Tawi Atayr Sinkhole EarthCache
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The Tawy Atayr Sinkhole is one of the largest in the world. There is a walkway down to the middle level. Go down there to imagine its impressive dimensions.
Formation of the sinkhole:
The Tawy Atayr shaft is certainly a karst sinkhole feature rather than a meteor impact as some people once believed. Features of karst topography are evident by the numerous waterholes in the surrounding area. The abundance of stalactites, stalagmites and flowstone at various levels of the sinkhole indicate a series of migrating downward cave systems which later collapsed in an upward sequence. Large caves ultimately breake through to the surface to become sinkholes. The upper levels of the sinkhole were therefore older caves than the lower but the latter collapsed earlier.
The walls of the sinkhole are decorated by cave formations of stalactites, stalagmites and flowstones. The water table can be seen from the platform in the middle level. The dissolution of limestone is continuing and in the waterlevel the creation of further chambers is possible.
Climate facts of the Dhofar area:
The basis for the humidity is the Khareef a southwest monsoon comming from India and reaching the Dhofar region from mid of June to mid of September. During this time there are rarely hard rainshowers like in India but a permanent heavy moisture causing condensation at the Qara-mountains. Hence the summits are covered with clouds in this time and light rain is falling out of the fog. This metrological fact influences temperature in the whole Arabian-Peninsula.
Speleological terms and definitions:
A cave is a vug emerged by a natural process which is partially or completely surrounded by bedrock. These natural caves can be charged partly or completely by air, water or sediments. In addition spelaeology demands caves to be acceded by humans and in minimum five meters in lengh. Spelaeology differentiates in between semicaves (=niches), rock-arches, cave-systems and shafts. The most familiar species of cave minerals is sinter and dripstone. This is a segregation of calcite or aragonite from dripingwater from the caves roof-ridge. Primarily fragile thin calcitetubes consisting of consecutive rings are formed. By accumulation of more calcium they become longer and flatter. Depending on amount and dripingspeed of the water various forms can develop. When dripstones grow, they are called stalactites, when they come from the top and stalagmites when the grow from the bottom. When stalactites and stalagmites meet, they become a sintercolumn.
Geology of the Dhofar area:
Dhofar is characterised by the costal plain and steep mountains rising to form its backdrop. These mountains form a large plateau which constitutes Jabal Samhan and Jabal Qamar, both of which are dominated by limestone rocks.
The geological map of Dhofar area shows the Precambrian crystalline rocks which are exposed in Marbat and the Hallaniyat Islands. These rocks form the foundation of the geology of Dhofar. They are made up of granite and gneiss rocks. These basement rocks are overlain unconformably by the pre-Permiam equivalent Marbat Formation and El-Hota-Ain Sarit Formation. The former is made up of glacial sediments similar to those found in the northern Oman mountains (Mistal Formation). The latter comprises shales and grey sandstones. Unconformably overlying these rocks are sedimentary rocks belonging to the Cretaceous and made up of dolomitic limestone and sandstone (Qishn Formation), marl and limestone (Kharfut and Dhalgut Formations). These are much thicker westwards in Jabal Qamar near the Yemen border. The end of the Cretacerous is marked by the limestone of Aruma Group. The Cretacerous rocks are overlain by a Tertiary sequence with a marked unconformity. The Tertiary is a thick carbonate similar to those found in northern Oman except being grey in colour. They belong to the Hadhramaut, Dhofar and Fars Groups. Most Dhofar caves are in the Hadrammaut Group which comprises four formations. From bottom to top they are: Umm er Radhuma (limestones), Rus (limestones and evaporites), Dammam (limestone) and Aydim (limestone). These formations are again equivalent to the Jafnayn, Rusayl and Seeb Formations of the northern Oman mountains but note that the Aydim Formation has no equivalent in northern Oman. The Rus Formation is made of shales, dolomites andevaporites and is underlain and overlain by carbonates (limestone and dolomite) belonging to the Umm er Radhuma, Dammsn and Aydim Formations.
The Dhofar Group is made of the Zaluma, Ashawq and the lower part of the Mughsayl Formation. The remainder of the Mughsayl, Adawnib and Nar Formations belong to the Fars Group. These formations start with lacustrine limestone (Zalumah Formation) passing up to marl, sandstone and limestone (Ashawq Formation).The Mughsayl Formation is a striking white turbiditic chalk up to 700m thick. The Adawnib Formation of the Fars Group is shallow marine limestone and conglomerate rocks, while the top of Nar Formation is alluvial red conglomerate.
Fauna:
The Tawi Atayr sinkhole is a magnificent site for bird watching and ist major attraction is the sound of singing birds, thus in Arabic it is called „the Well of the Birds“. There have been cave fish (Garra dunsira) found in the water sections.
Entrance:
The sinkhole is approached from the west along the paved road and the parking area. Follow the well-used path, it decends along a steep gully leading to the first horizontal gallery (upper level) which is a bedding plane. The second (middle level) is the biggest level, is also horizontal, parallel to another bed and is equipped with a metal platform overlooking an 80m vertical drop to the bottom of the shaft. This platform offers a view of fallen boulders together with a lake at the bottom. TO ACCEDE THE PLATFORM IS HIGHLY DANGEROUS – VISITORS HAVE TO BE SAFEGUARDED BY EXPERIENCED PERSONS WITH A ROPE!
Conclusion:
The tranquillity of the place and the hudge size of the shaft will print an unforgettable impression on visitor´s minds – enjoy the site!
How to log your visit:
You need a picture of you and your GPS taken at the middle level with the iron platform in the background. Prelog your visit with the picture(s) – no answers in your log. Please answer the questions and send only the correct answers to: nordicwalker@gmx.at
I am sorry to say that logs without picture and sending the right answers will be deleted.
Please answer the following questions:
A) What kind of gas in rainwater causes dissolution of limestone and is responsible for cave developement in limestone?
B) What is „Karst“?
C) Where do the birds of Tawi Atayr Singhole like to sit on high up the shaft?
D) In which sequence occured the breakdown of the caves to create this hughe sinkhole?
For help in answering A+B look up: www.geoadventure.at and www.nhm-wien.ac.at
Source: Samir Hanna and Mohamed Al Belushi (Sultan Qaboos University, Dep. of Earth Siences, Muscat)
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