Tuesday, May 15, 2012

Beautiful Weathering structure on the rocks around Ranchi city, India.


Around Ranchi city typical structures are encountered on the rocks.
by
Dr. Nitish Priyadarshi
Below are the pictures of the typical weathering structures on the Rocks of the Ranchi city.
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind and gravity.
Two important classifications of weathering processes exist – physical and chemical weathering. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals (also known as biological weathering) in the breakdown of rocks, soils and minerals.
Rocks (mainly granite gneiss and schist) around Ranchi city of Jharkhand State are covered with different types of weathered structures. Many people sometimes confused these structures with some man made rock cuttings or some ancient Archeological sites. 
In a small hill north of Ranchi city a  granite peak  was formed through a long-term differential weathering process due to the developed vertical joints and fissures in granite body. The wind erosion shaped these peak perfectly round, just like Buddhist images of different gestures.
Some of the hills also contain small caves. Lots of mythological stories are told about such caves. But according to geology all such caves are the products of different types of weathering. Some of the caves near Ranchi follow the patterns of joints in the rock; that they are "joint controlled".   

These caves may classify under Corrasional cave or erosional cave. Corrasional or erosional caves are those that form entirely by erosion by flowing streams carrying rocks and other sediments. These can form in any type of rock, including hard rocks such as granite. Generally there must be some zone of weakness to guide the water, such as a fault or joint.

In and around Ranchi city typical structures are encountered on the rocks. Sometimes it resembles to hood of the king cobra, some times foot prints of giant animals or man made structures of Archaeological importance. It may be good example of differential weathering. Differential weathering is the difference in degree of discoloration, disintegration, etc., of rocks of different kinds exposed to the same environment. 

Sometimes many outcrops contain more than one rock type. Typically, the different  rock types will weather at different  rates. This is also known as differential weathering.


 Such types of weathering occurs due to chemical weathering. 

Dolphin like structure 


Small cave formed due to weathering on the top a hill south of Ranchi city.

 Structure similar to Buddhist images of different gestures in Sutiambe hill north of Ranchi.



 Alternate weathering of rocks.


Weathering along the joints.


Alteration of hard and soft rocks due to differential weathering on  Rifle range, Bariatu.


Formation of Pot hole on top of the hill near Ranchi.

Small cave on the hill near Ranchi.
 Type of differential weathering similar to pillar like structure.

Another example of differential weathering north of Ranchi city.
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