Lake Suguta is a former lake in

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

. It formed in the Suguta Valley, which is part of the East African Rift, south of Lake Turkana during the

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 togeth ...

African humid period The African humid period (AHP) (also known by other names) is a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, ...

. The lake existed a number of times during history, most recently during the early and middle Holocene when a stronger

monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal osci ...

caused increased precipitation in the basin of the lake. The lake then reached a top elevation of above sea level, when it overflowed into the

Kerio River The Kerio River is a river in Turkana County, Kenya. It flows northward into Lake Turkana. It is one of the longest rivers in Kenya, originating near the equator. Course The Kerio River rises on the north slopes of the Amasya Hills to the west ...

and then into Lake Turkana. The lake possibly ultimately drained into the

Nile The Nile, , Bohairic , lg, Kiira , Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest ...

. Between 8,000 and 5,000 years ago the lake progressively dried up; today only the small

Lake Logipi Lake Logipi is a saline, alkaline lake that lies at the northern end of the arid Suguta Valley in the northern Kenya Rift. It is separated from Lake Turkana by the Barrier Volcano, Barrier volcanic complex, a group of young volcanoes that last eru ...

occupies the area.

Geography and geology

Lake Suguta lies in the Kenya Rift, which is part of the East African Rift. Starting with the

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

plate tectonics Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

resulted in the pulling apart of the crust and the formation of the rift valley along with volcanoes; these include

The Barrier The Barrier is a lava dam retaining the Garibaldi Lake system in southwestern British Columbia, Canada. It is over thick and about long where it impounds the lake. The area below and adjacent to The Barrier is considered hazardous due to the u ...

volcano which starting from 1.3 million years ago and definitively from 0.2-0.1 million years ago separates Lake Suguta from Lake Turkana farther north. Volcanic activity in the region occurred as recently as 200 years ago. The Suguta valley today is about wide and long, dropping down northwards to a lowermost elevation of above sea level. It is relatively remote.

The lake

At highstand Lake Suguta had a roughly rectangular shape with the long side trending north-northeast from Emuruangogolak volcano in the south to The Barrier in the north, and between the Loriu Plateau west and Tirr Tirr Plateau east of the valley. The lake covered a total area of and was about deep. The

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene 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 ...

Namarunu volcano formed a peninsula on the western coast, while the Kamuge River valley at the southwestern end of the lake was occupied by a bay. A cinder cone formed an island at the northern end of Lake Suguta and was reached by humans, judging by the presence of obsidian artifacts; traces of human activity have also been encountered Wavecut terraces are found at the former shorelines of Lake Suguta, particularly at elevations of which is where the main shoreline of Lake Suguta and also its highstand is located. Volcanism occurred in the area of Lake Suguta when it existed, resulting in the formation of

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discont ...

s and phreatomagmatic activity, lava flows of Emuruangogolak volcano reached the lake on its southern margin 11,000 - 9,000 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 ...

, and a layer of

tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they re ...

was deposited in parts of the lake 8,770 years before present. A number of cinder cones have been modified by Lake Suguta, and the increased availability of water allowed the onset of

fumarolic 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 volc ...

activity at volcanoes today too dry to support fumaroles, such as on The Barrier where fumarole sinter was emplaced when Lake Suguta existed. Some shorelines have been offset by faults, and the entire lake basin is tectonically tilted eastward, resulting in a corresponding vertical offset of shorelines. The existence of the lake itself affected regional tectonics; its disappearance and resulting unloading of the crust resulted in

isostatic rebound Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound ...

in the area.

Hydrology

The lake had two inflows, the Suguta River to the south and the Baragoi River to the southeast. The Baragoi River drains the Tirr Tirr Plateau, while the long Suguta River drains an area of of the Kenya Rift valley almost all the way from Paka volcano close to the equator. Lake Suguta at highstand had a volume of about . Rivers transported sediments from the tectonically young terrain into the lake, forming

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D ( NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also ...

s and resulting in high sedimentation rates close to the inlet of the Suguta River. During the highstand period of Lake Suguta, local precipitation was over 26% higher than today. Most likely, the strengthening of the monsoon - especially the Indian monsoon - drew humid air from the Congo into the region of Lake Suguta, increasing precipitation.

Overflow

A presently high sill separates the headwaters of the

(which drains to Lake Turkana) from these of the Kamuge River. Lake Suguta overflowed through this sill into Lake Turkana. Overflow over this sill controlled the lake levels at highstand; that it is higher than the highstand shoreline is most likely a consequence of the tectonic tilting of the basin. In addition, it is likely that during the highstand of Lake Suguta the

Lake Baringo Lake Baringo is, after Lake Turkana, the most northern of the Kenyan Rift Valley lakes, with a surface area of and an elevation of . The lake is fed by several rivers: the Molo, Perkerra and Ol Arabel. It has no obvious outlet; the waters ar ...

farther south overflowed into the Suguta River drainage basin, while Lake Turkana overflowed into the

. While this theory was at first viewed with scepticism, it is now likely that Lake Suguta was part of a large drainage system that formed a headwater for the White Nile along the

Pibor River The Pibor River (also called the River Pibor) is a river in eastern South Sudan, which defines part of South Sudan's border with Ethiopia. From its source near Pibor Post it flows north for about , joining the Baro River to form the Sobat River, ...

and

Sobat River The Sobat River is a river of the Greater Upper Nile region in northeastern South Sudan, Africa. It is the most southerly of the great eastern tributaries of the White Nile, before the confluence with the Blue Nile. Geography The Sobat River i ...

which connected Lake Turkana with the Nile.

Climate

Climate in tropical Africa was dry during the Last Glacial Maximum. In the early

, an increase in the strength of the

caused a wet period in northern Africa, the

African Humid Period The African humid period (AHP) (also known by other names) is a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, ...

