The Hajar Mountains (
Arabic: جِبَال ٱلْحَجَر,
romanized: Jibāl al-Ḥajar, The
RockyMountains[3][4] or The Stone Mountains) are one of the highest mountain ranges in the
Arabian Peninsula,[citation needed] shared between northern
Oman and eastern
United Arab Emirates. Also known as "Oman Mountains",[1][2] they separate the low coastal plain of Oman from the high desert plateau, and lie 50–100 km (31–62 mi) inland from the
Gulf of Oman.
Al (اَلْ) means "the", and Ḥajar (حَجَر) means "stone" or "rock". So al-Ḥajar (اَلْحَجَر) is named as "the stone" or "the rock".
The Hajar Mountains extend for 700 kilometres (430 miles) through the
UAE and Oman.[5] They are located on the north-east corner of the
Arabian Plate, reaching from the
Musandam Peninsula through to the east coast of
Oman. The range is about 100 km (62 mi) wide, with
Jabal Shams being the highest peak at 3,009 m (9,872 ft) in the central region of the mountains.[6][7]
The Hajar Mountains are the product of polyphase
mountain building. Uplift and deformation of the Arabian passive margin began during the late cretaceous as the
African-Arabian Plate began to subduct under the
South Tethyan Oceanic Plate imitated at an
intra oceanic subduction zone. This initiation may have been the result of plate rotation due to the breakup of
Gondwana.[13]
Similar to the modern convergence of the
Australian passive margin under
Eurasian oceanic crust, Arabian passive margin sediments became highly deformed and shortened forming an imbricated thrust belt. This also coincided with the emplacement of the
Semail Ophiolite. By the early
Maastrichtian, deformation ceased, and stable
continental shelf conditions resumed.
A second episode of deformation began during the
Eocene Epoch around 45-40 Ma. This episode saw the reactivation of cretaceous
thrust faults and the development of long and short wavelength folding of Paleocene marine sediments that infilled previous
foredeep accommodation. Low temperature thermodchronometry of
apatite grains has given ages to this deformation and subsequent exhumation of the mountain belt. Exhumation occurred in two states, first between 45 and 40 Ma and again from 20 to 15 Ma. This later unroofing could also be related to tectonic uplift in the nearby Zagros
Mountains of
Iran.[13]
The high topography is around two major culminations: Jabal Akhdar and Saih Hatat, which are large scale
anticlines.[21] The Saih Hatat culmination contains
eclogite in the northeast at As Sifah.[22] These rocks were
subducted to about 80 km (50 mi) depth into the
mantle, and then
exhumed back to the surface.[19] This
exhumation event created possibly the largest
megasheath fold on Earth, the Wadi Mayh megasheath fold.[23] The common view is that these
eclogites were originally
basic volcanic rocks within the leading edge of the continental crust of the
Arabian Plate. This leading edge was then
subducted by a NE-dipping
subduction zone.[24][25] However, some geologists have interpreted that these
eclogites were subducted through a SW-dipping subduction zone.[26]
The two culminations are separated by the Semail Gap. This is a prominent linear structure, trending NNE—SSW. However, it is still debated as to what this structure is. Different geologists claim that it is a left-lateral (sinistral)
strike-slip fault,[27] a
normal fault,[21] a lateral ramp,[28] a
monocline due to a blind
thrust,[15] or a
fault with multiple phases of deformation.[29]
There is some debate over whether the topography of the Hajar Mountains is due to thin or thick-skinned tectonics (if
basement rocks were faulted during collision to create uplift due to thrust faults). Recent
Bouguer gravity and
magnetotelluric geophysical data suggest deep basement faults that have been activated as thrust faults during the collisional event that obducted the Semail Ophiolite. This has resulted in a much shallower depth to basement in the Hajar Mountains and a deeper depth to basement in the foreland basin to the west.[30] This has implications on economic geology such as the mining for precious minerals and the extraction of oil and gas.
