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Haruj
Haruj (Arabic: هروج, also known as Haroudj) is a large volcanic field spread across 42,000–45,000 km2 (16,000–17,000 sq mi) in central Libya. It is one of several volcanic fields in Libya along with Tibesti, and its origin has been attributed to the effects of geologic lineaments in the crust.
It contains about 150 volcanoes, including numerous basaltic scoria cones and about 30 small shield volcanoes, along with craters and lava flows. Most of the field is covered by lava flows that originated in fissure vents; the rest of the flows originated within small shield volcanoes, stratovolcanoes and scoria cones. Some of these vents have large craters. Volcanism in Haruj blocked ancient rivers and led to the formation of Lake Megafezzan.
Volcanic activity in Haruj began about 6 million years ago and continued into the late Pleistocene. A number of individual lava flow generations were emplaced in the Haruj volcanic field, the most recent ones in the Holocene 2,310 ± 810 years ago. There are reports of solfataric activity.
Haruj lies in central Libya and its highest summit is Garet es Sebaa, 1,200 metres (3,900 ft) above sea level. It was first identified as volcanic in 1797 and had a reputation for being challenging to access owing to its remoteness and the hostile terrain and was thus avoided by explorers. The town of Al-Foqaha is located 15 kilometres (9.3 mi) northwest of the margin of Haruj, and oil fields can be found north of the field.
The field is a low-relief expanse of volcanic rocks occasionally interrupted by volcanic cones which covers an area of 42,000–45,000 square kilometres (16,000–17,000 sq mi), making it the largest of the basaltic volcanic fields of Northern Africa. Its eruption products reach a thickness of 300 to 400 metres (980 to 1,310 ft) in the central sector in the form of stacked lava flows. The total volume of volcanic rocks has been estimated to be about 5,000 km3 (1,200 cu mi). The Al Haruj al Aswad ("Black mountain") field in the northern part of Haruj and Al Haruj al Abyad ("White mountain") south are considered to be subdivisions of the main Haruj volcanic field with Aswad covering a much larger surface than Abyad, or even two separate volcanoes that started overlapping each other during the Pliocene.
Older lava flows have been completely flattened by erosion, while more recent ones still display fresh surface structures and some of the recent flows flowed out of the mountains into the surrounding landscapes. Surface features include both aa lava traits and pahoehoe lava traits, and there are lava channels, skylights and tumuli. The volcanic rocks are usually not very thick, their thickness decreasing from 145 metres (476 ft) in the central sector to only a few metres at the margins, and thus the underlying sedimentary rocks often crop out between lava flows.
Most of the lavas appear to originate in fissure vents, under the influence of dykes and tectonic faults. In addition, there are about 150 individual volcanic massifs and more smaller volcanic cones, many of which form rows of cones and sometimes have large craters and which occur mainly in the Al Haruj al Abyad part of Haruj. Craters range from deep pits with steep inward walls to wide and shallow depressions, and the craters are often filled with material eroded from their flanks. Phreatomagmatic processes triggered by groundwater interacting with rising magma have generated some of these large craters, while others formed when lava lakes drained through gaps in their rims. Like the fissure vents, the position of individual cones and massifs is controlled by ground fractures and often reflect the activity of dykes, and some cones appear to have been active more than once.
There are about 30 shield volcanoes with heights of 100 to 400 metres (330 to 1,310 ft), such as Um el Garanigh and Um el Glaa, and smaller stratovolcanoes with heights of 80 to 250 metres (260 to 820 ft) such as Garet el Graabia in the field; some stratovolcanoes are located on shield volcanoes. Scoria cones consist of lapilli, lava bombs, and tuffs, with pyroclastic material exposed in the crater rims. The formation of scoria cones was at times accompanied by subplinian eruptions that deposited tephra over large areas.
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Haruj
Haruj (Arabic: هروج, also known as Haroudj) is a large volcanic field spread across 42,000–45,000 km2 (16,000–17,000 sq mi) in central Libya. It is one of several volcanic fields in Libya along with Tibesti, and its origin has been attributed to the effects of geologic lineaments in the crust.
It contains about 150 volcanoes, including numerous basaltic scoria cones and about 30 small shield volcanoes, along with craters and lava flows. Most of the field is covered by lava flows that originated in fissure vents; the rest of the flows originated within small shield volcanoes, stratovolcanoes and scoria cones. Some of these vents have large craters. Volcanism in Haruj blocked ancient rivers and led to the formation of Lake Megafezzan.
Volcanic activity in Haruj began about 6 million years ago and continued into the late Pleistocene. A number of individual lava flow generations were emplaced in the Haruj volcanic field, the most recent ones in the Holocene 2,310 ± 810 years ago. There are reports of solfataric activity.
Haruj lies in central Libya and its highest summit is Garet es Sebaa, 1,200 metres (3,900 ft) above sea level. It was first identified as volcanic in 1797 and had a reputation for being challenging to access owing to its remoteness and the hostile terrain and was thus avoided by explorers. The town of Al-Foqaha is located 15 kilometres (9.3 mi) northwest of the margin of Haruj, and oil fields can be found north of the field.
The field is a low-relief expanse of volcanic rocks occasionally interrupted by volcanic cones which covers an area of 42,000–45,000 square kilometres (16,000–17,000 sq mi), making it the largest of the basaltic volcanic fields of Northern Africa. Its eruption products reach a thickness of 300 to 400 metres (980 to 1,310 ft) in the central sector in the form of stacked lava flows. The total volume of volcanic rocks has been estimated to be about 5,000 km3 (1,200 cu mi). The Al Haruj al Aswad ("Black mountain") field in the northern part of Haruj and Al Haruj al Abyad ("White mountain") south are considered to be subdivisions of the main Haruj volcanic field with Aswad covering a much larger surface than Abyad, or even two separate volcanoes that started overlapping each other during the Pliocene.
Older lava flows have been completely flattened by erosion, while more recent ones still display fresh surface structures and some of the recent flows flowed out of the mountains into the surrounding landscapes. Surface features include both aa lava traits and pahoehoe lava traits, and there are lava channels, skylights and tumuli. The volcanic rocks are usually not very thick, their thickness decreasing from 145 metres (476 ft) in the central sector to only a few metres at the margins, and thus the underlying sedimentary rocks often crop out between lava flows.
Most of the lavas appear to originate in fissure vents, under the influence of dykes and tectonic faults. In addition, there are about 150 individual volcanic massifs and more smaller volcanic cones, many of which form rows of cones and sometimes have large craters and which occur mainly in the Al Haruj al Abyad part of Haruj. Craters range from deep pits with steep inward walls to wide and shallow depressions, and the craters are often filled with material eroded from their flanks. Phreatomagmatic processes triggered by groundwater interacting with rising magma have generated some of these large craters, while others formed when lava lakes drained through gaps in their rims. Like the fissure vents, the position of individual cones and massifs is controlled by ground fractures and often reflect the activity of dykes, and some cones appear to have been active more than once.
There are about 30 shield volcanoes with heights of 100 to 400 metres (330 to 1,310 ft), such as Um el Garanigh and Um el Glaa, and smaller stratovolcanoes with heights of 80 to 250 metres (260 to 820 ft) such as Garet el Graabia in the field; some stratovolcanoes are located on shield volcanoes. Scoria cones consist of lapilli, lava bombs, and tuffs, with pyroclastic material exposed in the crater rims. The formation of scoria cones was at times accompanied by subplinian eruptions that deposited tephra over large areas.
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