The Al Hajar mountains (which translate to the Rocky or Stone mountains) are the highest mountain range in the eastern Arabian peninsula. Spanning the 2 countries of Oman and the UAE, they stretch 700km along the Gulf of Oman. At 3009m the highest point in the range is Jebel Shams, located about 240km West of Muscat, Oman. Dubai’s highest point is Um Alnosoor peak = The Mother of Eagles at 1,286 m
Their formation is due to plate tectonics. The Eurasian and Arabian plates moving against each other. These are currently stable plates and there is very little chance of significant earthquake’s in the region. The Arabian Plate (which includes Fujairah) is moving north relative to the Eurasian Plate at about 2–3 cm per year.
The mountains were formed throughout the Mesozoic period, starting their formation 245 million years ago and taking a mere 180 million years for completion. In this time, they will have witnessed the Triassic, Jurassic and Cretaceous periods and the evolution of dinosaurs, mammals and birds. Unfortunately, they will also have witnessed the dinosaur’s demise. There is no evidence (such as fossils) that dinosaurs inhabited this part of the world. Mankind’s evolution wouldn’t be for another 60 million years after the Hajar mountains formation.
The rocks that form the Hajar mountains were originally on the sea floor and covered by between 500m and 1000m of sea water. The sea level didn’t drop but the plates pushing against each other forced the rocks up and formed the mountains we know today.
A brief history of a desert’s formation is that it is sand formed from rocks that have been eroded and exposed to intense weathering for a long time, with no rain and extremely high temperatures. The desert of the UAE is younger than the Hajar mountains.
There are 3 main categories of rock in the Hajars
The igneous rocks are formed from the cooling of lava magma. Shamal chert is prevalent in the north of Hajars and is a volcanic rock formed from lava. There were no volcanos in the area but merely breaks in the earth’s surface in which the lava flowed before cooling. You might be lucky enough to find a crystal in the mountains. This might be a piece of quartz and it is a crystal not a rock. They are formed in nature when liquids cool and start to harden. These crystals will have formed as a result of the liquid rock, called magma, cooling.
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth’s surface, followed by cementation. Sedimentary rocks found local to Hatta are limestone, chert, shale and mudstone.
The limestone quarried in the Hajars has multiple uses and can be used in the production of paper, pharmaceuticals, chicken feed, steel, iron, fertilizer and cement.
Chert is can be found in the Hajars. The same rock has different colourings due to oxidation.
• If the rock is red, it is chert with a high iron oxide content.
• If it is green, once again it is chert but with aluminum oxidation.
Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. An example of this is marble rock formed when limestone is exposed to high temperatures and pressures.
As a general rule, the rocks in Fujairah can be classified by region.
• In the north the rocks are hard igneous and sedimentary.
• In the central region they are largely metamorphic rocks.
• In the south are they are ophiolites and mostly igneous
Most caves found in the Hajars are formed within sedimentary rocks.
The Hajars have several locations where Petroglyphs can be found. There are writing and images carved into weathered limestone. The rocks themselves are grey all the way through but their exterior surface is darkened due to sun and heat.
The rocks you will see on the surface of the mountains will broadly fall into either smooth rock or sharp rocks. Don’t let their appearance fool you into thinking they are different rocks. They may well be the same but one has had the erosion of time smoothing it off and the other maybe recently has been exposed or broken off a larger rock. If you look at the mountains from a distance you will see mostly brown rocks and these (similar to the limestone petroglyphs) are darkened by the intense and continual heat they are subjected to.
Next time you are paddling in the sea, thinking how relaxing it is having the sand between your toes. Think about this. The beach sand came from the Hajar mountains with rocks washed down the wadies and eroded into what we now see as sand. The flatter coastal plain area between the sea and mountains are larger stones that still would have originated in the Hajar’s.