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Friday, September 5, 2014
Geology of Pithoria hills near Ranchi city, India.
hills of Ranchi
are generally small isolated residual hills.
Dr. Nitish Priyadarshi.
Fig.1. A small hill in Pithoria.
The hills of Ranchi
are generally small isolated residual hills. In Ranchi hills are generally steepsided made of
massive granite-gneiss. We have also found the hills which are not steepsided
but a mere irregular pile of huge boulders were found on the hills especially
in Pithoria area of Ranchi
district. This is the result of highly jointed elements of granite gneiss.
According to climatic geomorphologist like Tricart qualify
such hills as inselbergs. They are steepsided residual hills made of massive
granite-gneiss. But close by within a few kilometers or a few hundred meters we
have residuals which are not steepsided inselbergs but a mere irregular pile of
The rocks disintegrate along these joints under the
hydrothermal and atmospheric effects thus leading to the formation of tors or
rounded shapes of these ancient granite rocks are the result of cracking and
erosion from exposure to sun, wind and rain. The hill slopes are subjected to
complex attack by a variety of erosive weapons, water being the most active
agent for the removal of waste material from most of the slopes.
A tor commonly appearsas a pile
of rock slabs or a series of slabs standing on end, according to whether the
dominant joint system is horizontal or vertical. Weathering proceeds most
actively along joint planes, thus reducing an originally solid mass first to
piles of slabs and ultimately to a heap of loose boulders. Tors usually
overlie unaltered bedrock and are thought to be formed either by freeze–thaw weathering
or by groundwater weathering before exposure. There is often evidence of
spheroidal weathering of the squared joint blocks. Tors are seldom more than 15
metres (50 feet) high and often occur as residues at the summits of inselbergs
and at the highest points of pediments.
Fig.2. This is a picture of small granite tor near Ranchi city.
Fig.3. Tor like structure on top of Pithoria hill.
Fig.4. Irregular pile of huge boulders on the top of Pithoria hill.
Fig.5.Irregular pile of
huge boulders. They are the result of highly jointed elements
of granite gneiss.
Fig.6. A balancing rock was also seen on the top of the hill.
rock, also called balanced rock or precarious boulder, is a
naturally occurring geological formation featuring a large rock or boulder,
sometimes of substantial size, resting on other rocks, bedrock or on
glacial till. Some
formations known by this name only appear to be balancing but are in fact
firmly connected to a base rock by a pedestal or stem.
erosional remnant rock formation that remains after extensive
wind, water and/or chemical erosion. To the untrained eye it may appear to be
visually like a glacial erratic, but instead of being transported and deposited
it was carved from the local bedrock.