Jebel Jais (جَبَل جَيْس) is a mountain of the North-Western Hajar range. The summit is located on the Omani side, but a high point west of this peak is considered the highest point in the United Arab Emirates, at 1,892 m (6,207 ft) above sea level. A 20 km (12 mile) road has been built, which hairpins most of the way up the mountain. Near the top of the road, there are parking places, food providers, toilets and a viewing platform. After a security checkpoint, the road continues up a few kilometers, however it remains closed to the public.
This viewing area is close to the end of the accessable road and free. In addition, there is a lovely viewing area/park just before this one which is recommended but has a small cost (5 aed per person). If you wish to hike, please start from this park and for safety inform the park attendant (please be mindful of the weather conditions). It is acceptable to log this EarthCache from either location and hiking is not a requirement.
AL HAJAR MOUNTAINS
The name Al Hajar is basically a combination of two Arabic words, Al means ‘the’ while Hajar means ‘rock’ or ‘stone,’ which when combined, translates as ‘the rock’ or ‘the stone. ’Located on the eastern side of the UAE and northeastern part of Oman, the Hajar Mountain range is one of the most awe-inspiring destinations on the Arabian Peninsula. It spans 700 km across the two countries and is the highest mountain range in the region. The northwestern area of the Hajar Mountains includes Jebel Jais, the highest peak in the UAE.
It is believed that the Hajar Mountains were first formed on the Arabian-Eurasian convergent plate boundary, as a result of continental collision that began at least 30 millennia ago. Exactly when these mountains developed is still not known.
Al Hajar Mountains lie on the north-east corner of the Arabian Plate, starting from the Musandam Peninsula and stretching all the way to the east of Oman. The mountain’s geology is divided into four groups of rock layers:
- Base rocks like carbonates
- Continental shelf carbonates
- Rocks that have moved from their original positions, commonly known as nappes
- Marine and terrestrial sedimentary rocks
FORMATION
The Hajar Mountains, as we know them today, are the result of deformation in the late Oligocene and early Miocene (ca. 30–20 million years ago), followed by uplift and erosion under generally arid or semi-arid conditions, continuing to the present day. This deformation and uplift are presumed to be related to the slowmotion collision (i.e. tectonic convergence) of the Eurasian plate with the Afro-Arabian plate and other marginal plates, coupled with the opening of the Red Sea. Those interactions have been responsible for mountain building from the Alps to the Zagros to the Himalayas during the same time period. The Hajar Mountains, however, are situated relatively far from the relevant plate boundaries and no conceptual model has yet been proposed which fits this mid-Tertiary phase of activity more precisely into our evolving understanding of plate tectonics and its relationship to mountain building.
At the end of the Miocene, about 5 million years ago, the Arabian Platform began its collision with Asia, pushing up the Zagros Mountains along its leading edge and creating behind them the shallow downwarping that today contains the Arabian Gulf, which is nowhere more than 100 metres deep. During much of its life the Gulf has not been a marine basin but a broad river valley, draining Mesopotamia and, in wetter times, the Empty Quarter.
The Hajar Mountains as a whole have continued to rise slowly since the mid-Tertiary. Erosion of the Hajar Mountains has produced the broad gravel plains that border the mountains on both east and west, and the gravel terraces that fill major wadis. Within the mountains themselves, erosion has proceeded by alternation of cutting and filling. At present we are in a phase of cutting down, so that in virtually any mountain wadi one can observe that the current wadi bed is bordered intermittently by the steep walls of higher gravel terraces (up to as much as 30 metres higher) representing former base levels. These wadi walls provide excellent cross-sections for the study of sedimentary processes in the wadi environment, processes that continue today. The alternating phases of cutting and filling could be due in part to variations in the rate of regional uplift, but it seems evident that the role of climate has been paramount. Erosion of the mountains and deposition of gravels has been greatest when the climate has been wettest. Precipitation levels known from historical times are not sufficient to account for outwash gravels of the size and scale that exist. For this, the best explanation may lie in the climatic vicissitudes of the Quaternary Period. Direct dating of uplift and erosional phenomena in the mountains of the UAE, for example, terrace levels or wet and dry periods, has so far not been systematically undertaken. The recent discovery of an extensive cave and cave deposits at the present-day summit of Jebel Hafit, but presumptively formed originally at or near ground level, may contribute to more precise estimates of the timing of climatic events and erosion and uplift rates.
OPHIOLITE NAPPE
At the top of the main structural sequence of the Hajar mountains lies the ophiolite nappe, often called the Semail nappe by geologists. This nappe consists of a sheet of the upper mantle and oceanic crust dated at ca. 90–100 million years old. The total original thickness of the ophiolite nappe was some 15 kilometres, including more than 10 kilometres of upper mantle. In the UAE the top of the ophiolite nappe has generally been eroded and the rocks of the upper oceanic crust are therefore absent.
Mantle rock is distinctively low in silica and high in magnesium and iron, relative to ordinary rocks. The primary constituent of the upper mantle is a dark rock called (generically) peridotite, which is made up of the mineral olivine and one or more types of pyroxene, with minor trace minerals such as chrome spinel. The precise composition (and therefore the technical name) is variable. The most common peridotite in the Hajar Mountains is called harzburgite, but lherzolite and wehrlite are also found.
SOURCES
https://en.wikipedia.org/wiki/Jebel_Jais
https://www.bayut.com/mybayut/hajar-mountains-uae/
https://www.geoexpro.com/articles/2018/03/the-best-geological-site-in-the-middle-east
http://www.dnhg.org/uploads/4/0/9/9/40998945/uae_geological_overview_-_feulner__2005_.pdf
To claim this EarthCache you should visit GZ and enjoy the views the Jebel Jais has to offer. Even though the route up is entirely tarmac road, it is not advisable to drive up in bad weather as several sections of the road are prone to flooding (watch for the marker posts at the side of the road - if the water is on the red line, do not cross).
To claim a find please email or message the CO with answers to these questions
1) Why is it not clear how the Hajar Mountains formed?
2) What is ophiolite?
3) Take a reading using your GPS, phone or a nearby sign (at alternate GZ) to work out your current elevation. How much higher do you need to go to get to the highest point of the mountain?
4) Look across to the east/north-east. There is a slope down which abruptly turns into steep, distinctive looking cliff. Describe this cliff face and estimate its height. What do you think caused this cliff to look this way?
5) Find a dark rock or boulder to the west of GZ slightly off the road heading up (be careful!) or from near to the start of the hike at the alternate GZ. Describe its shape and size, including any details of fractures or holes. What does this rock feel like to touch?
Please submit a photograph of the view (optional).