Canyons and Floods, Northern Oman

Bilad Sayt in distance, on Al Jabal al Akhdar

Al Hajar al Gharbi
mountains of northern Oman

Background
Many canyons dissect the limestone mountains of Al Hajar, which sweep in an arc extending 700 km southwards from Musandam, curving eastwards towards the coast bordering the Arabian Sea south of Sur. The highest peak, at 3,075m, is Jabal Shams (mountain of the sun) which lies in Al Jabal al Akhdar (the green mountain) at the heart of the Al Hajar range. (See satellite image). The image will open in a separate window. The size is 72.5 K and the file takes up to 30 seconds to download fully at 28.8K.

This mountain range heaved into existence some 60-100 million years ago when Earth movements forced the Eurasian plate over the Arabian plate. Rocks formed deep within the Earth's mantle (ophiolites), deep sea limestones and other sediments now lie hundreds of metres above sea level. Wadi Ghul canyon (right) rivals the Grand Canyon of Colorado State, USA. Rainfall over Al Hajar averages just over 300 mm a year, mostly from occasional frontal troughs passing over Oman in winter and spring and from summer storms. Communities both north and south of the divide carefully husband as much of this water as they can before it is lost to sea or desert. The watershed at the crest of the mountains, shown on the right, divides wadis (ephemeral desert streams) flowing northwards across Al Batinah (the coastal plain) to the Gulf of Oman, from the southward flowing wadis which eventually dissipate in alluvial fans on the northern edge of the desert.
	The head of Wadi Ghul canyon

View south from the watershed of Al Hajar across gently dipping limestones, south to the Interior Plain, and the towns of Nizwa, an ancient capital of the old Imamate of Oman, and Adam.
Bilad Sayt, a village nestling on the northern flanks of Al Hajar. Agriculture is supported by springs and groundwater. Follow this link for an online guide to the unique aflaj water management system in Oman.

Rustaq and Nakhl are two major towns on the northern edge of Al Hajar sustained indirectly by mountain rainfall. Nizwa, Adam, Bahla and Al Hamra are major communities lying to the south.


Extensive date palm groves at Nizwa, as seen from the fort.		Cool date grove

Landscape
Physiographically, the landscape is young. The valleys are steep-sided. The wadi beds contain very poorly sorted alluvial deposits ranging from huge boulders to coarse gravel in size.

Gorge
Wadi deposits

Start of Snake Gorge walk Alluvial deposits in wadi near Rustaq

During the wetter pluvials of the Quaternary Period (the last one may have ended 7,000 years ago), the limestone rocks were eroded into karst formations. Clint and grike structures can be seen on Jabal Shams.

Clints and grikes in limestone pavement
on Jabal Shams

Snake Gorge is the narrow cleft in the middle
of the picture

Snake Gorge, aptly named for its winding, narrow nature, is a ravine of five kilometres length in the mountains to the west of Rustaq. Many long-term visitors take the Snake Gorge walk, which involves jumping off steep boulders and swimming through streams. At times, the walls of the ravine come together so closely that it seems more like swimming in a cave. Such intrepid adventurism incurs a risk.


Negotiating a pool in Snake Gorge		The water can be very deep

When it does rain, storms are usually very intense. Because there is hardly any vegetation or soil to trap the water, it runs off the bare rock very quickly into the wadis. The velocity of the flow is very strong, which is why huge boulders can be swept along wadi beds. A front of water a metre or more deep can advance with great force within minutes. This is known as a flash flood. Many people die in such events each year, so it is essential to observe local weather conditions, and never camp in a wadi bed. On a positive note, camping and walking in the wadis of northern Oman is a unique experience.

January 31st 1998. Wadi in Madinat al Sultan Qaboos, Muscat, in full flow

January 31st 1998. The same wadi two hours later. I have only seen it flow once

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