudan (; din, Paguot Thudän), officially the Republic of South Sudan ( din, Paankɔc Cuëny Thudän), is a landlocked country in East Africa. It is bordered by Ethiopia, Sudan, Central African Republic, Democratic Republic of the C ...
, the highest point of Sudan is on the margin of the caldera.
The caldera lies atop a
shield volcano
A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...
or ash cone in the southern Marra Mountains, which developed first as a pile of
basaltic
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...
lava flows
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
and later as layers of
volcanic ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
and
tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
, including the eruptions that formed the caldera. A large eruption occurred about 3,520 ± 100 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. Becaus ...
, and
hot springs
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 ...
and
fumaroles
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 ...
are active to the present day.
Deriba contains two lakes, one in the northeastern side of the main caldera and the other in a cone in the southwestern sector of the Deriba caldera. The fresher southwestern lake is smaller but considerably deeper than the saltier northeastern lake; in the late Pleistocene the caldera was filled with a larger lake.
Geography and geomorphology
Deriba lies in the
Marra Mountains of
Sudan
Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...
, Africa's geographic centre;
Deriba is in the southern sector of these mountains and close to the main summit thereof. The caldera rim became Sudan's new highest point, after the independence of
South Sudan
South Sudan (; din, Paguot Thudän), officially the Republic of South Sudan ( din, Paankɔc Cuëny Thudän), is a landlocked country in East Africa. It is bordered by Ethiopia, Sudan, Central African Republic, Democratic Republic of the C ...
.
The town of
Nyala
The lowland nyala or simply nyala (''Tragelaphus angasii'') is a spiral-horned antelope native to southern Africa. It is a species of the family Bovidae and genus ''Tragelaphus'', previously placed in genus ''Nyala''. It was first described in ...
lies south of Deriba. The volcano is poorly studied due to the ongoing
Darfur conflict
The War in Darfur, also nicknamed the Land Cruiser War, is a major armed conflict in the Darfur region of Sudan that began in February 2003 when the Sudan Liberation Movement (SLM) and the Justice and Equality Movement (JEM) rebel groups be ...
.
Deriba is an oval, wide and deep
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 ...
, with a
volcanic cone
Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and ...
occupying the southwestern part of the caldera floor. At least five overlapping vents form the volcanic cone. The rim of the caldera reaches a maximum elevation of in the southwest, and is steep almost vertical. The caldera is cut into
volcanic ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
,
lapilli
Lapilli is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' (singular: ''lapillus'') is Latin for "little stones".
By definition lapilli range f ...
,
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
s,
obsidian
Obsidian () is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock.
Obsidian is produced from felsic lava, rich in the lighter elements s ...
and
tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
s, and the floor is strewn with
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...
blocks. A gap lies in the eastern caldera wall.
Lakes
Deriba contains two lakes, which are known as the "Deriba lakes". A deep lake occupies the northeastern area of the caldera, and being located in the lowest part of the caldera floor it is the
sink
A sink is a bowl-shaped plumbing fixture for washing hands, dishwashing, and other purposes. Sinks have a tap (faucet) that supply hot and cold water and may include a spray feature to be used for faster rinsing. They also include a drain to ...
of Deriba. In 1918 it had dimensions of , but by 1964 the size of the lake had increased. The lake is surrounded by a gradually sloping muddy beach with the exception of the northern shore. This lake is also known as the "female" lake, with green salty water. The salt consists of
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
,
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
and
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
salts.
The volcanic cone has a lake as well, which is deep and smaller, with a roughly rectangular shape that extends in north-south direction. In comparison to the other lake northwest, this "male" lake had dimensions of in 1918. Steep slopes surround this lake, which is filled with
fresh
Fresh or FRESH may refer to:
People
*DJ Fresh (born 1977), UK-based drum and bass artist
*DJ Fresh (producer), US-based R&B producer born Marqus Brown
Arts, entertainment, and media Films
* ''Fresh'' (1994 film), a crime film
* ''Fresh'' (200 ...
er water. Reportedly, the local
Fur
Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...
people considered the lake
haunted
Haunted or The Haunted may refer to:
Books
* ''Haunted'' (Armstrong novel), by Kelley Armstrong, 2005
* ''Haunted'' (Cabot novel), by Meg Cabot, 2004
* ''Haunted'' (Palahniuk novel), by Chuck Palahniuk, 2005
* ''Haunted'' (Angel novel), a 200 ...
, but the lakes were also used as a source for
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
.