Modern topography
The late
Cretaceousobduction event created the proto-Hajar Mountains. However, this
topography subsided and shallow marine sedimentation covered the region, beginning in the
Paleocene.[18][31]Paleocene to
Eocene sedimentary rocks are found at 2,200 m (7,200 ft) above sea level within the Hajar,[28] and are
folded. This indicates that the present day
topography formed after the late
Eocene. The exact timing is debated, and various interpretations indicate the topography formed anywhere between the late
Eocene through to the
Miocene.[21][31][28][32][33]
The driving forces that formed the Hajar is also debated. Many geologists relate the
Zagros Collision as the reason for the
uplift forming the mountains,[18][31][34][35] as currently the
Musandam Peninsula (northwest corner of the mountain range) is
uplifting due to this collision. However,
Jabal Shams, the highest peak of the central mountains is over 300 km (190 mi) away from this zone. In addition, there is no major
seismicity within the central mountains,[36] indicating that the mountains are not currently deforming, even though the
Zagros collision is.[28] This indicates that the
uplift that created the present day
topography occurred in the past, possibly before the initiation of the
Zagros collision, by a mechanism that is not fully understood.
Geoconservation
Oman's geological record is extremely valuable to geologists, and needs to be
preserved.[37] It contains the most complete
ophiolite on Earth, of which it is most famous for among geologists. The
ophiolite sequence has spectacular
pillow basalt (Geotimes pillow lava), as well as exposures of the fossil crust-mantle boundary (
moho). Generally,
ophiolites are
obducted prior to
continental collision, which highly deforms the structure of the original
oceanic crust. However, because
continental collision has not occurred in the Hajar, the Semail
ophiolite is still intact. Oman also has one of the best exposed
mega-sheath folds ever discovered, the Wadi Mayh sheath fold.[23] Additionally, the relatively small outcrop of
eclogite is important. Eclogite is rare on the Earths surface, as it is a rock that forms at high pressures deep within the
crust or
mantle. Geologists can learn about what is occurring in the Earths interior and tectonic processes from these rocks. There are also various fossil localities in Oman that need to be protected. There is concern in the geological community that with the development of infrastructure these rocks that contain a great deal of information will be excavated and destroyed.[37]
The central section of the Hajar is the highest and wildest terrain in the country.
Jabal Shams is the highest of the range,[38] followed by
Jebel Akhdar. The latter[39] and the smaller Jebel Nakhl range are bounded on the east by the low
Samail Valley (which leads northeast to
Muscat).[40]
Eastern Hajar
East of Samail are the Eastern Hajar (
Arabic: ٱلْحَجَر ٱلشَّرْقِي,
romanized: Al-Ḥajar Ash-Sharqī), which run east (much closer to the coast) to the port city of
Sur,[41] almost at the easternmost point of Oman.