, and the sizes of numerous lakes in East Africa were larger during the early Holocene 15,000 - 5,000 years ago than today. This strengthening of the monsoon also affected the Asian monsoon. Increased insolation in the northern hemisphere is considered to be the cause of the African Humid Period; directed by the

precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In oth ...

al maximum of insolation continents became much warmer than the ocean and thus the monsoon strengthened. Other mechanisms also played a role, seeing as the reconstructed changes in precipitation were considerably more abrupt than the actual changes in insolation. Further, humidity did not increase simultaneously in all places; locations farther north (such as the

Omo River The Omo River (also called Omo-Bottego) in southern Ethiopia is the largest Ethiopian river outside the Nile, Nile Basin. Its course is entirely contained within the boundaries of Ethiopia, and it empties into Lake Turkana on the border with Keny ...

headwaters) reached maximum humidity (and thus maximum levels of the lakes fed by the rivers) later than locations farther south. This is because maximum humidity occurs when the maximum insolation coincides with the rainy season and this coincidence occurred later in history for the northerly water systems. Nowadays the Suguta Valley is among the driest areas - if not the driest are - close to the equator, with precipitation estimated to be less than most of which falls during spring. Precipitation is highly variable from year to year. This climate is a consequence of the annual migration of the

ITCZ The Intertropical Convergence Zone (ITCZ ), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the thermal ...

; however the moist air from the Congo Basin does not reach Lake Suguta and that along with the dryness of the Asian monsoon in East Africa explains the precipitation patterns.

Biology

Bivalves, freshwater snails,

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typi ...

oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...

prosobranch Prosobranchia was a large taxonomic subclass of sea snails, land snails and freshwater snails. This taxon of gastropods dates back to the 1920s. It has however been proven to be polyphyletic (consisting of more than one lineage of descent). G ...

gastropods and stromatoliths occurred in Lake Suguta. A

Nilotic The Nilotic peoples are people indigenous to the Nile Valley who speak Nilotic languages. They inhabit South Sudan, Sudan, Ethiopia, Uganda, Kenya, the Democratic Republic of the Congo, Rwanda, Burundi and Tanzania. Among these are the Burun-sp ...

fauna has been found in

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s associated with Lake Suguta, which endorses the idea that the lake was formerly connected with Lake Turkana and the Nile. Lake Logipi-4

History

The Suguta valley was occupied by a lake starting from 0.8-0.5 million years ago, but a lake existed here already 1–0.7 million years ago. A first highstand occurred 121,000 ± 20,000 years ago. A shoreline at elevation is dated to 30,000 - 27,000 years ago. Between 16,500 and 14,000 calibrated radiocarbon years ago Lake Suguta had an elevation of . After an interval where the lake elevation is unknown, 12,800 calibrated radiocarbon years ago Lake Suguta reached its highstand. A brief drop in lake levels occurred 12,700 - 11,800 calibrated radiocarbon years ago during the

Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stag ...

event; lake levels subsequently recovered. Such a lowstand at the time of the Younger Dryas has been observed in other African lakes. The lake has left a number of shorelines all the way from the valley floor up to , where the highest and also most noticeable shoreline exists. This shoreline and several lower ones have left staircase-shaped wavecut terraces along the former shorelines of Lake Suguta. Lake levels were not stable, with several brief rapid lake level increases and lake level drops occurring between 10,700 and 8,800 years before present. Such lake level drops are associated with episodic weakening of the monsoons. Beginning 8,500 calibrated radiocarbon years ago, lake levels started to decrease and reached a lowstand of above sea level around 7,300 calibrated radiocarbon years ago. Lake levels after that point are uncertain but undoubtedly very low in comparison to the earlier Lake Suguta. In contrast, one date indicates that water levels were close to highstand around 6,700 years before present. Water levels around 8,250 - 5,000 years ago (when the African Humid Period ended) are unclear, but highstand ended latest around 5,200 years before present. The lake level drop between 8,700 and 8,200 years before present may be associated with the 8.2 kiloyear event, which is linked to drying elsewhere. A last lake stand above the lake floor occurred towards the end of the Medieval Warm Period. Presently, the site of Lake Suguta is occupied by a broad valley and

, which is fed by the Suguta River as well as ephemeral river 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 c ...

s and whose surface varies from year to year. The area's arid climate is underscored by the scarce

xerophytic A xerophyte (from Greek ξηρός ''xeros'' 'dry' + φυτόν ''phuton'' 'plant') is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert such as the Sahara or places in the Alps or t ...

vegetation and the occurrence of

dunes A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...

. The valley flanks are more humid and feature

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...

woods. When the existence of a former lake in the Suguta Valley was first considered, it was proposed that Lake Suguta was originally part of Lake Turkana and dried up when volcanic activity separated both lakes; later it was determined that Lake Suguta existed long after the Suguta valley's separation from the Turkana basin.

References

Sources

* * * *

External links

* * {{cite journal, last1=Borchardt, first1=Sven, last2=Trauth, first2=Martin H., title=Remotely-sensed evapotranspiration estimates for an improved hydrological modeling of the early Holocene mega-lake Suguta, northern Kenya Rift, journal=Palaeogeography, Palaeoclimatology, Palaeoecology, date=15 November 2012, volume=361-362, issue=Supplement C, pages=14–20, doi=10.1016/j.palaeo.2012.07.009, ref=none

Suguta The Suguta Valley, also known as the Suguta Mud Flats, is an arid part of the Great Rift Valley in Kenya (Africa), directly south of Lake Turkana. Location The Suguta valley today is one of the driest parts of Kenya, with annual rainfall below . ...

Natural history of Kenya Holocene events