Water levels in these lakes are fairly stable from season to season although evidence for substantial fluctuations have been found that correlate to the regional climate and to fluctuations in the water levels of
Lake Chad
Lake Chad (french: Lac Tchad) is a historically large, shallow, endorheic lake in Central Africa, which has varied in size over the centuries. According to the ''Global Resource Information Database'' of the United Nations Environment Programme, ...
. Together with several perennial
stream
A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...
s they are thus perennial waterbodies. Around the Deriba caldera,
drainage
Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic conditio ...
occurs either southward or westward, leading into the
Bahr El-Arab of the
White Nile
The White Nile ( ar, النيل الأبيض ') is a river in Africa, one of the two main tributaries of the Nile, the other being the Blue Nile. The name comes from the clay sediment carried in the water that changes the water to a pale color. ...
and the
Chari River
The Chari River, or Shari River, is a long river, flowing in Central Africa. It is Lake Chad's main source of water.
Geography
The Chari River flows from the Central African Republic through Chad into Lake Chad, following the Cameroon border f ...
of
Lake Chad
Lake Chad (french: Lac Tchad) is a historically large, shallow, endorheic lake in Central Africa, which has varied in size over the centuries. According to the ''Global Resource Information Database'' of the United Nations Environment Programme, ...
respectively.
The lakes themselves have no surface outlets.
In the past, larger lakes existed inside the Deriba caldera. The first such lake stage has been dated to 23,000 or 19,000 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. Becaus ...
when water levels rose above the present-day levels, the second 19,600 - 16,000 years before present when they were higher than currently and the third 14,000 years before present, then above present-day. Similar lake stages have been documented in
Trou au Natron
Trou au Natron (French: "hole of natron") or ( Teda: "big hole") is a volcanic caldera of the Tibesti Massif in the nation of Chad in Northern Africa. The volcano is extinct. It is unknown when it last erupted. Its volcano number is 0205–01. T ...
in Tibesti, where shifts of the position of the
subtropical jet stream
Jet streams are fast flowing, narrow, meandering air currents in the atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds (flowing west to east). ...
and the
tropical depression
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depend ...
s associated with the jet stream have been invoked as an explanation.
These lake stages have left
shoreline
A shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past a ...
s and
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
deposits in the caldera, and it is likely that the lakes sometimes overflowed through the eastern caldera rim gap.
Geology
Deriba is part of
Jebel Marra
The Marrah Mountains or Marra Mountains (Fur, Fugo Marra; ar, جبل مرة, Jebel Marra are a range of volcanic peaks in a massif that rises up to . They are the highest mountains in Sudan.
Geography
The mountains are located in the center of t ...
volcano, which together with the
Tagabo Hills
The Tagabo Hills is a volcanic field in the region of Darfur in Sudan. It lies north of the Marrah Mountains and southwest of the larger Meidob Volcanic Field. The Tagabo Hills are also known as the Kutum Volcanic Field, after the town of Kutu ...
and the
Meidob Hills is one of three
volcanic field
A volcanic field is an area of Earth's crust that is prone to localized volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters of up to 100 volcanoes ...
s in
Darfur
Darfur ( ; ar, دار فور, Dār Fūr, lit=Realm of the Fur) is a region of western Sudan. ''Dār'' is an Arabic word meaning "home f – the region was named Dardaju ( ar, دار داجو, Dār Dājū, links=no) while ruled by the Daju, ...
; these form the little known Darfur Volcanic Province. The Jebel Marra volcano is maximally wide and long in north-south direction, where the northern segment is centered around Jebel Gurgei.
Jebel Marra consists of a pile of mostly
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic lava which has been covered by
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...
and
volcanic ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
as well as
pyroclastic
Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...
rocks and
ignimbrite
Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrou ...
s.
The Deriba caldera which forms the top of the entire complex, which around Deriba has the appearance of a large ash cone or
shield volcano
A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...
. Other, less spectacular
vents
Vent or vents may refer to:
Science and technology Biology
*Vent, the cloaca region of an animal
*Vent DNA polymerase, a thermostable DNA polymerase
Geology
*Hydrothermal vent, a fissure in a planet's surface from which geothermally heated water ...
are found elsewhere in the Marra Mountains. Erosion has cut
canyon
A canyon (from ; archaic British English spelling: ''cañon''), or gorge, is a deep cleft between escarpments or cliffs resulting from weathering and the erosion, erosive activity of a river over geologic time scales. Rivers have a natural tenden ...
s into the volcanic complex. The occurrence of volcanism has been explained with a
mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...
centered between Meidob and Jebel Marra.
