Bayuda volcanic field

Bayuda volcanic field
The volcanic field from space
Highest point
Elevation	670 m (2,200 ft)[1]
Coordinates	18°20′N 32°45′E / 18.33°N 32.75°E / 18.33; 32.75[1]
Geography
Bayuda volcanic field
Geology
Last eruption	1,102 ± 48 years ago

Bayuda volcanic field (also spelled Bayiuda^[1]) is a volcanic field in Sudan, within the Bayuda Desert. It covers a surface of about 11 by 48 kilometres (6.8 mi × 29.8 mi) and consists of a number of cinder cones as well as some maars and explosion craters. These vents have erupted 'A'ā lava flows.

The field rises above a Precambrian-Paleozoic basement that may be a domal uplift. There is little known about the occurrence of volcanic eruptions, but the last eruption has been dated to 1,102 ± 48 years before present.

Geography and geomorphology

The volcanic field is located in the Bayuda Desert within the great bend of the Nile,^[1] 300 kilometres (190 mi) north of Khartoum.^[2] It lies 80 kilometres (50 mi) away from Merowe; there are wells at Abu Khorit and Sani^[3] north of the volcanic field.^[4] The field was discovered by aerial photography in 1920.^[3] Numerous Middle Stone Age and Paleolithic archeological sites are found in the field.^[5]

Bayuda is an elongated volcanic field^[1] with fresh volcanic features^[3] extending over an area of 11 by 48 kilometres (6.8 mi × 29.8 mi) in northwesterly direction. Within this area, a number of volcanic vents within a narrow space have formed a continuous volcanic surface.^[6] Some individual lava fields cover over 20 square kilometres (7.7 sq mi) of surface,^[7] but surfaces of about 10 square kilometres (3.9 sq mi) are more typical.^[8] There are usually only a few flows per vent, although they often have lobate structures. The surface of the lava flows has varying textures and often contains hills or ridges,^[9] generally corresponding to aa lava.^[10] Some flows reach lengths of 10 kilometres (6.2 mi)^[11] and thicknesses of 30 metres (98 ft). The flows are often covered by ridges and hillocks.^[12]

Cinder cones make up the bulk of the field,^[1] of which there are about one hundred.^[13] Usually the cones reach heights of over 400 metres (1,300 ft)^[8] and are formed by volcanic ash, lapilli, lava bombs and scoria.^[14] Many of these aside from pyroclastics also erupted lava flows^[6] which then broke the crater rims.^[1] Explosion craters^[1] and sporadic maars are also found,^[2] they are surrounded by tephra deposits which form low rims of pyroclastic material^[15] and which also cover neighbouring volcanoes.^[4] Individual vents form two separate alignments.^[11]

Hosh ed Salam ("dark enclosure"^[16]) crater is 500 metres (1,600 ft) deep and 1,300 metres (4,300 ft) wide,^[1] other craters are Jebel Hebeish and El Muweilih which have formed shallow rises above the surrounding terrain and have cut into the basement rocks.^[10] El Muweilih contains a salt lake after which it is named and which was used as a source of salt,^[7] while Jebel El Abour contains a secondary cone. The Sergein hills and Jebel Azrub are composite volcanoes.^[6] Angalafib, Goan and Jebel El Abour are also quite high.^[7]

Pumice blocks from the field were found in Wadi Abu Dom,^[3] and scoria downstream in the Nile.^[16] Tephra identified in deposits on Mograt Island in the Nile most likely comes from this volcanic field.^[17] The volcanic field is a potential site for geothermal power development, with temperatures underground of about 200 °C (392 °F).^[18]

Geology

Volcanic activity has been taking place in Sudan since the Cretaceous, with most recent manifestations documented in the Bayuda volcanic field, Marra Mountains and Meidob volcanic field^[3] both in Darfur,^[19] and elsewhere in the form of small basaltic outcrops.^[20] Bayuda is a small volcanic field in comparison to other African volcanic fields.^[4] Volcanism at Bayuda may be associated with the Central African Shear Zone^[21] and of Precambrian faults,^[22] perhaps together with a mantle plume.^[23] The area features four more volcanic fields, the "Northern Field" northeast, the Abu Rugheiwa field southeast and Shaq Umm Bosh and Muqqodom southwest of Bayuda.^[24]

The basement consists of granites of Precambrian and Paleozoic age^[1] that belong to the Bayuda terrane,^[2] which together with gneisses form a gentle pediplain away from rougher landscape along the Nile.^[25] Later on during the Cretaceous the Nubian Formation was laid down and there are hints of a domal uplift in the Bayuda area,^[3] which probably predates the onset of volcanism and may have influenced the course of the Nile.^[25] The existence of such a dome has been questioned, however.^[26]

Composition

Bayuda has erupted basaltic rocks,^[6] with most collected rocks belonging to an alkali basalt suite^[27] although basanite, melabasanite, hawaiite and trachybasalt have been identified as well.^[2][28] Phenocrysts include clinopyroxene and olivine.^[27] Various xenoliths have been found, including garnet-containing clinopyroxenite, harzburgite, garnet hornblendite, amphibole-containing peridotite, olivine and spinel pyroxenite and websterite.^[29]

In general the composition resembles that of other Sudanese-Egyptian volcanoes,^[2] about two different magma families have been identified which originate from disparate mantle domains.^[11] Crystal fractionation of clinopyroxene, olivine and spinels took part in the formation of the magmas.^[30] The total volume of the volcanic rocks is about 18 cubic kilometres (4.3 cu mi),^[31] the rocks reach thicknesses of about 200 metres (660 ft) maximally.^[4]

Eruptive history

Volcanic activity has been dated to 1.7 - 0.9 million years ago,^[32] but it continued after the end of the latest wet period 5,000 years ago^[1] as indicated by the uneroded state of some of the volcanoes^[4] such as Hosh ed Salam.^[33] The presence of maars and volcanoes with signs of phreatomagmatic activity may indicate activity during pluvials.^[34] Volcanism at Bayuda commenced with isolated volcanoes. After a while, new edifices were constructed atop the older ones, influencing the morphology of the new volcanoes.^[31]

The most recent lava flow was dated to less than 1,100 years before present,^[1] with radiocarbon dating producing an age of 1,102 ± 48 years before present.^[8] Aside from this date, however, there is little information on the timing of recent volcanic activity in the Bayuda volcanic field.^[34]

References

Sources

This page was last edited on 9 March 2024, at 09:05