Western Hajar
The mountains to the west of Sama'il Valley, particularly those in Musandam Peninsula and the UAE,[42] are known as the Western Hajar (
Arabic: ٱلْحَجَر ٱلْغَرْبِي,
romanized: Al-Ḥajar Al-Gharbī),[43] also known as the "
Oman proper". Since Jabal Akhdar and mountains in its vicinity are west of the valley, they may be regarded as Western Hajar.[1][42]
The northernmost mountains of the Hajar range are found on the Musandam Peninsula. For this reason, the phrase Ru'us al-Jibal ("Heads of the Mountains") is applied to them, or the peninsula itself. Despite being physically part of the western Hajar, they differ in geology and hydrology to the rest of the range.[1][42] The highest point in the UAE is located at
Jebel Jais near
Ras Al Khaimah, which measures 1,911 m (6,270 ft) from sea level,[53][54] but since the summit is on the Omani side,
Jabal ar Rahrah, measuring over 1,691 m (1.051 mi), has the highest peak in the UAE.[55]
The mountains are rich in
plant life compared to most of Arabia, including a number of endemic species. The vegetation changes with altitude, the mountains are covered with shrubland at lower elevations, growing richer and then becoming woodland, including wild
olive and
fig trees between 3,630 and 8,250 ft (1,110 and 2,510 metres), and then higher still there are
junipers. Fruit trees such as
pomegranate and
apricot are grown in the cooler valleys and in places there are rocky outcrops with little vegetation. The flora shows similarities with mountain areas of nearby
Iran, as well as with areas along the
Red Sea in the
Horn of Africa. For example, the tree Ceratonia oreothauma is found here and also in
Somalia.[60]
Like the Ru'us al-Jibal,[65] the area of Jebel Hafeet is noted for hosting rare flora and fauna.[66][67] For example, in February 2019, an
Arabian caracal was sighted here,[68][69][70] and in March, a
Blanford's fox,[71][72] which has also been reported in the mountains of Ras Al-Khaimah.[73]
Threats and preservation
The Hajar are extensively grazed by domestic goats, camels and donkeys and the landscape has been cleared in parts for urban areas and for mining, which has damaged both vegetation and water supplies and uprooted traditional rural land management behaviours. Poaching of wildlife is another issue. The Oman government has created the Wadi Sareen Reserve and an area of Jebel Qahwan-Jebal Sebtah in the Eastern Hajar, for the protection of Arabian tahr and mountain gazelle. For visitors, there is a road into the mountains from the town of Birkat al-Mawz (on the road to
Nizwa from Muscat) and a walking route through Wadi al-Muaydin to the Saiq Plateau.[citation needed]
Trekking and hiking
There are 11 marked trails/routes of varying intensity (between Grade 1 to 3) and duration (between 1.5 hours to 18 hours) published by Ministry of Tourism, Oman along the Hajar range.[74] Some areas are inaccessible, and requires special equipment, as shown in a
Steve Backshall TV documentary.[75]
^Searle, M. P.; Cooper, D. J. W. (1986). "Structure of the Hawasina Window culmination, central Oman Mountains". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 77 (2): 143–156.
doi:
10.1017/S0263593300010798.
ISSN1473-7116.
S2CID130270339.
^
abcMann, A.; Hanna, S. S.; Nolan, S. C.; Mann, A.; Hanna, S. S. (1990). "The post-Campanian tectonic evolution of the Central Oman Mountains: Tertiary extension of the Eastern Arabian Margin". Geological Society, London, Special Publications. 49 (1): 549–563.
Bibcode:
1990GSLSP..49..549M.
doi:
10.1144/GSL.SP.1992.049.01.33.
ISSN0305-8719.
S2CID130934776.
^Rioux, Matthew; Bowring, Samuel; Kelemen, Peter; Gordon, Stacia; Miller, Robert; Dudás, Frank (May 2013). "Tectonic development of the Samail ophiolite: High-precision U-Pb zircon geochronology and Sm-Nd isotopic constraints on crustal growth and emplacement: TECTONIC HISTORY OF THE SAMAIL OPHIOLITE". Journal of Geophysical Research: Solid Earth. 118 (5): 2085–2101.
doi:
10.1002/jgrb.50139.
hdl:1721.1/85188.
S2CID7801342.
^Warren, C.J.; Miller, J.McL. (March 2007). "Structural and stratigraphic controls on the origin and tectonic history of a subducted continental margin, Oman". Journal of Structural Geology. 29 (3): 541–558.
Bibcode:
2007JSG....29..541W.
doi:
10.1016/j.jsg.2006.10.006.
^Searle, M. P; Warren, C. J; Waters, D. J; Parrish, R. R (2004-03-01). "Structural evolution, metamorphism and restoration of the Arabian continental margin, Saih Hatat region, Oman Mountains". Journal of Structural Geology. 26 (3): 451–473.
Bibcode:
2004JSG....26..451S.
doi:
10.1016/j.jsg.2003.08.005.