The basement is formed by crystalline rocks, mainly
metamorphosed
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
gneiss
Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...
es and
schist
Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...
s, and is a
mobile belt of
Panafrican age. They are in part covered by the
Nubian Sandstone
The Nubian Sandstone is a variety of sedimentary rock deposited on the Precambrian basement in the eastern Sahara, north-east Africa and Arabian Peninsula. It consists of continental sandstone with thin beds of marine limestones, and marls. T ...
s of
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
age and
aeolian sands, and by the Jebel Marra massif which occupies a surface of . Tectonic
uplift
Uplift may refer to: Science
* Geologic uplift, a geological process
** Tectonic uplift, a geological process
* Stellar uplift, the theoretical prospect of moving a stellar mass
* Uplift mountains
* Llano Uplift
* Nemaha Uplift
Business
* Uplif ...
of the
Darfur dome
Darfur Dome or Darfur Volcanic Province is an area of about 100x400 km in Western Sudan. As well as its best-known and central feature, Deriba Crater, it encompasses the surrounding Marra Mountains (Jebel Marra) and Tagabo Hills, both formed aro ...
commenced in the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
and resulted in a noticeable upwarp of the basement beneath Jebel Marra.
Two major tectonic
lineament ''See also Line (geometry)''
A lineament is a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will appear as a fault-aligned valley, a series of fault or fold-aligne ...
s intersect at Jebel Marra, one trending south-southeastward and the other east-northeastward.
Eruptive history
Volcanism in the Jebel Marra mountains appears to have begin 15 million years ago and continued in two stages, separated by an erosional period. Volcanism in the southwestern Marra mountains took place between 4.35 million years ago and 60,000 years ago, subdivided into an Old Series and a New Series which is younger than 2 million years ago.
After an initial stage, during which
olivine basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of ...
and small amounts of
pyroclastic
Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...
material were erupted,
trachyte
Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and al ...
were emplaced.
The Deriba caldera probably formed either in the early
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), 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 fina ...
, 60,000
or 3,520 ± 100 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. Becaus ...
(BP), but activity continued with the volcanic cone inside of the caldera and peripheral vents, possibly into historical time.
The 3,520 ± 100 BP eruption was a
Plinian eruption that deposited
pyroclastic
Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...
material containing blocks of basement material. The ash fall from the eruption reaches thicknesses of as far as away from Deriba,
while
pyroclastic flow
A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of bu ...
s have been identified as far as from the caldera. The eruption has an estimated
volcanic explosivity index of 4
and may be associated with the volcanic cone inside the caldera.
The volcano was formerly considered to be
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
.
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, whose temperature reaches and which may be supplied by
magmatic water
Magmatic water, also known as juvenile water, is an aqueous phase in equilibrium with minerals that have been dissolved by magma deep within the Earth's crust and is released to the atmosphere during a volcanic eruption. It plays a key role in ass ...
,
and
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, both within the caldera around the volcanic cone and in the surrounding Marra Mountains, indicate that Jebel Marra and the Deriba caldera are a
dormant volcano
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 ...
. Reportedly, the exhalations of the fumaroles can kill birds and insects,
and some fumarolic vents may have formed between 1964 and 1966,
implying that the fumarolic activity may reflect a recent change of volcanic activity.
Climate
Jebel Marra has a
humid subtropical climate
A humid subtropical climate is a zone of climate characterized by hot and humid summers, and cool to mild winters. These climates normally lie on the southeast side of all continents (except Antarctica), generally between latitudes 25° and 40° ...
(Cwa) bordering on a
subtropical highland climate
An oceanic climate, also known as a marine climate, is the humid temperate climate sub-type in Köppen classification ''Cfb'', typical of west coasts in higher middle latitudes of continents, generally featuring cool summers and mild winters ( ...
(Cwb). Precipitation on Jebel Marra is about , the mountain lies at the eastern margin of the
Sahel
The Sahel (; ar, ساحل ' , "coast, shore") is a region in North Africa. It is defined as the ecoclimatic and biogeographic realm of transition between the Sahara to the north and the Sudanian savanna to the south. Having a hot semi-arid c ...
and receives more precipitation than the surrounding region. Between 12,000 and 8,000 years before present, the climate was wetter as a consequence of a northward shift of climate zones.
Biology
Vegetation around Deriba consists of grassland with scarce trees such as the
wild olive Wild olive is a common name for several plants and may refer to:
*''Bontia daphnoides''
* Several species in the genus ''Elaeagnus'' (family Elaeagnaceae), particularly:
**''Elaeagnus angustifolia''
**''Elaeagnus latifolia''
*''Halesia carolina'' ( ...
. The plant life is classified as
Afromontane
The Afromontane regions are subregions of the Afrotropical realm, one of the Earth's eight biogeographic realms, covering the plant and animal species found in the mountains of Africa and the southern Arabian Peninsula. The Afromontane regions ...
, it also includes species from
temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...
climates. It is likely that past humid periods permitted the expansion of
Mediterranean
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
species into the Jebel Marra mountains. Presently, Jebel Marra is a suitable site for agriculture and used as such by the
Fur people
The Fur (Fur: ''fòòrà'', Arabic: فور ''Fūr'') are an ethnic group predominantly inhabiting western Sudan. They are concentrated in the Darfur region, where they are the largest ethnic group.Gettleman, Jeffrey, "Chaos in Darfur on rise as ...
.
Semidesert
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-ar ...
and
desert
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
landscapes dominate the region around the Marra Mountains.
The lakes are salty,
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 ...
poor and remote and thus contain little plant or animal life. Some vegetation grows around the smaller lake, as well as in other parts of the Deriba caldera where water is available.
Copepod
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...
s live in the smaller lake, while the larger one is populated by
blue-green algae and
rotifer
The rotifers (, from the Latin , "wheel", and , "bearing"), commonly called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals.
They were first described by Rev. John H ...
s. ''
Spirulina'' occurs in the large lake, and ''
Melosira
''Melosira'' is a genus of diatoms belonging to the family Melosiraceae.
The genus has cosmopolitan distribution, and inhabits both freshwater and marine habitats.
Species
Species:
*'' Gaillonella ampla''
*'' Gaillonella apiculata''
*'' G ...
'' and ''
Nitzscia''
diatom
A diatom (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 comprising sev ...
s have been identified in the small lake. The copepod ''
Eucyclops gibsoni'' has been encountered in the small lake. Among the rotifers are ''
Brachionus dimidiatus'', ''
Brachionus plicatilis
''Brachionus plicatilis'' is a euryhaline (tolerate a wide range of salinity) rotifer in the family ''Brachionidae'', and is possibly the only commercially important rotifer, being raised in the aquaculture industry as food for fish larvae. It has ...
'', ''
Hexarthra jenkinae'' and ''
Lecane bulla
''Lecane'' is a genus of rotifers belonging to the family Lecanidae. It is the only genus in the monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species i ...
'', some of which also occur in the smaller lake. ''
Ephedra Ephedra may refer to:
* Ephedra (medicine), a medicinal preparation from the plant ''Ephedra sinica''
* ''Ephedra'' (plant), genus of gymnosperm shrubs
See also
* Ephedrine
Ephedrine is a central nervous system (CNS) stimulant that is of ...
'' flies are widespread around the large lake, and other insects were collected on the small lake. Birds are uncommon, with
greenshank
The common greenshank (''Tringa nebularia'') is a wader in the large family Scolopacidae, the typical waders. The genus name ''Tringa'' is the New Latin name given to the green sandpiper by Aldrovandus in 1599 based on Ancient Greek ''trungas'' ...
s,
little grebe
The little grebe (''Tachybaptus ruficollis''), also known as dabchick, is a member of the grebe family of water birds. The genus name is from Ancient Greek ''takhus'' "fast" and ''bapto'' "to sink under". The specific ''ruficollis'' is from Latin ...
s,
sacred ibis
The African sacred ibis (''Threskiornis aethiopicus'') is a species of ibis, a wading bird of the family Threskiornithidae. It is native to much of Africa, as well as small parts of Iraq, Iran and Kuwait. It is especially known for its role in ...
and
stilt
Stilt is a common name for several species of birds in the family Recurvirostridae, which also includes those known as avocets. They are found in brackish or saline wetlands in warm or hot climates.
They have extremely long legs, hence the grou ...
s.
Gallery
File:Deriba lake in cone, looking west.jpg, Sketch of the Deriba lake looking west
File:Deriba caldera, northeastern lake.jpg, Northeast lake in Deriba, looking west
File:Sudan Jebel Marra Deriba Lakes.jpg, The southwestern lake
File:Sudan Jabal Marra.jpg, The caldera
References
Sources
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{{refend
External links
* Satellite image (large scale)
* Oblique aerial photo on page 27 (large scale)
Deriba Calderaat
NASA Earth Observatory
NASA Earth Observatory is an online publishing outlet for NASA which was created in 1999. It is the principal source of satellite imagery and other scientific information pertaining to the climate and the Environment (biophysical), environment whi ...
Marrah Mountains
Volcanoes of Sudan
Darfur
Volcanic crater lakes
Dormant volcanoes
Calderas of Africa
Highest points of countries
VEI-4 volcanoes