ISSN0191-8141.
^Le Métour, J.; Rabu, D.; Tegyey, M.; Béchennec, F.; Beurrier, M.; Villey, M. (1990). "Subduction and obduction: two stages in the Eo-Alpine tectonometamorphic evolution of the Oman Mountains". Geological Society, London, Special Publications. 49 (1): 327–339.
Bibcode:
1990GSLSP..49..327L.
doi:
10.1144/gsl.sp.1992.049.01.20.
ISSN0305-8719.
S2CID129165769.
^Ali, M. Y.; Sirat, M.; Small, J. (2009). "Integrated Gravity and Seismic Investigation Over the Jabal Hafit Structure: Implications for Basement Configuration of the Frontal Fold-and-Thrust Belt of the Northern Oman Mountains". Journal of Petroleum Geology. 32 (1): 21–37.
doi:
10.1111/j.1747-5457.2009.00433.x.
ISSN1747-5457.
S2CID128841976.
^El-Hussain, I.; Deif, A.; Al-Jabri, K.; Toksoz, N.; El-Hady, S.; Al-Hashmi, S.; Al-Toubi, K.; Al-Shijbi, Y.; Al-Saifi, M.; Kuleli, S. (2012-10-01). "Probabilistic seismic hazard maps for the sultanate of Oman". Natural Hazards. 64 (1): 173–210.
doi:
10.1007/s11069-012-0232-3.
hdl:1721.1/106473.
ISSN1573-0840.
S2CID62898298.
^
abSearle, Michael P. (2014). "Preserving Oman's geological heritage: proposal for establishment of World Heritage Sites, National GeoParks and Sites of Special Scientific Interest (SSSI)". Geological Society, London, Special Publications. 392 (1): 9–44.
Bibcode:
2014GSLSP.392....9S.
doi:
10.1144/sp392.2.
ISSN0305-8719.
S2CID129129788.
^Hillcoat, D., G. Lewis, and B. Verdcourt. "A New Species of Ceratonia (Leguminosae-Caesalpinioideae) from Arabia and the Somali Republic." Kew Bulletin 35, no. 2 (1980): 261-71. Accessed December 4, 2020. doi:10.2307/4114570.
^Nader, I. A. (1989).
"Rare and endangered mammals of Saudi Arabia"(PDF). In Abu-Zinada, A. H.; Goriup, P. D.; Nader, L. A (eds.). Wildlife conservation and development in Saudi Arabia.
Riyadh: National Commission for Wildlife Conservation and Development Publishing. pp. 226–228.
^Harrison, D. L.; Bates, P. J. J. (1991).
The mammals of Arabia(PDF). Vol. 354. Sevenoaks, UK: Harrison Zoological Museum. pp. 167–170.
^Simó-Riudalbas, M.; Metallinou, M.; De Pous, P.; Els, J.; Jayasinghe, S.; Péntek-Zakar, E.; Wilms, Thomas; Al-Saadi, Saleh; Carranza, Salvador (2017-08-02), "Cryptic diversity in Ptyodactylus (Reptilia: Gekkonidae) from the northern Hajar Mountains of Oman and the United Arab Emirates uncovered by an integrative taxonomic approach", PLOS One, 12 (8): e0180397,
Bibcode:
2017PLoSO..1280397S,
doi:10.1371/journal.pone.0180397,
PMC5540286,
PMID28767644, e0180397
Note: Mountains are sorted in alphabetical order, unless where it concerns ranges. The highest confirmed mountains in each country are indicated with 'HP', and those with the highest peak are indicated with 'HP', bearing in mind that in the UAE, the highest mountain and the mountain with the highest peak are different.
Outcrops are indicated with 'OC', and
outliers with 'OL', and
anticlines with 'AC'.
Volcanoes are indicated with 'V',
volcanic craters with 'VC',
lava fields with 'LF', and
volcanic fields with 'VF'.